0.1-MWe pilot-scale testing of TDA Research’s sorbent-based CO2 capture technology on syngas at facilities with different gasifiers (air-blown transport gasifier vs. oxygen-blown gasifier) and feedstocks (low-rank coals vs. petcoke), which allows researchers to assess process efficacy in very different gas streams.
Pre-combustion Capture separates carbon dioxide (CO2) from gasification and reforming processes in which a gaseous fuel, or “synthesis gas (syngas)”, is formed, consisting mainly of hydrogen (H2), carbon monoxide, and CO2. In an integrated gasification combined cycle (IGCC) power plant, a carbon-based fuel (i.e., coal) is reacted with steam and oxygen under pressure to form syngas, which is used to fuel a gas turbine generator to produce electricity. The recovered heat is used to produce steam that also drives a turbine generator designed to generate electricity. The carbon is captured from the syngas before it is combusted in the gas turbine.
In order to facilitate carbon capture and increase the hydrogen production, the syngas is shifted in a water-gas-shift (WGS) reaction to produce additional hydrogen and convert the carbon monoxide into CO2. Pre-combustion capture is typically more efficient than post-combustion capture from traditional pulverized coal power plants due to the higher concentration of CO2 after the WGS reaction and the high pressure of the syngas
Pre-combustion R&D efforts are focused on advanced solvents, solid sorbents, and membrane systems for the separation of H2 and CO2, with specific emphasis on high-temperature/novel materials, process intensification, and nanomaterials. Additionally, novel concepts, such as hybrid technologies that combine attributes from multiple technologies are being investigated.
Solvent-based CO2 capture involves chemical or physical absorption of CO2 into a liquid carrier and regenerating the absorption liquid by increasing the temperature or reducing the pressure to break the absorbent-CO2 bond. Commercially-available solvents are successful at removing acid gases such as hydrogen sulfide and CO2 from high pressure syngas streams; however, these solvents often have limitations, such as high water miscibility, high vapor pressure, low selectivity, and high viscosity, resulting in the need for operation at low temperature and subsequent high energy demands. R&D objectives include improving selectivity to reduce H2 losses and developing hydrophobic solvents with non-foaming behavior, low viscosity, and a high CO2 loading at above ambient temperatures to reduce energy loss associated with syngas cooling.
Sorbent-based CO2 capture involves the chemical or physical adsorption of CO2 using a solid sorbent. Solid sorbents generally are associated with a reduced regeneration energy penalty, operate at higher temperatures, and have a lower environmental impact compared to solvents. Sorbent-based technologies under development are aimed at improving the cost and performance of CO2 separation in IGCC plants. R&D objectives include novel sorbents (e.g. alkali ceramic-based, carbon-based, and calcium oxide-based sorbents) that maintain a high CO2 adsorption loading capacity, can withstand multiple regeneration cycles with minimal attrition, and perform efficiently at the high temperatures encountered in IGCC systems to avoid the need for syngas cooling and reheating.
Membrane-based technologies for separating CO2 and H2 in syngas produce a concentrated CO2 stream at a pressure near the syngas feed pressure, resulting in reduced energy and cost for compression of CO2 compared to solvent-based processes. Membrane designs include metallic, polymeric, or ceramic materials capable of operating at elevated temperatures and that utilize a variety of chemical and/or physical mechanisms for separation. R&D objectives are membranes that have high permeability and selectivity with low pressure drop, tolerance to contaminants (e.g., sulfur), and are capable of operation at system temperatures up to 500 °F. System advancements include the integration of WGS reaction with CO2/H2 separation into a single process step and the fabrication of membranes into a module configuration for reduced capital costs.
Novel Concepts are under investigation and include hybrid systems that combine attributes from multiple technologies, novel process conditions (e.g., heat integration), and novel catalyst materials for reaction rate enhancement. Technologies being developed include combining temperature-swing and pressure-swing regeneration to lower cost and energy penalties and integrating CO2 capture directly with the water-gas shift reaction to drive equilibrium toward CO2 and H2 production while eliminating the need for syngas cooling.