Thermal diagrams of boiler houses. Schematic diagram of a boiler room with steam boilers
Depending on the nature of the heat loads, boiler rooms are divided into the following types:
Production- designed to supply heat to technological consumers.
Industrial and heating- providing heat supply to technological consumers, as well as providing heat for heating, ventilation and hot water supply of industrial, public, residential buildings and structures.
Heating- generating thermal energy for the needs of heating, ventilation and hot water supply of residential, public, industrial buildings and structures.
According to the reliability of heat supply to consumers, boiler houses include:
The first category includes boiler houses, which are the only source of heat in the heat supply system and provide consumers of the first category who do not have individual backup heat sources;
Heat consumers in terms of heat supply reliability include:
The first category includes consumers whose disruption of heat supply is associated with a danger to human life or with significant damage to the national economy (damage to process equipment, mass defective products);
3.2.1. Thermal diagrams of boiler houses with hot water boilers and the basics of their calculation
In order for the thermal diagrams of boiler rooms with hot water boilers to be easily read, the following order of displaying equipment on them is recommended (see Fig. 3.1). On the upper right side of the sheet is placed hot water boilers, and on the left - deaerators, below the boilers they place recirculation and even lower network pumps, and under the deaerators - heat exchangers (heaters), tanks of deaerated and working water, make-up pumps, pumps raw water, drainage tanks and a purge well.
Operation of a heating boiler house, basic thermal scheme which is shown in Fig. 3.1 is carried out as follows. Water from the return line of heating networks with a small pressure enters the suction of the network pump 2 . Water is supplied from the feed pump there. 6 compensating for water leakage in heating networks. On the suction pump 2 served and hot water, the heat of which is partially used in heat exchangers 9 And 4 for heating, respectively, chemically purified and raw water.
In order to ensure that the water temperature in front of the boiler, set from the conditions for preventing corrosion, is fed into the pipeline after the mains pump using a regulator. circulation pump 12 required amount of hot water from the boiler 1 . The line through which hot water is supplied is called recirculation. In all operating modes of the heating network, except for the maximum winter, part of the water from the return line after the network pump 2 , bypassing the boiler, is fed through the bypass line into the supply line, where it, mixed with hot water from the boiler, provides the specified design temperature in the supply line of heating networks. Water intended to replenish leaks in heating networks is preliminarily supplied by a raw water pump 3 to raw water heater 4 , where it is heated to a temperature of 18–20 ºC and then sent to chemical water treatment. Chemically purified water is heated in heat exchangers 8 , 9 And 11 and deaerated in the deaerator 10 . Water for feeding heating networks from a deaerated water tank 7 picks up booster pump 6 and feeds back.
The main purpose of calculating any thermal scheme of a boiler house is the selection of the main and auxiliary equipment with the determination of the initial data for subsequent technical and economic calculations.
The reliability and efficiency of hot water boilers depend on the constancy of the water flow through them, which should not decrease relative to that set by the manufacturer. To avoid low temperature and sulfuric acid corrosion convective surfaces heating, the temperature of the water at the inlet to the boiler when burning sulfur-free fuels must be at least 60 ºС, low-sulfur fuels - at least 70 ºС and high-sulfur fuels - at least 110 ºС. To increase the water temperature at the inlet to the boiler at water temperatures below the specified recirculation pump.
Vacuum deaerators are often installed in boiler rooms with hot water boilers. But they require careful supervision during operation, so they prefer to install atmospheric deaerators.
The hot water supply system - closed or open - has a strong influence on the equipment of a boiler room with water-heating units. open is a system in which the heat carrier - hot water - is partially or completely used by the consumer. IN closed systems, water is heated for hot water supply by direct heating water in local heat exchangers.
With an open hot water supply system, the amount of water used to feed heating networks increases markedly and can reach 20% of the water flow through heating networks. Those. the amount of water that needs to be prepared for chemical water treatment, with an open hot water supply system, increases several times compared to a closed one.
Since water consumption in an open system is uneven, storage tanks for deaerated water are installed to even out the daily load schedule for hot water supply and reduce the estimated productivity of water treatment equipment. Of these, during the hours of maximum consumption, hot water is supplied by make-up pumps to the suction of network pumps.
The quality of water treatment for feeding an open heating system should be significantly higher than the quality of water for feeding a closed system, because. Hot water is subject to the same requirements as drinking tap water.
Before calculating the thermal diagram of a boiler house operating on closed system heat supply, you should choose a scheme for connecting local heat exchangers to the heat supply system that prepare water for the needs of hot water supply. Currently, three schemes for connecting local heat exchangers are mainly used, shown in fig. 3.2.
On fig. 3.2 but the scheme of parallel connection of local heat exchangers of hot water supply with the heating system of consumers is shown. On fig. 3.2 b, in two-stage serial and mixed circuits for switching on local heat exchangers for hot water supply are shown.
The choice of the scheme for connecting local heat exchangers for hot water supply is made depending on the ratio of the maximum heat consumption for hot water supply to maximum flow heat for heating. At Q g.w / Q o ≤0.06 connection of local heat exchangers is carried out according to a two-stage sequential scheme; at 0.6< Q g.w / Q o ≤1.2 - by two-stage mixed scheme; at Q g.w / Q o ≥1.2 – by parallel circuit. With a two-stage sequential scheme for connecting local heat exchangers, switching of the heat exchangers to a two-stage mixed scheme should be provided.
The calculation of the thermal circuit of a hot water boiler house is based on solving the equations of heat and material balance, compiled for each element of the circuit. When calculating the thermal scheme of a hot water boiler house, when there are no phase transformations of the heated and cooled media (water), the heat balance equation in general form can be written as follows
where G Oh, G m is the mass flow rate of the cooled and heated coolants, respectively, kg/s; c Oh, c n is the average specific heat of the cooled and heated coolants, respectively, kJ/(kg °C); 
are, respectively, the initial and final temperatures of the cooled coolant, °C; 
are, respectively, the initial and final temperatures of the heated coolant, °C; η is the efficiency of the heat exchanger.
If the discrepancy between the values previously taken in the calculation and those obtained as a result of the calculation is more than 3%, the calculation should be repeated, substituting the obtained values as the initial data.
When choosing the power of boilers, it is desirable to consider the following:
Rules for the use of gas and the provision of gas supply services in the Russian Federation, Appendix 2
up to 0.29 Gcal/h ( 340kW) |
SP 89.13330.2016
|
For boilers with water temperatures above 115°C: Industrial safety rules for hazardous production facilities using pressurized equipment
“Before firing up a gas-fired boiler, the tightness of the closing of the shut-off valves in front of the burners must be checked in accordance with current regulations” |
In addition, for boilers of any (?) heating capacity:
_____
* Considering the combination of three or more identical boilers by organizing a passing movement of the coolant (with a “Tichelmann loop”), I came to the following conclusion: the capacity Kv of the collector section before the second boiler and after the penultimate boiler should be at least 3⋅(n - 1 )⋅(Kv boiler branch), where n is the number of boilers.
3 Burner: my choice
If I chose a block burner, I would choose a burner with a mechanical gas-air connection (with one servo). Well, and, accordingly, the firebox - short-flame or long-flame. For example, the ELCO burner of the EK 9 G series is very attractive. It captivates with the adjustment mechanism for the supply of air and gas: with the help of support pins and “skis” sliding on them, you can make an almost linear relationship “angle of rotation - heat output”:
During commissioning and operation, there will be less hassle if the burner is not equipped with a “combustion manager”, but with a simpler device - a “combustion machine”. In the case of using a burner with a “combustion manager”, it is sometimes desirable to provide for automatic shutdown of its power supply in case of an unacceptable deviation in gas pressure.
The burner servomotor must be of “modulating” design (with a full stroke time of at least 20 seconds). In the mode of smooth change of heat output, in contrast to the two- and three-position control, the temperature of the heating surfaces of the boiler becomes maximum only in the hours or days of its operation. maximum load rather than, say, every 5-10 minutes. This minimizes the fur. voltage in the boiler, reduces the growth of deposits on the heating surfaces on the water side, increases efficiency.
Also, modulating burners allow, if desired / necessary, to receive water from the boiler with the highest possible temperature CONTINUOUSLY.
This is especially important if
In warm weather, the heating load is minimal or non-existent. In warm weather, the vacuum created by the chimney is also minimal. Despite this, stage burners sometimes operate at full power and at the same time create excess pressure in the flue gases. Modulating burners, on the other hand, can operate CONTINUOUSLY at partial load, while maintaining a vacuum in the chimneys.
Another of my technical sympathies is burners with an “automatic furnace”. But once I had a chance to set up a WM-G20/2-A with a “combustion manager” and a frequency controller. Initially, I set it up in violation of the manufacturer's instructions. But then I really liked how quietly the fan works at low boiler loads. The fact is that on a boiler with Qnom = 1 Gcal/h, 50% of the rotational speed of 2900 rpm was enough for the “gas-air” settings up to half of its heat output. Even at 0.7 Gcal/h the fan was still running quietly (62%).
And at a minimum of heat output (0.2 Gcal / h), it is pleasing that the angle of rotation of the air damper is 8.6 ° (if desired, there is room to reduce). Class!
When choosing the type of burner, it is desirable to consider the following:
4 Boiler control unit: my choice
As a boiler control unit, I would put a “3-position controller” thermostat and an emergency thermostat (for example, simple Vitotronic 100 KC3), and I would do smooth regulation and cascade control somehow separately (see).
The Vitotronic 300 GW2 is well suited for a single boiler. It has two temperature control channels (according to temperature charts). There is also connector 17A for connecting the boiler return temperature sensor “Therm-Control”, and connector 29 for connecting the boiler pump, and connector 50 “Failure”.
5 Increasing the survivability of the boiler house
Once upon a first acquaintance with Viessmann control units, I was annoyed by the fact that in beautiful orange cases for controlling the boiler room there was not so much provided for as one might expect. Like, if you want your backup pump to automatically turn on, buy and install some other device ... I reasoned like this. Here we are using a personal computer. Even if its cost is low, it can perform many operations per second. So, probably, it is better to make one shield in the boiler room with a freely programmable controller, which can be programmed to perform all the required actions.
But after I saw that when the gas was shut off, the “native” burner of the Viessmann boiler simply turned off without any ringing, and when the gas pressure appeared, it turned on as if nothing had happened, my opinion changed diametrically.
By the way. Loss of gas pressure (impermissible decrease in pressure) does not threaten either the boiler or the people in the boiler room. Therefore, it is quite logical that after the restoration of normal gas pressure, the burner automatically starts.
Likewise with power supply.
It is possible to significantly increase the survivability of the boiler house if the control is divided. There is water pressure at the inlet or outlet of the pump - it works, no - it turns off. And this must be implemented by the “local” pump control unit, not by the general boiler control unit!
The most noticeable increase in survivability is possible if it is possible to use single-phase electric motors. The power supply terminal block of the general boiler control unit has burnt out, or two phases of the power supply of the boiler room have “sunk”, but the boiler room is working!!!
More about power supply. Once upon a time, many years ago, I saw that in one boiler room the 2TRM1 meter-regulators “hung” after the “light flashed” (there was a transition to AVR). I think this problem can be solved for these controllers, and for others, if you put a time relay in the input panel and delay turning on the power supply for at least half a minute. And even better - put a "voltage monitor".
6 Butterfly valves at boiler inlets and outlets
Butterfly valves (DPZ, butterfly valves) installed at the boiler inlets serve to reduce the water flow of non-operating boilers to an insignificant flow rate necessary for the boilers to remain heated by the “return” (that is, the valves must be closed, but not tightly ). Control of the boiler DPZ - from the connector "29". The command “Turn on the boiler pump” is the opening of the DPZ, “switching off” is the closing.
Estimated water flow through the boiler (simplified formula):
design flow, m 3 / h \u003d maximum heat output of the boiler, Gcal / h 1000 / (tout.max - tin.max)
For example: 1.8 Gcal / h 1000 / (115-70) \u003d 40 m 3 / h
During single operation of each pump/boiler, it is necessary to set the water flow at a level between the “calculated” value for the boiler and the maximum allowable value for the pump (at first, closer to this maximum allowable value) .
7 About pumps
Firstly, you can not turn the pump into an air collector: you need to place it as low as possible. This minimizes the likelihood of cavitation, dry running, creates more suitable conditions for its maintenance and repair. The ideal orientation for an in-line pump (particularly a wet rotor) is one where water flows through it from bottom to top.
Secondly, in order to be able to remove / disassemble the pump for repair at any time (or take it to the workshop), single (not double) pumps should be used. At one of the pumps doubled for repair, it is necessary to stop both electric motors and disassemble everything on the spot. A single pump can be easily removed and sent to the workshop. In addition, single pumps are much more transportable.
Thirdly, a rigid hydraulic connection “pump-boiler” reduces the survivability of the boiler house. Something happened to the boiler pump - consider that one more efficient boiler has also become less. And vice versa.
In order to ensure that in the event of a failure of one pump it can be replaced by a backup pump, the pump outputs (boiler inputs) must be combined:
In a normal situation, the control unit of each boiler gives a command to turn on “its own” boiler pump. If this pump fails, then either the automation or the person turns on another pump from among those that are not working at that time (if there are any, of course).
Automatic control of boiler pumps from a circuit that, after the first start of the pump, will leave at least one boiler pump in operation if there is a command to turn on the heating system pump (using a kpi35 pressure switch or a pair of “EKM plus signaling device ROS-301R / SAU-M6” ).
In general, the number of boiler pumps turned on is equal to the number of boilers running.
If, nevertheless, instead of ATS of boiler pumps, a choice is made in favor of creating “pump-boiler” pairs, then it is advisable to combine the outputs of these pumps with at least an impulse tube (through taps 11b18bk?) so that idle boilers are heated by “input” water, and not by water coming from the outlet of the operating boiler (flow rate exceeding the leakage through the check valves):
In the case of two identical boilers, the flow capacity Kv at the orifice or valve must be greater than the value calculated from the formula “relative leakage ⋅ Kv boiler branch / Kv load branch of the boiler circuit”. For example, diaphragm Kv > (0.001⋅200)⋅150/300, i.e. diaphragm Kv >0.1. It is clear that in the case of three boilers a significantly higher Kv of the diaphragm is required. By the way, Kvs of a 11b18bk crane is about 0.8?
If it is expected that during operation there will be a relatively fast growth loads (for example, due to air handling units or greenhouses), then it is possible to preheat the reserve fire-tube-smoke boilers with water that flows in the opposite direction - from the output to the input ("leaky check valve").
Control of network pumps (heating pumps):
8 About three-way valves
It was probably in 2005: in one start-up boiler room, I encountered a failure of the electric drives of three-way rotary valves installed on the side of the heating water of plate water heaters). In some positions, the segment stuck (due to pressure drop?), and the steel gears (pressed?) broke their teeth ...
Here, in the TM-schemes, the three-way valve is shown installed at the mixing point of the boiler feed and return network water. Of course, it would be possible to install it at the point of separation - after the network pumps. The water temperature is lower there. But firstly, if the three-way valve is located in the upper node according to the scheme, then its operation does not affect the water pressure in the boiler (in the lower node, when it is “closing”, the water pressure in the boiler could significantly decrease). Secondly, when the rotary valve is used for mixing, the water pressure drop slightly “presses” the segment from the seat (saddles), which significantly reduces the load on the electric drive and eliminates vibration of the shutter:
And thirdly, to work with such an insignificant hydraulic resistance, which is hydraulic arrow(bridge), a valve with higher Kvs can be used. And for three-way valves with a linear electric actuator, Kvs is higher in mixing mode than in separation mode.
By the way, in the boiler room it is desirable to use as “large” three-way valves as possible - up to the value of Kvs = 4Gmax (I wrote about this on the ABOK forum).
Function bandwidth kv
This is how the graph of the change in the total Kv of a three-way valve and a water heater may look like:
As the three-way valve to the water heater opens, Kv decreases and, accordingly, the water flow through the boiler decreases.
Of course, there are thermal schemes in which such disgrace does not occur (see). Nevertheless, I decided that the scheme without heating water pumps for water heaters has the right to exist. Refuse the three-way valve and at the same time make sure that with an increase in the heat load, the water flow through the boiler at least does not decrease - these were my guidelines.
I think that using a ball valve and a DPZ instead of a three-way valve, this problem can be solved even for smooth control:
DPZ is selected with Kvs within one or two Kv of a new (clean) water heater. The ball valve is selected with such Kvs to ensure the water flow through one boiler with the water heater turned off (shut off) within 0.5–1 of the “calculated” value. The DPZ servo must be with a turn time of 90 degrees, 2 times longer than the turn time ball valve: the crane will work simultaneously with the DPZ when the latter is turned in the sector 45÷80 degrees (an additional limit switch should work at 45 degrees).
The graph shows that with an increase in the heat load (that is, when the DPZ of the water heater is opened), Kv increases monotonously. The flow of water through the boilers will also increase monotonously:
For water heaters with two loads, e.g. heating and domestic hot water:
This is how the three-way “ compound valve”(connection“ according to the Shtrenev scheme ”):
And an example of the calculation results:
In this scheme, it is highly desirable that the design pressure drop of the heating water for the water heater be within 0.5 kgf / cm 2.
To work with a water heater Kv 50 ... 60, as a result of the calculation, a three-way rotary valve Kvs40 and a DPZ Tecofi Dу50 Kvs117 were selected. Instead of the throttle diaphragm shown in the diagram, it is desirable to make the transition of the pipeline to a smaller diameter. For example, one meter can be used to obtain a Kv30 bandwidth steel pipe DN32.
In this case, the throughput values are related as 0.5: 0.7: 1: 2. When choosing a water heater with a higher Kv (for higher flow), this ratio may become somewhat different - for example, this: 0.1: 0, 2:1:6.
Such a “composite valve” can also be well suited for a boiler room with water heaters for heating and hot water:
It is advisable to take this into account when controlling the heat output in order to avoid excessive overshoot of the water temperature at the boiler outlet. During the commissioning of the boiler house, it is desirable to see in what range the water flow through the boiler operating “alone” for one water heater changes: does it exceed the maximum allowable value for the pump? In case of excess:
9 DHW heating
To smooth the peaks of the required power, high-speed water heaters can be combined with capacitive (relatively low power). This storage water heater can serve as a make-up tank when cold water is turned off:
For the "breathing" of the storage water heater, it is necessary to install an appropriate special device on it (or just an automatic air vent?).
The PID controller maintains a constant water temperature at the outlets of high-speed water heaters by smoothly changing the temperature of the heating water.
The fact that the temperature of the heating water is set to the minimum required level, minimizes the formation of deposits in water heaters.
Is it possible to use the "333" channel "heating circuit" for smooth temperature control DHW water or the temperature of the water at the inlets of the boilers? Logically, if it were possible to set one temperature graph for the M2 channel, and another for the M3 channel, then - no problem! IN technical description device (RE) it is written that “changing the slope and level heating characteristic carried out for each heating circuit separately”. Then the next step is to minimize the dependence of the set temperature, for example, on the M3 circuit (now it is the DHW temperature) on the outdoor temperature. If you set the set room temperature to 20°C, the “heating characteristic” level is +30, and the slope of the “heating characteristic” is 0.2, then at tnv=+20°С the set circuit temperature will be 50°С, and at tnv= -28° C - somewhere around 58 ° C.
The command for turning on the heating water pump can be taken from connector 20M3, and the DHW circulation pump from connector 28 (coding “73:7”).
The survivability of the boiler house is significantly increased due to the possibility of replenishment from a storage water heater in the event of a water supply interruption. In this case, you just need to open the valve at the inlet of the make-up pump and turn on this pump.
For the case when a “small” high-speed water heater is used, designed for an average daily load, and a “large” capacitive water heater -
If in DHW system If a storage tank is used, in order to automate its filling at night, it is convenient to use the Vitotronic 333's ability to set the "time program for the operation of the circulation pump" -
The throttle diaphragm is shown conditionally on the DHW circulation pipeline. In fact, throttle diaphragms must be installed in the circulation pipelines of consumers.
It is known that the maximum hourly thermal load DHW on weekdays exceeds its hourly value, averaged per day, as they say, at times. But often established thermal power the boiler room is selected in such a way that it becomes equal to the sum of the design loads of heating, ventilation and some significantly averaged DHW loads. As a result, during maximum load DHW temperature hot water is below normal. There are two ways out of this situation: heat accumulation on DHW needs, heat storage for heating. If it is possible to use the heat storage capacity of buildings, then the second solution may become preferable. In this case, it is necessary, firstly, to replace at least the high-speed DHW water heater with an increase in its calculated heat flow to the actual required value, and secondly, to create a priority of the DHW load. One of the options for such a priority can be implemented in a thermal scheme with an upstream DHW high-speed water heater:
Most likely, the following conditions will need to be met:
the heating water heater is manufactured based on a relatively low temperature difference - much lower than that which can be created in a given boiler room at the highest possible water temperature at the common outlet of the boilers;
the maximum possible water temperature at the common outlet of the boilers is high enough to use the entire installed heat output per hour, when the total load of DHW and heating is equal to or exceeds it;
deviations from the “paper” heating temperature graph are acceptable for the consumer: both a decrease in the supply temperature that occurs during hours of high DHW load, and its increase during the rest of the day (to compensate for temporary “underheating”, an increased temperature graph must be set to the direct network water regulator) .
Screenshot of the page in Excel with a template for my calculation of the upstream circuit (DHW water heater, heating water heater, three-way valves) -
An interesting option is a circuit with an upstream DHW heater, which has a pump with a frequency-controlled electric drive on the side of the heating water. In combination with this, it is possible to make a dependent connection to the heating network:
Due to the fact that the circuit of the boilers will turn out to be short-circuited (the taps in the closing section are always open), it will be possible to use water tube boilers with simple pumps. Some variability of water flow through the boiler will be acceptable: this is either an increase in flow due to the heating water pump (if the parameters of the heat generation mode are not high enough: the number of pumps/boilers started and the water temperature at their outlets), or an insignificant decrease in water flow through an already operating boiler from -for the launch of another pump/boiler (insignificant if the launch is “leading”, before the development of the previous situation).
10 Heating water temperature control
It will be much more convenient if the heating network water temperature controller that controls three-way valve(or a pair of DPZ), will support temperature chart the temperature not of the direct heating water, but the arithmetic mean (treq.set + treq.set)/2. This value is practically the same as the “average temperature of the heater” (if we imagine each consumer connected to the heating network as one heater). In this case, you can adjust the hydraulic regimes, that is, “press” the branches where required - in the course of this, the regulator itself will adjust the temperature of the direct network water (increase it).
I was not the first to come to this idea, it will be enough to refer at least to the following article:
To implement this, the Vitotronic 333 requires not one, but four clamp-on sensors for the “heating circuit flow temperature” – two each on the flow and return pipes, connected in parallel-series.
Such regulation can also be required simply with an unstable heat load - with heating combined with hot water and ventilation.
Maintaining the value (treq.set + trev.set)/2 is equivalent to maintaining the “generalizing temperature parameter P” in following form: P = treq.set + trev.set
For emergency make-up (in case of rapidly increasing or large leakage), an electrically operated ball valve can be supplied. Its inclusion (opening) can be adjusted, for example, to a threshold of 3 kgf / cm 2, switching off (closing) - to 3.2 kgf / cm 2. This can be done using a pair of "EKM plus signaling device ROS-301R / SAU-M6".
Compared to the well-known circuit (two relays for 220 V), this bundle (“EKM plus signaling device ROS-301R / SAU-M6”) has some advantages: EKM becomes electrically safe, the effect of EKM contact bounce is completely eliminated, the load is significantly reduced on contacts - they will not burn.
In a situation where the pressure of the return network water begins to exceed a predetermined value, it is desirable to form a continuous “close” command for the control valve.
Make-up of the heating system of the administrative building
(coolant leaks are insignificant, noise is acceptable)
In this case, as executive body opening the make-up, a solenoid valve can be used. IN simple version to turn it on, you can use the pressure switch kpi35. For the convenience of setting the thresholds for turning on and off the make-up, you can use a pair of “EKM plus annunciator ROS-301R/SAU-M6”.
You can limit the make-up in the event of a heating system break, for example, by placing in series with the solenoid valve “ three-way valve for pressure gauge” 11b18bk. In case of their revision-repair and for quick filling of the system, it is necessary to make a common bypass with a ball valve.
the Peace of "I",
Vyacheslav Shtrenev
Related articles:
Thermal diagrams of boiler houses with hot water boilers for closed heat supply systems
The choice of a heat supply system (open or closed) is made on the basis of technical and economic calculations. Using the data received from the customer and the methodology set out in § 5.1, they begin to draw up, then calculate the schemes, which are called thermal schemes of boiler rooms with hot water boilers for closed heat supply systems, since the maximum heat output of cast iron boilers does not exceed 1.0 - 1, 5 Gcal/h.
Since it is more convenient to consider thermal schemes on practical examples, below are the principal and detailed diagrams of boiler houses with hot water boilers. Schematic diagrams of boiler rooms with hot water boilers for closed heat supply systems operating on a closed heat supply system are shown in fig. 5.7.
Rice. 5.7. Principal thermal diagrams of boiler rooms with hot water boilers for closed heat supply systems.
1 - hot water boiler; 2 - network pump; 3 - recirculation pump; 4 - raw water pump; 5 - make-up water pump; 6 - make-up water tank; 7 - raw water heater; 8 - heater for the chemistry of purified water; 9 - make-up water cooler; 10 - deaerator; 11 - vapor cooler.
Water from the return line of heating networks with a small pressure (20 - 40 m of water column) flows to network pumps 2. Water is also supplied there from make-up pumps 5, which compensates for water leaks in heating networks. Hot network water is also supplied to pumps 1 and 2, the heat of which is partially used in heat exchangers for heating chemically treated 8 and raw water 7.
To ensure the water temperature in front of the boilers, set according to the conditions for preventing corrosion, the pipeline after the network pump 2 is supplied with required amount hot water coming out of hot water boilers 1. The line through which hot water is supplied is called recirculation. Water is supplied by a recirculation pump 3, which pumps heated water. In all operating modes of the heating network, except for the maximum winter one, part of the water from the return line after the network pumps 2, bypassing the boilers, is supplied through the bypass line in the amount of G lane to the supply line, where water, mixing with hot water from the boilers, provides the specified design temperature in the supply line of heating networks. The addition of chemically treated water is heated in heat exchangers 9, 8 11 and deaerated in deaerator 10. Water for feeding heating networks from tanks 6 is taken by make-up pump 5 and fed into the return line.
Even in powerful hot water boilers operating for closed heat supply systems, one make-up water deaerator with low productivity can be dispensed with. The capacity of make-up pumps is also reduced, the equipment of the water treatment plant is also reduced, and the requirements for the quality of make-up water are reduced compared to boilers for open systems. The disadvantage of closed systems is some increase in the cost of equipment for subscriber hot water supply units.
To reduce water consumption for recirculation, its temperature at the outlet of the boilers is maintained, as a rule, higher than the temperature of the water in the supply line of heating networks. Only with the calculated maximum winter mode, the water temperatures at the outlet of the boilers and in the supply line of the heating networks will be the same. To ensure the calculated temperature of the water at the inlet to the heating networks, the water leaving the boilers is mixed with network water from the return pipeline. To do this, a bypass line is installed between the pipelines of the return and supply lines, after the network pumps.
The presence of mixing and recirculation of water leads to operating modes of steel hot water boilers that differ from the mode of heating networks. Hot water boilers work reliably only if the amount of water passing through them is maintained constant. The water flow must be maintained within the specified limits, regardless of fluctuations in thermal loads. Therefore, the regulation of the supply of thermal energy to the network must be carried out by changing the temperature of the water at the outlet of the boilers.
To reduce the intensity of external corrosion of pipes on the surfaces of steel hot water boilers, it is necessary to maintain the temperature of the water at the inlet to the boilers above the flue gas dew point temperature. The minimum allowable water temperature at the inlet to the boilers is recommended as follows:
when working on natural gas - not lower than 60°С; when working on low-sulphur fuel oil - not lower than 70°С; when working on high-sulphur fuel oil - not lower than 110°С.
Due to the fact that the water temperature in the return lines of heating networks is almost always below 60 ° C, thermal schemes of boiler houses with hot water boilers for closed heat supply systems provide, as noted earlier, recirculation pumps and corresponding pipelines. To determine the required water temperature behind steel hot water boilers, the operating modes of heating networks must be known, which differ from schedules or regime boilers.
In many cases, water heating networks are calculated to work according to the so-called heating temperature curve of the type shown in fig. 2.9. The calculation shows that the maximum hourly flow of water entering the heating networks from the boilers is obtained at a mode corresponding to the break point of the water temperature graph in the networks, i.e. at an outside air temperature that corresponds to the lowest water temperature in the supply line. This temperature is kept constant even if the outside temperature rises further.
Based on the foregoing, the fifth characteristic mode is introduced into the calculation of the thermal scheme of the boiler room, which corresponds to the break point of the water temperature graph in the networks. Such graphs are built for each area with the corresponding last calculated outdoor temperature according to the type shown in Fig. 2.9. With the help of such a graph, the required temperatures in the supply and return lines of heating networks and the required water temperatures at the outlet of the boilers are easily found. Similar charts for determining water temperatures in heating networks for various design outdoor air temperatures - from -13°С to -40°С were developed by Teploelektroproekt.
Water temperatures in the supply and return lines, ° С, of the heating network can be determined by the formulas:
where t vn is the air temperature inside the heated premises, ° С; t H - calculated outdoor air temperature for heating, ° С; t′ H - time-varying outdoor temperature, °С; π′ i - water temperature in the supply pipeline at t n °С; π 2 - water temperature in the return pipeline at t n ° С; tн - water temperature in the supply pipeline at t′ n, ° С; ∆t - calculated temperature difference, ∆t = π 1 - π 2, ° С; θ \u003d π c -π 2 - estimated temperature difference in the local system, ° С; π 3 \u003d π 1 + aπ 2 / 1+ a - the calculated temperature of the water entering the heater, ° С; π′ 2 - temperature of water going to the return pipeline from the device at t "H, ° С; a - displacement coefficient equal to the ratio of the amount of return water sucked by the elevator to the amount of network water.
The complexity of the calculation formulas (5.40) and (5.41) for determining the water temperature in heat networks confirms the feasibility of using graphs of the type shown in fig. 2.9, built for an area with an estimated outdoor temperature of 26 °C. It can be seen from the graph that at outdoor air temperatures of 3°C and above, until the end of the heating season, the water temperature in the supply pipeline of heating networks is constant and equal to 70°C.
The initial data for calculating the thermal schemes of boiler houses with steel hot water boilers for closed heat supply systems, as mentioned above, are heat consumption for heating, ventilation and hot water supply, taking into account heat losses in the boiler house, networks and heat consumption for the boiler house's own needs.
The ratio of heating and ventilation loads and hot water supply loads is specified depending on the local operating conditions of consumers. The practice of operating heating boilers shows that the average hourly heat consumption per day for hot water supply is about 20% of the total heat output of the boiler. Heat losses in external heat networks are recommended to be taken in the amount of up to 3% of the total heat consumption. The maximum hourly calculated consumption of thermal energy for auxiliary needs of a boiler house with hot water boilers with a closed heat supply system can be taken according to the recommendation in the amount of up to 3% of the installed heat output of all boilers.
The total hourly water consumption in the supply line of the heating networks at the outlet of the boiler house is determined based on the temperature regime of the heating networks, and, in addition, depends on the leakage of water through leaks. Leakage from heat networks for closed heat supply systems should not exceed 0.25% of the volume of water in the pipes of heat networks.
It is allowed to take approximately the specific volume of water in local heating systems of buildings per 1 Gcal / h of the total estimated heat consumption for residential areas of 30 m 3 and for industrial enterprises- 15 m 3.
Taking into account the specific volume of water in the pipelines of heating networks and heating installations, the total volume of water in a closed system can approximately be taken equal to 45 - 50 m 3 for residential areas, for industrial enterprises - 25 - 35 MS per 1 Gcal / h of the total estimated heat consumption.
Rice. 5.8. Detailed thermal diagrams of boiler houses with hot water boilers for closed heat supply systems.
1 - hot water boiler; 2 - recirculation pump; 3 - network pump; 4 - network summer pump; 5 - raw water pump; 6 - condensate pump; 7 - condensate tank; 8 - raw water heater; 9 - heater of chemically purified water; 10 - deaerator; 11 - vapor cooler.
Sometimes, for a preliminary determination of the amount of network water leaking from a closed system, this value is taken up to 2% of the water flow in the supply line. Based on the calculation of the basic thermal diagram and after the selection of unit capacities of the main and auxiliary equipment of the boiler house, a complete detailed thermal diagram is drawn up. For each technological part of the boiler house, separate detailed schemes are usually drawn up, i.e. for the equipment of the boiler house itself, chemical water treatment and oil farm. A detailed thermal diagram of a boiler house with three hot water boilers KV-TS - 20 for a closed heat supply system is shown in fig. 5.8.
In the upper right part of this diagram, there are hot water boilers 1, and in the left - deaerators 10 below the boilers there are recirculation pumps below the network, under the deaerators - heat exchangers (heaters) 9, a deaerated water tank 7, saw pumps 6, raw water pumps 5, drainage tanks and purge well. When performing detailed thermal schemes of boiler rooms with hot water boilers, a general station or aggregate equipment layout scheme is used (Fig. 5.9).
General station thermal schemes of boiler houses with hot water boilers for closed heat supply systems are characterized by the connection of network 2 and recirculation 3 pumps, in which water from the return line of heat networks can be supplied to any of the network pumps 2 and 4 connected to the main pipeline supplying water to all boilers of the boiler house. Recirculation pumps 3 supply hot water from the common line behind the boilers to the common line that supplies water to all hot water boilers.
With the aggregate layout of the boiler room equipment shown in fig. 5.10, for each boiler 1, network 2 and recirculation pumps 3 are installed.
Figure 5.9 General layout of boilers for network and recirculation pumps. 1 - hot water boiler, 2 - recirculation, 3 - network pump, 4 - network summer pump.
Rice. 5-10. Aggregate layout of boilers KV - GM - 100, network and recirculation pumps. 1 - hot water pump; 2 - network pump; 3 - recirculation pump.
Water from the return line flows in parallel to all network pumps, and the discharge pipe of each pump is connected to only one of the water heaters. Hot water is supplied to the recirculation pump from the pipeline behind each boiler until it is included in the common falling main and is sent to the feed line of the same boiler unit. When arranging with a modular scheme, it is envisaged to install one for all hot water boilers. Figure 5.10 does not show the make-up and hot water lines to the main pipelines and the heat exchanger.
The aggregate method of placing equipment is especially widely used in projects of hot water boilers with large boilers PTVM - 30M, KV - GM 100, etc. The choice of a general station or aggregate method of arranging boiler equipment with hot water boilers in each individual case is decided based on operational considerations. The most important of them from the layout of the aggregate scheme is to facilitate the accounting and regulation of the flow rate and the parameter of the coolant from each unit of large-diameter main heat pipelines and to simplify the commissioning of each unit.
POSSIBILITIES FOR POWER GENERATION IN HOT WATER BOILERS
Ph.D. L. A. Repin, director, D.N. Tarasov, engineer, A.V. Makeeva, engineer, South Russian Energy Company CJSC, Krasnodar
The experience of recent years of operation of Russian heat supply systems in winter conditions shows that there are frequent cases of disruption in the power supply of heat sources. At the same time, a power outage to boiler rooms can lead to serious consequences both in the boiler room itself (stopping fans, smoke exhausters, failure of automation and protection), and outside it (freezing of heating mains, building heating systems, etc.).
One of the well-known and at the same time effective solutions to this problem, for relatively large steam boilers, is the use of turbine generator sets operating on excess steam pressure, i.e. organization of cogeneration based on external heat consumption . This allows not only to increase the efficiency of fuel use and improve the economic performance of the heat source, but also, by providing its power supply from its own power generator, to increase the reliability of the heat supply system.
With regard to the municipal thermal power industry, such a solution seems unrealistic, since the vast majority of boiler houses are hot water. In this case, to improve reliability, it is practiced to install diesel generators on the heat source, which, in the event of an accident in the power supply system, can provide for the boiler house's own needs. However, this requires significant
costs, and the utilization rate of installed equipment is approaching zero.
This article proposes another solution to this problem. Its essence is to organize its own production of electrical energy in a hot water boiler based on the implementation of the Rankine cycle, using a low-boiling substance as a working fluid, which we will later call "agent".
Schemes of power plants using low-boiling working fluids are well known and are used mainly in geothermal fields in order to utilize the heat of waste water. However, their main disadvantage is the low thermal efficiency of the cycle, which is associated with the need to remove the heat of agent condensation to the environment. In hot water boilers and steam boilers low power(where other cogeneration options are not feasible) the heat of condensation can be used to preheat raw water entering the water treatment plant or going to the DHW heaters if they are installed on the heat supply source. Schematic diagram of a hot water boiler house with an integrated power generation unit is shown in fig. one.
Part of the coolant at the outlet of the hot water boiler I is taken and, passing sequentially through the evaporator II and the agent heater III, provides it in the form of steam with parameters sufficient for use as a working fluid in a heat engine IV connected to an electric generator.
After completion of the expansion process, the exhaust steam enters the heat exchanger-condenser V, where the heat of condensation is utilized by the flow cold water, going to the HVO installation or, as shown in the figure, through an additional heater VI and storage tank VII to the DHW supply system.
For the practical implementation of the proposed scheme, it is necessary to consider several points.
1. Select a low-boiling substance (agent), which, according to its thermodynamic characteristics, would fit into the operating mode and parameters of the boiler house.
2. Determine the optimal parameters of the operating mode of the thermal power plant and heat-exchange equipment.
3. Spend quantification the maximum electrical power that can be obtained for the specific conditions of the boiler house in question.
When choosing a working fluid, a computational study of the Rankine cycle was carried out for the following agents: R134, R600a, R113, R114, R600. As a result, it was found that the highest efficiency of the cycle for its implementation in the conditions of a hot-water boiler is achieved using freon R600.
For the working fluid chosen in this way, an analysis was made of the effect on the generated power of the temperature of steam overheating (Fig. 2a), steam pressure at the inlet Pl (Fig. 2b) and outlet Pk (Fig. 2c) of the engine.
It follows from the graphs that the characteristics under consideration are practically independent of the working fluid overheating temperature and improve with an increase in Pn and a decrease in Pc. At the same time, linking the parameters of the cogeneration plant with the mode of operation of the heat source shows that the increase in Pn is limited by the need to ensure a sufficient temperature difference in the evaporator between the evaporating working fluid and the heating coolant, since the temperature of the latter is determined by the mode of operation of the boiler.
The final pressure Pk should be selected depending on the agent condensation temperature, which in turn is determined by the temperature level of the heat-receiving medium (cold water) and the required temperature difference in the condenser.
For specific calculations of the proposed scheme, a boiler house with three TVG-8 boilers was selected with a connected heat load of 14.1 MW for heating and 5.6 MW for hot water supply (winter mode). The boiler room has a boiler plant that provides heating of hot water for the needs of hot water supply. Estimated temperature of network water at the outlet of the boilers is 130 °C. The total power consumption is up to 230 kW during the heating period and up to 105 kW in summer.
The values of the parameters and flow rates of heat carriers at the nodal points of the scheme, obtained as a result of calculations, are given in the table.
The electrical power of the EGC during the heating period was 370 kW, in the summer 222 kW.
When carrying out calculations, the consumption of working heat was determined based on the possibility of
current of cold water to ensure complete condensation of the agent. The difference in power received in winter and summer periods of the heat source operation is associated with a decrease in the amount of agent that can be condensed due to an increase in the temperature of cold water entering the condenser (+15 °C).
conclusions
1. Exists real opportunity improve the energy efficiency of hot water boilers by organizing the production of electricity in plants using a low-boiling working fluid.
2. The amount of electrical power that can be obtained by cogeneration significantly exceeds the boiler house's own needs, which guarantees its autonomous power supply. At the same time, the rejection of purchased and the sale of excess electricity should significantly improve the economic performance of the heat source.
3. Despite the low values of the cycle efficiency, there are practically no losses of supplied heat in the circuit (except for losses in the environment).
environment), which allows us to speak about the high energy and economic efficiency of the proposed solution.
Literature
1. Repin L.A., Chernin R.A. Possibilities for the production of electrical energy in low-pressure steam boilers // Industrial Energy. 1994. No. 6. pp.37-39.
2. Patent 32861 (RU). Thermal diagram of a water-heating boiler room / L.A. Repin, A.L. Repin//2006.
3. Combined geothermal power plant with a binary cycle with a capacity of 6.5 MW / / Russian energy efficient technologies. 2002. No. 1.
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Extending the resource and reducing the consumption of natural gas by hot water boilers TVG-KVG. Boilers TVG (TVG-8, TVG-8M, TVG-4r) and their development Gas Institute of the National Academy of Sciences of Ukraine and are produced by the Monastyrishchensky Machine-Building Plant (VAT "TECOM", Monastyrishche, Cherkasy region). Almost all boilers have exceeded the factory service life (14 years) and continue to be used. TVG-KVG boilers are maintainable and their service life is limited by the failure of the convective heating surfaces, made of pipes with a diameter of Ø28 × 3 mm and the need to replace burners. After replacing these elements with improved boilers, they can work for another 10-14 years with increased efficiency and reduced consumption of natural gas by 4-5%. Methods for upgrading boilers TVG-8, TVG-8M, TVG-4r, KVG-7.56, KVG-4.65. 1. Replacing gas burners with improved hearth slotted burners of the 3rd generation MPIG-3 with profiled nozzles and an additional air distribution grille of the “chain mail” type. Advantages: unchanged cross-sectional geometry of gas nozzles that practically do not clog and the gas / air ratio remains very close to initially set during the regime adjustment, a long service life of the burner is 10-14 years, see fig. 2. Replacement of convective heating surfaces - pipes Ø32×3 mm or Ø38×3 mm were used instead of pipes Ø28×3 mm. Advantages: a) increasing the pipe diameter reduces the hydraulic resistance and poor quality water in the system, the convective surface does not break down so quickly; b) due to the increase in the heating surface, the efficiency of the boiler increases. As a result of the modernization of boilers TVG-8, TVG-8M, TVG-4r, KVG-7.56, KVG-4.65 by the above methods, it is possible to increase the efficiency of boilers up to 94-95%, reduce the consumption natural gas and emission of carbon monoxide, extend the life of boilers by 10-14 years. In table. the main indicators of the TVG-8M boiler before and after modernization are given (Kyiv, 2 Deputatskaya r / c, the test was carried out by the commissioning service of Zhilteploenergo Kievenergo) with the replacement of burners with new MPIG-3 hearth burners and a new convective surface made of pipes Ø32 ×3 mm.
Modernization, for example, of the boiler TVG-8 (TVG-8M) provides an economic effect on one boiler - 253.8 thousand UAH / year, (gas savings 172 thousand m 3 / year or 2.6 million m3 over 15 years 3) compared to the purchase and installation of a new factory boiler. The cost of upgrading one boiler TVG-8(TVG-8M) is 360 thousand UAH. Payback 1 year and 5 months. The Gas Institute of the National Academy of Sciences of Ukraine transfers technical documentation for the manufacture of burners and a convective heating surface (under the contract), supervision of installation and commissioning, if necessary, manufactures independently a convective heating surface and burners. |
Prospects for the modernization of the domestic fleet of steam and hot water boilers.
In Ukraine, a fleet of steam and hot water boilers of the DKVR, DE, E, TVG, KVGM, PTVM, etc. series is predominantly operated, providing thermal energy to both the production sector and the housing and communal services of Ukraine. The level of equipment and automation does not meet the current standards for the use of fuel, electricity and environmental indicators. And here you can read articles about low-rise construction on the construction portal. This problem can be solved in two ways: Complete replacement of boilers with new, modern ones; Modernization of the existing fleet of boilers. The first way requires large capital investments from the owners of heat generating installations, which today only some large successfully operating enterprises can do. For other enterprises, the second way is more realistic - upgrading their heat generating installations by replacing gas burners with imported analogues or using automation for boilers based on imported components using standard burners or new burners of the GMU series. Imported burners manufactured by "Weishopt", "Ecoflame" are installed on the boilers of the Monastyrishchensky plant E2.5-0.9 and the Ivano-Frankivsk plant VK-22. The operation of these boilers showed the satisfactory operation of all equipment. An example of the use of a regular burner GMG-4 on a steam boiler DKVR 6.5 / 13 is the Chizhevsk Paper Mill (ChPF). For the first time in the practice of operating boilers of the DKVR series gas-burner GMG-4 was transferred to the mode of full automatic ignition and load control of the steam boiler without the constant presence of maintenance personnel. Automatic load control according to steam pressure in the boiler drum makes it possible to keep the steam pressure at a set value of ±0.1 kgf/cm2 with significant changes in steam consumption (up to 70% on the consumer side). In the event of a stoppage of steam consumption, the boiler automation stops the burner until the next need for steam. This mode of operation of the boiler with a variable steam load can significantly save fuel. Rejection traditional methods throttle control of such parameters as the water level in the upper drum, vacuum in the boiler furnace, air pressure in front of the burner and the transition to fundamentally new way regulation of the above parameters by changing the number of revolutions of auxiliary equipment electric motors with the help of frequency converters made it possible to significantly reduce the cost of electricity for steam production. The electric power consumed by the electric motors of the auxiliary equipment per ton of produced steam before the reconstruction was 7.96 kW/t, and after the reconstruction it is 1.98 kW/t. Thus, over the period of annual operation of the boiler at the Chizhev paper mill, which is 8,000 hours, the energy savings reached 253,000 kW. The weighted average efficiency of the DKVR 6.5/13 boiler after reconstruction was 90-90.5% instead of 87.5%. For modern hydraulic circuits of hot water boilers, the problem of using a weather-dependent regulator that regulates the temperature of the coolant in the supply line, depending on the outdoor temperature, while maintaining the conditions for once-through hot water boilers tВХ≥70°С, has been solved. The problem is solved by using an adjustable hydraulic switch. Using a weather-compensated regulator allows you to save fuel up to 30%. At present, schemes for reconstruction using the above technologies have been developed for all standard sizes of domestic boilers. The payback period for the funds spent on the modernization of steam or hot water boilers is 1.0 ÷2.0 years, depending on the operating time during the year.
K category: Boiler installation
Schemes of boiler plants
On the thermal diagram of the boiler room, conditional graphic images show the main and auxiliary equipment connected by pipeline lines for transporting steam or water. Thermal diagrams can be basic, detailed and working or installation.
The thermal circuit diagram contains only the main equipment and main pipelines without fittings.
All boiler room equipment and all pipelines, including fittings and various auxiliary devices, are applied to the detailed diagram. Often, a detailed scheme is divided into independent technological parts according to a functional feature, for example, a water treatment scheme, a deaeration-feed plant scheme, a drainage scheme, a steam boiler purge scheme, etc.
A working, or installation, scheme is performed indicating the location of pipelines, dimensions, steel grades, fastening methods, weight of equipment, parts and other necessary information.
Schematic diagram of the boiler room with hot water boilers is shown in fig. 2. Water from the return line of heating networks flows to the network pumps. Water is supplied to them by make-up pumps from the tank, compensating for losses in the networks. To maintain the desired water temperature in front of the boilers, the necessary amount of hot water that has left the boilers is supplied to the pipeline behind the pump. With the help of a bypass between the return and supply lines, the temperature of the water going to the network is regulated. Raw water, after passing through the heater, water treatment plant WPU, heater, coolers and deaerator, is fed to the heating network.
Rice. 1. Schematic diagram of a boiler house with hot water boilers: 1 - hot water boiler, 2.5 - pumps, 3 - recirculation pump, 4 - raw water pump, 6 - make-up water tank, 7 - raw water heater, 8 - make-up water cooler. 9 - chemically treated water heater, 10 - vacuum deaerator, 11 - vapor cooler, 12 - control valve; VPU - water treatment plant
Rice. Fig. 4. Scheme of a boiler plant with a steam vertical water-tube boiler operating on solid fuel: 1 - conveyor, 2 - boiler drum, 3 - shut-off valve, 4-outlet superheater chamber, 5 - festoon, 6 - superheater, 7 - economizer, 8 - furnace heating surfaces, 9 - air heater, 10 - ash collector, 11 - chimney, 12 - smoke exhauster, 13 - fan, 14 - slag hopper, 15 - pump, 16 - chemical water treatment, 17 - grate, 18 - feeder, 19 - deaerator, 20 - coal bunker, 21, 22 - pipes
The technological scheme of the boiler plant with a vertical water-tube boiler operating on solid fuel is shown in fig. 3. The belt conveyor feeds the prepared solid fuel into the supply hopper, from where it enters the furnace through the feeder, where air heated in the air heater to a temperature of 250 ... 400 ° C is supplied in two directions. Part of the air is supplied to the place where fuel enters the furnace. Small particles of fuel are picked up by the air flow and burn in the furnace space on the fly in the form of a torch. The air that enters the furnace along with the fuel is called primary. Large chunks of fuel fall out of air flow onto a chain grate that is constantly moving. As the chain grate advances, the fuel burns out, and the slag and ash are dumped into the slag bin.
The air necessary for burning fuel on the chain grate is sucked in by a blower fan through the air intake shaft and is supplied through the air heater 9 under the fuel layer through special grates. This air is also called primary.
In the process of fuel combustion, non-combustible particles of ash melt and form slags. With layered combustion of fuel, the bulk of ash and slag remains on the grate. However, part of the ash in the form of liquid and pasty slags, together with unburned fuel particles, is captured by flue gases and carried out of the combustion chamber. For afterburning unburned fuel particles in upper part flares supply secondary air. To prevent sticking of slag particles on the pipes of festoon 5, the temperature of the flue gases at the outlet of the combustion chamber is maintained below the melting temperature of the ash (1000 ...) 100 ° C).
In the combustion chamber, the heat from the burning fuel is perceived by the heating surfaces in the form of radiant energy (radiation), which is called radiation. The heating surfaces located in the furnace are therefore called radiation. The transfer of heat by radiation is several times more efficient than the transfer of heat by convection, therefore, in modern boilers the walls of the combustion chamber tend to be more tightly closed with pipes. Radiation heating surfaces protect (shield) inner surface boiler lining from high temperatures and chemical effects of molten slag and therefore are called screen.
The rear furnace screen in the upper part of the furnace is sparse and forms a so-called scallop. Behind the scallop in the horizontal flue there are convective heating surfaces made of pipes with a diameter of 30...40 mm, which form a superheater. Having given part of the heat to the superheater, the flue gases enter the downcomer duct, in which the water economizer and the air heater are located. Outgoing flue gases, cooled to a temperature of 120 ... 180 ° C, pass through the ash catcher, where they are cleaned of fly ash, and are ejected through a smoke exhauster through chimney in atmosphere. Ash particles from the ash catcher and slag from the bunker are removed from the boiler house by the ash removal system.
The screen pipes of the furnace are located in the zone of high temperatures, so it is necessary to intensively remove heat with the help of water circulating in these pipes. If scale forms on the inner walls of screen pipes, this makes it difficult to transfer heat from hot combustion products to water or steam and can lead to overheating of the metal and rupture of pipes under the action of internal pressure. In order to prevent the formation of scale, the water supplied to feed the boilers is pre-treated.
Water treatment consists in the removal of most of the poorly water-soluble calcium and magnesium salts (hardness salts), as well as oxygen and carbon dioxide, which cause corrosion of the metal of pipes, drum and chambers. Pre-treatment of water is called water treatment, and treated water suitable for feeding boilers is called nutrient. The water inside the boiler is called boiler water.
Since the pressure in the boiler is above atmospheric pressure, feed water is forced into the boiler by a feed pump, which takes water from the deaerator and feeds it through the water economizer to the boiler drum. The drum serves to create the necessary supply of boiler water, ensure natural water circulation and steam separation.
From the drum, water through unheated drainage (water-supply) pipes and chambers enters the pipes of the heating surfaces, in which it heats up, boils and returns to the drum in the form of a steam-water mixture. The steam in the drum is separated by steam separation devices from boiler water droplets with a high salt content and is discharged to the superheater. The separated water is mixed in the boiler drum with additional feed water and returns to the pipes of the heating surfaces.
The natural circulation of water in the boiler is carried out due to the difference in densities of water in unheated (or poorly heated) culverts and the steam-water mixture in intensively heated pipes of heating surfaces. Since the density of the steam-water mixture is much less than the density of water, the total dead weight of the steam-water mixture column in intensively heated pipes is less than the dead weight of water in unheated or weakly heated culverts.
In cases where, for structural reasons, it is difficult to create a reliable circulation of boiler water due to natural pressure in steam boilers, special pumps are used that provide high speeds of water movement throughout the circulation circuit. This forced circulation system is also used in hot water boilers.
The salts continuously entering the boiler with feed water and the sludge formed in the boiler water accumulate in the water volume of the boiler. So that hardness and alkali salts do not accumulate in the boiler water, part of the water is continuously removed from the boiler, while feed water with a lower salt content is added at the same time. This process is called continuous blowing.
Continuous blowing is carried out from the upper drum of the boiler through perforated pipes. Water consumption during continuous blowing depends on its quality and is usually 1 ... 2% of the boiler capacity. The water removed from the boiler with continuous blowdown is sent to the expander (separator) and is further used in the technological scheme of the boiler plant for heating raw or chemically treated water.
To remove the sludge accumulating at the lower points of the boiler (lower chambers and drums), periodic blowing is used. During periodic blowdowns, water containing a significant amount of sludge is sent to the expander of periodic blowdowns (bubbler), from where the resulting steam is discharged into the atmosphere, and the rest of the water with sludge is drained into the sewer.
Together with the heated boiler water, which is removed from the boiler with continuous blowing, a significant amount of heat is removed, the greater, the greater the blowdown percentage. In addition, it is necessary to increase the consumption of feed water for feeding the boiler. Therefore, the amount of purge water must be kept to a minimum. To reduce the consumption of feed water during continuous blowing, two-stage evaporation is used.
Steam separation devices used to clean and dry steam can be inside or outside the drum. Out-of-drum steam separation devices are usually made in the form of remote cyclones.
In the superheater, the steam is brought to the nominal temperature and through the outlet chamber and gate valve is supplied through pipelines to the consumer.
In the event that the consumer needs to supply hot water, the steam obtained in the steam boiler is passed through a system of heat exchangers. At the same time, steam pressure is reduced in ROU, and in heat exchangers - water heaters, steam heats water network installation. Further, the heated network water is supplied through pipelines to the consumer.
Complexity technological scheme the boiler room depends on the type of fuel burned and the heat supply system, which can be open and closed.
In open heat supply systems, the water heated in the boiler room serves not only as a heat carrier, but also for hot water supply by direct analysis from the pipelines of the heat network without intermediate heaters of hot water supply subscriber units. In this case, the amount of make-up water is determined by losses in the networks and water consumption for hot water supply.
Closed heat supply systems are characterized by the presence of a closed (closed) circuit with a circulating coolant, which gives off its heat in water-to-water heaters of district heating points. The amount of make-up water is determined only by losses in the networks, therefore, even in powerful hot water boilers, one make-up deaerator of small capacity is installed.
The choice of the heat supply system is made by technical and economic calculations.
- Schemes of boiler plants
a common part
Boiler rooms with hot water boilers can be built to release heat only in the form of hot water when burning solid, gaseous and liquid fuels. Liquid fuel is usually supplied in tank trucks, i.e. in a heated state. These boiler houses can work both for closed and for open system heat supply.
The main purpose of calculating any thermal circuit of a boiler house is to select the main and auxiliary equipment with the definition of initial data for subsequent technical and economic calculations.
When developing and calculating the thermal schemes of boiler houses with hot water boilers, it is necessary to take into account the features of their design and operation.
Fig. 1Schemes for switching on deaerators: a- vacuum; b-atmospheric; c - atmospheric with deaerated water cooler
/ _ water jet ejector; 2 - vapor cooler; 3 - water-water heat exchanger; 4 - chemically purified water; 5 - deaerator; 6 - hot water from a straight line; 7 - deaerated water cooler; 8 - tank of deaerated water; 9 - make-up pump
The reliability and efficiency of hot water boilers depend on the constancy of water flow through them, which should not decrease relative to that set by the manufacturer. In order to avoid low-temperature and sulfuric acid corrosion of convective heating surfaces, the water temperature at the inlet to the boiler when burning sulfur-free fuels must be at least 60 °C, low-sulfur fuels - at least 70 °C and high-sulfur fuels - at least 110 °C. To increase the water temperature at the inlet to the boiler at water temperatures below the specified ones, a recirculation pump is installed. \/ Vacuum deaerators are often installed in boiler rooms with hot water boilers. However, vacuum deaerators require careful supervision during operation, therefore, in a number of boiler houses, they prefer to install deaerators. atmospheric type.
Applied switching schemes vacuum deaerators and atmospheric deaerators are shown in fig. one.
On fig. 1a shows a deaerator operating at an absolute pressure of 0.03 MPa. The vacuum in it is created by a water jet ejector. Make-up water after chemical water treatment is heated in a water-to-water heater with hot water from a direct line with a temperature of 130-150 °C. The released steam bubbling the flow of deaerated water and is directed to the vapor cooler. The water temperature after the deaerator is 70 °C.
On fig. 1, b shows the deaeration scheme at a pressure of 0.12 MPa, i.e., above atmospheric. At this pressure, the water temperature in the deaerator is 104 °C. Before being supplied to the deaerator, chemically purified water is preheated in a water-to-water heat exchanger.
On fig. 1, c shows a similar scheme for deaeration of make-up water, which differs from that described in that after deaeration column water enters the deaerated water cooler, heating the chemically treated water. Then the chemically purified water is sent to a heat exchanger installed in front of the deaerator. The water temperature after the deaerated water cooler is usually assumed to be 70 °C.
Before calculating the thermal scheme of a boiler house operating for a closed heat supply system, it is necessary to choose a scheme for connecting local heat exchangers to the heat supply system that prepare water for hot water supply needs. Currently, three schemes for connecting local heat exchangers are mainly used, shown in fig. 2.
On fig. 2, a shows a diagram of the parallel connection of local hot water heat exchangers with a consumer heating system. On fig. 2, b, c shows a two-stage sequential and mixed schemes for switching on local heat exchangers for hot water supply. In accordance with SNiP 11-36-73, the choice of the scheme for connecting local heat exchangers for hot water supply is made depending on the ratio of the maximum heat consumption for hot water supply to the maximum heat consumption for heating. At Q gv / Q about ≤0,06 connection of local heat exchangers is carried out according to a two-stage sequential scheme; at 0.6< Q гв / Q about ≤1.2 - two-stage mixed scheme; at Q gv / Q about ≥1.2 - in a parallel circuit. With a two-stage sequential scheme for connecting local heat exchangers, switching of the heat exchangers to a two-stage mixed scheme should be provided.
The calculation of the thermal circuit of the boiler house is based on solving the equations of heat and material balance, compiled for each element of the circuit. These equations are linked at the end of the calculation, depending on the adopted scheme of the boiler house. If the values previously taken in the calculation differ from those obtained as a result of the calculation by more than 3%, the calculation should be repeated, substituting the obtained values as the initial data.
Calculation of the thermal scheme of a boiler house with hot water boilers operating for a closed heat supply system for three operating modes of the boiler house
The boiler house is intended for heat supply of residential and public buildings for the needs of heating, ventilation and hot water supply. The boiler house is located in the city and operates on low-sulphur fuel oil. The calculation in accordance with SNiP 11-35-76 is carried out for three modes: maximum winter, coldest month and summer. For hot water supply, a two-stage sequential scheme for heating water for subscribers is adopted. Deaeration of chemically purified water is carried out in a deaerator at a pressure of 0.12 MPa. Heating network work according to the temperature schedule 150/70. The main initial and accepted data for the calculation are given in the task for the course work.
When calculating the thermal circuit in the following sequence, the following are determined:
1.Coefficient of reduction of heat consumption for heating and ventilation
K ov = 
2. Water temperature in the supply line for heating and ventilation for the coldest month
t 1 \u003d 18 + 64.5 K ov 0.8 + 67.5 K ov \u003d 115.077
3. Return network water temperature after heating and ventilation systems for the coldest month mode
t 2 \u003d t 1 - 80K ov \u003d 58.197
4. Release of heat for heating and ventilation for maximum winter regime Q O.V \u003d Q o + Q B \u003d 42 + 6.7 \u003d 48.7
for the coldest month
Q O.V \u003d (Q o + Q B) K ov \u003d (42 + 67) * 0.711 \u003d 34.625
5. Total heat supply for the needs of heating, ventilation and hot water supply:
8.Heat load of the second stage heater for the coldest month mode:Q 11 g.v = G cons g.v - Q 1 g.v \u003d 12-5.24 \u003d 6.76 MW
9. Consumption of network water for the local heat exchanger of the second stage, i.e. for hot water supply, for the mode of the coldest month:
10. Flow of network water to the local heat exchanger for summer mode:
G l g.v = 
11. Consumption of network water for heating and ventilation:
for the maximum winter regime
for the coldest month
G o.v = 
=523.13 t/h
12. Consumption of network water for heating, ventilation and hot water supply: for the maximum winter mode
G ext \u003d G o.v + G g.v \u003d 523.52 + 0 \u003d 523.52
for the coldest month
G ext \u003d G o.v + G o.v \u003d 523.52 + 102.20 \u003d 625.72
for summer mode
G ext \u003d G o.v + G o.v \u003d 0 + 140.72 \u003d 140.72
13. Return network water temperature after external consumers:
t under arr \u003d t 2 - 70 - \u003d 28.47
for the coldest month
t under arr \u003d t 2 - 58.197 -
for summer mode
t under arr \u003d t 1 - t 1 - 
14. Consumption of make-up water to replenish leaks in the heat network of external consumers:
for maximum - winter mode
G ut \u003d 0.01K tf G ext \u003d 0.01 * 1.8 * 523.52 \u003d 9.42 t / h
for the coldest month
G ut = 0.01K tf G ext = 0.01*1.8*625.72=11.26 t/h
for summer mode
G ut \u003d 0.01K tf G ext \u003d 0.01 * 2 * 140.72 \u003d 2.81 t / h
15. Consumption of raw water entering the chemical water treatment:
for maximum - winter mode
G d.v = 1.25 G ut = 1.25*9.42=11.77 t/h
for the coldest month
G d.v = 1.25 G ut = 1.25*11.26=14.07 t/h
for summer mode
G d.v = 1.25 G ut = 1.25*13.28=16.6 t/h
16. Temperature of chemically treated water after deaerated water cooler:
for maximum - winter mode
t II x.o.v = 
t I x.o.v = 20=48.53
for the coldest month
t II x.o.v = t I x.o.v, \u003d 20 \u003d 54.10
for summer mode
t II x.o.v = t I x.o.v \u003d 20 \u003d 60.22
17. Temperature of chemically purified water entering the deaerator:
for maximum - winter mode
t d x.o.v = 
t II x.o.v = 
48.53=67.23
for the coldest month
t d x.o.v = t II x.o.v = 54.10=72.80
for summer mode
t d x.o.v = t II x.o.v = 60.22=78.92
18. Raw water temperature is checked before chemical water treatment:
for maximum - winter mode
t I x.o.v = 
t s.v = 5=20.81
for the coldest month
t I x.o.v = t r.v., = 
15=18.2
for summer mode
t I x.o.v = t s.v 15=16.5
19. Heating water consumption for deaerator:
for maximum - winter mode
G gr d \u003d \u003d 1.60 t / h
for the coldest month
G gr d = 
= 
=2.46 t/h
for summer mode
G gr d = = 
=0.13 t/h
20. The consumption of chemically treated water for feeding the heating network is checked:
for maximum - winter mode
G cold water = G ut - G hot water d = 9.42-1.60=7.82 t/h
for the coldest month
G h.o.v = G ut - G g.v d \u003d 11.26-2.46 \u003d 8.8 t / h
for summer mode
G x.o.v = G ut + G g.v d = 2.81-0.13=2.67 t/h
21. Heat consumption for raw water heating:
for maximum - winter mode
Q r.v = 0.00116 
= 0,00116
for the coldest month
Q r.v = 0.00116 =0,00116
for summer mode
Q r.v = 0.00116 = 0,00116
22. Heat consumption for heating chemically treated water:
for maximum - winter mode
Q x.o.v = 0.00116 
= 0,00116
for the coldest month
Q x.o.v = 0.00116 = 0,00116
for summer mode
Q x.o.v = 0.00116 = 0,00116
23. Heat consumption for the deaerator:
for maximum - winter mode
Q d \u003d 0.00116 
= 0,00116
for the coldest month
Q d \u003d 0.00116 = 0,00116
for summer mode
Q d \u003d 0.00116 =0,00116
24. Heat consumption for heating chemically treated water in the deaerated water cooler:
for maximum - winter mode
Q cool = 0.00116 
= 0,00116
for the coldest month
Q cool = 0.00116 = 0,00116
for summer mode
Q cool = 0.00116 = 0,00116
25. The total heat consumption that must be obtained in hot water boilers:
for maximum - winter mode
∑Q \u003d Q + Q s.v + Q cold water + Q d - Q cool \u003d 60.7 + 0.22 + 0.17 + 0.15-0.25 \u003d 60.99 MW
for the coldest month
∑Q \u003d Q + Q s.v + Q cold water + Q d - Q cool \u003d 53.3 + 0.21 + 0.19 + 0.23-0.37 \u003d 53.56
for summer mode
∑Q \u003d Q + Q s.v + Q cold water + Q d - Q cool \u003d 9 + 0.02 + 0.05 + 0.007-0.13 \u003d 8.94 MW
26. Water consumption through hot water boilers:
for maximum - winter mode
G k \u003d \u003d 
for the coldest month
G k \u003d \u003d 
for summer mode
G k \u003d \u003d 
27. Water consumption for recycling:
for maximum - winter mode
G rec = 
=
for the coldest month
for summer mode
28. Water flow through the bypass line:
for maximum - winter mode
G lane = = 
for the coldest month
for summer mode
29. Consumption of network water from external consumers through the return line:
for maximum - winter mode
G arr \u003d G ext - G ut \u003d 523.52-9.42 \u003d 514.1 t / h
for the coldest month
G arr \u003d G ext - G ut \u003d 625.72-11.26 \u003d 614.46 t / h
for summer mode
G arr \u003d G ext - G ut \u003d 140.72-2.81 \u003d 137.91 t / h
30. Estimated water flow through boilers:
for maximum - winter mode
G to ׳ \u003d G ext + G gr under + G rec - G lane \u003d 523.52 + 5 + 224.04-0 \u003d 752.56 t / h
for the coldest month
G to ׳ \u003d G ext + G gr under + G rec - G lane \u003d 625.72 + 5 + 111.20-220.37 \u003d 521.55
for summer mode
G to ׳ \u003d G ext + G gr under + G rec - G lane \u003d 140.72 + 0.7 + 81.37-66.30 \u003d 154.49
31. Consumption of water supplied to external consumers in a straight line:
for maximum - winter mode
G ׳ \u003d G to ׳ - G gr d - G gr under - G rec + G lane \u003d 752.56-1.60-224.04 + 0 + 5 \u003d 531.9
for the coldest month
G ׳ \u003d G to ׳ - G gr d - G gr under - G rec + G lane \u003d 521.55-2.46-111.20 + 220.37 + 5 \u003d 633.26
for summer mode
G ׳ \u003d G to ׳ - G gr d - G gr under - G rec + G lane \u003d 156.49-0.133-81.37 + 66.30 + 0.7 \u003d 141.98
32. Difference between previously found and adjusted water flow
external consumers:
for maximum - winter mode
100% = 100%=1.60
for the coldest month
100% = 
100%=1.20
for summer mode
100% = 
100%=0.89
If the discrepancy is less than 3%, the calculation is considered completed.
Summary data of the calculation results of the thermal scheme are given in the table.
| . |
| Physical | Obo | Number | The value of the value for the characteristic modes of operation of the boiler house | ||
| magnitude | value | formulas | maxi low winter | coldest month | years old |
| Coefficient of reduction of heat consumption for heating and ventilation | Co. in | (1) | 0.7 | ||
| Water temperature in the supply line for heating and ventilation, °С | t1 | (2) | 115.07 | ||
| Return network water temperature after heating and ventilation systems, °С | t2 | (3) | 58.1 | ||
| after heating and ventilation systems, °С Heat output for heating and ventilation, MW | Q o.v | (4) | 48.7 | 34.6 | |
| Total heat supply for heating, ventilation, hot water supply, MW | Q | (5) | 60.7 | 53.3 | |
| Water consumption in the supply line for heating, ventilation and hot water supply, t/h | G ext | (12) | 523.52 | 625.72 | 140.72 |
| Return water temperature after external consumers, °C | (13) | 28.47 | 50.85 | 56.12 | |
| Consumption of make-up water to replenish leaks in the heating network of external consumers, t/h | G ut | (14) | 9.42 | 11.26 | 2.81 |
| Amount of raw water supplied to chemical water treatment, t/h | G r.v | (15) | 11.77 | 14.07 | 16.6 |
| Temperature of chemically treated water after deaerated water cooler, °С | (16) | 48.53 | 54.10 | 60.22 | |
| Temperature of chemically purified water entering the deaerator, °C | (17) | 67.23 | 72.80 | 78.92 | |
| Heating water consumption for deaerator, t/h Total heat consumption required in hot water boilers, MW Water consumption through hot water boilers, t/h | G gr d | (19) | 1.60 | 2.46 | 0.134 |
| ∑Q | (25) | 60.9 | 53.5 | 8.9 | |
| G to | (26) | 655.6 | 575.7 | 153.8 | |
| Water consumption for recirculation, t/h Water consumption through the bypass line, t/h | (10.31) | ||||
| G rec G lane | (27) (28) | 224.04 | 111.20 220.3 | 81.37 66.3 | |
| Water consumption through the return line, t/h | G arr | (29) | 514.1 | 614.4 | 137.9 |
| Estimated water flow through boilers | G to ׳ | (30) | 752.2 | 521.5 | 156.4 |
Summary table for calculating the thermal diagram of a boiler room with hot water boilers