Detection of Excess Emission Conditions for Rich Burn Engines Equipped with Non-Selective Catalytic Reduction Systems Operating at California Best Available Control Technology Limits
In response to proposed amendments to South Coast Air Quality Management District (SCAQMD) Rule 1110.2 an Industry Stakeholder Work Group conducted a series of field tests which investigated the ability of modern Air/Fuel Ratio Controllers (AFRC) applied to natural gas, rich burn engines with Non-Selective Catalytic Reduction (NSCR) systems to maintain control of engine emissions within the Best Available Control Technology (BACT) limits and detect out of control operations. Considerable effort was expended to field test various AFRCs on existing natural gas-fired rich-burn engines but none of the AFRC applied during the tests were able to consistently keep engine emissions in compliance, and engine load variations were particularly troublesome for the control systems. In addition, the alarm capabilities of existing AFRCs were not able to effectively detect all emission excursions. The tests found that proper programming of control parameters on each engine-AFRC system to be difficult and time consuming. The project demonstrated that existing AFRC technology diagnostics are not able to detect more complex out-of-compliance failure modes that can occur when the NSCR system drifts slightly outside the narrow window of compliance for SCAQMD limits. On the bright side, the data suggests certain parameters are closely correlated to emissions and these may be tapped for improved control or alarm algorithms. Based on these findings and other activities, it is expected that significant improvements in AFRC technology will develop in the coming years. While disappointing, the data provides hope that AFRC vendors can use such information to improve the performance and diagnostic functions of NSCR control systems.