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Technical Briefs

Prediction of Performance From PRB Coal Fired in Utility Boilers With Various Furnace and Firing System Arrangements

[+] Author and Article Information
B. Chudnovsky, A. Talanker

 Israel Electric Corporation, P.O. Box 10, 31000 Haifa, Israel

Y. Berman, R. Saveliev, M. Perelman, E. Korytnyi, B. Davidson

 Ben-Gurion University, P.O. Box 653, 84105 Beer-Sheva, Israel

E. Bar-Ziv1

 Ben-Gurion University, P.O. Box 653, 84105 Beer-Sheva, Israelbarziv@bgu.ac.il

1

Corresponding author.

J. Eng. Gas Turbines Power 132(12), 124502 (Sep 01, 2010) (4 pages) doi:10.1115/1.4001298 History: Received December 22, 2009; Revised December 27, 2009; Published September 01, 2010; Online September 01, 2010

The present regulatory requirements enforce the modification of the firing modes of existing coal-fired utility boilers and the use of coals different from those originally designed for these boilers. The reduction in SO2 and NOx emissions was the primary motivation for these changes. Powder river basin (PRB) coals, classified as subbituminous ranked coals, can lower NOx and SOx emissions from power plants due to their high volatile content and low sulfur content, respectively. On the other hand, PRB coals have also high moisture content, low heating value, and low fusion temperature. Therefore when a power plant switches from the designed coal to a PRB coal, operational challenges were encountered. A major problem that can occur when using these coals is the severe slagging and excess fouling on the heat exchanger surfaces. Not only is there an insulating effect from deposit, but there is also a change in reflectivity of the surface. Excess furnace fouling and high reflectivity ash may cause reduction in heat transfer in the furnace, which results in higher furnace exit gas temperatures (FEGTs), especially with opposite wall burners and with a single backpass. Higher FEGTs usually result in higher stack gas temperature, increasing the reheater spray flow and therefore decreasing the boiler efficiency with a higher heat rate of the unit. A successful modification of an existing unit for firing of PRB coals requires the evaluation of the following parameters: (1) capacities or limitations of the furnace size, (2) the type and arrangement of the firing system, (3) heat transfer surface, (4) pulverizers, (5) sootblowers, (6) fans, and (7) airheaters. In the present study we used a comprehensive methodology to make this evaluation for three PRB coals to be potentially fired in a 575 MW tangential-fired boiler.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Predicted gas temperature and normal gas velocity of the furnace near walls for the three PRB coals evaluated here and two cases for every coal—with dirty (0.003–0.0035 m2 K W−1) and clean furnaces (0.002 m2 K W−1) and with tilt of burners equal to 0 deg

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