Evaluation of a Venturi gas scrubber operating with sodium hydroxide solution for desulphurization of biogas with high H₂S concentrations

ABSTRACT

The methanation process has been successfully used as a biological treatment method for different effluent typologies. For biogas to energy conversion, the hydrogen sulfide (H₂S) is the most important compound that must be removed. The methanation of vinasse, which is the major effluent of the sugar and ethanol industry, results in a biogas with hydrogen sulfide concentrations that might exceed 30,000 ppmV. The concentrations may vary considerably according to the operational conditions of the production process. Chemical desulphurization processes are presented as an alternative that combines robustness and provides better operational process control. Moreover, the chemical desulphurization does not result in dilution of the methane concentration, which is side effect noticed in the biological desulphurization processes. However, the main disadvantage of the chemical desulphurization is exactly the high demand for chemical compounds, which results in high operational costs. The present research investigated the technical feasibility of applying a chemical desulphurization process to treat biogas with high hydrogen sulfide concentrations; the research also aimed to determine the sodium hydroxide (NaOH) concentration in the aqueous medium, as the NaOH presence enables high efficiency of hydrogen sulfide removal and allows the effluent regeneration by sulfo-oxidant microorganisms. The experiments were carried out using a Venturi absorption tower with a NaOH chemical solution of 5.00 x 10^-2 mol.L^-1. In the pH range favorable to this microorganisms, the H₂S removal efficiency varied from 99.3 to 99.9%. It was observed that it is possible to achieve maximum efficiency of removal of H₂S using solutions of 5.00 x 10^-3 mol.L^-1 NaOH, obtaining an effluent with proper pH to grow sulfo oxidant microorganisms. Moreover, it was verified that carbon dioxide significantly influenced the competition for the hydroxyls present in the solution.

Keywords:
chemical desulphurization; Sodium Hydroxide; biogas; Venturi; vinasse.