Ammonia distillation system capable of increasing liquid ammonia content and control method thereof

Abstract

The present invention relates to the field of fine chemical technology, and in particular to an ammonia distillation system capable of increasing the liquid ammonia content and a control method thereof. The system comprises a distillation tower, a first falling film heat exchange system and a second falling film heat exchange system connected in sequence; the feed port of the distillation tower is connected to an external material conveying device; the first falling film heat exchange system comprises a first falling film heat exchanger, a first evaporation chamber and a first MVR evaporation system, the first evaporation chamber is connected to the tube side of the first falling film heat exchanger, the first MVR evaporation system is arranged at the output end of the first evaporation chamber; and is connected to the air inlet of the distillation tower; the second falling film heat exchange system comprises a second falling film heat exchanger, a second evaporation chamber and a second MVR evaporation system, the second evaporation chamber is connected to the tube side of the second falling film heat exchanger, the second MVR evaporation system is arranged at the output end of the second evaporation chamber; and is connected to the first MVR evaporation system; ammonia-containing steam flows from the top of the distillation tower through the shell side of the first falling film heat exchanger and the second falling film heat exchanger in sequence, exchanges heat with condensed water added in the tube side, and obtains high-concentration ammonia-containing steam that can flow to the brine absorption tower after separating the condensed ammonia water.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemical industry, and in particular to an ammonia distillation system capable of increasing the content of liquid ammonia and a control method thereof. Background Art

[0002] The ammonia-soda process uses limestone and salt as the main raw materials for producing soda ash, and ammonia is used as an intermediate medium for recycling. The recycling of ammonia in the production system is achieved by distillation of hot mother liquor.

[0003] Distillation is a method of separating two substances by using the different boiling points of the two substances and using energy as the driving force of the process to perform partial condensation of mixed steam and partial evaporation of mixed liquid multiple times. It only needs to provide energy and coolant to obtain high-purity products. The operation is simple and mature, and it is an effective means of separating various organic mixtures. In the prior art, the mixed steam of ammonia and part of water in the ammonia distillation tower forms ammonia water vapor, which is stripped from the top or the middle and upper side of the distillation tower and enters the steam compressor. After being pressurized and heated, it flows back to the distillation tower. Although there is no waste of ammonia, due to the reaction equilibrium, a part of the ammonia cannot be stripped, which limits the circulation of ammonia to a certain extent.

[0004] In general distillation operations, the condenser designed at the top of the tower condenses the top steam and partially refluxes it and discharges it from the system. This not only requires cooling water as a cold source, but also wastes the heat of the top steam. Since the top steam temperature and pressure are low, it can generally no longer be used as a heat source. This makes the energy consumption of the entire distillation system huge.

[0005] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art known to those skilled in the art. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an ammonia distillation system which can increase the liquid ammonia content, improve the output ammonia concentration and avoid heat waste.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] An ammonia distillation system capable of increasing the liquid ammonia content.

[0009] It includes a distillation tower, a first falling film heat exchange system and a second falling film heat exchange system connected in sequence;

[0010] The feed inlet of the distillation tower is connected to an external device for conveying materials;

[0011] The first falling film heat exchange system includes a first falling film heat exchanger and a first MVR evaporation system, the first MVR evaporation system includes a first evaporation chamber and a first steam compression device, one end of the first falling film heat exchanger is provided with a condensed water inlet pipeline connected with its tube side, the gas outlet of the distillation tower is connected with the shell side of the first falling film heat exchanger, the first evaporation chamber is connected with the tube side of the first falling film heat exchanger, the first steam compression device is arranged at the output end of the first evaporation chamber; and is connected with the gas inlet of the distillation tower;

[0012] The second falling film heat exchange system comprises a second falling film heat exchanger and a second MVR evaporation system, the second MVR evaporation system comprises a second evaporation chamber and a second steam compression device, one end of the second falling film heat exchanger is provided with a condensate inlet pipe connected with its tube side, the gas outlet of the shell side of the first falling film heat exchanger is connected with the shell side of the second falling film heat exchanger, the second evaporation chamber is connected with the tube side of the second falling film heat exchanger, and the second steam compression device is arranged at the output end of the second evaporation chamber; and is connected with the first steam compression device;

[0013] The ammonia-containing steam flows from the top of the distillation tower through the shell side of the first falling film heat exchanger and the second falling film heat exchanger in sequence, exchanges heat with the condensed water added in the tube side, and after separating the condensed ammonia water, obtains high-concentration ammonia-containing steam that can flow to the brine absorption tower.

[0014] Furthermore, an ammonia water tank is connected between the feed inlet of the distillation tower and the liquid outlet of the upper shell side of the first falling film heat exchanger, and the liquid outlet of the upper shell side of the second falling film heat exchanger is connected to the ammonia water tank.

[0015] Furthermore, both ends of the tube side of the first falling film heat exchanger are connected by a pipeline and are provided with a first circulation pump for circulating the liquid in the tube side;

[0016] The two ends of the tube side of the second falling film heat exchanger are connected through a pipeline and are provided with a second circulation pump for circulating the liquid in the tube side.

[0017] Furthermore, the first steam compression device includes a first steam compressor A and a first steam compressor B, the air outlet of the first evaporation chamber is connected to the air inlet of the first steam compressor A, the air outlet of the first steam compressor A is connected to the air inlet of the first steam compressor B, and the air outlet of the first steam compressor B is connected to the air inlet of the distillation tower, thereby realizing a first-stage falling film and second-stage compression process in the first falling film heat exchange system.

[0018] Furthermore, the second steam compression device includes a second steam compressor, the air outlet of the second evaporation chamber is connected to the air inlet of the second steam compressor, and the air outlet of the second steam compressor is connected to the air inlet of the first steam compressor A, realizing the two-stage falling film three-stage compression process in the second falling film heat exchange system.

[0019] Furthermore, the first MVR evaporation system further includes a condenser and a condensate tank, the liquid outlet of the first steam compressor B is connected to the liquid inlet of the condenser, and the liquid outlet of the condenser is connected to the condensate tank.

[0020] Furthermore, a plate preheater is provided on the connecting pipeline between the distillation tower and the external material conveying equipment, and the plate preheater includes a raw material input port, a material output port, a steam input port, a steam output port and a condensed water output port; the external material conveying equipment is connected to the raw material input port, the feed port of the distillation tower is connected to the material output port, the liquid outlet of the first steam compressor B is connected to the liquid outlet of the condenser on the connecting pipeline, and the steam input port and steam output port of the plate preheater flow through the steam input port and the steam output port to preheat the raw material, and the condensed water output port is provided on the connecting pipeline between the liquid outlet of the condenser and the condensate tank.

[0021] The second technical problem to be solved by the present invention is to provide a control method for an ammonia distillation system which can increase the liquid ammonia content, thereby increasing the output ammonia concentration and avoiding heat waste.

[0022] A control method for an ammonia distillation system capable of increasing the liquid ammonia content comprises the following steps:

[0023] S1. Pump the raw material solution into the distillation tower; at the same time, deliver fresh steam to the distillation tower. After heat exchange, the distillation tower separates the gas and liquid, and the ammonia-containing steam at the top of the tower enters the shell side of the first falling film heat exchanger;

[0024] S2, conveying condensed water with a temperature of more than 75°C to the tube side of the first falling film heat exchanger to exchange heat with the ammonia-containing steam in the shell side of the first falling film heat exchanger. The liquid generated in the shell side after the heat exchange is passed into the ammonia water tank through the bottom of the first falling film heat exchanger, and the remaining ammonia-containing steam enters the shell side of the second falling film heat exchanger; part of the liquid in the tube side enters the first evaporation chamber for heating and vaporization, and the vaporized steam enters the first steam compression device, undergoes a first-stage falling film and a second-stage compression, and the steam temperature is raised to 106°C before entering the distillation tower as fresh steam;

[0025] S3. Condensate with a temperature of more than 70°C is transported to the tube side of the second falling film heat exchanger to exchange heat with the ammonia-containing steam in the shell side of the second falling film heat exchanger. The liquid produced in the shell side after the heat exchange is passed into the ammonia water tank through the bottom of the second falling film heat exchanger, and the remaining high-concentration ammonia-containing steam enters the brine absorption tower; part of the liquid in the tube side enters the second evaporation chamber for heating and vaporization, and the vaporized steam enters the second steam compression device. After the secondary falling film and tertiary compression, the steam temperature is increased to 106°C, and then it is mixed with the gas compressed by the first steam compressor and enters the distillation tower as fresh steam.

[0026] Furthermore, the ammonia water tank transports the liquid to the feed inlet of the distillation tower for further circulation and separation.

[0027] Furthermore, in step S2, the heat exchange time is controlled by controlling the flow rate of condensed water, so that the ammonia-containing steam in the shell side after heat exchange is kept in the first falling film heat exchanger for a sufficiently long time.

[0028] Furthermore, the condensed water after gas-liquid separation in the first evaporation chamber is transported to the tube side of the first falling film heat exchanger, and then the condensed water is circulated and transported in the first falling film heat exchanger by the first circulation pump;

[0029] The condensed water after gas-liquid separation in the second evaporation chamber is transported to the tube side of the second falling film heat exchanger, and then the condensed water is circulated and transported in the second falling film heat exchanger by the second circulation delivery pump.

[0030] The beneficial effects of the present invention are:

[0031] The present invention sets a first falling film heat exchange system and a second falling film heat exchange system and sequentially connects with a distillation tower, so that ammonia-containing steam sequentially exchanges heat with condensed water introduced into the tube side of the first falling film heat exchanger and the second falling film heat exchanger, and obtains high-concentration ammonia-containing steam that can flow to a brine absorption tower after separating the condensed ammonia water. At the same time, the higher-temperature water in the tube side of the first falling film heat exchanger and the second falling film heat exchanger is steam-recompressed to 106°C through the first MVR evaporation system and the second MVR evaporation system and then introduced into the distillation tower, and heat is recovered on the basis of increasing the concentration of ammonia-containing steam, which can greatly reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 Schematic diagram of the structure of an ammonia distillation system capable of increasing the liquid ammonia content in an embodiment of the present invention; DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0035] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0037] like Figure 1 An ammonia distillation system for increasing the liquid ammonia content is shown, comprising a distillation tower 10, a first falling film heat exchange system 20 and a second falling film heat exchange system 30 connected in sequence; the present invention adopts the first falling film heat exchange system 20 and the second falling film heat exchange system 30 to recover the heat from the top of the tower, and the bottom liquid of the tower is flashed twice through the original device to recover the heat, and the ammonia and carbon dioxide vapor enters the absorption tower of the original device for recovery, and the ammonia content after deammoniation is no higher than the level of the original device.

[0038] The feed inlet of the distillation tower 10 is connected to the external material conveying device 001;

[0039] The first falling film heat exchange system 20 includes a first falling film heat exchanger 21 and a first MVR evaporation system, the first MVR evaporation system includes a first evaporation chamber 22 and a first steam compression device 23, one end of the first falling film heat exchanger 21 is provided with a condensed water inlet pipe 002 connected with its tube side, the gas outlet of the distillation tower 10 is connected with the shell side of the first falling film heat exchanger 21, the first evaporation chamber 22 is connected with the tube side of the first falling film heat exchanger 21, and the first steam compression device 23 is arranged at the output end of the first evaporation chamber 22; and is connected with the gas inlet of the distillation tower 10;

[0040] The second falling film heat exchange system 30 includes a second falling film heat exchanger 31 and a second MVR evaporation system, the second MVR evaporation system includes a second evaporation chamber 32 and a second steam compression device 33, one end of the second falling film heat exchanger 31 is provided with a condensed water inlet pipe 003 connected with its tube side, the gas outlet of the shell side of the first falling film heat exchanger 21 is connected with the shell side of the second falling film heat exchanger 31, the second evaporation chamber 32 is connected with the tube side of the second falling film heat exchanger 31, and the second steam compression device 33 is arranged at the output end of the second evaporation chamber 32; and is connected with the first steam compression device 23;

[0041] The ammonia-containing steam flows from the top of the distillation tower 10 through the shell side of the first falling film heat exchanger 21 and the second falling film heat exchanger 31 in sequence, exchanges heat with the condensed water added in the tube side, and separates the condensed ammonia water to obtain high-concentration ammonia-containing steam that can flow to the brine absorption tower. In addition, in order to facilitate the actual process operation requirements and realize the switching of process operations such as distillation, falling film heat exchange, and mechanical compression, control valves are provided by default on the pipelines in the system.

[0042] During specific use, the external material conveying equipment preheats the raw material with an ammonia content of about 7.3% and a temperature of 88°C to 101°C through the plate preheater 26, and then conveys it to the distillation tower 10 through the feed port. At the same time, the external fresh steam is conveyed to the distillation tower 10 through the air inlet by the external equipment. The temperature of the fresh steam is 106°C. The fresh steam exchanges heat with the raw material, and the ammonia is separated into the steam and conveyed to the shell side of the first falling film heat exchanger 21. Condensed water with a temperature of >76°C is added to the tube side of the first falling film heat exchanger 21, and the liquid is circulated in the first falling film heat exchanger 21 by the first circulating conveying pump 211. The temperature of the ammonia-containing steam at the outlet of the distillation tower 10 here is 84°C, and it exchanges heat with the liquid with a temperature of 76°C circulated in the shell side. The 84°C ammonia-containing steam is condensed, and the 76°C hot water is converted into saturated water vapor at 76°C. The temperature difference between the cold and hot fluids is 8°C, and the ammonia-containing steam with a concentration of 41.2% and a temperature of 76°C is obtained, which is then passed into the shell side of the second falling film heat exchanger 31, and condensed water with a temperature of more than 70°C is added in the tube side of the second falling film heat exchanger 31. The liquid is circulated and transported in the second falling film heat exchanger 31 by the second circulating delivery pump 311, and heat is exchanged with the ammonia-containing steam with a temperature of 76°C and a concentration of 41.2%, and the 76°C ammonia-containing steam is converted into saturated water vapor at 70°C. The temperature difference between the cold and hot fluids is 6°C, and the ammonia-containing steam with a concentration of 49.9% and a temperature of 70°C is obtained, which is then passed into the pipeline and transported to the brine absorption tower. The present invention allows the first falling film heat exchanger 21 and the second falling film heat exchanger 31 to act simultaneously, so that less ammonia gas is condensed into an ammonia solution through the liquid outlet at the bottom of the upper shell of the first falling film heat exchanger 21 or the second falling film heat exchanger 31 and enters the ammonia water tank 40, thereby increasing the ammonia content of the ammonia-containing vapor entering the brine absorption tower. At this time, the ammonia water tank 40 transports the ammonia-containing liquid to the feed port of the distillation tower 10 again for separation.

[0043] It should be noted here that the following reactions are involved in the shell side of the falling film heat exchanger:

[0044] CO2+H2O→H2CO3 (1)

[0045] NH3+H2O→NH3.H2O (2)

[0046] H2CO3+2NH3.H2O→(NH4)2CO3 (3)

[0047] In ammonia-containing steam, because NH4 + and CO3 2- After double hydrolysis, most of it will become CO2 and NH3. CO2 has a large solubility in ammonia water and will not overflow, so a small amount of (NH4)2CO3 will be generated. The temperature of the ammonia-containing steam at the outlet of the distillation tower 10 of the present invention is 84°C, so the heat exchange must be maintained at a relatively high temperature. The higher the temperature, the more obvious the decomposition of carbonic acid. Therefore, maintaining a relatively high temperature for heat exchange can result in less carbonic acid intermediates. Therefore, in the first falling film heat exchange system 20, more water can be condensed instead of participating in the above reaction. On this basis, the heat exchange efficiency in the first falling film heat exchanger 21 can be adjusted by adjusting the flow rate of the condensed water introduced into the tube side of the first falling film heat exchanger 21 to ensure that sufficient water is condensed and the concentration of the ammonia-containing steam entering the shell side of the second falling film heat exchanger 31 is increased.

[0048] The present invention sets a first falling film heat exchange system 20 and a second falling film heat exchange system 30 and connects them to the distillation tower 10 in sequence, so that the ammonia-containing steam exchanges heat with the condensed water introduced into the shell side of the first falling film heat exchanger 21 and the second falling film heat exchanger 31 in sequence, and the condensed ammonia water is separated to obtain high-concentration ammonia-containing steam that can flow to the brine absorption tower. At the same time, the higher temperature water in the tube side of the first falling film heat exchanger 21 and the second falling film heat exchanger 31 is steam-recompressed to 106°C through the first MVR evaporation system and the second MVR evaporation system and then introduced into the distillation tower 10, and heat is recovered on the basis of increasing the concentration of ammonia-containing steam, which can greatly reduce production costs. Specifically, the first falling film heat exchanger 21 needs to be supplemented with about 18.73 tons / hour of condensed water > 75 degrees, the second falling film heat exchanger 31 needs to be supplemented with about 7.9 tons / hour of condensed water > 70 degrees, and the first steam compression device 23 and the second steam compression device 33 need to be supplemented with about 2.5 tons / hour of condensed water. Calculated at 0.69 yuan / KWh for electricity and 211.47 yuan / ton for steam, the average system cost per ton of raw materials in this application is 20.73 yuan / ton, including the entire process from feeding to discharging. The power consumption per ton of raw materials increases by less than 9.4KW (-6.49 yuan), the condensed water increases by 0.12 tons (-1.2 yuan), and the steam is saved by 0.12T (25.38 yuan). The operating cost per ton of raw materials is saved by 17.69 yuan, and the annual income is about 33.96 million yuan.

[0049] The specific system design technical parameters are shown in Table 1 below:

[0050] Serial number Technical indicators Design parameters 1 Equipment height ≤30m 2 Raw material feed concentration <![CDATA[Content is about 7.1% (by NH3 content)]]> 3 Feed temperature ≥75℃ 4 Feed rate 240T / h 5 Evaporation About 26.619T / h 6 Stripping temperature 77～106℃

[0051] A portion of the liquid with a temperature of >76°C in the upper tube side of the first falling film heat exchanger 21 enters the first evaporation chamber 22 for heating and vaporization, and the vaporized steam enters the first steam compression device 23 to be compressed to a steam temperature of 106°C and enters the distillation tower 10 as fresh steam for reuse, while a portion of the liquid with a temperature of >70°C in the upper tube side of the second falling film heat exchanger 31 enters the second evaporation chamber 32 for heating and vaporization, and the vaporized steam enters the second steam compression device 33 to be compressed to a steam temperature of 106°C and enters the distillation tower 10 as fresh steam for reuse. Through multiple evaporation and compression, excess water in the first falling film heat exchanger 21 and the second falling film heat exchanger 31 is better utilized, reducing the use of primary steam.

[0052] An ammonia water tank 40 is connected between the feed port of the distillation tower 10 and the upper shell side liquid outlet of the first falling film heat exchanger 21, and the upper shell side liquid outlet of the second falling film heat exchanger 31 is connected to the ammonia water tank 40. An ammonia water pump 41 is provided on the connecting pipeline between the ammonia water tank 40 and the distillation tower 10, for pumping the liquid in the ammonia water tank 40 into the distillation tower 10.

[0053] The two ends of the tube side of the first falling film heat exchanger 21 are connected by a pipeline and are provided with a first circulation pump 211 for circulating the liquid in the tube side; the condensed water after gas-liquid separation in the first evaporation chamber 22 is transported to the tube side of the first falling film heat exchanger 21, and then the condensed water is circulated and transported in the first falling film heat exchanger 21 by the first circulation pump 211; the two ends of the tube side of the second falling film heat exchanger 31 are connected by a pipeline and are provided with a second circulation pump 311 for circulating the liquid in the tube side. The condensed water after gas-liquid separation in the second evaporation chamber 32 is transported to the tube side of the second falling film heat exchanger 31, and then the condensed water is circulated and transported in the second falling film heat exchanger 31 by the second circulation pump 311.

[0054] The first steam compression device 23 includes a first steam compressor A231 and a first steam compressor B232. The air outlet of the first evaporation chamber 22 is connected to the air inlet of the first steam compressor A231, the air outlet of the first steam compressor A231 is connected to the air inlet of the first steam compressor B232, and the air outlet of the first steam compressor B232 is connected to the air inlet of the distillation tower 10, thereby realizing a first-stage falling film and second-stage compression process in the first falling film heat exchange system 20.

[0055] The second steam compression device 33 includes a second steam compressor 331. The air outlet of the second evaporation chamber 32 is connected to the air inlet of the second steam compressor 331. The air outlet of the second steam compressor 331 is connected to the air inlet of the first steam compressor A231, realizing the process flow of two-stage falling film three-stage compression in the second falling film heat exchange system 30.

[0056] The first MVR evaporation system further includes a condenser 24 and a condensate tank 25 . The liquid outlet of the first steam compressor B232 is connected to the liquid inlet of the condenser 24 , and the liquid outlet of the condenser 24 is connected to the condensate tank 25 .

[0057] A plate preheater 26 is also provided on the connecting pipeline between the distillation tower 10 and the external material conveying equipment 001, and the plate preheater 26 includes a raw material input port, a material output port, a steam input port, a steam output port and a condensed water output port; the external material conveying equipment 001 is connected to the raw material input port, the feed port of the distillation tower 10 is connected to the material output port, the liquid outlet of the first steam compressor B232 is connected to the liquid outlet of the condenser 24 on the connecting pipeline, and the steam flows through the steam input port and the steam output port of the plate preheater 26 to preheat the raw material, and the condensed water output port is arranged on the connecting pipeline between the liquid outlet of the condenser 24 and the condensate tank 25.

[0058] A control method for an ammonia distillation system capable of increasing the liquid ammonia content comprises the following steps:

[0059] S1, pumping the raw material solution into the distillation tower 10; at the same time, conveying fresh steam to the distillation tower 10, the distillation tower 10 separates the gas and liquid after heat exchange, and the ammonia-containing steam at the top of the tower enters the shell side of the first falling film heat exchanger 21;

[0060] S2. Condensate with a temperature of more than 75°C is transported to the tube side of the first falling film heat exchanger 21 to exchange heat with the ammonia-containing steam in the shell side of the first falling film heat exchanger 21. The liquid generated in the shell side after the heat exchange is passed into the ammonia water tank 40 through the bottom of the first falling film heat exchanger 21, and the remaining ammonia-containing steam enters the shell side of the second falling film heat exchanger 31; part of the liquid in the tube side enters the first evaporation chamber 22 for heating and vaporization, and the vaporized steam enters the first steam compression device 23, and after the first-stage falling film and second-stage compression, the steam temperature is increased to 106°C and then enters the distillation tower 10 as fresh steam; the heat exchange time is controlled by controlling the flow rate of condensed water, so that the ammonia-containing steam in the shell side after heat exchange is reserved in the first falling film heat exchanger 21 for a sufficiently long time.

[0061] S3, convey condensed water with a temperature of more than 70°C to the tube side of the second falling film heat exchanger 31, and exchange heat with the ammonia-containing steam in the shell side of the second falling film heat exchanger 31. After the heat exchange, the liquid generated in the shell side passes through the bottom of the second falling film heat exchanger 31 and enters the ammonia water tank 40, and the remaining high-concentration ammonia-containing steam enters the brine absorption tower; part of the liquid in the tube side enters the second evaporation chamber 32 for heating and vaporization, and the vaporized steam enters the second steam compression device 33. After the steam temperature is increased to 106°C by the second-stage falling film and the third-stage compression, it is mixed with the gas compressed by the first steam compressor and enters the distillation tower 10 as fresh steam. The ammonia water tank 40 conveys the liquid to the feed port of the distillation tower 10 for circulation and separation again.

[0062] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An ammonia distillation system capable of increasing the content of liquid ammonia, characterized in that: It includes a distillation tower, a first falling film heat exchange system and a second falling film heat exchange system connected in sequence; The feed inlet of the distillation tower is connected to an external device for conveying materials; The first falling film heat exchange system comprises a first falling film heat exchanger and a first MVR evaporation system, the first MVR evaporation system comprises a first evaporation chamber and a first steam compression device, one end of the first falling film heat exchanger is provided with a condensed water inlet pipeline connected with its tube side, the gas outlet of the distillation tower is connected with the shell side of the first falling film heat exchanger, the first evaporation chamber is connected with the tube side of the first falling film heat exchanger, and the first steam compression device is arranged at the output end of the first evaporation chamber and is connected with the gas inlet of the distillation tower; The second falling film heat exchange system comprises a second falling film heat exchanger and a second MVR evaporation system, the second MVR evaporation system comprises a second evaporation chamber and a second steam compression device, one end of the second falling film heat exchanger is provided with a condensed water inlet pipe connected with its tube side, the gas outlet of the shell side of the first falling film heat exchanger is connected with the shell side of the second falling film heat exchanger, the second evaporation chamber is connected with the tube side of the second falling film heat exchanger, and the second steam compression device is arranged at the output end of the second evaporation chamber and is connected with the first steam compression device; The ammonia-containing vapor flows from the top of the distillation tower through the shell sides of the first falling film heat exchanger and the second falling film heat exchanger in sequence, exchanges heat with the condensed water added in the tube sides thereof, separates the condensed ammonia water, and obtains high-concentration ammonia-containing vapor that can flow to the brine absorption tower; an ammonia water tank is connected between the feed port of the distillation tower and the liquid outlet of the upper shell side of the first falling film heat exchanger, and the liquid outlet of the upper shell side of the second falling film heat exchanger is connected to the ammonia water tank, and the ammonia water tank transports the liquid containing ammonia to the feed port of the distillation tower again for separation.

2. The ammonia distillation system for increasing the liquid ammonia content according to claim 1, characterized in that: The two ends of the tube side of the first falling film heat exchanger are connected by a pipeline and are provided with a first circulation pump for circulating the liquid in the tube side; The two ends of the tube side of the second falling film heat exchanger are connected by a pipeline and are provided with a second circulation pump for circulating the liquid in the tube side.

3. An ammonia distillation system capable of increasing the liquid ammonia content according to claim 1 or 2, characterized in that: The first steam compression device includes a first steam compressor A and a first steam compressor B. The air outlet of the first evaporation chamber is connected to the air inlet of the first steam compressor A, the air outlet of the first steam compressor A is connected to the air inlet of the first steam compressor B, and the air outlet of the first steam compressor B is connected to the air inlet of the distillation tower, so that a first-stage falling film and two-stage compression process is realized in the first falling film heat exchange system.

4. The ammonia distillation system for increasing the liquid ammonia content according to claim 3, characterized in that: The second steam compression device includes a second steam compressor, the air outlet of the second evaporation chamber is connected to the air inlet of the second steam compressor, and the air outlet of the second steam compressor is connected to the air inlet of the first steam compressor A, realizing a two-stage falling film three-stage compression process in the second falling film heat exchange system.

5. The ammonia distillation system for increasing the liquid ammonia content according to claim 4, characterized in that: The first MVR evaporation system further includes a condenser and a condensate tank. The liquid outlet of the first steam compressor B is connected to the liquid inlet of the condenser, and the liquid outlet of the condenser is connected to the condensate tank.

6. The ammonia distillation system capable of increasing the liquid ammonia content according to claim 5, characterized in that: A plate preheater is also provided on the connecting pipeline between the distillation tower and the external material conveying equipment, and the plate preheater includes a raw material input port, a material output port, a steam input port, a steam output port and a condensed water output port; the external material conveying equipment is connected to the raw material input port, the feed port of the distillation tower is connected to the material output port, the plate preheater is provided on the connecting pipeline between the liquid outlet of the first steam compressor B and the liquid inlet of the condenser, the liquid outlet of the first steam compressor B is connected to the steam input port of the plate preheater, the steam output port of the plate preheater is connected to the liquid inlet of the condenser to preheat the raw material, and the condensed water output port is provided on the connecting pipeline between the liquid outlet of the condenser and the condensate tank.

7. A control method for an ammonia distillation system capable of increasing the liquid ammonia content, characterized in that: The steps include: S1. Pump the raw material solution into the distillation tower; at the same time, deliver fresh steam to the distillation tower. After heat exchange, the distillation tower separates the gas and liquid, and the ammonia-containing steam at the top of the tower enters the shell side of the first falling film heat exchanger; S2, conveying condensed water with a temperature of more than 75°C to the tube side of the first falling film heat exchanger to exchange heat with the ammonia-containing steam in the shell side of the first falling film heat exchanger, and the liquid generated in the shell side after the heat exchange is passed into the ammonia water tank through the bottom of the first falling film heat exchanger, and the remaining ammonia-containing steam enters the shell side of the second falling film heat exchanger; part of the liquid in the tube side of the first falling film heat exchanger enters the first evaporation chamber for heating and vaporization, and the vaporized steam enters the first steam compression device, undergoes a first-stage falling film and a second-stage compression, and the steam temperature is raised to 106°C, and then enters the distillation tower as fresh steam; S3, convey condensed water with a temperature of more than 70°C to the tube side of the second falling film heat exchanger to exchange heat with the ammonia-containing steam in the shell side of the second falling film heat exchanger. After the heat exchange, the liquid generated in the shell side passes through the bottom of the second falling film heat exchanger and enters the ammonia water tank, and the remaining high-concentration ammonia-containing steam enters the brine absorption tower; part of the liquid in the tube side of the second falling film heat exchanger enters the second evaporation chamber for heating and vaporization, and the vaporized steam enters the second steam compression device. The steam compressed by the second steam compression device enters the first steam compression device, and after the steam temperature is increased to 106°C by the second-stage falling film and third-stage compression, it is mixed with the gas compressed by the first steam compressor and enters the distillation tower as fresh steam; The ammonia tank transports the liquid to the feed port of the distillation tower for further circulation and separation.

8. The control method of an ammonia distillation system capable of increasing the liquid ammonia content according to claim 7, characterized in that: The condensed water after gas-liquid separation in the first evaporation chamber is transported to the tube side of the first falling film heat exchanger, and then the condensed water is circulated and transported in the first falling film heat exchanger by the first circulation pump; The condensed water after gas-liquid separation in the second evaporation chamber is transported to the tube side of the second falling film heat exchanger, and then the condensed water is circulated and transported in the second falling film heat exchanger by the second circulation pump.

Images