The goal of the project is to examine whether Alaska low-rank coal from the Usibelli coal mine could be burned at a particle size distribution (PSD) coarser than 70 percent passing 200 mesh (the industry standard). Some specific issues to be investigated are the relationship between PSD and each of the following: plant efficiency; mill power consumption; emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon monoxide (CO), unburned carbon in bottom ash and fly ash, and mercury emissions in the stack (added in 2006.)

University of Alaska, Fairbanks, AK

Alaska’s low-rank, highly reactive coal has been a tough sell in the Pacific Rim countries due to its low HGI. Clients express concern over mill throughputs as a result of the low HGI numbers. However, the highly reactive nature of the coal could be exploited to alleviate the throughput issue. It was proposed that Alaska coal could be burned at a coarser PSD without any loss in combustion because the volatile content would cause the particles to explode—as soon as they entered the combustion chamber—effectively “grinding them finer.” Not having to grind the coal as fine as the industry standard would result in increased throughput.

Results 
The results to date have been very promising. No correlation between PSD and efficiency has been found. Additionally, burning coal at coarser PSD did not appear to impact emissions at all, although the impact on emissions has not yet been fully studied. Multivariate regression also revealed that mill power consumption was related to PSD, as expected (i.e., a coarser grind will consume less power). Carbon loss in bottom ash and fly ash has not been determined to be significant.

Benefits 
If the project is able to prove its hypothesis, it will help sell Alaska’s coal to the Pacific Rim nations and other countries where its low Hardgrove Grindability Index (HGI)—and hence mill throughput—has been an issue. This project will demonstrate that Alaska coal need not be ground as fine as bituminous coal, thereby alleviating grinding concerns and improving the marketability of Alaskan coal resources.

Summary 
This project was undertaken to prove that Alaskan low-rank coal could be burned at a coarser PSD than bituminous coal without adversely impacting plant efficiency and emissions. Tests are being conducted at Golden Valley Electric Association’s (GVEA) Healy Unit No. 1, a 28-MW pulverized coal power plant on the banks of the Nenana River in Healy, AK. It is hoped that the results of the study will make selling Alaska’s coal easier. Tests conducted to date have been very promising. A few more tests remain before conclusions can be finalized.

(April 2007)
The project is completed. The final project report is listed below under "Additional Information".

$661,411

$189,538 (22.3% of total)

NETL – Purna Halder ( Purna.Halder@NETL.DOE.Gov 918-699-2084)

Malav, D., Ganguli, R., Dutta, S., and Bandopadhyay, S., “Combustion of Alaskan Sub-bituminous Coal,” accepted for publication, Journal of Fuel Processing Technology.