Thermal NOx, Promt NOx: Meeting California Emission Limits

During the last 25 years, operating permits have reduced allowable NOx emissions to lower and lower levels. In 1970, the lowest prevailing NOx limit for industrial boilers was about 90 ppm. By 1990 the lowest requested limit was about 20 ppm. Some new units have been permited a t 9 ppm, requiring the use of SCR. Besides the project-specific permit levels, local control agencies have regulated reduced NOx emissions for broad categories of sources thoughout their districts. In the San Francisco area, the Bay Area Air Quality Management District's Regulation 9, Rule 7 will require 30 ppm NOx for all boilers with over ten million Btu/hour heat input . Further restrictions can be anticipated in California.