Biomass Handling Consulting
for the
25 MWe Tracy Biomass Power Plant

Client

Sigma Energy Solutions, Inc.
One Huntington Quadrangle
Melville, NY 11747

Completion Date

October, 2005

Project Description

GWF’s Tracy Power Plant is a 25 MWe plant located in Tracy CA. It has a Babcock & Wilcox boiler fitted with a Detroit Stoker hydrograte. The biomass fuel is a combination of agricultural and urban wood waste, which is received by trucks and stacked in outdoor stockpiles. The fuel is reclaimed via a payloader fitted with a large, wood chip bucket. Wood chips are stored in segregated piles by fuel type and supplier. The payloader reclaims the fuel, blending it with alternate scoops from different piles.

The primary fuel system consists of several components. Two under pile reclaimers (No. 10 and 12) discharge onto belt conveyor No. 14. Conveyor No. 14 is fitted with spike roller, a self-cleaning, cross-belt magnet, and metal detector. The spike roller is a plant retrofit that levels the uneven wood chip surcharge on the conveyor. The fuel is then routed to the disc screen and hog transfer, which load conveyor No. 18. Conveyor No. 18 is fitted with a belt scale. It elevates the wood chips and discharges to the plant’s distributing drag conveyor No. 20. This drag chain conveyor fills three (3) plant bins (No.’s 3, 2, and 1) in a cascade sequence. The fuel discharges from the drag conveyor from three 1ft x 2ft openings/chutes, directly above each bin. Excess fuel is discharge from the drag onto overflow conveyor No. 22, which stacks this material into a conical pile. This fuel system is largely seen in the above photograph.

Combustion problems were experienced when fuel properties stratify so that fuel fed to the north side of the boiler burns mostly in suspension while fuel fed to the south side burns on the hydrograte. This results in piles of fuel stacking on the south side, especially when the fuel is wet. Combustion conditions become upset and piles of fuel fail to completely combust. Misinterpretation of the situation exacerbates the problem when the fuel feed is increased and the pile of fuel on the hydrograte enlarges.

In addition to the combustion problems, a variety of material handling problems were experienced. In the fuel yard, there is a fair amount of dust, spillage, and flow problems. On the hydrograte as seen in the ash residue, a fair amount of dirt, metals, and unburned fuel is found.

Energy Associates conducted a condition assessment and recommended improvements to remedy these problems.