(771b) Membrane Processes Applied to Carbon Capture in Coal-Fired Power Plants: Multi-Stage Design and Economic Analysis

In order to reduce the greenhouse gases emissions from coal-fired power plants, membrane separation seems a promising alternative to conventional carbon capture technologies. The aim of this work, in collaboration with ETP – Energy Technology Partnership – and Scottish Power, is to investigate the process design of the capture system, ranging from the analysis of the single membrane modules to a complete multi-stage scheme.  The DOE case 9 – subcritical coal-fired power plant– has been assumed as reference case.

The modelling process involved the implementation of a membrane module simulation tool that we have developed to be able to predict the performance of countercurrent-sweep and cross-flow modules, which are the typical large scale industrial applications of membranes.  The module simulator includes also a new 2D cross-flow model which accounts for both feed and permeate flow directions on both sides.

The module simulator has been implemented with a software interface that allows us to study the complete integration of the membrane modules with a flowsheet for a coal-fired power plant in UniSim Design®, the Honeywell process simulator. In order to find the optimal design in terms of CO₂ purity, energy consumption and membrane area, single and multi-stage simulations have been carried out. Various configurations have been studied to achieve the desired targets in terms of CO₂ recovery (0.9) and purity (above 0.95).

As a result of the multi-stage analysis and initial optimisation, 2 options have been identified: a retrofit and a possible modification including the recycle of part of the CO₂ to the boiler. In both the configurations, after the membrane system, the CO₂-rich stream has then been compressed up to 150 bar and a final refrigeration stage has been included in order to increase the CO₂ purity.

In order to give an overall idea of the application of this technology to carbon capture, particular attention has been focused on the economic analysis: the capture costs have been calculated and a complete evaluation of the Levelised Cost of Electricity (LCOE) has been carried out. Starting from the calculation of the base-case scenario, represented by the DOE case 9, the contribution of the capture scheme has been included and its effect on both operative and capital cost has been identified. The implementation is based on European (ZEP - Zero Emission Platform) and UK (DECC - Department of Energy and Climate Change) references and it also includes the possible contribution of the EU Emission Trading Scheme. It represents a key feature in order to have a complete comparison between membrane gas separation and amine adsorption, the actual carbon capture commercial technology.