Lignite Fuel Enhancement (2010)

Pulverized coal power plants which fire lignites and other low-rank high-moisture coals generally operate with reduced efficiencies and increased stack emissions due to the impacts of high fuel moisture on stack heat loss and pulverizer and fan power. A process that uses plant waste heat sources to evaporate a portion of the fuel moisture from the lignite feedstock in a moving bed fluidized bed dryer (FBD) was developed in the U.S. by a team led by Great River Energy (GRE). The demonstration was conducted with Department of Energy (DOE) funding under DOE Award Number DE-FC26-04NT41763. The objectives of GRE's Lignite Fuel Enhancement project were to demonstrate reduction in lignite moisture content by using heat rejected from the power plant, apply technology at full scale at Coal Creek Station (CCS), and commercialize it. The Coal Creek Project has involved several stages, beginning with lignite drying tests in a laboratory-scale FBD at the Energy Research Center (ERC) and development of theoretical models for predicting dryer performance. Using results from these early stage research efforts, GRE built a 2 ton/hour pilot-scale dryer, and a 75 ton/hour prototype drying system at Coal Creek Station. Operated over a range of drying conditions, the results from the pilot-scale and prototype-scale dryers confirmed the performance of the basic dryer design concept and provided the knowledge base needed to scale the process up to commercial size. Phase 2 of the GRE's Lignite Fuel Enhancement project included design, construction and integration of a full-scale commercial coal drying system (four FBDs per unit) with Coal Creek Units 1 and 2 heat sources and coal handling system. Two series of controlled tests were conducted at Coal Creek Unit 1 with wet and dried lignite to determine effect of dried lignite on unit performance and emissions. Wet lignite was fired during the first, wet baseline, test series conducted in September 2009. The second test series was performed in March/April 2010 after commercial coal drying system was commissioned. Preliminary tests with dried coal were performed in March/April 2010. During the test Unit 2 was in outage and, therefore, test unit (Unit 1) was carrying entire station load and, also, supplying all auxiliary steam extractions. This resulted in higher station service, lower gross power output, and higher turbine cycle heat rate. Although, some of these effects could be corrected out, this would introduce uncertainty in calculated unit performance and effect of dried lignite on unit performance. Baseline tests with dried coal are planned for second half of 2010 when both units at Coal Creek will be in service to establish baseline performance with dried coal and determine effect of coal drying on unit performance. Application of GRE's coal drying technology will significantly enhance the value of lignite as a fuel in electrical power generation power plants. Although existing lignite power plants are designed to burn wet lignite, the reduction in moisture content will increase efficiency, reduce pollution and CO{sub 2} emissions, and improve plant economics. Furthermore, the efficiency of ultra supercritical units burning high-moisture coals will be improved significantly by using dried coal as a fuel. To date, Great River Energy has had 63 confidentiality agreements signed by vendors and suppliers of equipment and 15 utilities. GRE has had agreements signed from companies in Canada, Australia, China, India, Indonesia, and Europe.