Challenge:

The gas bag was required, at a minimum, to have a capacity of 440m3 above ground.  To do this we needed to build and install a raised platform. Other requirements were that it needed to;

• Be a concrete construction
• Enable access to remove pipework from the Gas Bag
• Leave an open gap between lower and upper platforms
• Be accessible for operations and maintenance
• Include all necessary hand-railing and access metal works
• Include all associated blowers and instrumentation (necessary to meet the needs of the biogas system pressure balancing)
• Include all necessary equipotential earthing and bonding
• Include lightning protection around the Gas Bag
• Have suitably sized Catch-Pots at all system low points, as required
• Ensure all Catch-Pots were located above ground (to eliminate any confined spaces)
• Ensure all Catch-Pots have hose connections for replenishment (correlating to site connection and/or providing further hose points as required)
• Have associated pipework of a suitable material, suitably sized and supported
• Have all necessary isolation, purge points and pressure relief valves between Digesters, Gas Bag and Users
• Ensure pressure relief valves have mechanical traps
• Include all necessary cabling and cable ducting

• Ensure all connections have blank flanges fitted
• Relocate existing flow meters (if suitable) to the new pipework from each digester to the Gas Bag
• Provide maintenance access to the flow meters
• Relocate existing emergency slam shut valve (if suitable) to new pipework to users
• Have all required MCC modifications
• Have removable Gas Bag Bypass pipework (to divert flow from Digesters to Flare for maintenance of Gas Bag)
• Have existing PLC coding modified to control the Gas Handling System and decommissioned Gas Bell
• Modify SCADA screens to add new Gas Bag and system and remove existing Gas Bell system
• Extend existing Zone fencing to accommodate new Gas Handling system
• New Gas Bag compound and pipework areas to be finished in concrete
• Suitable benched to existing drainage to allow the compound to be self-draining
• Include an extension of the drainage system, as required
• Provide new Zone signage for the Digester & Gas Bag compound
• Have existing foam isolation valves removed and subsequent PLC code from the digester outlets
• Be located at a safe distance from the Flare and other potentially hazardous systems

Solution:

A detailed Commissioning Plan was established within four weeks of the contract award and included, but not limited to:

• Decommissioning of existing Gas Bell
• Purging and making safe
• Sludge management and feeding plan
• Operational interface during commissioning of new system and decommissioning of existing system
• Connection of all new pipework
• Pressure testing
• Full commissioning and testing of the new Gas Bag
• 21 elapsed day reliability period

Results:

Following this we worked collaboratively with Yorkshire water to provide a detailed sludge management and feeding plan.