Negative Greenhouse Gas Emissions focuses on designs and strategies for modular gasification-based systems enabling negative lifecycle emissions of greenhouse gases. Biomass can have an important role in reducing carbon intensity of coal-based systems, as can application of advanced technologies integrating carbon capture. Likely approaches to be considered include co-utilization of biomass with coal as gasification feedstocks, integrated or pre-combustion capture of CO2 especially facilitated by gasification, and innovative technological approaches or combinations of technologies enabling extensive greenhouse gas reductions of modular gasification systems.
Interest in the concept of co-feeding biomass to coal-fueled plants including advanced gasification-based plants such as IGCC power plants, emerged from the idea that coal-biomass systems could become part of an early compliance strategy for carbon reduction, particularly across the large existing installed base of coal-based power plants. Recognizing that large biomass-alone power plants are constrained by low biomass energy density, feedstock water content, feedstock collection and preparation, and seasonal/regional feedstock availability, coal-biomass systems could benefit from the stability of a primarily coal-based feed mix, adding tractable amounts of biomass as constrained by technical/performance requirements and biomass availability.
Co-feeding biomass with coal can reduce the carbon intensity of power generation and other coal consuming processes, but to achieve zero or negative lifecycle greenhouse gas emissions in coal power plants some degree of carbon capture must be implemented. Gasification systems have the advantage considering that CO2 in typical syngas is much more concentrated and pressurized than the CO2 in the flue gas of combustion-based plants. Both concentration and pressure aid in separating CO2 from the syngas. Also, innovative modular gasification and water gas shift reactors afford opportunities for in situ oxygen production and gas separations which can facilitate or reduce the costs of CO2 capture.
Coal and biomass-based thermochemical co-conversion cycles consisting of: 1) gasification-based electricity production with carbon capture and storage, and 2) long-chain hydrocarbon fuels production via gasification and the Fischer–Tropsch process (or alternatives) with carbon capture and storage, or both (polygeneration) have been strongly advocated as viable/accommodating process systems for a feasible commercialization strategy for carbon-negative energy. The NETL Gasification Program accords with this strategy with its recent efforts in modular gasification-based systems for power production, its work in syngas-based fuels production, and many projects in the portfolio considering biomass additions to the feedstock mix for greenhouse gas reductions in power generation and fuels production, and others considering techno-economic advantages of polygeneration systems. R&D of these systems should continue towards demonstration of technical feasibility at commercial scale and reduction of investment risk, which have been identified by the R&D community as key research and policy needs in carbon negative energy systems development.
In the biomass gasification field, moving bed or fixed bed gasifiers and fluidized bed gasifiers comprise the vast majority of gasifiers used, given their relative flexibility in handling varying feed streams and suitability to the sizes needed for typical applications. However, high-temperature, oxygen- or steam-blown, pressurized, entrained-flow gasification of multiple biomass-containing feed streams has been advocated as an important area of focus for R&D, considering the higher efficiency and reaction intensity of entrained gasification. NETL has begun to make inroads into this area as it supports R&D of high-pressure modular gasifiers (mainly entrained flow type), high-pressure feeding of lower quality fuels including biomass/coal blends, lower cost air separation for modular systems, and so on. The R&D strategy is to continue pursuing gasifier technology for higher efficiency gasification of coal/biomass blends and reduction of those technology costs. This will strongly enable negative greenhouse gas emissions technology in gasification systems.
Currently, this Key Technology area includes one project specifically for advancing technology for negative GHG emissions in coal gasification for power production and coal to liquids applications.
Essentially, the technological innovation features reaction intensification by combining water gas shift catalyst with a high-temperature CO2 adsorbent in the syngas shift reactors, and operating in pressure swing mode. Process energy savings are possible over the conventional approach of multi-stage shift of syngas followed by conventional solvent-based CO2 capture.
Other key technologies within Gasification Systems include the following:
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