Research On The Separation Process And Equipment Of Dimethyl Ether Direct Synthesized From Coal-Based Syngas

The two important problems are energy and resource which puzzled us for many years. The energy structure of rich coal, poor oil and deficient gas made that our main energy consumption is coal. The coal ration of energy would decrease in the near future of 20 or 30 years but our energy structure would never change. We should develop car-used fuel made from coal and make up the shortage of oil resource in order to solve problem of energy safety in a long period. Less pollution indexes and rich resource than other fuel used today, dimethyl ether is also called"clean energy in 21 century".Dimethyl produced from syngas in one step has advantages such as high single path conversion, short process, low investment on equipment and low cost compared with two-step dimethyl ether synthesis. At present, researchers focused on double-functional catalysts and the design of reactors. There is no industrialized equipment so the research of separation of dimethyl ether is not common. Most of separation process are used in laboratory and models made by computer. These processes have not been take into practice and have many disadvantages which has great bad influence on the way to industrialization.In this paper, in order to improve recovery and reduce energy waste, we developed a new kind of separation process called efficient NS complicated plate which made with vertical-ladder-strip cap composited with structured packing considering process and equipment. After investigation on its hydrodynamics characters and mass transfer ability, we found that this kind of structure has advantages for need of separation and structure amplification.In NS plate, structured packing composited with double-dual flow tray has all advantages of plate tower and packing tower. A series of NS efficient plates with"full mixture", high point efficiency, low pressure drop and large flux were developed and also their hydrodynamics characters and mass transfer ability are investigated to provide technology support for energy saving and drainage reducing in industrialized instillation production and it also provide technology support for distillation theory transformation from practical-basis or semi-practical basis to semi-theory basis or theory-basis. Based on the investigation, we developed a non-equilibrium stage model for point efficiency and also a MEPSH mathematical model.Based on investigation of absorption and separation, we developed variable pressure absorption separation process in one step synthesis for dimethyl ether in which products made in process is used as absorbent. We adopted three kinds of absorbent such as methanol, water and methanol-water and optimized process by process model. After comparison of energy consumption of different process, we got the low energy consumption and high efficiency separation process for dimethyl ether which provide technology support and guarantee for dimethyl ether synthesis industrialization.On the other hand, we also made a hot model test in industrial separation related to composited plate absorption and separation.1 Investigation on absorption equipment in dimethyl ether separation in one step synthesis.(1) The pressure drop of NS composited plate is lower than ordinary ones. The dry pressure drop is 100% lower than F1 valve tray while wet pressure drop is 30% lower than F1 valve tray. Venturi orifice structure is better than plate structure. Structured packing has little influence on pressure drop.(2) NS composited plate'lower limits are controled by liquid leakage and its upper limits are controled by entrainment. Operation range F is 7~30 much larger than F1 valve tray's 4~13. The operation upper limit is improved efficiently by adding structured packings. (3) NS composited plate has great production ability. The gas flux in NS plate is two or three times of F1 valve tray because of tray free areas and spray operation improved. On the other hand, gas enters cap through poles on plate without flow through liquid layer on plate, liquid flow on the plate has little gas in it so liquid flow ability can be improved by 80%~100% with same downcomer.(4) Leakage and gas-liquid distribution on NS-3 plate with venture pole is better than NS-4 tray with horizontal hole structure and F1 valve tray.(5) mass transfer efficiency in efficiency area on NS-5 plate is 10%~30% much than F1 valve tray and when gas velocity is much than F1 valve operation upper limits but NS-5 is still in its operation range; according to NS-3 plate, efficient structured packing out of cap can strengthen mass transfer and reduce foam which made efficiency 10%~20% much than NS-5 plate and the operation upper limits are improved together.2 Investigations on efficient distillation equipment in one step dimethyl ether synthesis process.(1) considering the influence of NS efficient composited plate structure on hydrodynamics characters and mass transfer ability of dry and wet pressure drop, entrainment, foam height and liquid height, we adopted NS-8 standard structure with plate which has large opening ration and pole diameter and a doubled-plate with the ratio of diameter of pole and plate spacing is 3/1 and also structured packing is added under the composited plate. This structure can satisfied the need of high efficiency, large flux, low pressure drop, large operation range and stability operation. At the same time,"full mixture"structure makes it possible for simplifying modeling and improving modeling precision in distillation stage.(2) NS-6 plate with large opening ratio and pole diameter composited with double-plate which has pole diameter and plate spacing ratioed 3/1 is favorite to coking and blocking system.(3) We investigate the hydrodynamics characters of NS efficient plate. The results show that NS efficient plate has low pressure drop, low entrainment, large foam height and the empty tower kinetic energy factor can reach 2.41(m.s-1)(kg.m-3)1/2 .(4) NS composited plate can also split bubbles on trays to make a favorite foam layer and the reform ratio of gas-liquid contact is improved which can strengthen mass and heat transfer and improve efficiency. After comparison, mass transfer efficiency of composited plate is 20% much than ordinary ones and the efficiency in the full operation range is more than 80% almost near 100% at high gas velocity.3 Construction of non equilibrium stage model based on point efficiency.(1) Model for non equilibrium stage based on point efficiency is made based on series of composited efficient reflux plate. Combined point efficiency equation (P) with phase equilibrium equation (E), we adopted MEPSH equations to get the temperature, composition, flow and mathematical models of gas and liquid on plates in tower.(2) compared with calculation model of equilibrium staged distillation, calculation model of non equilibrium staged distillation based on Murphree gas plate efficiency EMV and mass transfer rate and three dimensional non equilibrium mixture model,"full mixture"of non equilibrium stage model based on point efficiency is true and practical. The result from MEPSH modeling can be tested in practical industrialized distillation but also can guide the distillation operation.4 Investigations on separation process of one step dimethyl ether synthesis in amplified engineering.(1) Considering operation pressure of dimethyl synthesis reactor related to adsorb-separation pressure and also the efficiency, energy saving and investment in large scaled production, we developed a new kind of variable pressure adsorb-separation process in dimethyl synthesis. In this process, CO2 is absorbed in high pressure stage while being desorbed at media press stage and dymethyl and methanol are separated and lower pressure stage, at the same time, a part of methanol recirculated as primary absorber while water as secondary absorber. The dymethyl recovery is higher than 99% with purity more than 99.5% and the purity of methanol is more than 99.7%.(2) Products or media-products such as methanol, water and methanol solution are adopted as absorber in simulation. We compared these three absorbers based on energy consumption and operation convenience and made water as absorber in re-absortion tower.(3) We simulated dimethyl synthesis process by one step from syngas and made sure the favourate operation conditions and theoreatical plate number, tower diameter, load of reboiler and condenser, full load of cooler and full energy consumption of separation.(4) Take pressure and flow parameters into consideration comprehensively, NS tilt composite plates are adopted in tower in separation process while NS efficient plates are adopted in dymethyl distillation tower and methanol distillation tower, diameter and height of the tower are decreased more than 40%.5 Hot model test on composite plate(1) In order to prove and valuate the efficiency of NS tilt composite plate, we adopted ethylene oxide produced from ethylene as model because the characters and composition of ethylene oxide are similar to dimethyl products. The industrial results showed that NS tilt composite plate is a new kind of efficient plate with super capacity and in capacity expansion revamping, the capacity of tower would be improved more than four times if only adopt NS plates and the also the efficiency would be improved more than 25%. These plates suitable to dimethyl separation in dimethyl synthesis by one step.(2) The advantages of NS plates such as super capacity and efficiency are the key factors in transformation of equipments to double their capacity and it can be implied widely in separation and absorption process such as chemical, medicine and oil refinery, especially in technological transformation of old equipment. After transformation, the production capacity and products yeild can be improved and energy consumption reduced.