Heat supply. District heating systems
Topic questions:
1. The concept of a system district heating.
2. Classification of central heating systems.
3. The device of central heating systems.
District heating provides heat to many consumers located outside the place of its generation.
The district heating system consists of a source of thermal energy, a heating network of a central heating point (CHP) or subscriber inputs and local systems of heat consumers.
According to the type of heat carrier, heat supply systems are divided into: water and steam.
For heat supply of residential, public and industrial buildings, mainly heated water is used as a heat carrier. Steam as a heat carrier is used in heating systems, hot water supply of industrial shops for the needs of technological processes.
Water, as a heat carrier, has a high heat capacity, easy mobility, due to which it is transported over a greater distance. When using water as a heat carrier, the connection of heating and hot water supply systems is simplified, and the possibility of effective regulation is created. In addition, water meets the increased requirements of sanitary and hygienic standards. Disadvantages: significant energy consumption for pumping during transportation. Big density, big hydro static pressure when climbing to a height, large leaks in accidents.
Steam, as a heat carrier, has a high energy potential and much more heat content and heat transfer than water. This allows you to reduce the size of the equipment and the diameters of communications. Steam transportation is carried out due to its internal energy, electricity is required for pumping condensate. With a steam coolant, it is easier to identify and eliminate accidents. In addition, steam has a low density, and when steam is supplied to a considerable height, the steam column exerts an insignificant hydrostatic pressure.
Lack of opportunity quality regulation and the complexity of schemes for connecting water heating systems to steam heating networks are the disadvantages of steam as a heat carrier and limit its use.
According to the method of connecting hot water supply systems to heating networks, heat supply systems are divided into closed and open.
Closed heating systems are connected to heating networks through water heaters, and all network water from the system returns to the heat supply source.
AT open in heat supply systems, hot water is taken directly from the heating network (figure).
By the number of heat pipelines, one-, multi-pipe (usually two-pipe) heat supply systems are distinguished.
According to the method of providing consumers with thermal energy, single- and multi-stage heat supply systems are distinguished.
AT single stage systems heat consumers are connected directly to heat networks. Hot water heaters, elevators, pumps, shut-off and control valves, instrumentation for servicing local heating and water fittings are installed at the nodes for connecting heat consumers to heating networks, called subscriber inputs. If a subscriber input is being constructed for any individual building or object, then it is called individual heating point(ETC).
In multistage systems between the source of thermal energy and consumers place central heat points(CHP), in which the parameters of the coolant can vary depending on the requirements of local consumers.
To increase the range of the heat supply system and reduce the amount of transported coolant and, accordingly, the cost of electricity for its pumping, as well as the diameters of heat pipelines, high-temperature (up to 180 0 C or more) water is used for heat supply purposes. The circulation of the coolant through heat-insulated heat pipes with a diameter of up to 1400 mm, which are laid underground in impassable and semi-passage channels, in through collectors and without channels, as well as above the ground on supports (masts), is ensured by pumping station source of thermal energy.
Questions for self-control:
1. What is called a district heating system?
2. How district heating systems are classified.
3. Describe the heat carriers used in heat supply systems.
4. Explain the diagram of an open heating system
5. Describe closed heating systems.
Bibliography:
1. N.K. Gromov "Water heating network", with. 280-287.
There are two types of heating- centralized and decentralized. With decentralized heat supply, the source and consumer of heat are close to each other. There is no heating network. Decentralized heat supply divided into local (heat supply from the local boiler house) and individual (furnace, heat supply from boilers in apartments).
Depending on the degree of centralization, district heating systems (DH) can be divided into four groups:
1. group heat supply (TS) of a group of buildings;
2. district - TS of the urban area;
3. city - TS of the city;
4. intercity - vehicles of several cities.
The DH process consists of three operations - heat carrier (HP) preparation, HP transport and HP use.
Preparation of HP is carried out at heat-preparation plants of CHP and boiler houses. HP transport is carried out through heating networks. The use of HP is carried out at heat-using installations of consumers.
The complex of installations designed for the preparation, transport and use of the coolant is called the district heating system.
There are two main categories of heat consumption:
For creating comfortable conditions work and life (household load). This includes water consumption for heating, ventilation, hot water supply (DHW), air conditioning;
For the production of products of a given quality (technological load).
According to the temperature level, heat is divided into:
Low potential, with temperature up to 150 0 С;
Medium potential, with temperature from 150 0 С to 400 0 С;
High-potential, with a temperature above 400 0 С.
refers to low-potential processes. Maximum temperature in heat networks does not exceed 150 0 С (in the direct pipeline), the minimum - 70 0 С (in the return pipeline). To cover the technological load, as a rule, water vapor with a pressure of up to 1.4 MPa is used.As heat sources, heat treatment plants of thermal power plants and boiler houses are used. The combined heat and power generation is carried out at the CHPP based on the heating cycle. Separate generation of heat and electricity is carried out in boiler houses and condensing power plants. With combined generation, the total fuel consumption is lower than with separate generation.
The whole complex of equipment for a heat supply source, heating networks and subscriber installations is called a district heating system.
Heat supply systems are classified according to the type of heat source (or method of preparing heat), the type of heat carrier, the method of supplying water to hot water supply, the number of pipelines of the heating network, the method of supplying consumers, the degree of centralization.
By type of heat source There are three types of heat supply:
District heating from CHP, called heating;
Centralized heat supply from district or industrial boiler houses;
Decentralized heat supply from local boiler houses or individual heating units.
Compared with centralized heat supply from boiler houses district heating has a number of advantages, which are expressed in fuel savings due to the combined generation of heat and electrical energy at the CHP; in the possibility of widespread use of local low-grade fuel, the combustion of which in boiler houses is difficult; in improving sanitary conditions and cleanliness of the air basin of cities and industrial areas due to the concentration of fuel combustion in a small number of points located, as a rule, at a considerable distance from residential areas, and more rational use nyu modern methods cleaning flue gases from harmful impurities.
By type of coolant heating systems are divided into water and steam. Steam systems distributed mainly in industrial enterprises, and water systems are used for heat supply of housing and communal services and some industrial consumers. This is explained by a number of advantages of water as a heat carrier in comparison with steam: the possibility of central high-quality regulation of the heat load, lower energy losses during transportation and a greater range of heat supply, the absence of losses of heating steam condensate, greater combined energy production at CHP, increased storage capacity.
According to the method of supplying water to hot water supply water systems are divided into closed and open.
AT closed systems network water is used only as a heat carrier and is not taken from the system. The local hot water supply installations receive water from the drinking water supply, heated in special hot water heaters due to the heat of the network water.
In open systems network water directly enters the local hot water supply installations. At the same time, additional heat exchangers are not required, which greatly simplifies and reduces the cost of the subscriber input device. However, water losses in an open system increase sharply (from 0.5–1% to 20–40% of the total water consumption in the system) and the composition of water supplied to consumers deteriorates due to the presence of corrosion products and lack of biological treatment.
The advantages of closed heat supply systems are that their use ensures a stable quality of hot water supplied to hot water supply installations, the same quality as tap water; hydraulic isolation of water supplied to hot water supply installations from water circulating in the heating network; ease of monitoring the tightness of the system by the amount of make-up.
The main disadvantages of closed systems are the complexity and cost of equipment and operation of subscriber inputs due to the installation of hot water heaters and corrosion of local hot water installations due to the use of non-deaerated water.
The main advantages of open systems heat supply lies in the possibility of maximizing the use of low-grade heat sources for heating a large number make-up water. Since in closed systems make-up does not exceed 1% of the flow network water, the possibility of utilizing the heat of waste and blowdown water at a CHPP with a closed system is much lower than in open systems. In addition, deaerated water enters local hot water installations in open systems, so they are less susceptible to corrosion and more durable.
The disadvantages of open systems are: the need for a powerful water treatment device at the CHP plant to feed the heating network, which increases the cost of station water treatment, especially with increased rigidity of the initial raw water; complication and increase in the volume of sanitary control over the system; complicating the control of the system tightness (since the amount of feed does not characterize the density of the system); instability of the hydraulic regime of the network.
By number of pipelines distinguish one-, two- and multi-pipe systems. Moreover, for an open system, the minimum number of pipelines is one, and for a closed system, two. The simplest and most promising for transporting heat to long distances is a single-pipe open heat supply system. However, the scope of such systems is limited due to the fact that its implementation is possible only if the water flow rate necessary to satisfy the heating and ventilation load is equal to the water flow rate for hot water supply to consumers of this district. For most regions of our country, the consumption of water for hot water supply is significantly less (3-4 times) than the consumption of network water for heating and ventilation, therefore, in the heat supply of cities, two-pipe systems are predominantly used. AT two-pipe system The heating network consists of two lines: supply and return.
By way of providing heat consumers are distinguished one-
step and multi-stage heat supply systems. In one-
In stepped systems, heat consumers are directly connected to heating networks. Nodes for connecting consumers to the network
are called subscriber inputs or local heating points (MTP). At the subscriber input of each building, hot water heaters, elevators, pumps, instrumentation and control valves are installed to change the parameters of the coolant in local consumer systems.
In multistage systems between the source of heat and consumers are located central heating points or sub-stations (CHP), in which the parameters of the coolant change depending on the consumption of heat by local consumers. The central heating station houses a central heating unit for hot water supply, a central mixing plant for network water, booster pumps for cold tap water, automatic control and instrumentation. The use of multi-stage systems with a central heating substation makes it possible to reduce the initial costs for the construction of a heating installation for hot water supply, pumping units and auto-regulating devices due to an increase in their unit power and a reduction in the number of equipment elements.
The optimal design capacity of the CHP depends on the layout of the area, the mode of operation of consumers and is determined on the basis of technical and economic calculations.
According to the degree of centralization heat supply can be divided into group - heat supply of a group of buildings, district - heat supply of several groups of buildings, urban - heat supply of several districts, intercity - heat supply of several cities.
The device and design of thermal networks.
The main elements of heat networks are a pipeline consisting of steel pipes interconnected by welding; an insulating structure that perceives the weight of the pipeline and the forces that arise during its operation.
Pipes are critical elements of pipelines and must meet the following requirements:
Sufficient strength and tightness at maximum values of pressure and temperature of the coolant,
Low coefficient of thermal deformation,
Providing small thermal stress with alternating thermal mode heating network,
Small roughness inner surface,
anti-corrosion resistance,
high thermal resistance pipe walls,
Contributing to the preservation of heat and temperature of the coolant,
Invariance of material properties during long-term exposure high temperatures and pressure, ease of installation,
Reliability of pipe connections, etc.
Available steel pipes do not fully satisfy all the requirements, however, their mechanical properties, simplicity, reliability and tightness of joints (by welding) ensured their predominant use in heating networks.
Pipes for heating networks are made mainly of steel grades St2sp, St3sp, 10, 20, 10G2S1, 15GS, 16GS.
In thermal networks, seamless hot-rolled and electric-welded ones are used. Seamless hot-rolled pipes are produced with outer diameters of 32 - 426mm. Seamless hot-rolled electric-welded pipes are used for all types of network laying. Electrowelded pipes are used in all ways of laying networks. Electrowelded with a spiral seam are recommended for use in channel and overhead network laying.
supports. When constructing heating networks, two types of supports are used: free and fixed. Free supports perceive the weight of the heat pipe and ensure its free movement during temperature deformations. Fixed supports are designed to fix the pipeline at the characteristic points of the network and perceive the forces that arise at the fixation point both in the radial and axial directions under the action of weight, temperature deformations and internal pressure.
Compensators . Compensation for temperature deformations in pipelines is carried out by special devices called compensators. According to the principle of action, they are divided into two groups:
Compensators are radial or flexible, perceiving the elongation of the heat pipe by bending or twisting the curved sections of pipes or by bending special elastic inserts of various shapes;
Axial expansion joints, in which elongation is taken up by telescopic movement of pipes or compression of spring inserts.
The most widely used in practice are flexible expansion joints of various configurations made from the pipeline itself (P - and -S-shaped, lyre-shaped with and without folds, etc.). Simplicity of device, reliability, no need for maintenance, unloaded fixed supports- advantage of these compensators.
The disadvantages of flexible expansion joints include: increased hydraulic resistance, increased pipe consumption, lateral movement of deformable sections, which requires an increase in the width of impassable channels and makes it difficult to use backfill insulation, channelless pipelines, as well as large dimensions that make it difficult to use them in cities when the route is saturated with urban underground utilities .
Axial compensators are made of sliding type (omental) and elastic (lens compensators).
Gland compensator It is made from standard pipes and consists of a body, a glass and a seal. When the pipeline is extended, the glass is pushed into the body cavity. The tightness of the sliding connection of the body and the glass is created by stuffing box packing, which is made of a graphite asbestos cord impregnated with oil. Over time, the packing wears out and loses elasticity, so periodic tightening of the stuffing box and replacement of the packing is required. Lens compensators made of sheet steel are free from this drawback. Welded type lens compensators are mainly used in pipelines low pressure(up to 0.4-0.5 MPa).
The design of the pipeline elements also depends on the method of its laying, which is selected on the basis of a technical and economic comparison of possible options.
, hot water supply) and technological needs of consumers. Distinguish between local and district heating. Local heat supply is focused on one or more buildings, centralized - on a residential or industrial area. In Russia and Ukraine, district heating has become the most important (in this regard, the term “Heat supply” is most often used in relation to district heating systems). Its main advantages over local heat supply 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.
Heat supply classification
Distinguish local and central heat supply. The local heat supply system serves one or more buildings, the centralized system serves a residential or industrial area. Highest value acquired district heating. Its main advantages over local heat supply 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 stoves, hot water boilers, water heaters (including solar), etc.
District heating system
The district heating system includes a heat source, a heat network and heat-consuming installations connected to the network through heat points. Sources of heat in district heating can be combined heat and power plants (CHP) that carry out combined generation of electrical and thermal energy; boiler plants high power, producing only thermal energy; devices for the utilization of industrial heat waste; installations for the use of heat from geothermal sources. Heat carriers in district heating systems are usually water with a temperature of up to 150 ° C and steam under pressure of 0.7-1.6 MN / m 2 (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. Distance over which heat is transported modern systems district heating, reaches several tens of kilometers. The cost of reference fuel per unit of heat supplied to the consumer is determined mainly by the efficiency of the heat supply source. The development of heat supply systems is characterized by an increase in the power of the heat source and unit capacities installed equipment. Thermal power modern thermal power plants reach 2-4 Tcal/h, district boiler houses 300-500 Gcal/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.
According to the schemes for connecting heating installations
According to the schemes for connecting heating installations, there are dependent and independent heating systems
In dependent systems, the heat carrier from the heating network enters directly into the heating installations of consumers, in independent- to an intermediate heat exchanger installed in the heating point, where it heats the secondary heat carrier circulating in the consumer's local installation. AT not dependent systems consumers' installations are hydraulically isolated from the heating network. These systems are mainly used in major 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 the conditions of their strength or when the static pressure created by the latter is unacceptable for the heat network (such, for example, heating systems of high-rise buildings).
According to the connection schemes for hot water supply installations
Depending on the scheme of connection of hot water supply installations, there are closed and open heating systems.
In closed systems, hot water supply is supplied with water from the water supply, heated to the required temperature (usually 0 ° C) by water from the heating network in heat exchangers installed in heating points. In 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 the inner surface of the pipeline, the water supplied to the heating network undergoes water treatment and deaeration. In open systems, the water must also meet the requirements for drinking water. The choice of system is determined mainly by the availability of a sufficient amount of water of drinking quality, its corrosive and scale-forming properties.
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 systems heating supplies are water and steam. Main the advantage of water as a heat carrier 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 greater density water. Reducing energy consumption makes it possible to transport water over long distances without being, energy loss. potential. AT large systems ah, the temperature of water decreases by about 1 ° on a path of 1 km, while the pressure of steam (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. Considering 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 it is impossible to 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. The unexhausted steam passes through the low-pressure cylinders of the turbine, gives off its energy and enters the condenser, where a vacuum is maintained (pressure 0.004-0.006 MPa), which corresponds to low condensing temperatures of 30-35 ° C, and the cooling water has an even lower temp-py, 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 allows you to drastically reduce the number of chimneys through which environment combustion products are emitted. Eliminates the need to create many small fuel depots for storage solid fuel, whence at 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: Main 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 is separated from the water and carbon dioxide, to-rye cause metal corrosion. Feed water from the deaerator by feed pumps is supplied to the steam power plants. boilers (steam generators). On the way, the water is heated in regenerative heaters high pressure(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. Close to node connections it is expedient to install branches to the master, it is advisable to install a heat pipeline "district heating 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... |
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A district heating system includes a heat supply source (CHP or district boiler house), pipelines for heat transport (heat networks) and subscriber units that consume heat.
Centralized heat supply systems from thermal power plants (TPPs) are the most efficient. At present, the implementation of a fundamentally new direction in the centralized heat supply of large cities on the basis of powerful nuclear heat supply stations is beginning.
Steam centralized heat supply systems are used in the Soviet Union, as a rule, in industrial areas.
In boiler houses of centralized heat supply systems, steam drum boilers with natural circulation and once-through water-heating boilers of serial production, as well as, in agreement with the customer, boilers of new types manufactured at installation sites. The type of boiler units depends on the type and method of fuel combustion, productivity, type and parameters of the coolant. Specifications boilers are accepted according to the manufacturer's data.
The implementation of separate and combined centralized heating systems for residential and industrial areas depends on the distance between the niches.
The above necessitated the creation of a special guide for the design of boiler plants of centralized heat supply systems.
In cases where a separate power supply scheme is economically feasible or the concentration of heat loads for the construction of a CHP is insufficient, boiler plants are designed as the main heat sources of centralized heat supply systems.
More than half of the supply of thermal energy (51%) from centralized sources is provided by combined heat and power plants. By the beginning of the eleventh five-year plan, centralized heating systems had been developed in 800 cities of the country.
Optimum Power district heating systems from boiler houses is determined by the heat supply scheme of the area or industrial site and depends on the nature of the heat loads of consumers included in the heat supply area (domestic loads or industrial-io-heating loads with a certain ratio of steam and hot water), capital investments in the construction of boiler houses and heating networks and operating costs for the system as a whole. The criterion that determines the boundaries of the choice of unit capacities of boiler houses and centralized heat supply systems is the reduced costs, determined, on the one hand, by a positive economic effect in the transition from moderate to more powerful heat sources, on the other hand, by a negative economic effect associated with additional costs for heat networks.
Inefficient sources of heat supply, consisting of individual small boiler houses, could not satisfy the grandiose construction being carried out in our country. In search of a solution to this problem, the idea of a centralized heating system was born, which is based on the combined generation of heat and electricity. There are two systems of district heating: district heating and district heating. In the first, the source of heat is a combined heat and power plant (CHP), and in the second, a large regional boiler house. At the CHPP, hot water is prepared in a special heat and power plant, which is equipped with main and peak water heaters (boilers), circulation and make-up pumps, deaerators and mud collectors.
The most efficient sources of heat supply, as is known, are centralized heat supply systems from CHPPs. Despite the obvious advantage of centralized sources, specific gravity individual and quarterly boiler houses of small and medium capacity in the total volume of heat supply sources is still quite large.
Increasing the lower limit of application efficiency combined scheme power supply and the corresponding expansion of the range of thermal loads for a separate scheme is associated with an enlargement of the thermal power of boiler houses and a relative increase in the technical and economic indicators of heat supply systems. In this regard, the design solutions for boiler houses of centralized heat supply systems are subject to increased requirements in terms of efficiency and modern technical level. Meanwhile, in the development of boiler projects by numerous design organizations, there is still an approach to their design as a solution to a local problem, without taking into account the requirements of heat supply schemes for the choice of heat sources.
Heating and ventilation technology has a long history of development. From heating dwellings by making fire on earthen floor, used in ancient times, to modern district heating systems with a range of several kilometers and automatically operating installations for creating an artificial climate in residential, public and industrial buildings - this is the path traveled by heating and ventilation technology.
Instructions for the design of rooftop boilers using as fuel natural gas contains Additional requirements to current regulatory documents when placing heat sources on the roofs of buildings. The use of such boiler houses is mainly caused by a shortage of thermal power of a centralized heat source or the inappropriateness of connecting the building to a centralized heat supply system according to a feasibility study.