July 15, 2007

Dynamic classifiers improve pulverizer performance and more

One size doesn't fit all

A dynamic classifier is retrofitted to a vertical-shaft pulverizer by installing a duplicate upper pulverizer casing that houses the classifier's fixed and rotating vanes, motor, and drive connections. A typical dynamic classifier assembly has a center coal feed pipe and several coal outlet pipes (Figure 6). The rotor drive is mounted on the side of the casing and driven by a belt. If the coal feed is off-center, the drive can be directly coupled, as was the case at the J.B. Sims Power Plant in Michigan (Figure 7).

6. Aftermarket leader. This is a typical LSKS dynamic classifier, with a central coal inlet pipe and four coal outlet pipes. Courtesy: Loesche Energy Systems

7. Nice installation. At the J.B. Sims Power Plant in Grand Haven, Mich., retrofitting each of three LSKS dynamic classifiers required mounting a direct drive for it in the center of the existing Model EL 56 pulverizer. Courtesy: Loesche Energy Systems

In most cases, dynamic classifiers can be installed as "slide-in" retrofits with little need to move existing equipment. Figure 8 shows another type of dynamic classifier, with one inlet and outlet, favored by the cement industry.

8. Top of the mark. This large LSKS dynamic classifier with one inlet and one outlet is being assembled prior to delivery to a cement plant. Courtesy: Loesche Energy Systems

It should go without saying that gains in fineness, capacity, or both, depend on many factors, such as the type of coal, the brand of existing pulverizers, and the design of the overall fuel-handling system. Likewise, the costs of a retrofit are site- and unit-specific, not so much for "as found" equipment but as a result of fuel system or other unit modifications.

To get you in the ball park, consider the following basic cost analysis recently completed for one of our customers. Only the final results are shown:

• Basis: 187-MW coal-fired boiler with four pulverizers
• Present vs. predicted UBC level: 30% vs. 5%
• Predicted NO_x reduction: 15%

For this job, the break-even point for fuel savings alone is estimated at 2.4 years. The break-even on fuel savings plus NO_x credits is 1.6 years (which falls to 1.3 years if revenues from sales of flyash with less UBC are factored in).

—Robert E. Sommerlad is strategic accounts manager for Loesche Energy Systems; he can be reached at rsommerl@aol.com. Kevin L. Dugdale is managing director of Loesche Energy Systems Ltd; he can be reached at kevin@loesche.co.uk.