Gasification of char from dried sewage sludge in fluidized bed: Reaction rate in mixtures of CO_2 and H_2O

摘要

The rate of gasification of char from dried sewage sludge (DSS) with a gas containing CO_2 and H_2O was studied. The tests were conducted in an atmospheric laboratory fluidized bed (FB), using CO_2-H_2O-N_2 mixtures as fluidizing gas and temperatures in the range of 800-900℃. The gasification rates were compared with those previously obtained for DSS char using one single reactant (either CO_2 or H_2O) in the gas, i.e. in mixtures of CO_2 and N_2 or H_2O and N_2. It was found that the char gasification rates measured in a mixture containing both reactants, i.e. CO_2 and H_2O, were well approximated as the sum of the individual rates measured separately with CO_2 and H_2O. Besides this result, an alternative method to accurately measure the char gasification in an FB using CO_2-H_2O-N_2 mixtures was employed, based on determining the char remaining in the reactor up to a certain time of gasification from the CO and CO_2 concentrations in the gas during the combustion of this char. It was shown that this method compares well with the traditional method (based on tracking the CO and CO_2 concentrations during gasification) when using a single reactant, but improves significantly the reliability of measurements for tests where both H_2O and CO_2 react simultaneously with char.