Multi-objective Optimization under Uncertainty of Novel CHPC Process

Combined Heat and Power (CHP) and biomethane upgrading plants are the two main processes that use biogas in Europe. The first converts biogas into electric energy and heat while the second consist of the purification of methane, via removal of other components, and its injection into the national natural gas distribution grid. They both are considered to be green technologies but the overall carbon balance is positive for both processes. Use of biogas as raw material in chemical synthesis allows to fix carbon in the chemical molecule and avoid its release as carbon dioxide. This is the basic idea of Combined Heat Power and Chemical plants (CHPC). Starting from biogas, CHPC produces methanol, a valuable and important building block for industrial chemistry. In this work we optimized the entire process by using multiple objective functions (economics and environmental) and considering the uncertainty of the feed composition. The results of mono-objective optimization show that the CHPC plant can be economically feasible with a net consumption of CO2. Multiple objective optimization identified the operating conditions in which payback time is reasonable and CO2 balance negative. Optimization under uncertainty allowed to design a more flexible and realistic process which can accommodate the variations in inlet biogas composition.