A heating system coupling a WNS gas boiler and a lithium bromide absorption heat pump

Abstract

The present invention discloses a heating system coupled with a WNS gas-fired boiler and a lithium bromide absorption heat pump. In the boiler drum of the WNS gas-fired boiler body, a first partition and a second partition are vertically arranged along the extension direction of the smoke pipe to divide the internal space of the boiler drum into three independent chambers, respectively constituting a generator, a return water heat exchanger, and an evaporator of the lithium bromide absorption heat pump system. Compared with the separate arrangement of the lithium bromide absorption heat pump and the WNS boiler, the cost and floor space are reduced. The WNS boiler and the lithium bromide absorption heat pump are arranged as an integrated whole. The high-temperature flue gas from the furnace sequentially heats the return water, the lithium bromide solution, the return water, and the refrigerant water, thereby increasing the temperature of the driving heat source entering the generator and reducing the outlet flue gas temperature. This solves the problem that when the heat pump is driven by boiler exhaust smoke, the outlet flue gas temperature of the heat pump cannot be reduced to a very low level due to the low flue gas temperature, resulting in low overall efficiency, thereby improving energy utilization efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of boilers, relates to the technical field of gas heating and flue gas waste heat recovery, and in particular to a heating system coupling a WNS type gas boiler and a lithium bromide absorption heat pump. Background Art

[0002] Existing natural gas boilers heat the heat supply network by heating the return water from the flue gas in the second and third return flue gas ducts. The flue gas temperature at the boiler outlet is generally 100-200°C. Placing a condensing heat exchanger at the flue gas outlet can cool the flue gas to a lower temperature. However, due to the high return water temperature of the condenser, which is close to the dew point of the water vapor in the flue gas, the water vapor in the flue gas is unlikely to undergo a phase change (from gas to liquid) to release its latent heat of vaporization. The water vapor in the flue gas lacks sufficient momentum to continue condensing, preventing the release of its latent heat of vaporization and thus preventing the recovery of a significant amount of the latent heat of vaporization.

[0003] Furthermore, existing lithium bromide absorption heat pumps for recovering waste heat from natural gas boiler flue gas often use a split system. The gas boiler and absorption heat pump are located separately, and the flue gas enters the absorption heat pump after leaving the boiler. At this point, the flue gas at the boiler outlet is too cold to serve as the heat source for the generator, preventing the recovery of a significant amount of latent heat in the flue gas. This split system increases system cost and floor space, making it less economical. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a heating system coupling a WNS type gas boiler and a lithium bromide absorption heat pump, which is used to fully utilize the heat of flue gas to improve boiler efficiency, while having low cost, small footprint and greater economy.

[0005] The present invention is achieved through the following technical solutions:

[0006] A heating system coupled with a WNS gas-fired boiler and a lithium bromide absorption heat pump includes a WNS gas-fired boiler body. A first baffle and a second baffle are vertically arranged in the boiler drum of the WNS gas-fired boiler body along the direction in which the flue gas pipe extends, thereby dividing the internal space of the boiler drum into three independent chambers. The first chamber is located on the side of the boiler drum away from the flue gas pipe, and the furnace, second return flue gas pipe, and third return flue gas pipe are partially located in the first chamber. The second chamber is located on the side of the boiler drum closer to the flue gas pipe, and the tail section of the third return flue gas pipe is located in the second chamber. The third chamber is located between the other two chambers, and the furnace, second return flue gas pipe, and third return flue gas pipe are partially located in the third chamber.

[0007] The first chamber is filled with lithium bromide solution to form the generator of the lithium bromide absorption heat pump. The second chamber is provided with a liquid distributor for spraying refrigerant to form the evaporator of the lithium bromide absorption heat pump. The third chamber is connected to the pipeline for adding return water to the heating network to serve as the return water heat exchanger of the WNS type gas boiler.

[0008] The absorber and condenser are both installed on the return water pipeline of the heating network. The hot water at the outlet of the return water heat exchanger is used to heat the user, and then cooled to become the return water of the heating network and enter the return water pipeline of the heating network. The return water of the heating network is heated in turn by the absorber and condenser, and then returns to the boiler return water heat exchanger to be heated into hot water to form a cycle;

[0009] The refrigerant channel of the condenser is connected to the generator and the evaporator respectively; the refrigerant steam inlet of the absorber is connected to the steam outlet of the evaporator, and the lithium bromide concentrated solution inlet and the lithium bromide dilute solution outlet of the absorber are connected to the generator through pipelines respectively; the water vapor generated by the generator enters the condenser for condensation and then passes into the liquid distributor in the evaporator, and the water vapor generated by the refrigerant evaporating after absorbing heat enters the absorber.

[0010] Furthermore, an adjusting branch pipe is connected between the second return smoke pipe and the same smoke pipe in the third return smoke pipe in the third chamber, and valves are installed on the adjusting branch pipe and the second return smoke pipe and the third return smoke pipe connected to the adjusting branch pipe. The conduction and shutdown between the second return smoke pipe and the third return smoke pipe in the third chamber are controlled by the adjusting branch pipe and the valve.

[0011] Furthermore, a solution heat exchanger is provided on the lithium bromide dilute solution and concentrated solution pipelines communicating between the absorber and the generator.

[0012] Furthermore, a solution pump is installed on the lithium bromide concentrated solution pipeline connecting the solution heat exchanger and the generator.

[0013] Furthermore, valves are respectively installed on the lithium bromide concentrated solution pipeline connecting the solution heat exchanger and the generator and on the pipeline connecting the refrigerant outlet of the condenser and the refrigerant inlet of the liquid distributor.

[0014] Furthermore, the cooling water inlet of the absorber is connected to the heat network return pipeline, the cooling water outlet of the absorber is connected to the cooling water inlet of the condenser, the cooling water outlet of the condenser is connected to the return water heat exchanger inlet, and the return water heat exchanger outlet is connected to the heat network pipeline.

[0015] Furthermore, a water pump is installed on the pipeline connecting the return water pipeline of the heat network and the cooling water inlet of the absorber.

[0016] Furthermore, the second return smoke pipe is a straight pipe, and the third return smoke pipe is an internally threaded pipe.

[0017] The present invention has the following beneficial effects:

[0018] The WNS gas-fired boiler's drum is divided into three independent chambers by vertically installed first and second baffles along the flue pipe's extension. These chambers house the generator, return water heat exchanger, and evaporator of the lithium bromide absorption heat pump system. These chambers are located within the drum, creating a relatively clean interior and fully utilizing unused space. This eliminates the need for a separate, larger installation area for the heat pump system outside the boiler. This reduces costs and floor space compared to separate installations of the lithium bromide absorption heat pump and WNS boiler. Furthermore, this internal arrangement reduces piping material and installation costs. The shortened piping not only reduces pipe purchase costs but also reduces installation labor and the number of pipe fittings.

[0019] The higher medium temperature inside the boiler drum facilitates the operation of the lithium bromide absorption heat pump system. The high-temperature flue gas from the boiler's second and third return flue ducts provides the heat source for the heat pump, while the evaporator provides the low-temperature cooling source for the flue gas. The coupling of the gas-fired boiler and the absorption heat pump reduces floor space, lowers costs, and improves energy efficiency. The generator's location within the boiler drum allows for better utilization of the high-temperature heat source within the drum, increasing the efficiency of lithium bromide solution generation. The return water heat exchanger and evaporator, due to their proximity to the heat source within the drum, offer improved heat transfer, reducing the need for additional heating or cooling equipment and improving the overall system's economic efficiency. The flue gas temperature in the generator flue duct is relatively high, so immersing the flue gas in the lithium bromide solution prevents the high temperature from causing the solution to evaporate.

[0020] The WNS boiler and lithium bromide absorption heat pump are integrated into a single unit. The generator is located at the rear of the second return and the front of the third return. The lithium bromide solution inside is separated from the return water by a partition. The evaporator is located at the rear of the third return. A horizontal falling-film distributor sprays refrigerant onto the flue gas pipe surface, where it absorbs heat and evaporates. The high-temperature flue gas from the furnace sequentially heats the return water, lithium bromide solution, return water, and refrigerant water, raising the temperature of the driving heat source entering the generator, lowering the outlet flue gas temperature, and improving energy efficiency. This solves the problem of low flue gas temperature, which prevents the outlet flue gas temperature from being sufficiently low and resulting in low overall efficiency when the heat pump is driven by boiler exhaust gas. The refrigerant solution in the evaporator is relatively low in temperature, and the distributor evenly distributes the refrigerant solution across the flue gas pipe surface to fully absorb the flue gas waste heat. This avoids the existing problem of insufficient recovery of the flue gas's latent heat of vaporization through the condenser, thereby improving heat exchange efficiency.

[0021] A regulating branch is provided between the second and third return flue pipes. When the boiler load changes, the regulating branch opens or closes some of the second and third return flue pipes, adjusting the amount of flue gas passing through generator 7 to regulate the generator's operation and adjust the operating conditions of the entire heating system. When the external heating network's water supply temperature changes, the system's flexible adjustment capability allows it to adapt to changes in heat load over time, ensuring stable operation under various operating conditions.

[0022] The second return smoke pipe is a straight pipe, and the third return smoke pipe is an internally threaded pipe, which improves the heat transfer coefficient of the flue gas in the pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0024] Figure numerals: 1, burner; 2, furnace; 3, backfire chamber; 4, front return smoke chamber; 5, second return smoke duct; 6, third return smoke duct; 7, generator; 8, return water heat exchanger; 9, evaporator; 10, smoke exhaust pipe; 11, liquid distributor; 12-1, first partition; 12-2, second partition; 13, boiler drum; 14, absorber; 15, condenser; 16, solution heat exchanger; 17, solution pump; 18, water feed pump; 19, first valve; 20, second valve; 21, third valve. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0026] See also Figure 1 The present invention provides a heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump, comprising a burner 1, a furnace 2, a backfire chamber 3, a front smoke return chamber 4, a second return smoke duct 5, a third return smoke duct 6, a generator 7, a return water heat exchanger 8, an evaporator 9, a smoke exhaust pipe 10, a liquid distributor 11, a first partition 12-1, a second partition 12-2, a boiler drum 13, an absorber 14, a condenser 15, a solution heat exchanger 16, a solution pump 17, a water supply pump 18, a first valve 19, a second valve 20, and a third valve 21.

[0027] In the boiler drum 13 of a WNS gas-fired boiler, a first baffle 12-1 and a second baffle 12-2 are disposed along the direction in which the flue gas pipe extends. The vertically disposed first baffle 12-1 and second baffle 12-2 divide the internal space of the boiler drum 13 into three independent chambers. The first baffle 12-1 is disposed on the side of the boiler drum 13 away from the boiler flue gas pipe 10, forming a first chamber within the drum 13 away from the flue gas pipe 10. The furnace 2, the second return flue gas pipe 5, and the front section of the third return flue gas pipe 6 are all located within the first chamber. The second baffle 12-2 is disposed on the side of the boiler drum 13 near the boiler flue gas pipe 10, forming a second chamber within the drum 13 near the flue gas pipe 10. The rear section of the third return flue gas pipe 6 is located within the second chamber. A third chamber is formed within the drum 13 between the first baffle 12-1 and the second baffle 12-2. The intermediate structures of the furnace 2, the second return flue gas pipe 5, and the third return flue gas pipe 6 are located within the third chamber.

[0028] The first chamber is filled with lithium bromide solution to form the generator 7 of the lithium bromide absorption heat pump. The second chamber is provided with a liquid distributor 11 for spraying refrigerant to form the evaporator 9 of the lithium bromide absorption heat pump. The third chamber is connected to the pipeline for adding return water from the heating network and is used to heat the return water from the heating network, serving as the return water heat exchanger 8 of the WNS type gas boiler. The generator 7, return water heat exchanger 8 and evaporator 9 are arranged inside the boiler drum 13 and separated by a first partition 12-1 and a second partition 12-2.

[0029] An absorber 14 and a condenser 15 are arranged above the boiler drum 13. Both the absorber 14 and the condenser 15 are installed on the return water pipeline of the heat network. The refrigerant inlet of the condenser 15 is connected to the steam outlet of the generator 7, and the refrigerant outlet of the condenser 15 is connected to the refrigerant inlet of the liquid distributor 11 provided in the evaporator 9. The cooling water inlet of the condenser 15 is connected to the return water pipeline of the heat network. The cooling water outlet of the condenser 15 is connected to the water inlet of the return water heat exchanger 8, and the water outlet of the return water heat exchanger 8 is connected to the heat network pipeline to provide users with high-calorie hot water.

[0030] The refrigerant vapor inlet of the absorber 14 is connected to the steam outlet of the evaporator 9, and the lithium bromide concentrated solution inlet and the lithium bromide dilute solution outlet of the absorber 14 are connected to the generator 7 through pipelines respectively; the cooling water inlet of the absorber 14 is connected to the heat network return pipeline, and the cooling water outlet of the absorber 14 is connected to the cooling water inlet of the condenser 15. The water vapor generated by the generator 7 directly enters the condenser 15 through the steam outlet above the boiler drum 13, and the water vapor generated by the evaporator 9 directly enters the absorber 14 through the steam outlet above the boiler drum 13.

[0031] A solution heat exchanger 16 is arranged on the dilute lithium bromide solution and concentrated lithium bromide solution pipeline connecting the absorber 14 and the generator 7. It is used to exchange heat between the dilute lithium bromide solution and the concentrated lithium bromide solution entering and exiting the boiler drum, thereby increasing the temperature of the dilute lithium bromide solution entering the boiler drum and improving the overall thermal efficiency of the boiler. A solution pump 17 is installed on the concentrated lithium bromide solution pipeline connecting the solution heat exchanger 16 and the generator 7 to provide driving force for the dilute lithium bromide solution to enter the generator 7. Valves are respectively installed on the concentrated lithium bromide solution pipeline connecting the solution heat exchanger 16 and the generator 7, and on the pipeline connecting the refrigerant outlet of the condenser 15 and the refrigerant inlet of the liquid distributor 11.

[0032] Generator 7 is filled with lithium bromide solution. Furnace 2, second return flue duct 5, and the front section of third return flue duct 6 are all immersed in the lithium bromide solution. The lithium bromide solution is heated to generate water vapor, which is then condensed in condenser 15 through the steam outlet above the boiler. Return water heat exchanger 8 is filled with heat network return water. Furnace 2, second return flue duct 5, and the middle section of third return flue duct 6 are all immersed in the heat network return water. A horizontal falling film distributor 11 is positioned above evaporator 9 to spray the refrigerant solution onto the surface of third return flue duct 6. The refrigerant solution at the inlet of evaporator 9 is evenly distributed across the flue duct surface by the horizontal falling film distributor 11, where it is heated and evaporated. The refrigerant vapor at the outlet of evaporator 9 is absorbed by the concentrated lithium bromide solution in absorber 14.

[0033] like Figure 1 As shown, to adapt to changes in the water supply temperature of the heating network and in the event of changes in boiler load, the heat pump load can be adjusted by opening or closing valves, providing the entire system with flexible adjustment capabilities. A regulating branch pipe is connected between a portion of the second return flue duct 5 and the third return flue duct 6 within the third chamber. This regulating branch pipe connects the second return flue duct 5 and the third return flue duct 6. A first valve 19 is installed on the regulating branch pipe. Correspondingly, a second valve 20 is installed on the second return flue duct 5 connected to the regulating branch pipe, and a third valve 21 is installed on the third return flue duct 6 connected to the regulating branch pipe. Along the direction of flue gas flow, the second and third valves 20 and 21 are located after the regulating branch pipe. When the load on the heating system increases, the second and third valves 20 and 21 are opened, and the first valve 19 is closed, closing the regulating branch pipe. The flue gas passes entirely through the generator 7, which has a high heat load. The lithium bromide absorption heat pump meets the heat output requirements under high loads. When the load of the heating system decreases, the first valve 19 is opened, and the second valve 20 and the third valve 21 are closed, so that the regulating branch pipe partially connects the second return smoke pipe 5 and the third return smoke pipe 6, reducing the amount of flue gas entering the generator 7. The heat load of the generator 7 is small, reducing the heat output of the lithium bromide absorption heat pump, and meeting the low-load operation requirements of the system.

[0034] The high-temperature flue gas from the furnace passes through the generator 7, the return water heat exchanger 8, and the evaporator 9 in three return passes: furnace 2, the second return flue pipe 5, and the third return flue pipe 6. The high-temperature flue gas from the furnace first enters the generator, where the flue gas temperature is highest and can provide sufficient heat to drive the generation process of the lithium bromide solution. Next, the flue gas, with a lower temperature, enters the return water heat exchanger, effectively heating the return water. The flue gas in the third return flue pipe enters the evaporator. Although the flue gas temperature has dropped, it still provides heat to the evaporator, achieving multiple heat exchanges. Through multiple heat recovery processes, the flue gas heat is fully utilized, thereby achieving full absorption of latent heat.

[0035] A water pump 18 is installed on the connecting pipe between the heat network return water pipeline and the cooling water inlet of the absorber 14. The hot water at the boiler outlet is supplied to the user for heating and then cooled to become the heat network return water. The heat network return water is first pressurized by the water pump 18 and then enters the absorber 14 and condenser 15 in turn to be heated, and finally returns to the boiler to be heated into hot water to form a cycle.

[0036] In order to further improve the heat exchange efficiency, the second return smoke pipe is a straight pipe, and the third return smoke pipe is an internally threaded pipe.

[0037] Table 1 System operation temperature table

[0038] variable unit Numerical Furnace outlet flue gas temperature ℃ 946 Generator inlet flue gas temperature ℃ 450 Generator outlet flue gas temperature ℃ 150 Evaporator inlet flue gas temperature ℃ 60 Evaporator outlet flue gas temperature ℃ 34.5 Absorber inlet return water temperature ℃ 50 Absorber outlet return water temperature ℃ 56.5 Condenser inlet return water temperature ℃ 58.5 Condenser outlet return water temperature ℃ 63.6 Generator inlet dilute solution temperature ℃ 89.7 Generator outlet concentrated solution temperature ℃ 123.1 Generator outlet steam temperature ℃ 123.1 Absorber outlet dilute solution temperature ℃ 54.3 Condenser inlet water vapor temperature ℃ 123.1 Condenser outlet liquid water temperature ℃ 69.1 Evaporator inlet liquid water temperature ℃ 21 Evaporator outlet water vapor temperature ℃ 22.2 Concentrated solution temperature at the inlet of solution heat exchanger ℃ 123.1 Dilute solution temperature at the inlet of solution heat exchanger ℃ 54.3 Concentrated solution temperature at outlet of solution heat exchanger ℃ 66.5 Dilute solution temperature at solution heat exchanger outlet ℃ 89.7

[0039] As shown in Table 1, testing of the heating system of the present invention, coupled with a WNS gas-fired boiler and a lithium bromide absorption heat pump, revealed that the flue gas temperature at the system's furnace 2 outlet was 946°C, the flue gas temperature at the generator 7 inlet was 450°C, the flue gas temperature at the generator 7 outlet was 150°C, the flue gas temperature at the evaporator 9 inlet was 60°C, and the flue gas temperature at the flue gas exhaust pipe 10 outlet was approximately 30°C. 80% of the water vapor in the flue gas was condensed. The return water had a temperature of 50°C upon entering the absorber 14, 56.5°C upon leaving the absorber 14 and entering the condenser 15, and 63.6°C upon leaving the condenser 15 and entering the boiler return water heater 8.

[0040] At the same time, the traditional split-type gas boiler and lithium bromide absorption heat pump heating system were tested. When no other driving heat source was provided in the generator, the flue gas temperature at the gas boiler outlet was 160°C, that is, the flue gas temperature at the generator inlet was 160°C, the flue gas temperature at the generator outlet was 110°C, the flue gas temperature at the evaporator inlet was 60°C, and the evaporator outlet temperature was 56°C. Most of the water vapor in the flue gas could not be condensed, the exhaust gas residual temperature reached 60°C, and a large amount of latent heat was wasted.

[0041] Through the above comparison, it can be found that, by adopting the heating system of the present invention coupling the WNS type gas boiler and the lithium bromide absorption heat pump, the waste heat in the flue gas is fully absorbed, thereby improving the heat exchange efficiency.

Claims

1. A heating system coupling a WNS gas boiler and a lithium bromide absorption heat pump, characterized by: The invention comprises a WNS type gas boiler body, wherein a first partition plate (12-1) and a second partition plate (12-2) are respectively arranged vertically in a boiler drum (13) along the extension direction of the smoke pipe to divide the internal space of the boiler drum (13) into three independent chambers; the first chamber is located on a side of the boiler drum (13) away from the smoke exhaust pipe (10), and the furnace (2), the second return smoke pipe (5), and the third return smoke pipe (6) are partially located in the first chamber; the second chamber is located on a side of the boiler drum (13) close to the smoke exhaust pipe (10), and the tail section of the third return smoke pipe (6) is located in the second chamber; the third chamber is located between the other two chambers, and the furnace (2), the second return smoke pipe (5), and the third return smoke pipe (6) are partially located in the third chamber; A lithium bromide solution is injected into the first chamber to form a generator (7) of a lithium bromide absorption heat pump, a liquid distributor (11) for spraying refrigerant is provided in the second chamber to form an evaporator (9) of the lithium bromide absorption heat pump, and the third chamber is connected to a pipeline for adding return water to the heat network to serve as a return water heat exchanger (8) of a WNS type gas boiler; The absorber (14) and the condenser (15) are both installed on the return water pipeline of the heating network. The hot water at the outlet of the return water heat exchanger (8) is used for heating the user and then cooled to become the return water of the heating network and enter the return water pipeline of the heating network. The return water of the heating network is heated in turn by the absorber (14) and the condenser (15) and then returns to the boiler return water heat exchanger (8) to be heated into hot water for supply, forming a cycle. The refrigerant channel of the condenser (15) is communicated with the generator (7) and the evaporator (9) respectively; the refrigerant vapor inlet of the absorber (14) is communicated with the vapor outlet of the evaporator (9), and the lithium bromide concentrated solution inlet and the lithium bromide dilute solution outlet of the absorber (14) are respectively communicated with the generator (7) through pipelines; the water vapor generated by the generator (7) enters the condenser (15) for condensation and then enters the liquid distributor (11) in the evaporator (9); the water vapor generated by the refrigerant evaporating after absorbing heat enters the absorber (14).

2. The heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump according to claim 1, characterized in that: An adjusting branch pipe is connected between the second return smoke pipe (5) and the third return smoke pipe (6) in the third chamber. Valves are installed on the adjusting branch pipe and on the second return smoke pipe (5) and the third return smoke pipe (6) connected to the adjusting branch pipe. The connection and disconnection between the second return smoke pipe (5) and the third return smoke pipe (6) in the third chamber are controlled by the adjusting branch pipe and the valve.

3. The heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump according to claim 2, characterized in that: A solution heat exchanger (16) is provided on the lithium bromide dilute solution and concentrated solution pipelines communicating between the absorber (14) and the generator (7).

4. The heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump according to claim 3, characterized in that: A solution pump (17) is installed on the lithium bromide concentrated solution pipeline connecting the solution heat exchanger (16) and the generator (7).

5. The heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump according to claim 4, characterized in that: Valves are respectively installed on the lithium bromide concentrated solution pipeline connecting the solution heat exchanger (16) and the generator (7) and on the pipeline connecting the refrigerant outlet of the condenser (15) and the refrigerant inlet of the liquid distributor (11).

6. The heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump according to any one of claims 1 to 5, characterized in that: The cooling water inlet of the absorber (14) is connected to the heat network return water pipeline, the cooling water outlet of the absorber (14) is connected to the cooling water inlet of the condenser (15), the cooling water outlet of the condenser (15) is connected to the water inlet of the return water heat exchanger (8), and the water outlet of the return water heat exchanger (8) is connected to the heat network pipeline.

7. The heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump according to claim 6, characterized in that: A water pump (18) is installed on a pipeline connecting a heat network return water pipeline and a cooling water inlet of an absorber (14).

8. The heating system coupled with a WNS gas boiler and a lithium bromide absorption heat pump according to claim 6, characterized in that: The second return smoke pipe (5) is a straight pipe, and the third return smoke pipe (6) is an internally threaded pipe.

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