Dry Low NOx Combustion Development for Electric Utility Gas Turbine Applications: A Status Report

Abstract

National standards for NOx control for gas turbines are being evaluated and modified throughout the world. These standards are often supplemented by local or site specific emission limits. The numeric value of any emission limit is influenced by both the local environmental conditions, and, importantly, by the actual NOx removal capacity of the specific technologies that can be applied to the processes and equipment that will be governed by the emission standards. That is, emission limits can not be so restrictive that there is no technology available that can be applied to meet the permit condition. However, as new technologies are developed to meet the ever increasingly restrictive emission limitations, they become the standard by which the next round of emission limit setting is guided. Current NOx control technologies for gas turbine applications employ fuel switching to a low nitrogen content fuel, wet combustion control (steam or water injection into the combustor), or exhaust gas treatment (selective catalytic reduction technology) or combinations of those controls. Recently, dry combustion controls have been, or are being, developed by the gas turbine manufacturers, and catalytic combustion control processes are being researched. This paper presents a brief overview of the national NOx emission requirements of Europe, Japan, and the United States. A discussion of the new dry, low NOx controls presently emerging in the electric utility, gas turbine market are then reviewed, with an emphasis on the commercial applications and typical operating results that have been experienced. In this paper, all NOx values are referenced to dry, 15% oxygen exhaust conditions unless otherwise stated. The units are volumetric, in parts per million (ppm), unless otherwise stated.