Screening method for solvent selection used in tar removal by the absorption process

Abstract

The aim of this paper is the study of the treatment of flue gas issued from a process of biomass gasification in fluidized bed. The flue gas contains tar which should be selectively removed from the fuel components of interest (e.g. H₂, CO and light hydrocarbons) to avoid condensation and deposits in internal combustion engine. The chosen flue gas treatment is the gas–liquid absorption using solvents, which present specific physicochemical properties (e.g. solubility, viscosity, volatility and chemical and thermal stability) in order to optimize the unit on energetic, technico-economic and environmental criteria. The rational choice of the proper solvent is essential for solving the tar issue. The preselection of the solvents is made using a Hansen parameter in order to evaluate the tar solubility and the saturation vapour pressure of the solvent is obtained using Antoine law. Among the nine families of screened solvents (alcohols, amines, ketones, halogenates, ethers, esters, hydrocarbons, sulphured and chlorinates), acids methyl esters arise as solvents of interest. Methyl oleate has then been selected and studied furthermore. Experimental liquid–vapour equilibrium data using bubbling point and absorption cell measurements and theoretical results obtained by the UNIFAC-Dortmund model confirm the high potential of this solvent and the good agreement between experimental and theoretical results.

Keywords:

• biomass
• tar removal
• gas–liquid absorption
• solvent screening
• vapour–liquid equilibrium