Combined utilization device for waste heat and waste gas of alkaline electrolytic cell for wind-solar power generation and hydrogen production

Abstract

The utility model relates to the technical field of energy recycling, and discloses a combined utilization device for waste heat and waste gas of an alkaline electrolytic cell for wind-solar power generation and hydrogen production, which comprises a hydrogen production unit, and an oxygen separation unit and a hydrogen separation unit are sequentially arranged on the right side of the hydrogen production unit from left to right. A primary oxygen conveying pipe is communicated between the hydrogen production unit and the oxygen separation unit, a primary hydrogen conveying pipe is communicated between the hydrogen production unit and the hydrogen separation unit, and an alkali liquor recovery assembly is arranged between the bottom of the hydrogen separation unit and the bottom of the oxygen separation unit; and a combustion chamber is arranged on the rear side of the hydrogen separation unit. According to the utility model, the hydrogen production loss is reduced by utilizing unqualified hydrogen in the start-up stage; secondly, heat generated during operation of hydrogen production equipment and combustion of waste gas is used for drying and heat supply in the whole hydrogen production process; and when heat is sufficient, the steam turbine can be used for self-generating electricity, municipal electricity consumption of a factory is reduced, and municipal electricity cost is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of energy recovery and utilization, in particular to a device for jointly utilizing waste heat and waste gas of an alkaline electrolyzer for producing hydrogen using wind and solar power generation. Background Art

[0002] As a green energy, new energy is developing rapidly. By the end of 2023, the installed capacity of new energy has reached 1.45 billion kilowatts. At the same time, leapfrogging development will also bring certain problems, the most obvious of which is the problem of electricity consumption. As a result, a series of industries have been spawned with the purpose of absorbing the excess power generation of new energy, and the use of new energy for hydrogen production has attracted attention as the current mainstream industrial model. The current more mature hydrogen production processes are alkaline water electrolysis and proton exchange membrane electrolysis. Due to technical problems, the maximum domestic single-stack hydrogen production capacity of proton exchange membrane water electrolysis is currently 300Nm3 / h, which is small in size and difficult to achieve large-scale use due to its high production cost. The alkaline water electrolysis process technology is mature and low in cost. At present, the largest single-stack hydrogen production capacity in China is 3000Nm3 / h, which is suitable for large-scale applications.

[0003] Due to the volatility of wind power and photovoltaic power, the electrolyzer cannot operate at full load for 24 hours, and the number of starts and stops will increase accordingly. Due to the limitations of alkaline electrolyzer technology, at least 1h-1.5h of cold start is required during the startup phase to reach the rated power. When the equipment is cold started, the gas purity does not meet the requirements, so it is usually discharged. When the gas purity is qualified, it is collected and purified and separated in the next step. In this process, a large amount of hydrogen is discharged and wasted.

[0004] Therefore, a device for combined utilization of waste heat and exhaust gas of alkaline electrolyzer for hydrogen production by wind and solar power generation is proposed to solve the above problems. Utility Model Content

[0005] In order to make up for the above shortcomings, the utility model provides a combined utilization device of waste heat and exhaust gas of alkaline electrolyzer for hydrogen production by wind and solar power generation, aiming to improve the problem in the prior art that when the equipment is cold started, the gas purity produced does not meet the requirements and is usually discharged externally. When the gas purity is qualified, it is collected and purified and separated in the next step. In this process, a large amount of hydrogen is discharged and wasted.

[0006] In order to achieve the above-mentioned purpose, the utility model adopts the following technical scheme: a combined utilization device of waste heat and waste gas of an alkaline electrolyzer for hydrogen production by wind and solar power generation, comprising a hydrogen production unit, an oxygen separation unit and a hydrogen separation unit are arranged on the right side of the hydrogen production unit from left to right, a primary oxygen delivery pipe is connected between the hydrogen production unit and the oxygen separation unit, a primary hydrogen delivery pipe is connected between the hydrogen production unit and the hydrogen separation unit, an alkali solution recovery component is arranged between the bottom of the hydrogen separation unit and the oxygen separation unit, and a combustion chamber is arranged at the rear side of the hydrogen separation unit. A secondary hydrogen delivery pipe is connected between the combustion chamber and the hydrogen separation unit, a water treatment unit is arranged on the left side of the combustion chamber, a water delivery pipe is connected between the water treatment unit and the combustion chamber, a delivery pump is fixedly connected to the left side of the water treatment unit, a water replenishment pipe is connected between the output end of the delivery pump and the hydrogen production unit, a hydrogen-oxygen separation unit is arranged on the front side of the hydrogen production unit, a jacket is connected between the hydrogen-oxygen separation unit and the hydrogen production unit, and a heat recovery component is installed outside the combustion chamber, and the heat recovery component is used to recover the heat generated when the device is in operation.

[0007] As a further description of the above technical solution:

[0008] The alkali liquid recovery component includes an alkali liquid recovery unit, which is located between the oxygen separation unit and the hydrogen separation unit. A Y-shaped tube is fixedly connected to the top of the alkali liquid recovery unit, and the two ends of the top of the Y-shaped tube are respectively connected to the bottom of the oxygen separation unit and the bottom of the hydrogen separation unit.

[0009] As a further description of the above technical solution:

[0010] An oxygen supply pipe is installed on the top of the combustion chamber, and a water supply pipe is installed on the top of the hydrogen production unit.

[0011] As a further description of the above technical solution:

[0012] The heat recovery assembly includes two heat-conducting sleeves, a heat exchanger 1, a circulation pump, a heat exchanger 2, a water pump and a jacket, wherein the inner side of one of the heat-conducting sleeves is fixedly connected to the outer side of the oxygen separation unit, the inner side of the other heat-conducting sleeve is fixedly connected to the outer side of the hydrogen separation unit, the inner side of the heat exchanger 1 is fixedly connected to the outer side of the combustion chamber, the circulation pump is arranged between the hydrogen separation unit and the combustion chamber, a water pump is connected between the input end of the circulation pump and the heat exchanger 1, a shunt pipe is connected between the output end of the circulation pump and the two heat-conducting sleeves, the inner side of the heat exchanger 2 is fixedly connected to the outer side of the combustion chamber, and the circulation pump is arranged between the input end of the circulation pump and the heat exchanger 1. The side of the jacket is fixedly connected to the outside of the hydrogen production unit, the bottom of the water pump is fixedly connected to the top of the water treatment unit, an inlet pipe is connected between the input end of the water pump and the heat exchanger one, and a water inlet pipe is connected between the output end of the water pump and the heat exchanger two. The inner side of the jacket is fixedly connected to the outside of the hydrogen and oxygen separation unit, an extraction pump is arranged between the jacket and the heat exchanger two, the bottom of the extraction pump is fixedly connected to the middle of the hydrogen production unit, the input end of the extraction pump is connected to the heat exchanger two through a pipeline, and a preheating pipe is connected between the output end of the extraction pump and the jacket.

[0013] As a further description of the above technical solution:

[0014] A thermoelectric conversion interface is installed on the left side of the second heat exchanger, and an electrolytic cell heating interface is installed on the front of the second heat exchanger.

[0015] As a further description of the above technical solution:

[0016] A reflux pipe is connected between the two heat-conducting sleeves and the heat exchanger 1, and a circulation pipe is connected between the heat exchanger 2 and the heat exchanger 1.

[0017] As a further description of the above technical solution:

[0018] A water return pipe is connected between the jacket and the second heat exchanger.

[0019] The utility model has the following beneficial effects:

[0020] In the utility model, unqualified hydrogen in the startup stage is utilized to reduce hydrogen production losses; secondly, the heat generated when the hydrogen production equipment is in operation and when the waste gas is burned is utilized for drying and heating the entire hydrogen production process; and when the heat is sufficient, the steam turbine can be used for self-generation to reduce the municipal electricity consumption in the plant area and the municipal electricity costs; the hydrogen waste gas generated in the startup stage is utilized, and the combustion-produced water can be collected and treated and recycled for hydrogen production, thereby reducing water consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a stereoscopic diagram from the first perspective of the device for combined utilization of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation proposed in the utility model;

[0022] Figure 2 A stereoscopic diagram from a second perspective of the device for combined utilization of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation proposed in the utility model;

[0023] Figure 3 This is a schematic diagram of the partial structure of the shunt pipe of the device for combined utilization of waste heat and exhaust gas from an alkaline electrolyzer for hydrogen production using wind and solar power generation proposed in the utility model.

[0024] Legend:

[0025] 1. Hydrogen production unit; 2. Oxygen separation unit; 3. Hydrogen separation unit; 4. Primary oxygen delivery pipe; 5. Primary hydrogen delivery pipe; 6. Y-type pipe; 7. Alkali recovery unit; 8. Combustion chamber; 9. Secondary hydrogen delivery pipe; 10. Oxygenation pipe; 11. Water treatment unit; 12. Water delivery pipe; 13. Delivery pump; 14. Water supply pipe; 15. Heat transfer sleeve; 16. Heat exchanger 1; 17. Circulation pump; 18. Pumping pipe; 19. Diverter pipe; 20. Reflux pipe; 21. Heat exchanger 2; 22. Water pump; 23. Water inlet pipe; 24. Water inlet pipe; 25. Circulation pipe; 26. Thermoelectric conversion interface; 27. Electrolyzer heating interface; 28. Water supply pipe; 29. ​​Hydrogen and oxygen separation unit; 30. Jacket; 31. Extraction pump; 32. Preheating pipe; 33. Return pipe. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0027] Reference Figure 1-Figure 3The utility model provides an embodiment: a combined utilization device of waste heat and waste gas of an alkaline electrolyzer for producing hydrogen by wind and solar power generation, comprising a hydrogen production unit 1, an oxygen separation unit 2 and a hydrogen separation unit 3 are arranged on the right side of the hydrogen production unit 1 from left to right, a primary oxygen delivery pipe 4 is connected between the hydrogen production unit 1 and the oxygen separation unit 2, a primary hydrogen delivery pipe 5 is connected between the hydrogen production unit 1 and the hydrogen separation unit 3, an alkali solution recovery component is arranged between the bottom of the hydrogen separation unit 3 and the oxygen separation unit 2, a combustion chamber 8 is arranged on the rear side of the hydrogen separation unit 3, and the combustion chamber 8 and the hydrogen separation unit 3 are connected. A secondary hydrogen delivery pipe 9 is connected between the gas separation units 3, a water treatment unit 11 is arranged on the left side of the combustion chamber 8, a water delivery pipe 12 is connected between the water treatment unit 11 and the combustion chamber 8, a delivery pump 13 is fixedly connected to the left side of the water treatment unit 11, a water supply pipe 14 is connected between the output end of the delivery pump 13 and the hydrogen production unit 1, a hydrogen-oxygen separation unit 29 is arranged on the front side of the hydrogen production unit 1, a jacket 30 is connected between the hydrogen-oxygen separation unit 29 and the hydrogen production unit 1, and a heat recovery component is installed on the outside of the combustion chamber 8, and the heat recovery component is used to recover the heat generated when the device is running. The alkali recovery component includes an alkali recovery unit 7, which is located between the oxygen separation unit 2 and the hydrogen separation unit 3, and a Y-shaped tube 6 is fixedly connected to the top of the alkali recovery unit 7, and the two ends of the top of the Y-shaped tube 6 are respectively connected to the bottom of the oxygen separation unit 2 and the hydrogen separation unit 3. An oxygenation pipe 10 is installed on the top of the combustion chamber 8, and a water supply pipe 28 is installed on the top of the hydrogen production unit 1.

[0028] Specifically, during the startup phase, the hydrogen and oxygen produced by the hydrogen production unit 1, due to gravity, enter the hydrogen separation unit 3 and the oxygen separation unit 2 together with the alkaline electrolyte through the primary hydrogen delivery pipe 5 and the primary oxygen delivery pipe 4. At this time, the drying work is mainly undertaken by electric heating. Then the oxygen separated in the oxygen separation unit 2 is discharged, and the hydrogen obtained in the hydrogen separation unit 3 is delivered to the combustion chamber 8 through the secondary hydrogen delivery pipe 9. Sufficient air is delivered to the combustion chamber 8 through the oxygenation pipe 10, and the hydrogen and oxygen are mixed and ignited at the same time, so as to generate water through the reaction. The water generated in the combustion chamber 8 is then sent to the water treatment unit 11 through the water delivery pipe 12 for treatment, and then the qualified water is re-added to the hydrogen production unit 1 through the delivery pump 13 and the water supply pipe 14 as a raw material for hydrogen production. The reuse of unqualified oxygen and hydrogen generated during the startup phase is achieved.

[0029] Reference Figure 1-Figure 3The heat recovery assembly includes two heat-conducting sleeves 15, a heat exchanger 1 16, a circulation pump 17, a heat exchanger 21, a water pump 22 and a jacket 30, wherein the inner side of one heat-conducting sleeve 15 is fixedly connected to the outer side of the oxygen separation unit 2, the inner side of the other heat-conducting sleeve 15 is fixedly connected to the outer side of the hydrogen separation unit 3, the inner side of the heat exchanger 1 16 is fixedly connected to the outer side of the combustion chamber 8, the circulation pump 17 is arranged between the hydrogen separation unit 3 and the combustion chamber 8, a water pump 18 is connected between the input end of the circulation pump 17 and the heat exchanger 1 16, a shunt pipe 19 is connected between the output end of the circulation pump 17 and the two heat-conducting sleeves 15, and the heat exchanger 2 1 is fixedly connected to the outside of the hydrogen production unit 1, the bottom of the water pump 22 is fixedly connected to the top of the water treatment unit 11, the input end of the water pump 22 and the heat exchanger 1 16 are connected by a water inlet pipe 23, the output end of the water pump 22 and the heat exchanger 2 21 are connected by a water inlet pipe 24, the inner side of the jacket 30 is fixedly connected to the outside of the hydrogen-oxygen separation unit 29, an extraction pump 31 is arranged between the jacket 30 and the heat exchanger 2 21, the bottom of the extraction pump 31 is fixedly connected to the middle of the hydrogen production unit 1, the input end of the extraction pump 31 is connected to the heat exchanger 2 21 through a pipeline, and the output end of the extraction pump 31 and the jacket 30 are connected by a preheating pipe 32. The left side of the heat exchanger 2 21 is installed with a thermoelectric conversion interface 26, and the front of the heat exchanger 2 21 is installed with an electrolytic cell heating interface 27. The two heat-conducting jackets 15 and the heat exchanger 1 16 are connected by a reflux pipe 20, and the heat exchanger 2 21 and the heat exchanger 1 16 are connected by a circulation pipe 25. A return pipe 33 is connected between the jacket 30 and the second heat exchanger 21 .

[0030] Specifically, when the reaction of hydrogen and oxygen is carried out inside the combustion chamber 8, a large amount of heat energy is accumulated inside the combustion chamber 8, and this heat energy will be absorbed by the heat exchanger 16 installed outside the combustion chamber 8, and then heat the cold water inside the heat exchanger 16. When the water temperature inside the heat exchanger 16 rises, the hot water inside the heat exchanger 16 can be pumped out through the pumping pipe 18 by starting the circulation pump 17, and the hot water can be transported to the inside of the heat-conducting sleeve 15 outside the oxygen separation unit 2 and the hydrogen separation unit 3 respectively through the shunt pipe 19, and the oxygen separation unit 2 and the hydrogen separation unit 3 are heated by the heat-conducting sleeve 15 to provide a stable temperature for their operation. At this time, it is not necessary to use electric auxiliary heating, thereby effectively reducing energy consumption. At the same time, the hot water in another part of the heat exchanger 16 is extracted through the water pump 22 and the water inlet pipe 23 and enters the inside of the heat exchanger 2 21 along the water inlet pipe 24, thereby heating the cold water inside the heat exchanger 2 21 until the operation of the device tends to be stable. At this time, the temperature generated by the operation of the hydrogen production unit 1 will be absorbed and stored by the heat exchanger 2 21. At this time, by starting the extraction pump 31, the hot water in the heat exchanger 2 21 can be extracted and transported to the inside of the jacket 30 through the preheating pipe 32, thereby heating the jacket 30, so that the jacket 30 can transfer heat to the hydrogen-oxygen separation unit 29 to provide temperature support for its operation. And when the temperature stored inside the heat exchanger 2 21 is sufficient, the heat can be transported to the electrolyzer equipment and the hydrogenation station through the electrolyzer heating interface 27 to maintain the working environment temperature of the equipment and the hydrogenation station. When the heat increases further, the hot steam is transported through the thermoelectric conversion interface 26, and a small steam turbine is used to generate electricity as the plant's own electricity, reducing municipal electricity consumption.

[0031] Working principle: The whole device includes a hydrogen-oxygen separation unit 29. During the startup phase, the hydrogen and oxygen produced by the hydrogen production unit 1 enter the hydrogen separation unit 3 and the oxygen separation unit 2 respectively due to gravity, together with the alkaline electrolyte. At this time, the drying work is mainly undertaken by electric heating, and the oxygen separated in the oxygen separation unit 2 is discharged, and the hydrogen obtained in the hydrogen separation unit 3 is transported to the combustion chamber 8 through the secondary hydrogen delivery pipe 9. On the other side, the alkali solution is discharged into the alkali solution recovery unit 7 through the Y-shaped pipe 6 for storage after cooling, and re-enters the hydrogen production unit 1 for recycling after treatment. After the hydrogen is mixed with the air in the combustion chamber 8 and ignited, a large amount of heat is released, which heats the cold water in the heat exchanger 16, and then passes through the circulating pump 17 to the hydrogen separation unit 3 and the oxygen separation unit 2 for auxiliary heating to reduce power consumption. The other part sends hot water into the heat exchanger 2 21 under the action of the water pump 22, which is used to heat the heat exchanger 2 21. A large amount of water is generated in the combustion chamber 8, which is discharged to the water treatment unit 11 through the water delivery pipe 12 and gravity, and after being treated and qualified, it is added to the hydrogen production unit 1 through the delivery pump 13 and the water supply pipe 14 as fresh water for hydrogen production. At the same time, the heat exchanger 21 stores and absorbs the heat generated by the hydrogen production unit 1 during the startup stage.

[0032] After the hydrogen quality is qualified, the device is in the normal hydrogen production stage, and the heat exchanger 21 starts to work normally. Under the operation of the extraction pump 31, the stored hot water is added to the jacket 30 through the preheating pipe 32, and the jacket 30 is heated to heat the hydrogen-oxygen separation unit 29. At the same time, the heat can also be transported to the electrolyzer equipment and the hydrogen refueling station through the electrolyzer heating interface 27 to maintain the working environment temperature of the equipment and the hydrogen refueling station. When the heat is sufficient, the hot steam is transported through the thermoelectric conversion interface 26, and a small steam turbine is used to generate electricity for the plant's own use, reducing municipal electricity consumption.

[0033] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A combined utilization device for waste heat and exhaust gas of an alkaline electrolyzer for producing hydrogen from wind and solar power generation, comprising a hydrogen production unit (1), characterized in that: An oxygen separation unit (2) and a hydrogen separation unit (3) are sequentially arranged on the right side of the hydrogen production unit (1) from left to right; a primary oxygen delivery pipe (4) is connected between the hydrogen production unit (1) and the oxygen separation unit (2); a primary hydrogen delivery pipe (5) is connected between the hydrogen production unit (1) and the hydrogen separation unit (3); an alkali solution recovery component is arranged between the bottom of the hydrogen separation unit (3) and the oxygen separation unit (2); a combustion chamber (8) is arranged on the rear side of the hydrogen separation unit (3); a secondary hydrogen delivery pipe (9) is connected between the combustion chamber (8) and the hydrogen separation unit (3); and the combustion chamber (8) and the hydrogen separation unit (3) are connected to each other. A water treatment unit (11) is arranged on the left side of the chamber (8), a water delivery pipe (12) is connected between the water treatment unit (11) and the combustion chamber (8), a delivery pump (13) is fixedly connected to the left side of the water treatment unit (11), a water supply pipe (14) is connected between the output end of the delivery pump (13) and the hydrogen production unit (1), a hydrogen-oxygen separation unit (29) is arranged on the front side of the hydrogen production unit (1), a jacket (30) is connected between the hydrogen-oxygen separation unit (29) and the hydrogen production unit (1), and a heat recovery component is installed on the outside of the combustion chamber (8), the heat recovery component is used to recover the heat generated when the device is in operation.

2. The combined utilization device of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation according to claim 1 is characterized by: The alkali liquid recovery component comprises an alkali liquid recovery unit (7), wherein the alkali liquid recovery unit (7) is located between the oxygen separation unit (2) and the hydrogen separation unit (3), and a Y-shaped tube (6) is fixedly connected to the top of the alkali liquid recovery unit (7), and the two ends of the top of the Y-shaped tube (6) are respectively connected to the bottom of the oxygen separation unit (2) and the bottom of the hydrogen separation unit (3).

3. The combined utilization device of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation according to claim 1 is characterized by: An oxygen supply pipe (10) is installed on the top of the combustion chamber (8), and a water supply pipe (28) is installed on the top of the hydrogen production unit (1).

4. The combined utilization device of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation according to claim 1 is characterized by: The heat recovery assembly comprises two heat-conducting sleeves (15), a heat exchanger 1 (16), a circulation pump (17), a heat exchanger 2 (21), a water pump (22) and a jacket (30), wherein the inner side of one of the heat-conducting sleeves (15) is fixedly connected to the outer side of the oxygen separation unit (2), the inner side of the other heat-conducting sleeve (15) is fixedly connected to the outer side of the hydrogen separation unit (3), the inner side of the heat exchanger 1 (16) is fixedly connected to the outer side of the combustion chamber (8), the circulation pump (17) is arranged between the hydrogen separation unit (3) and the combustion chamber (8), a water pump (18) is connected between the input end of the circulation pump (17) and the heat exchanger 1 (16), a shunt pipe (19) is connected between the output end of the circulation pump (17) and the two heat-conducting sleeves (15), the heat exchanger 2 (21) The inner side is fixedly connected to the outer side of the hydrogen production unit (1); the bottom of the water pump (22) is fixedly connected to the top of the water treatment unit (11); an inlet pipe (23) is connected between the input end of the water pump (22) and the first heat exchanger (16); an inlet pipe (24) is connected between the output end of the water pump (22) and the second heat exchanger (21); the inner side of the jacket (30) is fixedly connected to the outer side of the hydrogen-oxygen separation unit (29); an extraction pump (31) is arranged between the jacket (30) and the second heat exchanger (21); the bottom of the extraction pump (31) is fixedly connected to the middle of the hydrogen production unit (1); the input end of the extraction pump (31) is connected to the second heat exchanger (21) through a pipeline; and a preheating pipe (32) is connected between the output end of the extraction pump (31) and the jacket (30).

5. The combined utilization device of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation according to claim 4 is characterized by: A thermoelectric conversion interface (26) is installed on the left side of the second heat exchanger (21), and an electrolytic cell heating interface (27) is installed on the front of the second heat exchanger (21).

6. The combined utilization device of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation according to claim 4 is characterized by: A return pipe (20) is connected between the two heat-conducting sleeves (15) and the heat exchanger 1 (16), and a circulation pipe (25) is connected between the heat exchanger 2 (21) and the heat exchanger 1 (16).

7. The combined utilization device of waste heat and exhaust gas from an alkaline electrolyzer for producing hydrogen from wind and solar power generation according to claim 4 is characterized by: A water return pipe (33) is connected between the jacket (30) and the second heat exchanger (21).

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