Natural gas pipeline compressor stations, like this one on the Trailblazer Pipeline in northeastern
Colorado, offer strong opportunities for clean and renewable energy from waste heat recovery
Natural gas compressor stations using compressors driven by gas turbines or internal combustion engines offer strong opportunities for waste heat recovery.
Transporting natural gas from producers to consumers requires an extensive and elaborate distribution system, which consists of a complex network of pipelines. Compression stations, usually placed at 40 to 100 mile intervals along the pipeline, are required to ensure proper pressurization of natural gas. The natural gas enters the compressor station, where it is compressed by a turbine, or engine. Compressor stations move on average about 700 million cubic feet (MMcf) of natural gas per day, with the largest moving upwards of 4.6 billion cubic feet (Bcf) per day.
Although natural gas compressor stations vary widely in size and layout, the basic compressor systems are comprised of two components - the "mechanical drive" that provides the shaft power that drives the compressor, and the "compressor" itself. The mechanical drive can be an internal combustion (IC) engine, gas turbine, or electric motor. The compressor itself can be a reciprocating, centrifugal, or screw compressor. IC engine and gas turbine drives burn natural gas from the pipeline. Electric motor drives can be used on any type of compressor but require reliable electrical power supply.
Facts and Figures
According to U.S. DOE natural gas pipeline data, the U.S. features:
- More than 210 natural gas pipeline systems.
- 305,000 miles of interstate and intrastate transmission pipelines
- More than 1,400 compressor stations that maintain pressure on the natural gas pipeline network and assure continuous forward movement of supplies (see map).
- More than 11,000 delivery points, 5,000 receipt points, and 1,400 interconnection points that provide for the transfer of natural gas throughout the United States.
- 24 hubs or market centers that provide additional interconnections.
- 400 underground natural gas storage facilities.
- 49 locations where natural gas can be imported/exported via pipelines.
- 8 LNG (liquefied natural gas) import facilities and 100 LNG peaking facilities
Opportunity for Waste Heat Recovery
Compressor stations that use gas-fired mechanical drives are potentially very good candidates for waste heat recovery. Natural gas-fueled engines and turbines (mechanical drives) generate heat as a byproduct. Only about one third of the fuel energy consumed by an engine or turbine ends up as useful mechanical power, with the remaining two-thirds rejected as hot exhaust or in engine cooling systems.
Most of the waste heat associated with gas turbines is in the turbine exhaust. This coupled with the high exhaust temperature (850 to 1100°F) makes them particularly attractive for waste heat recovery. Waste heat recovery from IC engine exhaust (which ranges from 500 to 1200°F) is also practical, although the exhaust gases typically contain only about 40% of the waste heat. Most of the heat from IC engines is removed in the cooling water jacket, producing a low-quality heat source at about 140°F.
In either case, the excess heat produced by the compressor drive can be turned into renewable energy using the Rankine cycle, producing no excess pollution and requiring no additional fuel. More traditional waste heat recovery systems or CHP systems may also be practical if the site has hot water, steam or other thermal loads.
Highline Electric Association, a cooperative serving northeastern Colorado, installed a 4-MW pollution-free and fuel-free waste heat recovery system at a compressor station on the Trailblazer pipeline. The system is eligible as a renewable energy under Colorado’s renewable portfolio standard, and it saves the co-op $600,000 per year. Read more...