Method and apparatus for recovering waste heat in an ammonia-based desulfurization and decarbonation system

Abstract

The present invention relates to a method for recovering waste heat from an ammonia-based desulfurization and decarbonation system, in which the heat of the process gas before desulfurization is used to remove the heat of the decarbonation system, the process gas before desulfurization passes through a gas heat exchanger to heat an intermediate medium, the intermediate medium drives a chiller for cooling, and the refrigerant obtains cooling power and reduces the temperature of the decarbonated process gas through a liquid-liquid heat exchanger. The present invention can be used to fully utilize the waste heat in the process gas, cool the decarbonated process gas, and reduce energy consumption.

Description

[Technical field]

[0001] The present invention relates to the technical field of environmental protection, and in particular to a method and device for recovering waste heat in an ammonia-based desulfurization and decarbonation system. [Background technology]

[0002] Low-temperature flue gas from industrial boilers and other low-temperature industrial gases are directly discharged into the fields of oil refining, chemical industry and domestic heating. Although the waste heat of low-temperature gas is of low quality, its total amount is relatively large, so it has good potential for energy saving. In addition, with the worsening of environmental pollution and energy shortage, China has been actively advocating energy saving and emission reduction. Under this background, various enterprises are paying more and more attention to how to utilize the waste heat of low-temperature gas generated in the production process.

[0003] China Patent Publication No. 105240826 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, in which the low-temperature flue gas enters the heat collection tower and directly contacts with the droplets of intermediate fluid sprayed from the nozzle in the heat collection tower to exchange heat, the low-temperature flue gas is discharged from the heat collection tower after heat exchange and sent to the liquid heat exchanger, the liquid heat exchanger is connected to the circulating liquid pump to receive the intermediate fluid at the bottom of the heat collection tower, the liquid heat exchanger performs heat exchange between liquids, and the intermediate fluid flows through the liquid heat exchanger to the nozzle of the heat collection tower under the action of the head of the circulating liquid pump. This method only considers the recovery of exhaust heat from the flue gas, and uses the recovered heat to heat the boiler feed water, but does not consider the comprehensive energy utilization of exhaust heat recovery and flue gas desulfurization and decarbonation.

[0004] Chinese Patent Application No. 201410766487.4 proposes a process system and method for combining flue gas desulfurization and decarbonation. The system produces high-purity SO 2 Gas and CO 2 Finally, we obtain each gas, SO 2 and CO 2The temperature difference in the regeneration process of SO 2 CO as a heat source for regeneration 2 The waste heat from the regeneration process is used to 2 CO as a cooling source for gas-liquid separation after regeneration 2 The liquid water obtained after regeneration and separation is used to realize the temperature cascade utilization in the system, which fully utilizes the heat from the flue gas treatment process. However, this method does not consider the recovery and utilization of waste heat from the flue gas before desulfurization.

[0005] China Patent Application No. 201910225072.9 adopts the waste heat recovery technology of direct contact between flue gas and water, combined with a highly efficient water-water plate heat exchanger to realize the recovery and utilization of low-temperature flue gas waste heat, and also achieve desulfurization, but still produces a large amount of CO 2 is released.

[0006] China Utility Model Application No. 201920156807.2 refers to a regenerator flue gas waste heat recovery and reuse system, including a high-temperature flue gas waste heat recovery device, a low-temperature flue gas waste heat recovery device, etc. However, the regenerator relies on optical fiber transmission, has strict requirements for storage conditions, and does not have a recycling function.

[0007] China Utility Model Application No. 201920148383.5 refers to a catalytic flue gas waste heat recovery and recycle system capable of removing CO, which also uses an additional waste heat recovery device to recover the heat in the flue gas. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] China Patent Application Publication No. 105240826 [Patent Document 2] Chinese Patent Application No. 201410766487.4 [Patent Document 3] Chinese Patent Application No. 201910225072.9 [Patent Document 4] China Utility Model Application No. 201920156807.2 [Patent Document 5] China Utility Model Application No. 201920148383.5 Summary of the Invention

[0009] In response to the problems existing in the prior art described above, the present invention proposes a method and apparatus for recovering waste heat in an ammonia-based desulfurization and decarbonation system, in which the heat of the process gas before desulfurization is used to cool the decarbonated process gas, the process gas before desulfurization heats an intermediate medium through a heat exchanger, the intermediate medium drives a chiller for cooling, and the refrigerant in the chiller obtains cooling capacity to cool the decarbonated process gas through a liquid-liquid heat exchanger. The present invention makes full use of the waste heat in the process gas used to cool the decarbonated process gas and reduce energy consumption.

[0010] The object of the present invention is to solve the above problems in the prior art.

[0011] The inventors have surprisingly found that the objects of the invention are achieved by the following method and apparatus described herein.

[0012] In one aspect, the present invention relates to a method for recovering waste heat in an ammonia-based desulfurization and decarbonation system, characterized in that heat of a process gas before desulfurization is utilized to reduce the temperature of a decarbonated process gas.

[0013] In some embodiments of the invention, the process gases involved include coal-fired boiler flue gas, catalytic cracking regenerator flue gas, sulfur recovery incineration exhaust gas, etc. In certain embodiments of the invention, the process gas is CO 2 , S.O. 2 , O 2 , N 2 and dust particles.

[0014] In some embodiments of the present invention, the process gas before desulfurization passes through a process gas heat exchanger to heat the intermediate medium, which drives a chiller for cooling, and the refrigerant in the chiller removes heat from the decarbonation system through the circulating liquid after obtaining the cooling capacity. The circulating liquid refers to the circulating liquid associated with the cooling circulating pump or the decarbonation circulating pump, and may be a solution containing an ammonium salt. Both the cooling device and the decarbonation device include a circulating liquid distribution section. The circulating liquid distribution section includes a circulating pump, a circulating pipe, and a circulating liquid distributor. The circulating liquid is transported from the bottom of the device to the circulating liquid distributor through the circulating pump and the circulating pipe, contacts with the process gas, and is collected at the bottom of the device, and this is repeated in this manner. The circulating liquid of the cooling device is a solution mainly composed of ammonium sulfate in an amount of more than 0 wt % and not more than 5 wt % (based on the total weight of the solution), and the circulating liquid of the decarbonation device is a solution mainly composed of ammonium bicarbonate, ammonium carbonate, and ammonium carbamate.

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

[0016] In some embodiments of the present invention, the refrigerant comprises water (preferably chilled water), alcohol or a combination thereof, the alcohol comprises a monohydric alcohol, a dihydric alcohol or a polyhydric alcohol, the alcohol preferably comprises ethylene glycol, propylene glycol, or the like.

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

[0018] In some embodiments of the invention, the intermediate medium has a temperature of 60-90°C when it enters the gas heat exchanger and a temperature of 70-100°C when it leaves the gas heat exchanger, the temperature entering the gas heat exchanger being lower than the temperature leaving the gas heat exchanger.

[0019] In some embodiments of the invention, the refrigerant has a temperature of 0 to 30°C, preferably 0 to 20°C, when it enters the chiller and a temperature of -10 to 20°C, preferably -10 to 10°C, when it leaves the chiller.

[0020] In certain embodiments of the present invention, a refrigerant may be used to reduce the temperature of the process gas prior to decarbonation.

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

[0022] In some embodiments of the invention, a cooling device is provided prior to decarbonation, the device comprising at least one circulating liquid distribution section, in which a refrigerant passes through a liquid-liquid heat exchanger to reduce the temperature of the circulating liquid.

[0023] In some embodiments of the invention, the decarbonator comprises at least one circulating liquid distribution section, where the refrigerant passes through a liquid-liquid heat exchanger to reduce the temperature of the circulating liquid.

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

[0025] In another aspect, the present invention relates to a waste heat recovery apparatus in an ammonia-based desulfurization and decarbonation system, in which a waste heat recovery apparatus, a desulfurization apparatus, a cooling apparatus, a decarbonation apparatus, and an ammonia removal apparatus are provided in this order along the flow direction of a process gas, and the waste heat recovery apparatus includes a gas heat exchanger, a cooler, and a liquid-liquid heat exchanger, the gas heat exchanger is located before the desulfurization apparatus, the cooler is connected to the gas heat exchanger and the liquid-liquid heat exchanger via a pipeline, and the liquid-liquid heat exchanger is connected to the cooling apparatus.

[0026] In some embodiments of the present invention, the cooling device includes at least one circulating liquid section including a circulating pump, a circulating line, and a circulating liquid distributor.

[0027] In some embodiments of the invention, the liquid-liquid heat exchanger is disposed in the discharge line of the circulation pump.

[0028] In some embodiments of the invention, the liquid-liquid heat exchanger is a plate heat exchanger.

[0029] Unless otherwise specified, the above-described embodiments of the present invention can be combined with each other.

[0030] Unless otherwise specified, % in the present invention is % by weight. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 shows a schematic diagram of a method according to one embodiment of the present invention. [Diagram 2] FIG. 2 shows a schematic diagram of a method according to a comparative example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The invention will be explained in more detail below by means of examples with reference to the drawings, in which the same reference numbers refer to the same streams or components. These examples are not used to limit the invention but serve for a better understanding of the invention.

[0033] The technical effects achieved by the present invention are as follows: In response to the problem that the waste heat of low and medium temperature process gas is difficult to utilize and cannot be utilized effectively, the present invention proposes a method for recovering waste heat from an ammonia-based desulfurization and decarbonation system, which uses the waste heat of the process gas before desulfurization to cool the decarbonated process gas. The beneficial effect of the present invention is that the waste heat can be effectively recovered while performing desulfurization and decarbonation, thereby achieving the objectives of energy saving and emission reduction.

[0034] Specific Models for Implementing the Invention

[0043] The embodiments of the present invention are described in detail below in conjunction with examples, but those skilled in the art will understand that the following examples are intended to illustrate the present invention only, rather than limiting the scope of the present invention.

[0035] [Example] As shown in Figure 1, the temperature is 128°C and the flue gas volume is 857662 Nm 3 / h process gas 1 (i.e., CO 2 , S.O. 2 , O 2 , N 2 The intermediate medium 14 (i.e., water) passes through the gas heat exchanger 2, is heated from 72°C to 96°C, and then enters the cooler 3 to cool the cooling water 15 from 17°C to 7°C.

[0036] After desulfurization, the gas, with a temperature of 45°C, entered the cooling device 5 and the decarbonation device 7 in sequence. The cooling device 5 and the decarbonation device 7 had a tower structure and were separated by a liquid collector 6. The liquid collector 6 had a tray gas cap structure and allowed the gas to enter the decarbonation device 7 from the cooling device 5 through the gas cap. Both the cooling device 5 and the decarbonation device 7 were equipped with a circulating liquid distribution section, which included a circulating pump, a circulating line and a circulating liquid distributor, and the circulating liquid was transported from the bottom of the device to the circulating liquid distributor through the circulating pump and the circulating line, and after contacting with the process gas, was recovered at the bottom of the device, and the circulation was repeated in this manner. The cooling device 5 was equipped with a circulating liquid distributor 18 for the cooling device, and the temperature of the gas was reduced to 25°C through the action of the circulating pump 8 and the plate-type heat exchanger 9 through the cooling water 15 and the cooling water 16 supplied from the outside. The circulating liquid of the cooling device 5 was a solution mainly composed of 2% by weight (based on the total weight of the solution) of ammonium sulfate. After passing through the liquid collector 6, the flue gas enters the decarbonation device 7, which is equipped with a circulating liquid distributor 19 for the decarbonation device, and removes reaction heat and crystallization heat by the action of a circulating pump 10 and a plate-type heat exchanger 11 to produce ammonium hydrogen carbonate. The circulating liquid in the decarbonation device 7 is a solution mainly composed of ammonium hydrogen carbonate, ammonium carbonate, and ammonium carbamate. The decarbonated gas is introduced into an ammonia removal device 12 to control ammonia leakage, and then exhausted as 13.

[0037] Here, the consumption of cooling water supplied from outside was 2339t / h. At the same time, the temperature was lowered by waste heat recovery of the gas before desulfurization. The desulfurization reaction temperature was 45°C. After desulfurization, the ammonia leakage was only 2mg / Nm 3 The water replenishment rate for the desulfurization system was 6t / h.

[0038] Remarks: The method for detecting ammonia leakage was carried out in accordance with HJ 533-2009, and the detection of gas parameters such as flue gas volume was carried out in accordance with GBT 16157-1996.

[0039] [Comparative Example] As shown in Figure 2, the temperature is 128°C and the flue gas volume is 857662 Nm 3 Process gas 1 (the same CO as in Example 1) 2 , S.O. 2 , O 2 , N 2 The coal-fired boiler flue gas containing the sulfur dioxide and dust particles was directly fed to the desulfurization device 4 for desulfurization.

[0040] After desulfurization, the gas had a temperature of 49°C and entered the cooling device 5 and the decarbonation device 7 in sequence. The cooling device 5 and the decarbonation device 7 had a tower structure and were separated by a liquid collector 6. The liquid collector 6 had a tray gas cap structure and allowed the gas to enter the decarbonation device 7 from the cooling device 5 through the gas cap. Both the cooling device 5 and the decarbonation device 7 were equipped with a circulating liquid distribution section including a circulation pump, a circulation line, and a circulating liquid distributor. The circulating liquid was transported from the bottom of the device to the circulating liquid distributor through the circulation pump and the circulation line, contacted with the process gas, and then recovered at the bottom of the device, and the circulation was repeated in this manner. The cooling device 5 was provided with a circulating liquid distributor 18 for the cooling device, and the temperature of the gas was reduced to 25°C through the action of the circulation pump 8 and the plate-type heat exchanger 9 through the cooling water 16 supplied from the outside. The circulating liquid of the cooling device 5 was a solution mainly composed of 2% by weight (based on the total weight of the solution) of ammonium sulfate. After passing through the liquid collector 6, the flue gas enters the decarbonation device 7, which is equipped with a circulating liquid distributor 19 for the decarbonation device, and removes the reaction heat and crystallization heat by the action of a circulating pump 10 and a plate-type heat exchanger 11 to produce ammonium hydrogen carbonate. The circulating liquid in the decarbonation device 7 was a solution mainly composed of ammonium hydrogen carbonate, ammonium carbonate, and ammonium carbamate. The decarbonated gas was introduced into an ammonia removal device 12 to control ammonia leakage, and then vented as 13.

[0041] Here, the consumption of cooling water supplied from outside was 4267t / h. The desulfurization reaction temperature was 49°C, and the ammonia leakage after desulfurization was 5mg / Nm 3 The water replenishment rate for the desulfurization system was 21t / h.

[0042] Remarks: The method for detecting ammonia leakage was carried out in accordance with HJ 533-2009, and the detection of gas parameters such as flue gas volume was carried out in accordance with GBT 16157-1996.

[0043] From the above, it can be clearly seen that compared with the comparative examples, the examples of the present application showed significant reductions in cooling water consumption, temperature of the desulfurization reaction, ammonia leakage after desulfurization, and water make-up amount of the desulfurization system.

[0044] Furthermore, the present invention relates to the following non-limiting aspects. 1. A method for recovering waste heat from an ammonia-based desulfurization and decarbonation system, characterized in that heat from the decarbonation system is removed by utilizing heat from the process gas before desulfurization.

[0045] 2. The method according to aspect 1, characterized in that the process gas before desulfurization is used to heat an intermediate medium through a gas heat exchanger, the intermediate medium is used to drive a chiller for cooling, and the refrigerant in the chiller obtains cooling capacity and removes heat of the decarbonation system through the circulating liquid.

[0046] 3. The method of claim 2, wherein the heated intermediate medium comprises water.

[0047] 4. The method of any one of aspects 2 to 3, wherein the refrigerant comprises water, alcohol, or a combination thereof.

[0048] 5. The method according to aspect 2 or 3, characterized in that the process gas has a temperature of 90-300°C, preferably 110-180°C, more preferably 120-170°C before desulfurization, and the process gas has a temperature of 90-120°C after passing through the gas heat exchanger and a temperature of 40-60°C after desulfurization.

[0049] 6. The method according to aspect 2 or 3, wherein the intermediate medium has a temperature of 60-90°C when entering the gas heat exchanger and a temperature of 70-100°C when leaving the gas heat exchanger, wherein the temperature when entering the gas heat exchanger is lower than the temperature when leaving the gas heat exchanger.

[0050] 7. The method according to aspect 2 or 3, wherein the refrigerant has a temperature of 0 to 30° C. when it enters the chiller and has a temperature of −10 to 20° C. when it leaves the chiller.

[0051] 8. The method according to aspect 2 or 3, characterized in that a refrigerant can be used to reduce the temperature of the process gas before decarbonation.

[0052] 9. The method according to aspect 2 or 3, wherein the refrigerant can be used to remove the heat of decarboxylation reaction and the heat of crystallization.

[0053] 10. The method according to aspect 8, characterized in that a cooling device is provided before the decarbonation, which device comprises at least one circulating liquid distribution section, and a refrigerant is used to reduce the temperature of the circulating liquid via a liquid-liquid heat exchanger, which is preferably a plate heat exchanger.

[0054] 11. The method according to aspect 9, wherein the decarbonation device comprises at least one circulating liquid distribution section, and a refrigerant is used to reduce the temperature of the circulating liquid via a liquid-liquid heat exchanger.

[0055] 12. A waste heat recovery device for an ammonia-based desulfurization and decarbonation system, comprising a waste heat recovery device, a desulfurization device, a cooling device, a decarbonation device, and an ammonia removal device arranged in this order along the flow direction of the process gas, the waste heat recovery device comprising a gas heat exchanger, a cooler, and a liquid-liquid heat exchanger, the gas heat exchanger being located before the desulfurization device, the cooler being connected to the gas heat exchanger and the liquid-liquid heat exchanger via a pipeline, the liquid-liquid heat exchanger being connected to the cooling device, and the liquid-liquid heat exchanger being preferably a plate-type heat exchanger.

[0056] 13. The apparatus according to aspect 12, wherein the cooling device comprises at least one circulating liquid distribution section comprising a circulating pump, a circulating line, and a circulating liquid distributor.

[0057] 14. The device according to aspect 12 or 13, characterized in that the liquid-liquid heat exchanger is arranged in the discharge pipe of the circulation pump.

[0058] The above specific examples further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific examples of the present invention, and are not intended to limit the scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention. [Explanation of symbols]

[0059] 1 represents the process gas, 2 represents the gas heat exchanger, 3 represents the cooler, 4 represents the desulfurization device, 5 represents the cooling device, 6 represents the liquid collector, 7 represents the decarbonation device, 8 represents the cooling circulation pump, 9 represents the plate heat exchanger, 10 represents the decarbonation circulation pump, 11 represents the plate heat exchanger, 12 represents the ammonia removal device, 13 represents the process gas after decarbonation, 14 represents the intermediate medium of the gas heat exchanger, 15 represents the cooling water of the cooler, 16 represents the inflow of the cooling water, 17 represents the backflow of the cooling water, 18 represents the circulating liquid distributor of the cooling device, and 19 represents the circulating liquid distributor of the decarbonation device.

Claims

1. A method for recovering waste heat from an ammonia-based desulfurization and decarbonation system, comprising the steps of: removing heat from the decarbonation system using heat from a process gas before desulfurization;

2. 2. The method according to claim 1, characterized in that the process gas before desulfurization is used to heat an intermediate medium through a gas heat exchanger, the intermediate medium is used to drive a chiller for cooling, and the refrigerant in the chiller obtains cooling capacity and removes heat of the decarbonation system through a circulating liquid.

3. The method of claim 2 , wherein the heated intermediate medium comprises water.

4. 4. The method of claim 2 or 3, wherein the coolant comprises water, alcohol or a combination thereof.

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

6. 4. The method according to claim 2 or 3, characterized in that the intermediate medium has a temperature of 60-90°C when it enters the gas heat exchanger and has a temperature of 70-100°C when it leaves the gas heat exchanger, the temperature entering the gas heat exchanger being lower than the temperature leaving the gas heat exchanger.

7. 4. The method according to claim 2 or 3, characterized in that the refrigerant has a temperature of 0 to 30° C. when it enters the chiller and a temperature of −10 to 20° C. when it leaves the chiller.

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

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

10. 9. The method according to claim 8, characterized in that a cooling device is provided before the decarbonation, said device comprising at least one circulating liquid distribution layer, said refrigerant being used to reduce the temperature of the circulating liquid via a liquid-liquid heat exchanger, said liquid-liquid heat exchanger being preferably a plate heat exchanger.

11. 10. The method according to claim 9, characterized in that the decarbonator comprises at least one circulating liquid distribution section, and the refrigerant is used to reduce the temperature of the circulating liquid via a liquid-liquid heat exchanger.

12. A waste heat recovery device for an ammonia-based desulfurization and decarbonation system, comprising a waste heat recovery device, a desulfurization device, a cooling device, a decarbonation device, and an ammonia removal device, which are arranged in this order along a flow direction of a process gas; The waste heat recovery apparatus for an ammonia-based desulfurization and decarbonation system is characterized in that the waste heat recovery apparatus comprises a gas heat exchanger, a cooler, and a liquid-liquid heat exchanger, the gas heat exchanger is located before the desulfurization apparatus, the cooler is connected to the gas heat exchanger and the liquid-liquid heat exchanger via a pipeline, the liquid-liquid heat exchanger is connected to the cooling apparatus, and the liquid-liquid heat exchanger is preferably a plate-type heat exchanger.

13. 13. The apparatus according to claim 12, wherein the cooling device comprises at least one circulating liquid distribution section comprising a circulating pump, a circulating line, and a circulating liquid distributor.

14. 14. Apparatus according to claim 12 or 13, characterized in that the liquid-liquid heat exchanger is arranged in the discharge pipe of the circulation pump.

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