Biogas desulfurization: Performane study of a full-scale scrubber for biogas desulfurization
In this study, a set of full-scale two-stage-in-series scrubbing tower was constructed to test its performance for desulfurization of biogas from three anaerobic UASB (upflow anaerobic sludge blanket) reactors of a wastewater plant for treating corn-syrup processing wastewater. Each stage of the absorbing towers was constructed from a 0.6m ¡Ñ 6 m (I.D. ¡Ñ H) plastic column packed with plastic packings (4¡¨ K6 Heilex-Type or 2.5¡¨ Crown-Biopacks with packing heights of 5 m and 3.65 m, respectively). Effluent from the activated sludge sedimentation tank of the wastewater plant was used as a scrubbing liquid and the tower effluent liquid was discharged into the activated sludge tank for oxidation of the absorbed hydrogen sulfide.
Results of a continuous operation period of 20 weeks indicate that H2S of 380-19,000 ppm in the biogas could be reduced to 1-2,100 ppm by the scrubbing towers with superficial liquid and gas velocities of GL = 13.2-28.1 and GV = 306-642 m/h, respectively. On an average, the effluent gas contained a H2S concentration of less than 300 ppm and the removal efficacy was more than 96%. Results also indicate that as pH of the scrubbing liquid increased from 7.7 to 8.8, the overall H2S removal efficacy raised from 86 to 98%. About 1/3 of the absorbed H2S-S was detected as H2S-S and SO4-2-S in the tower effluent. The rest was supposed to be as elemental sulfur in a slimy form which sticked to the packing surface. This might be the reason for the increasing pressure drop with the operation time.
A set of performance and gas-liquid equilibrium equations were proposed to estimated the influence of liquid pH, gas and liquid flow rates, and packing height on the H2S removal efficacy. Calculation results indicate, at 30oC, the minimum liquid/gas ratios (L/G)min for the absorption are 0.043 and 0.014 m3/m3, respectively, for fresh absorbing liquids with pH = 8.0 and 8.5. Based on the proposed equations and the experimental data, the volumetric mass-transfer coefficient Kya for H2S absorption in the towers could be expressed approximately as Kya =1.15¡Ñ1017GV1.0GL-3.0 with GV =304-644 and GL = 15.1-28.1 m3/m2.h, and liquid pH 7.7-8.6. It was supposed that too much liquid loading leads to a decrease in the specific area a for mass transfer which results in the Kya decrease.
Advisor:Ju-Sheng Huang; Ming-Shean Chou; Mei-Juan Syu
School:National Sun Yat-Sen University
School Location:China - Taiwan
Source Type:Master's Thesis
Keywords:desulfurization absorption biogas hydrogen sulfide scrubbing
Date of Publication:07/13/2001