Options for effectively reducing NOx emissions in power boilers

In 22 states east of the Rockies, pending EPA legislation requires mills to lower NOx emissions by 2003

THE CLASS OF COMPOUNDS CALLED NITROgen odes (NOx) is an emission of combustion that forms ozone and smog when combined in the lower atmosphere with volatile organic compounds and sunlight. Ozone in the lower atmosphere is different than the protective ozone of the upper atmosphere.

The U.S. Environmental Protection Agency (EPA) worked with 37 states east of the Rocky Mountains forming the Ozone Transport Assessment Group (OTAG) and proposed the Ozone Transport Rules (OTR) in 1997 and 1998. These rules propose to reduce NOx emissions from utility and non-utility combustion sources in 22 states, including power and recovery hollers, as shown in Figure 1.

These emissions rules and limits for NOx emir sions are currently in litigation. Should the EPA prevail, the affected mill's NOx reductions will be left in the hands of the individual states to implement. The states' implementation plans (SIPS) have not yet determined who will be affected and how much reduction will be required.

The current federal date for compliance is May 2003; therefore, the time for implementation is rapidly decreasing, and operating companies need to plan now if they are going to be ready. The SIPS will ultimately determine the reduction required by each utility and non-utility source. Many industries, including pulp and paper, will likely be part of the overall reduction. More information is available at www epa.gov

The first step toward implementation is to decide which mills are affected.This step needs to be identified between the individual mill and the state and local environmental agencies. Identified mills must then know what equipment is available, as well as the capabilities of the different technologies, so that proper systems or combinations can be designed, manufactured, erected, and commissioned. Lead times for equipment manufacturing and construction must also be considered.

This article reviews technology solutions to reduce NOx emissions at pulp and paper mills. Most of this article is devoted to NOx reduction in a power boiler, since this is the greatest source of NOx emissions and where the greatest percentage of reduction is possible. Some reduction is also possible in the recovery boiler.