Biomethane Upgrade

Application Summary

Analysis Point Analyte Typ. Range Suitable Analyzer
Combined Heater
and Power Generation
H2S 0-10 PPM  OMA-300 Process Analyzer
CH4 70-100% MicroSpec MCP-200 Infrared Analyzer
CO2 0-1%

Introduction

Biogas production can be generated through a few different processes. The more common production methods come from capturing gas from the natural decomposition in landfills, and through decomposition of biomass collected specifically for use in biogas generation. Landfill gas (LFG) is a useful product of solid waste disposal. Landfills naturally generate CH4 and CO2 as waste decomposes over time. Biogas generation from a biomass feedstock, by contrast, is a dedicated process through which either waste biomass or biomass specifically grown for biogas production is digested to methane. The gas from both sources can be collected and, once it is purified, it can either be used to supplement natural gas, or it can be used as its own alternative fuel source.

Biomethane is created by upgrading the biogas produced by anerobic digestion of organic material. Biogas has a relatively low heating value as it typically only contains around 50% methane, with the balance being CO2 and other minor components. For the biogas to be sent to the natural gas grid or for it to be used as a natural gas replacement fuel, the methane concentration must be increased. This is typically done through either a sorption technique where the CO2 is scrubbed from the gas, through a membrane separation, or through a cryogenic separation. The upgraded biomethane typically contains 90-100% methane.

The sales-quality biomethane must meet local regulations in order to be injected into a pipeline. These regulations include methane, CO2, and H2S requirements. Methane needs to be kept at a high level to ensure that the heating value remains high enough for use as a replacement for natural gas. Lower heating values can cause issues with the equipment using the gas. H2S is an extremely dangerous chemical. Exposure can be lethal at around 500 PPM, and it is explosive at higher concentrations. H2S is also corrosive and can lead to sulfur stress cracking. For these reasons it is a closely monitored contaminant with permissible limits typically around 4 PPM. CO2 is another acidic gas. Higher levels should be minimized to protect downstream equipment in the case of higher moisture levels, and because it lowers the heating value. It is important that these specifications be met and closely monitored for variations.

The OMA-300 process analyzer continuously measures 0-10 PPM H2S in the biomethane stream to the natural gas distribution network. Monitoring the H2S concentration ensures that the sulfur is being kept below local regulatory levels. The MCP-200 continuously measures CH4 and CO2 in the biomethane stream. Monitoring the CH4 and CO2 concentration ensures that the gas maintains a consistent BTU value. Response time is critical for the biomethane upgrading system to ensure the biomethane being produced meets the regulations. An online analyzer at this location allows for rapid adjustments to keep the plant functioning at peak performance.

System Benefits

  • Continuously measures 0-10 PPM H2S, 70-100% CH4, and 0-1% CO2 in the upgraded biomethane stream.
  • Totally solid-state build with no moving parts — modern design for low maintenance.
  • Fast response time, analyzer updates reading in under 5 seconds.
  • Combined sampling system and controller allows for a cost-effective solution.

Example Biogas Sample Conditioner

0-10 PPM H2S, 0-1% CO2 and 70-100% CH4 in the combined biogas stream. Key features for this application include:


  • Stainless steel components/fittings & Viton or Kalrez gaskets for corrosion resistance.
  • Particulate filtration to remove solids that could influence the measurement.
  • Liquid filtration to remove droplets and mists that could influence the measurement.
  • Integrated MCP-200 analyzers housed in explosion-proof enclosures.

Further Reading