Simultaneous removal of hydrogen sulfide and ammonia using a combined system with absorption and electrochemical oxidation

Abstract

Hydrogen sulfide (H₂S) and ammonia (NH₃), common impurities in biogas, need to be removed before utilizing it. In this study, a combined system, which consisted of an absorption column and an electrochemical oxidation reactor, was tested to simultaneously remove these impurities. The effects of the current density and the chemical loading rate on the system performance were investigated. Firstly, the mass transfer coefficients for the absorption column were determined at various gas flow rates. More mass of NH₃ was transferred, compared with that of H₂S, because of its higher solubility. In the electro-oxidation reactor, reactive chlorine species (RCSs) were generated and oxidized both H₂S and NH₃; however, NH₃ started to degrade only after H₂S was completely eliminated. At a current density of 400 A/m², the current efficiencies of H₂S and NH₃ were 23.1% and 5.9%, respectively. In the combined system, the removal efficiency of H₂S was closely related to the mass ratio of the H₂S transferred and the RCSs generated. The removal efficiency of H₂S was greater than 99% when the ratio was less than 1. The mass transfer potential and the oxidation kinetics should be balanced to improve the system performance for the simultaneous removal of H₂S and NH₃.

Keywords:

• biogas pretreatment
• mass transfer
• electro-oxidation
• reactive chlorine species
• model simulation

Additional information

Funding

This work was supported by Korea Environment Industry & Technology Institute (KEITI) through Public Technology Program based on Environmental Policy Program, funded by Korea Ministry of Environment (MOE) (2017000700002). It was also supported by the Technology Development Program to Solve Climate Changes of the Korean National Research Foundation (NRF) funded by Korean Ministry of Science, ICT (2017M1A2A2086642).