CN106672898A - Method for synthesizing ammonia by taking byproduct tail gas in process of producing acetylene by pyrolyzing natural gas as raw material - Google Patents
Method for synthesizing ammonia by taking byproduct tail gas in process of producing acetylene by pyrolyzing natural gas as raw material Download PDFInfo
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- 239000007789 gas Substances 0.000 title claims abstract description 181
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 title claims abstract description 146
- 238000000034 method Methods 0.000 title claims abstract description 107
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 title claims abstract description 98
- 239000002994 raw material Substances 0.000 title claims abstract description 91
- 229910021529 ammonia Inorganic materials 0.000 title claims abstract description 70
- 230000008569 process Effects 0.000 title claims abstract description 66
- 239000006227 byproduct Substances 0.000 title claims abstract description 52
- 239000003345 natural gas Substances 0.000 title claims abstract description 40
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 title claims abstract description 34
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 title claims abstract description 34
- 230000002194 synthesizing effect Effects 0.000 title claims abstract description 27
- 230000015572 biosynthetic process Effects 0.000 claims abstract description 40
- 238000003786 synthesis reaction Methods 0.000 claims abstract description 40
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 31
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims abstract description 31
- 239000001257 hydrogen Substances 0.000 claims abstract description 29
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 29
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 15
- 238000000746 purification Methods 0.000 claims abstract description 14
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 10
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 7
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 claims abstract description 5
- 229910002091 carbon monoxide Inorganic materials 0.000 claims abstract description 5
- 238000006243 chemical reaction Methods 0.000 claims description 54
- 238000005336 cracking Methods 0.000 claims description 28
- 238000002360 preparation method Methods 0.000 claims description 23
- 238000004519 manufacturing process Methods 0.000 claims description 22
- 238000001179 sorption measurement Methods 0.000 claims description 18
- 239000003054 catalyst Substances 0.000 claims description 17
- 238000010438 heat treatment Methods 0.000 claims description 17
- 238000005984 hydrogenation reaction Methods 0.000 claims description 14
- 229910052757 nitrogen Inorganic materials 0.000 claims description 14
- 238000005262 decarbonization Methods 0.000 claims description 13
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims description 12
- 238000006477 desulfuration reaction Methods 0.000 claims description 10
- 230000023556 desulfurization Effects 0.000 claims description 10
- 239000002918 waste heat Substances 0.000 claims description 9
- 238000005261 decarburization Methods 0.000 claims description 7
- 239000011787 zinc oxide Substances 0.000 claims description 6
- 230000009471 action Effects 0.000 claims description 5
- 238000010926 purge Methods 0.000 claims description 5
- 238000011084 recovery Methods 0.000 claims description 3
- 229930195734 saturated hydrocarbon Natural products 0.000 claims description 3
- 230000035939 shock Effects 0.000 claims description 3
- 230000009466 transformation Effects 0.000 claims description 3
- PVXVWWANJIWJOO-UHFFFAOYSA-N 1-(1,3-benzodioxol-5-yl)-N-ethylpropan-2-amine Chemical compound CCNC(C)CC1=CC=C2OCOC2=C1 PVXVWWANJIWJOO-UHFFFAOYSA-N 0.000 claims description 2
- QMMZSJPSPRTHGB-UHFFFAOYSA-N MDEA Natural products CC(C)CCCCC=CCC=CC(O)=O QMMZSJPSPRTHGB-UHFFFAOYSA-N 0.000 claims description 2
- 239000003795 chemical substances by application Substances 0.000 claims description 2
- 230000003009 desulfurizing effect Effects 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims description 2
- 230000000694 effects Effects 0.000 abstract description 4
- 229910001873 dinitrogen Inorganic materials 0.000 abstract description 3
- 230000003044 adaptive effect Effects 0.000 abstract 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 12
- 239000003463 adsorbent Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 230000008901 benefit Effects 0.000 description 6
- 239000012535 impurity Substances 0.000 description 6
- 238000000926 separation method Methods 0.000 description 6
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 4
- 241000948268 Meda Species 0.000 description 4
- GLUUGHFHXGJENI-UHFFFAOYSA-N Piperazine Chemical compound C1CNCCN1 GLUUGHFHXGJENI-UHFFFAOYSA-N 0.000 description 4
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 3
- 239000003153 chemical reaction reagent Substances 0.000 description 3
- 239000011261 inert gas Substances 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- 239000005997 Calcium carbide Substances 0.000 description 2
- 241000931197 Themeda Species 0.000 description 2
- 150000001336 alkenes Chemical class 0.000 description 2
- 150000001345 alkine derivatives Chemical class 0.000 description 2
- 239000003245 coal Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000003795 desorption Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 230000007774 longterm Effects 0.000 description 2
- CRVGTESFCCXCTH-UHFFFAOYSA-N methyl diethanolamine Chemical compound OCCN(C)CCO CRVGTESFCCXCTH-UHFFFAOYSA-N 0.000 description 2
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- CLZWAWBPWVRRGI-UHFFFAOYSA-N tert-butyl 2-[2-[2-[2-[bis[2-[(2-methylpropan-2-yl)oxy]-2-oxoethyl]amino]-5-bromophenoxy]ethoxy]-4-methyl-n-[2-[(2-methylpropan-2-yl)oxy]-2-oxoethyl]anilino]acetate Chemical compound CC1=CC=C(N(CC(=O)OC(C)(C)C)CC(=O)OC(C)(C)C)C(OCCOC=2C(=CC=C(Br)C=2)N(CC(=O)OC(C)(C)C)CC(=O)OC(C)(C)C)=C1 CLZWAWBPWVRRGI-UHFFFAOYSA-N 0.000 description 2
- 241000196324 Embryophyta Species 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000009825 accumulation Methods 0.000 description 1
- 239000012190 activator Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000003034 coal gas Substances 0.000 description 1
- WHDPTDWLEKQKKX-UHFFFAOYSA-N cobalt molybdenum Chemical compound [Co].[Co].[Mo] WHDPTDWLEKQKKX-UHFFFAOYSA-N 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- TVZPLCNGKSPOJA-UHFFFAOYSA-N copper zinc Chemical compound [Cu].[Zn] TVZPLCNGKSPOJA-UHFFFAOYSA-N 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000007710 freezing Methods 0.000 description 1
- 230000008014 freezing Effects 0.000 description 1
- 239000002737 fuel gas Substances 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 229910003480 inorganic solid Inorganic materials 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 239000002808 molecular sieve Substances 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000002574 poison Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 238000001308 synthesis method Methods 0.000 description 1
- 230000004304 visual acuity Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
- C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
- C01B3/025—Preparation or purification of gas mixtures for ammonia synthesis
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
- C01C1/00—Ammonia; Compounds thereof
- C01C1/02—Preparation, purification or separation of ammonia
- C01C1/04—Preparation of ammonia by synthesis in the gas phase
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Analytical Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Combustion & Propulsion (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
The invention discloses a method for synthesizing ammonia by taking byproduct tail gas in a process of producing acetylene by pyrolyzing natural gas as a raw material. The method comprises the following steps: step S1, carrying out a tail gas purification procedure, wherein the content of hydrogen in purification raw material gas is 99.0 percent or more; step S2, carrying out a methanation procedure and forming ammonia synthetic gas by the purified raw material gas in the step S1 and nitrogen gas; enabling the sum of the content of carbon monoxide and carbon dioxide in qualified synthetic gas to be smaller than 10ppm; step S3, carrying out an ammonia synthesis procedure: conveying the qualified synthetic gas in the step S2 into the ammonia synthesis procedure, so as to prepare the ammonia. According to the method disclosed by the invention, a purification method is adopted and pure hydrogen gas is directly extracted from byproduct tail gas; the pure hydrogen gas is used as raw material gas of the ammonia synthesis procedure, so that the method can be adaptive to application of synthesizing the ammonia by the byproduct tail gas with low methane content. The byproduct tail gas in the process of producing the acetylene by pyrolyzing the natural gas is utilized and a pollution problem, caused by byproduct tail gas emission, to the environment is avoided; reutilization of energy sources are also realized; the method has very good demonstration and popularization effects.
Description
Technical Field
The invention relates to the technical field of ammonia synthesis processes, in particular to a method for synthesizing ammonia by taking byproduct tail gas generated in acetylene preparation through natural gas cracking as a raw material.
Background
The acetylene preparation method commonly used in industry comprises a calcium carbide method and a natural gas cracking method, and in areas with rich natural gas resources, the acetylene preparation method by natural gas cracking is more economical and environment-friendly than the acetylene preparation method by calcium carbide. By natural gas schizolysis system acetylene can produce a large amount of by-product tail gas, and the by-product tail gas composition is comparatively complicated, if directly discharge the by-product tail gas, can cause the waste of the energy on the one hand, still can destroy ecological environment on the other hand.
The process for synthesizing ammonia generally adopts coal or natural gas as raw material, and prepares synthetic gas through coal gasification or natural gas conversion, and the synthetic gas prepares liquid ammonia after purification and synthesis. However, if the ammonia gas is prepared from the byproduct tail gas from the preparation of acetylene by natural gas cracking, the content of methane in the byproduct tail gas is only 2.7%, so the method cannot be applied to the process for producing ammonia from coal and cannot be applied to the process for producing ammonia from natural gas. In the process for synthesizing ammonia by using natural gas as a raw material, the raw material hydrogen is methane, and the methane is generated through conversion reaction and water vapor, so if the byproduct tail gas adopts the process for producing ammonia by using natural gas, the investment cost of a device is high, and the cost of the whole production process is very high.
Therefore, if the ammonia can be synthesized by taking the byproduct tail gas generated in the preparation of acetylene by natural gas cracking as a raw material, the problem of tail gas emission can be solved, the problem of ammonia synthesis can also be solved, the economic benefit is very good, and the method has demonstration and popularization effects on factories producing PVC by an acetylene method.
Disclosure of Invention
The invention aims to provide a method for synthesizing ammonia by taking byproduct tail gas generated in preparation of acetylene by natural gas cracking as a raw material, which is used for solving the problem that the problem of emission of the byproduct tail gas generated in preparation of acetylene by natural gas cracking is difficult to solve.
In order to achieve the above purpose, the invention provides the following technical scheme: a method for synthesizing ammonia by taking byproduct tail gas generated in acetylene preparation by natural gas cracking as a raw material comprises the following steps:
step S1 exhaust gas purification step:
sequentially carrying out a desulfurization hydrogenation process, a transformation process, a decarburization process and a pressure swing adsorption hydrogen production process on a byproduct tail gas generated in the preparation of acetylene by natural gas cracking to form a purified feed gas, wherein the volume percentage of hydrogen in the purified feed gas is more than 99.0%;
step S2 methanation step:
obtaining qualified hydrogen from the purified raw material gas in the step S1 through methanation reaction; step S3 synthetic ammonia process:
and (4) conveying the qualified hydrogen and nitrogen in the step S2 to an ammonia synthesis process to prepare ammonia gas.
Preferably, the nitrogen produced by air separation enters through the inlet of the methanation process of the step S2, and the ratio of the nitrogen to qualified hydrogen according to the mass ratio of 1: 2.75-3.20 to form ammonia synthesis gas, and conveying the ammonia synthesis gas to an ammonia synthesis process.
Preferably, the ammonia synthesis gas is processed through a methanation process in step S2 to obtain qualified synthesis gas, and the sum of the contents of carbon monoxide and carbon dioxide in the qualified synthesis gas is less than 10 ppm.
Specifically, the step S1 is an exhaust gas purification process including the steps of:
(a) a desulfurization hydrogenation process:
the H in the byproduct tail gas is removed under the action of a desulfurizer2S component and C in the by-product tail gas under the action of hydrogenation catalyst2H2And C2H4Hydrogenating to obtain saturated hydrocarbon, forming a first raw material gas by-product tail gas after desulfurization and hydrogenation treatment, wherein C in the first raw material gas2H2Is less than 5ppm, C in the first raw material gas2H4The content of (A) is 20ppm or less;
(b) a conversion step:
subjecting the first raw material gas to a shift conversion process to remove CO in the first raw material gas to form a second raw material gas, wherein the volume percentage content of CO in the second raw material gas is less than 0.34% (dry basis);
(c) a decarburization process:
subjecting the second raw material gas to a decarbonization step to remove CO from the second raw material gas2Forming a third raw material gas, wherein H is contained in the third raw material gas2The volume percentage of the (B) is more than 95.4 percent;
(d) pressure swing adsorption hydrogen production:
and the third raw material gas is subjected to a pressure swing adsorption hydrogen production process to form purified raw material gas.
Preferably, the desulfurizing agent in the step S1(a) is zinc oxide.
Preferably, the conversion step in step S1(b) is a middle-shift and low-shift step, and the conversion step includes a heating furnace, a medium-temperature shift converter, and a low-temperature shift converter, which are connected in sequence.
Preferably, the medium-temperature shift converter comprises a first medium-temperature shift converter and a second medium-temperature shift converter, wherein 40-50% of the first raw material gas is input into the first medium-temperature shift converter through the heating furnace, and 50-60% of the first raw material gas is directly input into the second medium-temperature shift converter as cold shock gas.
Preferably, a waste heat recoverer is arranged between the second medium-temperature shift converter and the low-temperature shift converter and is connected with the heating furnace through a pipeline.
Preferably, the decarbonization step in step S1(c) is an MDEA decarbonization process, and the high-pressure flash gas treated by the decarbonization step is combined with the by-product tail gas and enters the tail gas purification step.
Preferably, the purge gas output in the ammonia synthesis process in step S3 is input from an inlet of the pressure swing adsorption hydrogen production process.
Compared with the prior art, the method for synthesizing ammonia by taking the byproduct tail gas from acetylene preparation by natural gas cracking as the raw material has the following advantages: the invention relates to an ammonia synthesis method which is designed based on careful research on the components of a byproduct tail gas generated by preparing acetylene by cracking natural gas and overall consideration of the balance of nitrogen generated by an air separation device, and is different from a method for synthesizing ammonia by taking natural gas as a raw material. The method can adapt to the method for producing ammonia gas by using the byproduct tail gas with low content of methane, realizes the utilization of the byproduct tail gas generated in the preparation of acetylene by cracking natural gas, avoids the problem of environmental pollution caused by the emission of the byproduct tail gas, realizes the reutilization of energy sources, and has good economic benefit.
The method has high utilization rate of hydrogen, can realize long-term continuous and stable production of ammonia, has simple and safe operation process, low investment of the adopted overall equipment and effectively reduces the production cost of synthetic ammonia.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. In the drawings:
FIG. 1 is a flow chart showing a method for synthesizing ammonia by using a byproduct tail gas from the production of acetylene by natural gas cracking as a raw material according to a preferred embodiment of the invention;
fig. 2 shows a flow chart of the conversion process of fig. 1.
Detailed Description
The present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific examples described in the following embodiments of the present invention are merely illustrative of specific embodiments of the present invention and do not limit the scope of the invention.
The invention is further described with reference to the following figures and detailed description of embodiments.
As shown in fig. 1, the embodiment provides a method for synthesizing ammonia by using a byproduct tail gas from acetylene preparation by natural gas cracking as a raw material, which includes the following steps:
step S1 exhaust gas purification step:
the method comprises the steps of sequentially carrying out (a) a desulfurization hydrogenation process, (b) a transformation process, (c) a decarburization process and (d) a pressure swing adsorption hydrogen production process on a byproduct tail gas generated in the preparation of acetylene by natural gas cracking to form a purified raw material gas, wherein the volume percentage content of hydrogen in the purified raw material gas is more than 99.0%. Wherein,
the desulfurization and hydrogenation step in step S1(a) includes a desulfurization step and a hydrogenation step. The byproduct tail gas contains H2S，H2S not only corrodes process piping and equipment, but also poisons the shift catalyst in the step S1(b) and the ammonia synthesizing catalyst in the step S3, so that the desulfurization step in this embodiment means to remove H in the by-product exhaust gas2S is removed, so that H in the byproduct tail gas2The S content is less than 0.1 ppm. Specifically, the desulfurizer used in this embodiment is zinc oxide, and the zinc oxide desulfurizer is an inorganic solid desulfurizer having a large internal surface area and a high sulfur capacity, and is capable of rapidly removing hydrogen sulfide, with active zinc oxide as a main component. The reaction principle is as follows: ZnO + H2S＝ZnS+H2O。
The hydrogenation step refers to the step of adding the alkyne C in the by-product tail gas under the action of the hydrogenation catalyst2H2And olefin C2H4By hydrogenation, saturated hydrocarbons, alkynes C, are formed which are easily removed2H2The content of (A) is reduced to less than 5ppm, and the olefin C2H4The content of (B) is reduced to below 20 ppm.
The purpose of the conversion process in the step S1(b) is to remove CO in the first raw material gas to meet the requirement of the later-stage ammonia synthesis process, and the reaction principle is CO + H2O→CO2+H2H in the equation2O participates in the reaction as steam, and the generated hydrogen gas can increase the raw material gas content of the ammonia synthesis process in step S3. And forming a second raw material gas after the conversion process, wherein the second raw material gas contains less than 0.34% of CO by volume.
The conversion process may be a medium temperature conversion process or a medium temperature conversion series low temperature conversion process (i.e., medium temperature conversion series low temperature conversion process), but if the medium temperature conversion process is adopted, the first raw material gas is treatedIn other words, since the equipment cost and the operation cost are high in response to the temperature requirement, the conversion step in the present embodiment is preferably a middle-to-low conversion step. In the present embodiment, if one medium-temperature shift converter is connected to one low-temperature shift converter, all the first raw material gas is directly fed into the medium-temperature shift converter, the medium-temperature shift converter is filled with a medium-temperature shift catalyst, and the medium-temperature shift catalyst generally used is Fe2O3The catalyst is an active component, has an active temperature of 320 ℃ or higher, and is packed in a low-temperature shift converter, and a cobalt-molybdenum-based catalyst or a copper-zinc-based catalyst is generally used as the low-temperature shift converter. When all the first raw material gas is input into the medium-temperature shift converter, the medium-temperature shift converter needs to reach the activity temperature of the medium-temperature shift catalyst, so that the first raw material gas needs to be heated by a heating furnace first, and a large amount of heating furnace fuel is consumed. Meanwhile, since the shift reaction is a reversible exothermic reaction according to the above reaction principle, the reaction rate constant increases due to temperature increase from the viewpoint of reaction kinetics, but the equilibrium constant of the reaction decreases with temperature increase, the equilibrium content of CO increases, the reaction driving force decreases, and the reaction is not favorable, so that an appropriate reaction temperature needs to be maintained in the medium-temperature shift converter, which is usually achieved by controlling the temperature at the inlet of the medium-temperature shift converter. In addition, the detection shows that the content of CO in the first raw material gas reaches more than 30%, and from the perspective of the reaction raw material steam, the amount of the steam is increased, so that the equilibrium conversion rate of CO can be improved, the residual content of CO is reduced, and the conversion reaction is accelerated. The presence of excessive water vapor ensures the active component Fe in the catalyst2O3The catalyst is stable and not reduced, and side reactions such as carbon precipitation, methane generation and the like are not easy to occur, however, the water vapor consumption is the most main consumption index in the conversion process, the reduction of the water vapor consumption to the greatest extent has important significance on the economy of the conversion process, if the steam proportion is too high, the resistance of a catalyst bed layer is increased, and C isThe O retention time is shortened, the load of the waste heat recovery equipment is increased, and the like, so the input of water vapor is reduced as much as possible in the conversion process, and the technical requirement is not favorable for directly configuring and inputting all the first raw material gas into the medium-temperature conversion furnace.
Based on the above analysis, as shown in fig. 2, in the present embodiment, it is preferable that two medium-temperature shift converters are provided between the heating furnace and the low-temperature shift converter, and the heating furnace, the first medium-temperature shift converter, the second medium-temperature shift converter, and the low-temperature shift converter are connected in sequence. And the calculation and experiment show that 40-50% of the first raw material gas prepared in the step S1(a) of the embodiment is conveyed into the first medium-temperature shift converter, and the inlet temperature of the first medium-temperature shift converter is controlled to be 360 ℃; and (c) conveying 50-60% of the first raw material gas prepared in the step (S1) (a) as cold shock gas into a second medium-temperature shift converter, wherein the inlet temperature of the second medium-temperature shift converter is 366 ℃. Namely, 40-50% of the first raw material gas is heated by the heating furnace and then is conveyed into the first medium-temperature conversion furnace together with external water vapor, conversion reaction occurs in the first medium-temperature conversion furnace, and then the first raw material gas and the rest 50-60% of the first raw material gas are mixed and conveyed into the second medium-temperature conversion furnace together.
The CO content in the gas material after the reaction of the first medium-temperature shift converter and the second medium-temperature shift converter is about 3.8% (dry basis), the gas material is cooled and is conveyed into the low-temperature shift converter, so that the CO is further subjected to shift reaction, and the volume percentage content of the CO in the second feed gas output from the low-temperature shift converter is less than 0.34% (dry basis).
Further, in order to recover heat in the conversion process, a waste heat recoverer is arranged between the second medium-temperature conversion furnace and the low-temperature conversion furnace, and is connected with the heating furnace through a pipeline. The waste heat recoverer recovers heat of gas materials output from the medium-temperature shift converter, so that the temperature of the gas materials is reduced, and the process requirements of the low-temperature shift converter are met. The heat recovered by the waste heat recoverer exists in the form of saturated steam, and the saturated steam recovered by the waste heat recoverer returns to the heating furnace through a pipeline and plays a role in heating the first raw material gas and supplying water vapor.
The waste heat recoverer in the embodiment can reduce the temperature of gas materials to meet the process requirements of the low-temperature shift converter, can recover the gas heat output by the second medium-temperature shift converter, returns the part of the heat to the heating furnace for reuse, reduces the fuel quantity of the heating furnace, reduces the steam usage of shift reaction, and has better economic benefit.
The decarbonization step in step S1(c) is to remove carbon dioxide from the second raw material gas after the shift reaction, and the decarbonization step in this embodiment is preferably an MEDA decarbonization step, wherein MEDA refers to methyldiethanolamine, commonly referred to as N-methyldiethanolamine, and the MEDA decarbonization step refers to a step of using a 45% to 50% reagent of MEDA in water solution and adding a small amount of piperazine as an activator to the reagent, by which a large amount of carbon dioxide can be removed from the second raw material gas, and piperazine in the reagent can accelerate CO2The specific process for the absorption rate is well known to those skilled in the art, and thus, the detailed description thereof is omitted here. CO treated via MEDA decarbonization Process2And sending the tail gas to downstream for emission or recycling, returning the high-pressure flash steam generated in the MEDA decarburization process to the previous step, and combining the flash steam with the byproduct tail gas for a new round of tail gas purification process, thereby effectively improving the utilization rate of the byproduct tail gas. The gas material treated by the decarburization procedure is a third raw material gas.
After the treatment of (a) to (c) in step S1, the volume percentage of hydrogen in the third raw material gas can generally reach more than 95.4%.
The pressure swing adsorption hydrogen production step in step S1(d) refers to the third step of using the adsorbent pairThe raw material gas is deeply purified, the adsorbent is generally a porous solid substance which can be a molecular sieve or activated carbon, the adsorption effect is based on the physical adsorption of the inner surface of the adsorbent to gas molecules, and the reversible adsorption process of the gas molecules between two pressure states is adopted. The principle is that the impurity component in the mixed gas has larger adsorption capacity under high pressure and smaller adsorption capacity under low pressure, namely stronger resolving power, and the ideal component H2Has a small adsorption capacity regardless of high pressure or low pressure, so that the impurities can be adsorbed on the adsorbent as much as possible at high pressure by increasing the partial pressure of the impurities, thereby increasing the amount of H in the mixed gas2The purity of (2). Desorption of the adsorbent can be achieved again at low pressure, thereby reducing the amount of impurities remaining in the adsorbent, i.e., CH in the third feed gas4、C2H6CO, etc. are separated by desorption of the adsorbent, and can be supplied to the heating furnace of step S1(b) as fuel gas, thereby reducing the overall cost of the entire process.
Through the pressure swing adsorption hydrogen production process in the step S1(d), purified feed gas can be prepared, and the volume percentage content of hydrogen in the purified feed gas can reach more than 99.0%.
Step S2: methanation step
Methanation refers to a reaction of reducing carbon monoxide and carbon dioxide with hydrogen to generate methane and water in the presence of a catalyst, and the qualified hydrogen containing only trace methane impurities is obtained by condensation and separation of water vapor through rear cooling.
It should be noted that in step S2 of this embodiment, nitrogen gas as another raw material gas of the ammonia synthesis process enters through the inlet of the methanation process, and is first mixed with the purified raw material gas prepared in step S1 to form the ammonia synthesis gas, wherein the ratio of the nitrogen gas to the amount of the purified raw material gas is 1: 2.75 to 3.20, and the ratio of the amount of nitrogen to the amount of material purifying the raw material gas is preferably 1: 3.
in this exampleThe purified raw material gas is treated by the tail gas purification process to remove a large amount of CO and CO2However, it is difficult to satisfy the process requirements of ammonia synthesis gas, and it is necessary to finally purify the purified raw material gas in order to prevent the catalyst from being poisoned in the ammonia synthesis step. Therefore, in step S2 of this example, the ammonia synthesis gas is subjected to a methanation step to obtain a qualified synthesis gas containing only a trace amount of methane impurities, wherein the sum of the contents of carbon monoxide and carbon dioxide is less than 10 ppm.
Wherein the nitrogen is provided by an air separation plant, and the content of the nitrogen is more than 99.5 percent. The air separation equipment refers to equipment which uses air as a raw material, changes the air into liquid by a compression cycle deep freezing method, and gradually separates and produces inert gas such as oxygen, nitrogen, argon and the like from the liquid air by rectification.
The nitrogen is supplemented through the inlet of the methanation process system, so that large-scale equipment such as a conversion process, an air compressor and the like in the original natural gas ammonia synthesis process can be omitted, the investment of pipelines and equipment of a purification system can be reduced, the production cost of the synthetic ammonia is reduced, and the operation process is simple and safe.
Step S3: synthetic ammonia process
The ammonia synthesis process refers to a process for directly synthesizing ammonia from nitrogen and hydrogen at high temperature and high pressure in the presence of a catalyst, and in this embodiment, the qualified synthesis gas in step S2 is sent to the ammonia synthesis process via a synthesis gas compressor to prepare ammonia gas. The detailed process is well known to those skilled in the art and will not be described again.
It should be noted that the purge gas generated in the ammonia synthesis process is recycled and input through the inlet of the pressure swing adsorption hydrogen production process, so as to further improve the utilization rate of the raw material in this example. Purge gas is used to prevent the formation of system inert gas (CH) in ammonia synthesis4+ Ar) accumulation affecting the synthesis conversion, it is necessary to release a portion of the synthesis gas to maintain the inert gas content of the synthesis processThe withdrawn synthesis gas is the purge gas in this example.
The method for synthesizing ammonia is designed based on careful research on the components of the byproduct tail gas generated by preparing acetylene by cracking natural gas and overall consideration of the balance of nitrogen generated by the air separation equipment, has high utilization rate of the tail gas, can realize long-term continuous and stable production of ammonia, is simple and safe in operation process, and can effectively reduce the production cost of the synthetic ammonia.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps not listed in a claim.
Claims (10)
1. A method for synthesizing ammonia by taking byproduct tail gas generated in acetylene preparation through natural gas cracking as a raw material is characterized by comprising the following steps:
step S1 exhaust gas purification step:
sequentially carrying out a desulfurization hydrogenation process, a transformation process, a decarburization process and a pressure swing adsorption hydrogen production process on a byproduct tail gas generated in the preparation of acetylene by natural gas cracking to form a purified feed gas, wherein the volume percentage of hydrogen in the purified feed gas is more than 99.0%;
step S2 methanation step:
obtaining qualified hydrogen from the purified raw material gas in the step S1 through methanation reaction;
step S3 synthetic ammonia process:
and (4) conveying the qualified hydrogen and nitrogen in the step S2 to an ammonia synthesis process to prepare ammonia gas.
2. The method for synthesizing ammonia from the byproduct tail gas generated in the preparation of acetylene by natural gas cracking as the raw material according to claim 1, wherein the nitrogen enters through an inlet of the methanation step of step S2, and the ratio of the nitrogen to the qualified hydrogen is 1: 2.75-3.20 to form ammonia synthesis gas, and conveying the ammonia synthesis gas to the step S3 ammonia synthesis process.
3. The method for synthesizing ammonia from the byproduct tail gas generated in the preparation of acetylene by natural gas cracking as the raw material according to claim 2, wherein the ammonia synthesis gas is treated in the methanation step S2 to obtain a qualified synthesis gas, and the sum of the contents of carbon monoxide and carbon dioxide in the qualified synthesis gas is less than 10 ppm.
4. The method for synthesizing ammonia from the tail gas, which is a byproduct in the preparation of acetylene by natural gas cracking, as a raw material according to claim 1, wherein the tail gas purification step of step S1 comprises the steps of:
(a) a desulfurization hydrogenation process:
the H in the byproduct tail gas is removed under the action of a desulfurizer2S component and C in the by-product tail gas under the action of hydrogenation catalyst2H2And C2H4Hydrogenating to obtain saturated hydrocarbon, forming a first raw material gas by-product tail gas after desulfurization and hydrogenation treatment, wherein C in the first raw material gas2H2Is less than 5ppm, C in the first raw material gas2H4The content of (A) is 20ppm or less;
(b) a conversion step:
subjecting the first raw material gas to a shift conversion process to remove CO in the first raw material gas to form a second raw material gas, wherein the volume percentage content of CO in the second raw material gas is less than 0.34% (dry basis);
(c) a decarburization process:
subjecting the second raw material gas to a decarbonization step to remove CO from the second raw material gas2Forming a third raw material gas, wherein H is contained in the third raw material gas2The volume percentage of the (B) is more than 95.4 percent;
(d) pressure swing adsorption hydrogen production:
and the third raw material gas is subjected to a pressure swing adsorption hydrogen production process to form purified raw material gas.
5. The method for synthesizing ammonia from the tail gas, which is a byproduct in the preparation of acetylene by natural gas cracking, as a raw material according to claim 4, wherein the desulfurizing agent in the step S1(a) is zinc oxide.
6. The method for synthesizing ammonia from a tail gas, which is a byproduct of acetylene production through natural gas cracking, as a raw material according to claim 4, wherein the conversion step in the step S1(b) is a medium-temperature-variable and low-temperature-variable step, and the conversion step includes a heating furnace, a medium-temperature converter and a low-temperature converter which are connected in sequence.
7. The method for synthesizing ammonia from the tail gas, which is a byproduct of acetylene preparation through natural gas cracking, as a raw material according to claim 6, wherein the medium-temperature shift converter comprises a first medium-temperature shift converter and a second medium-temperature shift converter, wherein 40-50% of the first raw material gas is input into the first medium-temperature shift converter through the heating furnace, and 50-60% of the first raw material gas is directly input into the second medium-temperature shift converter as cold shock gas.
8. The method for synthesizing ammonia from the tail gas, which is a byproduct of acetylene production through natural gas cracking, as a raw material according to claim 6, wherein a waste heat recovery device is arranged between the second medium-temperature shift converter and the low-temperature shift converter, and the waste heat recovery device is connected with the heating furnace through a pipeline.
9. The method for synthesizing ammonia from the tail gas, which is a byproduct in the preparation of acetylene by natural gas cracking, as a raw material according to claim 4, wherein the decarbonization step in the step S1(c) is an MDEA decarbonization process, and the high-pressure flash steam treated by the decarbonization step is combined with the tail gas, and then the mixture is introduced into a tail gas purification step.
10. The method for synthesizing ammonia from the tail gas, which is a byproduct of producing acetylene by natural gas cracking, as a raw material according to claim 1, wherein the purge gas output in the step S3 of synthesizing ammonia is input from an inlet of the pressure swing adsorption hydrogen production process.
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