Mother liquor dual-heating system based on ammonia-alkali method and working method of mother liquor dual-heating system

Abstract

The invention discloses a mother liquor dual-heating system based on an ammonia-alkali process and a working method thereof. The mother liquor dual-heating system comprises a washing tower and an ammonia distillation tower, in the washing tower, the cold mother liquor exchanges heat with the furnace gas and is heated into warm mother liquor; warm mother liquor is sent to the top of the ammonia still from the washing tower; at the top of the ammonia still tower, the warm mother liquor exchanges heat with ammonia gas and is heated into hot mother liquor; and the hot mother liquor is sent back into the ammonia still for ammonia still. A first shell-and-tube heat exchanger is arranged at the top of the ammonia still tower, warm mother liquor passes through the first shell-and-tube heat exchanger along a tube pass, ammonia gas passes through the first shell-and-tube heat exchanger along a shell pass, and the warm mother liquor and the ammonia gas are subjected to countercurrent flow heat exchange in the first shell-and-tube heat exchanger; the warm mother liquor is heated into hot mother liquor in the first shell-and-tube heat exchanger and then is sent back into the ammonia still. The mother liquor sequentially exchanges heat with the furnace gas and the ammonia gas, the mother liquor is heated twice and then enters the ammonia distillation tower for ammonia distillation, the use amount of steam is reduced, and the purposes of energy conservation and emission reduction are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical production, and particularly relates to a mother liquor double heating system based on an ammonia alkali method and a working method thereof. BACKGROUND

[0002] In the ammonia alkali method, cold mother liquor enters an ammonia distillation tower to perform ammonia distillation. In order to save the steam usage of the ammonia distillation tower, the cold mother liquor is preheated before entering the ammonia distillation tower. The current method is to exchange heat between the cold mother liquor and furnace gas, and recycle the heat of the furnace gas. Generally, the temperature of the mother liquor can be increased from about 30 DEG C to above 65 DEG C. However, the temperature of the mother liquor after preheating by the furnace gas is still relatively low, and it is necessary to provide a more reasonable mother liquor heating scheme. SUMMARY

[0003] The present application provides a mother liquor double heating system based on an ammonia alkali method and a working method thereof, which can heat the mother liquor by furnace gas and ammonia gas in sequence, and then the mother liquor is heated twice before entering the ammonia distillation tower to perform ammonia distillation, thereby reducing the steam usage and achieving the purpose of energy saving and emission reduction.

[0004] To achieve the above purpose, the mother liquor double heating system based on the ammonia alkali method comprises a washing tower and an ammonia distillation tower. In the washing tower, the cold mother liquor exchanges heat with the furnace gas and is heated to be warm mother liquor. The warm mother liquor is sent from the washing tower to the top of the ammonia distillation tower. In the top of the ammonia distillation tower, the warm mother liquor exchanges heat with the ammonia gas and is heated to be hot mother liquor. The hot mother liquor is sent back to the ammonia distillation tower to perform ammonia distillation.

[0005] Further, the top of the ammonia distillation tower is provided with a first tube-shell heat exchanger. The warm mother liquor passes through the first tube-shell heat exchanger along the tube side, and the ammonia gas passes through the first tube-shell heat exchanger along the shell side. The warm mother liquor and the ammonia gas exchange heat in the first tube-shell heat exchanger in countercurrent. The warm mother liquor is heated to be hot mother liquor in the first tube-shell heat exchanger and is then sent back to the ammonia distillation tower.

[0006] Further, a mother liquor barrel is arranged between the washing tower and the ammonia distillation tower. The warm mother liquor is sent from the washing tower to the mother liquor barrel. A heat exchange branch and a direct branch are arranged between the mother liquor barrel and the ammonia distillation tower. The warm mother liquor in the mother liquor barrel is divided into two parts. One part is pumped to the first tube-shell heat exchanger through the heat exchange branch, heated to be hot mother liquor, and then sent back to the ammonia distillation tower. The other part is directly pumped to the ammonia distillation tower through the direct branch.

[0007] Further, a distributor is arranged at the output end of the mother liquor barrel. Flow meters are arranged on the heat exchange branch and the direct branch respectively. The distributor can change the flow distribution ratio of the heat exchange branch and the direct branch.

[0008] Further, the straight-through branch is provided with a mixing device; the warm mother liquor in the heat exchange branch is heated to hot mother liquor in the first tube-shell heat exchanger, and then is sent to the mixing device to mix with the warm mother liquor in the straight-through branch to form mixed mother liquor, and the mixed mother liquor is sent to the ammonia evaporation tower for ammonia evaporation.

[0009] Further, the first temperature detector is arranged in the mother liquor tank to detect the temperature of the warm mother liquor; the second temperature detector is arranged at the output end of the mixing device to detect the temperature of the mixed mother liquor; the controller can receive the temperature information of the first temperature detector and the second temperature detector to obtain the temperature difference between the warm mother liquor and the mixed mother liquor; the controller can also monitor the pump power in the mother liquor tank, and combine the pump power and the temperature difference between the warm mother liquor and the mixed mother liquor to control the distributor to adjust the flow distribution ratio of the heat exchange branch and the straight-through branch.

[0010] Further, the upper part of the washing tower is a washing section, and the lower part is a condensing section, and the furnace gas passes through the washing section and the condensing section in sequence; the second tube-shell heat exchanger is arranged in the washing section, the cold mother liquor passes through the second tube-shell heat exchanger along the tube from top to bottom, and the furnace gas passes through the second tube-shell heat exchanger along the shell from bottom to top, and the cold mother liquor and the furnace gas exchange heat in the second tube-shell heat exchanger in countercurrent mode; the condenser is arranged in the condensing section to condense the furnace gas.

[0011] Further, the first tube-shell heat exchanger and the second tube-shell heat exchanger are both corrugated tube heat exchangers.

[0012] Further, the working method of the mother liquor double heating system based on the ammonia alkali method, the cold mother liquor is heated and warmed to warm mother liquor in the washing tower, and then is divided into two parts, one part of the warm mother liquor is pumped into the first tube-shell heat exchanger to exchange heat with ammonia gas and is heated to hot mother liquor, and then is sent back to the ammonia evaporation tower for ammonia evaporation; the other part of the warm mother liquor is directly pumped into the ammonia evaporation tower for ammonia evaporation.

[0013] Further, the ammonia evaporation tower needs to input heat source to evaporate ammonia in the mother liquor, and the warm mother liquor after heat exchange with ammonia gas can save the heat source input amount; the controller calculates the recovered ammonia heat according to the temperature difference between the warm mother liquor and the mixed mother liquor and the flow of the mother liquor, so as to obtain the heat source saving amount; the flow rate of the warm mother liquor passing through the first tube-shell heat exchanger along the tube is related to the pump power, and the controller obtains the electric energy consumption amount according to the pump power; the difference between the heat source saving amount and the electric energy consumption amount is regarded as the energy saving amount; when the controller controls the distributor to run, the flow distribution ratio of the heat exchange branch and the straight-through branch is adjusted, so that the energy saving amount tends to be maximum.

[0014] Beneficial effects: the mother liquor double heating system based on the ammonia alkali method and the working method thereof have the following beneficial effects:

[0015] 1) The mother liquor is sequentially heated by furnace gas and ammonia gas, the heat of the furnace gas and the heat of the ammonia gas can be recovered in the whole system, compared with using furnace gas or ammonia gas alone for heat exchange, the mother liquor can be heated to a higher temperature, thereby saving the steam usage in the ammonia stripping tower, and playing a role in energy saving and emission reduction;

[0016] 2) The cold mother liquor is heated by furnace gas to become warm mother liquor, and then is heat-exchanged with ammonia gas; since the temperature difference between the warm mother liquor and the ammonia gas is very small, if all the warm mother liquor is heat-exchanged with the ammonia gas, the flow rate of the mother liquor may increase, and the recovered heat of the ammonia gas may decrease, therefore, the warm mother liquor is delivered in parallel through a bypass branch and a heat exchange branch, and the flow distribution ratio of the heat exchange branch and the bypass branch is adjusted, so as to achieve a more optimal energy saving and emission reduction effect. BRIEF DESCRIPTION OF DRAWINGS

[0017] ATTACHED Figure 1 is a schematic diagram of the mother liquor double heating system of the present application. DETAILED DESCRIPTION

[0018] The present application will be further described below in combination with the drawings.

[0019] As shown in the attached Figure 1 The mother liquor double heating system based on the ammonia alkali method comprises a washing tower 1 and an ammonia stripping tower 2. The washing tower 1 is used for washing and condensing the furnace gas, in the washing tower 1, the cold mother liquor is heat-exchanged with the furnace gas through a heat exchange device, the temperature of the furnace gas is reduced, and the temperature of the cold mother liquor is increased, and the cold mother liquor becomes warm mother liquor after being heated. There is a transportation pipeline between the washing tower 1 and the ammonia stripping tower 2, and the warm mother liquor is sent from the washing tower 1 to the top of the ammonia stripping tower 2 through the transportation pipeline.

[0020] The ammonia stripping process is carried out in the ammonia stripping tower 2, the ammonia gas is discharged from the top of the ammonia stripping tower 2 and enters the ammonia absorption tower 3, then the ammonia gas reacts with the refined brine in the ammonia absorption tower 3 to generate ammonia brine, and then the ammonia brine reacts with carbon dioxide in the carbonation tower to generate sodium bicarbonate suspension and ammonium chloride. The ammonia gas needs to be cooled before entering the ammonia absorption tower 3, so in the prior art, there is also a heat exchange device at the top of the ammonia stripping tower 2, generally a box cooler is used at the top of the ammonia stripping tower 2 to heat-exchange the ammonia gas with water. In the present application, the warm mother liquor is heat-exchanged with the ammonia gas, the warm mother liquor is heat-exchanged with the ammonia gas through a heat exchange device, and the warm mother liquor becomes hot mother liquor after being heated. Then the hot mother liquor is sent back to the ammonia stripping tower 2 for ammonia stripping.

[0021] In the present application, the mother liquor is sequentially heated by furnace gas and ammonia gas, the heat of the furnace gas and the heat of the ammonia gas can be recovered in the whole system, compared with using furnace gas or ammonia gas alone for heat exchange, the mother liquor can be heated to a higher temperature, thereby saving the steam usage in the ammonia stripping tower 2, and playing a role in energy saving and emission reduction.

[0022] The first shell-and-tube heat exchanger 4 is provided at the top of the ammonia distillation tower 2. The warm mother liquor passes through the first shell-and-tube heat exchanger 4 from top to bottom along the tube side, and the ammonia gas passes through the first shell-and-tube heat exchanger 4 from bottom to top along the shell side. The warm mother liquor and the ammonia gas exchange heat in the first shell-and-tube heat exchanger 4 in countercurrent. The warm mother liquor is heated to hot mother liquor in the first shell-and-tube heat exchanger 4 and is then sent back to the ammonia distillation tower 2. In the first shell-and-tube heat exchanger 4, the warm mother liquor exchanges heat with the ammonia gas instead of the cold mother liquor, and the temperature difference between the warm mother liquor and the ammonia gas is small. Therefore, the warm mother liquor and the ammonia gas need to exchange heat in countercurrent to improve the heat exchange efficiency.

[0023] The mother liquor tank 6 is provided between the washing tower 1 and the ammonia distillation tower 2. The warm mother liquor is sent from the washing tower 1 to the mother liquor tank 6. The heat exchange branch 7 and the straight-through branch 8 are provided between the mother liquor tank 6 and the ammonia distillation tower 2, and each of the heat exchange branch 7 and the straight-through branch 8 is provided with a pump. The warm mother liquor in the mother liquor tank 6 is divided into two parts. One part is pumped to the first shell-and-tube heat exchanger 4 through the heat exchange branch 7, heated to hot mother liquor, and then sent back to the ammonia distillation tower 2. The other part is directly pumped to the ammonia distillation tower 2 through the straight-through branch 8.

[0024] The temperature difference between the warm mother liquor and the ammonia gas is small. If all the warm mother liquor exchanges heat with the ammonia gas, the flow rate of the warm mother liquor in the first shell-and-tube heat exchanger 4 will be very fast under the condition of a certain mother liquor flow rate, the heat exchange time is short, and it is difficult to fully exchange heat with the ammonia gas. In addition, the pressure drop of the tube side is proportional to the square of the flow rate. Therefore, as the flow rate of the warm mother liquor increases, the power of the pump body on the heat exchange branch 7 will increase rapidly, and the increased electricity cost will also be more. Therefore, when the flow rate of the warm mother liquor on the heat exchange branch 7 is too high, the increased electricity cost may be close to or even exceed the value of the recovered heat. Moreover, too high flow rate may induce equipment vibration or cause serious erosion. Therefore, only a part of the warm mother liquor exchanges heat with the ammonia gas, which can reduce the flow rate of the warm mother liquor in the first shell-and-tube heat exchanger 4. Under the condition that the temperature difference between the warm mother liquor and the ammonia gas is small, it has higher economic value.

[0025] The output end of the mother liquor tank 6 is provided with a distributor, which can change the flow distribution ratio of the heat exchange branch 7 and the straight-through branch 8. Flow meters are respectively provided on the heat exchange branch 7 and the straight-through branch 8 to measure the flow rate of the warm mother liquor on the heat exchange branch 7 and the straight-through branch 8.

[0026] The straight-through branch 8 is provided with a mixing device 10 capable of mixing the fluids. After the warm mother liquor in the heat exchange branch 7 is warmed into hot mother liquor in the first tube-shell heat exchanger 4, the hot mother liquor is first sent into the mixing device 10 to mix with the warm mother liquor in the straight-through branch 8 to form mixed mother liquor, and then the mixed mother liquor is sent into the ammonia evaporation tower 2 to evaporate ammonia. The feed of the ammonia evaporation tower 2 usually requires stable and uniform state. If the hot mother liquor and the warm mother liquor are respectively sent into the ammonia evaporation tower 2, the gas-liquid balance in the ammonia evaporation tower 2 may be affected, and the ammonia evaporation efficiency is reduced, so the hot mother liquor and the warm mother liquor are mixed and then sent into the ammonia evaporation tower 2.

[0027] The first temperature detector is arranged in the mother liquor barrel 6 to detect the temperature of the warm mother liquor in the mother liquor barrel 6. The second temperature detector is arranged at the output end of the mixing device 10 to detect the temperature of the mixed mother liquor. The controller can receive the temperature information of the first temperature detector and the second temperature detector to obtain the temperature difference between the warm mother liquor and the mixed mother liquor. The controller can also monitor the pump body power in the mother liquor barrel 6, and control the distributor to adjust the flow distribution ratio of the warm mother liquor in the heat exchange branch 7 and the straight-through branch 8 in combination with the pump body power and the temperature difference between the warm mother liquor and the mixed mother liquor, so as to maximize the economic benefit.

[0028] The upper part of the washing tower 1 is the washing section 11, and the lower part is the condensation section 12. The flue gas passes through the washing section 11 and the condensation section 12 in sequence. The second tube-shell heat exchanger 5 is arranged in the washing section 11. The cold mother liquor passes through the second tube-shell heat exchanger 5 along the tube from top to bottom. The flue gas enters from the middle of the washing tower 1 and passes through the second tube-shell heat exchanger 5 along the shell from bottom to top. The cold mother liquor and the flue gas exchange heat in the second tube-shell heat exchanger 5 in countercurrent. After the flue gas is discharged from the second tube-shell heat exchanger 5, it enters the condensation section 12 at the lower part of the washing tower 1. The condensation section 12 is provided with a cooler 9. The cooler 9 adopts a water tank type condensation to condense the flue gas. In the prior art, the washing section 11 of the washing tower 1 usually adopts a filler type. In the present application, the tube-shell heat exchanger is used, so that the flue gas condensate can be more effectively recovered.

[0029] The first tube-shell heat exchanger 4 and the second tube-shell heat exchanger 5 are both corrugated tube heat exchangers. The corrugated tube can destroy the boundary layer of the fluid, enhance the turbulent flow, and improve the heat transfer efficiency.

[0030] The application also provides a working method of the mother liquor double-warming system based on the ammonia alkali method. Specifically, after the cold mother liquor is warmed into warm mother liquor by heat exchange with the flue gas in the washing tower 1, the warm mother liquor is divided into two parts. One part of the warm mother liquor is pumped into the first tube-shell heat exchanger 4 to exchange heat with the ammonia gas and is warmed into hot mother liquor, and then the hot mother liquor is sent back into the ammonia evaporation tower 2 to evaporate ammonia. The other part of the warm mother liquor is directly pumped into the ammonia evaporation tower 2 to evaporate ammonia.

[0031] In the conventional technology, the mother liquor is either only heat-exchanged with the furnace gas or only heat-exchanged with the ammonia gas, and there is no technical solution for the mother liquor to be heat-exchanged with the furnace gas and the ammonia gas in turn. Therefore, the mother liquor heat-exchanged with the ammonia gas at the top of the ammonia stripping tower 2 is usually cold mother liquor at about 30℃, and the ammonia gas at the top of the ammonia stripping tower 2 is at about 83℃, so if the cold mother liquor is heat-exchanged with the ammonia gas, the heat-exchange temperature difference between the two is large, so if the flow rate of the cold mother liquor in the corrugated tube heat exchanger increases, the more ammonia gas heat recovered accordingly. Only when the flow rate of the cold mother liquor is too high, the bottleneck of no longer increasing the ammonia gas heat recovered will occur.

[0032] However, in the present application, the mother liquor is first heat-exchanged with the furnace gas and then heat-exchanged with the ammonia gas. The cold mother liquor at about 30℃ is heat-exchanged with the furnace gas and then heated to warm mother liquor at about 67℃, and it is mentioned above that the ammonia gas at the top of the ammonia stripping tower 2 is at about 83℃, so the temperature difference between the warm mother liquor and the ammonia gas is only about 16℃, the heat-exchange temperature difference is small, and therefore, when the warm mother liquor is heat-exchanged with the ammonia gas in the corrugated tube heat exchanger, if the flow rate of the warm mother liquor increases, the heat-exchange time between the warm mother liquor and the ammonia gas will be shortened, and because the heat-exchange temperature difference between the warm mother liquor and the ammonia gas is small, after the heat-exchange time is shortened, the temperature rise of the warm mother liquor will be reduced, resulting in no increase in the total ammonia gas heat recovered. In addition, for the pump body, the pressure drop in the tube is proportional to the square of the flow rate, so as the flow rate of the mother liquor increases, the power of the pump body in the heat-exchange branch 7 will increase rapidly, and the electricity cost will also increase more. Therefore, when the flow rate of the warm mother liquor increases, the economic benefit may actually decrease. Of course, the flow rate of the warm mother liquor in the corrugated tube heat exchanger cannot be too slow, otherwise scaling phenomenon is easy to occur.

[0033] Based on the above reasons, under the premise that the total flow rate of the mother liquor provided by the mother liquor tank 6 to the ammonia stripping tower 2 is unchanged, the warm mother liquor is selected to be pumped into the ammonia stripping tower 2 through the heat-exchange branch 7 and the straight-through branch 8 respectively, instead of all the warm mother liquor being heat-exchanged with the ammonia gas in the corrugated tube heat exchanger. Because part of the warm mother liquor is diverted to the straight-through branch 8, the flow rate of the warm mother liquor in the heat-exchange branch 7 will decrease, and accordingly, the flow rate of the warm mother liquor in the heat-exchange branch 7 will be lower, the total power of the pump bodies in the two branches will decrease, the electricity consumption will decrease accordingly, and higher economic benefit will be obtained.

[0034] Specifically, because the ammonia stripping tower 2 needs to input heat source, i.e. steam, to strip ammonia from the mother liquor, the warm mother liquor after heat-exchange with the ammonia gas can save the input amount of heat source, i.e. save the input amount of steam. The controller calculates the ammonia gas heat recovered according to the temperature difference between the warm mother liquor and the mixed mother liquor and the flow rate of the mother liquor measured by the flow meter. According to the ammonia gas heat, the saved steam input amount is calculated, and combined with the cost of unit steam, the heat source consumption saving amount, i.e. the cost saved corresponding to the saved steam input amount, can be calculated.

[0035] The flow rate of the warm mother liquor along the tube when passing through the first tube-shell heat exchanger 4 is related to the pump body power, and the controller obtains the amount of power consumption according to the power of each pump body on the heat exchange branch 7 and the straight-through branch 8, that is, the corresponding electricity cost.

[0036] The difference between the heat source consumption saving amount and the electricity consumption amount is regarded as the energy consumption saving amount. When the controller controls the operation of the distributor, the flow distribution ratio of the heat exchange branch 7 and the straight-through branch 8 is continuously adjusted, so that the energy consumption saving amount tends to be maximum.

[0037] Therefore, in the present application, since the warm mother liquor exchanges heat with ammonia, the heat exchange temperature difference is very small. If all the warm mother liquor exchanges heat with ammonia, the recovered ammonia heat may be reduced due to the increase of the mother liquor flow rate, so the parallel warm mother liquor conveying mode of the straight-through branch 8 and the heat exchange branch 7 is adopted, and the flow distribution ratio of the heat exchange branch 7 and the straight-through branch 8 is adjusted, so as to achieve a more optimal energy saving and emission reduction effect.

[0038] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the technical field, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be regarded as the protection scope of the present application.

Claims

1. A double warming system of mother liquor based on the ammonia process, characterized in that: The application relates to a mother liquor ammonia distillation device, which comprises a washing tower (1) and an ammonia distillation tower (2); in the washing tower (1), cold mother liquor is heated and warmed into warm mother liquor by exchanging heat with furnace gas; the warm mother liquor is sent from the washing tower (1) to the top of the ammonia distillation tower (2); at the top of the ammonia distillation tower (2), the warm mother liquor is heated and warmed into hot mother liquor by exchanging heat with ammonia gas; the hot mother liquor is sent back into the ammonia distillation tower (2) to distill ammonia.

2. The dual heating system for mother liquor based on ammonia process according to claim 1, characterized in that: The top of the ammonia distillation tower (2) is provided with a first shell-and-tube heat exchanger (4), the warm mother liquor passes through the first shell-and-tube heat exchanger (4) along the tube side, the ammonia gas passes through the first shell-and-tube heat exchanger (4) along the shell side, and the warm mother liquor and the ammonia gas exchange heat in the first shell-and-tube heat exchanger (4) in countercurrent mode; the warm mother liquor is warmed into hot mother liquor in the first shell-and-tube heat exchanger (4) and is then sent back into the ammonia distillation tower (2).

3. The dual warm-up system for mother liquor based on the ammonia process according to claim 2, characterized in that: The washing tower (1) and the ammonia distillation tower (2) are provided with a mother liquor barrel (6), the warm mother liquor is sent from the washing tower (1) to the mother liquor barrel (6); the mother liquor barrel (6) and the ammonia distillation tower (2) are provided with a heat exchange branch (7) and a direct branch (8); the warm mother liquor in the mother liquor barrel (6) is divided into two parts, one part is pumped into the first shell-and-tube heat exchanger (4) through the heat exchange branch (7), is warmed into hot mother liquor and is then sent back into the ammonia distillation tower (2); the other part is directly pumped into the ammonia distillation tower (2) through the direct branch (8).

4. The dual warm-up system for mother liquor based on the ammonia process according to claim 3, characterized in that: The output end of the mother liquor barrel (6) is provided with a distributor, flow meters are arranged on the heat exchange branch (7) and the direct branch (8) respectively; the distributor can change the flow distribution ratio of the heat exchange branch (7) and the direct branch (8).

5. The ammonia-alkali-based mother liquor dual warming system according to claim 4, characterized in that: A mixing device (10) is arranged on the direct branch (8); after the warm mother liquor of the heat exchange branch (7) is warmed into hot mother liquor in the first shell-and-tube heat exchanger (4), the warm mother liquor is first sent into the mixing device (10), is mixed with the warm mother liquor in the direct branch (8), forms mixed mother liquor and is then sent into the ammonia distillation tower (2) to distill ammonia.

6. The dual warm-up system for mother liquor based on the ammonia process according to claim 5, characterized in that: A first temperature detector is arranged in the mother liquor barrel (6) to detect the temperature of the warm mother liquor; a second temperature detector is arranged at the output end of the mixing device (10) to detect the temperature of the mixed mother liquor. A controller can receive the temperature information of the first temperature detector and the second temperature detector, obtain the temperature difference between the warm mother liquor and the mixed mother liquor; the controller can also monitor the power of a pump body in the mother liquor barrel (6) and control the distributor to adjust the flow distribution ratio of the heat exchange branch (7) and the direct branch (8) in combination with the power of the pump body and the temperature difference between the warm mother liquor and the mixed mother liquor.

7. The dual heating system for mother liquor based on ammonia process according to claim 2, characterized in that: The upper part of the washing tower (1) is a washing section (11) and the lower part is a condensation section (12), furnace gas passes through the washing section (11) and the condensation section (12) in sequence; a second shell-and-tube heat exchanger (5) is arranged in the washing section (11), cold mother liquor passes through the second shell-and-tube heat exchanger (5) from top to bottom along the tube side, furnace gas passes through the second shell-and-tube heat exchanger (5) from bottom to top along the shell side, and the cold mother liquor and the furnace gas exchange heat in the second shell-and-tube heat exchanger (5) in countercurrent mode; a cooler (9) is arranged in the condensation section (12) to condense the furnace gas.

8. The ammonia-alkali-based mother liquor dual warming system according to claim 7, characterized in that: The first shell-and-tube heat exchanger (4) and the second shell-and-tube heat exchanger (5) are both corrugated tube heat exchangers.

9. The method of working the mother liquor dual warming system based on the ammonia process according to claim 6, characterized in that: The cold mother liquor exchanges heat with the furnace gas in the washing tower (1) and is warmed to be warm mother liquor, and then is divided into two parts, one part of the warm mother liquor is pumped into the first tube-shell heat exchanger (4) to exchange heat with ammonia gas and is warmed to be hot mother liquor, and then is sent back to the ammonia distillation tower (2) to distill ammonia, and the other part of the warm mother liquor is directly pumped into the ammonia distillation tower (2) to distill ammonia.

10. The method of working a mother liquor dual warming system based on the ammonia process according to claim 9, characterized in that: The ammonia distillation tower (2) needs to input heat source to distill ammonia from the mother liquor, and the warm mother liquor after heat exchange with ammonia gas can save the heat source input amount; the controller calculates the recovered ammonia heat according to the temperature difference between the warm mother liquor and the mixed mother liquor and the flow of the mother liquor, so as to obtain the amount of heat source saving; the flow rate of the warm mother liquor along the tube when passing through the first tube-shell heat exchanger (4) is related to the pump body power, and the controller obtains the amount of electric energy consumption according to the pump body power; The difference between the amount of heat source saving and the amount of electric energy consumption is regarded as the amount of energy saving; when the controller controls the operation of the distributor, the flow distribution ratio of the heat exchange branch (7) and the straight-through branch (8) is adjusted to make the amount of energy saving tend to be maximum.

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