Process-integrated optimization and techno-economic analysis of membrane system for biogas upgrading: Effect of membrane performance from an economic perspective

Abstract

It is useful to be able to predict the potential economic performance of new membrane materials and the associated configurations of equipment which would give the best possible performance with these materials. In this study we propose a systematic search of ranges of different possible membrane properties. The properties varied here include the CO2 permeance and the CO2/CH4 selectivity, and a 2D grid with different values of each property is investigated. For each individual combination of properties a superstructure optimization is used to find the configuration and operating pressures which minimize the cost of biogas upgrading. Applying this to every point in the grid gives a surface of upgrading costs across the ranges of possible CO2 permeances and selectivities. Subsequently a correlation equation is fitted to this data which can be used to predict the potential economic performance of future possible materials within this range. In general the upgrading costs reduce when either of these parameters are increased but for different reasons. Higher permeances allow smaller area of membranes to be used allowing lower membrane costs while higher selectivities reduce the need for recycling and associated compression costs. The selectivity, in particular, is found to strongly affect the optimal configuration with high selectivities allowing for designs without recycling while lower selectivities force the process to include recycling streams in order to meet recovery and purity targets. It is expected that the proposed correlation could be used to quickly evaluate the economic performance of new materials as they are being developed and tested.