PDF《1.6.1 General1-6》

1 percent). Methane emissions are highest during periods of low-temperature combustion or incomplete combustion, such as the start-up or shut-down cycle for boilers. Typically, conditions that favor formation of N2O also favor emissions of CH4. 1.6.4 Controls Currently, the four most common control devices used to reduce PM emissions from wood-fired boilers are mechanical collectors, wet scrubbers, electrostatic precipitators (ESPs), and fabric filters. The use of multitube cyclone (or multiclone) mechanical collectors provides particulate control for many wood-fired boilers. Often, two multiclones are used in series, allowing the first collector to remove the bulk of the dust and the second to remove smaller particles. The efficiency of this arrangement varies from

25 to

65 percent. The most widely used wet scrubbers for wood-fired boilers are venturi scrubbers. With gas-side pressure drops exceeding

15 inches of water, particulate collection efficiencies of

85 percent or greater have been reported for venturi scrubbers operating on wood-fired boilers. ESPs are employed when collection efficiencies above

90 percent are required. When applied to wood-fired boilers, ESPs are often used downstream of mechanical collector precleaners which remove larger-sized particles. Collection efficiencies of

90 to

99 percent for PM have been observed for ESPs operating on wood-fired boilers. A variation of the ESP is the electrostati........