A heat pump heating system with multiple direct-fired engines

Abstract

A heat pump heating system composed of multiple direct-fired engines, including a cooling tower and at least two direct-fired engines; the cooling tower is used to allow the low-temperature heat source water inside to absorb heat from the atmosphere, and to transport the low-temperature heat source water after absorbing heat to the evaporator heat exchange tube of the second direct-fired engine to exchange heat with the refrigerant water outside the heat exchange tube; the low-temperature heat source water after releasing heat enters the cooling tower again to absorb heat from the atmosphere, and the cycle continues; the second direct-fired engine is used to allow the water vapor generated after the evaporator refrigerant water absorbs heat to enter the absorber of the second direct-fired engine, and the water vapor is absorbed by the solution in the absorber and releases heat, which is transferred to the secondary circulating water in the absorber heat exchange tube to heat up the secondary circulating water. The utility model does not need to change the internal structure of the direct-fired engine, but only needs to use multiple direct-fired engines and the configured cooling towers to absorb the heat of the environment and the waste heat of the flue gas of the direct-fired engine itself, and to operate in a heat pump mode by adjusting the solution concentration and the refrigerant water concentration, which is much higher than the direct heating mode of the direct-fired engine.

Description

Technical Field

[0001] The utility model relates to the technical field of heat pump heating, in particular to a heat pump heating system composed of multiple direct-fired engines. Background Art

[0002] Direct-fired lithium bromide absorption chillers (direct-fired machines for short) are fuel-driven and use lithium bromide aqueous solution as the working fluid to produce cold water for air conditioning and similar purposes in a vacuum environment. Their performance coefficient is greater than 1. Direct-fired heating methods, on the other hand, mostly use methods similar to vacuum phase change boilers, and their performance coefficient is often less than 1. They are currently restricted by energy conservation and emission reduction policies.

[0003] Direct-fired engines can actually operate as heat pumps, with a performance coefficient of more than 2.0; however, their temperature rise is around 30°C, and they cannot produce hot water that meets heating requirements (above 45°C) at low temperatures (such as below 10°C). Therefore, in most cases, direct-fired engines still operate inefficiently as vacuum phase change boilers.

[0004] In addition, direct-fired machines dissipate a lot of heat during cooling, so they are equipped with larger cooling towers, but the cooling towers are idle during the non-cooling season. Many direct-fired machine users often use more than two direct-fired machines to form a central air conditioning host system because of large cooling and heating needs or to ensure system reliability, and cannot use multiple direct-fired machines for heating in the form of heat pumps.

[0005] Others combine multiple direct-fired engines, flue gas heat exchange technology and heating-related equipment for cooling and heating, such as the heating room temperature flue gas direct-fired lithium bromide absorption cooling and hot water unit system disclosed in CN 105444463A. However, this technology only uses the heat of recycled flue gas for heating, which can only increase the thermal efficiency by 15% at most, and does not fully utilize the cooling tower to obtain heat in the air to achieve higher efficiency. Summary of the invention

[0006] The utility model aims to overcome the above-mentioned deficiencies of the prior art and to provide a heat pump heating system with a combination of multiple direct-fired engines having a simple structure, good evaporation effect and high heating efficiency.

[0007] The technical solution of the utility model is: a heat pump heating system with multiple direct-fired engines, comprising:

[0008] The cooling tower equipped for direct-fired refrigeration is used to make the low-temperature heat source water absorb the heat in the atmosphere. The low-temperature heat source water after absorbing the heat is transported to the evaporator heat exchange tube of the second direct-fired machine through a primary water pump to exchange heat with the refrigerant water outside the heat exchange tube. The low-temperature heat source water after releasing the heat enters the cooling tower again to absorb the heat in the atmosphere, and the cycle continues.

[0009] At least two direct-fired machines, including a first direct-fired machine and a second direct-fired machine, the second direct-fired machine is used to allow the water vapor generated after the refrigerant water in the evaporator absorbs heat and evaporates to enter the absorber of the second direct-fired machine, be absorbed by the solution in the absorber and release heat, and transfer the heat to the secondary circulating water in the absorber heat exchange tube, so that the secondary circulating water is heated; the first direct-fired machine is used to receive the heat of the heated secondary circulating water through the evaporator heat exchange tube, evaporate the refrigerant water outside the heat exchange tube, and the evaporated water vapor is absorbed by the surface solution of the first direct-fired machine absorber and releases heat, and the heat is transferred to the heat supply return water in the absorber heat exchange tube, so that it is heated and continuously supplies heat.

[0010] Furthermore, the low-temperature heat source water in the cooling tower is connected to the evaporator heat exchange pipe of the second direct-fired machine through a primary water pump, and then returns to the cooling tower after releasing heat through the heat exchange pipe of the evaporator of the second direct-fired machine, absorbing heat from the air to form a low-temperature water circulation pipeline.

[0011] Furthermore, the pipeline connection method for continuously heating up the secondary circulating water is as follows: the evaporator heat exchange tube of the first direct-fired machine is connected to the absorber heat exchange tube, condenser heat exchange tube and flue gas heat exchanger of the second direct-fired machine in sequence through a secondary water pump; or the evaporator heat exchange tube of the first direct-fired machine is connected to the absorber heat exchange tube and flue gas heat exchanger of the second direct-fired machine in sequence through a secondary water pump; and then returns to the evaporator heat exchange tube of the first direct-fired machine through the flue gas heat exchanger to form a secondary water circulation pipeline.

[0012] Furthermore, the heat return water end is connected to the absorber heat exchange tube and the condenser heat exchange tube of the first direct-fired engine in sequence through pipelines, and output from the condenser to the user end; the high temperature generators of the first direct-fired engine and the second direct-fired engine are both connected to the flue gas heat exchanger.

[0013] Furthermore, a fan is provided on the top or side of the cooling tower to generate airflow in the cooling tower. The lowest temperature low-temperature heat source water coming out of the second direct-fired engine evaporator convects against or transversely with the airflow, absorbs heat in the air, and is gathered at the bottom of the cooling tower and returned to the second direct-fired engine evaporator through a primary water pump.

[0014] Furthermore, the second direct-fired engine also includes a generator pump, and a conduit is provided between the outlet of the generator pump and the refrigerant water in the evaporator of the second direct-fired engine. The conduit is provided with a first vacuum valve that can be opened and closed, which is used to control the entry of part of the lithium bromide solution into the refrigerant water of the evaporator, so that the freezing point of the refrigerant water is lower than 0°C and can evaporate at a temperature below 0°C.

[0015] Furthermore, the second direct-fired engine also includes a refrigerant pump, and a conduit is also provided between the outlet of the refrigerant pump and the inlet of the generating pump of the direct-fired engine. The conduit is provided with a second vacuum valve that can be opened and closed, which is used to bypass the refrigerant water and allow it to enter the solution when the concentration of the lithium bromide solution in the refrigerant water in the evaporator is higher than the target concentration, so as to reduce the concentration of the lithium bromide solution in the refrigerant water.

[0016] Furthermore, during operation, the low temperature heat source water is 5-10° C. lower than the ambient temperature. In this way, the low temperature is conducive to absorbing heat from the environment, and avoids the second direct-fired engine from reducing the evaporator efficiency due to too low a temperature.

[0017] Beneficial effects of the utility model:

[0018] On the one hand, the utility model does not need to change the internal structure of the direct-fired engine, but only needs to set up at least two direct-fired engines, utilize multiple direct-fired engines and cooling towers, absorb heat from the environment, and operate in a heat pump mode to adjust the solution concentration and the refrigerant water concentration, which is much higher than the direct heating mode of the direct-fired engine; on the other hand, due to the existence of secondary circulating water with a lower temperature, the flue gas heat exchanger is provided to cool and condense the flue gas, so that the secondary circulating water can fully absorb the sensible heat and latent heat in the flue gas, thereby greatly improving the heating efficiency and reducing the environmental impact.

[0019] In addition, on the one hand, the utility model can ensure that the freezing point of the refrigerant water is lower than 0°C and meet the temperature requirement of the cold water by arranging a conduit and a first vacuum valve between the generator pump outlet and the refrigerant water; on the other hand, by arranging a conduit and a second vacuum valve between the generator pump inlet and the refrigerant pump outlet, it can ensure that the concentration of the lithium bromide solution in the refrigerant water in the evaporator will not affect the evaporation effect; it can be said that the utility model can meet the temperature requirement of the cold water without affecting the evaporation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of an embodiment of the utility model. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0022] Example 1

[0023] like Figure 1As shown: a heat pump heating system with multiple direct-fired machines, including a first direct-fired machine, a second direct-fired machine, a cooling tower and a flue gas heat exchanger; the low-temperature heat source water in the cooling tower is connected to the heat exchange pipe of the evaporator of the second direct-fired machine through a primary water pump, and then returns to the cooling tower through the heat exchange pipe of the evaporator of the second direct-fired machine, forming a low-temperature water circulation pipeline; the evaporator heat exchange pipe of the first direct-fired machine is connected to the absorber heat exchange pipe, condenser heat exchange pipe and flue gas heat exchanger of the second direct-fired machine in turn through a secondary water pump, and then returns to the evaporator heat exchange pipe of the first direct-fired machine through the flue gas heat exchanger, forming a secondary water circulation pipeline; the heat supply return water end is connected to the absorber heat exchange pipe and condenser heat exchange pipe of the first direct-fired machine in turn through a pipeline, and is output from the condenser to the user end; the high-temperature generators of the first direct-fired machine and the second direct-fired machine are both connected to the flue gas heat exchanger.

[0024] Specifically, in this embodiment, the flow directions of the solution, water and steam in the first direct-fired engine and the second direct-fired engine, as well as components such as heat exchangers, are the same as those of conventional direct-fired engines, and during the cooling season, each direct-fired machine, cooling tower, etc. operates in the original manner, so they will not be described in detail here.

[0025] In this embodiment, unlike the working mode of conventional direct-fired engines, the cooling tower is still started during the heating season. The cooling water can be water (above 5°C) or antifreeze (below 5°C), and cold water 5-10°C lower than the ambient temperature can be obtained, becoming low-temperature heat source water.

[0026] In this embodiment, after the first direct-fired engine is started, the heating return water is equivalent to the cooling water during refrigeration. When the heating return water passes through its absorber in the heat exchange tube, it absorbs the heat of the solution and heats up. The heat of the solution comes from the condensation heat generated by the solution absorbing water vapor. Then, when passing through the condenser in the heat exchange tube, it absorbs the condensation heat of the water vapor of the low-temperature generator, further heats up, and becomes hot water to be supplied to the end user.

[0027] In this embodiment, in the first direct-fired engine, a higher vacuum is generated due to the absorption of water vapor by its absorber, which promotes the evaporation of refrigerant water in the evaporator. The refrigerant water evaporates and cools down, absorbing the heat of water (secondary circulating water) in the evaporator heat exchange tube to cool it down. This temperature can be about 30°C lower than the hot water supply. If the heating temperature is 40-45°C, the temperature of the secondary circulating water is about 10-20°C. The secondary circulating water enters the absorber heat exchange tube of the second direct-fired engine, absorbs the heat of the lithium bromide solution in the absorber, reduces the temperature of the lithium bromide solution in the absorber, and makes it have a lower water vapor partial pressure, that is, the water absorption is enhanced, and a higher vacuum can be generated. This is conducive to the evaporation of water vapor in the evaporator of the second direct-fired engine.

[0028] In this embodiment, in the evaporator of the second direct-fired machine, ordinary condensed water (equivalent to pure water) is not used as refrigerant water, but a very dilute lithium bromide solution is used, so its freezing point is lowered, even below 0°C; and below 0°C, there is still a certain water vapor pressure, which produces water vapor evaporation, and this evaporation will absorb the heat in the heat exchange tube. In addition, the low-temperature heat source water with antifreeze added in the cooling tower enters the evaporator heat exchange tube of the second direct-fired machine through a primary water pump, releases heat, and the temperature of the low-temperature heat source water is reduced to 5-10°C below the ambient temperature. This low-temperature water enters the cooling tower (called the energy tower or heat source tower when heating) again through a primary water pump to absorb heat from the ambient atmosphere.

[0029] In this embodiment, a fan is provided above the cooling tower to generate airflow in the cooling tower; the antifreeze or water in the cooling tower is provided at the bottom layer, and air inlets are provided on both sides of the area above the antifreeze or water to deliver heat from the outside to the cooling tower for heat exchange with the low-temperature heat source water. The low-temperature heat source water with the lowest temperature output from the evaporator heat exchange tube of the second direct-fired engine enters the cooling tower from the top of the cooling tower, and in the process of falling, it convects against or transversely with the airflow, absorbs heat from the air, and gathers at the bottom of the cooling tower to form a low-temperature water circulation pipeline between the evaporator heat exchange tube of the second direct-fired engine, and then returns to the evaporator of the second direct-fired engine through a primary water pump.

[0030] In this embodiment, the flue gas generated by the two direct-fired engines exchanges heat with the secondary circulating water through the flue gas heat exchanger, and the heat is transferred to the secondary circulating water. Because the temperature of the secondary circulating water is low, the outlet temperature of the flue gas is about 25°C, which not only recovers the sensible heat in the flue gas (up to about 5% of the total calorific value of the fuel), but also condenses most of the water vapor in the flue gas into water, recovering the latent heat of the flue gas (up to about 10% of the total calorific value of the fuel), that is, increasing the heat recovery by 15%. In addition, water vapor and part of nitrogen oxides and sulfur dioxide in the flue gas are eliminated (eliminating white smoke), reducing environmental pollution.

[0031] In this embodiment, the flue gas heat exchanger is a water-gas heat exchanger, which can be a plate heat exchanger or a tube-fin heat exchanger, etc. In this case, the secondary circulating water can be a closed circulation. The water-gas heat exchanger can also use water to spray the flue gas for direct heat exchange, in which case the secondary circulating water is an open circulation, and the flue gas heat exchanger is located at the inlet end of the secondary water pump.

[0032] In this embodiment, the solution concentration of the first direct-fired engine is concentrated on the basis of the usual normal concentration (slightly different for different units and working conditions, generally around 60%), and its concentration is increased by 1-10%, preferably by 2-5%, which is beneficial to improve the absorption performance of the solution and obtain a higher heating water supply temperature. The solution concentration of the second direct-fired engine is slightly diluted according to the usual normal concentration, and its concentration is reduced by 1-10%, preferably by 3-6%, because the temperature of the secondary circulating water is low, even a low-concentration lithium bromide solution has good absorption performance, and crystallization caused by too low a solution temperature can be avoided. In addition, a small amount of lithium bromide solution is mixed into the refrigerant water of the second direct-fired engine, and its freezing point is -10~-2℃, preferably -8~-5℃.

[0033] The heating method of this embodiment comprises the following steps:

[0034] The antifreeze low-temperature heat source water, which is 5-10℃ lower than the ambient temperature, absorbs heat from the atmosphere through the air inlet of the cooling tower; the low-temperature heat source water after absorbing heat enters the evaporator heat exchange tube of the second direct-fired machine, exchanges heat with the antifreeze refrigerant water outside the heat exchange tube, and evaporates; this water vapor is absorbed by the solution in the absorber of the second direct-fired machine, releases heat, and is transferred to the secondary circulating water in the absorber heat exchange tube, so that the secondary circulating water is heated; the secondary circulating water enters the condenser heat exchange tube of the second direct-fired machine again under the drive of the secondary water pump, absorbs the condensation heat of the water vapor from the low-temperature generator, and enters The temperature is raised in one step, and then it enters the flue gas heat exchanger, where it absorbs the latent heat and sensible heat of the flue gas generated by the high-temperature generator to further heat it up, while the flue gas after heat exchange is cooled to about 25°C and discharged; the heated secondary circulating water enters the evaporator heat exchange tube of the first direct-fired engine, and the heat of the secondary circulating water is transferred to the refrigerant water in the evaporator of the first direct-fired engine, causing it to evaporate; this water vapor is absorbed by the solution in the absorber of the first direct-fired engine, releasing heat, and is transferred to the hot water in the absorber heat exchange tube, and the heating return water absorbs heat and heats up again after passing through the condenser of the first direct-fired engine, thereby providing heating for the user.

[0035] The heating process of this embodiment is as follows: the temperature of the antifreeze low-temperature heat source water is 5-10°C lower than the ambient temperature, the temperature of the secondary circulation water is higher than the temperature of the antifreeze low-temperature heat source water by up to 30°C, and can be up to about 25°C higher than the ambient temperature; the temperature of the heating return water is higher than the temperature of the secondary circulation water by up to 30°C, and can be higher than the ambient temperature by about 55°C. When the ambient temperature is not lower than -10°C, hot water above 45°C can be provided to meet the heating demand.

[0036] In this embodiment, since the total heat output of the heat pump = input heat of the high-temperature heat source (driving heat source) + heat of the low-temperature heat source, its performance coefficient (total heat output / input driving heat source) is greater than 1. According to the characteristics of the direct-fired engine, the performance coefficient is 2-2.4. If calculated with a performance coefficient of 2, absorbing 1 part of heat from the environment requires 3 parts of high-temperature heat source input, plus 0.45 (3*15%) parts of waste heat recovered from flue gas, its performance coefficient is 4.45 / 3=1.48, which is much higher than the maximum performance coefficient of 0.93 when the direct-fired engine is directly heated, which is equivalent to (1.48-0.93) / 0.93=59%, that is, energy saving of more than 59%. If the ambient temperature is high, the performance coefficient of the utility model will be further improved, even reaching more than 1.6, and energy saving (1.6-0.93) / 0.93=72%, that is, energy saving of more than 70%.

[0037] In summary, on the one hand, this embodiment does not need to change the internal structure of the direct-fired engine. It only needs to have at least two direct-fired engines, and use multiple direct-fired engines and existing cooling towers to absorb heat from the environment and operate in a heat pump mode to adjust the solution concentration and the refrigerant water concentration, which is much higher than the direct heating method of the direct-fired engine. On the other hand, due to the existence of secondary circulating water with a lower temperature, the flue gas heat exchanger is provided to cool and condense the flue gas, so that the secondary circulating water can fully absorb the sensible heat and latent heat in the flue gas, thereby greatly improving the heating efficiency and reducing the environmental impact.

[0038] Example 2

[0039] In this embodiment, a conduit is provided between the outlet of the generating pump (also called solution pump) of the second direct-fired machine and the refrigerant water in the evaporator of the direct-fired machine. The conduit is provided with a first vacuum valve that can be opened and closed, which is used to control the entry of part of the lithium bromide solution into the refrigerant water of the evaporator, so that the freezing point of the refrigerant water is lower than 0°C. According to the temperature requirements of the cold water, its freezing point is -10~-2°C, preferably -8~-5°C, and the freezing point of the refrigerant water is 3-5°C lower than the cold water outlet.

[0040] Among them, the generating pump is a standard configuration of the direct-fired engine, which is used to output the lithium bromide solution in the absorber of the direct-fired engine to other exchangers. This is the existing technology and will not be described in detail.

[0041] In this embodiment, a conduit is also provided between the outlet of the refrigerant pump of the second direct-fired engine and the inlet of the generating pump of the direct-fired engine. The conduit is provided with a second vacuum valve that can be opened and closed. When the concentration of the lithium bromide solution in the refrigerant water in the evaporator is too high (affecting the evaporation effect), the refrigerant water is bypassed to allow it to enter the solution and reduce the concentration of the solution.

[0042] Among them, the refrigerant pump is also a standard configuration of the direct-fired engine. The refrigerant pump of the existing direct-fired engine is used to transport the refrigerant water of the evaporator to the top of the evaporator heat exchange tube to exchange heat with the solvent in the heat exchange tube. On this basis, this embodiment sets a conduit between the refrigerant pump and the generator pump for valve control, thereby reducing the concentration of lithium bromide solution in the refrigerant water, and meeting the temperature requirements of the cold water without affecting the evaporation effect.

[0043] In this embodiment, a vacuum sampling valve is provided at the outlet of the refrigerant pump for manually testing the lithium bromide concentration (corresponding to the freezing point) of the refrigerant water; or a conductivity sensor is provided at the outlet of the refrigerant pump for testing the lithium bromide concentration (corresponding to the freezing point) of the refrigerant water by conductivity.

[0044] In this embodiment, the conductivity sensor, the first vacuum valve, and the second vacuum valve are all connected to a control circuit to form an automatic control system for refrigerant water concentration.

[0045] The working principle of this embodiment is:

[0046] When it is detected that the concentration of the refrigerant water in the evaporator of the second direct-fired machine is lower than the lower limit of the set value (for example: the operating conditions require the freezing point of the refrigerant water to be -3 to -5°C, equivalent to a concentration of 4.5%~7.5%. When the concentration is detected to be lower than 4.5%), the first vacuum valve located on the outlet of the generating pump of the second direct-fired machine and the inlet pipeline of the evaporator refrigerant water of the second direct-fired machine is controlled to open, allowing part of the dilute solution to enter the refrigerant water of the evaporator, so that the freezing point of the refrigerant water is lower than 0°C, and according to the temperature requirements of the cold water, the freezing point of the refrigerant water is made 3-5°C lower than the cold water outlet; when it is detected that the concentration of the refrigerant water is greater than or equal to the lower limit of the set value (continuing the above example, when the concentration is higher than 4.5%), the first vacuum valve is closed.

[0047] Sometimes, the lithium bromide solution in the absorber of the second direct-fired machine will splash into the refrigerant water, causing the concentration of the lithium bromide solution in the refrigerant water in the evaporator of the second direct-fired machine to increase. When it is detected that the lithium bromide solution in the refrigerant water of the evaporator of the second direct-fired machine is higher than the upper limit of the set value (continued from the above example, higher than 7.5%), the second vacuum valve located on the refrigerant pump outlet and the generating pump inlet pipeline of the second direct-fired machine is controlled to open, so that the refrigerant water enters the dilute solution; when the concentration of the lithium bromide solution is lower than the upper limit of the set value (continued from the above example, lower than 7.5%), the second vacuum valve is closed.

[0048] In summary, in this embodiment, on the one hand, by setting a conduit and a first vacuum valve between the generator pump outlet and the refrigerant water, it can ensure that the freezing point of the refrigerant water is lower than 0°C, thereby meeting the temperature requirement for cold water; on the other hand, by setting a conduit and a second vacuum valve between the generator pump inlet and the refrigerant pump outlet, it can ensure that the concentration of lithium bromide solution in the refrigerant water in the evaporator does not affect the evaporation effect.

Claims

1. A heat pump heating system with multiple direct-fired engines, characterized in that: include: The cooling tower equipped with the direct-fired machine for refrigeration is used to absorb the heat from the atmosphere by the low-temperature heat source water inside. The low-temperature heat source water after absorbing the heat is transported to the evaporator heat exchange tube of the second direct-fired machine through a primary water pump to exchange heat with the refrigerant water outside the heat exchange tube; the low-temperature heat source water after releasing the heat enters the cooling tower again to absorb the heat from the atmosphere, and the cycle continues; At least two direct-fired machines, including a first direct-fired machine and a second direct-fired machine, the second direct-fired machine is used to allow the water vapor generated after the refrigerant water in the evaporator absorbs heat and evaporates to enter the absorber of the second direct-fired machine, be absorbed by the solution in the absorber and release heat, and transfer the heat to the secondary circulating water in the absorber heat exchange tube, so that the secondary circulating water is heated; the first direct-fired machine is used to receive the heat of the heated secondary circulating water through the evaporator heat exchange tube, evaporate the refrigerant water outside the heat exchange tube, and the evaporated water vapor is absorbed by the surface solution of the first direct-fired machine absorber and releases heat, and the heat is transferred to the heat supply return water in the absorber heat exchange tube, so that it is heated and continuously supplies heat.

2. The heat pump heating system of multiple direct-fired engines according to claim 1 is characterized in that: The low-temperature heat source water in the cooling tower is connected to the evaporator heat exchange pipe of the second direct-fired machine through a primary water pump, and then returns to the cooling tower after releasing heat through the heat exchange pipe of the evaporator of the second direct-fired machine, absorbing heat from the air to form a low-temperature water circulation pipeline.

3. The heat pump heating system of multiple direct-fired engines according to claim 2 is characterized in that: The pipeline connection method for continuously heating up the secondary circulating water is as follows: the evaporator heat exchange tube of the first direct-fired engine is connected to the absorber heat exchange tube, condenser heat exchange tube and flue gas heat exchanger of the second direct-fired engine in sequence through a secondary water pump; or the evaporator heat exchange tube of the first direct-fired engine is connected to the absorber heat exchange tube and flue gas heat exchanger of the second direct-fired engine in sequence through a secondary water pump; and then returns to the evaporator heat exchange tube of the first direct-fired engine through the flue gas heat exchanger to form a secondary water circulation pipeline.

4. The heat pump heating system of multiple direct-fired engines according to claim 1 is characterized in that: The heat return water end is connected to the absorber heat exchange tube and the condenser heat exchange tube of the first direct-fired engine in sequence through pipelines, and output from the condenser to the user end; the high temperature generators of the first direct-fired engine and the second direct-fired engine are both connected to the flue gas heat exchanger.

5. The heat pump heating system of multiple direct-fired engines according to claim 1 is characterized in that: A fan is provided above or on the side of the cooling tower to generate airflow in the cooling tower. The lowest temperature low-temperature heat source water coming out of the second direct-fired engine evaporator convects against or transversely with the airflow, absorbs heat in the air, and is collected at the bottom of the cooling tower and returned to the second direct-fired engine evaporator through a primary water pump.

6. The heat pump heating system of multiple direct-fired engines according to claim 1 is characterized in that: The second direct-fired engine also includes a generator pump, and a conduit is provided between the outlet of the generator pump and the refrigerant water in the evaporator of the second direct-fired engine. The conduit is provided with a first vacuum valve that can be opened and closed, which is used to control the entry of part of the lithium bromide solution into the refrigerant water of the evaporator, so that the freezing point of the refrigerant water is lower than 0°C and can evaporate at a temperature below 0°C.

7. The heat pump heating system of multiple direct-fired engines according to claim 6 is characterized in that: The second direct-fired engine also includes a refrigerant pump, and a conduit is also provided between the outlet of the refrigerant pump and the inlet of the generating pump of the direct-fired engine. The conduit is provided with a second vacuum valve that can be opened and closed. When the concentration of the lithium bromide solution in the refrigerant water in the evaporator is higher than the upper limit of the set value, the refrigerant water is bypassed and allowed to enter the solution to reduce the concentration of the lithium bromide solution in the refrigerant water.

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