Description

The purpose of this manual is to provide general guidelines for use by industrial boiler operators to reduce stack emissions of nitrogen oxides and improve boiler operating efficiency.

These guidelines deal primarily with boiler adjustments which are typically within the control of boiler operators and plant engineering personnel. However, other techniques are also described in the Appendices which will usually require the assistance of outside combustion specialists due to the more critical dependence on specific boiler design, operating conditions and fuel characteristics.

Since efficiency and emissions are sensitive to many of the same boiler operating parameters, it is essential that both of these areas be simultaneously treated in one integrated set of guidelines. The recommended procedures in this report are based on the results of U.S.

Environmental Protection Agency (EPA) and Federal Energy Administration (FEA) sponsored programs (Refs. 1 and 2) during which various nitrogen oxides reduction methods were evaluated in the field and improvements in boiler efficiency were demonstrated.

Oxides of nitrogen are a major contributor to the total air pollution problem existing in industrial areas. Generally referred to as “NOx”, this gaseous pollutant includes both nitric oxide (NO) and nitrogen dioxide (NOz), although NO, generally comprises only five percent or less of the total NOx emissions from boilers. These compounds plus the new substances formed when they combine with other pollutants in the air are an important element in what is commonly referred to as “smog”.

Boilers used in industry produce a significant fraction of the total industrial emissions of NOx.

In fact, industrial boilers produce 50 percent of the NOx emitted from all stationary industrial combustion sources (Ref. 3). A reduction in emissions from just this single industrial source would obviously contribute greatly to improving the national air quality.

Industrial boilers currently account for over 15 percent of all the energy consumed in the United States, or more than 11 quadrillion Btu’s per year (Ref. 2). An increase in industrial boiler efficiency would therefore significantly impact energy conservation nationwide as well as reduce industries’ fuel costs. The EPA and FEA sponsored field test programs revealed that improvements in efficiency of up to several percent were frequently possible by simply adjusting the fuel/air ratio to minimize stack gas heat losses.

During the two-year EPA field test program, substantial reductions in nitrogen oxides emissions were achieved through careful adjustment of existing boiler equipment. Usually little or no deleterious effects on combustion controls or boiler reliability occurred when the optimum adjustments were established. In fact, substantial improvements in boiler efficiency often accompany “low NOx” operation. However, adjustments for improved efficiency occasionally conflicted with attempts to reduce emissions, requiring a tradeoff between emissions and fuel usage, or preferably the application of alternate NOx emission controls.