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¦POWER example is boiler efficiency monitoring. “We look for any significant changes based on a simple calculation of total fuel into the boiler (measured from a mix of meters in the plant) and steam out of the boiler (measured with steam flow meters),” Anderson says. “This gives us a baseline, and can help identify if a fuel has lower-than-expected Btu per pound, or if there are other issues within the boiler. This is especially useful for fuel transitions, say from woodchips to energy pellets.” Around 15 to 20 percent of biomass materials, including oat hulls, woodchips and pelletized miscanthus, are cofired with coal at the plant. The UI staff calculates the percentage of renewable energy generated by monitoring the total amount of million Btu from renewable sources and comparing that to the campus’s total energy usage (including purchased power). This percentage and why it’s higher or lower, as well as operating plans, are communicated at morning kickoff meetings, Anderson shares. Variations could be attributed to a number of factors—like truck unload issues, plugged systems, etc., he says, but the ultimate goal is to understand how the operating plan affects the percentage of renewable generation, and have everyone aware that their actions can help with achieving the targets.

Feedstock Variety

Most biomass plants collect fuel from a variety of suppliers. Since UI introduces a few different types of biomass into its plant, the added variability leaves opportunity for issues to arise. “I think the power plant has done a nice job of more closely monitoring our systems, as we’re changing out fuels or increasing fuels, so we have enough data to go back and say introducing this fuel at this percentage might have caused this issue in the handling system or might have caused this spike in NOx emissions,” says Ingrid Anderson, UI environmental compliance specialist. Gillespie recalls the wet spring in Georgia around Atlantic Power’s Piedmont plant— when wet, biomass fuel can wreak havoc on efficiencies. “It’s important to carefully monitor moisture content to the fuel coming in, and then you adjust your operating parameters to mitigate the risk of NOx exceedances or poor performance,” he says. “Moisture content is evaluated once or more per shift, and then we have fuel managers at all of our sites whose job it is to go out and procure the best quality fuel possible.” Eagle Valley is the only utility-scale biomass power plant in the state of Colorado, so the facility developed its own biomass fuel market. “You get what’s available, or what suppliers are offering—whether it’s a certain species or cer-

tain kind of beetle-kill wood,” Wait says. Fuel is secured from a dozen different locations for the plant, and the staff also monitors the fuel yard multiple times a day, both through computer monitoring and visual inspections. Monitoring air emissions is also important at biomass power plants. UI just received a plantwide applicability limit (PAL) permit, which establishes a facility-wide cap on emissions for several different pollutants across campus. Ingrid says this gives them a lot of flexibility operationally, but the tradeoff is they do more emissions monitoring by keeping track of monthly data on all sources to comply with the permit. The Elk River Energy Recovery Station has monitors installed on the high-speed AVP Anhydro rotary atomizers in the exhaust gas scrubbers, which are commonly used in power plant scrubbers to reduce airborne pollutants before they reach the baghouse. Emerson worked with the plant to implement what’s called the CSI 9420 Machinery Health Transmitter for predictive monitoring of these atomizers. Various parameters are measured on the instruments mounted on the atomizers at the energy recovery station, including overall vibration velocity, maximum waveform and speed.

2017 January Biomass Magazine