Small Pilot Test Results from a Polaris Membrane 1 MWe CO2 Capture System

To mitigate the harmful effects of global climate change, CO2 in combustion sources must be captured and either sequestered or utilized. Membrane technology is an attractive CO2 capture option because of advantages such as energy-efficient passive operation, small footprint, no hazardous chemical emissions, handling or storage issues, near instantaneous response, no steam use, and reduced water requirements. Working with the U.S. Department of Energy (DOE), Membrane Technology and Research, Inc. (MTR) has developed new membranes and process designs to recover CO2 from combustion gases. The Polaris™ class of membranes offer the highest combination of CO2 permeance and CO2/N2 selectivity of any commercial membrane today. These membranes are combined with a novel two-step process design that uses incoming combustion air to sweep membranes and recycle CO2 to the combustion process. The benefits of this two-step membrane design include an increased CO2 concentration to the membrane capture step and a reduction in the fraction of CO2 removal required by the capture step. Design calculations estimate that this membrane process can capture CO2 at a cost of <$40/tonne under partial capture conditions. Between 2012 and 2015, MTR operated a bench-scale test system at the U.S. National Carbon Capture Center (NCCC) in Wilsonville, AL testing commercial-scale Polaris membrane modules capturing 1 tonne CO2/day. Overall, this system accumulated a run time of over 11,000 hours, and demonstrated stable membrane performance while processing real coal-fired flue gas. The test system also operated as a field laboratory that allowed for evaluation of new membrane module designs and validation of advanced membranes under real world conditions. With this experience, MTR designed and built a scaled-up small pilot unit to treat 20 tonnes CO2/day from a slipstream at NCCC (equivalent to 1 MWe-scale coal-fired power generation). This system was operated for approximately 1,500 hours in 2015 over two different test campaigns. The small pilot membrane system exhibited stable performance and reached up to a 90% capture rate during operation in both winter and summer field test conditions. During the second test campaign, advanced Polaris sweep modules demonstrating higher packing density, lower pressure drop, and higher permeance were validated.