Small-medium scale polygeneration systems: Methanol and power production

The feasibility and attractiveness of the integrated production of chemicals and electrical power is dependent upon on the nature of the products and their demands. This study focuses on the small-to-medium scale combined production of methanol (200,000tonnes/year) and electrical power (200MW). The integrated system considers both recycle (recycle ratio=5) and once-through (no recycle) modes of methanol synthesis. The results of simulations show that, when compared to separate stand-alone plants for methanol and power production, the integrated systems show lower consumption of total fresh synthesis gas for recycle and once-through operation of 2.8% and 3.7%, respectively. In addition, simulations show that the advantage over stand-alone plants increases further in the face of decreasing catalyst activity or selectivity, rising to over 10% in several scenarios. This is because the off-spec material from methanol production in an integrated plant can be diverted to the power generation section of the plant. These savings in operating costs are over and above the substantial capital cost savings which can be realized in the design of a once-through integrated plant.