Separating Process For Syngas Based One-Step DME Synthesis

DME is considered as a clean fuel in the 21st century. The one-stepproduction of DME from synthesis gas is an important way for cleaningutilization of coal, which contributes to reducing the CO2 emission andprotecting our environment. This paper proposes a novel separation processfor one-step production of DME from synthesis gas on the basis of DMEseparation process at present. The novel process can not only gain highpurity DME from production gas on the premise of high DME reclaim ratiobut also reclaim a part of high purity CO2. At the same time, the highefficiency of energy utilization can be reached in the separation process. Firstly, Gibbs-Duhem equation is applied to make the thermodynamicconsistency test and thermodynamic model estimation for CO2/DME,DME/CH3OH, CO2/CH3OH, and DME/C2H5OH on the basis of thevapor-liquid equilibrium experimental data referred, and presents feasiblethermodynamic model. The study shows that PR-NRTL model combinationis suitable for the above four systems. This paper develops the vapor-liquid IV北京化工大学硕士研究生毕业论文equilibrium database of PR-NRTL model with DME based on experimentaldata, which is a base of computer simulation of the DME separationprocess. Secondly, this paper designs and develops a novel one-step productionof DME separation process from synthesis gas based on rationale andseparate aim of chemical separation process, which contains separate-absorb and rectify-separate cell. The results of the separation processsimulated by Aspen plus soft shows that the reclaim ratio of DME fromproduction gas is over 99%, the purity of DME attains 99.5%, CO2 purity isover 95% and the utilizing ratio of CO2 is over 17%. Through the study ofseparate-absorb, which contains H2O, CH3OH and C2H5OH, H2O is anappropriate absorbing solvent for the separation process. Thirdly, this paper studies the operation condition of separate-absorband rectify-separate cell. The higher G/L (the ratio of gas and liquid) isappropriate at high pressure and the lower G/L is appropriate at lowpressure in the absorbing operation. It obtains the optimize conditionthrough the study of the rectify-separate cell. The condition of the firstrectification column is: operation pressure ranges from 1.6MPa to 2.5MPa,temperature of the top column ranges from -25.6℃ to -12.9℃, temperatureof the bottom column ranges from 126.3℃ to 151.8℃, reflux ratio rangesfrom 1.2 to 2.0. The condition of the second rectification column is:operation pressure ranges from 0.7MPa to 1.1MPa, temperature of the top V北京化工大学硕士研究生毕业论文column ranges from -25.6℃ to -12.9℃, temperature of the bottom columnranges from 29.4℃ to 46.7℃, reflux ratio ranges from 1.0 to 1.5. The Energy-flow Framework Diagram (EFD) is the graphicthermodynamic analysis novel tool applied in energy analysis andintegration. Finally, this paper proposes the revelatory criterions of the EFD,and presents an energy-saving novel DME process through an applicationstudy on a 0.18kt·a-1one-step production of DME from synthesis gas basedon the EFD. The novel process realizes that the reacted heat of the systemis applied to generate stream, the ammonia absorb chiller is applied togenerate cool energy in order to utilize the reclaimed heat Steam turbineadopted applies the chemical exergy to generate high-pressure steam thatmeet the need of the process. Comparing novel process with originalprocess, the electricity consumption reduces by 64.9%, steam spares3.22MW and cool energy spares 3.52MW. The exergy loss decreases by33.6%.