(697d) Economic Recovery of Greenhouse Gases Enabled by Process Intensification
AIChE Annual Meeting
Friday, November 17, 2006 - 4:45pm to 5:15pm
Process intensification technologies have traditionally been geared toward the synthesis or purification of high value products. The technology may also be applied to the capture and purification of green house gases, including methane and carbon dioxide. Specifically, highly intensified microchannel hardware is in development to capture and concentrate methane from both coal mine and geological sources. In addition, the technology may be applied to the capture of carbon dioxide from power plant flue gas. Methane capture for economic utilization is enabled by rapid thermal swing adsorption (TSA) in microchannel architecture. By swing the gas mixture's temperature, instead of the pressure, compression costs can be avoided. However, the time to swing adsorbent beds over a temperature range sufficient to affect the separation can be relatively long, which means the equipment must be very large and therefore economically unattractive. Microchannel architecture can overcome this historic shortfall by rapidly swinging temperatures, thereby greatly reducing the size of TSA processing equipment. The microchannel approach to TSA is based on using this technology's enhanced heat and mass transfer capabilities to achieve rapid temperature swings of the adsorbent bed. Enhanced heat transfer allows TSA cycle times of seconds, compared to several minutes or hours for conventional systems. Improved mass transfer allows sufficient adsorption to occur during the shorter cycles. A similar approach can be taken to the concentration of carbon dioxide (CO2) from flue gas and other large point sources for the purpose of sequestration. For this application minimizing backpressure imposed on the adjoining combustion process is vital to maintain high efficiency operation. In addition, TSA systems are well suited to operate partially, or completely, off of waste heat, which is readily available at power plants. This presentation will describe the application of rapid TSA to the separation of nitrogen from methane, which is one of the most significant challenges in recovering low-purity methane streams. Results from laboratory experiments show that microchannel adsorbent beds can be swung over the desired temperature range in cycles less than 5 seconds. It has also been demonstrated that flowing and purging gas mixtures through the device concentrates the methane product stream. Successful development of this application could enable the recovery of 3.5 trillion standard cubic feet of sub-quality natural gas.