Air Pollution Control Equipment Services, Emissions

Urea-Based SCR Technology Achieves 12 ppm NOx On Natural Gas Engine

Issue 10 and Volume 106.

By Ravi Krishnan,
RJM Corp.

RJM’s ARIS SCR technology recently achieved a 95.9 percent NOx reduction on a 320 kW lean burn natural gas engine. The system was installed at the corporate headquarters of Clean Air Partners located in San Diego, California, a locale subject to some of the nation’s most stringent air quality regulations.

ARIS, which stands for advanced reagent injection system, meters precise amounts of a safe, easy-to-use reagent into the exhaust stream of diesel or lean-burn natural gas. Once in the exhaust, the reagent decomposes and forms ammonia, which passes over a catalyst to turn ozone-forming oxides of nitrogen (NOx) into water, nitrogen and CO2.

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The system was delivered and installed on the natural gas engine at Clean Air Partners in less than two months and achieved a 95.9 percent reduction, resulting in a final NOx emission rate of 12 ppm. The unit was tested at an outside temperature of 60 F, and produced an exhaust temperature of 968 F. The high temperature catalyst used in the system operates up to a temperature of 1,022 F.

The calculated urea consumption for the engine when operating at 98.5 percent load was approximately 0.38 gallons/hour. At a urea cost of $1.25/gallon (bulk delivery) and assuming 4,000 hours of annual operation, total urea consumption cost is less than $1,900 per year. Urea consumption for natural gas engines is considerably lower than that of diesel engines because of the lower baseline NOx emissions associated with natural gas engines.

Total annualized cost of the system is estimated at $3,846 per ton of NOx removed at 4,000 hours of operation. The ARIS system becomes more attractive at 8,000 hours of operation, with annual cost/ton estimates of NOx removed at $2,205. Such compliance cost estimates are exceptionally attractive for a natural gas engine, which have lower baseline NOx emissions (and therefore lower NOx tonnage reduction potential when compared to diesel) besides lower additive (urea) cost. Moreover, as the rated capacity of engines increase, the relative cost of compliance is lower due to the fixed nature of hardware and catalyst cost. Exhibit 1 compares the cost of compliance for the 320 kW natural gas engine at 4,000 hours and 8,000 hours of operation.