System for deep recovery of flue gas waste heat of composite heat pump

Abstract

The present application relates to flue gas waste heat recovery technical field, provide composite heat pump's flue gas waste heat depth recovery system, including: spray tower, rain cap layer, absorption heat pump, compression heat pump, water water board exchange, circulating water pipeline and heat network pipeline etc..Rain cap layer divides spray tower into high temperature spray section and low temperature spray section, high temperature circulating water will high temperature spray section flue gas heat deliver to absorption heat pump, low temperature circulating water will low temperature spray section flue gas heat deliver to compression heat pump;Flue gas enters high temperature spray section from flue gas entrance, and directly contact heat exchange with high temperature circulating water, then enters low temperature spray section, and directly contact heat exchange with low temperature circulating water, finally from flue gas outlet exit.The present application reduces flue gas temperature to close to ambient temperature through reasonable process design and combined use of compression heat pump and absorption heat pump, depth recovery flue gas waste heat, can be applicable to the condition that absorption heat pump is used alone and cannot fully recover waste heat due to working condition limitation.

Description

Technical Field

[0001] This invention relates to the field of waste heat recovery technology, and in particular to a deep waste heat recovery technology for flue gas from coal-fired boilers based on the combined action of an electric compression heat pump and an absorption heat pump. Background Technology

[0002] A prior art disclosure discloses a centralized heating system (CN102242946B) that utilizes an absorption heat pump to recover waste heat from flue gas. This system combines a direct-contact flue gas-water heat exchanger with an absorption heat pump to recover heat from the flue gas. This system can significantly reduce the exhaust gas temperature and, to some extent, reduce the concentration of nitrogen oxides in the exhaust gas. However, due to limitations imposed by the absorption heat pump's operating conditions, when the actual operating temperature of the return water in the heating network is generally not lower than 50℃, the low-temperature water produced by a single-effect absorption heat pump can only reach around 20℃. The exhaust gas temperature after heat exchange is generally above 25℃, resulting in significant waste heat loss compared to the winter ambient temperature in northern regions. Although using a two-stage absorption heat pump can theoretically further recover waste heat and reduce the exhaust gas temperature, the large investment and complex process of two-stage absorption heat pumps lead to poor economic efficiency, and therefore, there are no practical applications. In addition, in traditional single-stage spray heat exchange, the specific heat capacity of flue gas changes significantly during the cooling process as water vapor condenses, while the specific heat capacity of spray water remains almost unchanged. If the flow rate of spray water does not change, it is difficult to effectively match the temperature difference between the two fluids in terms of heat exchange, which also results in a relatively large irreversible heat transfer loss.

[0003] As mentioned above, while the currently widely used flue gas waste heat recovery and whitening projects based on absorption heat pumps significantly reduce the exhaust gas temperature and pollutant emissions, the actual operating exhaust gas temperature is generally between 25-30℃ under current operating conditions due to the limitations of the absorption heat pump unit's performance. Compared with the ambient air temperature in winter, this still contains a large amount of waste heat. Therefore, this invention proposes an innovative concept of segmented heat exchange, utilizing electric compression heat pumps and absorption heat pumps respectively to deeply recover waste heat from flue gas. Summary of the Invention

[0004] The purpose of this invention is to provide a deep waste heat recovery system for flue gas that can significantly improve the efficiency of waste heat recovery with less equipment investment.

[0005] To address the aforementioned problems, this invention provides a flue gas waste heat recovery system, comprising: a spray tower, a rain cap layer, an absorption heat pump, a compression heat pump, a water-to-water plate heat exchanger, a low-temperature circulating pump, a high-temperature circulating water pipeline, a low-temperature circulating pipeline, a heat network pipeline I, a heat network pipeline III, and a heat network pipeline II.

[0006] The spray tower is equipped with a rain cap layer, which divides the spray tower into a high-temperature spray section and a low-temperature spray section;

[0007] Flue gas enters the high-temperature spray section from the flue gas inlet, releases heat to the high-temperature circulating water, and then enters the low-temperature spray section through the rain cap layer to exchange heat, releases heat to the low-temperature circulating water, and then leaves the system from the flue gas outlet.

[0008] The bottom of the low-temperature spray section is connected to the input end of the heat absorption side of the compression heat pump via a low-temperature circulating pump, and the output end of the heat absorption side of the compression heat pump is connected to the spray pipe system in the low-temperature spray section via a low-temperature circulating pipeline; the heat generated by the compression heat pump is output to the first heat network pipeline.

[0009] The bottom of the high-temperature spray section is connected to the input end of the absorption heat pump via a high-temperature circulating pump, and the output end of the absorption heat pump is connected to the spray pipe system in the high-temperature spray section via a high-temperature circulating water pipeline; the heat generated by the absorption heat pump is output to the second heat network pipeline.

[0010] Furthermore, the high-temperature circulating pipeline at the bottom outlet of the high-temperature spray section is bypassed to a water-to-water heat exchanger. All or part of the high-temperature circulating water is bypassed to the water-to-water heat exchanger before entering the absorption heat pump. The other side of the water-to-water heat exchanger is connected to the third heat network pipeline, and the other end of the third heat network pipeline is connected to the first heat network pipeline. When the circulating water temperature at the outlet of the high-temperature spray section is higher than the water temperature in the first heat network pipeline, the high-temperature circulating water heats the first heat network pipeline, meaning the heat from the high-temperature circulating water is directly output to the heat user. When the circulating water temperature at the outlet of the high-temperature spray section is lower than the water temperature in the first heat network pipeline and the heat generated by the compression heat pump exceeds the user's demand, the first heat network pipeline heats the high-temperature circulating water. That is, part of the heat generated by the compression heat pump serves as a low-grade heat source for the absorption heat pump, which heats the water and outputs it to the second heat network pipeline.

[0011] Furthermore, a circulation booster pump is installed on the high-temperature circulation pipeline bypassing the water exchanger.

[0012] Furthermore, a heating network booster pump is installed on the third heating network pipeline.

[0013] Furthermore, the rain cap layer is composed of multiple rain caps.

[0014] Furthermore, the first and second heating network pipelines are connected in series to form a loop, and the heating network water first enters the absorption heat pump and then enters the compression heat pump for series cascade heating.

[0015] Furthermore, the spray tower is one of the following: a spray-type cavity structure direct contact heat exchanger, a tray structure direct contact heat exchanger, or a packed structure direct contact heat exchanger.

[0016] Furthermore, the driving energy for the absorption heat pump is steam, gas, or high-temperature hot water, while the driving energy for the compression heat pump is electricity.

[0017] The flue gas releases heat in the spray tower, and the temperature drops. The water vapor in the flue gas will condense and precipitate. Therefore, the water volume in the two spray towers will gradually increase during operation. In order to maintain the water volume balance in the spray tower, a flue gas condensate overflow port or outlet is set at the bottom of the spray tower or on the circulating water pipeline to discharge the excess circulating water from the system.

[0018] The above-described technical solution of the present invention has the following beneficial technical effects:

[0019] (1) The flue gas / water spray heat exchange tower is divided into a high-temperature spray heat exchange section and a low-temperature spray heat exchange section by a rain cap layer. The rain cap layer can effectively block the exchange of spray water between the two sections, while allowing the flue gas to pass through smoothly without generating excessive flue gas resistance. The flue gas heat in the high-temperature spray section is recovered by an absorption heat pump, and the flue gas heat in the low-temperature spray section is recovered by an electric compression heat pump. The combined application of absorption heat pump and compression heat pump can take advantage of the energy-saving effect of absorption heat pump and the strong adaptability of electric compression heat pump to recover waste heat at lower temperatures, thereby achieving efficient and economical deep recovery of flue gas waste heat.

[0020] (2) Two heat exchange sections are set up from bottom to top in the spray tower. By adjusting the temperature and flow rate of the heat exchange medium water, the two heat exchange sections have a stepped heat exchange capacity for flue gas at different temperatures. Specifically, the flue gas flows from bottom to top, and its temperature and moisture content gradually decrease; the heat exchange medium water flows from top to bottom. By adding water at different temperatures and flow rates in two sections, the heat capacity of the flue gas and water is matched, which reduces irreversible heat transfer loss and further improves the efficiency of flue gas waste heat recovery. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of Embodiment 1 provided by the present invention;

[0022] Figure 2 This is a schematic diagram of the structure of Embodiment 2 provided by the present invention;

[0023] Figure 3 This is a schematic diagram of the structure of Embodiment 3 provided by the present invention.

[0024] Figure label:

[0025] 1. Spray tower; 1-1. High-temperature section of spray tower; 1-2. Low-temperature section of spray tower; 2. Rain cap layer; 3. Compression heat pump; 4. Absorption heat pump; 5. Water-to-water heat exchanger; 6. Low-temperature circulating pump; 7. High-temperature circulating pump; 8. Circulating booster pump; 9. Heating network pipeline one; 10. High-temperature circulating water pipeline; 11. Heating network pipeline three; 12. Heating network pipeline two; 13. Low-temperature circulating pipeline; 14. Flue gas inlet; 15. Flue gas outlet; 16-1. High-temperature section overflow port; 16-2. Low-temperature section overflow port; 17. Heating network booster pump. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0027] Example 1,

[0028] like Figure 1 As shown, the flue gas waste heat deep recovery system of the composite heat pump is characterized by comprising: a spray tower 1, a rain cap layer 2, an absorption heat pump 4, a compression heat pump 3, a water-to-water plate heat exchanger 5, a low-temperature circulating pump 6, a high-temperature circulating pump 7, a circulating booster pump 8, a high-temperature circulating water pipeline 10, a low-temperature circulating pipeline 13, a heating network pipeline 1 9, a heating network pipeline 3 11, a heating network pipeline 2 12, a flue gas inlet 14, a flue gas outlet 15, a high-temperature section overflow port 16-1, a low-temperature section overflow port 16-2, and a heating network booster pump 17.

[0029] The spray tower 1 is a direct-contact heat exchanger with a hollow cavity structure and a rain cap layer 2 inside. The rain cap layer 2 divides the spray tower 1 into a high-temperature spray section 1-1 and a low-temperature spray section 1-2. Each of the low-temperature and high-temperature spray sections has a spray pipe system at its top. Circulating water enters through the spray pipe system, disperses into uniformly distributed droplets, and flows downwards by gravity. The flue gas flows upwards, forming a counter-current flow with the droplets for direct contact heat exchange.

[0030] Flue gas enters the high-temperature spray section 1-1 from the flue gas inlet 14, releases heat to the high-temperature circulating water, and then enters the low-temperature spray section 1-2 through the rain cap layer 2 for heat exchange. After releasing heat to the low-temperature circulating water, it leaves the system from the flue gas outlet 15.

[0031] The bottom of the low-temperature spray section 1-2 is connected to the input end of the heat absorption side of the compression heat pump 3 via the low-temperature circulating pump 6. The output end of the heat absorption side of the compression heat pump 3 is connected to the spray pipe system in the low-temperature spray section 1-2 via the low-temperature circulating pipe 13. Driven by the low-temperature circulating pump 6, the low-temperature circulating water enters the compression heat pump to release heat and cool down, and then enters the low-temperature spray section 1-2 to absorb heat and heat up, thus circulating. The compression heat pump 3 is driven by electric energy, and the generated heat is output to the heating network pipe 9.

[0032] The bottom of the high-temperature spray section 1-1 is connected to the input end of the absorption heat pump 4 via a high-temperature circulating pump 7. The output end of the absorption heat pump 4 is connected to the spray pipe system in the high-temperature spray section 1-1 via a high-temperature circulating water pipeline 10. Driven by the high-temperature circulating pump 7, the high-temperature circulating water enters the absorption heat pump to release heat and cool down, and then enters the high-temperature spray section 1-1 to absorb heat and heat up, thus circulating. The absorption heat pump 4 is driven by steam, and the generated heat is output to the second heating network pipeline 12.

[0033] The outlet pipe of the high-temperature circulating pump 7 at the bottom of the high-temperature spray section 1-1 is bypassed to the water exchanger 5. Driven by the circulating booster pump 8, all or part of the high-temperature circulating water is routed to the water exchanger 5 before entering the absorption heat pump. The other side of the water exchanger 5 is connected to the heating network pipeline 3 11. The inlet and outlet of the heating network pipeline 3 11 are connected to the outlet section of the compression heat pump on the heating network pipeline 1 9. A heating network booster pump 17 is installed on the heating network pipeline 3 11. When the heat generated by the compression heat pump 3 exceeds the user's demand, a portion of the heating network water, driven by the heating network booster pump 17, enters the water exchanger 5 to heat the high-temperature circulating water. That is, a portion of the heat generated by the compression heat pump 3 serves as a low-grade heat source for the absorption heat pump 4, and after being heated by the absorption heat pump, it is output to the heating network pipeline 2 12.

[0034] An overflow port 16-1 is provided at the bottom of the high-temperature spray section, and an overflow port 16-2 is provided at the bottom of the low-temperature spray section. The height of the overflow port is lower than the height of the flue gas inlet. During the flue gas heat exchange process, water vapor will liquefy and flow into the circulating water of the spray. The circulating water will gradually increase. The overflow port will automatically discharge the excess circulating water in the spray tower so that the liquid level in the spray tower is lower than the flue gas inlet.

[0035] Example 2,

[0036] like Figure 2 As shown, unlike the first embodiment, the flue gas waste heat deep recovery system of the composite heat pump provided in this embodiment has its inlet end of heat network pipeline 311 connected to heat network pipeline 9 at the inlet of the compression heat pump 3, and its outlet end connected to heat network pipeline 9 at the outlet of the compression heat pump 3. The heat network return water is connected in parallel to the compression heat pump 3 and the water-to-water heat exchanger 5 for heating, and then merged into one line to supply heat users. This embodiment is suitable for situations where the outlet circulating water temperature of the high-temperature spray section is higher than the water temperature of heat network pipeline 9, that is, the heat of the high-temperature circulating water is directly output to the heat users, resulting in better energy-saving effect.

[0037] Example 3,

[0038] like Figure 3As shown, unlike the first embodiment, in the flue gas waste heat recovery system of the composite heat pump provided in this embodiment, the return water of the heating network pipeline 9 flows out of the system after being heated in a series of stages by the absorption heat pump 4 and the compression heat pump 3. Because the low-temperature return water of the heating network first enters the absorption heat pump for heating, the heating temperature of the absorption heat pump is reduced, and the energy-saving characteristics are fully utilized.

[0039] The present invention isolates the low-temperature spray section and the original high-temperature spray section in the spray tower through a rain cap layer, which can effectively block the exchange of spray water between the two sections and allow the flue gas to pass through smoothly without generating excessive flue gas resistance.

[0040] The high-temperature and low-temperature spray sections adjust the temperature and flow rate of the heat exchange medium, water, to provide each section with a stepped heat exchange capacity tailored to flue gas at different inlet temperatures. This matches the heat capacity of the flue gas and water, reducing irreversible heat transfer losses and further improving the efficiency of flue gas waste heat recovery.

[0041] In this invention, the heating side and the low-temperature side of the absorption heat pump waste heat recovery system are coupled through a water / water plate heat exchanger. When the heat demand of the users in the heating network 9 during the early and late cold periods is lower than the heat output of the compression heat pump, the flow rate of the valve or the booster pump is adjusted to allow some of the heating network water to exchange heat with the circulating water of the absorption heat pump system. The excess heat is then provided to the absorption heat pump waste heat recovery system and finally input into the heating network 212, which has a greater heat demand and a higher temperature.

[0042] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A deep waste heat recovery system for flue gas from a composite heat pump, characterized in that, include: Spray tower (1), rain cap layer (2), absorption heat pump (4), compression heat pump (3), water-to-water plate heat exchanger (5), low temperature circulating pump (6), high temperature circulating pump (7), high temperature circulating water pipeline (10), low temperature circulating pipeline (13), heating network pipeline one (9), heating network pipeline three (11), heating network pipeline two (12); The spray tower (1) is provided with a rain cap layer (2), which divides the spray tower (1) into a high-temperature spray section and a low-temperature spray section; The flue gas enters the high-temperature spray section from the flue gas inlet (14), releases heat to the high-temperature circulating water, and then enters the low-temperature spray section through the rain cap layer (2) for heat exchange. After releasing heat to the low-temperature circulating water, it leaves the system from the flue gas outlet (15). The bottom of the low-temperature spray section is connected to the input end of the heat absorption side of the compression heat pump (3) via a low-temperature circulating pump (6). The output end of the heat absorption side of the compression heat pump (3) is connected to the spray pipe system in the low-temperature spray section via a low-temperature circulating pipeline (13). The heat generated by the compression heat pump (3) is output to the first heat network pipeline (9). The bottom of the high-temperature spray section is connected to the heat absorption side input end of the absorption heat pump (4) via the high-temperature circulating pump (7), and the heat absorption side output end of the absorption heat pump (4) is connected to the spray pipe system in the high-temperature spray section via the high-temperature circulating water pipeline (10); the heat generated by the absorption heat pump (4) is output to the second heat network pipeline (12). The high-temperature circulating pipeline at the bottom outlet of the high-temperature spray section is bypassed to the water plate heat exchanger (5). All or part of the high-temperature circulating water is bypassed to the water plate heat exchanger (5) and then enters the absorption heat pump (4). The other side of the water plate heat exchanger (5) is connected to the third heat network pipeline (11), and the other end of the third heat network pipeline (11) is connected to the first heat network pipeline (9). When the outlet circulating water temperature of the high-temperature spray section is higher than the water temperature in the first (9) of the heat network pipeline, the high-temperature circulating water heats the first (9) of the heat network pipeline, and the heat from the high-temperature circulating water is directly output to the heat user; when the outlet circulating water temperature of the high-temperature spray section is lower than the water temperature in the first (9) of the heat network pipeline and the heat generated by the compression heat pump (3) is greater than the user's demand, the first (9) of the heat network pipeline heats the high-temperature circulating water, and part of the heat generated by the compression heat pump (3) is used as a low-temperature heat source for the absorption heat pump (4), and after being heated by the absorption heat pump (4), it is output to the second (12) of the heat network pipeline.

2. The flue gas waste heat deep recovery system of the composite heat pump according to claim 1, characterized in that, A circulation booster pump (8) is installed on the pipeline that bypasses the high-temperature circulation pipeline to the water plate heat exchanger (5).

3. The flue gas waste heat deep recovery system of the composite heat pump according to claim 1, characterized in that, A heating network booster pump (17) is installed on heating network pipeline 3 (11).

4. The flue gas waste heat deep recovery system of the composite heat pump according to claim 1, characterized in that, The spray tower (1) is one of the following: a spray-type cavity structure direct contact heat exchanger, a tray structure direct contact heat exchanger, or a packed structure direct contact heat exchanger.

5. The flue gas waste heat deep recovery system of the composite heat pump according to claim 1, characterized in that, The driving energy for the absorption heat pump (4) is steam, gas or high-temperature hot water.

6. The flue gas waste heat deep recovery system of the composite heat pump according to claim 1, characterized in that, The driving energy for the compression heat pump (3) is electrical energy.

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