An optimization-oriented green design for methanol plants

摘要

A new design for a methanol plant is proposed in which CO _2 addition, as one of the important parameters, is used to optimize the synthesis gas composition. An attempt has been made to assess the environmental features as well as the process operability of the proposed plant, in which the required CO _2 is provided from reformer flue gas. As a starting point, simulation of a conventional reference methanol case (RMC) and also the proposed green integrated methanol case (GIMC) are performed to obtain operational and kinetic parameters. In order to compare properly GIMC and RMC, the objective function is defined so that SynGas production, and thereby methanol production, in the GIMC is equal to that of the RMC. Results: In the optimization the optimum values of decision variables are calculated using a genetic algorithm. In the best case, the eco-efficiency indicators of GIMC would decrease to 330.3 kg CO _2 tonne ~(-1) MeOH, which is 15% lower than that of RMC. The environmental damage cost of 2.9 million dollars could also be prevented in GIMC when compared with RMC. Conclusion: It was found that the CO _2 needed in GIMC could be provided by an environmentally friendly process and that the GIMC is a cleaner process compared with RMC. Furthermore, the proposed GIMC would be capable of reducing CO _2 emission while its mitigation potential depends significantly on the type of solvent employed in the GIMC. The results obtained show that environmental damage cost would be important and should be considered in the process design.