Demonstration of a Piston Plug feed System for Feeding Coal/Biomass Mixtures across a Pressure Gradient for Application to a Commercial CBTL System
Producing liquid transportation fuels and power via coal and biomass to liquids (CBTL) and integrated gasification combined cycle (IGCC) processes can significantly improve the nation's energy security. The Energy Independence and Security Act of 2007 mandates increasing renewable fuels nearly 10-fold to >2.3 million barrels per day by 2022. Coal is abundantly available and coal to liquids (CTL) plants can be deployed today, but they will not become sustainable without large scale CO{sub 2} capture and storage. Co-processing of coal and biomass in CBTL processes in a 60 to 40 ratio is an attractive option that has the potential to produce 4 million barrels of transportation fuels per day by 2020 at the same level of CO{sub 2} emission as petroleum. In this work, Southern Research Institute (Southern) has made an attempt to address one of the major barriers to the development of large scale CBTL processes - cost effective/reliable dry-feeding of coal-biomass mixtures into a high pressure vessel representative of commercial entrained-flow gasifiers. Present method for dry coal feeding involves the use of pressurized lock-hopper arrangements that are not only very expensive with large space requirements but also have not been proven for reliably feeding coal-biomass mixtures without the potential problems of segregation and bridging. The project involved the development of a pilot-scale 250 lb/h high pressure dry coal-biomass mixture feeder provided by TKEnergi and proven for feeding biomass at a scale up to 6 ton/day. The aim of this project is to demonstrate cost effective feeding of coal-biomass mixtures (50:50 to 70:30) made from a variety of coals (bituminous, lignite) and biomass (wood, corn stover, switch grass). The feeder uses a hydraulic piston-based approach to produce a series of plugs of the mixture that act as a seal against high back-pressure of the gasification vessel in to which the mixture is being fed. The plugs are then fed one by one via a plug breaker into the high pressure gasification vessel. A number of runs involving the feeding of coal and biomass mixtures containing 50 to 70 weight % coal into a high pressure gasification vessel simulator have shown that plugs of sufficient density can be formed to provide a seal against pressures up to 450 psig if homogeneity of the mixture can be maintained. However, the in-homogeneity of coal-biomass mixtures can occur during the mixing process because of density, particle size and moisture differences. Also, the much lower compressibility of coal as opposed to biomass can contribute to non-uniform plug formation which can result in weak plugs. Based on present information, the piston plug feeder offered marginal economic advantages over lock-hoppers. The results suggest a modification to the piston feeder that can potentially seal against pressure without the need for forming plugs. This modified design could result in lower power requirements and potentially better economics.
- Research Organization:
- Southern Research Institute
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- NT0006523
- OSTI ID:
- 1035865
- Country of Publication:
- United States
- Language:
- English
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