Emission Characteristics of PM (PMtotal, PM10, PM2.5), NOx, CO and VOCs Emitted from LNG-fired Gas Turbine and Small Domestic Boiler

Abstract

In recent years, natural gas is increasingly being used in the heating and power generation sectors as a clean fuel with an aim to reduce air pollution. In this study, a standard test method was used to measure air pollutants and identify emission characteristics for gas turbines and small domestic boilers, which use LNG as fuel. For gas turbines, the air pollutants were measured at 14 sites, whereas for small domestic boilers, six of them were installed in a laboratory to run tests due to limitations in on-site measuring and testing. However, the small domestic boilers were all new machines and were operated for long consecutive hours for testing, meaning that the results could vary from that of on-site boilers. The results show that gas turbines and small domestic boilers not only emit PM_2.5, but also particulate matters larger than PM_2.5. According to the measurements, the average concentration level of PM_total, PM₁₀, and PM_2.5 generated from gas turbines are 51.8, 38.5, and 28.1 µg/m³ (@O₂ 15%), respectively. Those generated from small domestic boilers were 31.3, 26.2, and 20.0 µg/m³ (@O₂ 4%), respectively. The NOx concentration levels complied with the emission limits. Especially where a NOx control device was in place, both the NOx and CO concentration levels were relatively low. However, the NOx and CO concentration levels were generated from small domestic boilers were relatively high, since the emission limits were not applied. VOCs were measured at 10 facilities where 28 samples were collected. The compounds that were identified were Aromatics, Oxygenated VOCs, Alkanes, in that order, which were consistent across the samples. Aromatics consisted mostly of toluene, o,m,p-xylenes, benzene, and ethylbenzene. Among oxygenated VOCs, ethyl acetate, vinyl acetate, and isopropyl alcohol, etc. were identified. In other words, gas turbines generated a wider range and higher concentration levels of VOCs compared to small domestic boilers. The emission factors of gas turbines and small domestic boilers were derived from the measurements, and then compared with the standard emission factors of other countries (NAER, U.S. EPA AP-42, EMEP/EEA). PM emission factors calculated in this study were lower than that of existing emission factors and the calculated NOx emission factors (uncontrolled) for the small boilers were also lower. The CO emission factor for gas turbines was lower than that of existing emission factors, but higher for the small domestic boilers. Emission factors of benzene, toluene, and xylenes, which are hazardous air pollutants, were lower than those of U.S. EPA AP-42.