The effects of wood particle size and different process variables on the performance of steam‐oxygen blown circulating fluidized‐bed gasifier

Abstract

Pressurized circulating fluidized‐bed gasification by steam‐oxygen has been developed at VTT for syngas applications. In this process, wood feedstocks are first converted into raw gasification gas, which is then filtered at about 600°C before catalytic reforming of tars and hydrocarbon gases. This article presents results of the gasification and gas filtration tests carried out with wood pellets, crushed pellets, bark, and crushed forest residues. The effects of operating pressure, bed material used, and other main operating variables were examined. Dolomite, magnesium oxide, and sand were used as bed materials. Gasification pressure was in the range 0.25–0.6 MPa and operating temperature 860–930°C. In best operating conditions, over 98% carbon conversion was achieved with very smooth long‐term operation. The feedstock particle size, operation pressure, and the presence of calcium‐based bed material had strong effects on tar formation and filter operability. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 681–687, 2014

Co-production of synthetic fuels and district heat from biomass residues, carbon dioxide and electricity: Performance and cost analysis

“…The wet biomass feedstock is first dried from its initial moisture of 50 wt% to 15 wt% in a belt dryer operated with hot water recovered from the gasification plant. The dried chips are pressurised with lock-hoppers to 0.4 MPa and fed to a circulating fluidised-bed gasification reactor operating at 850 C. The gasifier is fluidised with equal amounts of steam and oxygen and used to convert wood chips into a raw product gas containing CO, H 2 , CO 2 , H 2 O, CH 4 and small amount of higher hydrocarbons and tars [32]. Before filtration, the gas is cooled 3 down to 550 C to condense alkali metals and to avoid blinding of the filter elements during dust removal [33].…”

Steam–oxygen gasification of forest residues and bark followed by hot gas filtration and catalytic reforming of tars: Results of an extended time test

“…In these studies we observed that CFB gasification is a stable and easily controlled process when the gasifier is operated at pressures up to 0.4 MPa, whereas operation above 0.5 MPa is challenging due to overheating of the bottom part of the gasifier bed, resulting in ash sintering problems. At lower gasification pressures, the bed material calcium as well as the inherent wood calcium is in the form of CaO, which has many positive effects on gasification as discussed in more detail in [11,16]. At higher pressures calcium is in the form of CaCO 3 , which does not have similar positive effects on tar decomposition and ash chemistry.…”

“…Our previous study [16] focused on the initial development of the process concept and described the effects of the gasifier operating pressure, used bed material and other main gasifier operating variables on the gasifier performance. The main focus was on the gasifier operation, whereas the performance of the filter unit and the reformer was not yet studied in detail.…”

“…The commercialization of CFB gasifiers in the Finnish power and heat market had also created valuable industrial experience and a good technical basis for designing gasifiers for more demanding syngas applications. In 2007-2012, pressurised steam-oxygen-blown Circulating Fluidised Bed (CFB) gasification was intensively developed at VTT [12,16]. The R&D impetus was related to industrial plans for the production of liquid transportation fuels from forest residues.…”

“…The gasification process was operated according to the basic process concept identified in the previous R&D stage [16] to be most reliable from the operation point of view. In this extended-time test run, the gasifier was operated at 0.2-0.25 MPa and at 910°C, filtration was carried out at ca.…”