Characterization of CO2 flux through hollow-fiber membranes using pH modeling

doi:10.1016/j.memsci.2019.117389

Coal represents a significant source of U.S. fossil fuel energy and also serves as a potential feedstock for many industrial chemicals. To make full and efficient use of coal in power generation or chemical feedstock, the major components of coal must be converted to a gaseous state. During gasification, the main components of coal (C and H) are converted to a gas that contains H2, CO, CO2, and H2O (steam), with many of the coal impurities converted to gaseous species such as H2S and NH3. The gasification process is typically performed at elevated pressures (20 to 50 bar) and temperatures,more » and the resulting fuel gas components (H2 and CO) are used for efficient generation of electricity in gas turbines, steam turbines, or fuel cells. The integrated gasification combined cycle (IGCC) process is more efficient than coal combustion for generating electric power because gas turbines generate electricity more efficiently than steam turbines. To capture CO2 in pre-combustion applications with the current technology, syngas stream must be cooled to near-ambient temperature followed by reheating of the fuel gas before sending to turbines. An analysis by the Department of Energy’s (DOE’s) National Energy Technology Laboratory (NETL) has shown that by eliminating the need to cool and reheat the fuel gas, the net power plant efficiency is increased by 1 to 3 percentage points [1, 2]. Their analysis also showed that a 2-point efficiency gain results in an 18% decrease in the cost of electricity (COE). Therefore, H2 separation and CO2 capture processes that can be operated at high temperature and pressure are imperative for pre-combustion applications to preserve the sensible heat in the hot syngas and improve the thermal efficiency of overall process. Additionally, CO2 is captured at high pressure, reducing the number of compression stages needed to pressurize to the pipeline pressure and therefore significantly lowering the capital and operational costs. SRI International (SRI), in collaboration with ENERFEX, EPRI, Generon, IGS, PBI Performance Products, Inc., and Energy Commercialization, LLC, performed a 48-month effort to evaluate, at a bench-scale size, a technically and economically viable CO2 capture system based on a high-temperature polybenzimidazole (PBI, PBI Performance Products) polymer membrane gas separation process and to optimize the membrane separation system for integration into an integrated gasification combined cycle (IGCC) plant. The separation process is based on a PBI polymer that has been fabricated as asymmetric hollow-fiber membranes (HFM) and assembled into membrane modules to separate hydrogen, steam and CO2 from syngas streams of oxygen-blown gasifiers. A test skid (50-kWth capacity) was designed and built to accommodate the gas separation HFM modules. The HFM modules separate a pre-combustion syngas stream into a hydrogen-rich permeate stream and a retentate stream that mainly consists of high-pressure CO2. The modules were mounted in high-pressure vessels and the skid was assembled along with syngas feed, retentate, and permeate connections and instrumentation. The skid was transported to the National Carbon Capture Center [NCCC]), Wilsonville, AL, where it was tested at 150- 225°C and at 5-15 bar under various operating conditions, including long-term steady-state conditions. As the gasifier at NCCC was air-blown, and H2 and CO2 gases were added to the feed stream for some test runs to obtain a close representative syngas composition of an oxygen-blown gasifier. The data collected from these tests was used to prepare a techno-economic analysis (TEA) and an environmental, health and safety (EH&S) risk assessment. At the end of the test program, the test skid was decommissioned and transported to SRI. The project program consisted of seven tasks: Task 1: Program Management Task 2: Establish Performance Database Task 3: Installation of 50-kWth Test Unit at the Field Site Task 4: Operation of the Test Unit Task 5: Process Design and Engineering Study Task 6: Environmental and Techno-Economic Analysis Task 7: Dismantling and Removal of the Field Test Unit

Title: Characterization of CO2 flux through hollow-fiber membranes using pH modeling

Citation Formats