Study On Process Optimization And Energy Conservation Of Methanol To Olefin Based On Organic Rankine Cycle

Ethylene and propylene are important low-carbon olefins in chemical production,which are mainly produced by naphtha cracking at present.Nowadays,petroleum resources are becoming increasingly scarce,and the MTO process using coal or natural gas as raw materials to produce methanol,and then producing low-carbon olefins such as ethylene and propylene,has gradually gained the attention of academia and industry.In this paper,Aspen plus software is used to simulate and optimize the process of methanol-to-light olefins(MTO),and the energy consumption of the process is analyzed to tap the potential of energy saving.In this paper,the MTO process with 1.8 million tons of methanol a year is simulated and the heat exchange network is analyzed.It is found that there are two low-temperature heat sources in the process: quench water(110 ～ 40℃,35MW)and washing water(95 ～ 55℃,113MW).After the low-temperature energy recycled by the reboilers of the downstream olefin separation unit,61.5% of the total energy or 91 MW of energy are still unused and discharged into the environment.If this part of energy can be recycled,the energy consumption in MTO process will be greatly reduced.Organic Rankine Cycle(ORC)is an important utilization measure of low-grade heat energy.In order to recover energy from two underutilized low-temperature heat sources in MTO process by ORC method,seven kinds of organic working fluids were comparatively studied in this paper,and the influence of cycle operating parameters evaporation pressure on cycle system performance was studied,and the multi-stream ORC system with multi-stream heat sources was comprehensively optimized.The results show that R227 EA is the better working fluid,ORC condensation temperature is set at 45℃ and the scheme with branch stream can obtain the best output work and the highest efficiency in the investigation range under the operating pressure of 1.7MPa,and the output work is 5MW.In this paper,the possibility of further improving the energy conversation by using mixed working fluids is further explored.In this paper,the effects of six different binary mixtures on five design schemes are discussed.And the influence of the mass fraction of binary mixture on the system performance is analyzed.The results show that output power of the mixed refrigerants is not better than that of the optimal pure refrigerants.Considering energy saving effect and production maintenance,it is recommended to use pure working medium.