Cutting the scale for coal gasification
Researchers investigating the modularization of a scaled down process for power generation in UAF and in rural communities
A team from the University of Alaska Fairbanks is investigating the possibility of developing small modularized coal gasification systems that could be used for power generation in Alaska and elsewhere, Brent Sheets, acting director of the Petroleum Development Laboratories in the University of Alaska Fairbanks Institute of Northern Engineering, told the Alaska Support Industry Alliance’s Meet Alaska conference on Jan. 19. An initial focus is the development of a coal gasification system that could replace the coal-fired steam turbines at the university - the existing coal-fired system provides power and heat for the university but is more than 50 years old and nearing the end of its life.
The use of a coal gasification system for power generation at the university could also benefit the power supply system in Fairbanks - Golden Valley Electric Association is partnering with the university in the research, Sheets said.
A cheap resourceCoal, an abundant and relatively cheap energy resource in Alaska, has been used as a means of power generation for the Fairbanks area and for the nearby Fort Wainwright military base for a number of years. If research at the university succeeds, it could be possible to convert other aging coal fired systems to the use of coal gasification. There is also the possibility of using coal gasification systems to reduce the cost of power generation for rural communities, Sheets said.
The gasification process coverts coal into syngas, primarily a mixture of carbon monoxide and hydrogen. The syngas can be used as a fuel, in a similar manner to natural gas. And, in the context of power generation, syngas can fuel a steam turbine generation system. Or the gas can fuel a reciprocating engine system. Virtually all modern diesel engines can be converted to run on natural gas, Sheets said.
Moreover, the use of coal-generated syngas in a reciprocating engine is 10 percent more efficient than burning the coal to generate steam for a steam turbine, Sheets said.
The UAF team is engaged in a front-end engineering and design study for the concept. The U.S. Department of Energy is providing $1.5 million in funding for the $2 million project, with Aurora Energy, GVEA and the owners of the coal gasification system intellectual property sharing the remainder of the cost, Sheets said. Aurora Energy operates a coal-fired power generation plant in Fairbanks.
UAF power generationIn addition to two aging coal-fired boilers for heat and power generation, UAF has an oil boiler, a boiler that can run on oil or natural gas, and a diesel generator. The diesel generator is not currently used because its exhaust fails to meet emissions standards for Fairbanks, Sheets said. The university also purchases some power from GVEA.
Were a coal gasification system to replace the coal-fired boilers, the syngas could be fed into the existing diesel generator, suitably converted for gas use, Sheets said. One particular benefit of this arrangement would be the possibility of then using the diesel generator to counterbalance the continuously varying power generation from GVEA’s Eva Creek wind farm - whereas the naphtha fueled turbine that GVEA can currently use to counterbalance the wind power is very inefficient at the low power outputs needed when the wind power is strong, the gas-fueled diesel generator would be relatively efficient across a wide range of power settings, thus reducing the cost of integrating the wind system, Sheets explained.
Moreover, the cost of coal energy at about $4.47 per million Btu is much lower than the cost of other fuels available in the Fairbanks region, even if the operation of the coal gasification system were to double the cost of the coal energy, Sheets said. By comparison, oil currently costs $17.17 per million Btu, while the Interior Gas Utility’s new gas supply contract with Hilcorp Alaska will deliver natural gas to the Fairbanks city gate at about $15.20 per million Btu, he said.
The challenge of scaleThe main technical challenge for the concept of using coal gasification in the Alaska Interior revolves around scaling down the technology relative to the size of the seven to 10 major gasification plants that operate in the United States. These plants operate on a gigawatt scale, compared to the 5 to 10 megawatts needed for the Fairbanks application. And use in rural communities would require even further scaling down, to less than 1 megawatt.
So, the research team is looking into ways of stripping out ancillary equipment, such as oxygen plants, associated with the large facilities, and simplifying the technology. It may also be possible to reduce manpower and monitoring needs through the use of automation.
But reducing the size of the plant could multiply the per-energy-unit cost of power generation by a factor of four while also reducing the plant’s thermal efficiency, Sheets said. However, the Fairbanks research team hopes to be able to reduce costs through the development of a modular syngas plant design. And so the team’s current effort is focused on building a plant for the university, with a design that can ultimately be modularized and mass produced. The high cost of the research project reflects the difficulty in doing this, Sheets said.
The research team thinks that it could be possible to develop a plant for the university for about $15 million, a cost far below the $240 million cost of a traditional coal-fired power plant, Sheets said.
Rural deploymentSheets also sees major scope for deployment of the technology to rural communities, if the modularized coal gasification design proves out at an appropriately small scale and workable cost. Alaska’s Division of Geological and Geophysical Surveys has identified 37 Alaska villages that have coal seams at or near the village sites. Moreover, the town of Nenana, a hub for barge transportation on the Alaska river system, is located just 60 miles from the Usibelli coal mine at Healy, Sheets said. Use of coal for power generation in the villages would also eliminate the risk of environmental damage from a diesel fuel spill, he commented.