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NHD Desulfurization-Methanol Synthesis Of Methyl Mercaptan 45,000 Tons / Year ProjectDesign Summary2017年“东华科技-陕鼓杯”第十一届全国大学生化工设计竞赛参赛学校：桂林理工大学参赛团队：快乐的小鸡参赛队员：廖坚良 陈志和 邓家炬 陈燕萍 林小芳指导教师：李和平 杨 文 黎 燕 及方华 刘 峥NHD脱硫-甲醇合成法年产4.5万吨甲硫醇项目设计Design SummaryNHD Desulfurization-Methanol Synthesis Of Methyl Mercaptan 45,000 Tons / Year ProjectDesign SummaryContents1. Project Description12. A brief description of the process flow13. Innovative notes54. Site selection and plant layout105. Equipment design and control126. Environment and safety137. Economic Analysis138. Summary14141. Project DescriptionMethyl mercaptan is an important intermediate product which is widely used in the feed industry, pharmaceutical industry, health care and food industry. Especially for the synthesis of methionine, with the development of feed additives industry and the rise, Methionine demand is increasing In recent years, Also stimulated the development of methyl mercaptan production. The demand for methyl mercaptan of China is very large. The production of methionine is 150,000 tons or so in 2016, about 70,000 tons of mercaptan, coupled with the pharmaceutical, agriculture and other industries continue to grow in 2017 ,so that the demand of methyl mercaptan is about 110,000 tons in China, While only a few domestic production, the production is very small which can not meet the demand of market. As a result of the production of methyl mercaptan two major raw materials, methanol and hydrogen sulfide, methanol raw material market, the status of severe saturation and a large number of sulfur emissions from the plant serious problems, combined with the two cases, we can see the market prospects of synthetic methyl mercaptan is very broad.Combined with the actual situation of the project, taking into account the natural conditions, geographical location and other factors, the final choice of Sinochem Quanzhou Petrochemical Co., Ltd. for the project production site. The first step of the project using polyethylene glycol dimethyl ether desulfurization method (NHD method) will be separated from the hydrogen sulfide gas, the method has a large absorption capacity, high degree of purification The second step is based on the advanced hydrogen sulfide - methanol gas phase synthesis technology, in the active - alumina supported potassium tungstate catalyzed, continuous reaction of the direct production of methyl mercaptan. The method is improved by our design group, the conversion rate of methanol is 82.9%, the purity of methyl mercaptan is more than 95%, and the product quality is excellent and the production process is stable. After the implementation of the project, with an annual output of 45,000 tons of the main products of methyl mercaptan, 2700 tons by-product of dimethyl sulfide.2. A brief description of the process flow(1) Summary of NHD Desulphurization Process1) Summary of NHD Desulfurization UnitThe feed gas enters from the bottom of the absorption tower T0101, and the NHD is pumped to the top of the absorber T0101, where the feed gas and NHD are fully contacted to selectively absorb all H2S and drain most of the N2, CO2 and Light hydrocarbon. The discharged gas is further passed to the alkali absorption device. Absorbent tower T0101 at the bottom of the tower containing the acid gas-rich liquid first in the desulfurization flash tank vacuum decompression, flashing part of the hydrocarbons and carbon dioxide, absorption tower T0101 tower bottom liquid from the H2S concentration tower T0102 bottom , The NHD enters from the top of the column, both are fully contacted, selectively absorbs all H2S, and discharges most of the N2, CO2 and light hydrocarbons at the top of the T0102. The discharged gas is further passed to the alkali absorption device. At present, a large number of N2, CO2 and light hydrocarbons have been basically removed, H2S concentrated tower bottom of the acid-containing gas-rich liquid first in the desulfurization flash tank vacuum decompression flash, flash out part of most of the N2, CO2 And light hydrocarbons, and then from the upper into the regeneration tower, by taking the regeneration of the way regeneration, rich liquid from the top of the regeneration tower T0103 downward flow through the filler layer, dissolved in the solvent in the acid gas desorption, Then out from the bottom of the tower. Flash gas and regeneration tower top of the acid gas once again cycle to the use of desulfurization tower, the regeneration tower after the regeneration of the poor liquid by heat transfer, after the pressure sent to the desulfurization tower recycling. NHD desulfurization process shown in Figure 1.Figure 1 NHD desulfurization process flow chart2) Summary of H2S Absorption Tower T0101The main role of the absorption tower T0101 is to absorb H2S in the feed gas. As the solvent has a selective absorption of H2S. Therefore, under high pressure, the solvent can remove most of the H2S in the feed gas and take away part of the acid gas. The raw material gas from the absorption tower into the low, and desulfurization tower absorption of lean liquid countercurrent contact, so as to achieve the purpose of desulfurization. The rich liquid rich in H2S is discharged from the bottom of the column into the next unit, and most of the N2, CO2and light hydrocarbons are discharged from the top of the column. The discharged gas is passed through the alkali absorption device to absorb the CO2 discharged. Further processing to meet national emission standards.3) Summary of H2S Concentration Tower T0102 ElementAfter recovering the useful component H2S in the flash unit. NHD rich liquid dissolved in addition to the analysis of a small amount of hydrocarbon gas, the main left CO2 and H2S two gases, and some propylene. As the solubility of CO2 and H2S in NHD is quite different, the concentration of H2S can be achieved by releasing CO2 gas by lowering the pressure. The rich liquid rich in H2S is discharged from the bottom of the column into the next unit, and most of the N2, CO2 and light hydrocarbons are discharged from the top of the column. The discharged gas is passed through the alkali absorption device to absorb the CO2 discharged. Further processing to meet national emission standards. 4) Summary of NHD Thermal Regeneration TowerNHD rich liquid followed by H2S concentration unit, flash unit and heat transfer, the removal of dissolved CH4, N2, C3H8 and CO2 and other major gases, the rest is mainly strong dissolution of H2S. In order to completely remove the H2S gas, the NHD solvent can be recycled to be recycled, and it is critical to adjust the pressure of the regeneration column T0103 and the temperature of the kettle. The rich liquid flows down from the top of the regeneration tower T0103 and is desorbed by the acid layer dissolved in the solvent, and the lean liquid is discharged from the bottom of the column. Flash gas and regeneration tower top of the acid gas once again cycle to the use of desulfurization tower, the regeneration tower after the regeneration of the poor liquid by heat transfer, after the pressure sent to the desulfurization tower recycling. To maximize the economic benefits.The NHD thermal regeneration tower T0103 is essentially a distillation column. Its main role is to NHD rich liquid in the gas phase components of the complete analysis, so as to reproduce the purity of 99.9% (mass fraction) above the NHD poor solution to do the absorption tower solvent. In order to achieve a better removal effect, a reboiler is provided at the bottom of the column of the analytical column, and a condensation device is provided for the condensation of the gas in order to achieve gas condensation. The acid gas after condensation of the tower, H2S concentration of 74% mole fraction), available for sulfur recovery system recovery of sulfur. In the thermal regeneration tower, H2S can almost 100% of the removal, and finally from the tower kettle is the solute gas is completely removed after the NHD liquid.The flow into the thermal recovery tower is from the H2S concentrated tower T0102 bottom out, after flashing, heat transfer after the NHD rich liquid. Since the column belongs to the distillation column, there is a reboiler and a condenser heat transfer device, so the rational use of the energy of the system is critical to the overall system. For the thermal regeneration tower, there are many factors that can be adjusted, such as the reboiler reboiling amount, the eluent temperature and so on.(2) Hydrogen Sulfide - Methanol Gas Phase Synthesis ProcessThe hydrogen sulfide gas and methanol from the NHD desulfurization section were mixed by a mixer and then heated to 320 and pressurized to 0.6 MPa. The reactor R0201 was subjected to hydrogen sulfide-methanol gas phase synthesis of methyl mercaptan, from the upper part of the reactor Of the reaction is rich in most of the water vapor, through the flash unit, the majority of water and part of the main products of methyl mercaptan, and then into the hydrogen sulfide recycling tower T0201 precipitation of unreacted hydrogen sulfide, the top of the tower did not react H2S cycle to the raw material after the import of heat into the reactor to further reaction from the separation unit out of the propylene through the ethylbenzene / anti-hydrocarbon mixture device to absorb propylene, From the reaction section (part of the methyl mercaptan synthesis section) out of the main product of methyl mercaptan, through the product separation tower T0202 further analysis, from the top of the precipitation of methyl mercaptan containing some of the propylene and a small amount of unreacted hydrogen sulfide Gas, so once again in the distillation tower T0203 vacuum distillation, methyl mercaptan distillation tower T0203 out of the bottom of the methyl mercaptan by drying the finished product purity of up to 95%. The top of the tower in the discharge of hydrogen sulfide and propylene through the ethylbenzene / anti-hydrocarbon mixture to absorb propylene, from the product separation tower T0202 bottom out of the dimethyl sulfide, water, unreacted methanol through the dimethyl thioether distillation tower T0204 From the top of the column, 97% of the by-product of dimethyl sulfide was removed from the top of the column, and the methanol and water from the bottom of the column were separated and passed through the flash unit. The purity of the methanol was 98%. After further treatment, the reaction was recycled to the reactor for further reaction The To maximize the economic benefits. Synthetic methyl mercaptan process shown in Figure 2.Figure 2 hydrogen sulfide - methanol gas phase synthesis process flow chart3. Innovative notes(1) Brief Introduction to Process InnovationThe project uses polyethylene glycol dimethyl ether (NHD) desulfurization - methanol synthesis method of preparation of methyl mercaptan, by-product of dimethyl sulfide. The process consists of two sections, polyethylene glycol dimethyl desulfurization section and methyl mercaptan synthesis section. Our existing technology has been modified and optimized.In the process design, we used the four cycles, the polyethylene glycol dimethyl ether, hydrogen sulfide, methanol, water recycling, and through the process route optimization, to achieve the use of hydrogen sulfide and methanol resources maximize.Compared with the traditional process, NHD desulfurization method has a high degree of purification, selectivity, solvent no corrosion, low demand for equipment, less investment, less volatile loss, good chemical stability and thermal stability, solvent non-toxic and tasteless, Less environmental pollution, easy operation and low energy consumption advantages.(2) Recycling of resource recycling1) Description of raw materialsOur main raw materials are sulfur-containing waste gas, polyethylene glycol dimethyl ether, methanol, the catalyst active -alumina, potassium tungstate.2) Meet the requirements of environmental protection and resource utilizationSulfur from the raw materials from the gas from the Fujian Province, Quanzhou Petrochemical Co., Ltd. to waste gas as raw material, both to reduce environmental pollution, but also to create economic value.3) Our resources to achieve a recycling.In the process of choice, we focus on the production process of resource utilization, and strive to maximize the utilization of raw materials in the production process of multi-cycle recycling materials, namely, hydrogen sulfide cycle, polyethylene glycol dimethyl ether cycle. For chemical production, material recycling can greatly improve the continuity of the process, reduce the number of open parking and operating costs, enhance production capacity, will maximize production capacity. The main circulating process in the process of NHD and methanol, NHD as a desulfurization agent in the entire desulfurization process, but may be in the separation process will be depleted, need to be supplemented from the outside world. Methanol as a synthetic raw material, unreacted completely methanol can be separated from the purity of 95% or more, and then recycling recycling.When we used Aspen Plus to simulate the entire process, the higher purity NHD and methanol were separated by adjusting the operating parameters of each distillation column and recycled. Thus reducing the amount from the outside world, saving resources and improving the economy of production.(3) Heat exchange network optimizationThe project uses the pinch analysis and thermal integration energy-saving technology, the use of Aspen Energy Analyzer software to achieve a larger energy reuse heat transfer network design. So that the hot and cold logistics within the plant within a reasonable range of heat transfer, so as to achieve the purpose of saving energy. The results show that the whole process can be compared with the reasonable energy matching, after the transformation of the heat transfer network, and finally get the thermal integration program before and after the comparison chart.1) Pinch and minimum cold and hot utility quantitiesThe flow rate of the whole process was determined by Aspen Energy Analyzer, and the temperature difference of the whole process was 8 . Set the minimum heat transfer temperature difference of 8 , the temperature enthalpy diagram and composite curve. Figure 3 for the total cost and minimum heat transfer temperature difference diagram, Figure 4 for the whole process of temperature enthalpy diagram.Figure 3 Total cost and minimum heat transfer temperature differenceFigure 4 Total process enthalpy diagram2) Build and optimize heat transfer networksBased on the heat exchange matching in the sub - section, the logistics of the different temperature grades should be re - selected for the integration of the logistics matching. As the shunt processing is difficult to achieve in the process, so the logistics of the project did not split. Taking into account the equipment investment and other reasons, less heat transfer between the logistics is not matched. Considering the feasibility of the process and the principle of matching, design the whole process heat transfer network. Matching before the heat transfer network shown in Figure 5.Figure 5 before the matching of the TU mapThe matching heat transfer network is shown in Fig 6.Figure 6 matched postureMatching before and after the hot network cost parameters and performance comparison shown in Table 1:Table 1 Comparison of parameters and performance of heat exchange network before and after matchingMatch beforeAfter matchingNetworkCost IndexesCost Index%of TargetCost Index%of TargetHeating(Cost/s)0.23249.099.1510-2100Cooling(Cost/s)2.8810-249.475.8210-2100Operating(Cost/s)0.26174.760.15101.89Capital(Cost)4.6510696.295.06106105.06Total Cost(Cost/s)0.30155.030.20102.69NetworkperformanceHEN%of TargetHEN%of TargetHeating(KJ/h)1.25108161.117.76107100.18Cooling(KJ/h)1.0110881.001.24108100.11Number of Units1356.522295.65Number of Shells1513.896257.41Total Aream21547.3816.977819.8885.77It can be seen from Table 1 that the heat transfer network after the design match is closer to the target value than the value of the heat exchange network before matching, and the total cost after optimization is lower than the total cost before optimization. Equipment costs are fixed investment, and operating costs are accumulated over the years, so not only is the optimized cost of the equipment is lower than the pre-optimization, and its operating costs lower than the pre-optimization, so the total cost is lower than the pre-optimization The internet.(4) Environmental protection innovationThe main components of the waste gas of this project are propylene and hydrogen sulfide. The use of styrene in this project is to reduce the propylene in the dry gas by using ethylbenzene as the absorbent. The use of low temperature and high absorbent / dry gas volume ratio is beneficial The mixture of the ethylbenzene / paraffinic compound is absorbed by the dry gas and the absorbed gas can be desorbed under certain conditions. The absorbent after desorption can be recycled and used by using the styrene-based ethylbenzene unit , The remaining hydrogen sulfide gas circulation to the hydrogen sulfide reaction section, the remaining exhaust gas using high-temperature combustion method, high-temperature combustion (AOGI) is a variety of organic pollutants containing the most effective way.Taking into account the many advantages of high-temperature combustion, the project to take this method to deal with waste gas. The exhaust gas part of the distillation tower is