Based on a typical gas composition from a methanol-to-propylene (MTP) reactor

and guided by a requirement to recover both propylene and ethylene

three separation strategies are studied and simulated by using PROⅡ package. These strategies are sequential separation

front-end dethanization

and front-end depropanization. The process does not involve an ethylene refrigeration system

using the separated stream as absorbent

and absorbing further the medium-pressure demethanization

and a proprietary technology by combining intercooling oil absorption and throttle expansion. Influences of different process streams as absorbent are studied on energy consumptions

propylene and ethylene recovery percentages

and other key-performance indicators of the separation strategies. Based on a commercial MTP plant with a methanol capacity of 1700 kt·a

-1

the simulated results show that the front-end dethanization using the C

4

mixture as absorbent is the optimal separation strategy

in which the standard fuel oil consumption (a key-performance indicator of energy consumption) is 18.97 kt·h

-1

the total power consumption of two compressors is 22.4 MW

the propylene recovery percentage is 99.70%

and the ethylene recovery percentage is 99.70%. For a further improvement

the pre-dethanization and thermal coupling methods are applied. By using front-end pre-dethanization (partial cutting) with debutanizeroverhead

i.e

. the C4 mixture

as absorbent

the power consumption of the compressors decreases to 19.9 MW

an 11% reduction compared with the clear-cutting method. The energy consumption for the dual compressors for crude gaseous product mixture and main product propylene refrigeration is 16.69 MW

16.55% lower than that of the present MTP industrial plant with the same scale

and a total energy consumption of 20 MW for the triple compressors including product gas mixture compression

and ethylene and propylene refrigeration.