Method and system for recovering heat energy of melamine tail gas

Abstract

The invention relates to the technical field of heat energy recovery, in particular to a heat energy recovery method and system for melamine tail gas. According to the heat energy recovery method for the melamine tail gas, desorbed gas obtained by a desorption tower is mixed with carbonized ammonia water and then subjected to first heat exchange with a first liquid-phase working medium, heat in the desorbed gas is recovered, the first liquid-phase working medium is changed into a gas phase from a liquid phase, after compression and pressurization heating, second heat exchange is conducted, heat exchange with desorption liquid obtained by the desorption tower is conducted, and the heat energy of the first liquid-phase working medium is recovered. Heat in the first gas-phase working medium is absorbed, a cooled first liquid-phase working medium and heat exchange steam are obtained, the cooled first liquid-phase working medium enters the first heat exchange process to be recycled after being decompressed, and part of the heat exchange steam enters the desorption tower to be circulated. The utilization rate of water resources can be increased; by means of phase change, heat absorption and heat release of a working medium, heat transfer efficiency is improved, heat energy recovery rate is increased, energy consumption of the whole recovery system is reduced, and productivity is not affected by the size of equipment.

Description

Technical Field

[0001] The invention relates to the technical field of heat recovery, and in particular to a method and system for recovering heat from melamine tail gas. Background Art

[0002] Industrial waste heat resources in my country account for 17%-67% of the total fuel consumption, and the recovery rate can reach 60%, especially in the steel industry, chemical industry, cement industry, building materials industry and petroleum industry, etc. However, the utilization of waste heat resources in various industries has not been optimized and improved.

[0003] Industrial waste heat resources can be divided into many different types, such as high-temperature flue gas waste heat, cooling medium waste heat, exhaust gas waste heat, chemical reaction waste heat, etc. In the existing melamine tail gas device, Figure 3 As shown, the heat of water vapor is used to desorb ammonia and carbon dioxide in the process liquid of the desorption tower, pure water is obtained at the bottom of the tower, and desorbed gas is obtained at the top of the tower. The heat in the gas phase of the desorption tower is used to cool and condense the desorbed gas using air coolers and other equipment, so that the heat is lost to the air and cannot be recovered. The liquid water needs to be sent to the outside for reuse. However, the desorption tower in the melamine tail gas device requires a large amount of water vapor to desorb the process liquid. The heat of the two cannot match, resulting in high energy consumption of the overall device. The air cooler uses air to cool the desorbed gas, and the heat transfer efficiency is low. In addition, the air cooler is large in size, which limits the increase in the production capacity of the device.

[0004] Therefore, how to adjust and optimize the heat energy recovery method and system of melamine tail gas to improve the heat energy recovery rate and reduce the energy consumption of the overall recovery system is a technical problem that urgently needs to be solved in this field. Summary of the invention

[0005] In view of this, the present invention provides a method for recovering heat energy of melamine tail gas, so as to improve the heat energy recovery rate of melamine tail gas and reduce the energy consumption of the overall recovery system.

[0006] Correspondingly, the present invention also provides a heat energy recovery system for melamine tail gas used in the above method.

[0007] The present invention provides a method for recovering heat energy from melamine tail gas, comprising the following steps:

[0008] (1) treating melamine tail gas in a carbon dioxide absorption tower and / or a carbon dioxide scrubbing tower to obtain methylammonium liquid, and sending the methylammonium liquid to a carbon separation tower to separate carbon dioxide to obtain carbonized ammonia water;

[0009] (2) sending part of the carbonized ammonia water in step (1) into a desorption tower after heat exchange and decompression, and performing desorption by using water vapor to obtain desorbed gas and desorbed liquid;

[0010] (3) mixing the desorbed gas obtained in step (2) with the remaining portion of the carbonized ammonia water in step (1) and performing a first heat exchange with the first liquid phase working medium to obtain desorbed gas condensate and the first gas phase working medium respectively;

[0011] (4) compressing the first gas phase working medium and performing a second heat exchange with part of the desorption liquid from the desorption tower to obtain a cooled first liquid phase working medium and heat exchange steam respectively; returning part of the heat exchange steam to step (2) as water vapor for desorption; and returning the cooled first liquid phase working medium to step (3) for the first heat exchange after being depressurized.

[0012] In some optional embodiments, in step (4), the cooled first liquid phase working medium is sequentially condensed and decompressed before being returned to the first heat exchange process;

[0013] In some optional embodiments, step (4) further comprises the step of adding water to the partial desorption liquid;

[0014] In some optional embodiments, the method further includes the step of compressing the remaining portion of the heat exchange steam, reducing the temperature, and then sending it out;

[0015] In step (4), the cooled first liquid phase working medium is condensed, decompressed to 0.05MPa-0.5MPa, 20°C-50°C, and then returned to the first heat exchange process;

[0016] In some optional embodiments, the heat exchange steam is compressed and cooled to

[0017] 0.25MPa-1.0MPa, 127℃-180℃ before delivery.

[0018] In some optional embodiments, in step (4), the cooled first liquid phase working medium is condensed, decompressed to 0.05MPa-0.5MPa, 20°C-50°C, and then returned to the first heat exchange process;

[0019] In some optional embodiments, the process of reducing the temperature of the heat exchange steam further includes a water replenishment process;

[0020] In some optional embodiments, the process of reducing the temperature of the remaining portion of the heat exchange steam also includes a process in which the temperature of the make-up water in the make-up water process is 127-180° C. and the pressure is 0.25 MPa-1.0 MPa.

[0021] In some optional embodiments, the mass ratio of the carbonized ammonia water in step (2) to the carbonized ammonia water in step (1) is 70-79%;

[0022] In some optional embodiments, the mass ratio of water vapor to carbonized ammonia water in step (2) is (25-35):100;

[0023] In some optional embodiments, the mass ratio of the desorbed gas and the desorbed liquid obtained in step (2) is (25-35):100;

[0024] In some optional embodiments, the mass ratio of the desorbed gas obtained in step (2) to the remaining portion of the carbonized ammonia water in step (3) is (0.8-0.9):1;

[0025] In some optional embodiments, in step (3), the mass ratio of the desorbed gas to the first liquid phase working fluid is (25-35): (230-500);

[0026] In some optional embodiments, in step (3), the mass ratio of the total mass of the desorbed gas mixed with the remaining portion of the carbonized ammonia water to the first liquid phase working fluid is 1:(3.4-7.4);

[0027] In some optional embodiments, in step (4), the mass ratio of the partial desorption liquid to the total desorption liquid is 25-35%;

[0028] In some optional embodiments, the mass ratio of the supplementary water added to the partial desorption liquid to the partial desorption liquid is (1-42): (25-35);

[0029] In some optional embodiments, the mass ratio of the supplementary water added in the process of replenishing water during the process of reducing the temperature of the remaining part of the heat exchange steam to the remaining part of the heat exchange steam is 1: (10-30).

[0030] In some optional embodiments, in step (2), the temperature of part of the carbonized ammonia water after heat exchange and decompression is 93-130° C. and the pressure is 0.22-0.6 MPa;

[0031] In some optional embodiments, in step (3), the temperature of the remaining portion of the carbonized ammonia water is 150° C.-180° C., and the pressure is 1.5 MPa-2.5 MPa;

[0032] In some optional embodiments, the mass composition of the carbonized ammonia water in step (1) includes: NH3: 4%-12%, CO2: 1%-8%, H2O: 80%-95%.

[0033] In some optional embodiments, in step (2), the temperature of the desorbed gas is 90°C-126°C and the pressure is 0.15-0.55 MPa;

[0034] In some optional embodiments, the temperature of the desorption liquid is 110°C-155°C, and the pressure is 0.15-0.55 MPa;

[0035] In some optional embodiments, the mass composition of the desorbed gas includes: NH3: 35%-55%, CO2: 5%-20%, H2O: 25%-45%;

[0036] In some optional embodiments, the temperature of the supplementary water added to the partial desorption liquid is 110° C.-155° C., and the pressure is 0.15-0.55 MPa.

[0037] In some optional embodiments, in step (3), the temperature of the first liquid phase working fluid is 20° C.-50° C. and the pressure is 0.05-0.5 MPa;

[0038] In some optional embodiments, the temperature of the first gas phase working fluid is 20-95° C. and 0.05-0.5 MPa;

[0039] In some optional embodiments, the temperature of the desorbed condensate is 30°C-60°C and the pressure is 0.15-0.55 MPa;

[0040] In some optional embodiments, the mass composition of the desorbed condensate includes: NH3: 22%-40%, CO2: 5%-15%, H2O: 45%-65%.

[0041] In some optional embodiments, in step (4), the first gas phase working fluid is compressed to 210-283° C. and 0.8-1.9 MPa before being fed into the second heat exchanger;

[0042] In some optional embodiments, the temperature of the cooling first liquid phase working fluid is 115-157° C. and the pressure is 0.8-1.9 MPa;

[0043] In some optional embodiments, the heat exchange steam sent to the desorption tower has a temperature of 110-155° C. and a pressure of 0.15-0.55 MPa.

[0044] The present invention also provides a heat recovery system for the melamine tail gas described above, characterized in that it comprises:

[0045] A carbon separation tower, the carbon separation tower comprising a first liquid outlet for melamine tail gas and carbonized ammonia water and a second liquid outlet for carbonized ammonia water;

[0046] A desorption tower, the desorption tower comprising a first liquid inlet for carbonized ammonia water, a desorption gas outlet and a desorption liquid outlet; a water vapor inlet; wherein the first liquid inlet for carbonized ammonia water is connected to the first liquid outlet for carbonized ammonia water;

[0047] A first heat exchanger, wherein the first heat exchanger comprises a first feed inlet and a desorbed gas condensate outlet, a first liquid phase working medium feed inlet and a first gas phase working medium outlet; wherein the first feed inlet is connected to the desorbed gas outlet of the desorber and the second outlet of the carbonized ammonia water of the carbon separation tower;

[0048] A first compression device, the first compression device comprising a first gas-phase working medium feed port and a pressurized first gas-phase working medium discharge port; wherein the first gas-phase working medium feed port is connected to the first gas-phase working medium discharge port of the first heat exchanger;

[0049] A second heat exchanger, wherein the second heat exchanger comprises a desorption liquid inlet and a first steam outlet, a pressurized first gas phase working medium feed inlet and a cooled first liquid phase working medium outlet; wherein the desorption liquid inlet is connected to the desorption liquid outlet of the desorption tower; the first steam outlet is connected to the desorption steam inlet; and the pressurized first gas phase working medium feed inlet is connected to the pressurized first gas phase working medium outlet;

[0050] The pressure reducing valve comprises a pressure reducing valve feed port and a pressure reducing valve discharge port, wherein the pressure reducing valve feed port is connected to the outlet of the cooling first liquid phase working medium; and the pressure reducing valve discharge port is connected to the first liquid phase working medium feed port of the first heat exchanger.

[0051] In some optional embodiments, the method further comprises: a cooling device, wherein the feed inlet of the pressure reducing valve is connected to the outlet of the cooling first liquid phase working medium through the cooling device; the cooling device comprises a feed inlet of the cooling device and a discharge outlet of the cooling device, wherein the outlet of the cooling first liquid phase working medium is connected to the feed inlet of the cooling device, and the discharge outlet of the cooling device is connected to the feed inlet of the pressure reducing valve;

[0052] In some optional embodiments, the second compression device further comprises a second compression device, wherein the second compression device comprises a second compression device feed port and a second compression device discharge port;

[0053] The second heat exchanger includes a second steam outlet; wherein the second compression device feed port is connected to the second heat exchanger including the second steam outlet;

[0054] A cooling device, wherein the cooling device comprises a cooling device feed port and a cooling device discharge port; the cooling device comprises a cooling device feed port connected to a second compression device discharge port;

[0055] In some optional embodiments, a water replenishment port is further provided between the desorption liquid inlet of the second heat exchanger and the desorption liquid outlet of the desorption tower;

[0056] In some optional embodiments, a water supply port is further provided between the discharge port of the second compression device and the feed port of the cooling device.

[0057] In some optional embodiments, the first heat exchanger further includes an initial liquid-phase working fluid injection port.

[0058] It can be understood that the initial liquid-phase working fluid injection port is used to inject liquid-phase working fluid when the system is started, or to replenish the first liquid-phase working fluid when the first liquid-phase working fluid of the system is consumed.

[0059] In some optional embodiments, the first heat exchanger is at least one of an evaporator and a condenser;

[0060] In some optional embodiments, the second heat exchanger is at least one of an evaporator and a condenser;

[0061] In some optional embodiments, the second compression device is a steam compressor.

[0062] In some optional embodiments, the first gas phase working fluid material is selected from at least one of dichloromethane and hydrofluorocarbon compounds.

[0063] In some optional embodiments, the hydrofluorocarbon compounds include but are not limited to HFO-1336mzz(Z), HFC-245fa, and HFC-236fa.

[0064] The ammonia-carbon separation of the present invention comprises the following steps: melamine tail gas is subjected to carbon dioxide absorption treatment by using carbonized ammonia water and concentrated ammonia water through a carbon dioxide absorption tower and a carbon dioxide washing tower to obtain methylammonium liquid; the methylammonium liquid is pressurized to above 1.8MPa, preheated to above 140°C and then flashed to obtain a gas phase and a liquid phase, the gas phase and the liquid phase are respectively sent to a carbon separation tower, a desorption liquid from a desorption tower with a temperature not higher than 126°C is added to the middle of the carbon separation tower, a desorption liquid cooled to not higher than 55°C is added to the top, carbon dioxide separation treatment is carried out under the condition of 1.8MPa-4.0MPa, carbon dioxide with an ammonia content of less than 100ppm is obtained at the top of the tower, and carbonized ammonia water with an ammonia / carbon mass ratio of 4-10:1 is obtained at the bottom of the tower, the carbonized ammonia water is cooled to 80-90°C by heat exchange with the feed of the carbon separation tower and then divided into two streams, one stream enters the desorption tower, and the other stream is mixed with the desorption gas of the desorption tower and heat exchanged with the first liquid phase working medium.

[0065] In the present invention, the amount of carbonized ammonia water generated by 1 ton of melamine tail gas is 4-5 tons.

[0066] The technical solution of the present invention has the following advantages:

[0067] 1. The heat energy recovery method of melamine tail gas provided by the present invention comprises the following steps: (1) treating melamine tail gas through a carbon dioxide absorption tower and / or a carbon dioxide washing tower to obtain methylammonium liquid, and sending the methylammonium liquid into a carbon separation tower for carbon dioxide separation to obtain carbonized ammonia water; (2) sending part of the carbonized ammonia water in step (1) into a desorption tower after heat exchange and decompression, and desorbing by water vapor to obtain desorbed gas and desorbed liquid; (3) mixing the desorbed gas obtained in step (2) with the remaining part of the carbonized ammonia water in step (1) and then performing a first heat exchange with a first liquid phase working medium to respectively obtain desorbed gas condensate and a first gas phase working medium; (4) compressing the first gas phase working medium and performing a second heat exchange with part of the desorbed liquid from the desorption tower to respectively obtain a cooled first liquid phase working medium and heat exchange steam; returning part of the heat exchange steam to step (2) as water vapor for desorption; and returning the cooled first liquid phase working medium to step (3) after decompression, performing a first heat exchange.

[0068] The present invention utilizes the desorbed gas obtained by desorption in the desorption tower to be mixed with carbonized ammonia water and then subjected to a first heat exchange with a first liquid phase working medium, so that the heat in the desorbed gas can be recovered. At the same time, the first liquid phase working medium is changed from liquid phase to gas phase, and after being compressed, pressurized and heated, a second heat exchange is performed to exchange heat with the desorption liquid obtained in the desorption tower, so as to absorb the heat in the first gas phase working medium and obtain cooled first liquid phase working medium and heat exchange steam. After the cooled first liquid phase working medium is depressurized, it enters the first heat exchange process for recycling, and part of the heat exchange steam enters the desorption tower for circulation.

[0069] In the whole heat energy recovery process, the present invention utilizes the desorption liquid to absorb heat to generate water vapor which is circulated in the desorption tower to realize the water-water vapor-water cycle. There is no need to send the water in the device outward, which can improve the utilization rate of water resources. At the same time, the phase change of the first liquid phase working medium, the first gas phase working medium and the cooling first liquid phase working medium is utilized to absorb and release heat, so as to improve the heat transfer efficiency, improve the heat energy recovery rate, reduce the energy consumption of the overall recovery system, and the production capacity is not affected by the size of the equipment.

[0070] 2. The present invention provides a method for recovering heat energy from melamine tail gas. The remaining carbonized ammonia water provides water to absorb ammonia and carbon dioxide contained in the desorbed gas to maintain the water balance of the entire device.

[0071] 3. The present invention provides a method for recovering heat energy from melamine tail gas. Water is added to the liquid phase inlet of the second heat exchanger to absorb more heat. The obtained water vapor can be directly sent out, thereby reducing overall energy consumption and increasing economic added value. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0073] Figure 1 The recovery system of embodiment 1 of the present invention;

[0074] Figure 2 The recovery system of Embodiment 2 to Embodiment 5 of the present invention;

[0075] Figure 3 It is the recovery system of Comparative Example 1 of the present invention;

[0076] Description of reference numerals:

[0077] Evaporator 100, compressor 101, condenser 102, desorption tower 103 of ammonia-carbon separation device, cooling device 104, steam compressor 105, pressure reducing valve 106, carbon separation tower 107 of ammonia-carbon separation, cooler 200, air cooler 300, initial liquid phase working fluid injection port 1001. DETAILED DESCRIPTION

[0078] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0079] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0080] The present invention is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0081] In the Examples and Comparative Examples, t represents tons.

[0082] The working fluid used in the embodiment is dichloromethane.

[0083] Example 1

[0084] This embodiment provides a heat recovery system for melamine tail gas, such as Figure 1 As shown, including:

[0085] A carbon separation tower 107, comprising a carbonized ammonia water inlet, a carbonized ammonia water first outlet, and a carbonized ammonia water second outlet;

[0086] The carbonized ammonia water at the carbonized ammonia water inlet is obtained by treating the melamine tail gas in a carbon dioxide absorption tower and / or a carbon dioxide washing tower to obtain methylammonium liquid, and sending the methylammonium liquid to a carbon separation tower for carbon dioxide separation to obtain carbonized ammonia water;

[0087] The desorption tower 103 includes a first inlet for carbonized ammonia water, a desorption gas outlet and a desorption liquid outlet; a water vapor inlet; wherein the first inlet for carbonized ammonia water is connected to the first outlet for carbonized ammonia water of the carbon separation tower 107;

[0088] The evaporator 100 comprises a first feed inlet and a desorbed gas condensate outlet, a first liquid phase working fluid feed inlet and a first gas phase working fluid outlet; wherein the first feed inlet is connected to the desorbed gas outlet and the second outlet of the carbonized ammonia water; the evaporator 100 also comprises an initial liquid phase working fluid injection inlet 1001, the initial liquid phase working fluid injection inlet 1001 is used to inject the liquid phase working fluid when the system is started, or to supplement the first liquid phase working fluid when the first liquid phase working fluid of the system is lost.

[0089] A compressor 101, wherein the compressor 101 comprises a first gas-phase working medium feed port and a pressurized first gas-phase working medium discharge port; wherein the first gas-phase working medium feed port and the first gas-phase working medium discharge port are connected;

[0090] The condenser 102 includes a desorption liquid inlet, a first steam outlet, a second steam outlet, a pressurized first gas phase working medium feed inlet, and a cooled first liquid phase working medium outlet; wherein the desorption liquid inlet is connected to the desorption liquid outlet; the first steam outlet is connected to the water vapor inlet of the desorption tower 103; the pressurized first gas phase working medium feed inlet is connected to the pressurized first gas phase working medium outlet;

[0091] A cooler 200, the cooler 200 comprises a cooler feed port and a cooler discharge port, wherein the outlet of the cooling first liquid phase working medium is connected to the cooler feed port;

[0092] The pressure reducing valve 106 comprises a pressure reducing valve feed port and a pressure reducing valve discharge port, wherein the pressure reducing valve discharge port is connected to the first liquid phase working medium feed port;

[0093] The steam compressor 105 comprises a steam compressor discharge port and a steam compressor feed port; the steam compressor feed port is connected to the second steam outlet;

[0094] The cooling device 104 includes a cooling device feed port and a cooling device discharge port; wherein the cooling device feed port is connected to the steam compressor 105 discharge port; and a water supply port is also included between the cooling device feed port and the steam compressor 105 discharge port.

[0095] This embodiment provides a method for recovering heat energy from melamine tail gas, comprising the following steps:

[0096] (1) 28 t / h of melamine tail gas is treated by carbon dioxide absorption in a carbon dioxide absorption tower and a carbon dioxide washing tower using carbonized ammonia water and concentrated ammonia water to obtain methylammonium liquid; the methylammonium liquid is pressurized to 2.0 MPa, preheated to 150° C. and then flashed to obtain a gas phase and a liquid phase, which are respectively sent to a carbon separation tower, a desorption liquid at 126° C. from a desorption tower is added to the middle of the carbon separation tower, and a desorption liquid cooled to 40° C. is added to the top, and carbon dioxide separation treatment is carried out under the condition of 1.9 MPa, carbon dioxide with an ammonia content of less than 100 ppm is obtained at the top of the tower, and 134 t / h of carbonized ammonia water with an ammonia / carbon mass ratio of 5:1 is obtained at the bottom of the tower; wherein the temperature of the carbonized ammonia water is 170° C., the pressure is 1.9 MPa, and the components are NH3 8%, CO2 2%, and H2O 90%.

[0097] (2) 99 t / h of carbonized ammonia water is depressurized to a temperature of 103°C and a pressure of 0.3 MPa through heat exchange and is fed into a desorption tower 103, where it is desorbed using 30 t / h of water vapor from a condenser 102 to obtain 29 t / h of desorbed gas and 100 t / h of desorbed liquid. The desorbed liquid has a temperature of 126°C and a pressure of 0.24 MPa; the desorbed gas has a temperature of 101°C and a pressure of 0.24 MPa, and its components are 48% NH3, 11% CO2, and 41% H2O.

[0098] (3) 29 t / h of desorbed gas is mixed with 35 t / h of carbonized ammonia water and then fed into the evaporator 100 to exchange heat with 221 t / h of the first liquid phase working medium at a temperature of 37° C. and a pressure of 0.5 MPa to obtain 64 t / h of desorbed gas condensate and the first gas phase working medium; wherein the desorbed gas condensate has a temperature of 42° C. and a pressure of 0.24 MPa, and its components are 33% NH3, 10% CO2, and 57% H2O; and the first gas phase working medium has a temperature of 95° C. and a pressure of 0.5 MPa.

[0099] (4) After 221 t / h of the first gas phase working medium is pressurized and heated to 210°C and 1.9 MPa by the compressor 101, it is sent to the condenser 102 for heat exchange with 30 t / h of desorption liquid from the desorption tower 103 and 1.38 t / h of supplementary water with a temperature of 126°C and a pressure of 0.24 MPa, so as to obtain the first liquid phase working medium with a temperature of 128°C and a pressure of 1.9 MPa and 31.38 t / h of water vapor with a temperature of 126°C and a pressure of 0.24 MPa. The 30 t / h of water vapor is sent to the desorption tower 103, and the remaining 1.38 t / h of water vapor is sent to the steam compressor 105 and supplemented with 0.11 t / h of supplementary water with a temperature of 155°C and a pressure of 0.55 MPa in the temperature reducing device 104 to generate 1.49 t / h of water vapor with a temperature of 155°C and a pressure of 0.55 MPa, which is then sent out.

[0100] (5) The cooled first liquid phase working medium is cooled and reduced in pressure to a temperature of 37° C. and a pressure of 0.5 MPa via the cooler 200 and the pressure reducing valve 106 and then returned to the evaporator 100 for circulation.

[0101] Example 2

[0102] This embodiment provides a heat recovery system for melamine tail gas, such as Figure 2 As shown, including:

[0103] A carbon separation tower 107, comprising a carbonized ammonia water inlet, a carbonized ammonia water first outlet, and a carbonized ammonia water second outlet;

[0104] The carbonized ammonia water at the carbonized ammonia water inlet is obtained by treating the melamine tail gas in a carbon dioxide absorption tower and / or a carbon dioxide washing tower to obtain methylammonium liquid, and sending the methylammonium liquid to a carbon separation tower for carbon dioxide separation to obtain carbonized ammonia water;

[0105] The desorption tower 103 includes a first inlet for carbonized ammonia water, a desorption gas outlet and a desorption liquid outlet; a water vapor inlet; wherein the first inlet for carbonized ammonia water is connected to the first outlet for carbonized ammonia water of the carbon separation tower 107;

[0106] The evaporator 100 includes a first feed inlet and a desorbed gas condensate outlet, a first liquid phase working fluid feed inlet and a first gas phase working fluid outlet; wherein the first feed inlet is connected to the desorbed gas outlet and the second outlet of the carbonized ammonia water; the evaporator 100 also includes an initial liquid phase working fluid injection inlet 1001, the initial liquid phase working fluid injection inlet 1001 is used to inject the liquid phase working fluid when the system is started, or to supplement the first liquid phase working fluid when the first liquid phase working fluid of the system is lost;

[0107] A compressor 101, wherein the compressor 101 comprises a first gas-phase working medium feed port and a pressurized first gas-phase working medium discharge port; wherein the first gas-phase working medium feed port and the first gas-phase working medium discharge port are connected;

[0108] The condenser 102 includes a desorption liquid inlet, a first steam outlet, a second steam outlet, a pressurized first gas phase working medium feed inlet, and a cooled first liquid phase working medium outlet; wherein the desorption liquid inlet is connected to the desorption liquid outlet; the first steam outlet is connected to the water vapor inlet of the desorption tower 103; the pressurized first gas phase working medium feed inlet is connected to the pressurized first gas phase working medium outlet;

[0109] The pressure reducing valve 106 comprises a pressure reducing valve feed port and a pressure reducing valve discharge port, wherein the pressure reducing valve discharge port is connected to the first liquid phase working medium feed port; the cooling first liquid phase working medium outlet is connected to the pressure reducing valve feed port;

[0110] The steam compressor 105 comprises a steam compressor discharge port and a steam compressor feed port; the steam compressor feed port is connected to the second steam outlet;

[0111] The cooling device 104 includes a cooling device feed port and a cooling device discharge port; wherein the cooling device feed port is connected to the steam compressor discharge port.

[0112] This embodiment provides a method for recovering heat energy from melamine tail gas, comprising the following steps:

[0113] (1) 28 t / h of melamine tail gas is treated by carbon dioxide absorption in a carbon dioxide absorption tower and a carbon dioxide washing tower using carbonized ammonia water and concentrated ammonia water to obtain methylammonium liquid; the methylammonium liquid is pressurized to 2.0 MPa, preheated to 150° C. and then flashed to obtain a gas phase and a liquid phase, which are respectively sent to a carbon separation tower, a desorption liquid at 113° C. from a desorption tower is added to the middle of the carbon separation tower, and a desorption liquid cooled to 40° C. is added to the top, and carbon dioxide separation treatment is carried out under the condition of 1.5 MPa, carbon dioxide with an ammonia content of less than 100 ppm is obtained at the top of the tower, and 134 t / h of carbonized ammonia water with an ammonia / carbon mass ratio of 5:1 is obtained at the bottom of the tower; wherein the temperature of the carbonized ammonia water is 150° C., the pressure is 1.5 MPa, and the components are NH3 8%, CO2 2%, and H2O 90%.

[0114] (2) 99 t / h of carbonized ammonia water is depressurized to a temperature of 93°C and a pressure of 0.22 MPa through heat exchange and is fed into a desorption tower 103, where it is desorbed using 30 t / h of water vapor from a condenser 102 to obtain 29 t / h of desorbed gas and 100 t / h of desorbed liquid. The desorbed liquid has a temperature of 110°C and a pressure of 0.15 MPa; the desorbed gas has a temperature of 90°C and a pressure of 0.15 MPa, and its components are 48% NH3, 11% CO2, and 41% H2O.

[0115] (3) 29 t / h of desorbed gas is mixed with 35 t / h of carbonized ammonia water and then fed into the evaporator 100 to exchange heat with 361 t / h of the first liquid phase working medium at a temperature of 20° C. and a pressure of 0.05 MPa to obtain 64 t / h of desorbed gas condensate and the first gas phase working medium; wherein the desorbed gas condensate has a temperature of 30° C. and a pressure of 0.15 MPa, and its components are 33% NH3, 10% CO2, and 57% H2O; and the first gas phase working medium has a temperature of 20° C. and a pressure of 0.05 MPa.

[0116] (4) 361 t / h of the first gas phase working medium is pressurized and heated to 240°C and 0.8 MPa by the compressor 101, and then sent to the condenser 102 for heat exchange with 30 t / h of desorption liquid from the desorption tower 103 and 29.1 t / h of make-up water with a temperature of 110°C and a pressure of 0.15 MPa, so as to obtain the first liquid phase working medium cooled at a temperature of 115°C and a pressure of 0.8 MPa and 59.1 t / h of steam with a temperature of 110°C and a pressure of 0.15 MPa. 30 t / h of water vapor is sent to the desorption tower 103, and the remaining 29.1 t / h of water vapor is compressed by the steam compressor 105 and supplemented with 1.06 t / h of make-up water with a temperature of 127°C and a pressure of 0.25 MPa in the temperature reducing device 104 to generate 30.16 t / h of water vapor with a temperature of 127°C and a pressure of 0.25 MPa, which is then sent out.

[0117] (5) The cooled first liquid phase working medium is cooled and reduced in pressure to a temperature of 21° C. and a pressure of 0.5 MPa via the pressure reducing valve 106 and then returned to the evaporator 100 for circulation.

[0118] Example 3

[0119] This embodiment provides a heat recovery system for melamine tail gas, which has the same structure as the system in Embodiment 2.

[0120] This embodiment provides a method for recovering heat energy from melamine tail gas, comprising the following steps:

[0121] (1) 28 t / h of melamine tail gas is treated by carbon dioxide absorption in a carbon dioxide absorption tower and a carbon dioxide washing tower using carbonized ammonia water and concentrated ammonia water to obtain methylammonium liquid; the methylammonium liquid is pressurized to 2.0 MPa, preheated to 150° C. and then flashed to obtain a gas phase and a liquid phase, which are respectively sent to a carbon separation tower, a desorption liquid at 126° C. from a desorption tower is added to the middle of the carbon separation tower, and a desorption liquid cooled to 40° C. is added to the top, and carbon dioxide separation treatment is carried out under the condition of 1.9 MPa, carbon dioxide with an ammonia content of less than 100 ppm is obtained at the top of the tower, and 134 t / h of carbonized ammonia water with an ammonia / carbon mass ratio of 5:1 is obtained at the bottom of the tower; wherein the temperature of the carbonized ammonia water is 170° C., the pressure is 1.9 MPa, and the components are NH3 8%, CO2 2%, and H2O 90%.

[0122] (2) 99 t / h of carbonized ammonia water is depressurized to a temperature of 103°C and a pressure of 0.3 MPa through heat exchange and is fed into a desorption tower 103, where it is desorbed using 30 t / h of water vapor from a condenser 102 to obtain 29 t / h of desorbed gas and 100 t / h of desorbed liquid. The desorbed liquid has a temperature of 126°C and a pressure of 0.24 MPa; the desorbed gas has a temperature of 101°C and a pressure of 0.24 MPa, and its components are 48% NH3, 11% CO2, and 41% H2O.

[0123] (3) 29 t / h of desorbed gas is mixed with 35 t / h of carbonized ammonia water and then fed into the evaporator 100 to exchange heat with 381 t / h of the first liquid phase working medium at a temperature of 40° C. and a pressure of 0.1 MPa to obtain 64 t / h of desorbed gas condensate and the first gas phase working medium; wherein the desorbed gas condensate has a temperature of 42° C. and a pressure of 0.24 MPa, and its components are 33% NH3, 10% CO2, and 57% H2O; and the first gas phase working medium has a temperature of 40° C. and a pressure of 0.1 MPa.

[0124] (4) 381 t / h of the first gas phase working medium is pressurized and heated to 226°C and 1.05 MPa by the compressor 101, and then sent to the condenser 102 for heat exchange with 30 t / h of desorption liquid from the desorption tower 103 and 27.9 t / h of supplementary water with a temperature of 126°C and a pressure of 0.24 MPa, so as to obtain the first liquid phase working medium with a temperature of 127°C and a pressure of 1.05 MPa and 57.9 t / h of water vapor with a temperature of 126°C and a pressure of 0.24 MPa. 30 t / h of water vapor is sent to the desorption tower 103, and the remaining 27.9 t / h of water vapor is compressed by the steam compressor 105 and supplemented with 2.3 t / h of supplementary water with a temperature of 155°C and a pressure of 0.55 MPa in the temperature reducing device 104 to generate 30.2 t / h of water vapor with a temperature of 155°C and a pressure of 0.55 MPa, which is then sent out.

[0125] (5) The cooled first liquid phase working medium is cooled and reduced in pressure to a temperature of 40° C. and a pressure of 0.1 MPa via a pressure reducing valve 106 and then returned to the evaporator 100 for circulation.

[0126] Example 4

[0127] This embodiment provides a heat recovery system for melamine tail gas, which has the same structure as the system in Embodiment 2.

[0128] This embodiment provides a method for recovering heat energy from melamine tail gas, comprising the following steps:

[0129] (1) 28 t / h of melamine tail gas is treated by carbon dioxide absorption using carbonized ammonia water and concentrated ammonia water to obtain methylammonium liquid; the methylammonium liquid is pressurized to 2.0 MPa, preheated to 150° C. and then flashed to obtain a gas phase and a liquid phase, which are respectively fed into a carbon separation tower, a desorption liquid at 155° C. from a desorption tower is added to the middle of the carbon separation tower, and a desorption liquid cooled to 40° C. is added to the top, and carbon dioxide separation treatment is carried out under the condition of 2.5 MPa, carbon dioxide with an ammonia content of less than 100 ppm is obtained at the top of the tower, and 134 t / h of carbonized ammonia water with an ammonia / carbon mass ratio of 5:1 is obtained at the bottom of the tower; wherein the temperature of the carbonized ammonia water is 180° C., the pressure is 2.5 MPa, and the components are NH3 8%, CO2 2%, and H2O 90%.

[0130] (2) 99 t / h of carbonized ammonia water is depressurized to a temperature of 128°C and a pressure of 0.6 MPa through heat exchange and is fed into a desorption tower 103, where it is desorbed using 30 t / h of water vapor from a condenser 102 to obtain 29 t / h of desorbed gas and 100 t / h of desorbed liquid. The desorbed liquid has a temperature of 155°C and a pressure of 0.55 MPa; the desorbed gas has a temperature of 126°C and a pressure of 0.55 MPa, and its components are 48% NH3, 11% CO2, and 41% H2O.

[0131] (3) 29 t / h of desorbed gas is mixed with 35 t / h of carbonized ammonia water and then fed into the evaporator 100 to exchange heat with 471 t / h of the first liquid phase working medium at a temperature of 50° C. and a pressure of 0.15 MPa to obtain 64 t / h of desorbed gas condensate and the first gas phase working medium; wherein the desorbed gas condensate has a temperature of 60° C. and a pressure of 0.55 MPa, and its components are 33% NH3, 10% CO2, and 57% H2O; and the first gas phase working medium has a temperature of 50° C. and a pressure of 0.15 MPa.

[0132] (4) After 471 t / h of the first gas phase working medium is pressurized and heated to 258°C and 1.8 MPa by the compressor 101, it is sent to the condenser 102 for heat exchange with 30 t / h of desorption liquid from the desorption tower 103 and 38.1 t / h of make-up water with a temperature of 155°C and a pressure of 0.55 MPa, so as to obtain the first liquid phase working medium with a temperature of 157°C and a pressure of 1.8 MPa and 68.1 t / h of water vapor with a temperature of 155°C and a pressure of 0.55 MPa. 30 t / h of water vapor is sent to the desorption tower 103, and the remaining 38.1 t / h of water vapor is compressed by the steam compressor 105 and supplemented with 2.4 t / h of make-up water with a temperature of 180°C and a pressure of 1 MPa in the temperature reducing device 104 to generate 40.5 t / h of water vapor with a temperature of 180°C and 1 MPa, which is then sent out.

[0133] (5) The cooled first liquid phase working medium is cooled and reduced in pressure to a temperature of 50° C. and a pressure of 0.15 MPa via the pressure reducing valve 106 and then returned to the evaporator 100 for circulation.

[0134] Example 5

[0135] This embodiment provides a heat recovery system for melamine tail gas, which has the same structure as the system in Embodiment 2.

[0136] This embodiment provides a method for recovering heat energy from melamine tail gas, comprising the following steps:

[0137] (1) 28 t / h of melamine tail gas is treated by carbon dioxide absorption in a carbon dioxide absorption tower and a carbon dioxide washing tower using carbonized ammonia water and concentrated ammonia water to obtain methylammonium liquid; the methylammonium liquid is pressurized to 2.0 MPa, preheated to 150° C. and then flashed to obtain a gas phase and a liquid phase, which are respectively sent to a carbon separation tower, a desorption liquid at 126° C. from a desorption tower is added to the middle of the carbon separation tower, and a desorption liquid cooled to 40° C. is added to the top, and carbon dioxide separation treatment is carried out under the condition of 1.9 MPa, carbon dioxide with an ammonia content of less than 100 ppm is obtained at the top of the tower, and 134 t / h of carbonized ammonia water with an ammonia / carbon mass ratio of 5:1 is obtained at the bottom of the tower; wherein the temperature of the carbonized ammonia water is 170° C., the pressure is 1.9 MPa, and the components are NH3 8%, CO2 2%, and H2O 90%.

[0138] (2) 99 t / h of carbonized ammonia water is depressurized to a temperature of 103°C and a pressure of 0.3 MPa through heat exchange and is fed into a desorption tower 103, where it is desorbed using 30 t / h of water vapor from a condenser 102 to obtain 29 t / h of desorbed gas and 100 t / h of desorbed liquid. The desorbed liquid has a temperature of 126°C and a pressure of 0.24 MPa; the desorbed gas has a temperature of 101°C and a pressure of 0.24 MPa, and its components are 48% NH3, 11% CO2, and 41% H2O.

[0139] (3) 29 t / h of desorbed gas is mixed with 35 t / h of carbonized ammonia water and then fed into the evaporator 100 for heat exchange with 381 t / h of the first liquid phase working medium (dichloromethane) at a temperature of 40° C. and a pressure of 0.1 MPa to obtain 64 t / h of desorbed gas condensate and the first gas phase working medium; wherein the desorbed gas condensate has a temperature of 42° C. and a pressure of 0.24 MPa, and its components are 33% NH3, 10% CO2, and 57% H2O; and the temperature of the first gas phase working medium is 40° C. and a pressure of 0.1 MPa.

[0140] (4) 381 t / h of the first gas phase working medium is pressurized and heated to 283°C and 1.9 MPa by the compressor 101, and then sent to the condenser 102 for heat exchange with 30 t / h of desorption liquid from the desorption tower 103 and 35 t / h of make-up water with a temperature of 126°C and a pressure of 0.24 MPa, so as to obtain the first liquid phase working medium with a temperature of 128°C and a pressure of 1.9 MPa and 65 t / h of water vapor with a temperature of 126°C and a pressure of 0.24 MPa. 30 t / h of water vapor is sent to the desorption tower 103, and the remaining 35 t / h of water vapor is compressed by the steam compressor 105 and supplemented with 2.9 t / h of make-up water with a temperature of 155°C and a pressure of 0.55 MPa in the temperature reducing device 104 to generate 37.9 t / h of water vapor with a temperature of 155°C and a pressure of 0.55 MPa, which is then sent out.

[0141] (5) The cooled first liquid phase working medium is cooled and reduced in pressure to a temperature of 40° C. and a pressure of 0.1 MPa via the pressure reducing valve 106 and then returned to the evaporator 100 for circulation.

[0142] Comparative Example 1

[0143] like Figure 3 As shown, this comparative example provides a heat recovery system for melamine tail gas, including: a desorption tower 103, an air cooler 300, and a carbon separation tower 107; specifically:

[0144] The carbon separation tower 107 has an inlet connected to the outlet of the melamine tail gas after being absorbed and washed by carbon dioxide;

[0145] a desorption tower 103, whose process inlet is connected to the outlet of the carbon separation tower;

[0146] The inlet of the air cooler 300 is connected to the process outlet of the desorption tower 103 and the outlet of the carbon separation tower respectively.

[0147] This comparative example provides a method for recovering heat energy from melamine tail gas, comprising the following steps:

[0148] The same method as in Example 1 is used to obtain the steps of carbonized ammonia water, and 30 t / h steam purchased at a temperature of 126°C and a pressure of 0.24 MPa is used to enter the desorption tower to desorb part of the carbonized ammonia water that has been decompressed by heat exchange, so as to obtain a desorbed gas with a temperature of 101°C and a pressure of 0.24 MPa. The desorbed gas is mixed with the remaining part of the carbonized ammonia water and then enters the air cooler, where it is cooled to 55°C by air. The desorbed gas condensate obtained after cooling is sent to the next step, and the desorbed liquid obtained at the bottom of the desorption tower is sent to other devices for reuse.

[0149] Experimental example

[0150] The relative cost of treating each ton of melamine tail gas for each of the above embodiments and comparative examples was calculated, and the results are shown in the table below.

[0151] Table 1 Consumption of tail gas treatment per ton of melamine

[0152]

[0153]

[0154] The compressor power is obtained by statistics of the actual power of the compressor in the given heat energy recovery method in the embodiment.

[0155] In Examples 1 to 5 of the present invention, the water vapor generated by the absorption of heat by the liquid phase water at the bottom of the moisture tower can be directly used for desorption in the moisture tower, and the water vapor generated by the absorption of heat by the supplementary water is the external water vapor. In Example 1, a cooler and a pressure reducing valve are used to reduce the pressure and cool the working fluid, which will lose some heat, but the amount of external water vapor generated at the same time is relatively low, which is suitable for areas with high electricity costs; in Examples 2 to 5, a pressure reducing valve is used to reduce the pressure and cool the working fluid, and it is directly sent to the evaporator without losing heat. The liquid phase working fluid consumption required to absorb the heat of the process gas and the returned working fluid is relatively large, and the first gas phase working fluid that needs to be compressed is also relatively large, so it is necessary to increase the power and water replenishment of the compressor to generate more external water vapor, which is suitable for areas with low electricity costs. Comparative Example 1 requires the purchase of 1.07t / t of water vapor to desorb the moisture tower, which consumes a lot of energy and has a low added value. Compared with Comparative Example 1, the present invention absorbs the latent heat in the process gas by evaporation, compression, and condensation, and has a high economic added value.

[0156] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for recovering heat energy from melamine tail gas, characterized in that: The steps include: (1) treating melamine tail gas in a carbon dioxide absorption tower and / or a carbon dioxide scrubbing tower to obtain methylammonium liquid, and sending the methylammonium liquid to a carbon separation tower to separate carbon dioxide to obtain carbonized ammonia water; (2) sending part of the carbonized ammonia water in step (1) into a desorption tower after heat exchange and decompression, and performing desorption by using water vapor to obtain desorbed gas and desorbed liquid; (3) mixing the desorbed gas obtained in step (2) with the remaining portion of the carbonized ammonia water in step (1) and performing a first heat exchange with the first liquid phase working medium to obtain desorbed gas condensate and the first gas phase working medium respectively; (4) compressing the first gas phase working medium and performing a second heat exchange with part of the desorption liquid from the desorption tower to obtain a cooled first liquid phase working medium and heat exchange steam respectively; returning part of the heat exchange steam to step (2) as water vapor for desorption; and returning the cooled first liquid phase working medium to step (3) for the first heat exchange after being depressurized.

2. The method for recovering heat energy from melamine tail gas according to claim 1, characterized in that: In step (4), the cooled first liquid phase working medium is sequentially condensed and decompressed before being returned to the first heat exchange process; And / or, step (4) further comprises the step of adding water to the partial desorption liquid; And / or, it also includes the step of compressing the remaining part of the heat exchange steam, reducing the temperature and then sending it out; and / or, the heat exchange steam is compressed, cooled to 0.25MPa-1.0MPa and 127°C-180°C, and then sent out; Preferably, in step (4), the cooled first liquid phase working medium is condensed, decompressed to 0.05MPa-0.5MPa, 20°C-50°C, and then returned to the first heat exchange process; Preferably, the process of reducing the temperature of the heat exchange steam also includes a water replenishment process; Preferably, the process of reducing the temperature of the remaining part of the heat exchange steam also includes a process in which the temperature of the make-up water in the make-up water process is 127-180° C. and the pressure is 0.25 MPa-1.0 MPa.

3. The method for recovering heat energy from melamine tail gas according to claim 2, characterized in that: The mass ratio of the carbonized ammonia water in step (2) to the carbonized ammonia water in step (1) is 70-79%; Preferably, in step (2), the mass ratio of water vapor to carbonized ammonia water is (25-35):100; Preferably, the mass ratio of the desorbed gas and the desorbed liquid obtained in step (2) is (25-35):100; Preferably, the mass ratio of the desorbed gas obtained in step (2) to the remaining portion of the carbonized ammonia water in step (3) is (0.8-0.9):1; Preferably, in step (3), the mass ratio of the desorbed gas to the first liquid phase working fluid is (25-35): (230-500); Preferably, in step (3), the mass ratio of the total mass of the desorbed gas mixed with the remaining portion of the carbonized ammonia water to the first liquid phase working fluid is 1:(3.4-7.4); Preferably, in step (4), the mass ratio of the partial desorption liquid to the total desorption liquid is 25-35%; Preferably, the mass ratio of the supplementary water added to the partial desorption liquid to the partial desorption liquid is (1-42): (25-35); Preferably, the mass ratio of the supplementary water added in the process of replenishing water during the process of cooling the remaining part of the heat exchange steam to the remaining part of the heat exchange steam is 1: (10-30).

4. The method for recovering heat energy from melamine tail gas according to any one of claims 1 to 3, characterized in that: In step (2), the temperature of the carbonized ammonia water after heat exchange and decompression is 93-130° C. and the pressure is 0.22-0.6 MPa; And / or, in step (3), the temperature of the remaining portion of the carbonized ammonia water is 150° C.-180° C., and the pressure is 1.5 MPa-2.5 MPa; And / or, the mass composition of the carbonized ammonia water in step (1) includes: NH3: 4%-12%, CO2: 1%-8%, H2O: 80%-95%.

5. The method for recovering heat energy from melamine tail gas according to any one of claims 1 to 4, characterized in that: In step (2), the temperature of the desorbed gas is 90°C-126°C and the pressure is 0.15-0.55 MPa; And / or, the temperature of the desorption liquid is 110°C-155°C and the pressure is 0.15-0.55MPa; And / or, the mass composition of the desorbed gas includes: NH3: 35%-55%, CO2: 5%-20%, H2O: 25%-45%; Preferably, the temperature of the supplementary water added to the partial desorption liquid is 110° C.-155° C., and the pressure is 0.15-0.55 MPa.

6. The method for recovering heat energy from melamine tail gas according to any one of claims 1 to 5, characterized in that: In step (3), the temperature of the first liquid phase working fluid is 20°C-50°C and the pressure is 0.05-0.5MPa; And / or, the temperature of the first gas phase working fluid is 20-95°C and 0.05-0.5MPa; and / or, the temperature of the desorbed condensate is 30°C-60°C and the pressure is 0.15-0.55MPa; And / or, the mass composition of the desorbed condensate includes: NH3: 22%-40%, CO2: 5%-15%, H2O: 45%-65%.

7. The method for recovering heat energy from melamine tail gas according to any one of claims 1 to 6, characterized in that: In step (4), the first gas phase working fluid is compressed to 210-283° C. and 0.8-1.9 MPa and then fed into the second heat exchanger; And / or, the temperature of the cooling first liquid phase working medium is 115-157° C. and the pressure is 0.8-1.9 MPa; And / or, the heat exchange steam sent to the desorption tower has a temperature of 110-155° C. and a pressure of 0.15-0.55 MPa.

8. A heat recovery system for melamine tail gas according to any one of claims 1 to 7, characterized in that: include: A carbon separation tower, the carbon separation tower comprising a first liquid outlet for melamine tail gas and carbonized ammonia water and a second liquid outlet for carbonized ammonia water; A desorption tower, the desorption tower comprising a first liquid inlet for carbonized ammonia water, a desorption gas outlet and a desorption liquid outlet; a water vapor inlet; wherein the first liquid inlet for carbonized ammonia water is connected to the first liquid outlet for carbonized ammonia water; A first heat exchanger, wherein the first heat exchanger comprises a first feed inlet and a desorbed gas condensate outlet, a first liquid phase working medium feed inlet and a first gas phase working medium outlet; wherein the first feed inlet is connected to the desorbed gas outlet of the desorber and the second outlet of the carbonized ammonia water of the carbon separation tower; A first compression device, the first compression device comprising a first gas-phase working medium feed port and a pressurized first gas-phase working medium discharge port; wherein the first gas-phase working medium feed port is connected to the first gas-phase working medium discharge port of the first heat exchanger; A second heat exchanger, wherein the second heat exchanger comprises a desorption liquid inlet and a first steam outlet, a pressurized first gas phase working medium feed inlet and a cooled first liquid phase working medium outlet; wherein the desorption liquid inlet is connected to the desorption liquid outlet of the desorption tower; the first steam outlet is connected to the desorption steam inlet; and the pressurized first gas phase working medium feed inlet is connected to the pressurized first gas phase working medium outlet; The pressure reducing valve comprises a pressure reducing valve feed port and a pressure reducing valve discharge port, wherein the pressure reducing valve feed port is connected to the outlet of the cooling first liquid phase working medium; and the pressure reducing valve discharge port is connected to the first liquid phase working medium feed port of the first heat exchanger.

9. The melamine tail gas heat recovery system according to claim 8, characterized in that: Also includes: A cooling device, wherein the pressure reducing valve feed port is connected to the cooling first liquid phase working medium outlet through the cooling device; the cooling device comprises a cooling device feed port and a cooling device outlet, wherein the cooling first liquid phase working medium outlet is connected to the cooling device feed port, and the cooling device outlet is connected to the pressure reducing valve feed port; And / or, further comprising: a second compression device, wherein the second compression device comprises a second compression device feed port and a second compression device discharge port; The second heat exchanger includes a second steam outlet; wherein the second compression device feed port is connected to the second heat exchanger including the second steam outlet; A cooling device, wherein the cooling device comprises a cooling device feed port and a cooling device discharge port; the cooling device comprises a cooling device feed port connected to a second compression device discharge port; And / or, a water replenishment port is further provided between the desorption liquid inlet of the second heat exchanger and the desorption liquid outlet of the desorption tower; And / or, a water supply port is also provided between the discharge port of the second compression device and the feed port of the cooling device.

10. The melamine tail gas heat recovery system according to claim 8 or 9, characterized in that: The first heat exchanger is at least one of an evaporator and a condenser; And / or, the second heat exchanger is at least one of an evaporator and a condenser; And / or, the second compression device is a steam compressor.

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