Device and method for purifying gas in reaction process of urea and propylene glycol

Abstract

The invention discloses a device and a method for purifying gas in a reaction process of urea and propylene glycol, and belongs to the technical field of chemical separation. The device comprises a reaction gas phase condenser, an organic matter separator, a washing tower, a washing tower top condenser, a water separator, a washing liquid cooler, a spraying liquid cooler, a washing liquid circulating pump and a spraying liquid circulating pump. The purification method comprises the following steps: (1) condensing and separating reaction gases of urea and propylene glycol; (2) feeding the crude ammonia gas into a washing tower for washing; (3) circularly cooling the washing liquid and the spraying liquid; and (4) condensing and separating washing gas. According to the invention, organic matters can be effectively recovered, carbon dioxide is removed, relatively pure ammonia gas is obtained, and favorable conditions are created for obtaining a high-purity liquid ammonia product and stable operation of a subsequent ammonia recovery unit.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of purification device and method of gas in urea and propylene glycol reaction process, specifically relates to a kind of purification method of gas containing ammonia, carbon dioxide, organic matter generated in the process of preparing propylene carbonate by urea and propylene glycol reaction, belongs to chemical separation technical field. BACKGROUND

[0002] In the process of indirectly producing dimethyl carbonate by urea alcoholysis method, gas and propylene carbonate liquid are generated by the reaction of urea and propylene glycol, and the main components of the gas are ammonia, as well as a small amount of carbon dioxide, water, propylene glycol and propylene carbonate and other organic matters, and carbon dioxide and water in the gas are generated due to other side reactions; due to the excess of propylene glycol in the reaction process of urea and propylene glycol, part of the unreacted propylene glycol liquid and the propylene carbonate liquid generated by the reaction volatilize into the gas at the reaction temperature of urea and propylene glycol. At a lower temperature, ammonia and carbon dioxide, water in the gas are easy to react to form ammonium salt crystals, which block the equipment and pipelines, so that the production cannot continue. The recovery rate of propylene glycol and propylene carbonate and other organic matters in the gas is low, which significantly increases the production cost, and this is also a technical problem restricting the industrialization of urea alcoholysis method for indirectly producing dimethyl carbonate.

[0003] At present, the treatment of gas in the reaction process of urea and propylene glycol is as follows: liquid ammonia with high purity is obtained by recovering ammonia gas, which needs to be purified to remove carbon dioxide, and propylene glycol and propylene carbonate and other organic matters are recovered. The scrubbing agent of ammonia gas washing tower is lye, which reacts with carbon dioxide to form carbonate solution, and the extracted carbonate solution is removed by crystallization and filtration, and the mother liquor is recycled for washing. In the washing, crystallization and filtration process, new carbonate is generated, which is easy to cause equipment and pipeline blockage, short production cycle, high operation difficulty and high labor intensity. In addition, the separation equipment for recovering propylene glycol and propylene carbonate and other organic matters has low efficiency, which causes high production cost.

[0004] In order to simplify the process flow, reduce the operation difficulty, improve the operation stability of production device and efficiently recover organic matters, the present application provides a kind of purification device and method of gas in the reaction process of urea and propylene glycol. SUMMARY

[0005] The present application aims to provide a kind of purification device and method of gas in the reaction process of urea and propylene glycol, which can effectively recover organic matters, remove carbon dioxide and obtain relatively pure ammonia gas, thereby creating favorable conditions for obtaining high-purity liquid ammonia product and stable operation in subsequent ammonia recovery unit.

[0006] In the present application, the scrubbing agent of the scrubbing tower is changed from lye to soft water, and the concentrated carbamide liquid at the bottom of the scrubbing tower is taken out as by-product. The cooling medium of the scrubbing liquid cooler and the spraying liquid cooler is changed from circulating water to refrigerated water, so as to reduce the temperature of the scrubbing liquid and the spraying liquid and improve their ability of scrubbing and absorbing carbon dioxide. The organic matter separator of the urea and propylene glycol reaction gas is reformed, and a high-efficiency cyclone separator is added, so as to effectively recover the organic matter. A scrubbing tower top cooler is added at the top outlet of the scrubbing tower, so as to ensure the temperature of the outlet of the scrubbing tower. The process improvement of the present application includes: ① since the lye is changed to soft water, no sodium carbonate is generated in the scrubbing tower, so the problem of carbonate blocking the packing of the scrubbing tower is solved; after the soft water is changed, the operations of sodium carbonate crystallization and filtration are no longer carried out on site, so the labor intensity is reduced; ② the cooling medium of the scrubbing liquid cooler and the spraying liquid cooler is changed from circulating water to refrigerated water, so the operating temperature in the scrubbing tower is changed; when the cooling medium of the scrubbing liquid cooler and the spraying liquid cooler is circulating water, the operating temperature at the bottom of the scrubbing tower is 50-60℃; when the cooling medium of the scrubbing liquid cooler and the spraying liquid cooler is refrigerated water, the operating temperature at the bottom of the scrubbing tower is 20-30℃; ③ a high-efficiency cyclone separator is added in the organic matter separator, so the separation of the organic matter is realized.

[0007] The present application provides a kind of gas purification device in urea and propylene glycol reaction process, including reaction gas phase condenser, organic matter separator, scrubbing tower, scrubbing tower top condenser, water separator, scrubbing liquid cooler, spraying liquid cooler, scrubbing liquid circulating pump, spraying liquid circulating pump;Organic matter separator is equipped with high-efficiency cyclone separator, can effectively separate the organic matter droplet entrained in gas.

[0008] Reaction gas phase condenser top is equipped with the inlet of reaction gas, and reaction gas phase condenser bottom is equipped with the outlet of gas-liquid mixture, and is connected with organic matter separator;Organic matter separator side is equipped with gas-liquid mixture inlet, and is connected with reaction gas phase condenser bottom outlet, and organic matter separator bottom is equipped with liquid outlet, and organic matter separator top is equipped with gas outlet, and is connected with scrubbing tower; Scrubbing tower bottom side is equipped with gas inlet, and scrubbing tower bottom is equipped with a circulating loop, which is composed of scrubbing liquid circulating pump, scrubbing liquid cooler and scrubbing liquid inlet in the middle of scrubbing tower in sequence;Scrubbing liquid circulating pump outlet is equipped with carbamide liquid outlet;Scrubbing tower middle part is equipped with a circulating loop, which is composed of spraying liquid circulating pump, spraying liquid cooler and upper part of scrubbing tower in sequence;Scrubbing tower top side is equipped with soft water inlet;Scrubbing tower top is equipped with gas outlet, and is connected with scrubbing tower top condenser; Scrubbing tower top condenser top is equipped with gas inlet, and is connected with scrubbing tower top;Scrubbing tower top condenser bottom is equipped with gas-liquid mixture outlet, and is connected with water separator;Water separator bottom is equipped with liquid outlet, and is connected with scrubbing tower top;Water separator top is equipped with gas outlet.

[0009] Further, the reaction gas phase condenser and the organic matter separator are arranged on the same plane, installation is facilitated, and a U-shaped bend is prohibited from being installed on a connecting pipe between the reaction gas phase condenser and the organic matter separator in order to prevent liquid sealing; and a cyclone separator is added in the organic matter separator.

[0010] Further, the cyclone separator separates liquid drops in the reaction gas, and reduces the content of the organic matter carried in the reaction gas. The cyclone separator has a center cylinder, an outer wall of the center cylinder is connected with guide plates, the guide plates are composed of upper and lower arc plates, the upper and lower arc plates are arranged obliquely downward along the outer wall of the center cylinder, and gaps are left between adjacent two arc plates, which are beneficial to gas transportation; vanes are arranged between the upper and lower arc plates; and the arc plates are connected with the inner wall of the organic matter separator and the center cylinder at two ends thereof. The gas-liquid mixture enters from the bottom of the organic matter separator, and the cyclone separator is located at the top of the organic matter separator; after the liquid organic matter contacts the arc plates and the vanes, the liquid organic matter flows to the bottom of the organic matter separator along the guide plates and the inner wall of the organic matter separator under the action of gravity, and the gas passes through the gaps between the arc plates and the vanes and is discharged upward from the top of the organic matter separator.

[0011] The present application provides a method for purifying gas in the reaction process of urea and propylene glycol, which comprises the following steps: (1) condensing and separating the reaction gas of urea and propylene glycol: The reaction gas containing a small amount of carbon dioxide, water, and propylene glycol and propylene carbonate organic matter is cooled to 45-55℃ by the reaction gas phase condenser, and the propylene glycol and propylene carbonate organic matter are condensed due to the temperature reduction; the gas-liquid mixture enters the organic matter separator for gas-liquid separation, and the crude ammonia gas containing a small amount of carbon dioxide, water, and a small amount of organic matter is obtained from the top of the organic matter separator and is sent to the washing tower; and the recovered organic matter is obtained from the bottom of the organic matter separator; The cooling medium of the reaction gas phase condenser is water, and the cooling medium is prohibited from being stopped, so as to prevent a large amount of organic matter from entering the washing tower and causing low yield of the organic matter; and the temperature of the cooling medium is controlled to be 20-30℃, and the reaction gas is cooled to 45-55℃; The operating conditions of the organic matter separator are as follows: the temperature is 45-55℃, the pressure is -55 to -45 kPa, and the content of the organic matter in the crude ammonia gas obtained from the top of the organic matter separator is 0.1-0.5 wt%.

[0012] (2) sending the crude ammonia gas to the washing tower for washing: The crude ammonia gas obtained from the top of the organic matter separator is sent to the washing tower from the gas inlet at the bottom of the washing tower, and the soft water (normal temperature, flow rate 1-2 m 3h) is added from the top of the washing tower; the crude ammonia gas is in turn contacted with the washing circulating liquid at the bottom of the washing tower, the middle spraying circulating liquid, and the top soft water in reverse, wherein a small amount of carbon dioxide and trace amounts of organic matter are absorbed by the ammonia water formed by the soft water and the ammonia gas; the ammonia gas carrying gaseous water and trace amounts of carbon dioxide is extracted from the top of the washing tower; the operating conditions of the washing tower are: the top temperature is 30-40°C, the bottom temperature is 20-30°C, the operating pressure is -60 to -50 kPa, and the composition of the ammonia gas extracted from the top of the washing tower is: CO2: 50-100 ppm, H2O: 0.75-1.2 wt%.

[0013] The washing circulating liquid at the bottom of the washing tower and the middle spraying circulating liquid are carbon ammonium solutions, most of which are ammonia water. The formation of ammonia water is due to the dissolution of ammonia gas in water, and the ammonia water absorbs part of the carbon dioxide to form a carbon ammonium solution. Since a large amount of heat is released during the dissolution of ammonia gas in water, it will cause the temperature of the washing tower to rise, and the temperature rise will reduce the rate of carbon dioxide absorption by ammonia water, thereby increasing the carbon dioxide content in the ammonia gas extracted from the top of the washing tower, causing abnormalities in the subsequent process. The main purpose of the circulating liquid is to remove the heat released during the dissolution of ammonia in water by exchanging heat with the refrigerated water in the washing liquid cooler and the spraying liquid cooler, thereby reducing the operating temperature of the washing tower and increasing the solubility of carbon dioxide.

[0014] Since the soft water is added from the top of the washing tower, the soft water flows from top to bottom in the washing tower, absorbs ammonia gas to form ammonia water during the flow process, and the crude ammonia gas enters from the bottom of the washing tower. The ammonia water absorbs the carbon dioxide in the crude ammonia gas to form a carbon ammonium solution. Due to the mass transfer effect in the washing tower, the carbon dioxide content in the washing circulating liquid at the bottom of the washing tower is higher than that in the middle spraying circulating liquid, and the carbon dioxide content in the gas phase from the bottom of the washing tower to the top of the washing tower decreases.

[0015] (3) Circulating cooling of washing liquid and spraying liquid: The washing liquid (temperature 20-30°C, flow rate 35-45 m 3 / h) at the bottom of the washing tower is pressurized by a washing liquid circulating pump, a part of which is cooled to 15-25°C by a washing liquid cooler, and returned to the washing tower as washing liquid. The return flow rate of the washing liquid is 30-40 m 3 / h, and the temperature of the washing liquid cooled by the washing liquid cooler is reduced, which is beneficial to the absorption of carbon dioxide; the other part is extracted as a byproduct of carbon ammonium solution and stored; the washing liquid (temperature 15-25°C, flow rate 10-15 m 3h) The spray liquid is pumped by a spray liquid circulating pump, and is cooled to 15-25 DEG C by a spray liquid cooler, and is returned to the washing tower as spray liquid. The composition of the ammonium carbonate solution pumped by the washing liquid circulating pump is NH3: 18.5-20.4 wt%, CO2: 13.2-15.3 wt%, H2O: 63.3-68.1 wt%, and organic matter: 0.2-1.0 wt%; (4) Washing gas condensation and separation: The ammonia gas taken from the top of the washing tower, containing a certain amount of gaseous water and a small amount of carbon dioxide, is cooled to -5-0 DEG C by a washing tower top condenser to form a gas-liquid mixture, and then the gas-liquid mixture enters a water separator for gas-liquid separation. The separated water is taken from the bottom of the water separator and sent to the upper part of the washing tower. The relatively pure ammonia gas is taken from the top of the water separator. The operating conditions of the water separator are temperature -5-0 DEG C and pressure -60--50 kPa. The composition of the ammonia gas taken from the water separator is: ammonia content ≥ 99.2 wt%, water content ≤ 0.8 wt%, and CO2: 0-5 ppm.

[0016] The beneficial effects of the present application are: (1) The present application replaces the scrubber of the washing tower with soft water, reduces the operation units of carbonate solution crystallization and filtration, simplifies the process flow, reduces the operation difficulty and intensity, and improves the stability of the process device.

[0017] (2) The organic matter separator provided by the present application realizes efficient separation of organic matter, reduces the loss of organic matter, and reduces the cost.

[0018] (3) The present application replaces the cooling medium of the washing liquid cooler and the spray liquid cooler with chilled water, adopts a low-temperature washing method, improves the washing and absorption capacity of the scrubber, enhances the washing effect, and obtains relatively pure ammonia gas. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a gas purification device diagram in the urea and propylene glycol reaction process of the present application; Figure 2 is a structural schematic diagram of a cyclone separator; Figure 3 is a top view of Figure 2 ; and Figure 4 is a connection relationship diagram of the upper arc plate and the lower arc plate.

[0020] In the diagram: 1-Reaction gas phase condenser, 2-Organic matter separator, 3-Scrubber, 4-Scrubber liquid circulation pump, 5-Scrubber liquid cooler, 6-Spray liquid circulation pump, 7-Spray liquid cooler, 8-Scrubber top condenser, 9-Water separator, 10-Upper arc plate, 11-Lower arc plate, 12-Blade, 13-Inner wall of organic matter separator, 14-Central cylinder; A-Reaction gas, B-Organic matter, C-Soft water, D-Ammonia, E-Ammonium bicarbonate solution. Detailed Implementation

[0021] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments.

[0022] like Figure 1 As shown, the present invention provides a gas purification device for the reaction process of urea and propylene glycol, including a reaction gas phase condenser 1, an organic matter separator 2, a scrubbing tower 3, a scrubbing tower top condenser 8, a water separator 9, a scrubbing liquid cooler 5, a spray liquid cooler 7, a scrubbing liquid circulation pump 4, and a spray liquid circulation pump 6; the organic matter separator 2 is equipped with a high-efficiency cyclone separator, which can effectively separate organic liquid droplets entrained in the gas.

[0023] The top of the reaction gas phase condenser 1 is provided with an inlet for reaction gas A, and the bottom of the reaction gas phase condenser 1 is provided with an outlet for a gas-liquid mixture, which is connected to the organic matter separator 2; the side of the organic matter separator 2 is provided with an inlet for a gas-liquid mixture, which is connected to the bottom outlet of the reaction gas phase condenser 1; the bottom of the organic matter separator 2 is provided with a liquid outlet to discharge organic matter B; the top of the organic matter separator 2 is provided with a gas outlet, which is connected to the scrubbing tower 3. The bottom side of the scrubbing tower 3 has a gas inlet. The bottom of the scrubbing tower 3 has a circulation loop, which consists of a scrubbing liquid circulation pump 4, a scrubbing liquid cooler 5 connected in sequence to the scrubbing liquid inlet in the middle of the scrubbing tower 3. The outlet of the scrubbing liquid circulation pump 4 has an ammonium bicarbonate liquid outlet. The middle of the scrubbing tower 3 has a circulation loop, which consists of a spray liquid circulation pump 6, a spray liquid cooler 7 connected in sequence to the upper middle of the scrubbing tower 3. The top side of the scrubbing tower 3 has a soft water C inlet. The top of the scrubbing tower 3 has a gas outlet, which is connected to the top condenser 8 of the scrubbing tower. The top of the condenser 8 at the top of the scrubbing tower is provided with a gas inlet, which is connected to the top of the scrubbing tower 3; the bottom of the condenser 8 at the top of the scrubbing tower is provided with a gas-liquid mixture outlet, which leads to the water separator 9; the bottom of the water separator 9 is provided with a liquid outlet, which is connected to the top of the scrubbing tower 3; the top of the water separator 9 is provided with a gas outlet, which discharges ammonia D.

[0024] Further, the reaction gas phase condenser 1 and the organic matter separator 2 are arranged on the same plane, installation is convenient, in order to prevent liquid seal, the U-shaped bend is prohibited to be installed on the connecting pipeline between the reaction gas phase condenser and the organic matter separator. The cyclone separator is added in the organic matter separator. The cyclone separator mainly separates the liquid drops in the reaction gas, and reduces the content of the organic matter carried in the reaction gas.

[0025] Specifically, the cyclone separator is provided with a center cylinder 14 (for supporting) in the middle, the outer wall of the center cylinder is connected with guide plates, the guide plates are composed of upper and lower arc plates, the upper arc plate 10 and the lower arc plate 11 are arranged on the outer wall of the center cylinder 14 in a slanting downward manner, and a gap is left between adjacent two arc plates, which is beneficial to the transportation of gas; the blades 12 are arranged between the two layers of arc plates; and the two ends of the arc plates are connected with the inner wall of the organic matter separator and the center cylinder respectively. The gas-liquid mixture enters from the bottom of the organic matter separator, and the cyclone separator is located at the top of the organic matter separator; after the liquid organic matter contacts the arc plates and the blades, the liquid organic matter flows to the bottom of the organic matter separator along the guide plates and the inner wall 13 of the organic matter separator under the action of gravity, and the gas passes through the gap between the arc plates and the blades and is discharged from the top of the organic matter separator upward.

[0026] The application provides a method for purifying gas in a reaction process of urea and propylene glycol, reaction gas A enters a reaction gas phase condenser 1 for cooling; organic matter in the gas is cooled and liquefied into liquid, and uncooled carbon dioxide and ammonia gas enters an organic matter separator 2 for separation. Liquid organic matter is extracted from the bottom of the organic matter separator 2, and carbon dioxide and ammonia gas enters a washing tower 3 from the top of the organic matter separator 2 for washing. Soft water C enters the top of the washing tower 3, the washing tower 3 is in reverse contact with carbon dioxide and ammonia gas to separate carbon dioxide in the ammonia gas. The tower bottom liquid of the washing tower 3 is circulated by a washing tower circulating pump 4, part of the tower bottom liquid is cooled by a washing liquid cooler 5 and then recycled for washing, and part of the carbonammonium solution E is extracted. The liquid in the washing tower 3 is circulated by a spraying liquid circulating pump 6 and then enters a spraying liquid cooler 7 for cooling, and then enters the washing tower 3 for recycling for washing. The gas phase at the top of the washing tower 3 is cooled by a washing tower top condenser 8 and then enters a water separator 9 for separation, and pure ammonia gas D is obtained.

[0027] The application steps are as follows: soft water C enters the top of the washing tower 3, the liquid level of the tower bottom of the washing tower 3 is raised, when the liquid level reaches 30-40% of the height of the tower bottom, the washing liquid circulating pump 4 is started to establish the circulation of the washing liquid circulating pump 4 and the washing liquid cooler 5. When the reaction gas A is ready to continuously enter the reaction gas phase condenser 1, the soft water C continuously enters the washing tower 3, and the liquid level of the liquid accumulation disc arranged in the middle of the washing tower 3 is raised to 90% of the height of the liquid accumulation disc, the spraying liquid circulating pump 6 is started to establish the circulation of the spraying liquid circulating pump 6 and the spraying liquid cooler 7. The flow of the soft water C is determined according to the flow of the reaction gas A.

[0028] When the organic matter separator 2 has liquid, it is discharged into the corresponding equipment in time, and when the water separator 9 has liquid, it is self-flowed into the washing tower 3 through the height difference. When the ammonia content in the carbon ammonium solution E reaches 20% or more, it is extracted in time through the washing liquid circulating pump 4 and the liquid level of the washing tower 3 is kept stable.

[0029] The purification method of gas in the reaction process of urea and propylene glycol is described below through specific examples: Example 1

[0030] The present application provides a purification method of gas in the reaction process of urea and propylene glycol, comprising the following steps: (1) Condensation and separation of the reaction gas of urea and propylene glycol: The reaction gas containing a small amount of carbon dioxide, water, and organic matters such as propylene glycol and propylene carbonate is cooled to a certain temperature of 45-55°C through the reaction gas phase condenser 1, and almost all the organic matters such as propylene glycol and propylene carbonate are condensed. The gas-liquid mixture enters the organic matter separator 2 for gas-liquid separation, and the crude ammonia gas containing a small amount of carbon dioxide, water, and a small amount of organic matters is extracted from the top of the organic matter separator 2 and sent to the washing tower 3. The recovered organic matters are extracted from the bottom of the organic matter separator 2. The operating conditions of the organic matter separator 2 are: temperature 45°C, pressure -55kPa, and the organic matter content in the crude ammonia gas extracted from the top of the organic matter separator 2 is 0.1wt%.

[0031] (2) The crude ammonia gas is sent to the washing tower for washing: The crude ammonia gas extracted from the top of the organic matter separator 2 is sent to the washing tower from the gas inlet at the bottom of the washing tower, and is in contact with the washing circulating liquid at the bottom of the washing tower, the spraying circulating liquid in the middle, and the soft water at the top in turn from bottom to top, wherein a small amount of carbon dioxide and a small amount of organic matters are washed down, and the ammonia gas containing a certain amount of water and a small amount of carbon dioxide is extracted from the top of the washing tower. A certain amount of soft water (room temperature, flow rate 1-2m 3 / h) is added to the washing tower from the top of the washing tower 3. The operating conditions of the washing tower 3 are: tower top temperature 30°C, tower bottom temperature 20°C, operating pressure -60kPa, and the composition of the ammonia gas extracted from the top of the washing tower: CO2: 50ppm, H2O: 0.75wt%.

[0032] (3) Circulating cooling of the washing liquid and the spraying liquid: The washing liquid (temperature 20-30°C, flow rate 35-45m 3 / h) at the bottom of the washing tower is pressurized by the washing liquid circulating pump 4, a part of which is cooled to 15°C by the washing liquid cooler 4 and returned to the washing tower as the washing liquid, and the other part is extracted as the by-product of the carbon ammonium solution. The washing liquid (temperature 15°C, flow rate 10-15m 3h) is pressurized by the spray liquid circulating pump 6, is cooled to 15°C by the spray liquid cooler 7, and is returned to the scrubbing tower as spray liquid. The composition of the ammonium carbonate solution obtained from the scrubbing tower is NH3: 20.4 wt%, CO2: 15.3 wt%, H2O: 68.1 wt%, and organic matter: 0.2 wt%.

[0033] (4) Scrubbing gas condensation and separation: The ammonia gas obtained from the top of the scrubbing tower, containing a certain amount of water and a trace amount of carbon dioxide, is cooled to -5°C by the scrubbing tower top condenser 8 to form a gas-liquid mixture, and then the gas-liquid mixture is introduced into the water separator 9 for gas-liquid separation. The separated water is obtained from the bottom of the water separator and is fed to the upper part of the scrubbing tower 3. The relatively pure ammonia gas is obtained from the top of the water separator. The operating conditions of the water separator are a temperature of -5°C and a pressure of -60 kPa. The composition of the ammonia gas obtained from the water separator is: ammonia content 99.5%, water content ≤0.5 wt%, and CO2 not detected.

[0034] Example 2 (1) Condensation and separation of the reaction gas of urea and propylene glycol: The reaction gas containing a small amount of carbon dioxide, water, and organic matter such as propylene glycol and propylene carbonate is cooled to a certain temperature of 50°C by the reaction gas condenser 1, and almost all of the organic matter such as propylene glycol and propylene carbonate is condensed. The gas-liquid mixture is introduced into the organic matter separator 2 for gas-liquid separation. The crude ammonia gas containing a small amount of carbon dioxide, water, and a trace amount of organic matter is obtained from the top of the organic matter separator and is fed to the scrubbing tower 3. The recovered organic matter is obtained from the bottom of the organic matter separator. The operating conditions of the organic matter separator are a temperature of 50°C and a pressure of -50 kPa. The organic matter content in the crude ammonia gas obtained from the top of the organic matter separator is 0.3 wt%.

[0035] (2) Feeding the crude ammonia gas to the scrubbing tower for scrubbing: The crude ammonia gas obtained from the top of the organic matter separator 2 is fed to the scrubbing tower from the gas inlet at the bottom of the scrubbing tower 3. From bottom to top, the crude ammonia gas is in turn contacted with the scrubbing circulating liquid at the bottom of the scrubbing tower, the spray circulating liquid in the middle of the scrubbing tower, and the soft water at the top of the scrubbing tower in the reverse direction. A small amount of carbon dioxide and a trace amount of organic matter are scrubbed down, and the ammonia gas containing a certain amount of water and a trace amount of carbon dioxide is obtained from the top of the scrubbing tower. A certain amount of soft water (room temperature, flow rate 1-2 m 3 / h) is added to the scrubbing tower from the top of the scrubbing tower. The operating conditions of the scrubbing tower at the top are a tower top temperature of 35°C, a tower bottom temperature of 25°C, and an operating pressure of -55 kPa. The composition of the ammonia gas obtained from the top of the scrubbing tower is CO2: 80 ppm, and H2O: 0.85 wt%.

[0036] (3) Circulating cooling of the scrubbing liquid and the spray liquid: The scrubbing liquid (flow rate 35-45 m3 (h) A part of the scrubbing liquid is pumped by the scrubbing liquid circulating pump, cooled to 20°C by the scrubbing liquid cooler, and returned to the scrubbing tower as scrubbing liquid. Another part is taken out as the by-product of carbon ammonium liquid. The scrubbing liquid taken from the middle of the scrubbing tower is pumped by the spraying liquid circulating pump, cooled to 20°C by the spraying liquid cooler, and returned to the scrubbing tower as spraying liquid. The composition of the carbon ammonium liquid taken out is NH3: 19.5wt%, CO2: 14.6wt%, H2O: 65.4wt%, and organic matter 0.5wt%.

[0037] (4) Scrubbing gas condensation and separation: The ammonia gas taken from the top of the scrubbing tower, containing a certain amount of water and a small amount of carbon dioxide, is cooled to -3°C by the scrubbing tower top condenser to form a gas-liquid mixture, and then the gas-liquid mixture enters the water separator for gas-liquid separation. The separated water is taken from the bottom of the water separator and sent to the upper part of the scrubbing tower. The relatively pure ammonia gas is taken from the top of the water separator. The operating conditions of the water separator are temperature -3°C and pressure -55kPa. The composition of the ammonia gas taken from the water separator is: ammonia content 99.3%, water content 0.7wt%, and CO2: 3ppm.

[0038] Example 3 (1) Condensation and separation of reaction gas of urea and propylene glycol: The reaction gas containing a small amount of carbon dioxide, water, and organic matter such as propylene glycol and propylene carbonate is cooled to a certain temperature of 45-55°C by the reaction gas condenser, and almost all the organic matter such as propylene glycol and propylene carbonate is condensed. The gas-liquid mixture enters the organic matter separator for gas-liquid separation to obtain crude ammonia gas containing a small amount of carbon dioxide, water, and a small amount of organic matter, which is taken from the top of the organic matter separator and sent to the scrubbing tower. The recovered organic matter is taken from the bottom of the organic matter separator. The operating conditions of the organic matter separator are temperature 55°C and pressure -45kPa. The organic matter content in the crude ammonia gas taken from the top of the organic matter separator is 0.5wt%.

[0039] (2) The crude ammonia gas is sent to the scrubbing tower for scrubbing: The crude ammonia gas taken from the top of the organic matter separator 2 is sent to the scrubbing tower 3 from the gas inlet at the bottom of the scrubbing tower, and is in contact with the scrubbing circulating liquid at the bottom of the scrubbing tower, the spraying circulating liquid in the middle of the scrubbing tower, and the soft water at the top of the scrubbing tower from bottom to top. A small amount of carbon dioxide and a small amount of organic matter are scrubbed down, and the ammonia gas containing a certain amount of water and a small amount of carbon dioxide is taken from the top of the scrubbing tower. A certain amount of soft water (room temperature, flow rate 1-2m 3 (h) The soft water is added to the scrubbing tower from the top of the scrubbing tower. The operating conditions of the scrubbing tower at the top of the scrubbing tower are tower top temperature 40°C, tower bottom temperature 30°C, operating pressure -50kPa, and the composition of the ammonia gas taken from the top of the scrubbing tower is CO2: 100ppm and H2O: 1.2wt%.

[0040] (3) Scrubbing liquid and spray liquid circulation cooling: The scrubbing liquid from the bottom of the scrubbing tower is pressurized by the scrubbing liquid circulation pump 4, and a part of it is cooled to 25°C by the scrubbing liquid cooler 5 and returned to the scrubbing tower as scrubbing liquid. Another part is taken out as a by-product of carbon ammonium liquid. The scrubbing liquid taken from the middle of the scrubbing tower is pressurized by the spray liquid circulation pump 6, and cooled to 25°C by the spray liquid cooler 7 and returned to the scrubbing tower as spray liquid. The carbon ammonium liquid E taken out is composed of NH3: 18.5wt%, CO2: 13.2wt%, H2O: 68.1wt%, and organic matter 1.0wt%.

[0041] (4) Scrubbing gas condensation and separation: The ammonia gas taken from the top of the scrubbing tower 3, containing a certain amount of water and a small amount of carbon dioxide, is cooled to 0°C by the scrubbing tower top condenser 8 to form a gas-liquid mixture, and then the gas-liquid mixture enters the water separator 9 for gas-liquid separation. The separated water is taken out from the bottom of the water separator and sent to the upper part of the scrubbing tower. The relatively pure ammonia gas is taken out from the top of the water separator. The operating conditions of the water separator are temperature 0°C and pressure -50kPa. The composition of the ammonia gas taken out from the water separator is: ammonia content 99.2wt%, water content 0.8wt%, and CO2: 5ppm.

Claims

1. A gas purification device for the reaction of urea and propylene glycol, characterized in that: It includes a reaction gas phase condenser, an organic matter separator, a scrubbing tower, a scrubbing tower top condenser, a water separator, a scrubbing liquid cooler, a spray liquid cooler, a scrubbing liquid circulation pump, and a spray liquid circulation pump; the organic matter separator is equipped with a cyclone separator to separate organic liquid droplets entrained in the gas; The top of the reaction gas phase condenser has an inlet for the reaction gas, and the bottom of the reaction gas phase condenser has an outlet for the gas-liquid mixture, which is connected to the organic matter separator; the side of the organic matter separator has an inlet for the gas-liquid mixture, which is connected to the bottom outlet of the reaction gas phase condenser; the bottom of the organic matter separator has a liquid outlet, and the top of the organic matter separator has a gas outlet, which is connected to the scrubbing tower. The scrubbing tower has a gas inlet on its bottom side and a circulation loop at the bottom, consisting of a scrubbing liquid circulation pump, a scrubbing liquid cooler, and a scrubbing liquid inlet in the middle of the tower connected in sequence. The scrubbing liquid circulation pump outlet has an ammonium bicarbonate liquid outlet. The middle of the scrubbing tower has a circulation loop consisting of a spray liquid circulation pump, a spray liquid cooler, and a circulation loop in the upper middle section of the tower connected in sequence. The top of the scrubbing tower has a soft water inlet on its top side and a gas outlet at the top, connected to the top condenser. The top of the condenser at the top of the scrubbing tower has a gas inlet connected to the top of the scrubbing tower; the bottom of the condenser at the top of the scrubbing tower has a gas-liquid mixture outlet leading to a water separator; the bottom of the water separator has a liquid outlet connected to the top of the scrubbing tower; and the top of the water separator has a gas outlet.

2. The gas purification device during the reaction of urea and propylene glycol according to claim 1, characterized in that: The reaction gas phase condenser and the organic matter separator are installed on the same plane, and U-shaped bends are prohibited on the connecting pipes between the reaction gas phase condenser and the organic matter separator.

3. The gas purification device during the reaction of urea and propylene glycol according to claim 1, characterized in that: The cyclone separator has a central cylinder in the middle, and the outer wall of the central cylinder is connected to the guide plate. The guide plate consists of two layers of arc plates, with the upper and lower arc plates evenly and obliquely arranged along the outer wall of the central cylinder. There is a gap between two adjacent arc plates to facilitate gas transport. Blades are installed between the two layers of arc plates. The two ends of the arc plates are connected to the inner wall of the organic matter separator and the central cylinder, respectively.

4. A method for purifying gas during the reaction of urea and propylene glycol, comprising the gas purification apparatus for the reaction of urea and propylene glycol as described in any one of claims 1 to 3, characterized in that... Includes the following steps: (1) Condensation and separation of the reaction gases of urea and propylene glycol: The reaction gas containing small amounts of carbon dioxide, water, propylene glycol, and propylene carbonate organic matter is passed through a reaction gas phase condenser and cooled to 45–55°C. The propylene glycol and propylene carbonate organic matter are condensed due to the decrease in temperature. The gas-liquid mixture enters an organic matter separator for gas-liquid separation. Crude ammonia gas containing small amounts of carbon dioxide, water, and trace amounts of organic matter is collected from the top of the organic matter separator and sent to a scrubbing tower. The recovered organic matter is collected from the bottom of the organic matter separator. (2) Crude ammonia gas is sent to a scrubbing tower for washing: The crude ammonia gas extracted from the top of the organic matter separator is sent into the scrubbing tower through the gas inlet at the bottom of the scrubbing tower, while soft water is added from the top of the scrubbing tower. The crude ammonia gas comes into counter-current contact with the scrubbing circulating liquid at the bottom of the scrubbing tower, the spray circulating liquid in the middle, and the soft water at the top in sequence from bottom to top. A small amount of carbon dioxide and trace amounts of organic matter are absorbed by the ammonia water formed by the soft water and ammonia gas. The ammonia gas carrying gaseous water and trace amounts of carbon dioxide is extracted from the top of the scrubbing tower. (3) Circulation and cooling of washing liquid and spray liquid: The washing liquid at the bottom of the washing tower is pressurized by a washing liquid circulation pump. A portion of it is cooled to 15-25°C by a washing liquid cooler and returned to the washing tower as washing liquid, with a return flow rate of 30-40 m³ / h. 3 / h, the temperature of the washing liquid is reduced by the washing liquid cooler, which is beneficial for the absorption of carbon dioxide; another part is collected and stored as ammonium bicarbonate liquid by-product; the washing liquid collected from the middle of the washing tower is pressurized by the spray liquid circulation pump, cooled to 15-25°C by the spray liquid cooler, and returned to the washing tower as spray liquid. (4) Scrubbing gas condensation and separation: The ammonia gas collected from the top of the scrubbing tower contains gaseous water and trace amounts of carbon dioxide. After passing through the condenser at the top of the scrubbing tower, it is cooled to -5 to 0°C, forming a gas-liquid mixture. The gas-liquid mixture then enters the water separator for gas-liquid separation. The separated water is collected from the bottom of the water separator and sent to the top of the scrubbing tower; the purer ammonia gas is collected from the top of the water separator.

5. The method for purifying gas during the reaction of urea and propylene glycol according to claim 4, characterized in that: In step (1), the gas-liquid mixture enters from the bottom of the organic matter separator, and the cyclone separator is located at the top of the organic matter separator; after the liquid organic matter comes into contact with the arc plate and blades, it flows along the guide plate and the inner wall of the organic matter separator to the bottom of the organic matter separator under the action of gravity, and the gas passes through the gap between the arc plate and blades and is discharged upward from the top of the organic matter separator; the cyclone separator separates the liquid droplets in the reaction gas and reduces the organic matter content carried in the reaction gas.

6. The method for purifying gas during the reaction of urea and propylene glycol according to claim 4, characterized in that: In step (1), the cooling medium of the reaction gas phase condenser is water. It is forbidden to stop using the cooling medium to prevent a large amount of organic matter from entering the washing tower, which would result in a low yield of organic matter. The water temperature of the cooling medium is controlled at 20-30°C, and the reaction gas is cooled to 45-55°C. The operating conditions for the organic matter separator are: temperature of 45-55℃, pressure of -55--45kPa, and organic matter content of the crude ammonia gas extracted from the top of the organic matter separator is 0.1-0.5wt%.

7. The method for purifying gas during the reaction of urea and propylene glycol according to claim 4, characterized in that: In step (2), the operating conditions of the scrubbing tower are: top temperature of 30-40℃, bottom temperature of 20-30℃, operating pressure of -60 to -50 kPa, and the ammonia gas composition at the top of the scrubbing tower is: CO2: 50-100 ppm, H2O: 0.75–1.2 wt%; soft water at room temperature, flow rate 1–2 m³ / h 3 / h, the washing circulating liquid at the bottom of the washing tower and the spray circulating liquid in the middle are ammonium bicarbonate solutions.

8. The method for purifying gas during the reaction of urea and propylene glycol according to claim 4, characterized in that: In step (3), the temperature of the washing liquid at the bottom of the washing tower is 20-30℃, and the flow rate is 35-45m³. 3 / h; the temperature of the washing liquid collected in the middle of the washing tower is 15-25℃, and the flow rate is 10-15m³ / h. 3 / h; The composition of the ammonium bicarbonate solution collected by the washing liquid circulation pump is NH3: 18.5~20.4wt%, CO2: 13.2~15.3wt%, H2O: 63.3~68.1wt%, and organic matter 0.2~1.0wt%.

9. The method for purifying gas during the reaction of urea and propylene glycol according to claim 4, characterized in that: In step (4), the operating conditions of the water separator are: temperature -5~0℃, pressure -60~-50kPa, and the composition of the ammonia gas extracted by the water separator is: ammonia content ≥99.2wt%, water content ≤0.8wt%, CO2: 0~5ppm.

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