Development of Ca Looping Three-Towers CFB Biomass/Coal gasification

It is a prerequisite for the increasing use of biomass energy that its introduction and acceptance be increased. The technologies for biomass use face the challenge of overcoming the following issues: (1) Stable supply of gasification material; (2) Heat supply for biomass gasification; (3) Auxiliary facilities for post-gasification tar removal, gas composition adjustment, and desulfurization; (4) Use of various biomass; We proposed Ca looping three-tower biomass/coal co-gasification process. CaO circulates as the heat transfer material, catalyst and a CO2/H2S sorbent. Biomass and supplemental fuel coal are supplied to the gasification tower and generate volatile matter and char through the pyrolysis and gasification, as well as a part of CO2 in volatile matter are absorbed by CaO to form CaCO3 and release heat for the pyrolysis and gaisification. The volatile matter is then introduced to the reforming tower for the catalytic reforming of hydrocarbon (CH4, Tar et al.) by contact with the CaO particles. The char and CaCO3 are introduced to the combustion tower. The char is burnt using air to heat the CaO particle and CaCO3 for decomposition to CaO. The heated CaO particles return to the reforming tower and the gasification tower through a cyclone. The CaO particle heated in the combustion tower provides heat to the catalytic reforming of hydrocarbon as CH4, tar et al. in reforming tower. The catalytic action of CaO for hydrocarbon reforming was investigated by using a two stage fluidized bed reactor which upper stage is reforming reactor, and lower stage is gasification reactor. Biomass/coal were fed in to gasification reactor, and volatile matter produced by biomass/coal gasification was raised in to reforming reactor. It also shows that, with CaO catalysis in the reforming reactor, no tar remained in the cooling zone and condenser from biomass gasification 2.5hr. However without CaO addition, tar generated terribly after biomass supply only 3 minutes. Liquid products from reforming reactor for biomass and coal gasification were collected by using ice water and liquid nitrogen baths. Total carbon (TOC) contained in the liquid product was analyzed. Tar contained in product gas from biomass and coal gasification were estimated by the amount of total carbon. The results shown that, only 5.7 mg/m(3) and 2.5 mg/m(3) tar contained in products gas for biomass and coal gasification, respectively. In this study, we also built a small hot 3-T CFB facility, to investigate the particle circulating and fluidization. And, the effect of CaO catalysis on steam reforming of hydrocarbons as methane, tar produced by biomass or coal gasification also be investigated. First we tested silica sand and CaO particle circulating in the three-tower CFB. Results shown that, three-tower type CFB can make stability particle circulating not only under room temperature and also circulated well under high temperature 800 degrees C. Control the differential pressure (Delta P) between exits of cyclone and reformer is much important for the stability of circulating of 3-T CFB. Particle circulating velocity, Gs was obtained about 100-200. (C) 2014 Published by Elsevier Ltd.