CN116081642A - Process for producing liquid ammonia by low-pressure ammonia synthesis - Google Patents

Abstract

The invention relates to a low-pressure ammonia synthesis production liquid ammonia process, wherein a reaction device comprises an ammonia synthesis reaction system, a waste heat recovery system, an ammonia recovery system, a rectification purification system and a circulating gas pressurization system; the ammonia synthesis reaction does not need additional pressurization, so that the compression power consumption is reduced; the ammonia content in the circulating gas is very low, so that the single-pass conversion rate of the synthesis reaction is improved; the ammonia separation and recovery adopts the ways of absorption and rectification, and compared with the existing ice machine refrigeration scheme, the method reduces the compression mechanical loss and improves the energy utilization efficiency; the rectification heat source can adopt a low-grade heat source, which is beneficial to improving the energy utilization efficiency of the whole plant. The invention adopts the conventional heat exchanger, the tower, the container and the reactor, only one circulating gas compressor and the conventional machine pump are adopted in mechanical equipment, the operating condition of the circulating gas compressor is mild, compared with the conventional synthesis process, the investment is obviously reduced, and the reliability of the mechanical equipment is obviously improved.

Description

Process for producing liquid ammonia by low-pressure ammonia synthesis

Technical Field

The invention relates to the technical field of liquid ammonia production, in particular to a process for producing liquid ammonia by low-pressure ammonia synthesis.

Background

Liquid ammonia is an important fertilizer raw material and a hydrogen carrying medium, and the ammonia synthesis process is widely applied to the fields of fertilizer and hydrogen storage. At present, the raw material hydrogen for producing the liquid ammonia has various sources, is prepared by directly converting fossil raw materials and hydrolyzing water, and also has refinery byproducts. Regardless of the source, the pressure of the hydrogen is lower, such as fossil feedstock coal gasification, the pressure of the hydrogen produced is generally below 5.5MPag (coal water slurry gasification has a few operating performance of 8.7 MPag), while the pressure of the hydrogen produced by water electrolysis and refinery by-products (such as propane dehydrogenation, naphtha reforming) is lower.

According to the reaction characteristics of ammonia synthesis, the existing ammonia synthesis liquid ammonia production process adopts a pressurizing and cooling separation method, wherein the ammonia synthesis pressure is generally above 10MPag, an iron-based catalyst is adopted, the pressure of the low-pressure ammonia synthesis production process which is currently mainstream is 13-14 MPag, a fixed bed reactor is adopted, the net value of ammonia synthesis can reach above 18%vol, high-temperature synthesis gas at the outlet of the reactor is subjected to waste heat recovery and then is cooled to separate liquid ammonia, and the synthesis gas after the separation of the liquid ammonia is circulated and returned to an ammonia synthesis tower. As shown in FIG. 1, a representative ammonia synthesis process flow in the prior art mainly comprises a synthesis reaction, waste heat recovery, refrigeration and start-up heating system, wherein fresh ammonia synthesis gas is pressurized (generally 13-14 MPag) and then mixed with refrigeration separated circulating synthesis gas, the ammonia content is generally less than 3 percent (vol), the mixture is pressurized by a circulating gas compressor and then sent to a synthesis tower for carrying out ammonia synthesis reaction, the ammonia content of the synthesis gas reacted in the synthesis tower is generally more than 20 percent (vol), the temperature exceeds 400 ℃, and then the synthesis gas enters a waste heat recovery system, and medium-pressure steam is generated as a byproduct; after the waste heat is recovered, the synthesis gas further passes through a hot gas heat exchanger, a water cooler, a cold gas heat exchanger and an ammonia cooler, and then enters an ammonia separator for liquid ammonia separation; the temperature of the ammonia cooler is generally-12-4 ℃, and the ammonia cooler is provided by an ice machine; the process is generally provided with a start-up heating furnace (device) which is used when the original start-up or the temperature of the catalyst is raised.

The existing ammonia synthesis process is provided with an ammonia synthesis gas compressor, an ice maker and a circulating gas compressor, wherein the ammonia synthesis gas compressor and the circulating gas compressor are integrated into a multi-cylinder multi-section compressor, the ice maker is usually an ammonia ice maker, and single-cylinder two-section compression is adopted. Although the flow is simpler, the high-pressure operation condition has strict requirements on equipment, the equipment cost of a compressor is high, the equipment cost of the compressor is basically about 6000 ten thousand, and the equipment investment is high in a conventional 30 ten thousand ton/year ammonia synthesis device; and because the equipment cost of the compressor is high, the compressor adopts a single series of configuration schemes, and once the compressor fails, the device is stopped, and the overall operation reliability depends on the stability of the compressor.

Disclosure of Invention

Aiming at the current state of the art, the invention provides a low-pressure ammonia synthesis liquid ammonia production process which separates and purifies ammonia in a mode of ammonia absorption and rectification so as to reduce a compressor, cancel the setting of an ice maker and further reduce equipment investment and energy consumption.

The technical scheme adopted for solving the technical problems is as follows:

the reaction device adopted in the low-pressure ammonia synthesis production liquid ammonia process comprises an ammonia synthesis reaction system, a waste heat recovery system, an ammonia recovery system, a rectification purification system and a circulating gas pressurization system; the low-pressure ammonia synthesis production liquid ammonia process comprises the following steps:

(1) The ammonia synthesis fresh gas from the upstream enters an ammonia synthesis reactor R-001 together with the circulating synthesis gas to carry out ammonia synthesis reaction, ammonia-containing synthesis gas generated by the reaction is sent out from the top of the ammonia synthesis reactor to enter a catalyst filter S-001 to remove fine catalyst particles entrained by the synthesis gas, the catalyst particles return to the ammonia synthesis reactor R-001 through gravity, and purified ammonia-containing synthesis gas exiting the catalyst filter S-001 enters a waste heat recovery system;

(2) The high-temperature synthesis gas from the ammonia synthesis reaction system enters a steam generator E-001 and then enters a boiler water preheater E-002 to recover waste heat, then enters a circulating gas heat exchanger E-003 to exchange heat with the synthesis gas at the outlet of a circulating gas compressor K-001, and the synthesis gas after heat exchange enters a water washing system; the synthesis gas of the ammonia synthesis reactor K-001 is sent into the ammonia synthesis reactor after the heat exchange temperature is increased;

(3) The synthesis gas from the waste heat recovery system enters a water cooler E-004 for further cooling and then is sent into an ammonia washing tower C-001, gas phase ammonia in the synthesis gas is dissolved in a liquid phase, and the synthesis gas at the top of the ammonia washing tower C-001 is cooled by an ammonia washing tower top cooler E-011 and is sent to a circulating gas pressurizing system after the liquid phase is separated by an ammonia washing tower top separator V-003; the ammonia washing solvent at the bottom of the ammonia washing tower C-001 is cooled by an ammonia washing tower circulating pump P-001, one part of the ammonia washing solvent is circulated back to the top of the ammonia washing tower C-001 after being cooled by a circulating ammonia-rich liquid cooler E-009 and is used as the ammonia washing solvent, and the other part of the ammonia washing solvent is sent to an ammonia rectifying and purifying system after being depressurized;

(4) The ammonia-containing solvent from the ammonia recovery system is decompressed and then sent into a flash tank V-002, a small amount of hydrogen and nitrogen dissolved in ammonia-rich liquid are flashed out, the flashed liquid phase is heated by a rectifying tower feeding heat exchanger E-010 and then enters an ammonia rectifying tower C-002, high-concentration ammonia gas at the top of the tower is cooled by a rectifying tower top cooler E-006 and then enters an ammonia rectifying tower top reflux tank V-001, noncondensable gas at the top of the reflux tank is discharged, one part of the liquid phase is returned to the rectifying tower C-002 by an ammonia rectifying tower top reflux pump P-003, and the other part of the liquid phase is cooled by an ammonia cooler E-009 and then is sent out as a product;

(5) The synthesis gas carrying trace ammonia solvent from the top of the ammonia scrubber C-002 enters a circulating gas purifying molecular sieve R-002 to remove trace solvent, so that the oxygen atom content in the synthesis gas entering an ammonia synthesis reactor is controlled, and the service life of the catalyst is ensured; the synthesis gas passing through the circulating gas purifying molecular sieve R-002 enters a circulating gas compressor K-001 to be pressurized so as to balance the pressure drop of the system, and the pressurized circulating synthesis gas enters an ammonia synthesis reactor R-001 together with fresh ammonia synthesis gas after heat exchange and temperature rise of a circulating gas heat exchanger E-003.

The invention adopts a low-pressure fluidized bed ammonia synthesis reactor, the granularity of the catalyst is in the micron order, and the preferable density of main particles is less than 100 mu m. The reaction pressure is less than 10MPag, the air inlet pressure of the ammonia synthesis gas is matched with the upstream hydrogen pressure, a synthesis gas compressor is not arranged, the operation pressure is 2.8MPag corresponding to pulverized coal gasification, the operation pressure is 5.0MPag corresponding to coal water slurry gasification and oil gasification, and the operation pressure is 1.2MPag corresponding to water electrolysis hydrogen production. The synthesis gas ammonia recovery adopts a mode of absorbing and rectifying a solvent, ammonia rich liquor of an ammonia washing tower is circulated, lean ammonia liquor of the rectifying tower is circulated and returned to the ammonia washing tower to be used as an ammonia washing solvent, and the ammonia washing solvent is an ammonia-containing mixed solution with a proper range of ammonia concentration, so that the ammonia content in the synthesis gas at the outlet of the ammonia washing tower is low, the concentration of an oxygen-containing medium is low, and the energy consumption of rectification is low, thereby minimizing the energy consumption and the operation cost of the whole process flow. The circulating gas purification of the invention removes oxygen-containing medium in the circulating synthetic gas by means of circulating water cooling and molecular sieve purification and thermal regeneration, and ensures continuous operation. The energy consumption of the invention is mainly the heat consumption of the reboiler of the rectifying tower, the power source of the reboiler can select low-grade steam to improve the utilization rate of low-grade heat of the whole plant, and the power source of the reboiler is selectively coupled with the hot synthesis gas at the outlet of the synthesis reactor to reduce the dependence of external power steam.

In step (1), when the apparatus is started up or the temperature of the ammonia synthesis reactor R-001 is low, the ammonia synthesis fresh gas is heated by the start-up heater F-001 to promote the ammonia synthesis reaction.

In the step (3), another ammonia washing solvent at the top of the ammonia washing tower C-001 comes from the ammonia-containing solvent returned by the ammonia rectification and purification system, and the ammonia washing solvent of the ammonia washing tower C-001 is supplemented from the top of the tower to balance the trace ammonia washing solvent loss carried by the synthesis gas at the top of the tower.

In the step (4), ammonia lean liquid at the bottom of the ammonia rectification C-002 tower is sent to an ammonia recovery system through a lean liquid booster pump P-002.

In the step (5), R-002 is provided with a device and a device, and continuous operation is realized by a steam heating regeneration mode.

The ammonia synthesis reactor R-001 comprises:

the shell is internally hollow and is provided with a first part and a second part which are connected up and down, the upper part of the second part forms a reaction area, the lower part of the second part forms a catalyst accommodating area, the diameter of the first part is larger than that of the second part to form a catalyst separation area, and the top of the shell is provided with an air outlet;

the first mixing section is arranged at the upper part of the second part and extends vertically, the top of the first mixing section is provided with an ammonia synthesis fresh gas inlet and a first circulating gas inlet, and the bottom of the first mixing section is provided with an outlet;

the heat exchanger is connected below the first mixing section and is used for preheating the mixed gas output by the first mixing section to a temperature above the activation temperature of the catalyst;

the second mixing section is connected below the heat exchanger, the top of the second mixing section is provided with a second circulating gas inlet for further mixing the preheated mixed gas output by the heat exchanger with the second circulating gas, and the bottom of the second mixing section is provided with an output port for outputting the mixed reaction gas to the catalyst accommodating area;

the inner edge of the partition plate is connected with the outer wall of the second mixing section, the outer edge of the partition plate is connected with the inner wall of the shell, the partition plate is used for separating the second part into a relatively independent reaction area and a catalyst accommodating area, and a plurality of openings which can be matched with the reaction gas at a high speed to enable the catalyst carried by the reaction gas and the reaction gas to form a fluidization state and enter the reaction area are formed in the partition plate.

The ammonia synthesis reactor R-001 of the invention is used for injecting the raw material gas into a plurality of streams, which is beneficial to improving the uniformity of gas flow distribution; the preheated reaction gas is used for uniformly distributing the catalyst in the reaction area after fluidization, and the raw material gas is fully contacted with the catalyst, so that the reaction efficiency and the reaction conversion rate are improved; the reaction gas in the reaction area and the produced high-temperature synthesis gas are always in contact with the heat exchange part, heat is recovered in real time and used for preheating the mixed gas, so that the energy utilization rate is improved, the energy consumption of the device is reduced, and meanwhile, the temperature of the gas in the reaction area after the heat is recovered is controlled, so that the reaction conversion rate is further improved.

Preferably, the gas separated by the catalyst separation area is output through the gas outlet, and the separated catalyst is settled into the reaction area under the gravity to be mixed with the fluidized material conveyed upwards and participate in the fluidized reaction; the high-temperature synthesis gas generated by the fluidized reaction is used as a heat source to preheat the mixed gas conveyed to the second mixing section through the heat exchanger. The high temperature synthesis gas generated in the reaction zone of the present invention has the following effects: (1) The catalyst is conveyed upwards to impact the separated and sinking catalyst, so that the catalyst can immediately participate in fluidized reaction, and the catalyst and the reaction gas in the reaction area are uniformly mixed, so that the reaction efficiency is improved; (2) The mixed gas which is downwards conveyed by the heat exchanger is preheated by being used as a heat source, so that the energy benefit rate is improved; (3) The heat of the high-temperature synthesis gas is partially recovered while the material in the heat exchanger is preheated as a heat source, so that the temperature is reduced, the reaction is facilitated, and the reaction conversion rate is improved.

Preferably, the first mixing section, the heat exchanger and the second mixing section are mutually connected from top to bottom to form a whole vertically arranged in the second part of the shell, the upper end of the first mixing section forms an upwards arched flow guiding surface, the first part and the second part are connected through a transition section with gradually increased diameter from bottom to top, and the flow guiding surface is lower than the transition section.

Preferably, the catalyst filter S-001 is arranged at the top of the shell and is connected in series with the shell, an inlet of the catalyst filter S-001 is connected with an air outlet at the top of the shell, a synthesis gas outlet is arranged at the top of the catalyst filter S-001, and a reflux pipeline for allowing the separated catalyst to reflux into the shell is arranged at the bottom of the catalyst filter S-001.

Compared with the prior art, the invention has the advantages that: the ammonia synthesis reactor R-001 adopts a micron-sized catalyst, has high reaction efficiency, can complete the synthesis reaction under low pressure, has sufficient contact between raw material gas in the reactor and the catalyst, is favorable for improving the catalytic activity and the single-pass conversion rate, and ensures better ammonia net value under the low-pressure operation condition;

the invention adopts the conventional heat exchanger, the tower, the container and the reactor, only one circulating gas compressor and the conventional machine pump are adopted in the mechanical equipment, the operating condition of the circulating gas compressor is mild, compared with the conventional synthesis process, the investment is obviously reduced, and the reliability of the mechanical equipment is obviously improved;

because the ammonia synthesis reactor R-001 has low operating pressure, obviously reduced hydrogen partial pressure and low leakage risk, the manufacturing and material selection requirements of equipment are reduced, and meanwhile, the connection of pipelines, valves and the like can be flange connection due to the reduction of the operating pressure, thereby being beneficial to equipment maintenance and thoroughly solving the phenomenon of ammonia odor in the environment of the existing ammonia synthesis device;

the ammonia synthesis reaction does not need additional pressurization, so that the compression power consumption is reduced; the ammonia content in the circulating gas is very low, so that the single-pass conversion rate of the synthesis reaction is improved; the ammonia separation and recovery adopts the ways of absorption and rectification, and compared with the existing ice machine refrigeration scheme, the method reduces the compression mechanical loss and improves the energy utilization efficiency; the rectification heat source can adopt a low-grade heat source, which is beneficial to improving the energy utilization efficiency of the whole plant.

Drawings

FIG. 1 is a process flow diagram of the background art of the invention;

FIG. 2 is a process flow diagram of an embodiment of the present invention;

FIG. 3 is a diagram showing a structure of the ammonia synthesis reactor R-001 and the catalyst filter S-001 in FIG. 2.

Detailed Description

The invention is described in further detail below with reference to the embodiments of the drawings.

As shown in fig. 2 and 3, the device adopted in the low-pressure ammonia synthesis process for producing liquid ammonia in this embodiment comprises an ammonia synthesis reaction system, a waste heat recovery system, an ammonia recovery system, a rectification purification system and a recycle gas pressurization system, wherein the ammonia synthesis reaction system comprises an ammonia synthesis reactor R-001, a start-up heater F-001 and a catalyst filter S-001; the waste heat recovery system comprises a steam generator E-001, a boiler water preheater E-002 and a circulating gas heat exchanger E-003; the ammonia recovery system comprises a water cooler E-004, an ammonia washing tower C-001, an ammonia washing tower circulating pump P-001, an ammonia washing tower water cooler E-005, a circulating ammonia-rich liquid cooler E-009, an ammonia washing tower top cooler E-011 and an ammonia washing tower top separator V-003; the ammonia water rectification system comprises a rectification tower C-002, a flash tank V-002, an ammonia rectification tower top cooler E-006, an ammonia rectification tower top reflux tank V-001, a lean solution booster pump P-002, an ammonia rectification tower top reflux pump P-003, an ammonia cooler E-007, a rectification tower reboiler E-008 and a rectification tower feeding heat exchanger E-010; the circulating gas pressurizing system comprises a circulating gas purifying molecular sieve R-002 and a circulating gas compressor K-001; the specific arrangement and connection of the components are consistent with fig. 2.

The low-pressure ammonia synthesis production liquid ammonia process of the embodiment comprises the following steps:

(1) The ammonia synthesis fresh gas from the upstream enters an ammonia synthesis reactor R-001 together with the circulating synthesis gas to carry out ammonia synthesis reaction, ammonia-containing synthesis gas generated by the reaction is sent out from the top of the ammonia synthesis reactor to enter a catalyst filter S-001 to remove fine catalyst particles entrained by the synthesis gas, the catalyst particles return to the ammonia synthesis reactor R-001 through gravity, and purified ammonia-containing synthesis gas exiting the catalyst filter S-001 enters a waste heat recovery system; heating ammonia synthesis fresh gas by a start-up heater F-001 to promote ammonia synthesis reaction when the device is started or the temperature of an ammonia synthesis reactor R-001 is low;

(2) The high-temperature synthesis gas from the ammonia synthesis reaction system enters a steam generator E-001 and then enters a boiler water preheater E-002 to recover waste heat, then enters a circulating gas heat exchanger E-003 to exchange heat with the synthesis gas at the outlet of a circulating gas compressor K-001, and the synthesis gas after heat exchange enters a water washing system; the synthesis gas of the ammonia synthesis reactor K-001 is sent into the ammonia synthesis reactor after the heat exchange temperature is increased;

(3) The synthesis gas from the waste heat recovery system enters a water cooler E-004 for further cooling and then is sent into an ammonia washing tower C-001, gas phase ammonia in the synthesis gas is dissolved in a liquid phase, and the synthesis gas at the top of the ammonia washing tower C-001 is cooled by an ammonia washing tower top cooler E-011 and is sent to a circulating gas pressurizing system after the liquid phase is separated by an ammonia washing tower top separator V-003; the ammonia washing solvent at the bottom of the ammonia washing tower C-001 is cooled by an ammonia washing tower circulating pump P-001, one part of the ammonia washing solvent is circulated back to the top of the ammonia washing tower C-001 after being cooled by a circulating ammonia-rich liquid cooler E-009 and is used as the ammonia washing solvent, and the other part of the ammonia washing solvent is sent to an ammonia rectifying and purifying system after being depressurized; the other ammonia-washing solvent at the top of the ammonia-washing tower C-001 comes from the ammonia-containing solvent returned by the ammonia rectification and purification system, and the ammonia-washing solvent of the ammonia-washing tower C-001 is supplemented from the top of the tower to balance the trace ammonia-washing solvent loss carried by the synthesis gas at the top of the tower;

(4) The ammonia-containing solvent from the ammonia recovery system is decompressed and then sent into a flash tank V-002, a small amount of hydrogen and nitrogen dissolved in ammonia-rich liquid are flashed out, the flashed liquid phase is heated by a rectifying tower feeding heat exchanger E-010 and then enters an ammonia rectifying tower C-002, high-concentration ammonia gas at the top of the tower is cooled by a rectifying tower top cooler E-006 and then enters an ammonia rectifying tower top reflux tank V-001, noncondensable gas at the top of the reflux tank is discharged, one part of the liquid phase is returned to the rectifying tower C-002 by an ammonia rectifying tower top reflux pump P-003, and the other part of the liquid phase is cooled by an ammonia cooler E-009 and then is sent out as a product; ammonia lean liquor at the bottom of the ammonia rectification C-002 tower is sent to an ammonia recovery system through a lean liquor booster pump P-002;

(5) The synthesis gas carrying trace ammonia solvent from the top of the ammonia scrubber C-002 enters a circulating gas purifying molecular sieve R-002 to remove trace solvent, so that the oxygen atom content in the synthesis gas entering an ammonia synthesis reactor is controlled, and the service life of the catalyst is ensured; the synthesis gas passing through the circulating gas purifying molecular sieve R-002 enters a circulating gas compressor K-001 to be pressurized so as to balance the pressure drop of the system, and the pressurized circulating synthesis gas enters an ammonia synthesis reactor R-001 together with fresh ammonia synthesis gas after heat exchange and temperature rise of a circulating gas heat exchanger E-003; r-002 is provided with a first device and a second device, and continuous operation is realized by a steam heating regeneration mode.

The ammonia synthesis reactor R-001 includes:

the shell 1 is internally hollow and is provided with a first part 101 and a second part 102 which are connected up and down, the upper part of the second part 102 is provided with a reaction area 1021, the lower part of the second part 102 is provided with a catalyst accommodating area 1022, the diameter of the first part 101 is larger than that of the second part 102 to form a catalyst separation area, and the top of the shell 1 is provided with an air outlet N4;

the first mixing section 10a is arranged at the upper part of the second part 102 and extends vertically, the top of the first mixing section 10a is provided with an ammonia synthesis fresh gas inlet 01, a first circulating gas inlet 02 and the bottom is provided with an outlet;

a heat exchanger 3 connected below the first mixing section 10a for preheating the mixed gas output from the first mixing section 10a to a temperature above the catalyst activation temperature; the heat exchanger of the embodiment adopts the tube type heat exchange tube 9, and the tube type heat exchange tube 9 is provided with the stress compensator 7, which is not limited to natural compensation or mechanical compensation;

the second mixing section 4 is connected below the heat exchanger 3, the top of the second mixing section 4 is provided with a second circulating gas inlet 03 for further mixing the preheated mixed gas output by the heat exchanger 3 with the second circulating gas, and the bottom of the second mixing section 4 is provided with an output port 5 for outputting the mixed reaction gas to the catalyst accommodating area 1022; a plurality of first mixing plates 10 which are arranged at intervals up and down and are staggered are arranged in the first mixing section 10a, and a plurality of second mixing plates 11 which are arranged at intervals up and down and are staggered are arranged in the second mixing section 4, so that the structure is beneficial to improving the gas mixing effect;

the inner edge of the partition plate 6 is connected with the outer wall of the second mixing section 4, the outer edge of the partition plate is connected with the inner wall of the shell 1, and the partition plate 6 is used for separating the second part 102 into a relatively independent reaction area 1021 and a catalyst accommodating area 1022, and a plurality of openings capable of forming a fluidization state with the catalyst carried by the reaction gas and the reaction gas into the reaction area 1021 by being matched with the reaction gas flow. The partition 6 is gradually arranged in a downward slope from the outside to the inside.

A catalyst loading opening N6 arranged below the partition plate 6 is arranged on the side wall of the shell 1, and a catalyst unloading opening N7 is arranged at the bottom of the shell 1. In this example, conventional iron-based or ruthenium-based catalysts, novel catalysts having high activity at low temperatures and low pressures, and the like can be used as long as the particle size and strength satisfy the requirements.

In this embodiment, the gas separated by the catalyst separation zone is output through the gas outlet N4, and the separated catalyst is settled into the reaction zone 1021 under gravity to be mixed with the fluidized material conveyed upwards and participate in the fluidized reaction; the high-temperature synthesis gas generated by the fluidized reaction is used as a heat source to preheat the mixed gas conveyed to the second mixing section 4 through the heat exchanger 3. The high temperature synthesis gas produced in the reaction zone 1021 of this example has the following effects: (1) The catalyst is conveyed upwards to impact the separated and sunk catalyst, so that the catalyst can immediately participate in fluidized reaction, and the catalyst and the reaction gas in the reaction area 1021 are uniformly mixed, so that the reaction efficiency is improved; (2) As a heat source, the mixed gas conveyed downwards through the heat exchanger 3 is preheated, so that the energy utilization rate is improved; (3) The heat of the high-temperature synthesis gas is partially recovered while the materials in the heat exchanger 3 are preheated as a heat source, so that the temperature is reduced, the reaction is facilitated, and the reaction conversion rate is improved.

The lower end of the second mixing section 4 extends to the inner bottom wall of the shell 1 to form a blind end, and the output port 5 is arranged on the side wall of the second mixing section 4 in a mesh-shaped mode and is close to the inner bottom wall of the shell 1, so that the reaction gas is uniformly sprayed out by the structure, and the fluidized reaction materials uniformly distributed are favorably and rapidly formed. The inner bottom wall of the shell 1 is shaped into a downward arched structure, and the lower end of the second mixing section 4 is arranged corresponding to the central part of the arched structure, so that the structure is beneficial to guiding the output airflow upwards and improving the mixing effect with the catalyst.

The first mixing section 10a, the heat exchanger 3 and the second mixing section 4 are mutually connected from top to bottom to form a whole which is vertically arranged in the second part 102 of the shell 1, the upper end of the first mixing section 10a forms an upwards arched flow guiding surface, the first part 101 is connected with the second part 102 through a transition section with gradually increased diameter from bottom to top, and the flow guiding surface is lower than the transition section. The integral structure realizes the respective mixing and heat exchanging effects, and simultaneously the formed integral body is positioned in the center of the shell 1, and the reaction area 1021 is restrained to be of an annular structure, so that the high-temperature synthesis gas generated in the reaction area 1021 uniformly surrounds the periphery of the heat exchanging area, and the heat recovery of the high-temperature synthesis gas and the preheating effect of the heat exchanger on the mixed gas are improved to the greatest extent.

The catalyst filter S-0012 is arranged at the top of the shell 1 and is connected in series with the shell 1, an inlet N8 of the catalyst filter S-0012 is connected with an air outlet N4 at the top of the shell 1, a synthesis gas outlet N9 is arranged at the top of the catalyst filter S-0012, and a return pipeline for returning separated catalyst to the shell 1 is arranged at a bottom outlet N10 of the catalyst filter S-0012. The junction N5 of the return line with the housing 1 is located below the transition section and above the flow guiding surface. The structure is favorable for improving the catalyst recovery effect, the recovered catalyst is input from the position, the catalyst utilization effect is favorable for improving, and the reaction efficiency is further improved.

The above scheme is described by taking water as an example for ammonia trapping solvent on a 1000 ton/day liquid ammonia scale, and the ratio of pure hydrogen to nitrogen (H ₂ /N ₂ =3), synthesis pressure 2.8MPag, theoretical ammonia net 12.73% (synthesis column outlet ammonia content minus synthesis column inlet ammonia content), reaction parameters as follows.

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Claims (9)

1. A low-pressure ammonia synthesis production liquid ammonia process is characterized in that: the reaction device adopted in the low-pressure ammonia synthesis production liquid ammonia process comprises an ammonia synthesis reaction system, a waste heat recovery system, an ammonia recovery system, a rectification purification system and a circulating gas pressurization system; the low-pressure ammonia synthesis production liquid ammonia process comprises the following steps:

(1) The ammonia synthesis fresh gas from the upstream enters an ammonia synthesis reactor R-001 together with the circulating synthesis gas to carry out ammonia synthesis reaction, ammonia-containing synthesis gas generated by the reaction is sent out from the top of the ammonia synthesis reactor to enter a catalyst filter S-001 to remove fine catalyst particles entrained by the synthesis gas, the catalyst particles return to the ammonia synthesis reactor R-001 through gravity, and purified ammonia-containing synthesis gas exiting the catalyst filter S-001 enters a waste heat recovery system;

(2) The high-temperature synthesis gas from the ammonia synthesis reaction system enters a steam generator E-001 and then enters a boiler water preheater E-002 to recover waste heat, then enters a circulating gas heat exchanger E-003 to exchange heat with the synthesis gas at the outlet of a circulating gas compressor K-001, and the synthesis gas after heat exchange enters a water washing system; the synthesis gas of the ammonia synthesis reactor K-001 is sent into the ammonia synthesis reactor after the heat exchange temperature is increased;

(3) The synthesis gas from the waste heat recovery system enters a water cooler E-004 for further cooling and then is sent into an ammonia washing tower C-001, gas phase ammonia in the synthesis gas is dissolved in a liquid phase, and the synthesis gas at the top of the ammonia washing tower C-001 is cooled by an ammonia washing tower top cooler E-011 and is sent to a circulating gas pressurizing system after the liquid phase is separated by an ammonia washing tower top separator V-003; the ammonia washing solvent at the bottom of the ammonia washing tower C-001 is cooled by an ammonia washing tower circulating pump P-001, one part of the ammonia washing solvent is circulated back to the top of the ammonia washing tower C-001 after being cooled by a circulating ammonia-rich liquid cooler E-009 and is used as the ammonia washing solvent, and the other part of the ammonia washing solvent is sent to an ammonia rectifying and purifying system after being depressurized;

(4) The ammonia-containing solvent from the ammonia recovery system is decompressed and then sent into a flash tank V-002, a small amount of hydrogen and nitrogen dissolved in ammonia-rich liquid are flashed out, the flashed liquid phase is heated by a rectifying tower feeding heat exchanger E-010 and then enters an ammonia rectifying tower C-002, high-concentration ammonia gas at the top of the tower is cooled by a rectifying tower top cooler E-006 and then enters an ammonia rectifying tower top reflux tank V-001, noncondensable gas at the top of the reflux tank is discharged, one part of the liquid phase is returned to the rectifying tower C-002 by an ammonia rectifying tower top reflux pump P-003, and the other part of the liquid phase is cooled by an ammonia cooler E-009 and then is sent out as a product;

(5) The synthesis gas carrying trace ammonia solvent from the top of the ammonia scrubber C-002 enters a circulating gas purifying molecular sieve R-002 to remove trace solvent, so that the oxygen atom content in the synthesis gas entering an ammonia synthesis reactor is controlled, and the service life of the catalyst is ensured; the synthesis gas passing through the circulating gas purifying molecular sieve R-002 enters a circulating gas compressor K-001 to be pressurized so as to balance the pressure drop of the system, and the pressurized circulating synthesis gas enters an ammonia synthesis reactor R-001 together with fresh ammonia synthesis gas after heat exchange and temperature rise of a circulating gas heat exchanger E-003.

2. The process for producing liquid ammonia by low-pressure ammonia synthesis according to claim 1, wherein: in step (1), when the apparatus is started up or the temperature of the ammonia synthesis reactor R-001 is low, the ammonia synthesis fresh gas is heated by the start-up heater F-001 to promote the ammonia synthesis reaction.

3. The process for producing liquid ammonia by low-pressure ammonia synthesis according to claim 1, wherein: in the step (3), another ammonia washing solvent at the top of the ammonia washing tower C-001 comes from the ammonia-containing solvent returned by the ammonia rectification and purification system, and the ammonia washing solvent of the ammonia washing tower C-001 is supplemented from the top of the tower to balance the trace ammonia washing solvent loss carried by the synthesis gas at the top of the tower.

4. The process for producing liquid ammonia by low-pressure ammonia synthesis according to claim 1, wherein: in the step (4), ammonia lean liquid at the bottom of the ammonia rectification C-002 tower is sent to an ammonia recovery system through a lean liquid booster pump P-002.

5. The process for producing liquid ammonia by low-pressure ammonia synthesis according to claim 1, wherein: in the step (5), R-002 is provided with a device and a device, and continuous operation is realized by a steam heating regeneration mode.

6. The low-pressure ammonia synthesis production process according to any one of claims 1 to 5, characterized in that: the ammonia synthesis reactor R-001 comprises

The shell is internally hollow and is provided with a first part and a second part which are connected up and down, the upper part of the second part forms a reaction area, the lower part of the second part forms a catalyst accommodating area, the diameter of the first part is larger than that of the second part to form a catalyst separation area, and the top of the shell is provided with an air outlet;

the first mixing section is arranged at the upper part of the second part and extends vertically, the top of the first mixing section is provided with an ammonia synthesis fresh gas inlet and a first circulating gas inlet, and the bottom of the first mixing section is provided with an outlet;

the heat exchanger is connected below the first mixing section and is used for preheating the mixed gas output by the first mixing section to a temperature above the activation temperature of the catalyst;

the second mixing section is connected below the heat exchanger, the top of the second mixing section is provided with a second circulating gas inlet for further mixing the preheated mixed gas output by the heat exchanger with the second circulating gas, and the bottom of the second mixing section is provided with an output port for outputting the mixed reaction gas to the catalyst accommodating area;

the inner edge of the partition plate is connected with the outer wall of the second mixing section, the outer edge of the partition plate is connected with the inner wall of the shell, the partition plate is used for separating the second part into a relatively independent reaction area and a catalyst accommodating area, and a plurality of openings which can be matched with the reaction gas at a high speed to enable the catalyst carried by the reaction gas and the reaction gas to form a fluidization state and enter the reaction area are formed in the partition plate.

7. The process for producing liquid ammonia by low-pressure ammonia synthesis according to claim 6, wherein: the gas separated by the catalyst separation area is output through the gas outlet, and the separated catalyst is settled into the reaction area under the gravity to be mixed with the upward-conveyed fluidization material and participate in fluidization reaction; the high-temperature synthesis gas generated by the fluidized reaction is used as a heat source to preheat the mixed gas conveyed to the second mixing section through the heat exchanger.

8. The process for producing liquid ammonia by low-pressure ammonia synthesis according to claim 6, wherein: the first mixing section, the heat exchanger and the second mixing section are mutually connected from top to bottom to form a whole which is vertically arranged in the second part of the shell, the upper end of the first mixing section forms an upwards arched flow guiding surface, the first part and the second part are connected through a transition section with gradually increased diameter from bottom to top, and the flow guiding surface is lower than the transition section.

9. The process for producing liquid ammonia by low-pressure ammonia synthesis according to claim 8, wherein: the catalyst filter S-001 is arranged at the top of the shell and is connected with the shell in series, an inlet of the catalyst filter S-001 is connected with an air outlet at the top of the shell, a synthesis gas outlet is arranged at the top of the catalyst filter S-001, and a backflow pipeline for backflow of the separated catalyst into the shell is arranged at the bottom of the catalyst filter S-001.

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