Dessulfuração de biogás da metanização da vinhaça: uma nova abordagem para remoção de altas concentrações de H2S

Abstract

This study aimed to develop a chemical desulfurization system using sodium hydroxide coupled to a system with biological regeneration of hydroxyl, in order to obtain high H2S removal efficiencies associated with reduced use of alkalizing agent in the system, configuring a system for removal of high concentrations of H2S from biogas. The research included the development of a desulfurization pilot plant, which was installed at Usina Monte Alegre (Adecoagro's Group) where is in operation a vinasse methanation pilot plant (Methanum´s technology), with constant generation of biogas to supply the experiment. The desulphurization plant developed was comprised of the following components: venturi absorption tower (TAV), biological regeneration tower (TRB) and lamellar settler (DL). The study was based on two main experiments, namely: i) definition of the ideal pH threshold at which the system has the largest molar fraction disulfide in the solution; ii) TAV's continuous operation associated with the biological regeneration of hydroxyls. The first experiment demonstrated that the corresponding alkalinity 5x10-3 mol L-1 was adequate to maintain the pH around 8.0, reducing the competition for hydroxyls due to the release of the CO2 present in the biogas and contributing to the development of sulfo-oxidant bacteria (suitable pH for its development). The second experiment was carried out in 145 days. The H2S concentration in the biogas ranged between 15,150 and 26,277ppmV and the maximum load applied was 17.4 kg.H2S.m3.h-1, with an average H2S removal efficiency of 99.8% for this period. In addition, an increase in the methane concentration in the biogas of around 10.7% was observed. Sulfoxidizing organisms were identified in the biological system, which helped to maintain the pH of the medium and promoted the regeneration of hydroxyl, in a manner that the demand of NaOH of the system was 1.4% compared to the stoichiometric demand required for a standard chemical system. The proposed system sets up a new biological desulfurization process approach, with the main advantage of getting high H2S removal efficiency, avoid the dilution of biogas with O2 and N2, and promote increased concentration of methane in the biogas.