For more than 30 years, elaborate and highly effective catalytic air pollution control systems have been abating volatile organic compounds (VOCs) and NOx at utility size power plants. Yet operators of small reciprocating engines typically employed for cogeneration applications and on-site power have relied on devices that are essentially catalytic mufflers, operated by estimating how much NOx was coming from an engine at a certain load, then injecting ammonia at a level judged to be adequate. Furthermore, such devices don’t destroy VOCs and NOx with a single unit.
Today, increasingly rigid demands on small power installations, such as those imposed in California’s South Coast Air Quality Management District (SCAQMD) — the toughest air emission standards in the U.S. and possibly the world — are driving the need for better SCR at small power units. One solution comes from a process used in chemical, processing and manufacturing plants of various kinds. It is now being applied to gas-fired reciprocating engine power plants in California and in other locations where rigorous regulations often challenge the ability of conventional reduction systems to meet emission standards while operating at maximum efficiency.
“What used to be good enough for reciprocating engines or turbines slightly below or above the 1 MW range probably won’t be adequate anymore,” says Don Ciccolella, vice president of CSM Worldwide, provider of industrial air pollution control projects for NOx, CO, VOC and particulate matter abatement. “High performance SCR is now required, and SCR alone is not enough because you have to abate carbon monoxide and VOCs. You need additional catalysts to do it.”
CSM is now entering the power generation market with a product line that contains multiple catalytic reduction systems with combined heat and power (CHP) in a small package. “Frankly the best you can achieve using the approach traditionally applied with small engines is maybe an 80 to 85 percent reduction in NOx,” says Ciccolella. “And since you don’t know how much ammonia to inject, sometimes you don’t even get that. That was usually okay in the past.”
Today’s restrictions for small generators are driving the need for better catalytic emission reduction systems, which substantially reduce CO, VOC and NOx emissions for small power units. California now requires more than 95 percent reduction of NOx to achieve emissions of 9 parts per million or less. “You can’t do that just by guestimating using load mapping,” Ciccolella says. “You need NOx analyzers in place and real-time ammonia control so that you inject just the right amount of ammonia for high NOx reduction.”
The package uses a low cost, electro-chemical NOx analyzer to measure NOx emissions from the outlet of the catalytic NOx abatement system. This analyzer is then integrated into a closed-loop control scheme to inject the correct amount of ammonia, resulting in high performance SCR.
Such a system can routinely achieve ultra low emission levels of less than 9 ppm of NOx, and 30 ppm for CO and VOC, meeting BACT for California’s SCAQMD, says Ciccolella.