Amoco Production Company installed two of its first onshore cogeneration units during late 1983 and mid-1984 in west-central Wyoming, USA. These 2.4 megawatt cogeneration units were placed in an oil field that uses steam and hot water injection in the recovery of a viscous crude oil and in the operation of a natural gas sweetening plant that uses steam for its heat-medium requirements. This paper examines the operating performance of both units over the past six years, improvements made in these systems to achieve high online operating factors and the economic justification for their installation.
Cogeneration is defined by the United States (USA) government as the dual production of electricity and thermal energy from a single fuel supply. One of the provisions from the 1978 Public Utility Regulatory Policies Act (PURPA) requires that the state utility regulatory agencies must allow co-generators the right to interconnect with public utility companies for the purpose of providing back-up electrical power to the co-generator. Because of this provision in PURPA, as well as other economic incentives, Amoco was able to justify the installation of two, small power, cogeneration units. The first began operation in December, 1983, in a mature, heavy oil reservoir stimulated by an active steam flood. The second unit became operational in June, 1984, in a natural gas sweetening plant using steam for the regeneration of mine in its hydrogen sulfide extraction process.
Both of Amoco's cogeneration units use a nominal 2.4 megawatt, industrial grade, natural gas-fired, turbine to convert thermal energy to electricity. A cut-away of the turbine is shown in Figure 1. Ambient air enters through an inlet air filtration system and passes into the air compression section of the turbine. Here, the air is compressed from atmospheric pressure to 105 psig (774 KPa) through 11 axial flow, compression stages. As the air leaves the compression section, it is channeled either into the fuel combustor or around the combustor for internal engine cooling. Natural gas enters the turbine through one of ten fuel gas injectors. One of the fuel injectors also contains a spark igniters to start ignition of the fuel at 15 percent of full engine speed. After ignition, combustion is then self-sustaining through all the fuel injectors. The engine, operating at about 1,120 °F (604 °C), converts this continuous thermal energy process to mechanical energy by dropping both pressure and temperature of the combustion gases across the three stages of the turbine rotor section. These gases then leave the turbine at about 800 °F (427 °C) and enter the waste heal recovery device. The turbine rotor, which is turning at 15,000 revolutions per minute (RPM), transmits the mechanical energy back through the single shaft to the gearbox. At the gearbox, output shaft speed is reduced to 1,800 RPM before entering the generator, where the mechanical energy is converted to electricity. A side view of the different components in the cogeneration system is shown in Figure 2.