Series and parallel combined type ammonia synthesis system

Abstract

The utility model discloses a combined ammonia synthesis system combining series connection and parallel connection. The combined ammonia synthesis system comprises a first reaction and heat recovery unit, a second reaction and heat recovery unit, a cold recovery unit, a separation unit, a flash evaporation unit and a compression circulation unit, the first reaction and heat recovery unit is used for carrying out first-stage reaction and carrying out cooling and heat recovery on first-stage reaction gas; the second reaction and heat recovery unit is used for carrying out second-stage reaction and carrying out cooling and heat recovery on second-stage reaction gas; the cold recovery unit is used for respectively condensing the first-stage reaction gas and the second-stage reaction gas which are subjected to cooling and heat recovery and recovering cold energy; the separation unit is used for performing gas-liquid separation on the condensed primary reaction gas and the condensed secondary reaction gas respectively, supplementing the gas separated from the secondary reaction gas and then feeding the gas into the circulator, and supplementing the gas separated from the primary reaction gas and then feeding the gas into the second reaction and heat recovery unit. The system is low in circulation volume, high in synthetic tower operation efficiency, high in catalyst reaction efficiency and low in circulation power consumption.

Description

Technical Field

[0001] The utility model relates to the field of chemical equipment, in particular to a series-parallel combined ammonia synthesis system. Background Art

[0002] The synthesis reaction of ammonia is the synthesis of 1 N2 molecule and 3 H2 molecules to generate 2 NH3 molecules. It must be carried out under high pressure (under current conditions, the pressure of iron-based catalysts is 13.0MPa to 32.0MPa), high temperature (350C to 520C), and catalyst conditions. It is a "reversible" exothermic reaction. Increasing pressure, increasing temperature, and reducing reactant concentrations can make the reaction proceed in a favorable direction. Since the ammonia content generated each time the gas contacts the catalyst is limited (generally less than 20%), a cyclic reaction mode must be set up for the process.

[0003] In engineering, we generally use appropriate low temperature, appropriate operating pressure and lower circulation volume to achieve comprehensive balance of efficiency, energy saving, etc. In actual operation, under the condition of a certain amount of catalyst, we should try to reduce the ammonia content in the reaction inlet gas and try to increase the ammonia content at the outlet of the ammonia synthesis tower to maximize the catalyst reaction efficiency. Therefore, using more catalysts, improving catalyst efficiency, and reducing the "circulation volume" (or "circulation ratio") of the gas are commonly used engineering optimization methods.

[0004] The existing ammonia synthesis reaction system generally adopts a single-tower circulation method. For example, Chinese patent CN105883852A discloses an ammonia synthesis reaction system, including: an ammonia synthesis tower, a combined waste boiler, a feedwater heater, a circulating gas heat exchanger, a water cooler, a combined ammonia cooler, a diammonia cooler, an ammonia separator, a liquid ammonia tank, and a circulation machine. The gas preheated in the circulating gas heat exchanger enters the ammonia synthesis tower, and the reacted gas directly enters the combined waste boiler from the bottom of the ammonia synthesis tower. The gas circulation ratio of the single-tower process is generally 3.0 to 3.8, the gas circulation volume is large, the net ammonia value of the synthesis tower is low, and the operation efficiency of the synthesis tower is low. Utility Model Content

[0005] In order to solve the above problems, the utility model proposes a combined ammonia synthesis system combining series and parallel connections.

[0006] The technical solution adopted by the utility model is as follows:

[0007] It includes a first reaction and heat recovery unit, a second reaction and heat recovery unit, a cold recovery unit, a separation unit, a flash unit and a compression cycle unit; the first reaction and heat recovery unit is used for performing a first-stage ammonia synthesis reaction and cooling and recovering heat from a first-stage reaction gas generated by the first-stage ammonia synthesis reaction; the second reaction and heat recovery unit is used for performing a second-stage ammonia synthesis reaction and cooling and recovering heat from a second-stage reaction gas generated by the second-stage ammonia synthesis reaction; the cold recovery unit is used for condensing and recovering cold from the first-stage reaction gas and the second-stage reaction gas after cooling and heat recovery respectively; the separation unit includes a separator A and a separator B, Separator A and separator B are used for gas-liquid separation of the condensed primary reaction gas and secondary reaction gas respectively, and the gas separated from the secondary reaction gas is fed into the circulation machine after gas replenishment, and the gas separated from the primary reaction gas is fed into the second reaction and heat recovery unit after gas replenishment; the compression circulation unit includes a compressor and a circulation machine, the compressor is used for compressing the fresh raw gas and feeding it to the circulation machine inlet and the second reaction and heat recovery unit respectively; the circulation machine is used for allowing the compressed gas to enter the first reaction and heat recovery unit; the flash unit includes a flash tank, and the flash tank is used for flashing the crude ammonia at the bottom of separator A and separator B to obtain finished liquid ammonia.

[0008] Furthermore, the first reaction and heat recovery unit includes an ammonia synthesis tower A, a steam superheater A, a steam generator A, a feed water preheater A, a heat exchanger A and a water cooler A. The reactant outlet A at the bottom of the ammonia synthesis tower A is connected to the steam superheater A tube side, the steam generator A tube side, the feed water preheater A tube side, the heat exchanger A tube side and the feed water cooler A shell side in sequence.

[0009] Furthermore, the second reaction and heat recovery unit includes an ammonia synthesis tower B, a steam superheater B, a steam generator B, a feed water preheater B, a heat exchanger B and a water cooler B. The reactant outlet B at the bottom of the ammonia synthesis tower B is connected in sequence to the steam superheater B tube side, the steam superheater B tube side, the steam generator B tube side, the feed water preheater B tube side, the heat exchanger B tube side and the water cooler B shell side.

[0010] Furthermore, the shell side inlets of feedwater preheater A and feedwater preheater B are both connected to the boiler feedwater pipe, the shell side outlet of feedwater preheater A is connected to the shell side inlet of steam generator A, the shell side outlet of steam generator A is connected to the shell side inlet of steam superheater A, the shell side outlet of steam superheater A is connected to the superheated steam pipe, the shell side outlet of feedwater preheater B is connected to the shell side inlet of steam generator B, the shell side outlet of steam generator B is connected to the shell side inlet of steam superheater B, and the shell side outlet of steam superheater B is connected to the shell side inlet of steam superheater A.

[0011] Furthermore, the shell side inlets of the feed water preheater A and the feed water preheater B are connected to the boiler feed water pipe through respective pipelines and valves.

[0012] Furthermore, cooling water A and cooling water B are introduced into the shell sides of water cooler A and water cooler B respectively.

[0013] Further, the cold recovery unit includes a combined cooling condensation evaporator, which includes a first-stage cooling condenser, a second-stage cooling condenser and a third-stage cooling condenser. The first-stage cooling condenser includes two heat exchange cavities A and a heat exchange cavity B which are not connected to each other. The heat exchange cavity A is provided with a first heat exchange tube A, a first shell-side inlet A and a first shell-side outlet A, and the heat exchange cavity B is provided with a first heat exchange tube B, a first shell-side inlet B and a first shell-side outlet B; the second-stage cooling condenser is provided with a heat exchange cavity C, and the heat exchange cavity C is provided with a second heat exchange tube A and a second heat exchange tube B, a second shell-side inlet A and a second shell-side outlet B; the third-stage cooling condenser is provided with a heat exchange cavity D, and the heat exchange cavity D is provided with a third heat exchange tube A and a third heat exchange tube B, a third shell-side inlet A and a third shell-side outlet B;

[0014] The first heat exchange tube A, the second heat exchange tube A, and the third heat exchange tube A are connected in sequence, and the first heat exchange tube B, the second heat exchange tube B, and the third heat exchange tube B are connected in sequence; the inlet of the first heat exchange tube A is connected to the shell outlet of the feed water cooler B, and the inlet of the first heat exchange tube B is connected to the shell outlet of the feed water cooler A; the first shell inlet A is connected to the top air outlet of the separator A, the first shell outlet A is connected to the air inlet of the circulation machine, the first shell inlet B is connected to the top air outlet of the separator B, the first shell outlet B is connected to the shell inlet of the heat exchanger B, the outlet of the third heat exchange tube A is connected to the feed port of the separator A, and the outlet of the third heat exchange tube B is connected to the feed port of the separator B.

[0015] Furthermore, the compressor outlet is connected to the circulation machine and the heat exchanger B through respective pipelines and valves.

[0016] Furthermore, the liquid outlet at the bottom of the flash tank is connected to the tube side of the ammonia heat recovery device; the second shell side inlet A and the third shell side inlet A are both connected to the shell side outlet of the ammonia heat recovery device, the second shell side outlet B and the third shell side outlet B are respectively connected to the gaseous refrigerant tube A and the gaseous refrigerant tube B, and the shell side inlet of the ammonia heat recovery device is connected to the liquid refrigerant tube.

[0017] Beneficial effects of the utility model:

[0018] 1. The present application adopts two identical ammonia synthesis towers and corresponding heat recovery equipment, cooling and separation equipment to form a "series + parallel" combined ammonia synthesis system. The system improves the separation effect and the catalyst reaction efficiency by two-stage ammonia synthesis reaction, two-stage ammonia cooling and condensation, and two-stage ammonia separation, thereby achieving a 45% to 50% reduction in the synthesis cycle volume and saving cycle power consumption.

[0019] 2. The net ammonia value of the first-stage synthesis tower of the present application can reach 17.11%; the net ammonia value of the second-stage synthesis tower can reach 17.45%, and the circulation ratio of the first-stage synthesis tower and the circulation ratio of the second-stage synthesis tower reach 1.6481 and 1.6868 respectively; the reaction efficiency of ammonia synthesis of the two reaction gases is relatively high.

[0020] 3. The present application sets up a "combined cooling condensing refrigerant evaporator" device with two separate streams, and passes the reaction gas after ammonia synthesis from the two reaction series through a combined device to realize the process of "secondary cooling", "two-stage cold exchange" and "evaporation and freezing" of the dual streams of refrigerant completed at one time.

[0021] 4. The present application only uses a single circulation machine and a single compressor as process equipment configuration to form a set of "series and parallel combination" combined ammonia synthesis system method. By using a circulation machine and a compressor to feed fresh gas into two synthesis towers, the ammonia production of the two synthesis towers can be basically the same, the catalyst load is basically the same, and the efficiency of the synthesis towers is basically the same, so that both synthesis towers can achieve very high operating efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the combined ammonia synthesis system of the utility model.

[0023] Figure 2 It is a structural schematic diagram of a combined cooling condensing evaporator of the utility model. DETAILED DESCRIPTION

[0024] See also Figure 1-2 The present embodiment provides a combined ammonia synthesis system in series and parallel connection, including a first reaction and heat recovery unit, a second reaction and heat recovery unit, a cold recovery unit, a separation unit, a flash unit and a compression cycle unit.

[0025] The first reaction and heat recovery unit includes an ammonia synthesis tower A10, a steam superheater A11, a steam generator A12, a feed water preheater A13, a heat exchanger A14 and a water cooler A15. The ammonia synthesis tower A10 is provided with a reactant outlet A at the bottom and a reactant inlet A at the top; the steam superheater A11 has reaction gas A passing through the tube side and steam passing through the shell side; the steam generator A12 has reaction gas A passing through the tube side and hot water passing through the shell side; the feed water preheater A13 has reaction gas A passing through the tube side and boiler feed water 01 passing through the shell side; the heat exchanger A14 has reaction gas A passing through the tube side and raw gas passing through the shell side; the water cooler A15 has reaction gas A passing through the shell side and cooling water 03 passing through the tube side.

[0026] The reactant outlet A at the bottom of the ammonia synthesis tower A10 is connected in sequence to the steam superheater A11 tube side, the steam generator A12 tube side, the feed water preheater A13 tube side, the heat exchanger A14 tube side, and the feed water cooler A15 shell side. The reaction gas A produced in the ammonia synthesis tower A10 is cooled in sequence by the steam superheater A11, the steam generator A12, the feed water preheater A13, the heat exchanger A14 and the water cooler A15 to complete the first stage reaction and heat recovery, and then enters the cold recovery separation unit.

[0027] The second reaction and heat recovery unit includes an ammonia synthesis tower B20, a steam superheater B21, a steam generator B22, a feed water preheater B23, a heat exchanger B24 and a water cooler B25. The ammonia synthesis tower B20 is provided with a reactant outlet B at the bottom and a reactant inlet B at the top; the tube side of the steam superheater B21 is passed through the reaction gas B, and the shell side is passed through steam; the tube side of the steam generator B22 is passed through the reaction gas B, and the shell side is passed through hot water; the tube side of the feed water preheater B23 is passed through the reaction gas B, and the shell side is passed through boiler feed water 01; the tube side of the heat exchanger B24 is passed through the reaction gas B, and the shell side is passed through the raw gas; the shell side of the water cooler B25 is passed through the reaction gas B, and the tube side is passed through cooling water 04.

[0028] The reactant outlet B at the bottom of the ammonia synthesis tower B20 is connected in sequence to the steam superheater B21 tube side, the steam superheater B21 tube side, the steam generator B22 tube side, the feed water preheater B23 tube side, the heat exchanger B24 tube side, and the water cooler B25 shell side. The reaction gas B produced in the ammonia synthesis tower B20 is cooled in sequence by the steam superheater B21, the steam generator B22, the feed water preheater B23, the heat exchanger B24 and the water cooler B25 to complete the first stage reaction and heat recovery, and then enters the cold recovery separation unit.

[0029] Preferably, the shell side inlets of feed water preheater A13 and feed water preheater B23 are respectively connected to the boiler feed water pipe 01 through respective pipes and valves, the shell side outlet of feed water preheater A13 is connected to the shell side inlet of steam generator A12, the shell side outlet of steam generator A12 is connected to the shell side inlet of steam superheater A11, the shell side outlet of steam superheater A11 is connected to the superheated steam pipe 02, the shell side outlet of feed water preheater B23 is connected to the shell side inlet of steam generator B22, the shell side outlet of steam generator B22 is connected to the shell side inlet of steam superheater B21, and the shell side outlet of steam superheater B21 is connected to the shell side inlet of steam superheater A11.

[0030] The boiler feed water passes through the boiler feed water pipe 01 and is adjusted in flow rate by valve A131 and valve B231 before entering the feed water preheater A13 and feed water preheater B23 respectively. It exchanges heat with the reaction gas for the first time and is heated to high-temperature hot water. The high-temperature hot water enters the steam generator A12 and steam generator B22 respectively and exchanges heat with the reaction gas for the second time and is heated to saturated steam. The saturated steam enters the steam superheater A11 and steam superheater B21 respectively and exchanges heat with the reaction gas for the third time to generate superheated steam.

[0031] By means of the above method, the reaction heat generated by the two synthesis towers can be used to produce steam, and superheated steam or only saturated steam can be produced as required.

[0032] Preferably, cooling water A03 and cooling water B04 are introduced into the shell side of water cooler A15 and water cooler B25 respectively. The temperature of the reaction gas entering the cold recovery separation unit is adjusted by cooling water A03 and cooling water B04, which is conducive to controlling the energy balance of the whole system.

[0033] Since the water cooler is relatively easy to clog and leak, a separate water cooler is set up for easy maintenance.

[0034] The cold recovery unit includes a combined cooling condenser evaporator 30. Figure 2 The combined cooling condensing evaporator 30 includes a primary cooling condenser 31 , a secondary cooling condenser 32 and a tertiary cooling condenser 33 .

[0035] The primary cooling condenser 31 includes a shell A and two heat exchange cavities A and heat exchange cavity B which are not connected to each other and are arranged in the shell A. In specific implementation, a partition can be arranged in one shell to separate the inner cavity of the shell into two independent cavities, namely, the heat exchange cavity A and the heat exchange cavity B. The heat exchange cavity A is provided with a first heat exchange tube A311, a first shell-side inlet A314 and a first shell-side outlet A315, and the heat exchange cavity B is provided with a first heat exchange tube B312, a first shell-side inlet B313 and a first shell-side outlet B316; the first heat exchange tube A311 passes through the reaction gas B, and the shell side of the heat exchange cavity A passes through the separated gas of the reaction gas B; the first heat exchange tube B312 passes through the reaction gas A, and the heat exchange cavity B passes through the separated gas of the reaction gas A.

[0036] The secondary cooling condenser 32 includes a shell B and a heat exchange cavity C surrounded by the shell B. The heat exchange cavity C is provided with a second heat exchange tube A321 and a second heat exchange tube B322, a second shell side inlet A323 and a second shell side outlet B324; the second heat exchange tube A321 passes through the reaction gas B, the second heat exchange tube B322 passes through the reaction gas A, and the heat exchange cavity C passes through a high-temperature liquid refrigerant.

[0037] The three-stage cooling condenser 33 includes a shell C and a heat exchange cavity D surrounded by the shell C. The heat exchange cavity D is provided with a third heat exchange tube A331 and a third heat exchange tube B332, a third shell side inlet A333 and a third shell side outlet B334; the third heat exchange tube A331 passes through the reaction gas B, the third heat exchange tube B332 passes through the reaction gas A, and the heat exchange cavity D passes through a high-temperature liquid refrigerant.

[0038] The primary cooling condenser 31, the secondary cooling condenser 32, and the tertiary cooling condenser 33 are connected in sequence through their heat exchange tubes, that is, the inlets and outlets of the first heat exchange tube A311, the second heat exchange tube A321, and the third heat exchange tube A331 are connected in sequence, and the inlets and outlets of the first heat exchange tube B312, the second heat exchange tube B322, and the third heat exchange tube B332 are connected in sequence. The inlets of the first heat exchange tube A311 and the first heat exchange tube B312 of the primary cooling condenser 31 are respectively connected to the shell outlet of the feed water cooler B25 and the shell outlet of the feed water cooler A15; the first shell inlet A314 and the first shell inlet B313 of the primary cooling condenser 31 are respectively connected to the top gas outlet of the separator A41 and the top gas outlet of the separator B42. The third heat exchange tube A331 and the third heat exchange tube B332 of the tertiary cooling condenser 33 are respectively connected to the reactant inlets of the separators A41 and B42.

[0039] The separation unit includes separator A41 and separator B42. Separator A41 and separator B42 both use gas-liquid separators, which are mainly composed of a cylinder, a cyclone separation cylinder, a high-efficiency foam breaking net, a sewage valve and other main components. The side wall of the cylinder is provided with a reactant inlet, the top of the cylinder is provided with a separation gas outlet, and the bottom of the cylinder is provided with a crude ammonia outlet.

[0040] After water cooling, the circulating gas needs to be further cooled to condense the produced ammonia, which is beneficial for separation. In order to recover the cold at the same time, the present application sets up a combined cooling condensing evaporator, so as to achieve the process effect of cooling and recovering cold by subjecting the two process gases to primary cooling, secondary cooling, primary cold exchange, and secondary cold exchange respectively.

[0041] The flash unit includes a flash tank 70 and an ammonia heat recovery device 80. The compression cycle unit includes a circulation machine 50 and a compressor 60.

[0042] The first shell side outlet A315 and the first shell side outlet B316 of the primary cooling condenser 31 are respectively connected to the air inlet of the circulation machine 50 and the shell side inlet of the heat exchanger B24; the air outlet of the circulation machine 50 is connected to the shell side inlet of the heat exchanger A14, and the shell side outlet of the heat exchanger A14 is connected to the top feed port of the ammonia synthesis tower A10; the shell side outlet of the heat exchanger B24 is connected to the top feed port of the ammonia synthesis tower B20.

[0043] The crude ammonia outlets at the bottom of separators A41 and B42 are connected to the feed port of flash tank 70, the top air outlet of flash tank 70 is connected to the air inlet of compressor 60, the air outlet of compressor 60 is connected to the air inlet of circulating machine 50 and the shell inlet of heat exchanger B24 through their own pipelines and valves, the bottom liquid outlet of flash tank 70 is connected to the pipe side of ammonia heat recovery device 80; the air inlet of compressor 60 is also connected to the raw material inlet pipe 08. The second shell outlet B324 of secondary cooling condenser 32 and the third shell outlet B334 of tertiary cooling condenser 33 are connected to gaseous refrigerant pipe A05 and gaseous refrigerant pipe B06 respectively, and the shell inlet of ammonia heat recovery device 80 is connected to liquid refrigerant pipe 07.

[0044] The working principle of the utility model is:

[0045] The reaction gas A from the outlet of the circulating machine 50 enters the shell side of the heat exchanger A14 for temperature increase, and then enters the ammonia synthesis tower A10 for reaction. After the reaction, the reaction gas A with increased temperature and ammonia content enters the superheater A11 tube side, the steam generator A12 tube side, the feed water preheater A13 tube side, the heat exchanger A14 tube side, and the water cooler A15 shell side in sequence for separate cooling and heat recovery. After completing the first-stage reaction and heat recovery and cooling work, the reaction gas A then enters the combined cooling condenser evaporator 30 in sequence. The first heat exchange tube B312, the second heat exchange tube B322, and the third heat exchange tube B332 are cooled and exchanged separately. The reaction gas A after cooling and recovering the cold enters the separator B42 for gas-liquid separation. The gas separated by the separator B42 returns to the heat exchange cavity B of the primary cooling condenser 31 for separate cold recovery. The gas coming out of the primary cooling condenser 31 is added with a certain amount of supplementary air and then enters the shell side of the heat exchanger B24. After being heated, it enters the ammonia synthesis tower B20 for the second stage reaction.

[0046] After the secondary reaction, the reaction gas B with increased temperature and ammonia content then enters the steam superheater B21 tube side, steam generator B22 tube side, feed water preheater B23 tube side, heat exchanger B24 tube side and water cooler B25 shell side in sequence for separate cooling and heat recovery. After completing the second-stage reaction and heat recovery and cooling work, the reaction gas B then enters the first heat exchange tube A311, the second heat exchange tube A321 and the third heat exchange tube A331 of the combined cooling condenser evaporator 30 in sequence for separate cooling and cold exchange. After cooling and recovering cold, the reaction gas B enters the separator A41 for gas-liquid separation. The gas separated by the separator A41 returns to the heat exchange cavity A of the primary cooling condenser 31 for separate cold recovery. A certain amount of fresh gas is added to the gas coming out of the primary cooling condenser 31 and then enters the inlet of the circulating machine 50. After being pressurized together with the circulating gas, it enters the heat exchanger A14 shell side for temperature increase and then enters the ammonia synthesis tower A10, completing an ammonia synthesis cycle.

[0047] The crude ammonia at the bottom of the separator A41 and the separator B42 first enters the flash tank 70 for flash evaporation. During the flash evaporation, the gas dissolved in the crude ammonia is flashed out due to the pressure reduction. The flashed gas is returned to the inlet of the compressor 60 through the gas phase pipeline at the top of the flash tank. The crude ammonia at the bottom of the flash evaporator then enters the ammonia heat recovery device 80 for heat recovery and is then sent to the ammonia storage as finished liquid ammonia.

[0048] The raw gas after purification and refining first enters the compressor 60 to increase the gas pressure, and then is divided into two routes to enter the two synthesis towers respectively: the first route of gas supply is supplemented to the inlet of the circulation machine 50 through the gas supply regulating valve A61, and after the pressure is increased together with the circulating gas, it enters the heat exchanger A14 shell side to increase the temperature, and then enters the ammonia synthesis tower A10; the second route of gas supply is supplemented to the circulating gas pipeline at the shell side inlet of the heat exchanger B24 through the gas supply regulating valve B61, and after the gas temperature is increased, it enters the ammonia synthesis tower B20 together with the circulating gas for reaction.

[0049] The present application can realize an ammonia synthesis process route with two-stage reaction, two-stage heat recovery, two-stage cooling and separation, and only one set of circulating machine. The "circulating gas" flows in "series", the "supplementary gas" flows in "parallel" and the replenishment is adjusted on demand. The "supplementary gas" is replenished at the inlet of the circulating machine when entering the ammonia synthesis tower A10, which can greatly reduce the compression power consumption.

[0050] The above is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A combined ammonia synthesis system in series and parallel, characterized in that: It includes a first reaction and heat recovery unit, a second reaction and heat recovery unit, a cold recovery unit, a separation unit, a flash unit and a compression cycle unit; The first reaction and heat recovery unit is used for performing the first-stage ammonia synthesis reaction and cooling and heat recovery of the first-stage reaction gas generated by the first-stage ammonia synthesis reaction; The second reaction and heat recovery unit is used for performing the second stage ammonia synthesis reaction and cooling and heat recovery of the secondary reaction gas generated by the second stage ammonia synthesis reaction; The cold recovery unit is used to condense and recover cold energy of the primary reaction gas and the secondary reaction gas that have been cooled and heat recovered; The separation unit comprises a separator A (41) and a separator B (42), wherein the separator A (41) and the separator B (42) are respectively used to perform gas-liquid separation on the condensed primary reaction gas and the secondary reaction gas, and to feed the gas separated from the secondary reaction gas into the circulation machine, and to feed the gas separated from the primary reaction gas into the second reaction and heat recovery unit; The compression circulation unit comprises a compressor (60) and a circulation machine (50), wherein the compressor (60) is used to compress the fresh raw gas and then supply it to the circulation machine inlet and the second reaction and heat recovery unit respectively; the circulation machine (50) is used to allow the compressed gas to enter the first reaction and heat recovery unit; The flash unit comprises a flash tank (70), which is used to flash the crude ammonia at the bottom of the separator A (41) and the separator B (42) to obtain finished liquid ammonia.

2. A series and parallel combined ammonia synthesis system according to claim 1, characterized in that: The first reaction and heat recovery unit comprises an ammonia synthesis tower A (10), a steam superheater A (11), a steam generator A (12), a feed water preheater A (13), a heat exchanger A (14) and a water cooler A (15). The reactant outlet A at the bottom of the ammonia synthesis tower A (10) is connected in sequence to the tube side of the steam superheater A (11), the tube side of the steam generator A (12), the tube side of the feed water preheater A (13), the tube side of the heat exchanger A (14) and the shell side of the feed water cooler A (15).

3. A series and parallel combined ammonia synthesis system according to claim 1 or 2, characterized in that: The second reaction and heat recovery unit comprises an ammonia synthesis tower B (20), a steam superheater B (21), a steam generator B (22), a feed water preheater B (23), a heat exchanger B (24) and a water cooler B (25). The reactant outlet B at the bottom of the ammonia synthesis tower B (20) is connected in sequence to the steam superheater B (21) tube side, the steam superheater B (21) tube side, the steam generator B (22) tube side, the feed water preheater B (23) tube side, the heat exchanger B (24) tube side and the water cooler B (25) shell side.

4. A series and parallel combined ammonia synthesis system according to claim 3, characterized in that: The shell side inlets of the feed water preheater A (13) and the feed water preheater B (23) are both connected to the boiler feed water pipe (01), the shell side outlet of the feed water preheater A (13) is connected to the shell side inlet of the steam generator A (12), the shell side outlet of the steam generator A (12) is connected to the shell side inlet of the steam superheater A (11), the shell side outlet of the steam superheater A (11) is connected to the superheated steam pipe (02), the shell side outlet of the feed water preheater B (23) is connected to the shell side inlet of the steam generator B (22), the shell side outlet of the steam generator B (22) is connected to the shell side inlet of the steam superheater B (21), and the shell side outlet of the steam superheater B (21) is connected to the shell side inlet of the steam superheater A (11).

5. A series and parallel combined ammonia synthesis system according to claim 4, characterized in that: The shell side inlets of the feed water preheater A (13) and the feed water preheater B (23) are connected to the boiler feed water pipe (01) through respective pipelines and valves.

6. A series and parallel combined ammonia synthesis system according to claim 3, characterized in that: Cooling water A (03) and cooling water B (04) are introduced into the shell side of water cooler A (15) and water cooler B (25) respectively.

7. A series and parallel combined ammonia synthesis system according to claim 3, characterized in that: The cold recovery unit comprises a combined cooling condensation evaporator (30), the combined cooling condensation evaporator (30) comprising a primary cooling condenser (31), a secondary cooling condenser (32) and a tertiary cooling condenser (33), the primary cooling condenser (31) comprising two heat exchange chambers A and B which are not connected to each other, the heat exchange chamber A is provided with a first heat exchange tube A (311), a first shell-side inlet A (314) and a first shell-side outlet A (315), the heat exchange chamber B is provided with a first heat exchange tube B (312), a first shell-side inlet B (313) and a first shell side outlet B (316); the secondary cooling condenser (32) is provided with a heat exchange cavity C, in which a second heat exchange tube A (321) and a second heat exchange tube B (322), a second shell side inlet A (323) and a second shell side outlet B (324) are provided; the tertiary cooling condenser (33) is provided with a heat exchange cavity D, in which a third heat exchange tube A (331) and a third heat exchange tube B (332), a third shell side inlet A (333) and a third shell side outlet B (334) are provided; The first heat exchange tube A (311), the second heat exchange tube A (321), and the third heat exchange tube A (331) are connected in sequence; the first heat exchange tube B (312), the second heat exchange tube B (322), and the third heat exchange tube B (332) are connected in sequence; the inlet of the first heat exchange tube A (311) is connected to the shell outlet of the feed water cooler B (25); the inlet of the first heat exchange tube B (312) is connected to the shell outlet of the feed water cooler A (15); the first shell inlet A (314) is connected to The top gas outlet of the separator A (41) is connected, the first shell side outlet A (315) is connected to the gas inlet of the circulation machine (50), the first shell side inlet B (313) is connected to the top gas outlet of the separator B (42), the first shell side outlet B (316) is connected to the shell side inlet of the heat exchanger B (24), the third heat exchange tube A (331) outlet is connected to the feed port of the separator A (41), and the third heat exchange tube B (332) outlet is connected to the feed port of the separator B (42).

8. A series and parallel combined ammonia synthesis system according to claim 7, characterized in that: The air outlet of the compressor (60) is connected to the circulation machine (50) and the heat exchanger B (24) through respective pipelines and valves.

9. A series and parallel combined ammonia synthesis system according to claim 7, characterized in that: The bottom liquid outlet of the flash tank (70) is connected to the tube side of the ammonia heat recovery device (80); the second shell side inlet A (323) and the third shell side inlet A (333) are both connected to the shell side outlet of the ammonia heat recovery device (80); the second shell side outlet B (324) and the third shell side outlet B (334) are respectively connected to the gaseous refrigerant pipe A (05) and the gaseous refrigerant pipe B (06); the shell side inlet of the ammonia heat recovery device (80) is connected to the liquid refrigerant pipe (07).

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