Determination of biomass-coal blending ratio by 14C measurement in co-firing flue gas

Abstract

To verify the feasibility of using radiocarbon detection for the measurement of the biomass-coal blending ratio in co-firing heat and power plants, 14C activity detection technology that uses benzene synthesis as the sample preparation method and a liquid scintillation counter as the detection instrument was studied. A benzene synthesis system was built to enrich carbon in the combustion flue gas in the form of benzene. The benzene sample was mixed with scintillator (butyl-PBD) and 14C activity was measured using a liquid scintillation counter (Quantulus 1220). Three kinds of coal and six kinds of biomass were tested repeatedly. The measured 14C activity was 0.3365 DPM/gC in Zhundong lignite, 0.2701 DPM/gC in Shenmu bitumite, and 0.3060 DPM/gC in Changzhi anthracite. These values were much higher than the instrument background activity. For the co-fired experiment, we used groups with biomass ratios (based on the carbon) of 6.51%, 12.95%, and 20.75%. A modified empirical expression to determine the biomass, coal blending ratio based on the 14C activity measured in the co-firing flue gas, was proposed by analyzing and verifying measurement accuracy. From the 14C measurements of the co-fired samples, the corresponding estimated biomass ratios were (5.54±0.48)%, (12.31±0.67)%, and (19.49±0.90)%. The absolute measurement error was around 1% for a typical biomass-coal co-firing application.