The BioChemical DeSulphurization Process (BCSP) from HydroThane is a simple biological process that removes hydrogen sulphide (H2S) from biogas with a minimal use of chemicals.
The biogas is fed into vertical scrubber column(s) with packing media inside. In counter current flow, a slightly alkaline washing liquid is used for absorbing the H2S and cleaning the biogas (reaction 1).
(1) H2S + NaOH ↔ NaHS + H2O
The HydroThane STP ® BCSP can be seen as a combination of a conventional chemical scrubber and a biological oxidation step. The sulphide rich washing liquid is forwarded to the aeration tank. A controlled amount of air is pumped in to provide sufficient oxygen for the sulphur oxidizing bacteria.
The sulphur oxidizing micro-organisms (thiobacillus) in the aeration tank metabolize the dissolved sulphide into S (elemental sulphur) mainly and some H2SO4 (sulphuric acid) following:
(2) NaHS + ½O2 ↔ S0 + NaOH
(3) 2 NaHS + 4O2 ↔ Na2SO4 + H2SO4
The main part of the alkalinity consuming H2S absorption in the scrubber (reaction 1) is compensated by the oxidation reaction to elemental sulphur (reaction 2). The small amount of generated H2SO4 (from side reaction 3) needs to be neutralized by means of caustic dosing. Preventing accumulation of salts (e.g. Na2SO4) a small bleed stream is required. The produced sulphur (in the reactor tank) is separated from this effluent bleed stream by means of a settler unit. These separated, harmless, residual products can be directly discharged or reused.
The HydroThane STP® BCSP is accomplished in a closed reactor system and reduces the odour, toxicity and corrosiveness of the biogas.
The benefits from the HydroThane STP® BCSP are:
• Extreme low operational costs (limited caustic consumption)
• Hardly no nutrient requirement (selective biological process)
• Low energy requirement
• Simple and safe to operate (no hazardous chemicals used/formed)
• Low maintenance