Research Boosts the Power of CoalBy Derrill Holly | ECT Staff Writer Published: June 4th, 2013
Utility operators, including generation and transmission cooperatives, are working to ensure that coal-based generation continues to help meet U.S. energy demands.
And despite uncertainty in domestic and international environmental policy, the results are paying off. Research supported by cooperatives indicates promising technology could potentially save co-op consumer members millions of dollars and help G&Ts meet emissions standards.
“Our goal is to test emerging and commercial technologies in combinations that provide multiple pollutant controls,” said Dale Bradshaw, the liaison for generation and environmental control technologies for NRECA’s Cooperative Research Network and an NRECA consultant. “The key issues are emissions of mercury, some sulfur dioxide and acid gases, as well as nitrogen oxides.”
CRN has been working with the Tennessee Valley Authority and industry partners including Shaw Environmental, now part of Chicago CBI, and NatronX Technologies on multi-pollutant control demonstration projects since late 2010. The testing is also supported by a consortium of 10 G&Ts and ATCO group, an investor-owned utility with operations in Canada. More than $1 million has been committed to date.
Tests conducted so far have concentrated on dry sorbent injection of trona, a soda ash mineral, and hydrogen bromide, a water soluble gas, to dramatically reduce compounds subject to regulatory control, such as mercury and acid gases.
The tests are designed to identify economical alternatives to costly scrubber technology, or methods of enhancing its performance to help meet current or future environmental regulations.
“We want to reduce technology capital costs by a factor greater than 10,” said Bradshaw, during a webinar held to update industry executives. “G&Ts that now are using or plan to use activated carbon injection technology to help control emissions could potentially save up to $60 million a year in operating costs by adding hydrogen bromide to the treatment process.”
Projects have already been tested at San Miguel Electric Cooperative’s 410-megawatt coal-based plant near Atascosa, Texas, and at Arizona Electric Power Cooperative’s 408-MW Apache Generating Station near Cochise.
San Miguel EC, based in Jourdanton, Texas, and Benson-based Arizona EPC both reported success in achieving the required emission limits set under EPA’s mercury and air toxic standards by spraying hydrogen bromide acid downstream of the plant economizer.
“Injection of activated carbon could not achieve the emission limits, but injection of hydrogen bromide did achieve the emission limits,” Bradshaw said.
CRN is now pursuing a new round of tests specifically involving slurry injection of micronized limestone in coal-based generation units not equipped with scrubbers. Maple Grove, Minn.,-based Great River Energy has agreed to host a test at its 188 MW Stanton Station facility on the Missouri River in North Dakota, beginning in late 2013.
Limestone injection could address industry concerns about degrading the quality of fly ash, now sold by G&Ts and other coal combustion interests for manufacturing concrete, cement fabrication and in oil field waste disposal, said Bradshaw. “The limestone additive could actually enhance the fly ash.”
CRN is also tracking a number of other projects designed to help make coal-based generation more efficient, or reduce the wear and tear that changes in operating conditions cause on expensive coal-fired equipment.
Intermittent use of coal-based or natural gas combined-cycle power plants, as more wind and solar resources are added to regional power grids, is a growing concern among power plant operators, said Bradshaw.
“Multiple two-shift operations can reduce the efficiency of those plants, increase emissions and dramatically reduce reliability,” said Andrew Cotter, a CRN program manager. “That can lead to problems with corrosion, metal failure and significantly higher maintenance and operating costs.”
While combined-cycle natural gas generation units can be designed for quick startups and use as peaking plants, renewable energy requirements could force G&Ts to use portions of their coal-based fleets to balance intermittent supply.
“That’s the operational equivalent of stop-and-go driving for a precision machine designed for highway performance,” said John Hewa, NRECA’s vice president for research, engineering and technical services.
“G&Ts are using valuable assets built for long-term continuous operation, which may now be used sporadically, to meet the demands of a changing power grid,” said Hewa. “Beyond degrading efficiency, there’s also an added risk of component failure as these systems are repeatedly taken in and out of service. Those could result in long outages and a dramatic increase in costs.”