Optimisation of cogeneration systems – combined production of methanol and electricity

This paper discusses an example of cogeneration, viz. the combined production of methanol and electricity. In this regard technical and economic criteria of a typical MegaMethanol plant (capacity: 5000 metric tons per day) and a gas-steam power plant on natural gas basis (capacity: 750 MW) are presented. A mathematical simulation model summarises the specific criteria of both systems. Aim of this study is the optimisation of the combined production of methanol and electricity. A specific approach to optimise the exergy and/or cost efficiency is applied. Therefore, the energy supply design of the MegaMethanol plant is analysed and evaluated in terms of combined thermodynamic and economic aspects. The significance of different dimensioning parameters of the energy supply design is demonstrated by means of sensitivity analyses. These sensitivity analyses categorise the power plant design parameters in relation to the potential to affect the methanol and electricity costs. Accordingly the energy supply design of the MegaMethanol plant is modified successively in an iteration process. The optimisation results in a gas-steam power plant design characterised by increased exergy efficiency and decreased cost efficiency. Recommendations for advanced optimisation studies of cogeneration concepts are made.