Aeroderivative Gas Turbines Can Meet Stringent NOx Control Requirements

Abstract

Gas Turbines operating in the United States are required to meet federally mandated emission standards. This article will discuss how General Electric's LM industrial aeroderivative gas turbines are meeting NOx requirements as low as 25 parts per million using steam injection. The article will also describe the technical aspects of how water or steam injection can be used to supress NOx, what emission levels GE will guarantee and detail some recently obtained test results. The side benefits of water or steam injection for controlling NOx emissions will be discussed. Steam injection has a very favorable effect on engine performance raising both the power output and efficiency. As an example, full steam injection in the GE LM5000 gas turbine increases the power output from 34 MW to 52 MW while lowering the heat rate from 9,152 Btu/kWh to 7,684 Btu/kWh when fired on natural gas. Water injection increases power output at a slightly decreased thermal efficiency. When steam is injected, NOx can be controlled to 25 ppm (referenced to 15 percent O2) which is sufficient to comply with the most stringent requirements imposed in areas where water or steam injection is considered best available control technology (BACT). Selective Catalytic Reduction (SCR) systems are currently employed in areas with Lowest Achievable Emissions Requirements. SCRs have been proposed as BACT in several areas such as the Bay area of California and the state of New Jersey. These systems are expensive to install and operate, and this cost impact can cause many projects to become economically non-viable. Cost comparisons for NOx removal using an SCR in combination with the steam injection will demonstrate the large incremental cost incurred when NOx is controlled using an SCR. Lastly, a case will be made for not imposing SCR as BACT in that it would close the door on further research and development for better, cost-effective methods of NOx control.