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CN-121990873-A - Direct conversion methanol preparation process

CN121990873ACN 121990873 ACN121990873 ACN 121990873ACN-121990873-A

Abstract

The application relates to the technical field of preparing methanol from natural gas, and discloses a process for preparing methanol by direct conversion, the process comprises six core units of raw material pretreatment, vaporization and steam addition, natural gas conversion, methanol synthesis, methanol rectification and carbon capture recovery. The raw materials are pretreated, the impurities are removed, the raw materials are mixed with recovered steam, the water-carbon ratio is regulated, the raw materials are directly converted into synthesis gas, the synthesis gas is circularly synthesized into crude methanol, the crude methanol is rectified and purified to obtain refined methanol, and meanwhile CO 2 in the flue gas is captured and fed back to a raw material unit system. The raw material pretreatment adopts the design of nickel-molybdenum hydrogenation catalyst desulfurization and serial-parallel desulfurization reactors, the vaporization link maintains the water-carbon ratio of 2.5:1 through double-path steam supply, the natural gas conversion combines the pre-conversion and the one-stage conversion process, the methanol synthesis adopts a double-reactor parallel circulation system, the rectification adopts a three-tower mode, and the cyclic utilization of process water is realized. The process has the advantages of high methane conversion rate, low energy consumption, high carbon utilization rate, low investment cost and the like.

Inventors

  • SHEN YANG
  • PAN DONG
  • SONG YANKUN
  • ZHANG XINYU
  • FEI ZHONGHUA
  • Shen Debiao

Assignees

  • 上海卓然工程技术股份有限公司

Dates

Publication Date
20260508
Application Date
20260121

Claims (10)

  1. 1. A process for preparing methanol by direct conversion includes such steps as pretreating raw material, vaporizing, adding steam, natural gas converting, synthesizing methanol, rectifying methanol, collecting carbon, removing impurities, mixing with recovered steam, regulating water-carbon ratio, direct conversion to generate synthetic gas, cyclic synthesizing coarse methanol, rectifying to obtain refined methanol, and collecting fume And (5) a feed unit system is supplemented.
  2. 2. The direct conversion methanol production process according to claim 1, wherein the raw material pretreatment step comprises the steps of dividing the raw material into two equal parts, removing heavy components through a buffer tank, mixing the raw material with hydrogen-rich gas of a methanol synthesis loop, converting organic sulfur into hydrogen sulfide through a nickel-molybdenum hydrogenation catalyst, and deeply removing sulfur through a desulfurization reactor arranged in series-parallel connection to ensure that the sulfur and chlorine content is reduced below a catalyst tolerance threshold.
  3. 3. The direct conversion methanol production process according to claim 1, wherein the vaporizing and steam adding step adopts a two-way steam supply design, one way is in direct contact with circulating water through a saturation tower, 90% of process water is recovered to generate saturated steam, the other way is directly added with process steam, the water-carbon ratio is maintained to be 2.5:1 through a water-carbon ratio controller, and a fixed steam flow branch is arranged at the downstream of the pre-conversion reactor for purging protection during the failure of the conversion reactor.
  4. 4. The direct conversion methanol production process according to claim 1, wherein the natural gas conversion step comprises pre-conversion and primary conversion, wherein the mixed gas is preheated at 450-500 ℃, and then the heavy hydrocarbon is decomposed into light components in a pre-conversion reactor, and then enters a conversion furnace, and the reaction temperature is maintained at 850-880 ℃ by using the waste heat of the flue gas in the radiation section, and the mixed gas is directly converted under the action of a catalyst to produce the synthetic gas.
  5. 5. The direct conversion methanol preparation process according to claim 1, wherein the methanol synthesis adopts a double-reactor parallel circulation system, synthesis gas reacts under copper/zinc catalyst and 7.5-8.0MPa pressure, reaction heat is released for medium-pressure steam generation, mixed gas from the synthesis reactor enters a separation tank after being cooled, crude methanol product is discharged to a rectifying unit through the bottom of the separation tank, unreacted gas with inert gas is mostly returned to the reactor after being pressurized by a circulating compressor, and the unreacted gas is discharged to be used as a fuel of a reformer, and the whole system does not need additional circulating hydrogen.
  6. 6. The direct conversion methanol-producing process according to claim 1, wherein the methanol rectification adopts a three-column mode, flash steam is sent to a reformer for combustion recovery of heat, excess water produced by rectification is sent back to a saturation column for cyclic utilization, and alcohols dissolved in water are recycled to participate in the conversion reaction along with water circulation.
  7. 7. The direct conversion methanol production process according to claim 1, wherein the carbon capturing system is additionally arranged to capture flue gas at the outlet of the reformer by a chemical absorption method, a physical absorption method, a membrane separation method or a cryogenic separation method To be recovered Supplementing the raw material unit system, improving the utilization rate of carbon and increasing the yield of methanol.
  8. 8. The direct conversion methanol production process according to claim 1, wherein the raw materials comprise methane-containing gases such as natural gas, coke oven gas, oil refining tail gas and the like, and the production capacity can be adjusted according to project requirements, and the direct conversion methanol production process is suitable for a methanol production device of 1000-25000 t/d scale.
  9. 9. The direct conversion methanol production process according to claim 4, wherein the pre-conversion reactor is filled with The composite catalyst has an operation temperature of 450-500 ℃ and an operation pressure of 0.8-1.2MPa; The primary reformer is filled with the reactants in sections in turn along the flow direction Modified Catalyst layer A solid solution promoting layer.
  10. 10. The direct conversion methanol production process according to claim 5, wherein a ceramic-polymer composite membrane separator is provided between the parallel outlet of the double reactor and the recycle compressor; The rejection rate of the composite membrane separator to H 2 is more than or equal to 98%, and the permeability coefficient to inert gas is 15-20 times that of H 2 ; the hydrogen-rich gas separated by the membrane separator is returned to the inlet of the circulating compressor, the inert gas at the permeation side is discharged out of the system, and the crude methanol liquid obtained by separation is directly sent into the rectifying unit.

Description

Direct conversion methanol preparation process Technical Field The application relates to the technical field of methanol preparation from natural gas, in particular to a process mode for preparing methanol by direct conversion. Background Methanol is an important chemical raw material and clean fuel, and is widely applied in the fields of chemical synthesis, energy and the like. Along with global energy transformation and 'double carbon' target promotion, the methanol demand continues to increase, and exploration of efficient and low-energy production processes becomes an industry key. The current mainstream methanol production process mostly adopts a conversion route of coal gasification, synthesis gas, methanol or natural gas, synthesis gas and methanol, and the pain points such as long flow, high energy consumption, high carbon emission intensity and the like generally exist. The process needs complex procedures of raw material gasification, synthesis gas deep purification, compression and the like, relies on large-scale devices such as a steam reformer, a gasifier, a synthesis tower and the like, and has extremely high input cost of early-stage equipment. In particular, in the coal-based synthesis gas preparation link, pure oxygen is generally required to be introduced for ensuring the reaction efficiency, and the requirement directly increases the construction cost of a matched air separation device, thereby further increasing the overall investment of projects and the economic burden of long-term operation. Even with natural gas as a feedstock, conventional processes face similar bottlenecks. The technology adopts a combined process route of pre-conversion and one-stage conversion, firstly cracks heavy hydrocarbon components into light small molecules, and then sends the light small molecules into a reformer for reaction, breaks through the limit of the traditional process from the thermodynamic aspect, obviously improves the methane single-pass conversion rate, greatly exceeds the 80% horizontal upper limit of the traditional one-stage conversion process, and greatly reduces the energy consumption and the equipment load pressure caused by unreacted methane circulation. By the design of the double-path steam supply process, 90% of process water can be recovered to generate saturated steam, the redundant water generated by the rectifying system is completely returned to the saturated tower for recycling, the synthesizing system does not need additional outsourcing hydrogen supplement, the purge gas can be recovered to the reformer to be used as fuel, only the purge gas can recover the heat value of about 27MW, the comprehensive energy consumption is reduced by more than 15% compared with the traditional process, and the unit consumption of the methanol raw material gas can be controlled at the high-efficiency level less than or equal to 330Nm 3/t. In addition, the technology is matched with a carbon trapping system, and can recycle the flue gas of the reformerAnd is fed back to the raw material system, compared with the traditional method for preparing methanol by using coal, the method has the advantages of about 3.5-4 tonsThe carbon utilization rate of the process is improved by more than 20 percent, the carbon reduction effect is obvious, pure oxygen is not needed in the whole process, the high power consumption of an air separation device is thoroughly avoided, the generation of phenol-containing and cyanide-containing wastewater is avoided, and the environmental protection treatment cost is greatly reduced. Meanwhile, the technology omits complex intermediate procedures such as synthesis gas preparation, deep purification and the like, does not need auxiliary facilities such as an air separation device and the like, obviously reduces the overall equipment investment compared with the traditional coal gasification route, adopts a series-parallel skid-block design, supports the online replacement of the catalyst, and can flexibly balance the operation load by the parallel layout of the double reactors, thereby obviously reducing the operation and maintenance cost. The technology is compatible with various methane-containing raw material gases such as natural gas, coke oven gas, oil refining tail gas and the like, is suitable for methanol production devices of different scales, and has extremely strong scene applicability and popularization value. Disclosure of Invention Aiming at the defects of the prior art, the application provides a direct conversion methanol preparation process mode, which improves the methane single-pass conversion rate, breaks through the thermodynamic limit of the traditional process, reduces the synthesis circulation gas quantity, reduces the load and the energy consumption of a compressor, and comprehensively recycles the process water and the flue gasLow-carbon production is realized, the investment of auxiliary facilities is reduced, and the equipment cost and the operat