Twenty years ago on page 6 of the January 1988 edition of Power Engineering magazine, a full-age ad introduced “POWER-GEN ‘88” to the world. The inaugural event, which grew to become POWER-GEN International, was held at the Orlando Convention Center from December 6-8. The event covered fossil and solid fuel power generation, including coal, oil, natural gas, municipal solid waste and other waste fuels. “Paper abstracts are invited,” the ad read. That opened the floodgates, which, over the next 20 years, would see thousands of papers researched, written and presented at the world’s largest and most prestigious exhibition and conference for the power generation industry.
Power Engineering magazine has been PGI’s flagship media sponsor since the beginning 20 years ago. This year to celebrate PGI’s 20th anniversary we’ll take a look back at some of the issues and events that were making news. A lot of the same issues continue to make news today.
In the September 1988 issue, senior editor Douglas J. Smith wrote that the newest buzz word in the power engineer’s vocabulary was “repowering.” For many engineers, he wrote, repowering was just another part of life extension. He obviously was writing in an era before New Source Review would make it difficult to perform even routine maintenance let alone repower a generating unit.
But 20 years ago the U.S. Department of Energy was holding a positive view of the environmental benefits and potential increases in capacity from replacing older coal-fired boilers with fluidized bed or gasification combined cycle units.
“According to DOE,” the article said, “repowering today’s fossil-fueled power plants can lower sulfur pollutant emissions by 4.4 to 9.3 million tons per year, compared to 1980 emission levels.” If existing coal-fired plants were repowered, the article continued, and if clean coal technologies such as fluidized bed were used for new plants “we could see greater sulfur dioxide emission reductions by the year 2005.”
The DOE report cited in the article said that the cost of repowering a plant would be 35 percent to 60 percent less than refitting the plant with scrubbers or other conventional pollution control devices. Counting the benefits of higher plant reliability and fuel flexibility, the DOE report said a power plant could see emission reductions at “virtually no cost.” At the same time, repowering could boost electrical capacity by 19,000 MW to 156,000 MW.
The article went on to outline three potential repowering technologies:
- Integrated gasification combined cycle (IGCC)
- Pressurized fluidized bed combustion combined cycle (PFBC), and
- Atmospheric fluidized bed combustion (AFBC).
The article explained that IGCC and AFBC had been successfully demonstrated in smaller commercial applications, although PFBC had yet to be applied commercially in the United States. An IGCC repowering project would replace the existing coal-fired boiler with a gasifier, gas steam clean-up system, gas turbine and waste heat recovery boiler. Repowering with IGCC was expected to raise plant efficiency by about 3 percent while boosting plant output from 50 percent to 170 percent.
Combustion in an AFBC would take place in a furnace where a bed of solid coal and limestone would be suspended in a stream of upward flowing air. Besides controlling SO2 and NOX emissions, AFBC was also expected to increase a plant’s capacity.
In a PFBC combined cycle repowering, a pressurized fluidized bed combustor would suspend crushed coal or limestone in a stream of upward flowing pressurized air. Steam generated by the combustor would drive a steam turbine and hot gases exiting the pressurized furnace would be used to drive a gas turbine.
Turbulence of the coal and limestone (sorbent) in the fluidized bed, and the subsequent contact between the air and the particles, would allow efficient combustion and absorption of SO2 by the sorbent.
Several test projects were outlined in the September 1988 article. For example, a 160 MW bubbling bed unit was being demonstrated by TVA at a plant in Paducah, Ky. And a circulating fluidized bed was being demonstrated in a 110 MW repowering project at Colorado Ute’s Nucla plant. Repowering Nucla involved retrofitting a circulating fluidized bed and a 74 MW steam turbine generator. Three existing 12 MW steam turbine generators were retained and were powered by extraction steam from the new steam turbine.
A less advanced technology, the article said, PFBC combined cycle was being used in a 60 MW repowering demonstration at Ohio Power’s Tidd station. A new 16.5 MW gas turbine was to be installed. High-pressure combustion air was to be supplied by the gas turbine to the combustor. Simultaneously, steam generated in the combustor tube bundles were to drive the steam turbine. The project was to have been completed in 1990, in time for a three-year demonstration project.
Editor’s Note: A 2003 DOE review of the Tidd project reported SO2 removal efficiency of 90 percent was achieved at full load and NOX emissions were 0.150.33 lb/106 Btu. CO emissions were less than 0.01 lb/106 Btu and particulate emissions were less than 0.02 lb/106 Btu. On the operations side, combustion efficiency ranged from an average 99.3 percent at low bed levels to an average 99.5 percent at moderate to full bed levels. DOE also concluded that an ASEA Stal GT-35P gas turbine proved capable of operating commercially in a PFBC flue gas environment.