Modified respiratory quotient to evaluate the environmental impact of Chinese coal combustion

Considering the effect of ash and moisture on CO2 emission during combustion, a modified respiratory quotient (RQ(m)) was employed to determine the CO2 emission potential of anthracite, bituminous, lignite, and peat in China. It was found that the conventional RQ of different Chinese coals was almost the same (from 0.9 to 1), but RQ(m) of coals varies significantly. The low-rank coals such as peat and lignite have significantly high RQ(m) which can go up to 7. The high-rank coals such as anthracite and bituminous coals have RQ(m) between 1 and 2. Higher RQm means more CO2 emission since more energy is required to transport or process the low-rank coals. Moreover, correlations between O/C and H/C ratios of the coals and RQ(m) were also analysed. It was found that low-rank coals such as lignite and peat have higher H/C and O/C ratios and their RQm are correspondingly higher.