The most obvious constraint on carbon emissions arises from climate change. Burning fossil fuels accounts for about three-fourths of the anthropogenic carbon dioxide emitted in the US. While all fossil fuels contain carbon, coal is the most carbon-intensive, putting coal at a disadvantage in a carbon-controlled world. Because electricity generation is the single largest contributor to CO2 emissions and over half of the electricity generated in the US is from coal, there is a pressing need to develop viable carbon-control technologies, which can be implemented in a practical and affordable manner. There are three ways to reduce CO2 emissions from electricity generation. The first and best method is to use energy more efficiently to reduce our needs from fossil fuel combustion. Another way is to increase our supply from renewable, low-carbon, and carbon-free energy. The third is to separate, capture and securely store carbon dioxide (i.e., carbon sequestration).
With support from utilities and state government, CAER is working on (1) post-combustion CO2 capture (heat-integrated Amine, and Ammonia scrubbing process); (2) oxyfuel combustion through chemical looping combustion (CLC) for solid fuels; (3) green power production via biomass utilization (co-firing, biomass liquefaction, and biodiesel by-product glycerin combustion); and (4) plant performance improvement and process optimization.
The process under development at CAER for utility post-combustion CO2 enrichment consists of two regenerative gas-to-liquid heat exchangers for heat integration, open tower design for absorber, pressurized stripper/CO2 separation, and low energy consumption sorbent. The Aspen simulation indicated the process could lower the energy penalty by 20-30% for CO2 capture by comparing to available post-combustion CO2 separation technologies.
During the Summer of 2011, the U.S. DOE announced that the UK CAER Power Generation Research Group will receive a $14.5M grant for a project titled "Application of a Heat Integrated Post-Combustion CO2 Capture System with Hitachi Advanced Solvent into Existing Coal-Fired Power Plant". The research will help develop ways to reduce the cost and improve the efficiency of advanced carbon capture systems used at coal-fired power plants.
Work has also been undertaken at CAER to investigate additional novel carbon capture enhancement technologies including a capacitive deionization process (CDI) for temporary amine concentration, an absorption solvent/catalytic membrane hybrid post-combustion CO2 capture process for existing coal-fired power plants and solvent/catalyst formulation for post-combustion CO2 capture.
Starting from the introduction of CLC in 1983, the majority of studies have been with gaseous fuels such as methane and natural gas. Solid fuels such as coal and biomass have been ignored due to technical problems, including the oxygen carrier (OC) separation and deactiviation, slow reaction between fuels and OC, and possible CO2 leakage from the reducing reactor to the oxidizing reactor. Our focus on chemical looping combustion is to develop a first-of-kind process to burn solid fuel. To overcome the challenge of combusting solid fuel, the in-situ gasification and fly ash separation from oxygen carrier technologies were proposed and investigated. A dual-layer oxygen carrier has been developed in which the inner core is made with less expensive Fe-, Cu-, or Ca-based compounds. The outer layer contains lower concentrations of Ni-, Co-, or other metal-based catalyst compounds, which can help minimize OC costs while maximizing the reactivity and mechanical properties of the OC while suppressing agglomeration.
- Development and Heat Optimization in an Amine-based CO2 Scrubber - CAER Project Factsheet Summary
- Development of Chemical Looping Combustion/Gasification for Solid Fuels - CAER Project Factsheet Summary
Contact: Kunlei Liu
Biomass can be converted by thermal or biological routes into various forms of energy including process heat, steam, motive power, and electricity, as well as liquid fuels, chemicals and synthesis gas. It is a ubiquitous feedstock. Compared to carbon dioxide sequestration from fossil-fuel combustion sources, thermochemical processing of biomass with CO2 sequestration will create a "real" CO2 reduction credit for greenhouse gas emission control. However, biomass feedstocks have economic deficiencies that we must overcome if they are to be viable. The low density and high water content of biomass makes shipping costs prohibitive in many cases, yet most subsequent refining processes require centralized facilities, where large-scale operations greatly increase process efficiencies.
In collaboration with CAER's Biofuels and Environmental Catalysis group and the Carbon Materials group, we are focusing on technical hurdles to distributed processing of biomass. Specifically, can biomass be economically densified on-farm to a crude bio-oil for shipment to a centralized refinery or power plant for electricity generation, or co-briquetted with coal fines for premium utility fuels, and how does the solid residual (biochar) impact agriculture productivity and CO2 natural cycle?
Contact: Kunlei Liu
"Energy Efficiency" can be thought of as "The Fifth Fuel" in addition to coal, natural gas, nuclear and renewable energy. Assuming an average plant efficiency of 35% in our existing sub-critical coal-fired generation fleet, a 1% efficiency improvement for a 500 MWe unit could result in:
- 2.8% less primary fossil fuel consumption, which would be 1.7 Mt less coal consumed over the 40 year lifetime coal-fired power generation.
- 4.5 million fewer tons of carbon dioxide generated over the 40 year lifetime of coal-fired power plant, which would have the equivalent CO2 reduction impact of:
- —over 26,000 large (1 kW) Solar Panels.
- —Taking 11,000 cars off the road.
We are using process simulation software (Aspen and ChemCad) to simulate power plant individual component and optimize the streamline of power production. The output simulations will guide plant performance improvement, resource management and engineering modification.
Contact: Kunlei Liu
The University of Kentucky's Center for Applied Energy Research has been continuously active in binder and briquetting/agglomeration research since 1997. The primary goal of this effort is the development of technologies that can economically move fine waste coal and biomass residues from the areas where it is available in abundance, to the utility site, where it can be used to generate power.
Kentucky is the largest producer of timber products east of the Mississippi, generating an estimated 700,000 tons of sawdust per year in East Kentucky alone with biomass availability from all sources estimated at five million tons per year. However, before biomass can become a meaningful contributor in our energy strategy, several economic and practical limitations must be resolved including its inherently low energy density, making its transport over even moderate distances, cost prohibitive. Additionally, the capital investment required to use the biomass near the point of production, or to add the equipment needed to handle and process biomass at the utility is a major deterrent. We also discard about 3 million tons of fine coal each year and have in excess of 500 million tons of additional waste coal stored in impoundments and waste piles around the state. Methods to recover a high-Btu product from waste coal fines are known and reasonably inexpensive. However, similar to biomass, the utilization of fine coal suffers from problems associated with its high and difficult-to-remove moisture content that lowers its heat value and creates handling, storage, and transportation problems. Nonetheless, a number of factors including higher energy and waste-disposal costs, tax incentives, public demand, and potential legislative limits on CO2 emissions have sparked renewed interest in finding beneficial uses for these materials.
One promising approach for addressing the marketing issues posed by fine coal and biomass residues is to co-briquette these materials to produce a high-quality, reduced-moisture fuel that can be transported as dense, free-flowing solids, and then stored, crushed, and conveyed in existing equipment. In a prior study, waste coal was cleaned to about 3% ash, combined with sawdust, and co-briquetted using binders that were identified as the most cost effective. Durable, high-Btu briquettes (>200 lbf compressive strength; ~14,000 Btu/lb) were formed which exhibited excellent integrity and carbon burn-out characteristics during combustion. An economic analysis based on the results from this study indicated that fine coal/sawdust briquettes can be produced for less ~$17/ton. Work in this promising area is ongoing with a continued emphasis on development of cost effective binders and an expanded focus on co-briquetting and densification of agricultural residues.
Contact: Darrell Taulbee