CN112850645B - System and method for preparing synthetic ammonia by deeply purifying coke oven gas - Google Patents
System and method for preparing synthetic ammonia by deeply purifying coke oven gas Download PDFInfo
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Abstract
The invention provides a system and a method for preparing synthetic ammonia by deeply purifying coke oven gas, belonging to the field of coke oven gas purification. Through setting up the prewashing tower for hypergravity rotary device, make the coke oven gas after the benzene removal can carry out the preliminary desorption of impurity through hypergravity rotary technology in the prewashing tower, with harmful substance such as the interior dust of degree of depth desorption coke oven gas, benzene, tar, naphthalene, ammonia and sulphur, the problem of sulfur in the coke oven gas, ammonia exceeds standard and can influence back system steady operation has been solved, tar in the coke oven gas has still been solved, the problem that the naphthalene can cause the compression system to block up, the problem that the unusual fine desulfurization running cost that leads to the fact of coarse desulfurization increases has still been solved. Through pretreatment, the coke oven gas does not need to be desulfurized again after being returned to the coke oven, and the investment of a flue gas desulfurization device and the generation of desulfurization waste liquid can be reduced. The decarbonization operation is carried out through the low-temperature methanol washing operation, so that the decarbonization precision is improved, the yield of hydrogen can be improved without consuming hydrogen in the decarbonization process, and the efficiency and the yield of the synthetic ammonia are improved.
Description
Technical Field
The invention relates to the technical field of coke oven gas purification, in particular to a system and a method for preparing synthetic ammonia by deeply purifying coke oven gas.
Background
Coke oven gas is an important by-product obtained in the coking process, and the research on the composition of coke oven gas has become quite mature in recent years. The coke oven gas belongs to medium-heat value natural gas, the hydrogen content is 50-60%, and the methane content is 22-24%, wherein the coke oven gas has great utilization value. A large amount of coke oven gas can be generated while producing coke, if the generation amount of the coke oven gas in China is basically maintained at 1800 billions of cubic meters according to the calculation of producing 430 cubic meters of coke oven gas by producing 1 ton of coke, wherein about 45-50% of the coke oven gas returns to the coke oven, and the residual coke oven gas is considerable. Therefore, how to recycle the coke oven gas has important significance for realizing the cyclic utilization of resources and the sustainable development of economy. The purification of the coke oven gas becomes the most important thing before the coke oven gas is comprehensively utilized.
The hydrogen content of the coke oven gas is about 55-60%. The hydrogen has the advantages of high heat value, pure quality and the like, and is popular among people. As a clean energy with the most development potential, hydrogen has wide development and application prospects, and can be widely applied to the fields of energy, industry, transportation, buildings and the like. Raw materials, reducing agents and high-quality heat sources are provided for the industries of refining, steel, metallurgy and the like, and carbon emission can be effectively reduced; the fuel cell can also be applied to the fields of automobiles, rail transit, ships and the like through the fuel cell technology, so that the dependence of transportation on petroleum and natural gas is reduced; the system can also be applied to distributed power generation and power supply and heating for family houses, commercial buildings and the like. Therefore, as a link of multi-energy transmission and fusion interaction, hydrogen energy is known as the secondary energy with the greatest development prospect in the 21 st century, and is one of the cores of future clean low-carbon energy systems.
The high content of hydrogen in the coke oven gas makes the coke oven gas as an ideal raw material for preparing synthetic ammonia, and the hydrogen becomes an important way for promoting the industrial upgrading of the coking industry and developing hydrogen energy sources in China gradually. However, because the coke oven gas contains impurities such as benzene, naphthalene, ammonia, tar, dust, sulfur and the like, a great deal of test is faced in the process of preparing synthetic ammonia by using the coke oven gas. The main manifestations are as follows:
(1) the coke oven gas contains excessive sulfur and ammonia, and the normal operation of subsequent purification and synthesis is influenced.
When the coke oven gas is only used as fuel gas, the requirement for H is that 2 S is less than 500mg/Nm 3 Ammonia content of less than 100mg/Nm 3 However, the acid gas and ammonia in actual operation exceed the standards, which affects the stable operation of the system. Along with the expansion of coking scale and industrial aggregation, the coke oven gas becomes an important chemical raw material gas for use, and the change of the application of the coke oven gas causes that the design index of the deep purification of the original coke oven gas can not meet the requirement of the current use index.
(2) The coke oven gas contains tar and naphthalene, which seriously affect the normal operation of the compressor, mainly because the coke oven gas contains the tar and the naphthalene is high in content, and the gas temperature is increased during compression to gasify and coke the tar; and naphthalene is condensed and crystallized to cause naphthalene blockage of the compressor, so that the compressor cannot normally run and is forced to stop repairing, and the compressor is stopped for repairing only by opening for 1-2 days, so that the production is quite passive and is usually the situation of 1 opening for 2 spare or 1 opening for 3 spare.
(3) The desulfurization agent for fine desulfurization fails in advance due to abnormal rough desulfurization, which affects production operation, mainly sulfur penetration, and the desulfurization agent is forced to be replaced in advance, so that the desulfurization agent is replaced frequently, and the operating cost is increased.
(4) The traditional decarburization process adopts a methanation process, a certain amount of hydrogen is consumed in the decarburization process, the decarburization precision needs to be improved, the yield of the hydrogen is reduced, and the efficiency and the yield of synthetic ammonia are influenced.
Disclosure of Invention
The invention provides a system and a method for preparing synthetic ammonia by deeply purifying coke oven gas, aiming at solving the technical problems that the prior hydrogen preparation by coke oven gas can affect the stable operation of a rear system, can cause the blockage of a compressor, can cause the premature failure of a desulfurizing agent for fine desulfurization, thereby increasing the operation cost, and can cause the lower yield of hydrogen to affect the efficiency and the yield of the synthetic ammonia.
In order to solve the technical problems, the invention adopts the technical scheme that:
the utility model provides a system for coke oven gas deep purification system synthetic ammonia, it includes prewashing tower, desulfurizing tower, decarbonization tower, smart desulfurizing tower, reformer, shift converter, liquid nitrogen wash tower and synthetic ammonia tower, the prewashing tower is hypergravity rotary device, wherein: the gas holder is connected with the gas phase inlet at the lower part of the prewashing tower through a first heat exchanger, the liquid phase outlet at the bottom of the prewashing tower is connected with a gas-liquid separation device, the gas outlet at the top of the prewashing tower is connected with the gas inlet at the lower part of the desulfurizing tower through a first compressor, a second heat exchanger and a third heat exchanger, the gas outlet at the top of the desulfurizing tower is connected with the coke oven through a fourth heat exchanger and a second compressor, the gas outlet at the top of the desulfurizing tower is also connected with the gas inlet at the top of the fine desulfurizing tower through a fifth heat exchanger and a third compressor, the liquid outlet at the bottom of the desulfurizing tower is connected with the liquid inlet at the upper part of the decarbonizing tower through a sixth heat exchanger, a seventh heat exchanger and a fourth compressor, the gas outlet at the bottom of the decarbonizing tower is connected with the liquid phase inlet at the upper part of the prewashing tower through an eighth heat exchanger and a fifth compressor, the gas outlet at the top of the decarburization tower is connected with the gas inlet at the lower part of the liquid nitrogen washing tower through a ninth heat exchanger and a sixth compressor, the gas outlet at the top of the liquid nitrogen washing tower is connected with the gas inlet at the top of the synthetic ammonia tower through a tenth heat exchanger, and the gas outlet at the bottom of the synthetic ammonia tower is connected with the eleventh heat exchanger.
Optionally, the prewashing tower comprises a transmission device, a rotating shaft and a prewashing shell, the transmission device is connected with one end of the rotating shaft, the other end of the rotating shaft is connected with a rotor, the rotor is arranged at the middle lower part of an inner cavity of the prewashing shell, a gas outlet is connected in the middle of the top of the prewashing shell, a liquid outlet is connected at the bottom of the prewashing shell, a gas inlet is connected at the bottom of one side of the prewashing shell, a liquid inlet is connected at the middle upper part of the other side of the prewashing shell, an L-shaped liquid pipeline is connected to the liquid inlet, a vertical pipe of the L-shaped liquid pipeline extends to the middle part of the rotor, a plurality of liquid nozzles are installed on the vertical pipe of the L-shaped liquid pipeline, a demister is arranged at the top of the inner cavity of the prewashing shell, a separation plate is installed between the bottom of the demister and the top of the rotor, the middle part of the top of the rotor and the separation plate are sealed by a first sealing gasket, and the middle part of the two sides of the bottom of the rotor and the rotating shaft are respectively sealed by a second sealing gasket and a third sealing gasket, the rotor is filled with a filler layer.
The method for preparing the synthetic ammonia by deeply purifying the coke oven gas adopts the system for preparing the synthetic ammonia by deeply purifying the coke oven gas, and comprises the following steps of:
s1, the coke oven gas after benzene elution is sent into the prewashing tower from the lower part of the prewashing tower after the heat exchange of the coke oven gas is carried out to 20-25 ℃ through the first heat exchanger, and meanwhile, a gas detergent from the bottom of the decarbonizing tower is sent into the prewashing tower from the upper part of the prewashing tower after the heat exchange of the eighth heat exchanger and the pressurization of the fifth compressor; wherein, the prewashing tower is a supergravity rotating device;
s2, performing pretreatment by the countercurrent or cross-flow contact of the coke oven gas after heat exchange and a gas detergent in a prewashing tower, and discharging the pretreated gas detergent to a gas-liquid separation device after gathering on the inner wall of the prewashing tower under the supergravity action of the prewashing tower;
s3, pressurizing the pretreated coke oven gas to 0.3-1.0MPa by a first compressor, then exchanging heat by a second heat exchanger, conducting deep cooling by a third heat exchanger to-22-28 ℃, then entering a desulfurizing tower, carrying out low-temperature methanol washing operation on the lean methanol introduced into the desulfurizing tower and the desulfurizing tower to remove impurities in the coke oven gas so as to obtain deeply purified coke oven gas, reheating 42-50% of the deeply purified coke oven gas by a fourth heat exchanger, decompressing to 8-10kPa by a second compressor, then returning the deeply purified coke oven gas as coke oven gas to heat a coke oven, reheating the rest of the deeply purified coke oven gas by a fifth heat exchanger, compressing and pressurizing by a third compressor, and then entering a fine desulfurizing tower;
s4, carrying out fine desulfurization on the coke oven gas entering the fine desulfurization tower under the action of a desulfurization adsorbent of the fine desulfurization tower;
s5, the coke oven gas after fine desulfurization enters a converter and is introduced with O in the converter 2 And CO 2 The mixed gas is converted, and the converted coke oven gas enters a shift converter;
s6, converting the converted coke oven gas in a conversion furnace with steam introduced into the conversion furnace;
s7, the transformed coke oven gas enters a decarbonization tower for decarbonization after being subjected to heat exchange by a sixth heat exchanger, a seventh heat exchanger and pressurization by a fourth compressor, the decarbonized coke oven gas enters a liquid nitrogen washing tower for liquid nitrogen washing operation after being subjected to heat exchange by a ninth heat exchanger and compression by a sixth compressor, the hydrogen-nitrogen ratio of the coke oven gas and liquid nitrogen entering the liquid nitrogen washing tower is adjusted to be 2.7-3.0 in the liquid nitrogen washing tower, and the coke oven gas enters a synthetic ammonia tower for synthetic ammonia operation after being subjected to heat exchange by a tenth heat exchanger;
and S8, liquefying the ammonia synthesized in the ammonia synthesis tower by an eleventh heat exchanger to obtain liquid ammonia.
Optionally, the amount of the coal gas washing agent is 0.20-0.32 kg/m 3 The dosage of the poor methanol in the desulfurizing tower of the coke oven gas is 1.30-1.50kg/m 3 Coke oven gas.
Optionally, the temperature of the low-temperature methanol washing operation is-20 ℃ to-40 ℃, and the pressure is 0.3 MPa to 1.5 MPa.
Optionally, the desulfurization adsorbent is zinc oxide or iron oxide; the operation temperature in the fine desulfurization tower is 250-450 ℃, the pressure is 0.8-5.0 MPa, and the space velocity is 500-1500 h -1 。
Optionally, the gas conversion temperature in the converter is 1200-1300 ℃, the operating pressure is 2-6 MPa, the residence time is 1-5 s, and the oxygen: carbon dioxide: the coke oven gas ratio is 0.25-0.27: 0.02-0.04: 1.
Optionally, the reaction in the conversion furnace adopts an isothermal conversion technology, the conversion temperature is 180-350 ℃, the conversion pressure is 3-5 MPa, and the water-steam ratio is 0.4-0.6.
Optionally, the temperature of the liquid nitrogen washing operation is-185 ℃ to-195 ℃, and the pressure is 5.0MPa to 6.0 MPa.
Optionally, the operation temperature of the synthetic ammonia is 400-500 ℃, the pressure is 15-20 MPa, the catalyst adopts an iron-based catalyst, the iron ratio is 0.4-0.6, and the space velocity is 0-30000 h -1 。
The invention has the beneficial effects that:
the pre-washing tower is arranged and is a super-gravity rotating device, so that the debenzolized coke oven gas can be subjected to primary impurity removal in the pre-washing tower through a super-gravity rotating technology, and harmful substances such as dust, benzene, tar, naphthalene, ammonia, sulfur and the like in the debenzolized coke oven gas can be deeply removed through pretreatment of the pre-washing tower, so that the problem that the stable operation of a rear system is influenced by the over-standard sulfur and ammonia in the coke oven gas is solved, and the stability of the operation of the system can be improved; the problem that the compression system is blocked due to tar and naphthalene in the coke oven gas is solved, and possible blocking abnormity in the subsequent working section is avoided; the problem that the operation cost is increased due to the fact that the desulfurization adsorbent for fine desulfurization fails in advance due to abnormal coarse desulfurization is solved, and the fine desulfurization catalysis and the service life of chemical products produced subsequently are prolonged by at least more than one year. In addition, through pretreatment, the coke oven gas does not need to be desulfurized again after being returned to the coke oven, so that the investment of a flue gas desulfurization device and the generation of desulfurization waste liquid can be reduced. Further, desulfurization and decarburization are carried out through low-temperature methanol washing, impurities in the coke oven gas are further purified deeply, the cleanliness of the coke oven gas is improved, consumption of desulfurization liquid and treatment cost of desulfurization waste liquid in the traditional process are avoided, purification cost is further reduced, simultaneously, desulfurization waste gas is sent to acid making, the acid making concentration is high, the quality is good, decarburization precision is improved, hydrogen is not consumed in the decarburization process, the recovery rate and the utilization rate of the hydrogen can be improved, and therefore ammonia synthesis efficiency and yield can be improved.
The system and the method provided by the embodiment of the invention not only meet the requirements of pressurizing and conveying coke oven gas and subsequent deep purification, achieve the purpose of purifying the produced chemical synthesis system, but also improve the yield of hydrogen and the synthesis efficiency and yield of ammonia. The invention has the advantages of low investment, small equipment volume and occupied area, high efficiency of removing impurities such as tar dust, naphthalene and the like in the coke oven gas, low energy consumption, high washing efficiency and the like.
Drawings
FIG. 1 is a schematic diagram of the system components of the present invention.
FIG. 2 is a schematic view of the structure of the preliminary washing column in FIG. 1.
Fig. 3 is a schematic structural view of a gas-liquid separation device used in the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
As shown in fig. 1, an embodiment of the present invention provides a system for deep purification of coke oven gas to produce synthetic ammonia, which includes a prewashing tower 1, a desulfurizing tower 2, a decarbonizing tower 3, a fine desulfurizing tower 4, a reformer 5, a shift converter 6, a liquid nitrogen washing tower 7, and a synthetic ammonia tower 8, where the prewashing tower 1 is a supergravity rotating device, and in which: the gas holder is connected with a gas phase inlet 103 at the lower part of the prewashing tower 1 through a first heat exchanger 21, a liquid phase outlet 102 at the bottom of the prewashing tower 1 is connected with a gas-liquid separation device 20, a gas outlet 107 at the top of the prewashing tower 1 is connected with a gas inlet at the lower part of the desulfurizing tower 2 through a first compressor 22, a second heat exchanger 9 and a third heat exchanger 10, a gas outlet at the top of the desulfurizing tower 2 is connected with a coke oven through a fourth heat exchanger 11 and a second compressor 12, a gas outlet at the top of the desulfurizing tower 2 is also connected with a gas inlet at the top of the fine desulfurizing tower 4 through a fifth heat exchanger 13 and a third compressor 14, a liquid outlet at the bottom of the desulfurizing tower 2 is connected with a liquid inlet at the upper part of the decarbonizing tower 3, a gas outlet at the bottom of the fine desulfurizing tower 4 is connected with a gas inlet at the top of the reforming furnace 5, a gas outlet at the bottom of the reforming furnace 5 is connected with a gas inlet at the bottom of the reforming furnace 6, a gas outlet at the top of the reforming furnace 6 is connected with a gas inlet at the lower part of the decarbonizing tower 3 through a sixth heat exchanger 15, a seventh heat exchanger 16 and a fourth compressor 17, a liquid outlet at the bottom of the decarbonizing tower 3 is connected with a liquid phase inlet 109 at the upper part of the prewashing tower 1 through an eighth heat exchanger 18 and a fifth compressor 19, a gas outlet at the top of the decarbonizing tower 3 is connected with a gas inlet at the lower part of the liquid nitrogen washing tower 7 through a ninth heat exchanger 23 and a sixth compressor 24, a gas outlet at the top of the liquid nitrogen washing tower 7 is connected with a gas inlet at the top of the synthetic ammonia tower 8 through a tenth heat exchanger 25, and a gas outlet at the bottom of the synthetic ammonia tower 8 is connected with an eleventh heat exchanger 26.
The system provided by the embodiment of the invention is applied to removing impurities such as dust, benzene, tar, naphthalene, ammonia and sulfur in various forms in the coke oven gas after the coke oven gas is initially cooled, electrically trapped with tar, precooled, intercooled, ammonia-removed, finally cooled and benzene-eluted, and is used for preparing synthetic ammonia. The system for preparing synthetic ammonia by deeply purifying coke oven gas relates to the treatment procedures of prewashing, desulfuration, decarburization, fine desulfuration, conversion, transformation, liquid nitrogen washing and ammonia synthesis.
Optionally, as shown in fig. 2, the prewashing tower 1 includes a transmission device 101, a rotating shaft 115 and a prewashing housing 108, the transmission device 101 is connected to one end of the rotating shaft 115, the other end of the rotating shaft 115 is connected to a rotor 104, the rotor 104 is disposed at the middle lower part of the inner cavity of the prewashing housing 108, a gas outlet 107 is connected to the middle of the top of the prewashing housing 108, a liquid outlet 102 is connected to the bottom of the prewashing housing 108, a gas inlet 103 is connected to the bottom of one side of the prewashing housing 108, a liquid inlet 109 is connected to the middle upper part of the other side of the prewashing housing 108, an L-shaped liquid pipeline is connected to the liquid inlet 109, a vertical pipe of the L-shaped liquid pipeline extends to the middle of the rotor 104, a plurality of liquid nozzles 111 are mounted on the vertical pipe of the L-shaped liquid pipeline, a demister 106 is disposed at the top of the inner cavity of the prewashing housing 108, a partition plate 105 is mounted between the bottom of the demister 106 and the top of the rotor 104, a first seal 110 is disposed between the top of the rotor 104, the two sides of the middle of the bottom of the rotor 104 are sealed with the rotating shaft 115 through a second sealing gasket 112 and a third sealing gasket 113 respectively, and the interior of the rotor 104 is filled with a packing layer 114.
Optionally, the porosity of the filler layer 114 is 80% to 99%; the filler of the filler layer 114 adopts large corrugated wire mesh filler and small corrugated wire mesh filler. The small corrugated filler with the length accounting for 5% -10% of the radius of the prewashing shell 108 is arranged near the rotating shaft 115, preferably 5% -8%. The average pore diameter of the large corrugated wire mesh packing is 5-10 mm, and preferably 4-8 mm; the average pore diameter of the small corrugated wire mesh packing is 1-5 mm, preferably 2-4 mm. The packing mode is beneficial to uniform atomization of liquid-phase washing liquid, the impurity trapping effect is improved, the large-ripple packing can reduce the gas-liquid phase resistance, and the anti-blocking capacity of the packing is improved.
Alternatively, as shown in fig. 3, the gas-liquid separation device 20 is a horizontal three-weir type gas-liquid four-phase separator, the four-phase separator includes a separation shell 218, and an inner cavity of the separation shell 218 is divided into an inlet section i, a settling separation section ii and a collection section iii from left to right; the inlet section I is provided with a gas-liquid separator 206, a baffle 207 and a calming plate 208, the feed inlet 201 is arranged outside the separation shell 218 and is connected with the top of the separation shell 218, the gas-liquid separator 206 is arranged below the feed inlet 201, the bottom end of the calming plate 208 is connected with the bottom of the separation shell 218, and the top end of the baffle 207 is connected with the top of the separation shell 218 and is positioned between the gas-liquid separator 206 and the calming plate 208; the sedimentation separation section II is provided with a coalescer 209; the collection section III is provided with a heavy phase fluid overflow weir 217, a heavy phase fluid collection tank 219, a light phase fluid collection tank 220 and an intermediate phase fluid overflow weir 216, the heavy phase fluid overflow weir 217 is arranged on one side of the coalescer 209 and is connected with the bottom of the separation shell 218, the top end of the heavy phase fluid collection tank 219 is connected with the bottom of the separation shell 218 and is positioned between the coalescer 209 and the heavy phase fluid overflow weir 217, a first liquid level meter 213 is respectively arranged on the top and the bottom of the side wall of the heavy phase fluid collection tank 219, a heavy phase fluid outlet 203 is connected with the bottom of the heavy phase fluid collection tank 219, a second liquid level meter 212 is respectively arranged on the top and the bottom of the separation shell 218 above the heavy phase fluid collection tank 219, the light phase fluid collection tank 220 is arranged on one side of the heavy phase fluid overflow weir 217, the front wall of the light phase fluid collection tank 220 is a light phase fluid overflow weir 214, and the height of the light phase fluid overflow weir 214 is lower than that of the rear wall 215 of the light phase fluid collection tank 220, a third liquid level meter 210 is respectively arranged at the top and the bottom in the light phase fluid collecting tank 220, a light phase fluid outlet 204 is connected to the bottom of the light phase fluid collecting tank 220, the light phase fluid outlet 204 is positioned outside the separating shell 218, a demister 222 is arranged above the light phase fluid collecting tank 220, the gas phase outlet 202 is arranged outside the separating shell 218 and is connected with the demister 222, an intermediate phase fluid overflow weir 216 is arranged at one side of the light phase fluid collecting tank 220 and is connected with the bottom of the separating shell 218, the intermediate phase fluid overflow weir 216 and the space at the tail part of the separating shell 218 form an intermediate phase fluid collecting tank 221, a fourth liquid level meter 211 is respectively arranged at the top and the bottom at one side of the intermediate phase fluid overflow weir 216, and the intermediate phase fluid outlet 205 is connected to the bottom of the separating shell 218 at one side of the intermediate phase fluid overflow weir 216.
Wherein gas-liquid separator 206 and calming plate 208 are conventional components of inlet section i, wherein gas-liquid separator 206 has the primary function of effecting gas-liquid pre-separation, and may take a variety of forms in practical application, acting to provide uniform initial distribution or redistribution of liquid at the top of the packing or at a certain height, to enhance the effective surface for mass and heat transfer, to improve phase-to-phase contact, and thereby to enhance the separation efficiency of the column. The main function of the static plate 208 is to slow down the two-phase fluctuation of the liquid phase region of the inlet section I, and also to have the function of liquid-liquid pre-separation, but mainly to inhibit the fluctuation to provide stable operation conditions for the sedimentation separation section II. The coalescer 209 is primarily intended to enhance the separation efficiency by promoting coalescence of the light phase (e.g., oil droplets) on the plate surface, and also has the function of suppressing fluctuation of the liquid phase region in the settling section ii.
Optionally, the length ratio of the inlet section i, the sedimentation separation section ii, and the collection section iii is 1: 3.2-4.2: 2.
Optionally, the top end of the ballast plate 208 is at the same level as the second level gauge 212 at the top of the separation housing 218; the bottom end of the baffle 207 is 400 mm and 500mm higher than the top end of the sedation plate 208, and the bottom end of the baffle 207 is not less than 200mm lower than the bottom end of the gas-liquid separator 206.
Alternatively, the height of the coalescer 209 is the same as the height of the light phase fluid weir 214 (H1), the height of the heavy phase fluid weir 217 is 500mm above the bottom end of the light phase fluid collection tank 220, the height of the light phase fluid weir 214 is 1/2-3/4 of the diameter of the four phase separator, the height of the back wall 215 of the light phase fluid collection tank 220 (H2) is 200mm above the bottom end of the demister 222, and the height of the intermediate phase fluid weir 216 (H3) is 20-100mm below the height of the light phase fluid weir 214.
The three overflow weir plates of the heavy phase fluid overflow weir 217, the light phase fluid overflow weir 214 and the middle phase fluid overflow weir 216, the three heavy phase fluid collecting tanks 219, the light phase fluid collecting tank 220 and the middle phase fluid collecting tank 221 are arranged in the collecting section III, so that the length of the collecting section III of the four-phase separator is greater than that of a common separator, but the liquid-liquid interface in the operation process is well controlled due to the arrangement, the stable operation of the separation process is ensured, and the influence of working condition fluctuation on the process of the sedimentation separation section II is reduced or avoided. The control of the liquid-liquid interface of the four-phase separator in the embodiments of the invention comes from two aspects: the three overflow weir plates and the three liquid phase collecting groove structures enable a liquid-liquid interface to be simultaneously controlled by hydrostatic pressure of light phase/intermediate phase and heavy phase, so that the liquid-liquid interface is relatively stable; the light phase fluid collecting tank 220 and the intermediate phase fluid collecting tank 221 provide buffer space for fluctuation of upstream and downstream (inlet and outlet) flow in the operation process, so that influence of fluctuation of working conditions on the separation process of the settling section is reduced or avoided. By arranging the components such as the static plate 208, the coalescer 209 and the like, the lower transverse flow velocity is ensured to ensure that the fluid in the liquid phase region has enough retention time to realize liquid-liquid sedimentation separation, meanwhile, the sedimentation or the buoyancy of a dispersed phase is facilitated, the fluctuation of the liquid phase region is also reduced, the separation time is shortened, and the size of equipment is reduced.
In all embodiments of the present invention, the four-phase separator shown in fig. 3 is used for gas-liquid separation, and the influence factors of the pressure distribution at the tail end of the descending separation section ii under the actual separation condition are comprehensively considered, including: the height of the light phase fluid weir 214 and the difference in height of the three weirs, the slice thickness at the weir crest and the slice flow rate at the weir crest and the flow resistance at the bottom of the light phase collection tank 220.
In the embodiment of the invention, the coal gas washing liquid pretreated by the prewashing tower 1 enters the four-phase separator, the coal gas washing liquid pretreated by the prewashing tower 1 contains impurities such as tar, dust, crude benzene, naphthalene, ammonia, organic sulfur and the like, and the residual gas, heavy oil, light oil and intermediate phase liquid in the coal gas washing liquid are recovered and treated by the four-phase separator. The gas separated by the four-phase separator is discharged from a gas phase outlet 202, the heavy oil separated by the four-phase separator is discharged from a heavy phase fluid outlet 203, the light oil separated by the four-phase separator is discharged from a light phase fluid outlet 204, and the intermediate phase liquid separated by the four-phase separator is discharged from an intermediate phase fluid outlet 205.
The embodiment of the invention also provides a method for preparing synthetic ammonia by deeply purifying coke oven gas, which adopts the system for preparing synthetic ammonia by deeply purifying coke oven gas, and comprises the following steps:
s1, the coke oven gas after benzene elution is sent into the prewashing tower 1 from the lower part of the prewashing tower 1 after the heat exchange of the coke oven gas is carried out to 20-25 ℃ through the first heat exchanger 21, and meanwhile, the gas detergent from the bottom of the decarbonizing tower 3 is sent into the prewashing tower 1 from the upper part of the prewashing tower 1 after the heat exchange of the eighth heat exchanger 18 and the pressurization of the fifth compressor 19; wherein, the prewashing tower 1 is a supergravity rotating device.
The coke oven gas after benzene elution contains impurities such as dust, benzene, tar, naphthalene, ammonia, sulfur in various forms, and the like. Generally, the coke oven gas after benzene elution contains 5-15mg/m of tar dust 3 10-200mg/m of naphthalene 3 Ammonia 15-100mg/m 3 Sulfur less than 500mg/m 3 And other minor impurities.
S2, the coke oven gas after heat exchange and the gas detergent are in countercurrent or cross-current contact in the prewashing tower 1 for pretreatment, and the pretreated gas detergent is collected on the inner wall of the prewashing tower 1 under the supergravity action of the prewashing tower 1 and then discharged to the gas-liquid separation device 20.
Alternatively, the operating conditions of the prewash column 1 are: the operation temperature is 15-20 ℃, the operation pressure is 3-6 kPa, and the specific surface area of the filler is 500-4000 m 2 /m 3 The rotating frequency of the filler is 30-60 Hz, and the gas-liquid ratio is 1000-6000. The amount of the coal gas detergent is 0.20-0.32 kg/m 3 Coke oven gas.
Since the coke oven gas after benzene elution includes impurities such as dust, benzene, tar, naphthalene, ammonia, and various forms of sulfur, the embodiment of the present invention first pretreats the coke oven gas after benzene elution by using the pre-washing tower 1 adopting the supergravity rotation technology to primarily remove the impurities such as dust, benzene, tar, naphthalene, ammonia, and various forms of sulfur from the coke oven gas after benzene elution.
Specifically, in the prewashing tower 1, the gas detergent is uniformly distributed through the liquid-phase nozzle 111 of the prewashing tower 1 and then enters the packing layer 114, and then enters the transmission device 101 and the rotating shaft 115 under the action of the rotor 104, the gas washing agent is split into liquid microelements (liquid films, liquid threads and liquid drops) and is in countercurrent contact with the coke oven gas after benzene elution to remove impurities in the coke oven gas after benzene elution. Because the prewashing tower 1 is a supergravity rotating device, the embodiment of the invention utilizes the supergravity rotating technology to remove impurities. The cutting grain diameter of the super-gravity rotating technology reaches 10 -8 m, the particle diameter of the coal gas washing agent passing through the packing layer 114 almost reaches the molecular level, and the coal gas washing agent is gathered in the supergravity rotating device and then removed together with impurities. According to the embodiment of the invention, the coke oven gas after benzene elution is pretreated by using a supergravity rotation technology, so that the washing effect can be enhanced, the particle size cutting size of washing is reduced, and meanwhile, under the action of liquid phase spraying and supergravity, liquid drops are more uniformly distributed and have larger contact surface with impurities in the coke oven gas, so that the impurity elution effect is improved. The supergravity rotating device has the characteristics of good particle trapping effect, small gas phase pressure drop, difficult blockage of the rotating filler and the like, so that harmful substances such as dust, benzene, tar, naphthalene, ammonia, sulfur and the like in the coke oven gas are deeply removed, the pressurized conveying and the subsequent deep purification of the coke oven gas are met, and the purpose of purifying the production chemical synthesis system is achieved. The coke oven gas after impurity removal is defoamed by the demister 106 to obtain pretreated coke oven gas, and the gas detergent after impurity removal is thrown to the inner wall of the prewashing shell 108 and flows into the gas-liquid separation device 20 from the liquid phase outlet 102.
Furthermore, the embodiment of the invention determines the optimal temperature for pretreating the coke oven gas to be 20-25 ℃ through experiments, the gas washing agent at least comprises methanol and crude benzene, the gas washing agent also can comprise one or the combination of two or more of desalted water, ethanol, wash oil and tar, and the gas washing agent has good pretreatment effect when the temperature is lower than 20 ℃.
The coke oven gas pretreatment is that naphthalene in the coke oven gas is easy to crystallize and separate out at the temperature of less than 20 ℃ through tests under different temperatures, pressures and detergents. In order to avoid the blockage of equipment and pipelines caused by naphthalene crystallization at low temperature, the embodiment of the invention removes naphthalene in coke oven gas by adding a prewashing tower 1 and using prewashing methanol. Because the pre-washed methanol contains crude benzene, the benzene and the naphthalene belong to aromatic compounds, and the naphthalene is dissolved in the gas detergent according to the similar compatibility principle. After the coke oven gas after benzene elution is pretreated under the conditions, practice proves that the collection efficiency of tar ash reaches more than 99 percent, and particles with the particle size of more than 3 mu m can be completely removed; the removal rate of naphthalene is more than 80%; the removal rate of tar and dust reaches more than 60 percent; the removal rate of the organic sulfur reaches more than 85 percent; the removal rate of ammonia reaches more than 50 percent; the removal rate of the benzene reaches more than 50 percent; the removal rate enables the pretreated coke oven gas to meet the requirements of subsequent compression and deep purification.
S3, pressurizing the pretreated coke oven gas to 0.3-1.0MPa by a first compressor 22, then exchanging heat by a second heat exchanger 9, carrying out deep cooling by a third heat exchanger 10 to-22-28 ℃, then entering a desulfurizing tower 2, carrying out low-temperature methanol washing operation on the lean methanol introduced into the desulfurizing tower 2 and the desulfurizing tower 2 to remove impurities in the coke oven gas, thus obtaining the coke oven gas after deep purification, reheating 42-50% of the coke oven gas after deep purification by a fourth heat exchanger 11, decompressing to 8-10kPa by a second compressor 12, using the coke oven gas as return gas for heating the coke oven, reheating the rest coke oven gas after deep purification by a fifth heat exchanger 13, compressing and pressurizing by a third compressor 14, and then entering a fine desulfurizing tower 4.
Optionally, the dosage of the lean methanol in the desulfurizing tower 2 is 1.30-1.50kg/m 3 Coke oven gas. The temperature of the low-temperature methanol washing operation is-20 ℃ to-40 ℃, and the pressure is 0.3 MPa to 1.5 MPa.
Methanol in the desulfurizing tower 2 absorbs NH in the process gas while absorbing acid gas 3 This has a certain influence on the low-temperature methanol washing system (the desulfurization tower 2 and the decarbonization tower 3). NH at low temperature 3 Solubility in methanol is much higher than that of CO 2 And H 2 Since acidic gases such as S have solubility in methanol, they are easily accumulated in the methanol washing system. CO 2 2 And H 2 After the acidic gases such as S and the like are dissolved in the methanol, the pH value of the methanol is reduced, and the corrosion of low-temperature methanol washing system equipment is caused. In order to reduce the corrosion of the equipment and prolong the service life and the transportation of the equipmentThe line period, the existing low-temperature methanol washing process can allow a certain content of NH in the system 3 However, NH must be strictly controlled 3 Content in low-temperature methanol washing system if NH 3 The low content can cause the aggravation of equipment corrosion; when NH is present 3 The content of sulfur in the process gas exceeds the standard to a certain extent. Therefore, NH in the low-temperature methanol washing system must be well controlled 3 Content, therefore, the embodiment of the present invention needs to control the ammonia gas concentration in the purification within a range that maintains NH in the lean methanol (circulated in the desulfurization tower 2, the decarbonization tower 3 and the pre-washing tower 1) that is circulated 3 The content is less than 20 × 10 －6 ppm and pH value of 8-10.
According to H in coke oven gas 2 The solubility of the S in methanol is 0.9-6 Nm at 0.3-1.0MPa and-20-40 DEG C 3 H 2 S/m 3 ，CO 2 The solubility in methanol at 0.3-1.0MPa and-20-40 ℃ is 0.8-5 Nm 3 CO 2 /m 3 It can be determined that the amount of the lean methanol in the desulfurizing tower 2 (i.e., the amount of the lean methanol introduced into the desulfurizing tower 2) is 1.30 to 1.50kg/m 3 Coke oven gas.
The coke oven gas has complex components and a plurality of impurities, and the gas components comprise CO and H 2 、CO 2 、CH 4 、H 2 S, organic sulfur, C 2 H 4 、C 2 H 6 、C 3 H 8 、C 4 H 10 、HCN、N 2 Ar and tar, fatty acid, monophenol, polyphenol, naphtha, anthracene oil, naphthalene oil, fly ash, etc. Removing CO and H from these components 2 An active ingredient and CH 4 、 N 2 Ar and hydrocarbons other than inert gas, all other components including CO 2 And sulfides are harmful impurities that need to be removed, and the purification task is difficult. Along with the implementation of policies of going into a garden and upgrading and transforming with the return of coking enterprises, large-scale and high-end formation is the development direction of the coking industry, the requirement of coke oven gas desulfurization is increased, and various harmful components such as CO in the coke oven gas can be cleanly removed by adopting a low-temperature methanol cleaning method 2 、H 2 S、COS、C 4 H 4 S、HCN、NH 3 、H 2 O、C 2 The above hydrocarbons (including light oil, aromatic hydrocarbon, naphtha, olefin, colloid substance, etc.) and other carbonyl compounds, etc., which cannot be achieved by any other purification process. In addition, the low-temperature methanol is adopted to elute and remove the sulfur impurities with complex components in the coke oven gas, thereby not only ensuring the index of purified gas, but also solving the problem that the coking desulfurization waste liquid can not be treated radically through the regeneration and recycling of the methanol.
And (3) performing low-temperature methanol washing operation to almost completely remove organic sulfur impurities in the deeply purified coke oven gas, wherein the total sulfur content in the coke oven gas is less than 10 ppm. The coke oven gas after deep purification is returned to the coke oven as fuel gas, so that the investment of a flue gas desulfurization device and the generation of desulfurization waste liquid can be reduced.
S4, carrying out fine desulfurization on the coke oven gas entering the fine desulfurization tower 4 under the action of the desulfurization adsorbent of the fine desulfurization tower 4.
Optionally, the desulfurization adsorbent is zinc oxide or iron oxide; the operation temperature in the fine desulfurization tower 4 is 250-450 ℃, the pressure is 0.8-5.0 MPa, and the space velocity is 500-1500 h -1 . The sulfur content in the coke oven gas after the fine desulfurization is less than 0.1 ppm. On the basis of preliminary desulfurization of low-temperature methanol washing operation, further fine desulfurization operation is carried out, and the service life of the desulfurization adsorbent can be prolonged by 300-500 times.
S5, the coke oven gas after fine desulfurization enters the reformer 5 and is introduced with O in the reformer 5 2 And CO 2 The mixed gas is converted, and the converted coke oven gas enters a shift converter 6.
The coke oven gas conversion process mainly uses CH in the coke oven gas 4 Reacting unsaturated hydrocarbon with oxygen to convert into H 2 CO and CO 2 。
Optionally, the gas conversion temperature in the converter 5 is 1200-1300 ℃, the operating pressure is 2-6 MPa, the retention time is 1-5 s, and the oxygen: carbon dioxide: the coke oven gas ratio is 0.25-0.27: 0.02-0.04: 1. Under the operating condition, the content of methane in the converted coke oven gas is less than 10ppm and CH 4 The residual quantity of unsaturated hydrocarbon is less than 1 percentThe hydrogen content is increased by 15-20% (dry basis V%).
And S6, converting the converted coke oven gas in the shift converter 6 with the steam introduced into the shift converter 6.
The coke oven gas conversion process mainly converts CO in the converted coke oven gas into H 2 The hydrogen content is increased by 3 percent to 6 percent (dry basis V percent) by one step, so that the overall hydrogen recovery rate is more than or equal to 99.5 percent.
Optionally, the reaction in the shift converter 6 adopts an isothermal shift technology, the shift temperature is 180-350 ℃, the shift pressure is 3-5 MPa, and the water-steam ratio is 0.4-0.6. Under the operating condition, the carbon monoxide content in the converted coke oven gas is less than 20 ppm.
S7, the transformed coke oven gas enters the decarbonization tower 3 for decarbonization after heat exchange through the sixth heat exchanger 15 and the seventh heat exchanger 16 and pressurization through the fourth compressor 17, the decarbonized coke oven gas enters the liquid nitrogen washing tower 7 for liquid nitrogen washing operation after heat exchange through the ninth heat exchanger 23 and compression through the sixth compressor 24, the hydrogen-nitrogen ratio of the coke oven gas in the liquid nitrogen washing tower 7 and liquid nitrogen entering the liquid nitrogen washing tower 7 is adjusted to be 2.7-3.0, and the coke oven gas enters the synthetic ammonia tower 8 for ammonia synthesis after heat exchange through the tenth heat exchanger 25.
Optionally, the decarbonization operation temperature is-20 ℃ to-40 ℃, and the operation pressure is 0.3 MPa to 1.5 MPa. Under the operating condition, the decarbonization operation can remove CO and CH in the coke oven gas 4 Ar, etc., and the CO content in the decarbonized coke oven gas is less than 1ppm and CH 4 The content is less than 1ppm, the Ar content is less than 0.1ppm, and the hydrogen recovery rate is more than or equal to 99.5 percent. CO in the gas after shift reaction 2 The content is 5 to 10 percent, and the mixture enters a low-temperature methanol washing procedure again for decarburization to obtain gases containing 92 to 95 percent of hydrogen, 5 to 7 percent of nitrogen and a small amount of other impurities.
Optionally, the temperature of the liquid nitrogen washing operation is-185 ℃ to-195 ℃, and the pressure is 5.0MPa to 6.0 MPa. The operation temperature of the synthetic ammonia is 400-500 ℃, the pressure is 15-20 MPa, the catalyst adopts an iron-based catalyst, the iron ratio is 0.4-0.6, and the airspeed is 0-30000 h -1 。
And S8, liquefying the ammonia synthesized in the ammonia synthesizer 8 by the eleventh heat exchanger 26 to obtain liquid ammonia.
It should be noted that the heat source medium used in each heat exchanger can be selected according to needs, and this is not described in detail in the embodiments of the present invention.
It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and scope of the invention, and such modifications and improvements are also considered to be within the scope of the invention.
Claims (9)
1. The utility model provides a system for coke oven gas deep purification system synthetic ammonia which characterized in that, includes prewashing tower (1), desulfurizing tower (2), decarbonization tower (3), smart desulfurizing tower (4), reborner (5), shift converter (6), liquid nitrogen washing tower (7) and synthetic ammonia tower (8), prewashing tower (1) is hypergravity rotary device, wherein: the gas holder is connected with a gas phase inlet (103) at the lower part of the prewashing tower (1) through a first heat exchanger (21), a liquid phase outlet (102) at the bottom of the prewashing tower (1) is connected with a gas-liquid separation device (20), a gas outlet (107) at the top of the prewashing tower (1) is connected with a gas inlet at the lower part of the desulfurizing tower (2) through a first compressor (22), a second heat exchanger (9) and a third heat exchanger (10), a gas outlet at the top of the desulfurizing tower (2) is connected with a coke oven through a fourth heat exchanger (11) and a second compressor (12), a gas outlet at the top of the desulfurizing tower (2) is also connected with a gas inlet at the top of the fine desulfurizing tower (4) through a fifth heat exchanger (13) and a third compressor (14), a liquid outlet at the bottom of the desulfurizing tower (2) is connected with a liquid inlet at the upper part of the decarbonizing tower (3), a gas outlet at the bottom of the fine desulfurizing tower (4) is connected with a gas inlet at the top of the converting furnace (5), a gas outlet at the bottom of the converter (5) is connected with a gas inlet at the bottom of the shift converter (6), a gas outlet at the top of the shift converter (6) is connected with a gas inlet at the lower part of the decarbonization tower (3) through a sixth heat exchanger (15), a seventh heat exchanger (16) and a fourth compressor (17), a liquid outlet at the bottom of the decarbonization tower (3) is connected with a liquid phase inlet (109) at the upper part of the prewashing tower (1) through an eighth heat exchanger (18) and a fifth compressor (19), a gas outlet at the top of the decarbonization tower (3) is connected with a gas inlet at the lower part of the liquid nitrogen washing tower (7) through a ninth heat exchanger (23) and a sixth compressor (24), a gas outlet at the top of the liquid nitrogen washing tower (7) is connected with a gas inlet at the top of the synthetic ammonia tower (8) through a tenth heat exchanger (25), and a gas outlet at the bottom of the synthetic ammonia tower (8) is connected with an eleventh heat exchanger (26);
the prewashing tower (1) comprises a transmission device (101), a rotating shaft (115) and a prewashing shell (108), the transmission device (101) is connected with one end of the rotating shaft (115), the other end of the rotating shaft (115) is connected with a rotor (104), the rotor (104) is arranged at the middle lower part of the inner cavity of the prewashing shell (108), a gas outlet (107) is connected in the middle of the top of the prewashing shell (108), a liquid phase outlet (102) is connected at the bottom of the prewashing shell (108), a gas phase inlet (103) is connected at the bottom of one side of the prewashing shell (108), a liquid phase inlet (109) is connected at the middle upper part of the other side of the prewashing shell (108), an L-shaped liquid pipeline is connected with the liquid phase inlet (109), a vertical pipe of the L-shaped liquid pipeline extends to the middle part of the rotor (104), a plurality of liquid phase nozzles (111) are installed on the vertical pipe of the L-shaped liquid pipeline, a demister (106) is arranged at the top of the inner cavity of the prewashing shell (108), a partition plate (105) is installed between the bottom of the demister (106) and the top of the rotor (104), the middle of the top of the rotor (104) and the partition plate (105) are sealed through a first sealing gasket (110), the middle of the bottom of the rotor (104) and the rotating shaft (115) are respectively sealed through a second sealing gasket (112) and a third sealing gasket (113), and a packing layer (114) is filled inside the rotor (104).
2. The method for preparing the synthetic ammonia by deeply purifying the coke oven gas adopts the system for preparing the synthetic ammonia by deeply purifying the coke oven gas as claimed in claim 1, and is characterized by comprising the following steps of:
s1, the coke oven gas after benzene elution is subjected to heat exchange by a first heat exchanger (21) to 20-25 ℃, and then is sent into a prewashing tower (1) from the lower part of the prewashing tower (1), and meanwhile, a gas washing agent from the bottom of a decarbonizing tower (3) is subjected to heat exchange by an eighth heat exchanger (18) and pressurization by a fifth compressor (19) and then is sent into the prewashing tower (1) from the upper part of the prewashing tower (1); wherein, the prewashing tower (1) is a supergravity rotating device;
s2, performing pretreatment by the countercurrent or cross-flow contact of the coke oven gas after heat exchange and a gas detergent in the prewashing tower (1), and discharging the pretreated gas detergent to a gas-liquid separation device (20) after gathering on the inner wall of the prewashing tower (1) under the supergravity action of the prewashing tower (1);
s3, pressurizing the pretreated coke oven gas to 0.3-1.0MPa by a first compressor (22), exchanging heat by a second heat exchanger (9), carrying out deep cooling by a third heat exchanger (10) to-22-28 ℃, then feeding the coke oven gas into a desulfurizing tower (2), carrying out low-temperature methanol washing operation on the coke oven gas and poor methanol introduced into the desulfurizing tower (2) in the desulfurizing tower (2) to remove impurities in the coke oven gas, so as to obtain the deeply purified coke oven gas, reheating 42-50% of the deeply purified coke oven gas by a fourth heat exchanger (11), reducing the pressure of the deeply purified coke oven gas to 8-10kPa by a second compressor (12), using the deeply purified coke oven gas as return gas for heating the coke oven, reheating the rest of the deeply purified coke oven gas by a fifth heat exchanger (13) and compressing and pressurizing by a third compressor (14), and feeding the deeply purified coke oven gas into a fine desulfurizing tower (4);
s4, carrying out fine desulfurization on the coke oven gas entering the fine desulfurization tower (4) under the action of a desulfurization adsorbent of the fine desulfurization tower (4);
s5, the coke oven gas after fine desulfurization enters a converter (5) and is introduced with O in the converter (5) 2 And CO 2 The mixed gas is converted, and the converted coke oven gas enters a shift converter (6);
s6, converting the converted coke oven gas in a shift converter (6) with steam introduced into the shift converter (6);
s7, the converted coke oven gas enters a decarbonization tower (3) for decarbonization after heat exchange through a sixth heat exchanger (15) and a seventh heat exchanger (16) and pressurization through a fourth compressor (17), the decarbonized coke oven gas enters a liquid nitrogen washing tower (7) for liquid nitrogen washing operation after heat exchange through a ninth heat exchanger (23) and compression through a sixth compressor (24), the hydrogen-nitrogen ratio of the coke oven gas in the liquid nitrogen washing tower (7) and liquid nitrogen entering the liquid nitrogen washing tower (7) is adjusted to be 2.7-3.0, and the coke oven gas enters a synthetic ammonia tower (8) for ammonia synthesis after heat exchange through a tenth heat exchanger (25);
s8, liquefying the ammonia synthesized in the ammonia synthesizer (8) by the eleventh heat exchanger (26) to obtain liquid ammonia.
3. The method for preparing synthetic ammonia by deeply purifying coke oven gas according to claim 2, wherein the amount of the gas washing agent is 0.20-0.32 kg/m 3 The dosage of the poor methanol in the desulfurizing tower (2) of the coke oven gas is 1.30-1.50kg/m 3 Coke oven gas.
4. The method for preparing synthetic ammonia by deeply purifying coke oven gas according to claim 2, wherein the temperature of the low-temperature methanol washing operation is-20 ℃ to-40 ℃, and the pressure is 0.3 MPa to 1.5 MPa.
5. The method for preparing synthetic ammonia by deeply purifying coke oven gas according to claim 2, wherein the desulfurization adsorbent is zinc oxide or iron oxide; the operation temperature in the fine desulfurization tower (4) is 250-450 ℃, the pressure is 0.8-5.0 MPa, and the space velocity is 500-1500 h -1 。
6. The method for preparing synthetic ammonia by deeply purifying coke oven gas according to claim 2, wherein the conversion temperature of the gas in the converter (5) is 1200-1300 ℃, the operating pressure is 2-6 MPa, the retention time is 1-5 s, and the oxygen: carbon dioxide: the coke oven gas ratio is 0.25-0.27: 0.02-0.04: 1.
7. The method for preparing synthetic ammonia by deep purification of coke oven gas according to claim 2, characterized in that isothermal conversion technology is adopted for reaction in the shift converter (6), the conversion temperature is 180-350 ℃, the conversion pressure is 3-5 MPa, and the water-steam ratio is 0.4-0.6.
8. The method for preparing synthetic ammonia by deeply purifying coke oven gas according to claim 2, wherein the liquid nitrogen washing operation is carried out at a temperature of-185 ℃ to-195 ℃ and a pressure of 5.0 to 6.0 MPa.
9. The method for preparing synthetic ammonia by deeply purifying coke oven gas according to claim 2, wherein the synthetic ammonia is operated at 400-500 ℃ under 15-20 MPa, the catalyst is an iron-based catalyst, the iron ratio is 0.4-0.6, and the airspeed is 0-30000 h -1 。
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