Biomass supercritical water gasification

Process scheme of the supercritical water gasification pilot plant at FZ Karlsruhe. (Reproduced from Boukis, N., Galla, U., Diem, V., and Dinjus, E., Science in Thermal and Chemical Biomass Conversion, CPL Press, Victoria, 2004, 975-990. With permission.)... 

Hydrogen can be produced from biorenewable feedstocks via thermochemical conversion processes such as pyrolysis, gasification, steam gasification, steam reforming of bio-oils, and supercritical water gasification (SWG) of biomass. 

Hydrogen from Biomass by Supercritical Water Gasification... 

The cost of transporting wood chips by truck and by pipeline as a water slurry was determined. In a practical application of field delivery by truck of biomass to a pipeline inlet, the pipeline will only be economical at large capacity (>0.5 million dry t/yr for a one-way pipeline, and >1.25 million dry t/yr for a two-way pipeline that returns the carrier fluid to the pipeline inlet), and at medium to long distances (>75 km [one-way] and >470 km [two-way] at a capacity of 2 million dry t/yr). Mixed hardwood and softwood chips in western Canada rise in moisture level from about 50% to 67% when transported in water the loss in lower heating value (LHV) would preclude the use of water slurry pipelines for direct combustion applications. The same chips, when transported in a heavy gas oil, take up as much as 50% oil by weight and result in a fuel that is >30% oil on mass basis and is about two-thirds oil on a thermal basis. Uptake of water by straw during slurry transport is so extreme that it has effectively no LHV. Pipeline-delivered biomass could be used in processes that do not produce contained water as a vapor, such as supercritical water gasification. 

In addition to these cost elements, transport of biomass for a direct combustion application by water creates a prohibitive drop in the LHV of the fuel because of absorbed water. These issues limit the application of pipeline transport of biomass to large applications that use oil as a carrier medium, or that supply a process for which the heat content of the fuel is not degraded by the requirement to remove absorbed water as vapor, such as a supercritical water gasification process. 

Furthermore, water transport of mixed hardwood and softwood chips causes an increase in moisture level to 65% or greater, which so degrades the LHV of the biomass that it cannot be economical for any process, such as direct combustion, that produces water vapor from water contained in the biomass. The impact on straw is greater, in that moisture levels are so high that the LHV is negative. Pipeline transport of biomass water slurries can only be utilized when produced water is removed as a liquid, such as from supercritical water gasification. 

Gasification of Liquidized Biomass Supercritical Water Using Partial Oxidation... 

Minowa et al. [17] at the National Institute for Resources and Environment, Japan, proposed treatment of city garbage at ten cratures lower than 200 C to "liquidize the garbage. This operation is different from conventional liquidization because the product material is not oil but a biomass slurry that can be obtained at much lower temperature. Specifically, they were able to liquidize a mixture of cabbage, steamed rice, clam shells, dried sardines, and butter en loyed as a garbage model by treating it in an autoclave. The product was a slurry, and solid conqronents were found to precipitate with time. However, when they operated at 150 C for 1 hour, the solid components could be suspended for more than several hours. They proposed that this process could be applied as an effective pretreatment for supercritical water gasification,... 

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Biomass treatment in supercritical water. The way from total oxidation to the gasification... 

Boukis, N. Schmieder, H. Abeln, J. Dinjus, E. Kruse, A. Kluth, M. Petrich, G. Schacht, M. Sadri, E. (2000). Gasification of High Moisture Waste Biomass in Supercritical Water. The fiflh international symposium on supercritical fluids, ISSF 2000 Proceedings April 8-12, 2000, Atlanta, USA(in press). 

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