SCR: California cleaning

5 August 2002

RJM ARIS* (Advanced Reagent Injection System) selective catalytic reduction (SCR) technology recently achieved a 95.9 per cent cut in NOx emissions on a lean burn natural gas engine in California.

The RJM ARIS SCR system was installed on an engine at the corporate headquarters of Clean Air Partners located in San Diego, California. This 320 kW lean burn natural gas engine is expected to generate reliable prime power, but being located in Southern California, it is subject to some of the USA's most stringent air quality regulations.

ARIS SCR technology meters precise amounts of a safe, easy-to-use reagent into the exhaust stream of a diesel or lean-burn natural gas engine. Once in the exhaust, the reagent decomposes and forms ammonia, which passes over a catalyst to turn NOx into H2O, N and CO2.

The ARIS SCR system was delivered and installed on the Clean Air Partners engine in less than two months. The 95.9 per cent reduction achieved has resulted in a NOx level of 12 ppm.

The unit was tested at an outside temperature of 15ºC (60°F), exhaust temperature of 520 °C. The high temperature catalyst used in the system operates up to 550°C. Table 1 shows NOx reductions for various load factors.

Urea consumption and economics

The calculated urea consumption for the engine when operating at 98.5 per cent load conditions was approximately 0.38 gallons/hour. Cost of the urea is about $1.25/gallon in bulk. For example, at 4000 hours of annual operation, total urea consumption cost is less than $1900 per year. Urea consumption for natural gas engines is considerably lower than for diesel engines because of lower baseline NOx emissions associated with natural gas engines.

Total annualised cost of the system is estimated to be $3846 per ton of NOx removed, at 4000 hours of operation per year (Table 2). The ARIS SCR system becomes more attractive at 8000 hours of operation, with annual cost/ton estimates for NOx removed falling to $2205.

Such compliance cost estimates are exceptionally attractive for a natural gas engine, which has lower baseline NOx emissions (and therefore lower NOx tonnage reduction potential) when compared with diesel as well as lower additive (urea) costs.

Moreover, as the rated capacity increases the relative cost of compliance is lower due to the fixed nature of hardware and catalyst costs.

Clean and reliable

The successful test results from Clean Air Partners clearly prove that a natural gas engine can generate clean and reliable prime power at an affordable compliance cost.

Emissions reduction: an expanding armoury


Table 1. Performance of ARIS SCR system installed on 320 kW gas engine at Clean Air Partners for various load fctors
Table 2. NOx compliance costs for SCRs on natural gas engines

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