A system for heating boiler feedwater using waste heat from low-temperature flue gas

Abstract

This utility model discloses a system for heating boiler feedwater using waste heat from low-temperature flue gas, comprising a wet desulfurization tower, a slurry heat exchanger, an absorption heat pump, a steam auxiliary heater, a raw water heater, and a demineralized water heater. The desulfurization slurry outlet pipe on the wet desulfurization tower is connected to the uppermost spray layer inside the tower via the slurry heat exchanger. The slurry heat exchanger is connected to the evaporator of the absorption heat pump via a low-temperature waste hot water pipe to form a circulation loop. The absorber of the absorption heat pump is sequentially connected to the condenser, steam auxiliary heater, and raw water heater via a hot water circulation pipe to form a circulation loop. The demineralized water heater is connected in parallel to the raw water heater on the hot water circulation pipe. This utility model can effectively recover the waste heat from the low-temperature flue gas after desulfurization, replacing part of the boiler steam extraction for heating boiler raw water and demineralized water, thereby reducing steam consumption and improving boiler efficiency.

Description

Technical Field

[0001] This utility model belongs to the field of boiler flue gas waste heat recovery technology, specifically relating to a system for heating boiler feedwater using low-temperature flue gas waste heat. Background Technology

[0002] The statements herein provide only background information related to this invention and do not necessarily constitute prior art.

[0003] In the operation of thermal power plants, the treatment and heating of boiler feedwater are crucial for ensuring the safe and stable operation of the units. The water treatment unit, as the core equipment for purifying raw water, has specific requirements for the influent temperature, especially in winter. To ensure water treatment efficiency and effluent quality, the raw water influent temperature needs to be controlled within the range of 25-30℃. Currently, the industry commonly uses steam-type heat exchangers to heat the raw water, introducing boiler steam as a heat source to raise the raw water temperature. Simultaneously, the demineralized water produced after water treatment needs to enter a deaerator for deoxygenation. The deaerator also relies on boiler steam as a heat source to remove dissolved oxygen from the water, preventing damage to the boiler and piping system due to oxygen corrosion.

[0004] However, the aforementioned traditional processes have significant energy utilization problems: the dual consumption of boiler steam by the steam heat exchanger and deaerator directly leads to an increase in boiler steam extraction. This not only reduces the boiler's steam utilization efficiency, causing some high-quality steam that could be used for power generation to be used for low-temperature heating processes, resulting in a waste of energy quality, but also indirectly affects the overall cycle efficiency of the generator unit, increasing the power plant's coal consumption and operating costs.

[0005] On the other hand, the boiler tail section of a thermal power plant generates a large amount of desulfurized low-temperature flue gas (typically around 50-55°C), which contains considerable waste heat resources. However, in current technology, this low-temperature waste heat is often not effectively recovered and is directly emitted into the atmosphere through the chimney, resulting in energy waste. Utility Model Content

[0006] The purpose of this invention is to provide a system that utilizes the waste heat of low-temperature flue gas to heat boiler feedwater. This system can effectively recover the waste heat of low-temperature flue gas after desulfurization, replacing part of the boiler steam extraction for heating boiler raw water and demineralized water, thereby reducing steam consumption and improving boiler efficiency.

[0007] To achieve the above objectives, this utility model is implemented through the following technical solution: In the first aspect, embodiments of this utility model provide a system for heating boiler feedwater using waste heat from low-temperature flue gas, including a wet desulfurization tower, a slurry heat exchanger, an absorption heat pump, a steam-assisted heater, a raw water heater, and a demineralized water heater. The desulfurization slurry outlet pipe on the wet desulfurization tower is connected to the uppermost spray layer inside the wet desulfurization tower via a slurry heat exchanger; the slurry heat exchanger is connected to the evaporator of the absorption heat pump via a low-temperature waste hot water pipe to form a circulation loop; the absorber of the absorption heat pump is connected in sequence to the condenser, steam auxiliary heater, and raw water heater of the absorption heat pump via a hot water circulation pipe to form a circulation loop; the demineralized water heater and the raw water heater are connected in parallel on the hot water circulation pipe; the low-temperature raw water pipe is connected in sequence to the raw water heater, the reverse osmosis water treatment device, and the demineralized water heater.

[0008] As a further technical solution, the flue gas generated by the boiler enters a flue gas duct, which is connected to a wet desulfurization tower.

[0009] As a further technical solution, a bypass pipeline is connected to the desulfurization slurry outlet pipeline, and the slurry heat exchanger is installed on the bypass pipeline.

[0010] As a further technical solution, a first slurry switching valve is provided at the slurry inlet of the slurry heat exchanger, a second slurry switching valve is provided at the slurry outlet, and a third slurry switching valve is provided at the location of the desulfurization slurry outlet pipeline connected in parallel with the bypass pipeline.

[0011] As a further technical solution, the generator of the absorption heat pump is connected to the boiler steam extraction via a steam pipe, and the steam pipe is also connected to a steam auxiliary heater. The generator of the absorption heat pump and the steam auxiliary heater are arranged in parallel.

[0012] As a further technical solution, the condensate outlet of the generator of the absorption heat pump is connected to the steam condensate tank via a condensate pipe.

[0013] As a further technical solution, the condensate outlet of the steam auxiliary heater is connected to the steam condensate tank via a condensate pipe.

[0014] As a further technical solution, a slurry circulation pump is installed on the desulfurization slurry outlet pipeline, a waste hot water circulation pump is installed on the low-temperature waste hot water pipeline, and a hot water circulation pump is installed on the hot water circulation pipeline.

[0015] As a further technical solution, both the raw water heater and the demineralized water heater are equipped with water flow regulating valves at their hot water inlets.

[0016] As a further technical solution, the demineralized water outlet of the demineralized water heater is connected to a deaerator via a pipeline, and the deaerator is connected to the boiler feedwater pipeline.

[0017] The beneficial effects of the above-described embodiments of this utility model are as follows: This invention recovers the waste heat of low-temperature flue gas after desulfurization through a slurry heat exchanger and an absorption heat pump, replacing the reliance on boiler steam extraction by traditional steam heat exchangers. The low-temperature waste heat generated by the absorption heat pump heats the raw water and demineralized water, reducing boiler steam extraction consumption and minimizing energy waste from using high-quality steam for low-temperature heating.

[0018] This invention utilizes three sets of slurry switching valves. By switching these valves, the flue gas waste heat recovery system can be put into operation or shut down without affecting the existing boiler system. During normal operation, the first and second slurry switching valves are opened while the third slurry switching valve is closed. The desulfurization slurry flows through the slurry heat exchanger, cooling down by 25–30°C and enhancing the flue gas cooling effect. In case of system maintenance or waste heat recovery failure, the system switches to open the third slurry switching valve and close the first and second slurry switching valves, allowing the slurry to flow directly to the spray layer, thus preventing desulfurization interruptions caused by waste heat system malfunctions.

[0019] This invention features a steam-assisted heater and a water flow regulating valve installed on a hot water circulation pipe. By adjusting the steam-assisted heater and the water flow regulating valve, the hot water outlet temperature is maintained at a constant level, thus ensuring the stability of the raw water outlet temperature. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of this utility model. The illustrative embodiments of this utility model and their descriptions are used to explain this utility model and do not constitute an improper limitation of this utility model.

[0021] Figure 1 This is a schematic diagram of the system for heating boiler feedwater using waste heat from low-temperature flue gas, according to this utility model. The diagram is for illustrative purposes only. The components include: 1. Wet desulfurization tower; 2. Slurry circulation pump; 3-1. First slurry switching valve; 3-2. Second slurry switching valve; 3-3. Third slurry switching valve; 4. Slurry heat exchanger; 5. Waste hot water circulation pump; 6. Absorption heat pump; 6-1. Evaporator; 6-2. Absorber; 6-3. Generator; 6-4. Condenser; 7. Steam auxiliary heater; 8-1. First water flow regulating valve; 8-2. Second water flow regulating valve; 9. Raw water heater; 10. Reverse osmosis water treatment device; 11. Demineralized water heater; 12. Hot water circulation pump; 13. Steam condensate tank; 14. Steam condensate discharge pump. Detailed Implementation

[0022] It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0023] Example 1 In a typical embodiment of this utility model, such as Figure 1 As shown, a system for heating boiler feedwater using waste heat from low-temperature flue gas is provided, including a wet desulfurization tower 1, a slurry heat exchanger 4, an absorption heat pump 6, a steam auxiliary heater 7, a raw water heater 9, and a demineralized water heater 11. The desulfurization slurry outlet pipe on the wet desulfurization tower 1 is connected to the uppermost spray layer inside the wet desulfurization tower 1 via the slurry heat exchanger 4; the slurry heat exchanger 4 is connected to the evaporator of the absorption heat pump 6 via the low-temperature waste hot water pipe to form a circulation loop; the absorber 6-2 of the absorption heat pump 6 is connected in sequence to the condenser 6-4, the steam auxiliary heater 7, and the raw water heater 9 of the absorption heat pump 6 via the hot water circulation pipe to form a circulation loop; the demineralized water heater 11 is connected in parallel with the raw water heater 9 on the hot water circulation pipe; the low-temperature raw water is connected in sequence to the raw water heater 9, the reverse osmosis water treatment device 10, and the demineralized water heater 11.

[0024] The above system recovers the waste heat of the low-temperature flue gas after desulfurization through slurry heat exchanger 4 and absorption heat pump 6, replacing the dependence of traditional steam heat exchangers on boiler steam extraction; the low-temperature waste heat generated by absorption heat pump 6 heats the raw water and demineralized water at the same time, reducing boiler steam extraction consumption and reducing the energy waste of high-quality steam used for low-temperature heating.

[0025] In this embodiment, the flue gas generated by the boiler is connected to the wet desulfurization tower 1 through a flue gas duct. The flue gas generated by the boiler is desulfurized by the wet desulfurization tower 1. In the wet desulfurization tower 1, the waste heat of the flue gas is recovered by the desulfurization slurry. The desulfurization slurry enters the slurry heat exchanger 4 and exchanges heat with the waste hot water from the evaporator of the absorption heat pump 6. The heat of the desulfurization slurry is provided to the waste hot water.

[0026] In this embodiment, a bypass pipeline is connected to the desulfurization slurry outlet pipeline, and the slurry heat exchanger 4 is installed on the bypass pipeline. Further, a first slurry switching valve 3-1 is provided at the slurry inlet of the slurry heat exchanger 4, a second slurry switching valve 3-2 is provided at the slurry outlet, and a third slurry switching valve 3-3 is provided at the location of the desulfurization slurry outlet pipeline connected in parallel with the bypass pipeline.

[0027] Understandably, by switching the first slurry switching valve 3-1, the second slurry switching valve 3-2, and the third slurry switching valve 3-3, the waste heat recovery system can be put into operation or cut off independently, ensuring that the desulfurization tower can operate continuously without being affected by maintenance and improving the reliability of the system.

[0028] In this embodiment, the generator 6-3 of the absorption heat pump 6 is connected to the boiler steam extraction via a steam pipe, which is also connected to the steam auxiliary heater 7. The generator 6-3 and the steam auxiliary heater 7 are connected in parallel. Furthermore, the condensate outlet of the generator 6-3 of the absorption heat pump 6 is connected to the steam condensate tank 13 via a condensate pipe; the condensate outlet of the steam auxiliary heater 7 is also connected to the steam condensate tank 13 via a condensate pipe.

[0029] Understandably, the high-temperature steam extracted from the boiler enters the generator 6-3 and the steam auxiliary heater 7 of the absorption heat pump 6, respectively. The high-temperature steam provides driving force for the generator 6-3 of the absorption heat pump 6 and provides supplementary heating for the steam auxiliary heater 7. Existing steam-type heat exchangers consume a large amount of steam to heat the raw water, while the high-quality steam in this embodiment is only used to drive the heat pump and provide supplementary heating, reducing waste from direct use for low-temperature heating; steam consumption is reduced by 25%, improving boiler thermal efficiency. Furthermore, the condensate produced by the generator 6-3 and the steam auxiliary heater 7 of the absorption heat pump 6 enters the steam condensate tank 13 for temporary storage and is discharged through the steam condensate discharge pump 14.

[0030] In this embodiment, a slurry circulation pump 2 is installed on the desulfurization slurry outlet pipeline, a waste hot water circulation pump 125 is installed on the low-temperature waste hot water pipeline, and a hot water circulation pump 12 is installed on the hot water circulation pipeline. The slurry circulation pump 2, the waste hot water circulation pump 125, and the hot water circulation pump 12 provide driving force for slurry circulation, waste hot water circulation, and hot water circulation.

[0031] In this embodiment, both the raw water heater 9 and the demineralized water heater 11 are equipped with water flow regulating valves at their hot water inlets. Specifically, the raw water heater 9 is equipped with a first water flow regulating valve 8-1 at its hot water inlet, and the demineralized water heater 11 is equipped with a second water flow regulating valve 8-2 at its inlet. By using these water flow regulating valves, the hot water distribution ratio can be adjusted according to changes in the raw water temperature (such as low temperatures in winter), reducing outlet water temperature fluctuations and meeting the requirements of the water treatment process.

[0032] In this embodiment, the demineralized water outlet of the demineralized water heater 11 is connected to the deaerator via a pipeline, and the deaerator is connected to the boiler feedwater pipeline.

[0033] Understandably, the heated demineralized water is connected to the deaerator before entering the boiler feedwater pipeline. Preheating and deoxygenating the demineralized water reduces steam consumption in the deaerator and lowers the risk of oxygen corrosion in the boiler, thus extending equipment lifespan.

[0034] It is understood that the steam-assisted heater 7, raw water heater 9, and demineralized water heater 11 used in the system of this embodiment all adopt existing heat exchanger structures, and the two fluids entering the heat exchanger achieve heat exchange through the temperature difference between them. In addition, the remaining components of the system are also existing structures and do not involve structural improvements.

[0035] The working principle of the system for heating boiler feedwater using waste heat from low-temperature flue gas provided in this embodiment is as follows: Most power plants use wet desulfurization. The core equipment of wet desulfurization includes wet desulfurization tower 1, which usually has 3-5 spray layers to spray the flue gas, thereby removing pollutants such as SO2 contained in the flue gas. In this embodiment, the uppermost spray layer of the desulfurization system is selected. A slurry valve is installed on the slurry pipeline. The purpose is to switch the slurry valve to enable or disable the flue gas waste heat recovery system. Under normal operating conditions, the first and second slurry valves are open, and the third slurry valve is closed. The slurry enters the slurry heat exchanger 4 through the slurry circulation pump 2 to exchange heat with the low-temperature waste water from the evaporator in the absorption heat pump 6. The temperature of the desulfurization slurry is reduced to 25-30°C. The cooled desulfurization slurry enters the wet desulfurization tower 1 for spraying, thereby reducing the temperature of the flue gas to 40-45°C. The heat in the flue gas is absorbed by the desulfurization slurry. The desulfurization slurry falling to the bottom of the wet desulfurization tower 1 is pumped into the slurry heat exchanger 4 through the slurry circulation pump 2 for heat exchange, and the cycle continues.

[0036] The low-temperature waste water from the evaporator in the absorption heat pump 6 exchanges heat with the desulfurization slurry through the slurry heat exchanger 4. The low-temperature waste water is heated to 30-35℃ and enters the evaporator in the absorption heat pump 6. The low-temperature waste water at 30-35℃ releases heat and becomes low-temperature waste water at 25-30℃, which then enters the slurry heat exchanger 4 to exchange heat with the desulfurization slurry, and the cycle repeats.

[0037] A portion of the boiler steam is extracted and enters the generator 6-3 in the absorption heat pump 6 to drive the heat pump operation. The boiler steam is extracted and released heat in the generator 6-3 of the absorption heat pump 6, turning into steam condensate which enters the steam condensate tank 13.

[0038] Hot water from the hot water circulation pump 12 enters the absorber 6-2 in the absorption heat pump 6 for initial heating, and then enters the condenser 6-4 in the absorption heat pump 6 for secondary heating. The temperature of the heated hot water can be controlled between 60-70℃. The hot water from the absorption heat pump 6 enters the steam auxiliary heater 7 for supplemental heating to maintain a constant hot water temperature. The supplemental heated hot water enters the raw water heater 9 to heat the raw water to 25-30℃. The heated raw water enters the reverse osmosis water treatment device 10 to produce demineralized water. The demineralized water enters the demineralized water heater 11 for heating to 55-65℃. Water flow regulating valves are installed on the pipes before entering the raw water heater 9 and the demineralized water heater 11. The water flow entering the raw water heater 9 and the demineralized water heater 11 is adjusted by the first water flow regulating valve 8-1 and the second water flow regulating valve 8-2 to ensure the stability of the outlet temperature of the raw water and demineralized water.

[0039] Hot water at 60-70℃ enters the raw water heater 9 and the demineralized water heater 11 to release heat. Part of the hot water enters the raw water heat exchanger to heat the raw water at 5-10℃ to 25-30℃ before entering the reverse osmosis water treatment device 10. Another part of the hot water enters the demineralized water heater 11 to heat the demineralized water to between 55-65℃. After releasing heat, the temperature of the hot water drops to 40-45℃. This part of the hot water is pumped into the absorption heat pump 6 through the hot water circulation pump 12 to absorb the residual heat of the low-temperature waste water and then heat up, and the cycle continues.

[0040] The heat source in the steam auxiliary heater 7 comes from the boiler steam extraction. The function of the steam auxiliary heater 7 is to supplement the hot water from the absorption heat pump 6, so as to maintain the constant hot water outlet temperature. The steam condensate after heat release enters the steam condensate tank 13, and the steam condensate is discharged to the power plant condensate makeup water tank through the steam condensate discharge pump 14.

[0041] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model. Various modifications and variations can be made to this utility model by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A system for heating boiler makeup water using low temperature flue gas heat, comprising: This includes wet desulfurization towers, slurry heat exchangers, absorption heat pumps, steam-assisted heaters, raw water heaters, and demineralized water heaters; The desulfurization slurry outlet pipe on the wet desulfurization tower is connected to the uppermost spray layer inside the wet desulfurization tower via a slurry heat exchanger; the slurry heat exchanger is connected to the evaporator of the absorption heat pump via a low-temperature waste hot water pipe to form a circulation loop; the absorber of the absorption heat pump is connected in sequence to the condenser, steam auxiliary heater, and raw water heater of the absorption heat pump via a hot water circulation pipe to form a circulation loop; the demineralized water heater and the raw water heater are connected in parallel on the hot water circulation pipe; the low-temperature raw water pipe is connected in sequence to the raw water heater, the reverse osmosis water treatment device, and the demineralized water heater.

2. The system for heating boiler makeup water with low-temperature flue gas waste heat according to claim 1, characterized in that, The flue gas generated by the boiler enters the flue gas duct, which is connected to the wet desulfurization tower.

3. The system for heating boiler make-up water using low temperature flue gas heat recovery as claimed in claim 1 wherein, A bypass pipeline is connected to the desulfurization slurry outlet pipeline, and the slurry heat exchanger is installed on the bypass pipeline.

4. The system for heating boiler feedwater using waste heat from low-temperature flue gas as described in claim 3, characterized in that, The slurry heat exchanger is equipped with a first slurry switching valve at the slurry inlet, a second slurry switching valve at the slurry outlet, and a third slurry switching valve at the desulfurization slurry outlet pipeline connected in parallel with the bypass pipeline.

5. The system for heating boiler feedwater using waste heat from low-temperature flue gas as described in claim 1, characterized in that, The generator of the absorption heat pump is connected to the boiler steam extraction via a steam pipe, which is also connected to a steam auxiliary heater. The generator of the absorption heat pump and the steam auxiliary heater are arranged in parallel.

6. The system for heating boiler feedwater using waste heat from low-temperature flue gas as described in claim 5, characterized in that, The condensate outlet of the generator of the absorption heat pump is connected to the steam condensate tank via a condensate pipe.

7. The system for heating boiler feedwater using waste heat from low-temperature flue gas as described in claim 5, characterized in that, The condensate outlet of the steam-assisted heater is connected to the steam condensate tank via a condensate pipe.

8. The system for heating boiler feedwater using waste heat from low-temperature flue gas as described in claim 1, characterized in that, A slurry circulation pump is installed on the desulfurization slurry outlet pipeline, a waste hot water circulation pump is installed on the low-temperature waste hot water pipeline, and a hot water circulation pump is installed on the hot water circulation pipeline.

9. The system for heating boiler feedwater using waste heat from low-temperature flue gas as described in claim 1, characterized in that, Both the raw water heater and the demineralized water heater are equipped with water flow regulating valves at their hot water inlets.

10. The system for heating boiler feedwater using waste heat from low-temperature flue gas as described in claim 1, characterized in that, The demineralized water outlet of the demineralized water heater is connected to the deaerator via a pipeline, and the deaerator is connected to the boiler feedwater pipeline.

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