Removal of NH3 from Biomass Gasification Producer Gas by Water Condensing in an Organic Solvent Scrubber

Producer gas from biomass gasification contains NH3, H2S, and high molecular weight organic compounds (tars), which must be removed prior to the gas utilization step. A highly effective approach toward the removal of tars is absorption into organic solvents. As a secondary effect, condensation of water takes place in the scrubber, allowing removal of gaseous trace components such as NH3 and H2S from the gas stream. The present work focuses on the coabsorption of NH3 and CO2 into condensing water. The general aim is to decrease the clean gas NH3 concentration by appropriate adjustment of the operating parameters without additional gascleaning steps. A mathematical model of a countercurrent column, which covers mass and energy balances, gas-liquid equilibrium, and electrolyte dissociation, is presented. The scrubber geometry does not enter the model; therefore, it promises universal applicability. Property data on electrolyte dissociation and Henry’s law constants are taken from the literature. A computer code has been developed in order to study the sensitivity of NH3 removal toward certain process parameters. The results agree well with data measured at the 2000 Nm3/h (gas load) scrubber at the biomass gasification plant in Guessing, Austria.