Technology Solutions Focused on Reliability, Short Lead-Time, & Ease of Maintenance
Drawing on the experience of the CCT team, a review was undertaken of a variety of technical approaches for the processing of raw digester or landfill gas into Renewable Natural Gas (RNG) which meets standards to assure:
The maximum generation of RINs with the highest methane recovery rate
The lowest overall capital expenditure
The lowest operating expenses and highest percentage uptime
The earliest time to full operations to maximize economics.
It is believed that this strategy allows the project owner to have a fully functional RNG facility that produces a high net recovery of methane (>95%) while keeping operational uptime high and capital / operations costs low and the earliest ‘online’ timing.
A unique design is created which assures the following components are properly addressed:
Efficient removal of H2S, siloxanes, and VOCs with minimal environmental issues
Assuring efficient application of operating horsepower
Providing for availability of spares and emergency service from the domestic market
Providing a platform for addressing environmental permitting issues and mitigating potential operational environmental issues
Selecting components with best delivery lead times
To achieve each of these, most of the CCT equipment packages include:
A fully regeneratable liquid H2S scavenger system. The discharge from the system is benign elemental sulfur. Therefore, no air emissions issues are created.
The primary compression skid includes two units which are each capable of handling 100% of the maximum inlet loading providing full redundancy for operational stability and maximization of RIN generation.
The siloxane and VOC removal system combines reduction of the process dewpoint to -20°F with removal of siloxanes down to ppb levels by use of deep chilling technology. The captured siloxanes and VOCs are removed in an aqueous discharge stream which is of Publicly Owned Treatment Works (POTW) quality or suitable for septic discharge. Therefore no air emissions issue is created. The unit has two refrigeration compressors operating in parallel to assure the unit is never completely out of service. This system removes up to 99% of inlet siloxanes and VOCs and with additional filtration, the system can achieve ppb outlet levels.
The CO2 separation will be achieved using a selective membrane kit with a relatively quick delivery time. With no moving parts, the maintenance factor for membranes is very low. The alternative is a unique system utilizing an inhibited MEA amine system followed by a mol sieve-based dryer.
To maximize utility while simultaneously mitigating overall capital expenditures, CCT is utilizing a methane liquefaction approach to encompass the removal of entrained nitrogen and oxygen while maximizing the percentage of inlet methane captured for sale. This approach has a number of positive elements including elimination of Thermal Oxidizer (TO) units with attendant air emissions, elimination of a Nitrogen Rejection Unit (NRU) system and Deoxygenation (DeOx) unit with air emission issues, and recompression to pipeline requirements. To maximize project economics, the Liquid Natural Gas (LNG) product may either be trucked offsite for direct use as motor fuel and / or revaporized into an existing natural gas pipeline using the coefficient of expansion of the LNG in lieu of further compression.