The project will design, build, and test a high-pressure linear-motor-driven leak recovery compressor for the cost-effective recovery of methane leaks within the transmission, storage, gathering, and processing sectors of the natural gas value chain.
Gas Technology Institute (GTI); Des Plaines, Illinois
University of Texas Center for Electromechanics; Austin, Texas
Large reciprocating and centrifugal compressors are central to the natural gas value chain. Across the U.S., around 8,000 compressors move gas through over 250,000 miles of large transmission lines and store it underground in high-pressure geological formations for use during high demand periods. These compressors are concentrated at about 2,000 compressor stations where they are maintained and operated year-round. These compressor stations also contain pneumatic controllers, storage tanks, and purge systems that are required to operate the compressors or direct flow in and out of the station.
These compressor stations represent potential methane emission sources, and though relatively small in number, they contribute a disproportionately large percentage (about 20%) of the total methane emissions from the entire value chain. The primary challenge preventing the capture and mitigation of these leaks is not a lack of will or desire, but rather the absence of a suitably engineered and priced solution.
The project team will design, build, and test a fully functional linear-motor-driven leak recovery compressor and package it onto a full leak recovery system designed specifically to gather and recompress methane emissions from midstream transmission and storage compressor stations. The linear motor leak recovery compressor is uniquely suited to provide variable flow capabilities to match the variable leak rates inherent to this application. It is being designed for a high-pressure discharge to compress the gas back to midstream operating pressures, often over 1,000 psig. The team’s goal is to develop a unit that is less expensive than current compressors while still capable of reaching a discharge pressure of 1500 psig or more.
Figure 2. Simulated results using control strategy based on inlet pressure. The mass flow graph is showing the leak rate into the leak recovery buffer tank which varies both sinusoidally and using a step change. Input tank pressure shows the variation in the suction tank pressure as the leak recovery compressor control system adapts to the changing leak rate. The suction pressure is always maintained within 500 pascals (2 inches water column) of the target pressure, ensuring vents at compressor stations are not over-pressurized.
The project team is running additional simulations with different control strategies to identify the most effective approach.
GTI is working to finalize the compressor design using 3 stages of compression. The design will include necessary force balance, flow, heat transfer, and system integration/maintenance considerations. GTI is starting sourcing of all the components required for preliminary testing, including motor, compressor, and balance of plant components.