Centralized heating. Central heating and district heating
Gives the following definition of the term "heat supply":
Heat supply- a system for providing heat to buildings and structures, designed to provide thermal comfort for the people in them or to be able to comply with technological standards.
Any heating system consists of three main elements:
- heat source. This may be a CHP plant or a boiler house (with a district heating system), or simply a boiler located in a separate building (local system).
- Thermal Energy Transportation System(heating network).
- Heat consumers(heating radiators (batteries) and heaters).
Classification
Heat supply systems are divided into:
- Centralized
- Local(they are also called decentralized).
They may be water and steam. The latter are rarely used today.
Local heating systems
Everything is simple here. In local systems, the source of heat energy and its consumer are located in the same building or very close to each other. For example, a boiler is installed in a separate house. The water heated in this boiler is subsequently used to meet the needs of the house in heating and hot water.
District heating systems
In a centralized heat supply system, the source of heat is either a boiler house that produces heat for a group of consumers: a quarter, a city district, or even an entire city.
With such a system, heat is transported to consumers through the main heating networks. From the main networks, the coolant is supplied to central heating points (CHP) or individual heating points (ITP). From the central heating station, heat is already delivered through quarterly networks to the buildings and structures of consumers.
According to the method of connecting the heating system, heat supply systems are divided into:
- Dependent systems- the heat carrier from the source of thermal energy (CHP, boiler house) goes directly to the consumer. With such a system, the scheme does not provide for the presence of central or individual heating points. In simple terms, water from heating networks flows directly into the batteries.
- Independent systems - in this system there are TsTP and ITP. The coolant circulating through the heating networks heats the water in the heat exchanger (1st circuit - red and green lines). The water heated in the heat exchanger circulates already in the heating system of consumers (circuit 2 - orange and blue lines).
With the help of make-up pumps, water losses through leaks and damages in the system are replenished and pressure is maintained in the return pipeline.
According to the method of connecting the hot water supply system, heat supply systems are divided into:
- Closed. With such a system, water from the water supply system is heated by a coolant and supplied to the consumer. I wrote about her in an article.
- Open. In an open heating system, water for DHW needs taken directly from the heating network. For example, in winter you use heating and hot water "from one pipe". For such a system, the figure of the dependent heat supply system is valid.
Energy saving in heat supply systems
Completed by: students of group T-23
Salazhenkov M.Yu.
Krasnov D.
Introduction
Today, the energy saving policy is a priority direction in the development of energy and heat supply systems. In fact, every state enterprise draws up, approves and implements plans for energy saving and energy efficiency improvement of enterprises, workshops, etc.
The country's heating system is no exception. It is quite large and cumbersome, consumes colossal amounts of energy and at the same time there are no less colossal losses of heat and energy.
Let's consider what the heat supply system is, where the greatest losses occur and what complexes of energy-saving measures can be applied to increase the "efficiency" of this system.
Heating systems
Heat supply - supply of heat to residential, public and industrial buildings (structures) to meet household (heating, ventilation, hot water supply) and technological needs of consumers.
In most cases, heat supply is the creation of a comfortable indoor environment - at home, at work or in a public place. Heat supply also includes heating of tap water and water in swimming pools, heating of greenhouses, etc.
The distance over which heat is transported in modern district heating systems reaches several tens of kilometers. The development of heat supply systems is characterized by an increase in the power of the heat source and unit capacities of the installed equipment. Thermal power of modern thermal power plants reaches 2-4 Tkal/h, regional boiler houses 300-500 Gkal/h. In some heat supply systems, several heat sources work together for common heat networks, which increases the reliability, flexibility and efficiency of heat supply.
The water heated in the boiler room can circulate directly to the heating system. Hot water is heated in the heat exchanger of the hot water supply system (DHW) to a lower temperature, about 50-60 ° C. Temperature return water can be an important factor in boiler protection. The heat exchanger not only transfers heat from one circuit to another, but also effectively copes with the pressure difference that exists between the first and second circuits.
The required floor heating temperature (30 °C) can be obtained by adjusting the temperature of the circulating hot water. The temperature difference can also be achieved by using a three-way valve that mixes hot water with return water in the system.
Regulation of heat supply in heat supply systems (daily, seasonal) is carried out both in the heat source and in heat-consuming installations. In water heating systems, the so-called central quality control of heat supply is usually carried out for the main type of heat load - heating or for a combination of two types of load - heating and hot water supply. It consists in changing the temperature of the heat carrier supplied from the heat supply source to the heat network in accordance with the accepted temperature schedule (that is, the dependence of the required water temperature in the network on the outside air temperature). Central qualitative regulation is supplemented by local quantitative regulation in heating points; the latter is most common in hot water applications and is usually carried out automatically. In steam heating systems, local quantitative regulation is mainly carried out; the steam pressure in the heat supply source is maintained constant, the steam flow is regulated by consumers.
1.1 Composition of the heating system
The heat supply system consists of the following functional parts:
1) source of heat energy production (boiler house, thermal power plant, solar collector, devices for the utilization of industrial heat waste, installations for the use of heat from geothermal sources);
2) transporting devices of thermal energy to the premises (heating networks);
3) heat-consuming devices that transfer thermal energy to the consumer (heating radiators, heaters).
1.2 Classification of heating systems
According to the place of heat generation, heat supply systems are divided into:
1) centralized (the source of heat energy production works for the heat supply of a group of buildings and is connected by transport devices with heat consumption devices);
2) local (the consumer and the source of heat supply are located in the same room or in close proximity).
The main advantages of district heating over local heating are a significant reduction in fuel consumption and operating costs (for example, by automating boiler plants and increasing their efficiency); the possibility of using low-grade fuel; reducing the degree of air pollution and improving the sanitary condition of populated areas. In local heating systems, heat sources are furnaces, hot water boilers, water heaters (including solar), etc.
According to the type of heat carrier, heat supply systems are divided into:
1) water (with temperature up to 150 °C);
2) steam (pressure 7-16 atm).
Water serves mainly to cover domestic, and steam - technological loads. The choice of temperature and pressure in heat supply systems is determined by the requirements of consumers and economic considerations. With an increase in the distance of heat transportation, an economically justified increase in the parameters of the coolant increases.
According to the method of connecting the heating system to the heat supply system, the latter are divided into:
1) dependent (the heat carrier heated in the heat generator and transported through heat networks enters directly into heat-consuming devices);
2) independent (the heat carrier circulating through the heating networks heats the heat carrier circulating in the heating system in the heat exchanger). (Fig.1)
AT independent systems consumers' installations are hydraulically isolated from the heating network. Such systems are mainly used in large cities - in order to increase the reliability of heat supply, as well as in cases where the pressure regime in the heat network is unacceptable for heat-consuming installations due to their strength or when the static pressure created by the latter is unacceptable for the heat network ( such are, for example, the heating systems of high-rise buildings).
Picture 1 - Schematic diagrams heating systems according to the method of connecting heating systems to them
According to the method of connecting the hot water supply system to the heat supply system:
1) closed;
2) open.
In closed systems, hot water supply is supplied with water from the water supply, heated to the required temperature by water from the heating network in heat exchangers installed in heating points. AT open systems water is supplied directly from the heating network (direct water intake). Water leakage due to leaks in the system, as well as its consumption for water intake, are compensated by additional supply of an appropriate amount of water to the heating network. To prevent corrosion and scale formation on inner surface pipeline, the water supplied to the heating network undergoes water treatment and deaeration. In open systems, the water must also meet the requirements for potable water. The choice of system is determined mainly by the presence of a sufficient amount of water of drinking quality, its corrosive and scale-forming properties. Both types of systems have become widespread in Ukraine.
According to the number of pipelines used to transfer the coolant, heat supply systems are distinguished:
single-pipe;
two-pipe;
multipipe.
Single-pipe systems are used in cases where the coolant is completely used by consumers and is not returned back (for example, in steam systems without condensate return and in open water systems, where all the water coming from the source is taken apart for hot water supply to consumers).
In two-pipe systems, the heat carrier is fully or partially returned to the heat source, where it is heated and replenished.
Multi-pipe systems suit, if necessary, allocation certain types heat load (for example, hot water supply), which simplifies the regulation of heat supply, operation mode and methods of connecting consumers to heating networks. In Russia, two-pipe heat supply systems are predominantly used.
1.3 Types of heat consumers
The heat consumers of the heat supply system are:
1) heat-using sanitary systems of buildings (systems of heating, ventilation, air conditioning, hot water supply);
2) technological installations.
The use of hot water for space heating is quite common. At the same time, a variety of methods for transferring water energy are used to create a comfortable indoor environment. One of the most common is the use of heating radiators.
An alternative to heating radiators is floor heating, when the heating circuits are located under the floor. The floor heating circuit is usually connected to the heating radiator circuit.
Ventilation - a fan coil unit that supplies hot air to a room, usually used in public buildings. Often used in combination heating devices e.g. heating and floor heating radiators or heating and ventilation radiators.
hot tap water became part of Everyday life and daily needs. Therefore, a hot water installation must be reliable, hygienic and economical.
According to the mode of heat consumption during the year, two groups of consumers are distinguished:
1) seasonal, requiring heat only during the cold season (for example, heating systems);
2) year-round, requiring heat all year round (hot water supply systems).
Depending on the ratio and modes of individual types of heat consumption, three characteristic groups of consumers are distinguished:
1) residential buildings (characterized by seasonal heat consumption for heating and ventilation and year-round - for hot water supply);
2) public buildings (seasonal heat consumption for heating, ventilation and air conditioning);
3) industrial buildings and structures, including agricultural complexes (all types of heat consumption, the quantitative ratio between which is determined by the type of production).
2 District heating
District heating is an environmentally friendly and reliable way to provide heat. District heating systems distribute hot water or, in some cases, steam from a central boiler plant between multiple buildings. There is a very wide range of sources that serve to generate heat, including the burning of oil and natural gas or the use of geothermal waters. The use of heat from low temperature sources, such as geothermal heat, is possible with the use of heat exchangers and heat pumps. The possibility of using non-utilized heat from industrial enterprises, surplus heat from waste processing, industrial processes and sewerage, target heating plants or thermal power plants in district heating, allows for the optimal choice of heat source in terms of energy efficiency. This way you optimize costs and protect the environment.
Hot water from the boiler house is fed to a heat exchanger that separates the production site from the distribution pipelines of the district heating network. The heat is then distributed to the final consumers and fed through the substations to the respective buildings. Each of these substations usually includes one heat exchanger for space heating and hot water.
There are several reasons for installing heat exchangers to separate a heating plant from a district heating network. Where significant pressure and temperature differences exist that could cause serious damage to equipment and property, a heat exchanger can protect sensitive heating and ventilation equipment from the ingress of contaminated or corrosive media. Another important reason for separating the boiler house, distribution network and end users is to clearly define the functions of each component of the system.
In a combined heat and power plant (CHP), heat and electricity are produced simultaneously, with heat being the by-product. Heat is usually used in district heating systems, leading to increased energy efficiency and cost savings. The degree of use of energy obtained from fuel combustion will be 85–90%. The efficiency will be 35–40% higher than in the case of separate production of heat and electricity.
In a thermal power plant, burning fuel heats water, which turns into steam. high pressure and high temperature. The steam drives a turbine connected to a generator that produces electricity. After the turbine, the steam is condensed in a heat exchanger. The heat released during this process is then fed into the district heating pipes and distributed to the final consumers.
For the end user district heating means uninterrupted energy supply. A district heating system is more convenient and efficient than small individual home heating systems. Modern fuel combustion and emission cleaning technologies reduce the negative impact on the environment.
In apartment buildings or other buildings heated by district heating, the main requirement is heating, hot water supply, ventilation and underfloor heating for a large number consumers with minimal energy consumption. Using high-quality equipment in the heating system, you can reduce overall costs.
Another very important task of heat exchangers in district heating is to ensure safety. internal system by separating end consumers from the distribution network. This is necessary because of the significant difference in temperature and pressure values. In the event of an accident, the risk of flooding can also be minimized.
In central heating points, a two-stage scheme for connecting heat exchangers is often found (Fig. 2, A). This connection means maximum heat utilization and low return water temperature when using the hot water system. It is particularly advantageous in combined heat and power plant applications where a low return water temperature is desired. This type A substation can easily supply heat to up to 500 apartments, and sometimes more.
A) Two-stage connection B) Parallel connection
Figure 2 - Scheme of connecting heat exchangers
Parallel connection of a DHW heat exchanger (Fig.2, B) is less complicated than a two-stage connection and can be applied to any size plant that does not need a low return water temperature. Such a connection is usually used for small and medium-sized heating points with a load of up to approximately 120 kW. Connection diagram for hot water heaters in accordance with SP 41-101-95.
Most district heating systems place high demands on the installed equipment. The equipment must be reliable and flexible, providing the necessary safety. In some systems, it must also meet very high hygiene standards. Another important factor in most systems is low operating costs.
However, in our country, the district heating system is in a deplorable state:
technical equipment and the level of technological solutions in the construction of heat networks correspond to the state of the 1960s, while the radii of heat supply have sharply increased, and there has been a transition to new standard sizes of pipe diameters;
the quality of metal of heat pipelines, thermal insulation, shut-off and control valves, construction and laying of heat pipelines are significantly inferior to foreign analogues, which leads to big losses thermal energy in networks;
poor conditions for thermal and waterproofing of heat pipelines and channels of heat networks contributed to an increase in the damage of underground heat pipelines, which led to serious problems in replacing the equipment of heat networks;
domestic equipment of large CHPPs corresponds to the average foreign level of the 1980s, and at present, steam turbine CHPPs are characterized by a high accident rate, since almost half of the installed capacity of the turbines has reached the design resource;
operating coal-fired CHP plants do not have flue gas purification systems from NOx and SOx, and the efficiency of trapping particulate matter often does not reach the required values;
The competitiveness of DH at the present stage can only be ensured by the introduction of specially new technical solutions, both in terms of the structure of systems, and in terms of schemes, equipment of energy sources and heating networks.
2.2 Efficiency of district heating systems
One of essential conditions normal operation of the heat supply system is the creation hydraulic mode, providing pressure in the heating network sufficient to create network water flows in heat-consuming installations in accordance with a given heat load. The normal operation of heat consumption systems is the essence of providing consumers with thermal energy of the appropriate quality, and for the energy supply organization it consists in maintaining the parameters of the heat supply mode at the level regulated by the Rules Technical Operation(PTE) of power plants and networks of the Russian Federation, PTE of thermal power plants. The hydraulic regime is determined by the characteristics of the main elements of the heat supply system.
During operation in the existing district heating system, due to a change in the nature of the heat load, the connection of new heat consumers, an increase in the roughness of pipelines, adjustments of the calculated temperature for heating, changes in the temperature schedule for the release of heat energy (TE) from the TE source, as a rule, uneven heat supply occurs consumers, overestimating network water costs and reducing pipeline throughput.
In addition to this, as a rule, there are problems in the heating systems. Such as misregulation of heat consumption modes, understaffing elevator nodes, unauthorized violation by consumers of connection schemes (established by projects, specifications and agreements). These problems of heat consumption systems are manifested, first of all, in the misregulation of the entire system, which is characterized by increased coolant flow rates. As a result, insufficient (due to increased pressure losses) available pressures of the coolant at the inlets, which in turn leads to the desire of subscribers to provide the necessary drop by draining the network water from the return pipelines to create at least a minimum circulation in heating appliances(violations of connection schemes, etc.), which leads to an additional increase in flow and, consequently, to additional pressure losses, and to the emergence of new subscribers with reduced pressure drops, etc. There is a "chain reaction" in the direction of a total misalignment of the system.
All this has a negative impact on the entire heat supply system and on the activities of the energy supply organization: the inability to comply with the temperature schedule; increased replenishment of the heat supply system, and when the water treatment capacity is exhausted, forced replenishment with raw water (consequence - internal corrosion, premature failure of pipelines and equipment); forced increase in heat supply to reduce the number of complaints from the population; increase in operating costs in the system of transport and distribution of thermal energy.
It should be pointed out that in the heat supply system there is always an interrelation of steady-state thermal and hydraulic regimes. A change in the flow distribution (including its absolute value) always changes the heat exchange condition, both directly in heating installations and in heat consumption systems. The result of abnormal operation of the heat supply system is, as a rule, a high temperature of the return network water.
It should be noted that the temperature of the return network water at the source of thermal energy is one of the main operational characteristics designed to analyze the state of the equipment of thermal networks and the modes of operation of the heat supply system, as well as to assess the effectiveness of measures taken by organizations operating thermal networks in order to increase the level operation of the heating system. As a rule, in the case of misalignment of the heat supply system, the actual value of this temperature differs significantly from its normative, calculated value for this heat supply system.
Thus, when the heat supply system is misaligned, the temperature of the network water, as one of the main indicators of the mode of supply and consumption of thermal energy in the heat supply system, turns out to be: in the supply pipeline, almost in all intervals of the heating season, it is characterized by low values; the temperature of the return network water, despite this, is characterized by increased values; temperature difference in the supply and return pipelines, namely this indicator (along with specific consumption network water per connected heat load) characterizes the level of quality of heat energy consumption, is underestimated compared to the required values.
It should be noted one more aspect related to the increase relative to the calculated value of network water consumption for the thermal regime of heat consumption systems (heating, ventilation). For direct analysis, it is advisable to use the dependence, which determines in case of deviation of the actual parameters and structural elements heat supply systems from the calculated ones, the ratio of the actual consumption of thermal energy in heat consumption systems to its calculated value.
where Q is the consumption of thermal energy in heat consumption systems;
g - consumption of network water;
tp and tо - temperature in the supply and return pipelines.
This dependence (*) is shown in Fig.3. The ordinate shows the ratio of the actual consumption of thermal energy to its calculated value, the abscissa shows the ratio of the actual consumption of network water to its calculated value.
Figure 3 - Graph of the dependence of the consumption of thermal energy by systems
heat consumption from the consumption of network water.
As general trends, it is necessary to point out that, firstly, an increase in network water consumption by n times does not cause an increase in thermal energy consumption corresponding to this number, that is, the heat consumption coefficient lags behind the network water consumption coefficient. Secondly, with a decrease in the consumption of network water, the supply of heat to the local heat consumption system decreases the faster, the lower the actual consumption of network water compared to the calculated one.
Thus, heating and ventilation systems react very poorly to excessive consumption of network water. Thus, an increase in the consumption of network water for these systems by 50% relative to the calculated value causes an increase in heat consumption by only 10%.
The point in Fig. 3 with coordinates (1; 1) displays the calculated, actually achievable mode of operation of the heat supply system after commissioning. Under the actually achievable mode of operation is meant such a mode, which is characterized by the existing position of the structural elements of the heat supply system, heat losses by buildings and structures and determined by the total consumption of network water at the outlets of the heat source, necessary to provide a given heat load with the existing heat supply schedule.
It should also be noted that the increased consumption of network water, due to the limited capacity of heat networks, leads to a decrease in the available pressures at the consumer inlets necessary for the normal operation of heat-consuming equipment. It should be noted that the pressure loss in the heating network is determined by a quadratic dependence on the network water flow:
That is, with an increase in the actual consumption of network water GF by 2 times relative to the calculated value GP, the pressure losses in the heating network increase by 4 times, which can lead to unacceptably small available pressures at the thermal nodes of consumers and, consequently, to insufficient heat supply to these consumers, which can cause unauthorized discharge of network water to create circulation (unauthorized violation by consumers of connection schemes, etc.)
Further development of such a heat supply system along the path of increasing the flow rate of the coolant, firstly, will require the replacement of the head sections of the heat pipelines, the additional installation of network pumping units, an increase in the productivity of water treatment, etc., and secondly, it leads to an even greater increase in additional costs - the cost of compensation for electricity, make-up water, heat losses.
Thus, it seems technically and economically more justified to develop such a system by improving its quality indicators - increasing the temperature of the coolant, pressure drops, increasing the temperature difference (heat removal), which is impossible without a drastic reduction in coolant consumption (circulation and make-up) in heat consumption systems and , respectively, in the entire heating system.
Thus, the main measure that can be proposed to optimize such a heat supply system is the adjustment of the hydraulic and thermal regime of the heat supply system. The technical essence of this measure is to establish the flow distribution in the heat supply system based on the calculated (i.e., corresponding to the connected heat load and the selected temperature schedule) network water consumption for each heat consumption system. This is achieved by installing appropriate throttling devices (automatic regulators, throttle washers, elevator nozzles) at the inputs to the heat consumption systems, the calculation of which is based on the calculated pressure drop at each input, which is calculated based on the hydraulic and thermal calculation of the entire heat supply system.
It should be noted that the creation of a normal mode of operation of such a heat supply system is not limited only to carrying out adjustment measures, it is also necessary to carry out work to optimize the hydraulic mode of the heat supply system.
Regime adjustment covers the main links of the district heating system: a water-heating installation of a heat source, central heating points (if any), a heat network, control and distribution points (if any), individual heating points and local heat consumption systems.
Commissioning begins with an inspection of the district heating system. The collection and analysis of initial data on the actual operating modes of the system of transport and distribution of heat energy, information on the technical condition of heat networks, the degree of equipment of the heat source, heat networks and subscribers with commercial and technological measuring instruments is carried out. The applied modes of heat energy supply are analyzed, possible defects in the design and installation are identified, information is selected to analyze the characteristics of the system. The analysis of operational (statistical) information (sheets of accounting for coolant parameters, modes of supply and consumption of energy, actual hydraulic and thermal modes of heating networks) is carried out with different values outside air temperature in the base periods, obtained according to the readings of standard measuring instruments, as well as an analysis of reports from specialized organizations.
In parallel, developed design scheme thermal networks. A mathematical model of the heat supply system is being created on the basis of the ZuluThermo calculation complex, developed by Politerm (St. Petersburg), capable of simulating the actual thermal and hydraulic operation of the heat supply system.
It should be pointed out that there is a fairly common approach, which consists in minimizing the financial costs associated with the development of measures to adjust and optimize the heat supply system, namely, the costs are limited to the acquisition of a specialized software package.
The "pitfall" in this approach is the reliability of the original data. The mathematical model of the heat supply system, created on the basis of unreliable initial data on the characteristics of the main elements of the heat supply system, turns out, as a rule, to be inadequate to reality.
2.3 Energy saving in DH systems
AT recent times there are critical remarks about district heating based on district heating - the joint generation of heat and electricity. As the main disadvantages, there are large heat losses in pipelines during heat transport, a decrease in the quality of heat supply due to non-compliance with the temperature schedule and the required pressure from consumers. It is proposed to switch to decentralized, autonomous heat supply from automated boiler houses, including those located on the roofs of buildings, justifying this with lower cost and no need to lay heat pipelines. But at the same time, as a rule, it is not taken into account that the connection of the heat load to the boiler room makes it impossible to generate cheap electricity for heat consumption. Therefore, this part of the ungenerated electricity should be replaced by its production by the condensation cycle, the efficiency of which is 2-2.5 times lower than that of the heating cycle. Consequently, the cost of electricity consumed by the building, the heat supply of which is carried out from the boiler house, should be higher than that of the building connected to the heating system of heat supply, and this will cause a sharp increase in operating costs.
S. A. Chistovich at the anniversary conference "75 years of district heating in Russia", held in Moscow in November 1999, proposed that home boiler houses complement district heating, acting as peak heat sources, where the missing throughput networks does not allow high-quality supply of heat to consumers. At the same time, heat supply is preserved and the quality of heat supply is improved, but this decision reeks of stagnation and hopelessness. It is necessary that the district heating supply fully performs its functions. Indeed, district heating has its own powerful peak boiler houses, and it is obvious that one such boiler house will be more economical than hundreds of small ones, and if the capacity of the networks is insufficient, then it is necessary to shift the networks or cut off this load from the networks so that it does not violate the quality of heat supply to other consumers.
Great success in district heating has been achieved by Denmark, which, despite the low concentration of heat load per 1 m2 of surface area, is ahead of us in terms of district heating coverage per capita. In Denmark, a special state policy is being pursued to prefer the connection to district heating of new heat consumers. In Western Germany, for example in Mannheim, district heating based on district heating is developing rapidly. In the Eastern lands, where, focusing on our country, district heating was also widely used, despite the rejection of panel housing construction, from central heating in residential areas that turned out to be inefficient in a market economy and Western way of life, the area of district heating based on district heating continues to develop as the most environmentally friendly and economically profitable.
All of the above indicates that at the new stage we must not lose our leading positions in the field of district heating, and for this it is necessary to modernize the district heating system in order to increase its attractiveness and efficiency.
All the advantages of joint generation of heat and electricity were attributed to electricity, district heating was financed according to the residual principle - sometimes the CHP had already been built, but the heating networks had not yet been brought up. As a result, low-quality heat pipelines with poor insulation and inefficient drainage were created, heat consumers were connected to heat networks without automatic regulation load, at best, with the use of hydraulic regulators for stabilizing the coolant flow of very poor quality.
This forced the supply of heat from the source according to the method of central quality control (by changing the temperature of the heat carrier depending on outdoor temperature according to a single schedule for all consumers with constant circulation in the networks), which led to a significant overconsumption of heat by consumers due to differences in their operating mode and the impossibility of joint operation of several heat sources on a single network for mutual redundancy. The absence or inefficiency of the operation of control devices at the points of connection of consumers to heating networks also caused an overrun of the volume of the coolant. This led to an increase in the return water temperature to such an extent that there was a danger of failure of the station circulating pumps and this forced the reduction of heat supply at the source, violating the temperature schedule even in conditions of sufficient power.
Unlike us, in Denmark, for example, all the benefits of district heating in the first 12 years are given to the side of thermal energy, and then they are divided in half with electrical energy. As a result, Denmark was the first country to manufacture pre-insulated pipes for ductless installation with a hermetic cover layer and automatic system leak detection, which dramatically reduced heat loss during its transportation. In Denmark, for the first time, silent, supportless "wet-running" circulation pumps, heat metering devices and effective systems for auto-regulating the heat load were invented, which made it possible to build automated individual heating points (ITP) directly in the buildings of consumers with automatic control of the supply and metering of heat in places of its use.
Total automation of all heat consumers made it possible: to abandon the qualitative method of central regulation at the heat source, which causes undesirable temperature fluctuations in the pipelines of the heating network; reduce the maximum water temperature parameters to 110-1200C; ensure the possibility of operation of several heat sources, including waste incinerators, on a single network with the most efficient use of each.
The temperature of the water in the supply pipeline of heating networks varies depending on the level of the established outdoor temperature in three steps: 120-100-80°C or 100-85-70°C (there is a tendency to an even greater decrease in this temperature). And inside each stage, depending on the change in load or the deviation of the outside temperature, the flow rate of the coolant circulating in the heat networks changes according to the signal of the fixed value of the pressure difference between the supply and return pipelines - if the pressure difference drops below the specified value, then the stations turn on subsequent heat generating and pumping units. Heat supply companies guarantee each consumer a specified minimum level of pressure drop in the supply networks.
Consumers are connected through heat exchangers, and, in our opinion, an excessive number of connection steps are used, which is apparently caused by the boundaries of property ownership. Thus, the following connection scheme was demonstrated: to the main networks with design parameters of 125 ° C, which are administered by the energy producer, through a heat exchanger, after which the temperature of the water in the supply pipeline drops to 120 ° C, distribution networks are connected, which are in municipal ownership.
The level of maintenance of this temperature is set by an electronic regulator that acts on a valve installed on the return pipeline of the primary circuit. In the secondary circuit, the coolant is circulated by pumps. Connection to these distributing networks of local heating and hot water supply systems of individual buildings is carried out through independent heat exchangers installed in the basements of these buildings with a full range of heat control and metering devices. Moreover, the regulation of the temperature of the water circulating in the local heating system is carried out according to the schedule, depending on the change in the temperature of the outside air. Under design conditions Maximum temperature water reaches 95°C, recently there has been a tendency to reduce it to 75-70°C, the maximum value of the return water temperature, respectively, 70 and 50°C.
The connection of heating points of individual buildings is carried out according to standard schemes with parallel connection of a hot water storage tank or according to a two-stage scheme using the potential of the heat carrier from the return pipeline after the heating water heater using high-speed hot water heat exchangers, while it is possible to use a hot water pressure storage tank with a pump for tank charging. In the heating circuit, pressure vessels are used to collect water when it expands from heating. membrane tanks, we have more use for atmospheric expansion tanks installed in top point systems.
To stabilize the operation of control valves at the inlet to the heating point, they usually install hydraulic regulator constant pressure drop. And for bringing to optimal mode operation of heating systems with pump circulation and facilitating the distribution of the coolant over the risers of the system - a "partner valve" in the form of a balance valve, which allows, according to the pressure loss measured on it, to set the correct flow rate of the circulating coolant.
In Denmark they don't pay special attention to increase the calculated flow rate of the heat carrier to the heating point when water heating is turned on for domestic needs. In Germany, it is forbidden by law to take into account the load on hot water supply when selecting heat power, and when automating heating points, it is accepted that when the hot water heater is turned on and when the storage tank is filled, the pumps that circulate in the heating system are turned off, i.e., the heat supply to the heating.
In our country, great importance is also attached to preventing an increase in the power of the heat source and the estimated flow rate of the heat carrier circulating in the heating network during the hours of the maximum hot water supply. But the solution adopted in Germany for this purpose cannot be applied in our conditions, since we have a much higher load ratio of hot water supply and heating, due to the large absolute consumption of household water and the higher population density.
Therefore, when automating the heat points of consumers, the limitation of the maximum water flow from the heating network is used when the specified value is exceeded, determined based on the average hourly load of the hot water supply. When heating residential areas, this is done by closing the valve of the heat supply regulator for heating during the hours of the maximum water consumption. By setting the heating controller to some overestimation of the maintained heat carrier temperature graph, which occurs when the maximum watershed is passed, the underheating in the heating system is compensated during periods of drawdown below the average (within set flow water from the heating network - related regulation).
The water flow sensor, which is a signal for limitation, is a water flow meter included in the heat meter kit installed at the heating network inlet to the central heating substation or ITP. The differential pressure regulator at the inlet cannot serve as a flow limiter, since it provides a given differential pressure in conditions of full opening of the valves of the heating and hot water supply regulators installed in parallel.
In order to increase the efficiency of the joint generation of heat and electricity and equalize the maximum energy consumption in Denmark, heat accumulators, which are installed at the source, are widely used. The lower part of the accumulator is connected to the return pipeline of the heating network, the upper part is connected to the supply pipeline through a movable diffuser. With a reduction in circulation in the distribution heating networks, the tank is charged. With an increase in circulation, the excess coolant flow from the return pipeline enters the tank, and hot water is squeezed out of it. The need for heat accumulators increases in CHP plants with backpressure turbines, in which the ratio of generated electrical and thermal energy is fixed.
If the calculated temperature of the water circulating in the heating networks is below 100 ° C, then storage tanks are used atmospheric type, at a higher design temperature, pressure is created in the tanks to ensure that hot water does not boil.
However, the installation of thermostats together with heat flow meters for each heating device leads to an almost double increase in the cost of the heating system, and in a single-pipe scheme, in addition, the required heating surface of the devices increases to 15% and there is a significant residual heat transfer of devices in the closed position of the thermostat, which reduces the efficiency of auto-regulation. Therefore, an alternative to such systems, especially in low-cost municipal construction, are façade automatic heating control systems - for extended buildings and central ones with correction of the temperature graph according to the deviation of air temperature in the collection ducts exhaust ventilation from the kitchens of apartments - for point buildings or buildings with a complex configuration.
However, it must be borne in mind that when reconstructing existing residential buildings, it is necessary to enter each apartment with welding to install thermostats. At the same time, when organizing façade autoregulation, it is enough to cut jumpers between façade branches of sectional heating systems in the basement and in the attic, and for 9-story non-attic buildings of mass construction of the 60-70s - only in the basement.
It should be noted that new construction per year does not exceed 1-2% of the existing housing stock. This shows the importance of reconstruction. existing buildings in order to reduce heating costs. However, it is impossible to automate all buildings at once, and in conditions where several buildings are automated, real savings are not achieved, since the heat carrier saved at automated facilities is redistributed among non-automated ones. The above once again confirms that it is necessary to build the PDC at the existing heat networks at a faster pace, since it is much easier to automate all the buildings that are fed from one PDC than from the CHP, and other already created PDCs will not let an excess amount of coolant into their distribution networks.
All of the above does not exclude the possibility of connecting individual buildings to boiler houses with an appropriate feasibility study with an increase in the tariff for consumed electricity (for example, when laying or re-laying a large number of networks is necessary). But in the conditions of the existing system of district heating from CHP, this should have a local character. The possibility of using heat pumps, transferring part of the load to CCGTs and GTUs is not ruled out, but given the current conjuncture of prices for fuel and energy carriers, this is not always profitable.
Heat supply of residential buildings and microdistricts in our country, as a rule, is carried out through group heating points (CHPs), after which individual buildings are supplied through independent pipelines with hot water for heating and for domestic needs with tap water heated in heat exchangers installed in the CHP. Sometimes up to 8 heat pipelines leave the central heating center (with a 2-zone hot water supply system and a significant ventilation load), and although galvanized hot water pipelines are used, due to the lack of chemical water treatment they are subject to intense corrosion and after 3-5 years of operation on them fistulas appear.
Currently, in connection with the privatization of housing and service enterprises, as well as with the increase in the cost of energy carriers, the transition from group heating points to individual (ITP) located in a heated building is relevant. This makes it possible to use a more efficient system of façade automatic heating control for long buildings or a central system with correction for the internal air temperature in point buildings, it allows to abandon hot water distribution networks, reducing heat losses during transportation and electricity consumption for domestic hot water pumping. Moreover, it is expedient to do this not only in new construction, but also in the reconstruction of existing buildings. There is such experience in the Eastern lands of Germany, where central heating stations were built in the same way as we did, but now they are left only as pumping water pumping stations (if necessary), and heat exchange equipment, together with circulation pumps, control and accounting units, are transferred to the ITP of buildings . Intra-quarter networks are not laid, hot water pipelines are left in the ground, and heating pipelines, as more durable ones, are used to supply superheated water to buildings.
In order to improve the manageability of heating networks, to which a large number of IHS will be connected, and to ensure the possibility of redundancy in automatic mode, it is necessary to return to the device of control and distribution points (CDP) at the points of connection of distribution networks to the main ones. Each KRP is connected to the main on both sides of the sectional valves and serves consumers with a thermal load of 50-100 MW. Switching electric valves at the inlet, pressure regulators, circulating-mixing pumps, a temperature regulator, a safety valve, heat and coolant consumption meters, control and telemechanics devices are installed in the KRP.
The automation circuit of the KRP ensures that the pressure is maintained at a constant minimum level in the return line; maintaining a constant predetermined pressure drop in the distribution network; reduction and maintenance of water temperature in the supply pipeline of the distribution network according to a given schedule. As a result, in the backup mode, it is possible to supply a reduced amount of circulating water with elevated temperature without disturbing the temperature and hydraulic regimes in distribution networks.
KRP should be located in ground pavilions, they can be blocked with water pumping stations (this will allow in most cases to refuse to install high-pressure, and therefore noisier pumps in buildings), and can serve as the boundary of the balance sheet ownership of the heat-releasing organization and the heat-distributing one (the next boundary between the heat-distributing and the wall of the building will be the heat-using organization). Moreover, the KRP should be under the jurisdiction of the heat-producing organization, since they serve to control and reserve the main networks and provide the ability to operate several heat sources for these networks, taking into account the maintenance of the coolant parameters specified by the heat-distributing organization at the outlet of the KRP.
Correct use of the coolant from the heat consumer is ensured by the use of effective control automation systems. Now there are a large number of computer systems that can perform any complexity of control tasks, but technological tasks and circuit solutions for connecting heat consumption systems remain decisive.
Recently, they began to build water heating systems with thermostats, which carry out individual automatic control of the heat transfer of heating devices according to the air temperature in the room where the device is installed. Such systems are widely used abroad, with the addition of mandatory measurement of the amount of heat used by the appliance as a share of the total heat consumption of the building's heating system.
In our country, in mass construction, such systems began to be used for elevator connection to heating networks. But the elevator is designed in such a way that, with a constant nozzle diameter and the same available pressure, it passes a constant flow rate of the coolant through the nozzle, regardless of the change in the flow rate of water circulating in the heating system. As a result, in 2-pipe heating systems, in which thermostats, when closed, lead to a reduction in the flow rate of the coolant circulating in the system, when connected to an elevator, the water temperature in the supply pipe will increase, and then in the opposite direction, which will lead to an increase in heat transfer from the unregulated part of the system (risers) and to underutilization of the coolant.
In a single-pipe heating system with permanent closing sections, when the thermostats are closed, hot water is discharged into the riser without cooling, which also leads to an increase in the water temperature in the return pipeline and, due to the constant mixing ratio in the elevator, to an increase in the water temperature in the supply pipeline, and therefore to the same consequences as in a 2-pipe system. Therefore, in such systems, it is mandatory to automatically control the temperature of the water in the supply pipeline according to the schedule, depending on changes in the outside air temperature. Such regulation is possible by changing the circuit design for connecting the heating system to the heating network: replacing a conventional elevator with an adjustable one, by using pump mixing with a control valve, or by connecting it through a heat exchanger with pump circulation and a control valve on network water in front of the heat exchanger. [
3 DECENTRALIZED HEATING
3.1 Development prospects decentralized heat supply
Earlier decisions to close small boiler houses (under the pretext of their low efficiency, technical and environmental hazard) today turned into over-centralization of heat supply, when hot water passes from the CHPP to the consumer, a path of 25-30 km, when the heat source is turned off due to non-payments or emergency situation leads to the freezing of cities with a million inhabitants.
Most of the industrialized countries went the other way: they improved the heat generating equipment by increasing the level of its safety and automation, the efficiency of gas burners, sanitary and hygienic, environmental, ergonomic and aesthetic indicators; created a comprehensive energy accounting system for all consumers; brought the regulatory and technical base in line with the requirements of expediency and convenience of the consumer; optimized the level of heat supply centralization; switched to the widespread introduction of alternative sources of thermal energy. The result of this work was real energy saving in all areas of the economy, including housing and communal services.
A gradual increase in the share of decentralized heat supply, maximum proximity of the heat source to the consumer, accounting by the consumer of all types of energy resources will not only create more comfortable conditions for the consumer, but also ensure real savings gas fuel.
A modern decentralized heat supply system is a complex set of functionally interconnected equipment, including an autonomous heat generating plant and building engineering systems (hot water supply, heating and ventilation systems). The main elements of the apartment heating system, which is a type of decentralized heat supply, in which each apartment in an apartment building is equipped with an autonomous system for providing heat and hot water, are a heating boiler, heating appliances, air supply and combustion products removal systems. The wiring is carried out using a steel pipe or modern heat-conducting systems - plastic or metal-plastic.
Traditional for our country, the system of centralized heat supply through CHPPs and main heat pipelines is known and has a number of advantages. But in the context of the transition to new economic mechanisms, the well-known economic instability and the weakness of interregional, interdepartmental ties, many of the advantages of the district heating system turn into disadvantages.
The main one is the length of heating mains. The average percentage of wear is estimated at 60-70%. The specific damage rate of heat pipelines has now increased to 200 registered damage per year per 100 km of heat networks. According to an emergency assessment, at least 15% of heating networks require urgent replacement. In addition to this, over the past 10 years, as a result of underfunding, the main fund of the industry has practically not been updated. As a result, heat energy losses during production, transportation and consumption reached 70%, which led to low quality heat supply at high costs.
The organizational structure of interaction between consumers and heat supply companies does not encourage the latter to save energy resources. The system of tariffs and subsidies does not reflect the real costs of heat supply.
In general, the critical situation in which the industry has found itself suggests that in the near future a large-scale crisis situation in the field of heat supply will arise, the resolution of which will require enormous financial investments.
pressing question– reasonable decentralization of heat supply, apartment heat supply. Decentralization of heat supply (DT) is the most radical, efficient and cheap way to eliminate many shortcomings. Reasonable use of diesel fuel in combination with energy-saving measures in the construction and reconstruction of buildings will provide greater energy savings in Ukraine. In the current difficult conditions, the only way out is the creation and development of a diesel fuel system through the use of autonomous heat sources.
Apartment heating is an autonomous supply of heat and hot water individual home or a separate apartment in high-rise building. The main elements of such autonomous systems is: heat generators - heating devices, pipelines for heating and hot water supply, fuel supply, air and smoke exhaust systems.
The objective prerequisites for the introduction of autonomous (decentralized) heat supply systems are:
the absence in some cases of free capacities at centralized sources;
densification of the development of urban areas with housing objects;
in addition, a significant part of the development falls on areas with undeveloped engineering infrastructure;
lower capital investment and the possibility of phased coverage of thermal loads;
the ability to maintain comfortable conditions in the apartment at one's own will, which in turn is more attractive compared to apartments with centralized heat supply, the temperature in which depends on the directive decision on the beginning and end of the heating period;
appearance on the market of a large number of various modifications of domestic and imported (foreign) heat generators of low power.
Today, modular boiler plants have been developed and are being mass-produced, designed to organize autonomous diesel fuel. The block-modular principle of construction provides the possibility of simple construction of a boiler house of the required power. The absence of the need to lay heating mains and build a boiler house reduces the cost of communications and can significantly increase the pace of new construction. In addition, this makes it possible to use such boiler houses for the prompt provision of heat supply in emergency and emergency situations during the heating season.
Block boiler rooms are a fully functionally finished product, equipped with all necessary automation and safety devices. The level of automation ensures the smooth operation of all equipment without the constant presence of an operator.
Automation monitors the object's need for heat, depending on weather conditions and independently regulates the operation of all systems to ensure the specified modes. This achieves better compliance with the thermal schedule and additional fuel savings. In the event of emergency situations, gas leaks, the security system automatically stops the gas supply and prevents the possibility of accidents.
Many enterprises, having oriented themselves to today's conditions and having calculated the economic benefits, are moving away from centralized heat supply, from remote and energy-intensive boiler houses.
The advantages of decentralized heat supply are:
no need for land allotments for heating networks and boiler houses;
reduction of heat losses due to the absence of external heating networks, reduction of network water losses, reduction of water treatment costs;
a significant reduction in the cost of repair and maintenance of equipment;
full automation of consumption modes.
If we take into account the lack of autonomous heating from small boiler houses and relatively low chimneys and, in connection with this, environmental damage, then a significant reduction in gas consumption associated with the dismantling of the old boiler house also reduces emissions by 7 times!
With all the advantages, decentralized heat supply also has negative aspects. In small boiler houses, including "roof" ones, the height of the chimneys, as a rule, is much lower than in large ones, because of the dispersion conditions deteriorate sharply. In addition, small boiler houses are located, as a rule, near the residential area.
The introduction of programs for the decentralization of heat sources makes it possible to halve the need for natural gas and several times reduce the cost of heat supply to end consumers. The principles of energy saving, incorporated in the current system of heat supply of Ukrainian cities, stimulate the emergence of new technologies and approaches that can fully solve this problem, and economic efficiency DT makes this area very attractive for investment.
The use of an apartment heating system for multi-storey residential buildings makes it possible to completely eliminate heat losses in heating networks and during distribution between consumers, and significantly reduce losses at the source. It will allow organizing individual accounting and regulation of heat consumption depending on economic opportunities and physiological needs. Apartment heating will lead to a reduction in one-time capital investments and operating costs, and also saves energy and raw materials for the generation of thermal energy and, as a result, leads to a decrease in the burden on the environmental situation.
The apartment heating system is an economically, energetically, environmentally efficient solution to the issue of heat supply for multi-storey buildings. And yet, it is necessary to conduct a comprehensive analysis of the effectiveness of the use of a particular heat supply system, taking into account many factors.
Thus, the analysis of the components of losses in autonomous heat supply allows:
1) for the existing housing stock, increase the coefficient of energy efficiency of heat supply to 0.67 versus 0.3 for district heating;
2) for new construction, only by increasing the thermal resistance of enclosing structures, increase the coefficient of energy efficiency of heat supply to 0.77 versus 0.45 for centralized heat supply;
3) when using the entire range of energy-saving technologies, increase the coefficient to 0.85 against 0.66 with district heating.
3.2 Energy efficient solutions for diesel fuel
With autonomous heat supply, new technical and technological solutions can be used to completely eliminate or significantly reduce all unproductive losses in the chain of generation, transportation, distribution and consumption of heat, and not just by building a mini-boiler house, but by the possibility of using new energy-saving and effective technologies, such as:
1) transition to fundamentally new system quantitative regulation of generation and supply of heat at the source;
2) effective use of frequency-controlled electric drive on all pumping units;
3) reducing the length of circulating heating networks and reducing their diameter;
4) refusal to build central heating points;
5) transition to a fundamentally new scheme of individual heat points with quantitative and qualitative regulation depending on the current outdoor temperature using multi-speed mixing pumps and three-way regulator valves;
6) installation of a "floating" hydraulic mode of the heating network and a complete rejection of hydraulic balancing of consumers connected to the network;
7) installation of regulating thermostats on apartment heating appliances;
8) apartment wiring of heating systems with installation individual counters heat consumption;
9) automatic maintenance of constant pressure on hot water supply devices for consumers.
The implementation of these technologies allows, first of all, to minimize all losses and creates conditions for the coincidence of the modes of the amount of generated and consumed heat in time.
3.3 Benefits of decentralized heating
If we trace the entire chain: source-transport-distribution-consumer, we can note the following:
1 Heat source - significantly reduced heat dissipation land plot, the cost of the construction part is reduced (no foundations are required for the equipment). The installed power of the source can be chosen almost equal to the consumed one, while it is possible to ignore the load of hot water supply, since during the maximum hours it is compensated by the storage capacity of the consumer's building. Today it is a reserve. Simplifies and reduces the cost of the control scheme. Heat losses are excluded due to the mismatch between the modes of production and consumption, the correspondence of which is established automatically. In practice, only the losses associated with the efficiency of the boiler remain. Thus, at the source it is possible to reduce losses by more than 3 times.
2 Heating networks - the length is reduced, the diameters are reduced, the network becomes more maintainable. Constant temperature regime increases the corrosion resistance of the pipe material. The amount of circulating water decreases, its losses with leaks. Eliminates the need for building complex scheme water treatment. There is no need to maintain a guaranteed differential pressure before entering the consumer, and in this regard, it is not necessary to take measures for the hydraulic balancing of the heating network, since these parameters are set automatically. Experts imagine what a difficult problem it is - to annually carry out hydraulic calculations and work on hydraulic balancing of an extensive heating network. Thus, losses in heat networks are reduced by almost an order of magnitude, and in the case of a roof-top boiler house for one consumer, these losses do not exist at all.
3 Distribution systems of TsTP and ITP. Required
Heat supply systems for large residential areas, cities, towns and industries. enterprises. Their heat sources are thermal power plants or large boiler houses with high efficiency, transporting and distributing the coolant through heating networks with a length of 10-15 km, with a maximum pipe diameter of 1000-1400 mm, which ensures the supply of coolant to consumers in the required quantities and with the required parameters . The capacity of CHP is 1000-3000 MW, boiler houses 100-500 MW. Large district heating systems have several. heat sources, communication backup heating mains, providing maneuverability and reliability of their operation. The centralized heat supply system also includes the heat supply systems of buildings associated with it by a single hydraulic system. and thermal conditions and a common control system. However, due to the variety of technical solutions for heat supply of buildings, they are separated into independent ones. tech. system, called heating system. Therefore, the C.st. starts with a heat source and ends with a subscriber input to the building.
Centralized heating systems are water and steam. Main The advantage of water as a heat carrier is in a much lower energy consumption for transporting a unit of heat in the form of hot water than in the form of steam, which is due to the higher density of water. Reducing energy consumption makes it possible to transport water to long distances without creatures, loss of energy. potential. In large systems, the water temperature decreases by about 1 ° on a path of 1 km, while the vapor pressure (its energy potential) at the same distance by about 0.1-0.15 MPa, which corresponds to 5-10 ° C . Therefore, the steam pressure in the turbine outlets of water systems is lower than that of steam systems, which leads to a reduction in fuel consumption at the CHP. Other advantages of water systems include the possibility of central control of the supply of heat to consumers by changing the temperature of the coolant and simpler operation of the system (no steam traps, condensate lines, condensate pumps).
The advantages of steam include the possibility of satisfying both heating and technology. loads, as well as small hydrostatic. pressure. Given the advantages and disadvantages of heat carriers, water systems are used to supply heat to residential areas, societies, and communes, buildings, enterprises that use hot water, and steam systems are used for industrial applications. consumers, the Crimea needs water vapor. Water C.st. - main systems providing heat supply to cities. Centralization of city heat supply is 70-80%. In large cities with predominantly modern buildings, the level of use of thermal power plants as sources of heat for housing and communal services. sector reaches 50-60%.
In the heating plant steam systems of high parameters (pressure 13, 24 MPa, temperature 565 ° C), produced in the energy. boilers, is fed into turbines, where, passing through the blades, it gives up part of its energy to generate electricity. Main part of the steam passes through the selections and enters the heating plant. heat exchangers, in which it heats the heat carrier of the heat supply system. That. CHPs use high potential heat to generate electricity, while low potential heat is used to supply heat. Combine-ditch. The generation of heat and electricity ensures high fuel efficiency and reduces fuel consumption.
In most district heating systems, the maximum hot water temperature is assumed to be 150°C. Steam temperature in the heating plant turbine sampling does not exceed 127°C. Consequently, at low temp-pax outdoor air in the heating plant. heat exchangers cannot heat water to the required level. For this, peak boilers are used, which operate only at low outdoor temperatures, i.e. remove the peak load. Because heats, the load changes with a change in the outside temperature, and the amount of steam taken from the turbine for heat supply also changes. Unused steam passes through the cylinders low pressure turbine, gives off its energy and enters the condenser, where a vacuum is maintained (pressure 0.004-0.006 MPa), which corresponds to low condensation temperatures of 30-35 ° C, and the cooling water has an even lower temperature, therefore it is not used for heat supply. Thus, only part of the steam passing through the turbine extractions is used for heat supply, which reduces savings. heating effect. However, fuel consumption for the generation of electricity and heat for heat supply is reduced by about 1/4-1/3 on average per year. Economical the effect is also given by the use of large district boiler plants (thermal plants) with high efficiency as sources of heat,
The coolant from heat sources is transported and distributed among consumers through developed heat networks. As a result, thermal networks cover all mountains, territories, and their construction causes the greatest urban development. and exploitation difficulties. During operation, they are subject to corrosion and destruction. Accidental damage leads to failures of heat supply, social and economic damage. As a result, heat networks, being the main element of large heat supply systems, also become the weakest part of them, which reduces savings. the effect of the centralization of heat supply, limits the max. power of the systems. Depending on the method of preparation of hot water C.S.T. divided into closed and open. In a closed system, the water circulating in it is used only as a heat carrier. Water is heated at a heat source, carries its enthalpy to consumers and gives it to heating, ventilation and hot water supply. Water for hot water supply was taken from the mountains. water pipes and is heated in surface heat exchangers by a circulating coolant to the required temperature. The system is closed with respect to atm. air. In open systems, hot water, which is used by the consumer, is taken from the heating network. Consequently, hot water in the system is used not only as a heat carrier, but also directly as water. Therefore, the heat supply system is partly circulating and partly direct-flow. Hot water is prepared at the source of heat, flows directly to consumers and is poured through taps into the atmosphere,
For large cities, the centralization of heat supply is a promising direction. Centralization. systems, especially telefication, consume less fuel. The reduction and enlargement of heat sources improve the conditions for urban development and the ecology of large cities. A smaller number of heat sources makes it possible to drastically reduce the number of chimneys through which combustion products are emitted into the environment. Eliminates the need to create many small fuel depots for storing solid fuels, from where decentralized systems heat supply has to deliver fuel, and from the spread, throughout the city, small boiler houses to take away ash and slag. In addition, with the centralization of heat sources, it is easier to clean flue gases from toxic components.
C.S.T. rationally hierarchical. principle (see Heat supply systems). The diagram shows the principle, the scheme of centralization. closed system heat supply, the source of heat is ukroy CHP (first hierarchy. level). To improve the reliability of heat supply CHP consists of several. energetic. boilers and steam turbines: Osn. CHP elements have reserves. Water vapor from the boilers through the superheater enters the turbines, where it gives up part of its thermal energy, which turns into mechanical energy. and further, in the electric generator, in the electric. The steam from the turbine extractions enters the heating plant. heaters, in which it heats the coolant circulating in the system up to 120°C. Unused steam enters the condenser, where the parameters are maintained: 0.005 MPa and 32 ° C, at which it condenses and gives off its heat to the cooling water. The condensate from the condenser is fed to the deaerator by means of a condensate pump. On the way to it, it passes regenerative heaters (not shown in the diagram). The deaerator receives make-up water from the chemical water treatment and steam from the turbine extraction to maintain the required temperature. In the deaerator, oxygen and carbon dioxide are released from the water, which cause corrosion of the metal. Feed water from the deaerator is fed by feed pumps to steam power plants. boilers (steam generators). On the way, water is heated in high-pressure regenerative heaters (not shown in the diagram). This heating increases the term cycle efficiency. Heating power the water circulating in the system is heated in the heating unit. heaters in the heat cooker. CHP installation. Heating is carried out by steam, which is taken from the turbine and condensed in the heaters. Steam enters the lower heater at a lower pressure (up to 0.2 MPa) than the upper one (up to 0.25 MPa). Condensate from the upper heater enters the lower heater through a steam trap and is then sent to the feed by a co-condensate pump. line. In heating systems, heaters, water can heat up to about 120°C (at 0.25 MPa, saturation temperature is 127°C). At low outside air temperatures, water is heated up to 150 C in peak boilers. Water circulation is provided by circulation. pumps, in front of which make-up water enters the pipeline.
Thermal networks are designed in the form of two levels: master, heat pipelines - the second hierarchy, the level and distribution networks of microdistricts and quarters - the third hierarchy, level. Master, thermal networks reserve.
With large diameters of heat mains, branches from them are connected in a duplicate way on both sides of the sectional valve. If the section to the right of the valve fails, the coolant moves along the branch to the left and vice versa. Such connection excludes the influence of failures of the master, heat pipelines on the reliability of heat supply. Near the connection point of the branch to the main, it is expedient to install a heat pipeline "district heat point - main. the construction of a heating system for the microdistrict, a cut provides automatic. operation management. and emergency hydraulic and thermal conditions. Management is carried out from the control room using a telesystem (see Telecontrol and telecontrol of heat supply). Buildings are connected to the heating networks of microdistricts and quarters through individual heat points, groups of buildings - through central heat points. These networks do not reserve and perform dead ends, therefore their diameters are limited to 300-350 mm. Hot water heat exchangers and a heating and ventilation system connection unit are installed in an individual, heating points, hot water supply heaters are also installed in the center, but heating and ventilation system connection units are located in buildings. Therefore, a four-pipe system goes from the central heating station to the buildings: two pipes with a design temperature of 150-70 ° C for heating and ventilation, one with a temperature of 60 "C and circulation, for hot water supply.
The reliability of the functioning of the heating network system is checked by calculation. Reliability standards ultimately determine the share of non-reserve. networks, the degree of partitioning and duplication otd. elements of the system.
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Production of thermal energy from nuclear fuel for district heating systems... |
With the beginning of the new heating season, the press, as usual, flares up a discussion: what is preferable for our vast and cold country - traditional central heating networks or newfangled individual boiler houses? It would seem that solid economic calculations, extensive experience accumulated Western countries, several successful Russian trials and the general trend in the development of the long-suffering domestic housing and communal services. But, developing concepts and giving peremptory recommendations, aren't we getting too carried away? Is it really outdated and lagged behind today's realities centralized system heating, and are there any possibilities and ways to make it more efficient? Let's try to understand this difficult issue.
Turning to history, one can see that successful attempts to organize central heating of urban areas were made as early as the 19th century. They were caused by both an urgent need and technological progress. Everything is reasonable: it is easier to maintain one large heating boiler, make one chimney, bring fuel, etc. As soon as they appeared Electricity of the net and reliable pumps powerful enough to pump significant volumes of hot water, large district heating networks have also sprung up.
For many reasons, both objective and subjective, the widespread development of centralized heating systems in the Soviet Union began in the 1920s. objective reasons economic and technical arguments became, and subjective - the desire for collectivism, even in such a purely everyday area. The development of heating networks was associated with the implementation of the GOELRO plan, which is still considered an outstanding engineering and economic project of our time. Work on laying communications was not interrupted even during the Great Patriotic War.
As a result of these titanic efforts, by the end of the 20th century. (and at the same time by the decline of the existence of the USSR) in the country there were about 200 thousand km of heating networks, at the very least heating most large, medium and even small cities and towns. All this infrastructure was quite successfully managed, repaired and maintained at a workable level. The reverse side of the unique and rather efficient system in its own way was extremely high heat and energy losses (mainly due to insufficient thermal insulation of pipes and energy-intensive pumping substations). This was not given much importance - the country richest in energy resources did not consider the cost of coolants, and trenches with green grass outgoing steam were a familiar winter landscape throughout the Soviet Union.
Everything changed in the early 90s. The giant collapsed and, among other things, the cellar under the ruins and the housing and communal complex, which includes communications of the central heating supply. Over the 10 years that have passed since the beginning of the collapse of the state, the networks that were repaired from time to time have practically fallen into disrepair. As a result, since the beginning of the new millennium, Russia has been hit by a number of man-made disasters. Far East, Siberia, Karelia, Rostov-on-Don - the geography of unfrozen heating systems extensive. AT heating season 2003-2004 according to the most conservative estimates, more than 300 thousand people found themselves without heating in the dead of winter. The fatality of the situation is that the number of accidents at heating plants due to burst pipes, failure of extremely worn out and inefficient equipment is growing exponentially. Heat losses on still functioning heat pipelines are up to 60%. It is worth considering that the cost of laying 1 km of a heating main is about $300 thousand, while in order to eliminate the existing critical wear and tear of heating networks, more than 120 thousand km of pipelines need to be replaced!
In the current situation, it became clear that in order to get out of this extremely difficult situation, systemic solutions would be required, related not only to the direct investment of money in the "spot" repair of heating mains, but also to a radical revision of the entire policy regarding housing and communal services in general and district heating - in particular . That is why there were projects for the transition of the municipal industry to the systems of individual boiler houses. Indeed, Western experience (Italy, Germany) testified that the organization of such mini-boiler houses reduces heat losses and reduces energy costs. At the same time, however, the fact was ignored that the countries where such heating systems are most developed have a rather mild climate, and such systems are used in houses that have undergone additional (and very expensive!) Re-equipment. While in Russia there is no specific targeted program for the rehabilitation of housing, a massive transition to offline sources heat supply looks at least utopian. However, it must be admitted that in some cases they can be a very successful solution: for example, when building new areas remote from general city communications, when large earthworks or in the Far North, in permafrost conditions, where the construction of heating plants is undesirable for a number of reasons. But for large cities, autonomous boiler houses are not a real alternative to central heating and, according to experts, their share, under the most promising prospects, will not exceed 10-15% of the total heat consumption.
While in Central Europe the idea of autonomous heat supply is actively lobbied, in the countries of Northern Europe (where the climate is close to ours), district heating, on the contrary, is very developed. And, interestingly, largely thanks to the Soviet experience.
In large cities such as Helsinki and Copenhagen, the share of district heating approaches 90%. A quite reasonable question may arise: why in Russia heating plants are a headache for public utilities and the population and a black hole that absorbs money, while in developed European countries- a way to deliver heat cheaply and efficiently to where it is needed?
The answer to this question is complex and involves many aspects. Summarizing, we can say, following the well-known saying: the devil is in the details. And these details are quite simple: using modern equipment, it is possible to ensure that heat losses in the central networks are reduced to a minimum, and since the overhead costs of a large CHP plant in terms of the heated area are lower, the cost of a heat unit is also lower than that of an autonomous point. In addition, a large, well-equipped CHP plant generates less environmental issues than several small ones, giving a total of the same amount of heat. There is another aspect: heating engineers know that only in large installations it is possible to implement the most efficient thermodynamic cycles for cogeneration (co-production of heat and electricity), which is today the most advanced technology. All this led the Scandinavians to opt for district heating. Particularly interesting in this context is the experience of the most energy efficient country in Europe - Denmark.
By the beginning of the 1990s, there was a shift in the interests of the state and society from energy independence issues to social and environmental aspects. At the same time, the priority public policy became the “3E” rule, i.e. maintaining a balance between economic development, energy security and environmental correctness (Economic Development, Energy security, Environmental protection). It must be said that Denmark is probably the only country in the world in which one department is responsible for energy and the environmental situation - the Ministry of Environmental Protection and Energy. In 1990, the Danish parliament adopted the Energy 2000 plan, which proposes to reduce CO2 emissions into the atmosphere by 20% by 2005 (compared to 1998 levels). It should be said that this indicator was already achieved by 2000, largely due to a consistent policy aimed at modernizing and enlarging the existing heating networks. Already by the mid-1990s, the share of district heating systems was about 60% of the total heat consumption (up to 90% in large cities). More than 500,000 installations are connected to the district heating system, providing heat to more than 1 million buildings and industrial facilities. At the same time, the consumption of energy resources per 1 m2 only in the decade since the beginning of the reform in 1973 (see the reference in the margins of "The Experience of Denmark") has decreased by 2 times.
The efficiency of Danish district heating networks is due to low losses in pipelines due to the introduction of new materials and technologies: pipes made of polymers (for example, developed by UPONOR), effective thermal insulation and modern pumping equipment. The fact is that, unlike most countries in Denmark, the operation of district heating systems is regulated not by a change in the temperature of the coolant, but by a change in the circulation rate, which automatically adjusts to consumer demand. At the same time, the use of frequency-controlled pumps is widespread, which can significantly reduce energy consumption. In this niche, the pumping equipment of the GRUNDFOS concern occupies a leading position: its use allows you to save up to 50% of the electricity consumed by the pumps.
Thanks to the listed set of innovations, the heat losses of the main and distribution pipelines in Denmark amount to only about 4%, while the CHP efficiency reaches 90%. Today, there are 170 thousand buildings left in the country (out of a total of 2.5 million) that are not connected to district heating. Most of them should soon switch to district heating.
In Denmark, it is legislated that local authorities are responsible for the implementation of heat and energy conservation programs and guarantee their environmental and economic correctness. This has led nationwide to almost all new buildings being designed with district heating in mind. District heating systems are ubiquitous in densely built-up areas, with CHP plants using cogeneration making up the majority of energy generating enterprises.
As a result of these reforms, over 30 years Denmark has become the most energy efficient country in Europe, where heat and electricity tariffs not only do not increase, but often decrease. At the same time, the environmental situation in the country as a whole has clearly improved.
This convincing example clearly shows that district heating is by no means a deterrent to the development of housing and communal services. Moreover, district heating has resulted in significant energy and heat savings and improved both the quality of life and the environment.
It can be objected that the Danish experience is not applicable in our troubled country. However, the reform of the municipal complex that has begun should help attract investment in this area of economic activity, and these injections should be disposed of as reasonably as possible. Moreover, in Russia there is already a positive experience in the reconstruction of central heating, using, incl. and the Danish experience in this area. For example, in Izhevsk, a loan from the International Bank for Reconstruction and Development was used to rehabilitate worn-out heating networks as part of the improvement of public utilities. The project included, among other things, the modernization of several dozen quarterly ITPs and intra-quarter heating and water supply networks. At the same time, the heat exchangers were completely replaced with modern plate models, the efficiency of which is about 98%, highly efficient control and pumping equipment. New GRUNDFOS TR series mains pumps, circulation pumps for heating systems and CRE pumps with a frequency-controlled electric drive for the hot water supply system were installed in the renovated systems. I must say that thanks to energy savings, this equipment paid for itself after 2 years of operation, while the system was fully automated. At the same time, heating systems were modernized with the use of modern plastic pre-insulated pipes and effective thermal insulation, which made it possible to reduce heat losses in pipelines by 2-3 times and increase the service life of pipes due to the repeated slowing down of corrosion.
The result was a refurbished, efficient central heating and hot water system, and the loan repayments were not a heavy burden on the budget, as the savings in heat and energy were so significant that they more than offset these costs.
Thus, discussions about the feasibility of modernizing and developing existing district heating systems or their total replacement with autonomous heating points, rooftop boilers and apartment heating should be distracted from political aspects and pay attention to the experience of developed and successful countries. And he shows that in the complex complex of housing and communal services there are no single solutions for all occasions, and one should not abandon schemes that have long been tested by time and practice, obeying only fashion trends. Foreign experience has shown that with the use of modern equipment and materials, reconstructed central heating in combination with other technical solutions (including individual systems heat supply) can become the key to the development of new energy-saving technologies and the renewal of the entire housing and communal complex.
according to the materials of the Eurostroy magazine.
Heat supply is the most important utility service in modern cities and serves to meet the needs of the population in heating services for residential and public buildings, hot water supply and ventilation. It is the most energy-intensive segment of energy supply. The consumption of thermal energy in the housing and communal sector of Russia is about half of the total heat consumption in the country, which uses more than 25% of the fuel used annually. The organization of heat supply systems is a difficult task, as it requires significant capital investments, is closely related to the ecological and sanitary state of the environment, and is a socially significant sector of the energy complex. Heat supply systems are classified according to the following criteria:
Source of production of thermal energy;
Degrees of centralization;
The type of coolant;
The method of supplying water for hot water supply and heating;
The number of pipelines of heating networks;
The method of providing consumers with thermal energy, etc.
Without affecting the technical aspects of the whole complex of these features, which are the subject of study of individual disciplines, we will consider the organizational and economic issues of classification according to the source of heat production and the degree of centralization. These two elements of the heat supply system are decisive both for its functioning and for the choice of the form of management.
According to the source of heat production and the degree of centralization, two main types of heat supply are distinguished:
District heating based on combined heat and power generation at CHPPs (cogeneration) and from district heating boiler houses;
Decentralized heat supply from small boiler houses, individual heating devices, etc. At the same time, there are no heating networks and the associated losses of thermal energy.
District heating (DH) first of all, it was developed in cities and regions with predominantly multi-storey buildings. A modern centralized heat supply system consists of the following main elements: a heat source, heat networks and local consumption systems - heating, ventilation and hot water systems. For the organization of district heating, two types of heat sources are used: combined heat and power plants (CHP) and district boiler houses (RK) of various capacities.
District boiler houses of high power (150 - 200 Gcal / h) are built to provide heat to a large complex of buildings, several microdistricts or a city district. Such a concentration of heat loads allows the use of large units, modern technical equipment of boiler houses. This ensures high fuel utilization and efficiency of heat engineering equipment and provides a number of advantages over heat supply from small and medium-sized boiler houses. It is economically expedient to construct CHP plants at high thermal loads (more than 400 Gcal/h).
Combined generation of heat and electricity is carried out at the CHPP, which provides a significant reduction in specific fuel consumption when generating electricity (up to 40%). At the same time, the heat of the working heat-water steam is first used to generate electricity during the expansion of steam in turbines, and then the remaining heat of the exhaust steam is used to heat water in heat exchangers that make up the heating equipment of the CHP. Hot water is used for heating. Thus, in a CHP plant, high-potential heat is used to generate electricity, and low-potential heat is used to supply heat. This is the economic and energy benefits of combined heat and power generation. In general, the efficiency of combined production of heat and electricity using the same fuel is usually 40% higher than in the case of separate production of electricity in a condensing power plant and heat in boiler houses.
Thermal energy in the form of hot water or steam is transported from a CHP or boiler house to consumers through special pipelines called heating networks , which are complex engineering structures. Their length is tens of kilometers, and the diameter of the highways reaches 1400 mm. Heating networks are divided into main lines laid in the main directions of the settlement, distribution networks - within the quarter, microdistrict and branches to individual buildings and subscribers. complex thermal networks according to the ring scheme.
Ensuring the efficient functioning of heat supply systems requires their clear structural organization. The most successful form in this case is their hierarchical construction, in which the entire system is divided into a number of levels, each of which has its own task, decreasing in value from the top level to the bottom. The upper hierarchical level is made up of heat sources, the next level is main heating networks with district heating points (RTP), the lower one is distribution networks with subscriber inputs of consumers. Such a heat supply system makes it possible to ensure its controllability during operation.
The largest amount of heat is spent on heating buildings. Heating load changes with outside temperature. To maintain the conformity of heat supply to consumers, it uses central regulation at heat sources and additional automatic regulation at heat points at consumers. The water consumption for hot water supply is constantly changing, and in order to maintain a stable heat supply, the hydraulic regime of heat networks is automatically adjusted. In this case, the temperature of hot water must be maintained constant and equal to 65ºС.
Despite the advantages of centralized heat supply systems, they have a number of disadvantages, for example, a significant length of heating networks, the need for large investments in the modernization and reconstruction of its elements.
One of the main problems of energy consumption and inefficiency of district heating systems is the massive lack of metering devices and regulators of heat consumption among consumers. Until the beginning of the current century, there were almost no heating system regulators in residential buildings and apartments, and the consumer was deprived of the opportunity to regulate heat consumption for heating and hot water supply. Only at the end of the last century, a course was adopted for the installation of common house meters for heat energy and hot water. This event allowed the residents of such houses to replace the existing heat payment system in accordance with the standards with a payment system in accordance with the actually consumed heat energy. Thus, the possibility of including the cost of heat losses in networks in the bills issued to residents is excluded. Further more stringent strengthening of such requirements is provided by federal law « On Energy Saving and Improving Energy Efficiency and on Amendments to Certain Legislative Acts of the Russian Federation” No. 261-FZ dated November 23, 2009., which will be discussed in more detail later in a special chapter on energy efficiency and energy saving.
It should be noted that in some cases there may be serious competition between centralized and autonomous systems. This situation is facilitated by:
Existing distortions in tariff setting (low gas prices);
Significant losses during the transportation of the coolant, which are actually paid by the consumer;
Frequent shutdowns due to accidents and long-term shutdown of hot water supply in the summer.
The totality of these factors forces the consumer to look for a way out in the creation of an autonomous system, which at this stage also provides cheaper heat. However, a centralized system, in the case of timely modernization and normal functioning, has significant advantages over an autonomous system.
In general, for large cities, autonomous boiler houses are not competitors for large CHPPs and district boiler houses, but serve as their reasonable addition. According to experts, the expedient share of autonomous boiler houses in cities should be 10 - 15% of the potential heat energy market. The scope of autonomous boiler houses includes:
Separate newly built or modernized buildings in densely built-up areas covered by centralized heat supply, where, due to the limited capacity of the heating network, it is impossible to connect additional consumers to it, and the relocation or laying of new heating networks is difficult;
Buildings remote from DH areas;
Houses of low-rise manor buildings;
Buildings with temporary connection to a mobile autonomous source;
Objects with increased requirements for the mode of heat consumption, which cannot be guaranteed to be supplied with heat from the heating network;
Newly constructed facilities in areas where there is a shortage of heat from the main source.
In conclusion, it should be noted that the spontaneous development of autonomous systems can significantly worsen the city's infrastructure that has developed over decades and even lead to its destruction. Therefore, it is necessary to ensure a sufficiently strict urban planning regulation of this process with simultaneous intensive reconstruction of DH systems, which will reduce heat loss, reduce the tariffs for the supplied thermal energy, thereby making the spontaneous construction of autonomous sources in many cases uncompetitive.