Inert Gas Purging of Biogas Systems

Digester gas and air are a dangerous mix. Any time a digester, a gas line, or a gas storage vessel is opened up or brought back online, there is a point where the two can meet. Inert gas purging puts nitrogen between them.

We write the purge plan and stand with your operators while it is carried out, so digesters, gas piping, and gas storage come out of service and go back into service safely.

When Purging Is Needed

  • Digester cleaning. Before a digester is opened and entered for cleaning.

  • Cover or piping repair. Any work that opens the gas space or breaks into a gas line.

  • Startup. Returning a digester or gas system to service, or bringing a new one online.

  • Decommissioning. Taking a digester or gas system out of service for good.

How We Do It

  • Purge gas. Nitrogen.

  • Purge plan. Every purge starts with a written plan of action for your system. Each segment (digester gas space, cover piping, gas header, lines to the boiler and flare) is measured, its volume is calculated, and the nitrogen needed is worked out before anyone opens a valve. The plan sets the isolation, the injection and vent points, the sequence, and who does what.

  • Monitoring. Gas detection equipment is calibrated before the work and assigned to the people who need it. The purge is finished when gas readings at the vent reach the end point set in the plan.

  • Control. Nitrogen is introduced slowly while pressure and flow are watched, so nothing is over-pressurized.

  • Site safety. Non-sparking tools and fittings, hoses rated for the service, and barricades and signs around the work and the vent. Everyone is briefed on the plan and their role before the purge starts.

  • Both directions. Out of service: gas is replaced by nitrogen, then air. Into service: air is replaced by nitrogen, then gas.

  • Standards. Our procedures follow the American Gas Association (AGA) manual Purging Principles and Practice and the U.S. Environmental Protection Agency (EPA) AgSTAR Anaerobic Digester/Biogas System Operator Guidebook.

What You Receive

  • Written purge plan. A purge plan written for your system, with volumes, injection and vent points, and step-by-step procedures.

  • Onsite direction. We are at the plant during the purge, working alongside your operators.

  • Documentation. A record of the purge as it was carried out.

Past Projects

We have purged multiple anaerobic digesters and renewable natural gas (RNG) systems, at pressures up to 175 pounds per square inch (psi).

If you have a digester coming down or a gas system coming online, get in touch before the schedule is set.

Talk to us about a purge