Energy efficient methanol-to-olefins process

This paper deals with the conceptual design of an energy efficient and cost-effective methanol-to-olefin (MTO) process. The innovative solution consists in full recovery of the energy generated by reaction. The reactor effluent enthalpy can cover feed preheating, evaporation and superheating in a sequence of three feed-effluent-heat exchanger units. The novel method employs mechanical vapour compression for upgrading the temperature/enthalpy profile of the condensing water/hydrocarbon mixture, recovering a considerable amount of energy, otherwise lost by water quenching. Saved energy may pay back the compressor cost in about one year. The energy released in the reactor is used for running a combined heat and power cycle. The power is sufficient for driving the compressors, while the low-pressure steam may run an ammonia-absorption refrigeration plant that supplies most of the cold utilities in separations. The olefin separation and purification is handled in a compact scheme of five columns, energetically integrated with the reaction and preliminary separation sections. The ethylene/propylene splitter is designed for high recovery and flexible operation. Heat pump is implemented for propylene purification. Rigorous sizing is performed for the key units. Operation and capital costs are minimised since the design is almost neutral regarding energy requirements and employs a minimum number of units.