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Research and optimization of separation technology of methanol to propylene
Zizong WANG, Hongqian LIU, Jiming WANG
CIESC Journal    2019, 70 (1): 136-145.   DOI: 10.11949/j.issn.0438-1157.20171033
Abstract   (557 HTML20 PDF(pc) (925KB)(198)  

Based on the actual equipment of 1.7 million tons/year methanol to propylene (MTP), this paper studies and optimizes the MTP separation process, draws on the experience of separation of naphtha ethylene unit, and optimizes the formation characteristics of MTP product gas. The process combination, process simulation and optimization of the separation technology are carried out together with de-methanizer tower and its exhaust gas recovery system, highly thermal coupling decarburization system (de-ethanizer and ethylene rectifying column), sorbent selection, and screen out a more suitable separation technology consisting of the following process unit: pre-cutting front-end deethanizer, recovery of de-methanizer tail gas by combination of intercooling oil absorption and throttle expansion, highly thermally coupled deethanizer system, take carbon four mixture as absorbing agent, etc.Assuming that there are no ethylene, carbon four and carbon five cycles back to the MTP reactor, the ethylene loss in the exhaust meets the design requirements, using the optimized separation technique, the dual power of the compressor and propylene compressor is 19.8 MW. The simulation results show that the optimized flow has a good application prospect.


Fig.1 Schematic diagram of sequential separation technique (C3H8 as absorbent)
Extracts from the Article
优化的顺序分离流程如图1所示,来自反应器的产品气经压缩、净化,分别以气液相形式进入脱甲烷塔,脱甲烷塔塔顶尾气经中冷油吸收、膨胀节流回收乙烯后去燃料气系统, 脱甲烷塔段底部物料去脱乙烷塔;脱乙烷塔塔顶物料去乙烯精馏塔分离得到聚合级乙烯产品,塔底物料去脱丙烷塔; 脱丙烷塔塔顶物料去丙烯精馏塔分离得到聚合级丙烯产品,塔底物料去脱丁烷塔;脱丁烷塔分离塔顶为混合碳四,塔釜为碳五及更重组分。
对图1,2,3所示流程进行模拟计算、优化操作参数和换热网络,双机功耗、冷却水消耗、蒸汽消耗如表2所示,将表2中的公用工程消耗折算成标准燃料油消耗,如图4所示。从图4可以看到用丙烷C3H8做吸收剂时,前脱乙烷流程分离部分标准燃料油消耗最小。
用混合碳四做吸收剂时,对图1,2,3所示顺序分离、前脱丙烷和前脱乙烷流程进行优化,将吸收剂由丙烷C3H8改为来自脱丁烷塔塔顶的混合碳四C4S,优化后的流程分别如图5,6,7所示。需要说明的是,前脱丙烷和前脱乙烷流程都在第一个塔内将吸收剂和被吸收的轻烃分离开。
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