Biomass Gasification with Steam in Fluidized Bed:  Effectiveness of CaO, MgO, and CaO−MgO for Hot Raw Gas Cleaning

Abstract

The upgrading of the raw hot gas from a bubbling fluidized bed biomass gasifier is studied using cheap calcined minerals or rocks downstream from the gasifier. Biomass gasification is made with steam (not air) at 750-780 °C and about 0.5-1.0 kg of biomass/h. Calcined solids used are dolomite (MgO-CaO), pure calcite (CaO), and pure magnesite (MgO). Variables studied have been temperature of the secondary bed (780-910 °C), time of contact or space-time of the gas (0.08-0.32 kg‚h/m 3 n), and particle diameter (1-4 mm) and type of mineral. Their effects on tar conversion, tar amount in the exit gas, product distribution, and gas composition are presented. Using a macrokinetic model for the tar disappearance network, the activities of the stones are expressed by their apparent kinetic constant. Apparent energies of activation for tar elimination (42-47 kJ/mol) and preexponential and effectiveness factors are given for all tested solids of which the most active is the calcined dolomite.

Synthesis of Transportation Fuels from Biomass: Chemistry, Catalysts, and Engineering

“…Other researchers who have studied dolomite catalysts include Simell and coworkers [89][90][91] and Corella and co-workers. 92,93 The operating conditions for using dolomite catalyst are temperatures from 700 to 100°C and space times from 0.007 to 7 s. 56 Other nonmetallic oxide catalysts used for this reaction include MgO, 87 CaO, 87 and olivine (a magnesium aluminosilicate). 58,94,95 Ni-based catalysts are used industrially for steam reforming of naphtha and methane, 96,97 so it is not surprising that Nibased catalysts have proven to be very effective for hot gas conditioning of biomass gasification product gases.…”

The Influence of Feedstock Type and Operating Parameters on Tar Formation in the Process of Gasification and Co-Gasification

“…Alkali and alkaline earth metal compounds (salts and oxides) are natural, widely available and price competitive compounds. The catalytic activity of dolomite [16,[63][64][65][66][67][68], limestone [65], olivine [9,64] and ilmenite [69] has been widely studied. The comparative research work [64] showed that dolomite was the most active among all the mineral catalysts, even when short residence times were applied.…”

Fluidized Bed Gasification as a Mature And Reliable Technology for the Production of Bio-Syngas and Applied in the Production of Liquid Transportation Fuels—A Review

“…Delgado et al [86] reported that of the three natural rock minerals applied in the downstream fixed bed reactor for the upgrading of the product gas, calcined dolomite (CaO-MgO) showed the highest catalytic activity on tar cracking, followed by pure calcined magnesite (MgO) and calcined calcite (CaO). Also relatively low deactivation was observed for tar concentrations below 48 g m 3 n (which is even higher than the typical tar concentrations measured in reasonably operating (C)FB gasifiers), at temperatures above 800…”

“…An additional advantage was the simultaneous coke formation and its elimination by steam gasification, leading to the prolonged lifetime of the catalyst. The integration of the heats of CO 2 adsorption reaction and water-gas shift reaction into the complex network of (endothermal) gasification reactions will lead to the improvement of the product gas in terms of higher hydrogen yield and reduced amount of tar [64,83,[86][87][88][89]. Hanping et al [90] performed air-blown biomass gasification tests in a small-scale (ca.…”