Recirculating pumping units used in hot water boiler houses and in mixed type boiler houses (with steam and hot water boilers). Their purpose is to maintain the water temperature at the inlet to the hot water boiler at least acceptable, taking into account the fuel used. For that purpose recirculation pump Part of the heated water in the boiler is supplied again to the boiler inlet, where it is mixed with return water from the heating network and increases its temperature to a predetermined value. Sometimes in production it is important to have a Claus catalyst, which can only be purchased in a specialized store.

The temperature of the water entering the boiler depends on the type of fuel and its sulfur content. When burning coal and fuel oil, vapors of sulfur and its compounds are formed, which easily condense on the boiler screen pipes, where their temperature does not exceed 100ºC, which leads to intense erosion of the pipe surface and thinning of the wall. The use of natural and other energy gases as fuel for boilers makes it possible to reduce the minimum surface temperature of screen pipes to 60-70ºС, eliminating erosion of their surfaces.

The variety of conditions for covering year-round and peak heat loads on the territory of our country became the reason for the design of water heating installations with significant differences in the thermal scheme, which made it possible to more fully and efficiently provide heat to consumers in the industrial, social and housing sectors.

The second important purpose of recirculation pumps is to promptly regulate the heat load in accordance with the schedule and changes in atmospheric conditions. Effective regulation of the thermal load is only possible while maintaining a given level of system reliability. This, in part, is the reason for the design of water heating installations with significant differences in the thermal design.

The thermal circuit of the boiler room and the circuit for switching on the recirculation pump are strictly connected with the temperature schedule of heat supply to consumers in different seasons of the year and the need to more or less recharge the network installation.

The most common schemes for including recirculation pumps in thermal circuits hot water boiler houses and mixed type boiler houses are given below.

Most simple circuit turning on recirculation pumps is used in cases where the water temperature in the supply pipeline is more than 110ºС and the coolant is used to cover the ventilation and heating loads, Figure 1:

The recirculation pump is installed on the bypass connecting the inlet and outlet pipelines of the water heating boiler. In the pressure part of the bypass, before inserting into the supply pipeline, a feed regulator for the recirculation pump is installed. It is designed as a valve with an automatic drive. The control of the valve drive is related to the water temperature in the return pipeline - tOB. As tOB decreases, the valve partially rises and increases the performance of the recirculation pump, which leads to an increase in the water temperature at the inlet to the boiler - tВК to the calculated value. As tOB increases (to reduce the heat load), the valve rises, increasing the flow area, reducing the hydraulic resistance of the bypass, which leads to an increase in the productivity of the recirculation pump and an increase in the water temperature in the boiler supply pipe to the calculated value.

The advantages of this scheme are its simplicity and reliability.

In hot water boiler houses located in close proximity to heat consumers, when using natural gas as fuel, when closed scheme heating supply, the scheme for switching on recirculation pumps, shown in Figure 2, was used:

From the return pipeline cold water enters the input of the network pump. The recirculation pump also supplies water from the hot water boiler here, which first goes through one or two stages of heating raw water. Water from the circulation circuit, when mixed with water from the return pipeline, increases its temperature to 70ºC. At this temperature, water flows through the network pump into the hot water boiler, and from the boiler it is supplied to the direct current pipeline to cover the loads of external heat consumers.

Raw water, subjected to sequential heating, mechanical and chemical cleaning, secondary heating and deaeration, is supplied to storage tanks (the second stage heater and storage tanks are not shown in Fig. 2). As necessary, the make-up pump supplies water from the storage tanks to the return water pipeline of the heating network to maintain the design pressure in it.

In this scheme, the performance of the network pump should be assumed to be slightly greater than the water flow in the direct current pipeline, since the network pump supplies part of the water to the recirculation circuit. The performance of a recirculation pump can be 5-10 times or more less than that of a network pump.

The performance of the recirculation pump is regulated by a supply regulator, which is made in the form of a valve with an automatic drive. The valve actuator control is linked to the return water temperature. As the water temperature in the return pipeline increases, the valve partially closes and reduces the performance of the recirculation pump, which leads to a decrease in the temperature of the water entering the boiler to the calculated value (70ºС). As tOB decreases, the valve rises, increasing the flow area, reducing the hydraulic resistance of the bypass, which leads to an increase in the performance of the recirculation pump and an increase in the water temperature in the supply pipe of the network pump (boiler) to the calculated value.

Regulation of the heat load for external consumers in this scheme is possible both by changing the temperature of the water entering the boiler and by slightly changing the performance of the network pump.

The undoubted advantages of this scheme are its simplicity, high efficiency and reliability.

In peak water heating boiler houses located in close proximity to heat consumers, when using fuel oil as fuel, the scheme for switching on recirculation pumps, shown in Figure 3, has become widely used:

Recirculation pump, as in the diagram in Fig. 3, installed on the bypass connecting the inlet and outlet pipelines of the boiler. A pump supply regulator is installed in the pressure part of the bypass, in the form of a valve with an automatic drive.

Hot water from the boiler outlet with a temperature of 150ºC is supplied to:
– for fuel oil production;
– for heating make-up water;
– at the inlet of the recirculation pump;
– into the direct current pipeline.

Thermal load fuel oil economy changes both during the day and across the seasons of the year. Minimum thermal loads noted in summer season. The maximum heat loads of the fuel oil industry are observed in the winter season during the unloading of fuel oil from tanks into storage tanks. Winter heat loads of fuel oil facilities can exceed summer loads by 2-4 times. For this reason in northern regions in our country, to provide heat only for the fuel oil industry, water heating boiler houses are installed steam boilers low pressure. This requires additional space in the boiler shop and increases the capital costs of the project. Operating costs also increase, which increases the cost of 1 Gcal of heat supplied. An undoubted advantage in this case is the possibility of increasing the heat load on the external consumer. Cooled water from the heat exchangers of the fuel oil facility is mixed into the return water pipeline of external consumers.

The heat load for heating the make-up room depends on the heat supply scheme. In a closed circuit, coolant losses due to leaks should not exceed 1-2%. With an open heat supply circuit, losses of coolant in the network, and, consequently, selection hot water from the boiler for heating make-up water increase significantly. Cooled water from the make-up water heaters is supplied to the direct flow pipeline.

The performance of the recirculation pump is regulated by an automatic valve taking into account the temperature of the return water from the network of external heat consumers. With a closed heat supply circuit, the effect of the flow of heating water through the make-up water heaters on the operation of the recirculation pump is insignificant. For open-loop heat supply circuits, the performance of the recirculation pump is controlled over a wider range, which requires the use of other control techniques.

A relatively simple scheme for switching on recirculation pumps is also used in cases where tP< 100ºС, а теплоноситель используется только для покрытия нагрузок на вентиляцию и отопление рисунке 4:

The recirculation pump is installed in front of the boiler and supplies hot water through it to the direct current pipeline and to the bypass. In the forward pipeline, part of the hot water is mixed with water from the return pipeline and supplied to the consumer at temperature tP. The other part of the hot water from the boiler goes through the bypass to the inlet of the recirculation pump. Part of the return water, which passed through the network pump with an increase in pressure to the design pressure, also enters here.

In peak water heating boiler houses located in close proximity to heat consumers, when using fuel oil as fuel, for an open-loop heat supply circuit, a scheme was used to include recirculation pumps in the cut between the network heater and the boiler, Figure 5:

The recirculation pump supplies water to the boiler with a temperature of at least 110ºС, from where hot water with a temperature of 150ºС or more is supplied to the fuel oil system, to the make-up water heater and to the network heater. Cold water from the fuel oil facility is supplied to the return water pipeline, passes through the network heater and enters the network for heat consumers. Water from the network heater with a tP of at least 110ºC is supplied to the inlet of the recirculation pump. Raw water before chemical cleaning heated to a temperature of 20 ºС, for example, by a water-water heater and water from the fuel oil facility. After cold water treatment, make-up water is heated to 50-70 ºС and enters vacuum deaerator, and from it into storage tanks (not shown in Fig. 5).

Accumulation tanks accumulate water during periods of water withdrawal less than the daily average and release an additional amount of deaerated water into the circulation circuit of the boiler. The heating network is fed from the same circuit through the fuel oil facility. If necessary, the heating network can be recharged with a make-up water pump through a transverse jumper with a valve in front of the network heater (not shown in Fig. 5). Installing battery tanks allows the hot water supply equipment to operate with a constant average daily load, which is the most economical solution.

All boiler room equipment intended to feed the heating network should be counted on average hourly consumption water per day with maximum water consumption.

The heat load is regulated by changing the performance of the recirculation pump. For this purpose, a control valve with an automatic drive is installed on the supply pipeline. The valve is controlled taking into account the water temperature in the return pipeline. When the return water temperature decreases, the valve rises and increases the flow area, which leads to a decrease in the resistance of the recirculation circuit, an increase in the performance of the recirculation pump and a decrease in the thermal load on the network heater. At the same time, less fuel and air are supplied to the boiler to reduce its operating power.

The heat load control system is implemented in such a way that with any change in heat consumption tВК remains at least 110ºС.

An autonomous hot water supply (DHW) system often uses a circulation pump. If the heat source is a boiler, and a significant portion of hot water accumulates in the boiler, then the pump constantly pumps water from the storage tank to the heat exchanger and back. If you mean a hot water recirculation pump, then it eliminates the biggest disappointment autonomous systems DHW - makes it so that when you open the tap you don’t have to wait long for hot water to reach the consumer through the pipes.

Principle of operation

A recirculation pump is not at all necessary, but it significantly increases comfort and even the quality of hot water. Its main task is to pump water through a pipeline in a closed loop from the boiler to the intake points and back. For this purpose, devices with low productivity, low noise and low power consumption are specially developed. The main requirement for pumps is resistance to high temperature, stable operation provided that the water is heated to 65°C.

Taken together, recirculation pumps for hot water are still different from pumps for heating. The latter are designed for temperatures up to 90°C and with significantly higher productivity. Interchangeability is irrelevant in this case. If desired, the heating pump can be used in DHW recirculation, but the pump cannot be used the other way around.

A circulation pump is especially in demand in houses with an area of ​​more than 200 square meters, where the boiler is located in separate room or basement, and there are several water intake points spread throughout the house. You will have to wait a long time for cold water to drain from the pipes, which significantly increases consumption. If the water in the boiler heats up to 65-80°C, then almost all pathogenic bacteria die, but in the pipes where the water cools, they are able to actively multiply.

Regular pumping of water through pipes eliminates these problems in the bud. However, due to heat loss in the pipes, the load on the boiler or water heater increases, so the installation of a recirculation pump has a lesser impact on savings and is primarily responsible for the comfort of residents.

To use a recirculation pump, the DHW distribution throughout the house must be carried out in the form of a closed circuit connected to the boiler. All water intake points are already connected from it. If you take water from the top of the boiler, then this will be considered the beginning of the circuit, then the pump is installed at the second entrance to the boiler, located in the lower part of the storage tank at the same level as the entrance to the cold tap water supply.

The circulation pump must be installed together with a check valve, which will prevent the reverse flow of water in the circuit, because in this case only cold water will flow through the pipes, tied to the bottom of the boiler and the inlet water supply.

Characteristics

The list of main characteristics of circulation pumps:

• productivity, m3/hour (liter/min);
• pressure, generated pressure, meters or Pa;
• power consumption, W;
• control method (by timer or temperature sensor).

The recirculation pump requires little power and performance. It is necessary to pump water only in tubes with a small internal volume, and at low speed. A device with a capacity of only 0.2-0.6 cubic meters per hour is sufficient to constantly maintain the water temperature in pipes up to 40-50 meters long.

Pump consumption is also low and ranges from 5 to 20 W. This is enough for stable operation and completion of the assigned task.

It is more important to select the correct pressure generated by the pump. More often, in a house or, especially, an apartment, the wiring is carried out one floor at a time, then a pressure equivalent to 0.5-0.8 meters of water column is sufficient. However, if it is necessary to ensure trouble-free circulation of water in a house with several floors, then the pump must cope with the rise of water to a given height, and with a margin. Pump performance directly depends on the actual installed load.

Design

Used for water circulation centrifugal pumps. The main elements in them are the shell housing, the impeller and the engine. Water is supplied to the center of the impeller. The engine spins it, and under the influence of centripetal force, water moves with pressure along the outer edge of the shell to the outlet pipe.

For a recirculation pump, the advantages are noiselessness and small dimensions. Therefore, small pumps are used mainly with a wet rotor type. The rotor is the internal moving part of the engine, mounted on the same shaft as the impeller. Under the influence of variable magnetic field From the stator coil, the rotor acquires rotational motion.

The wet rotor is completely immersed in the pumped medium. Water acts as a heat sink and at the same time as a lubricant for the support bearings. The presence of water around the moving parts of the engine reduces noise and vibration during pump operation.

Control method

It is quite acceptable to constantly maintain the circulation of hot water in the pipes, but this is uneconomical and unjustified. Hot water is not used constantly. At night, while all the residents are sleeping, it is useless to keep the water in the pipes hot, the same applies to the time when everyone is at work or school.

If the pipes are laid out correctly, then thermal insulation is required, so that once hot water gets into the pipes, it does not cool down instantly. Therefore, there is no need to constantly pump water from the boiler into the pipes and back; periodic operation of the pump is sufficient, which reduces the load on it and the hot water system as a whole. There is no need to talk about saving electricity, since the consumption of the recirculation pump is low.

Two main control methods are used:

• according to temperature sensor readings;
• according to a timer (schedule).

Both options are in demand, although they differ significantly in their operating principles.

By temperature sensor

Grundfos UP 15-14 BT 80

In this case, the pump control unit relies on the readings of a temperature sensor immersed in water inside the circuit pipes. The pump resumes operation as soon as the water has cooled to a certain threshold temperature. This approach significantly reduces the load on the equipment and constantly keeps the water in the pipes heated. In addition, the safety of the hot water supply increases. Having set a sufficiently high response threshold, water is pumped more often through the boiler, where it is additionally heated and disinfected.

By timer

Grundfos UP 15-14 BU

The control unit alternately turns the pump on and off based on the time delays set in the settings. Knowing exactly the parameters DHW systems, length of pipes and their internal volume, thermal insulation and average heat loss can be selected optimal time, during which the water will not have time to cool. The pump is turned on by a timer signal and pumps all the water. In this case, the duration of operation is also calculated based on the volume of pipes and pump performance.

Another advantage of the timer is the ability to schedule the operation of the recirculation pump for a day or even a week. It is in this case that downtime is taken into account when hot water don't use it.

Installation diagrams

Depending on the number of connection points and the length of the pipes, the method of connecting the circulation pump and pipe routing is selected:

• serial connection with one circuit;
• parallel connection with the collector.

In the first case, all water intake points are connected in series and in one circuit. This is beneficial if you can easily combine bathrooms and kitchen into one water pipe without unnecessary material costs and a fairly short route. There is only one feature that concerns the pressure pump rather than the circulation pump. If several water intake points are open at the same time, the pressure in each of them will be divided equally. Alternatively, this can be solved by installing a gearbox on each tap and choosing a more powerful pump.

Parallel connection solves the problem with pressure and distribution of water using a manifold group and compact placement of gearboxes. In this case, recirculation pumps must be installed in each individual circuit or one more efficient pump must be selected for all groups at once. Such wiring is necessary if there are several bathrooms in the house, spaced far from each other and from the kitchen, or when, with a serial connection, the total length of the route becomes too long.

What is recycling? What are the pros and cons of this system? How to organize proper and comfortable water supply at home? These and other questions will be answered in an article on our website dedicated to the functionality of boilers - the water recirculation system

For comfortable use of hot water, when designing modern systems, it is common to use storage water heaters. They make it possible to always have the necessary supply of hot water for the needs of residents. How to correctly calculate the required volume of a water heater is described in our blog article.

Indirect heating boiler.
It is extremely beneficial to use an indirect heating boiler for heating hot water, which provides economic and design advantages over conventional electric water heater. In addition to the standard electric heating element, the indirect heating boiler has a built-in heat exchanger (or several heat exchangers), through which coolant can be passed from an alternative system (heating boiler, solar collector, heat pump etc.). This primarily provides the economic benefits of heating hot water. During heating season, the boiler will heat up perfectly from the house heating system, without turning on the electric heating element. And when using a boiler with solar collector In general, you can get a free solar water heating system all year round.

What is recycling?

Some indirect heating boilers are equipped with an additional recirculation pipe, which can be used in the hot water supply system to create additional comfort. When laying hot water pipes to the mixer, it is necessary to lay another return pipe for water recirculation. Thus, hot water will always circulate through the hot water supply pipes and when the tap is opened, the water can be used instantly.

Recirculation, in essence, is the movement of hot water through a closed pipe ring, with the possibility of its selection from this ring.

Where should the water recirculation from the boiler be installed?
First of all, recirculation is used in places where the water collection point is located at great distance from the boiler-heater. While you are not using hot water, it cools down in the pipes and, after opening the tap, you need to drain the cooled water for a certain period of time. Recycling makes all the difference this problem. If you don’t want to run water from the tap all the time, you should choose a system with hot water recirculation. A similar system has supply and return pipelines, but the system is very convenient and comfortable.
Additionally, a water heated towel rail can be connected to the hot water recirculation system. IN in this case, the heated towel rail will be warm all year round, because it will be powered not from heating, but from the hot water supply of the house

Disadvantages of the recirculation system.
The main disadvantage of the recirculation system is the complexity of installation due to the need to lay an additional pipe. These works can only be performed during the construction of a house or major repairs.
In addition, for the recirculation system to operate, you will need a circulation pump and Additional materials for strapping. To move water from the boiler through pipes and into reverse side circulation is used DHW pump, it is prohibited to use the pump for heating system. The pump is constantly connected to the network and consumes little electricity, approximately 25-80 watts per hour (depending on the model and performance of the pump).

It is worth noting that when recirculating hot water, the cost of heating water will increase, because it will constantly circulate, giving off heat to the walls, heated towel rail, etc., and the water will have to be heated more often than in a conventional closed-cycle heating boiler. You have to pay for comfort. To achieve the maximum level of energy savings, the return line, like the water supply, must be well insulated to reduce heat loss, otherwise, instead of a water supply system, you can get an additional wall heating system with a constantly running circulation pump.
You should not neglect the installation of an additional safety group - install an expansion tank, and at the same time an automatic air vent to prevent air from entering the pump. If desired, you can also install a safety valve to protect the water heater from excess pressure caused by the expansion of water during heating. When critical pressure is reached, the safety valve will release “excess” water. But in most cases it is enough to install only an expansion tank. It compensates for the pressure in the hot water supply system by removing excess water, thereby reducing the pressure during heating. The air pressure in the expansion tank must not exceed the pressure safety valve, otherwise the action of the expansion tank is useless. And the minimum air pressure must not be lower than the minimum pressure in the water supply system.

The choice of 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, we begin to compile and then calculate diagrams, which are called thermal diagrams of boiler houses with hot water boilers for closed systems heat supply, since the maximum heating capacity of cast iron boilers does not exceed 1.0 - 1.5 Gcal/h.

Since it is more convenient to consider thermal diagrams using practical examples, below are the basic and detailed diagrams of boiler houses with hot water boilers. Schematic thermal diagrams of boiler houses 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 houses 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 - chemically purified water heater; 9 - make-up water cooler; 10 - deaerator; 11 - vapor cooler.

Water from the return line of heating networks with low pressure (20 - 40 m water column) flows to network pumps 2. Water is also supplied there from make-up pumps 5, compensating 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 to heat chemically purified 8 and raw water 7.

To ensure the water temperature in front of the boilers, set according to the conditions for preventing corrosion, the required amount of hot water coming out of hot water boilers 1 is supplied to the pipeline behind the network pump 2. The line through which hot water is supplied is called recirculation. Water is supplied by recirculation pump 3, pumping heated water. In all modes of operation 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 per into the supply line, where the water, mixing with hot water from the boilers, provides the specified design temperature in the supply main of heating networks. The addition of chemically purified water is heated in heat exchangers 9, 8, 11 and deaerated in deaerator 10. Water for feeding heating networks is taken from tanks 6 by make-up pump 5 and supplied to the return line.

Even in powerful hot water boiler houses operating on closed heating systems, you can get by with one make-up water deaerator with low productivity. The power of make-up pumps and the equipment of the water treatment plant are also reduced, and the requirements for the quality of make-up water are reduced compared to boiler houses for open systems. The disadvantage of closed systems is a slight increase in the cost of equipment for hot water supply subscriber units.

To reduce water consumption for recirculation, its temperature at the outlet of the boilers is maintained, as a rule, above the water temperature in the supply line of the heating networks. Only at 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 design water inlet temperature heating network network water from the return pipeline is mixed with the water leaving the boilers. To do this, a bypass line is installed between the return and supply pipelines, after the network pumps.

The presence of water mixing and recirculation leads to operating modes of steel hot water boilers that differ from the mode of heating networks. Hot water boilers operate reliably only if the amount of water passing through them is maintained constant. Water flow must be maintained within specified limits regardless of fluctuations in thermal loads. Therefore, regulation of the supply of thermal energy to the network must be carried out by changing the temperature of the water leaving the boilers.

To reduce the intensity of external corrosion of pipes on the surfaces of steel water-heating boilers, it is necessary to maintain the water temperature at the inlet to the boilers above the dew point temperature of the flue gases. Minimum permissible temperature The recommended water inlet to the boilers is as follows:

• when working on natural gas- not lower than 60°C;
• when working on low-sulfur fuel oil - not lower than 70°C;
• when working on high-sulfur fuel oil - not lower than 110°C.

Due to the fact that the water temperature in the return lines of heating networks is almost always below 60 ° C, the thermal circuits of boiler houses with hot water boilers for closed heating 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 the schedules or operating boiler units.

In many cases, water heating networks are designed to operate according to the so-called heating temperature chart type shown in Fig. 2.9. The calculation shows that the maximum hourly flow rate of water entering the heating networks from the boilers is obtained at the mode corresponding to the break point of the water temperature graph in the networks, i.e. at the outside air temperature, which corresponds to the lowest water temperature in the supply line. This temperature is maintained constant even if the outside temperature rises further.

Based on the above, a fifth characteristic mode is introduced into the calculation of the boiler house thermal diagram, corresponding to the break point of the water temperature graph in the networks. Such graphs are constructed for each district with the corresponding last design temperature outside air as 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 can be easily found. Similar graphs for determining water temperatures in heating networks for various design temperatures of outside air - from -13°C to -40°C were developed by Teploelektroproekt.

The water temperatures in the supply and return lines, °C, of ​​the heating network can be determined using the formulas:

where t in - air temperature inside heated rooms, ° C; t H - design temperature of outside air for heating, °C; t′ H - time-varying outside air temperature, °C; π′ i - water temperature in the supply pipeline at t n °C; π 2 - water temperature in the return pipeline at tn °C; tn - water temperature in the supply pipeline at t′n, °C; ∆t - calculated temperature difference, ∆t = π 1 - π 2,°C; θ =π з -π 2 - calculated temperature difference in the local system, °C; π 3 = π 1 + aπ 2 / 1+ a - design temperature of water entering heating device, °C; π′ 2 - temperature of water flowing into the return pipeline from the device at t" H, ° C; a - displacement coefficient equal to the ratio of the amount of return water sucked in by the elevator to the amount network water.

The complexity of the calculation formulas (5.40) and (5.41) for determining the water temperature in heating networks confirms the advisability of using graphs of the type shown in Fig. 2.9, built for an area with a design outdoor temperature of 26 °C. The graph shows that at outdoor temperatures of 3°C and above, until the end of the heating season, the water temperature in the supply pipeline of the heating networks is constant and equal to 70°C.

The initial data for calculating thermal diagrams of boiler houses with steel water-heating 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 room, networks and heat consumption for own needs boiler room

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 boiler houses shows that the average hourly heat consumption per day for hot water supply is about 20% of the total heating capacity of the boiler house. Heat loss in external heating networks it is recommended to take up to 3% of the total heat consumption. Maximum hours estimated costs thermal energy for the own needs of a boiler house with hot water boilers with a closed heat supply system can be accepted according to the recommendation in the amount of up to 3% of the installed heating capacity of all boilers.

The total hourly water flow in the supply line of heating networks at the exit from the boiler room is determined based on the temperature conditions of operation of the heating networks, and, in addition, depends on water leakage through non-densities. Leakage from heating networks for closed heating systems should not exceed 0.25% of the volume of water in the pipes of heating networks.

It is allowed to approximately take the specific volume of water in local heating systems of buildings per 1 Gcal/h of the total calculated heat consumption for residential areas - 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 be approximately taken as equal for residential areas 45 - 50 m 3, for industrial enterprises - 25 - 35 MS per 1 Gcal/h of the total calculated 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 - summer network 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, to preliminary determine the amount of network water leaking from a closed system, this value is taken within the limits of up to 2% of the water flow in the supply line. Based on the calculation of the basic thermal diagram and after selecting the unit capacities of the main and auxiliary equipment the boiler room draws up a complete detailed thermal diagram. Separate detailed diagrams are usually drawn up for each technological part of the boiler house, i.e. for the equipment of the boiler house itself, chemical water treatment and fuel oil facilities. An expanded thermal diagram of a boiler room with three water heating 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 water heating boilers 1, and in the left - deaerators 10, below the boilers there are recirculation network pumps below, under the deaerators there are heat exchangers (heaters) 9, a deaerated water tank 7, filing pumps 6, raw water pumps 5, drainage tanks and a blow-off well. When performing detailed thermal diagrams of boiler houses with hot water boilers, a general station or unit equipment layout diagram is used (Fig. 5.9).

General station thermal circuits of boiler houses with hot water boilers for closed heating systems are characterized by the connection of network 2 and recirculation 3 pumps, in which water from the return line of the heating networks can flow to any of the network pumps 2 and 4 connected to the main pipeline supplying water to all boilers of the boiler room. 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 a block diagram of the boiler room equipment layout shown in Fig. 5.10, for each boiler 1, network 2 and recirculating pumps 3 are installed.

Fig. 5.9 General station layout of network boilers and recirculation pumps. 1 - hot water boiler, 2 - recirculation boiler, 3 - network pump, 4 - summer network pump.

Rice. 5-10. Aggregate layout of KV - GM - 100 boilers, network and recirculation pumps. 1 - water heating pump; 2 - network pump; 3 - recirculation pump.

Water from the return line flows in parallel to all network pumps, and the discharge pipeline of each pump is connected to only one of the water heating boilers. The recirculation pump receives hot water from the pipeline behind each boiler before it is included in the common fall line and is sent to the supply line of the same boiler unit. The layout of the unit diagram provides for the installation of one for all hot water boilers. In Fig. 5.10, the make-up and hot water lines to the main pipelines and heat exchanger are not shown.

The aggregate method of placing equipment is especially widely used in projects of water-heating boiler houses with large boilers PTVM - 30M, KV - GM 100, etc. The choice of a general station or aggregate method of arranging equipment for boiler houses with water-heating boilers is decided in each individual case based on operational considerations. The most important of them from the layout of the unit diagram is to facilitate the accounting and regulation of the flow and parameter of the coolant from each unit of large-diameter main heat pipelines and to simplify the commissioning of each unit.

Boiler plant Energia-SPB produces various models of hot water boilers. Transportation of boilers and other boiler auxiliary equipment is carried out by motor transport, railway gondola cars and river transport. The boiler plant supplies products to all regions of Russia and Kazakhstan.

For Kolvi fire-tube water heating boilers, the manufacturer recommends installing a recirculation line, which will ensure that the coolant temperature at the boiler inlet is constantly maintained at 55-60 degrees. Recirculation is necessary to counteract the possible occurrence of condensation on the surfaces of the boiler, which is especially possible when the boiler is operating at 50% or lower of the rated power.

Technical documentation For fire tube boilers, it is not recommended to operate the boiler in a power mode below 40% of the nominal value, since the following unfavorable phenomenon occurs here: the relatively low temperature of the flue gases is aggravated by low values ​​of the coolant temperature in the return line, which leads to the formation of condensation on steel structures boiler with known consequences. Therefore, it is necessary to ensure the above-mentioned 55-60 degrees at the “return” of the boiler, which is quite enough to protect against the “dew point” that the flue gases can reach.

To organize the mixing of hot coolant into the “return” line of a fire tube boiler, there are 2 main options:

• Installation of mixing three way valve.
• Installation of a circulation pump (recirculation pump).

In practice, the 2nd option is most often used - installing a recirculation pump. Such a pump is installed on a jumper between the supply and return lines, in close proximity to the boiler. Required condition is the ease of access for boiler room maintenance personnel to the pump and other components of the recirculation line.

Below is a typical diagram of a recirculation line:

The diagram below shows a typical recirculation scheme gas boiler(1), located as a jumper between the supply T1 (2) and return T2 (3) lines. The recirculation pump itself (4) with mating flanges must be installed together with shut-off valves (6) at the coolant inlet and outlet to make it possible to dismantle the pump if necessary. It is also advisable to install pressure gauges (5) before and after the pump to monitor the coolant pressure and visually determine the pressure drop values. After the pump discharge pipe, installation is required check valve(7) to ensure the correct direction of mutual circulation of water on the return and recirculation lines.

Methodology for calculating the required parameters of the recirculation pump:

The design parameters for these pumps are:

• Required coolant flow.
• The design pressure of the pump, allowing it to overcome the hydraulic resistance of all elements: boiler, pipes, shut-off valves. In this case, the required coolant flow must be ensured (see above).

The coolant flow for the recirculation line is determined by the thermal power of the boiler, the coolant flow through the boiler and the boiler operating temperature. The calculated flow rate of the recirculation pump is 1/3 of the coolant flow through the boiler. Below is an example of the calculation:

There is a Kolvi 250 gas fire tube boiler with a thermal output of 291 kW. Boiler efficiency is 92%. His temperature regime is 95/70 degrees.

1. Determination of boiler heat output: 291x0.92=268 kW

2. Determination of temperature gradient: 95-70=25 degrees.

3. Determination of water flow through the boiler: (0.86x268)/25 = 9.22 cubic meters. at one o'clock.

4. Determination of water flow for the recirculation pump: 9.22/3 = 3.08 cubic meters. at one o'clock.

The design pressure of the recirculation pump, as mentioned above, is determined by the local resistance of the boiler room elements. As practice shows, pressure parameters of 2-4 meters of water are acceptable. Art. (0.2-0.4 bar).