Moving natural gas through long-distance pipelines requires substantial energy, and much of that energy is lost when the gas must be reduced in pressure before it reaches end users. But a new project may demonstrate a way for gas transmission companies to recapture some of that energy and improve the efficiency of the letdown process, in addition to generating electricity that can be used onsite or sold to the grid.
Danbury, Conn.–based FuelCell Energy (FCE) and UIL Holdings Corp., the parent company of several Connecticut utilities, are collaborating on a facility that will replace the boilers and pressure reduction valves traditionally used to reduce gas pressure during letdown with a fuel cell and a turboexpander.
Normally when high-pressure gas arrives at its destination, it is bled through a valve to reduce the pressure. This pressure reduction absorbs substantial amounts of heat, which is normally supplied by gas-fired boilers that pre-heat the incoming gas.
FCE’s project, known as a Direct Fuel Cell–Energy Recovery Generation (DFC-ERG) system, instead replaces the valve with a turboexpander that is attached to a generator, producing about 600 kW of electricity. A small amount of gas is passed through a fuel cell, and the heat generated by the fuel cell replaces the heat from the boiler system. In addition, the fuel cell generates another 2.8 MW of electricity. Since the fuel cell can achieve efficiencies of up to 70%, it requires less gas than the boiler system in addition to producing far lower emissions.
One other benefit of the arrangement is that the distributed power it generates tends to follow demand peaks. As gas demand increases—and more gas flows through the system—the turboexpander and fuel cell will generate more power.
A video created by pipeline company Enbridge, the North American distributor of the DFC-ERG system, explains the process in more detail.
FCE and UIL announced on Dec. 4 that they will install the first facility at a gas pressure-reduction station in Glastonbury, Conn. The project will be owned by UIL but operated by FCE, and the power will be sold to Connecticut Power & Light under a 20-year power purchase agreement. The project is expected to come online late this year.
—Thomas W. Overton, POWER associate editor (@thomas_overton, @POWERmagazine)