Formaldehyde Emissions from Dry Low Emissions Industrial Gas Turbines

Abstract

Formaldehyde is listed as a Hazardous Air Pollutant (HAP) by various regulatory agencies around the world because of its role as a carcinogen. To address this impact, several countries have regulated formaldehyde emissions from land-based gas turbines. In the United States (U.S.), the federal regulatory level is 91 ppb and state level formaldehyde requirements vary significantly. In Germany, the formaldehyde limit is 5 mg/Nm3 (∼3.7 ppm) from 70–100% load. Formaldehyde emissions from gas turbines are formed due to incomplete combustion of natural gas and predictably track with carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions trends. This paper presents results from a formaldehyde measurement campaign completed in test cells at Solar Turbines on Dry Low Emissions (DLE) turbine products including the Mars® 100, Titan™ 130 and Titan™ 250 operating on pipeline natural gas. Theoretical modeling of formaldehyde formation using a Chemical Reactor Network (CRN) model are also presented. Measurements have been taken in the engine test cells over a range of operating conditions from full load* to idle. The latest Fourier Transform Infrared (FTIR) technology has been used to meet the challenges of accurately measuring formaldehyde down to the 10-ppb detection level. Formaldehyde emissions were found to range from near the detection limit to 50 ppb at full load with a small increase as load is decreased within the typical DLE operating range and a sharper increase outside of DLE mode to idle. The variation is attributed to differences between gas turbine models based on pressure ratio and combustion system design. CRN modeling predictions were compared with the test data, and the modeling results were used to gain insight into the formaldehyde emissions formation mechanisms.