| Title | Purification of geothermal gases for use in pilot and demonstration scale facilities |
|---|---|
| Authors | S. Wiseman, R. Lawson, C. Martinez, A. Mitchelmore, A. Marsh, A. Blair, P. Siratovich |
| Year | 2025 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | geothermal gas, NCG treatment, pilot scale, demonstration scale, glasshouses, microbe cultivation, H₂S removal |
| Abstract | Geothermal non-condensable gases (NCGs) represent a promising and underutilised source of CO2 and CH4 that has potential application in horticulture and microbial cultivation, among other industries. However, these gas streams contain H₂S and mercury that can inhibit microbial and plant growth or compromise biomass safety. Effective removal of these substances is essential, yet many existing treatment technologies are prohibitively expensive, overly complex, or generate excessive solid or liquid waste—making them unsuitable for small-scale applications. This study draws on work conducted during the conceptual design phases of a pilot-scale photobioreactor utilising geothermal CO2 and CH4 to grow extremophilic microbes, and of a geothermal CO2 supply for glasshouse CO2 enrichment. The facilities considered are a 1000 L pilot-scale bioreactor, and a 1 hectare, venlo-style glasshouse. This study reviews purification technologies currently in use, assesses their viability at the relevant scales, and presents practical and low-cost approaches for purifying geothermal gases that are less well-known than systems for large-scale purification. The results demonstrate the technical feasibility of purifying geothermal gases for a pilot scale bioreactor without costly infrastructure, high chemical consumption, or the generation of substantial solid or liquid waste. The CO2 supply for a 1-ha glasshouse requires H2S removal on the order of 0.1 tonne/day, nearing the threshold where systems producing elemental sulphur are often recommended. Optimal process selection must therefore consider several factors specific to the glasshouse site. This study aims to support the development of sustainable bioproduction systems that utilise geothermal NCGs and the findings are generally applicable to pilot-scale and demonstration-scale efforts in gas purification and conversion. |