Method and apparatus for waste heat recovery in ammonia-based desulfurization and decarbonization system

Abstract

A method and device for waste heat recovery in an ammonia-based desulfurization and decarbonization system. The heat of a process gas (1) before desulfurization is used to remove the heat of a decarbonization system; before desulfurization, the process gas (1) passes through a gas heat exchanger (2) to heat an intermediate medium (14), and a refrigerator (3) is driven by the intermediate medium (14) to refrigerate; after a secondary refrigerant obtains cooling capacity, it cools down a decarbonized process gas by means of a liquid-liquid heat exchanger, thereby reducing energy consumption.

Description

A method and device for recovering waste heat from an ammonia-based desulfurization and decarbonization system Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and in particular relates to a method and device for recovering waste heat from ammonia-based desulfurization and decarbonization. Background Art

[0002] Low-temperature flue gas from industrial boilers and other low-temperature industrial gases are widely used in the petroleum, chemical, and domestic heating industries. Although the quality of waste heat from these gases is relatively low, their large volume presents significant energy-saving potential. Furthermore, with increasing environmental pollution and energy shortages, China is vigorously promoting energy conservation and emission reduction. Against this backdrop, businesses are increasingly focusing on utilizing the waste heat from these low-temperature gases generated during production.

[0003] CN105240826A discloses a low-temperature flue gas waste heat recovery system, which includes a heat collection tower, a liquid storage tank, a circulating liquid pump, and a liquid heat exchanger. The low-temperature flue gas enters the heat collection tower and directly contacts droplets of an intermediate fluid ejected from a nozzle within the heat collection tower for heat exchange. After heat exchange, the low-temperature flue gas exits the heat collection tower and is delivered to a liquid heat exchanger. The liquid heat exchanger is connected to the circulating liquid pump, receiving the intermediate fluid at the bottom of the heat collection tower. Heat exchange is performed between the liquids within the liquid heat exchanger. Under the pressure of the circulating liquid pump, the intermediate fluid flows through the liquid heat exchanger to the nozzle of the heat collection tower. This solution only considers flue gas waste heat recovery, with the recovered heat used to heat boiler feed water. However, it does not consider the comprehensive energy utilization of waste heat recovery and flue gas desulfurization and decarbonization.

[0004] CN201410766487.4 proposes a process system and method for combined flue gas desulfurization and decarbonization. This system ultimately produces high-purity SO2 and CO2 gases, respectively. The system utilizes the temperature difference between the SO2 and CO2 regeneration processes, as well as the waste heat from the CO2 regeneration process, as a heat source for SO2 regeneration. The liquid water separated from the CO2 regeneration serves as a cooling source for gas-liquid separation after SO2 regeneration. This achieves a temperature gradient within the system, fully utilizing the heat from the flue gas treatment process. However, this solution does not consider the recovery and utilization of waste heat from the flue gas before desulfurization.

[0005] CN201910225072.9 adopts direct contact waste heat recovery technology of flue gas and water, and combines it with a high-efficiency water-water plate heat exchanger to realize the recovery and utilization of low-temperature flue gas waste heat. It also has desulfurization function, but still emits a large amount of CO2.

[0006] CN201920156807.2 mentions a regenerator flue gas waste heat recovery and reuse system, which includes a high-temperature flue gas waste heat recovery device and a low-temperature flue gas waste heat recovery device. However, the regenerator relies on optical fiber transmission, has strict storage requirements, and does not have a multiplexing function.

[0007] CN201920148383.5 mentions a catalytic flue gas waste heat recovery and reuse system that can remove CO and also utilizes an additional waste heat recovery device to recover heat in the flue gas.

[0008] Summary of the Invention

[0009] To address the aforementioned issues in the prior art, the present invention proposes a method and apparatus for recovering waste heat from an ammonia-based desulfurization and decarbonization system. This method utilizes the heat of the pre-desulfurization process gas to cool the decarbonized process gas. The pre-desulfurization process gas passes through a heat exchanger to heat an intermediate medium, which then drives a refrigeration unit. The secondary refrigerant in the refrigeration unit then cools the decarbonized process gas through a liquid-liquid heat exchanger. This method fully utilizes the waste heat in the process gas to cool the decarbonized process gas, saving energy.

[0010] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art.

[0011] The inventors surprisingly discovered that the objects of the present invention can be achieved by the following methods and devices described herein.

[0012] In one aspect, the present invention relates to a method for recovering waste heat from an ammonia-based desulfurization and decarbonization system, characterized in that the heat of the process gas before desulfurization is used to cool the decarbonized process gas.

[0013] In certain embodiments of the present invention, the process gas includes coal-fired boiler flue gas, catalytic cracking regeneration flue gas, sulfur recovery incineration tail gas, etc. In certain embodiments of the present invention, the process gas contains CO2, SO2, O2, N2 and dust particles.

[0014] In certain embodiments of the present invention, the process gas before desulfurization passes through a process gas heat exchanger to heat an intermediate medium, and the intermediate medium drives the refrigerator to refrigerate. After the refrigerant in the refrigerator obtains cold capacity, the heat of the decarbonization system is removed through the circulating liquid. The circulating liquid refers to the circulating liquid associated with the cooling circulation pump or the decarbonization circulation pump, which can be a solution containing ammonium salt. The cooling equipment and the decarbonization equipment are both provided with a circulating liquid distribution unit, which includes a circulating pump, a circulating pipe, and a circulating liquid distributor. The circulating liquid is transported from the lower part of the equipment to the circulating liquid distributor through the circulating pump and the circulating pipe. After contacting with the process gas, it is collected at the lower part of the equipment and circulated in this way. The circulating liquid component of the cooling equipment is mainly a solution containing greater than 0wt% to 5wt% of ammonium sulfate (based on the total weight of the solution), and the circulating liquid component of the decarbonization equipment is mainly a solution containing ammonium bicarbonate, ammonium carbonate, and ammonium carbamate.

[0015] In certain embodiments of the present invention, the heated intermediate medium comprises water.

[0016] In certain embodiments of the present invention, the coolant includes water (preferably chilled water), alcohols, or a combination thereof, wherein the alcohols include monohydric alcohols, dihydric alcohols, or polyhydric alcohols, and the alcohols preferably include ethylene glycol, propylene glycol, and the like.

[0017] In certain embodiments of the present invention, the process gas temperature before desulfurization is 90-300°C, preferably 110-180°C, more preferably 120-170°C, the process gas temperature after heat exchange through the gas heat exchanger is 90-120°C, preferably 95-110°C, and the temperature after desulfurization is 40-60°C, preferably 42-47°C.

[0018] In certain embodiments of the present invention, the intermediate medium inlet gas heat exchanger temperature is 60-90°C, and the outlet gas heat exchanger temperature is 70-100°C, wherein the inlet gas heat exchanger temperature is lower than the outlet gas heat exchanger temperature.

[0019] In certain embodiments of the present invention, the temperature of the brine entering the refrigerator is 0 to 30°C, preferably 0 to 20°C, and the temperature of the brine exiting the refrigerator is -10 to 20°C, preferably -10 to 10°C.

[0020] In certain embodiments of the present invention, a brine can be used to reduce the temperature of the process gas prior to decarburization.

[0021] In certain embodiments of the present invention, a brine can be used to remove the heat of decarburization reaction and the heat of crystallization.

[0022] In certain embodiments of the present invention, a cooling device is provided before decarburization. The device is provided with at least one layer of circulating liquid distribution unit, and the coolant reduces the temperature of the circulating liquid through a liquid-liquid heat exchanger.

[0023] In certain embodiments of the present invention, the decarbonization equipment is provided with at least one layer of circulating liquid distribution unit, and the coolant reduces the temperature of the circulating liquid through a liquid-liquid heat exchanger.

[0024] In certain embodiments of the present invention, the liquid-liquid heat exchanger comprises a plate heat exchanger.

[0025] In another aspect, the present invention relates to a device for recovering waste heat from an ammonia desulfurization and decarbonization system, characterized in that a waste heat recovery device, a desulfurization device, a cooling device, a decarbonization device, and an ammonia removal device are sequentially provided along the flow direction of the process gas, wherein

[0026] The waste heat recovery device includes a gas heat exchanger, a refrigerator, and a liquid-liquid heat exchanger. The gas heat exchanger is located in front of the desulfurization equipment. The refrigerator is connected to the gas heat exchanger and the liquid-liquid heat exchanger through pipelines. The liquid-liquid heat exchanger is connected to the cooling equipment.

[0027] In certain embodiments of the present invention, the cooling device is provided with at least one layer of circulating liquid unit, including a circulating pump, a circulating pipe, and a circulating liquid distributor.

[0028] In certain embodiments of the present invention, the liquid-liquid heat exchanger is located on the outlet pipe of the circulation pump.

[0029] In certain embodiments of the present invention, the liquid-liquid heat exchanger is a plate heat exchanger.

[0030] Unless otherwise stated, the above-described embodiments of the present invention can be combined with each other.

[0031] Unless otherwise specified, % herein is by weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be explained in detail below by way of example with reference to the accompanying drawings. These examples are not limiting of the present invention but are provided for a better understanding of the present invention.

[0033] FIG1 is a schematic diagram of a method according to an embodiment of the present invention.

[0034] FIG2 is a schematic diagram of a method according to a comparative example of the present invention.

[0035] In the drawings, the same figure marks refer to the same logistics or units, wherein: 1 represents process gas, 2 represents gas heat exchanger, 3 represents refrigerator, 4 represents desulfurization equipment, 5 represents cooling equipment, 6 represents liquid collector, 7 represents decarbonization equipment, 8 represents cooling circulation pump, 9 represents plate heat exchanger, 10 represents decarbonization circulation pump, 11 represents plate heat exchanger, 12 represents ammonia removal equipment, 13 represents process gas after decarbonization, 14 represents intermediate medium of gas heat exchanger, 15 represents refrigerator chilled water, 16 represents chilled water inlet, 17 represents chilled water return, 18 represents cooling equipment circulating liquid distributor, and 19 represents decarbonization equipment circulating liquid distributor.

[0036] Technical effects achieved by the present invention

[0037] To address the difficulty and ineffectiveness of utilizing waste heat from low- and medium-temperature process gases, this paper proposes a waste heat recovery method for an ammonia-based desulfurization and decarbonization system. This method utilizes the waste heat from the process gas prior to desulfurization to cool the decarbonization process gas. The present invention has the beneficial effect of effectively recovering waste heat while simultaneously performing desulfurization and decarbonization, achieving energy conservation and emission reduction. DETAILED DESCRIPTION

[0038] The embodiments of the present invention will be described in detail below by way of examples. However, it will be understood by those skilled in the art that the following examples are only used to illustrate the present invention, rather than to limit the scope of the present invention.

[0039] Example

[0040] As shown in Figure 1, the process gas 1 (i.e., coal-fired boiler flue gas, which contains CO2, SO2, O2, N2 and dust particles) has a temperature of 128°C and a flue gas volume of 857662 Nm 3 / h, passes through the gas heat exchanger 2 and is cooled to 100℃ before entering the desulfurization equipment 4. The intermediate medium 14 (i.e., water) passes through the gas heat exchanger 2 and is heated from 72℃ to 96℃. It then goes to the refrigerator 3 to cool the chilled water 15 from 17℃ to 7℃.

[0041] The gas temperature after desulfurization is 45°C, and it enters the cooling equipment 5 and the decarbonization equipment 7 in turn. The cooling equipment 5 and the decarbonization equipment 7 are tower structures, separated by a liquid collector 6. The liquid collector 6 is a tower plate gas cap structure, allowing the gas to pass through the gas cap from the cooling equipment 5 to the decarbonization equipment 7. The cooling equipment 5 and the decarbonization equipment 7 are both equipped with a circulating liquid distribution unit, which includes a circulating pump, a circulating pipe, and a circulating liquid distributor. The circulating liquid is transported from the lower part of the equipment to the circulating liquid distributor through the circulating pump and the circulating pipe. After contacting with the process gas, it is collected at the lower part of the equipment and circulated in this way. A cooling equipment circulating liquid distributor 18 is provided in the cooling equipment 5. Under the action of the circulating pump 8 and the plate heat exchanger 9, the gas temperature is cooled to 25°C through the chilled water 15 and the chilled water 16 provided externally. The circulating liquid component of the cooling equipment 5 is mainly a solution containing 2wt% ammonium sulfate (based on the total weight of the solution). After passing through the liquid collector 6, the flue gas enters the decarbonization unit 7, which is equipped with a circulating liquid distributor 19. A circulating pump 10 and a plate heat exchanger 11 remove the heat of reaction and crystallization to produce ammonium bicarbonate. The circulating liquid in the decarbonization unit 7 primarily consists of a solution containing ammonium bicarbonate, ammonium carbonate, and ammonium carbamate. The decarbonized gas then passes through an ammonia removal unit 12 to control ammonia escape before being discharged 13.

[0042] The externally provided chilled water consumption is 2339t / h. At the same time, due to the waste heat recovery of the gas before desulfurization, the temperature is reduced, the desulfurization reaction temperature is 45℃, and the ammonia escape after desulfurization is only 2mg / Nm 3 , the desulfurization system water make-up is 6t / h.

[0043] Note: The test method for ammonia escape is carried out in accordance with HJ 533-2009, and the test method for gas parameters such as flue gas volume is carried out in accordance with GBT 16157-1996.

[0044] Comparative Example

[0045] As shown in FIG2 , the process gas 1 (the same coal-fired boiler flue gas as in Example 1, which contains CO 2 , SO 2 , O 2 , N 2 and dust particles) has a temperature of 128° C. and a flue gas volume of 857662 Nm 3 / h, and directly enters the desulfurization equipment 4 for desulfurization.

[0046] The gas temperature after desulfurization is 49°C, and it enters the cooling equipment 5 and the decarbonization equipment 7 in turn. The cooling equipment 5 and the decarbonization equipment 7 are tower structures, separated by a liquid collector 6. The liquid collector 6 is a tower plate gas cap structure, allowing the gas to pass through the gas cap from the cooling equipment 5 to the decarbonization equipment 7. The cooling equipment 5 and the decarbonization equipment 7 are both equipped with a circulating liquid distribution unit, including a circulating pump, a circulating pipe, and a circulating liquid distributor. The circulating liquid is transported from the lower part of the equipment to the circulating liquid distributor through the circulating pump and the circulating pipe. After contacting with the process gas, it is collected at the lower part of the equipment and circulated in this way. . A cooling equipment circulating liquid distributor 18 is provided in the cooling equipment 5. Under the action of the circulating pump 8 and the plate heat exchanger 9, the gas temperature is cooled to 25°C by the externally provided chilled water 16. The circulating liquid component of the cooling equipment 5 is mainly a solution containing 2wt% ammonium sulfate (based on the total weight of the solution). After passing through the liquid collector 6, the flue gas enters the decarbonization unit 7, which is equipped with a circulating liquid distributor 19. A circulating pump 10 and a plate heat exchanger 11 remove the heat of reaction and crystallization to produce ammonium bicarbonate. The circulating liquid in the decarbonization unit 7 primarily consists of a solution containing ammonium bicarbonate, ammonium carbonate, and ammonium carbamate. The decarbonized gas then passes through an ammonia removal unit 12 to control ammonia escape before being discharged 13.

[0047] The externally provided chilled water consumption is 4267t / h. The desulfurization reaction temperature is 49°C and the ammonia escape after desulfurization is 5mg / Nm 3 , the desulfurization system water makeup is 21t / h.

[0048] Note: The test method for ammonia escape is carried out in accordance with HJ 533-2009, and the test method for gas parameters such as flue gas volume is carried out in accordance with GBT 16157-1996.

[0049] It can be clearly seen from the above that the embodiments of the present application significantly reduce the chilled water consumption, desulfurization reaction temperature, ammonia escape after desulfurization, and desulfurization system water makeup amount compared with the comparative examples.

[0050] Furthermore, the present invention relates to the following non-limiting aspects:

[0051] 1. A method for recovering waste heat from an ammonia-based desulfurization and decarbonization system, characterized in that the heat of the process gas before desulfurization is used to remove the heat from the decarbonization system.

[0052] 2. The method according to aspect 1 is characterized in that the process gas before desulfurization is used to heat the intermediate medium through a gas heat exchanger, and the intermediate medium is used to drive the refrigerator to cool. After the refrigerant in the refrigerator obtains cold capacity, the heat of the decarbonization system is removed through the circulating liquid.

[0053] 3. The method according to aspect 2, characterized in that the heated intermediate medium comprises water.

[0054] 4. The method according to aspect 2 or 3, characterized in that the coolant comprises water, alcohol, or a combination thereof.

[0055] 5. The method according to aspect 2 or 3 is characterized in that the process gas temperature before desulfurization is 90-300°C, preferably 110-180°C, more preferably 120-170°C, the process gas temperature after heat exchange through the gas heat exchanger is 90-120°C, and the temperature after desulfurization is 40-60°C.

[0056] 6. The method according to aspect 2 or 3 is characterized in that the intermediate medium inlet temperature of the gas heat exchanger is 60-90°C, and the outlet temperature of the gas heat exchanger is 70-100°C, wherein the inlet temperature of the gas heat exchanger is lower than the outlet temperature of the gas heat exchanger.

[0057] 7. The method according to aspect 2 or 3 is characterized in that the temperature of the coolant entering the refrigerator is 0 to 30°C, and the temperature of the coolant leaving the refrigerator is -10 to 20°C.

[0058] 8. The method according to aspect 2 or 3, characterized in that the coolant can be used to reduce the temperature of the process gas before decarburization.

[0059] 9. The method according to aspect 2 or 3, characterized in that the coolant can be used to remove decarburization reaction heat and crystallization heat.

[0060] 10. The method according to aspect 8 is characterized in that a cooling device is provided before decarburization, and the device is provided with at least one layer of circulating liquid distribution unit, and the coolant reduces the temperature of the circulating liquid through a liquid-liquid heat exchanger, wherein the liquid-liquid heat exchanger is preferably a plate heat exchanger.

[0061] 11. The method according to aspect 9 is characterized in that the decarbonization equipment is provided with at least one layer of circulating liquid distribution unit, and the coolant reduces the temperature of the circulating liquid through a liquid-liquid heat exchanger.

[0062] 12. A device for recovering waste heat from an ammonia-based desulfurization and decarbonization system, characterized in that a waste heat recovery device, a desulfurization device, a cooling device, a decarbonization device, and an ammonia removal device are sequentially provided along the flow direction of the process gas, wherein

[0063] The waste heat recovery device includes a gas heat exchanger, a refrigerator, and a liquid-liquid heat exchanger. The gas heat exchanger is located in front of the desulfurization equipment. The refrigerator is connected to the gas heat exchanger and the liquid-liquid heat exchanger through pipelines. The liquid-liquid heat exchanger is connected to the cooling equipment, and the liquid-liquid heat exchanger is preferably a plate heat exchanger.

[0064] 13. The device according to aspect 12 is characterized in that the cooling equipment is provided with at least one layer of circulating liquid distribution unit, including a circulating pump, a circulating pipe, and a circulating liquid distributor.

[0065] 14. The device according to aspect 12 or 13, characterized in that the liquid-liquid heat exchanger is located on the outlet pipe of the circulation pump.

[0066] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for recovering waste heat from an ammonia-based desulfurization and decarbonization system, characterized in that: The heat of the process gas before desulfurization is used to remove heat from the decarbonization system.

2. The method according to claim 1, characterized in that The process gas before desulfurization is used to heat the intermediate medium through a gas heat exchanger, and the intermediate medium drives the refrigerator to cool. The refrigerant in the refrigerator obtains cold capacity and removes the heat of the decarbonization system through the circulating fluid.

3. The method according to claim 2, characterized in that The heated intermediate medium includes water.

4. The method according to claim 2 or 3, characterized in that The coolant includes water, alcohol, or a combination thereof.

5. The method according to claim 2 or 3, characterized in that The process gas temperature before desulfurization is 90-300°C, preferably 110-180°C, more preferably 120-170°C. The process gas temperature after heat exchange through the gas heat exchanger is 90-120°C, and the temperature after desulfurization is 40-60°C.

6. The method according to claim 2 or 3, characterized in that The intermediate medium inlet temperature of the gas heat exchanger is 60-90° C., and outlet temperature of the gas heat exchanger is 70-100° C., wherein the inlet temperature of the gas heat exchanger is lower than the outlet temperature of the gas heat exchanger.

7. The method according to claim 2 or 3, characterized in that The temperature of the coolant entering the refrigerator is 0 to 30°C, and the temperature of the coolant leaving the refrigerator is -10 to 20°C.

8. The method according to claim 2 or 3, characterized in that The secondary coolant can be used to reduce the temperature of the process gas before decarburization.

9. The method according to claim 2 or 3, characterized in that The brine can be used to remove the heat of decarburization reaction and the heat of crystallization.

10. The method according to claim 8, characterized in that A cooling device is provided before decarburization, and the device is provided with at least one layer of circulating liquid distribution unit. The coolant reduces the temperature of the circulating liquid through a liquid-liquid heat exchanger, wherein the liquid-liquid heat exchanger is preferably a plate heat exchanger.

11. The method according to claim 9, characterized in that The decarbonization equipment is provided with at least one layer of circulating liquid distribution unit, and the coolant reduces the temperature of the circulating liquid through the liquid-liquid heat exchanger.

12. A device for recovering waste heat from an ammonia-based desulfurization and decarbonization system, characterized in that: Along the process gas flow direction, there are waste heat recovery equipment, desulfurization equipment, cooling equipment, decarbonization equipment, and ammonia removal equipment in sequence. The waste heat recovery device includes a gas heat exchanger, a refrigerator, and a liquid-liquid heat exchanger. The device is located in front of the desulfurization equipment, the refrigerator is connected to the gas heat exchanger and the liquid-liquid heat exchanger through pipelines, and the liquid-liquid heat exchanger is connected to the cooling equipment, wherein the liquid-liquid heat exchanger is preferably a plate heat exchanger.

13. The device according to claim 12, characterized in that The cooling equipment is provided with at least one layer of circulating liquid distribution unit, which includes a circulating pump, a circulating pipeline, and a circulating liquid distributor.

14. The device according to claim 12 or 13, characterized in that The liquid-liquid heat exchanger is located on the outlet pipe of the circulation pump.