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Biogas and Digester Gas Upgrading

Biogas from digesters (waste water treatment plants and other digesters) typically have a methane (CH4) content of about 50-60% with the remaining gas being mostly carbon dioxide (CO2) and saturated moisture.  Hydrogen sulfide (H2S), Volatile Organic Chemicals (VOC) and siloxanes generally amount to less than 0.5% of the biogas.

The common industry approach to upgrading the gas, pictured below, consists of using the following process flow:

  • Flow into H2S removal skid using a non-regenerable fixed bed media which is replaced on a regular basis (usually 3-4 months)
  • From the H2S removal skid, flow into a Refrigerated Dryer skid using a cooling process to remove the bulk of the water
  • Compress the resulting gas to about 200 PSIG 
  • Feed the compressed gas into a Pressure Swing Adsorption (PSA) dryer system to remove the water down to pipeline standards
  • Using a VOC Trap, condense the Volatile Organic Compounds out of the flow to protect the downstream membranes
  • If siloxanes are present in the feed gas, the gas flows to a non-regenerable carbon-based or alumina-based adsorbent bed vessel to remove siloxanes, which is also regularly replaced 
  • Multiple stages of membranes and associated compression to remove the CO2
Conventional Membrane Approach to Biogas Upgrading
This results in a complicated system, forcing the owner/operator to understand and maintain multiple technologies.  The Guild Associates approach is to use the Molecular GateTM advantage in a single step process.  The process flow is much simpler:
  • Compress the gas to 100 psig
  • Remove the bulk of the moisture using a cooling process, reheating the resulting gas with waste heat from the compressor
  • Remove moisture, CO2, siloxanes, H2S and VOCs in a Molecular Gate Pressure Swing Adsorption system
  • Deliver the resulting product gas to the local grid at 90 psig.  

This simple-to-operate technology has been installed at waste water treatment plants and commercial digesters such as hog farms and rendering plants.  The technology offers the benefits of:

  • Single step removal of impurities
  • All media is regenerated – no need for replacement
  • H2S completely removed from any level up to 7000 PPM
  • Siloxanes removed to non-detect levels
  • Dehydration to CNG requirements without a separate dryer required
  • No chillers required
  • Dry system operation, with no waste product other than condensed water from compression
Operation and maintenance is much simpler:
  • Automatic start-up and shutdown at a push of a button
  • Automatic product purity control without operator attention
This is Biogas Upgrading Made Easy!  Contact Guild Associates for a evaluation of your site for the Molecular GateTM advantage!

Do you have a Biogas project in mind? Download our CUSTOMER QUESTIONNAIRE, fill it out and send it to us at Information Requests.