将下列段落翻译 During combustion, various kinds of impurities are generated and some of them are found in the flue gas. Most of these are related to the composition of the biomass: particles from ash, NO , from nitrogen,S O 2 from sulphur,etc .We can also find impurities related to incomplete or bad combustion, e.g. particles such as soot and unburned matter, carbon monoxide and other gaseous organic compounds such as dioxin. Dioxin is aromatic molecule in which chlorine replaces hydrogen. It is very toxic .The impurities in the flue gas are harmful if they are emitted to the atmosphere. Flue gas cleaning must be installed to eliminate or at least reduce this problem.