Sewage Sludge Pyrolysis And Combustion Characters And Kinetics Reserch

The pyrolysis characteristics and kinetics of sewage sludge for different sizes (d < 0.25 mm, 0.25 mm < d <0.83 mm and d > 0.83 mm) and heating rates (5, 20 and 35℃min-1) were investigated in this paper. The STA 409 was used for the sewage sludge thermogravimetric analysis. FTIR analysis was used to study the functional groups and intermediates during the process of pyrolysis. Meanwhile, a new method was developed to calculate pyrolysis kinetic parameters (activated energy E, the frequency factor A and reaction order n) with surface fitting tool in software MATLAB. The results show that all the TG curves of sewage sludge pyrolysis are divided into three stages: evaporation temperature range (100–180℃), main decomposition temperature range (205–550℃) and final decomposition temperature range (550–900℃). sewage sludge combustion process are divided into four stages: water evaporation(100～180℃), volatile matter combustion (180～475℃), carbon combustion(475～595℃) and inorganic salt decompose(595～900℃). The sewage sludge of d < 0.25 mm obtains the largest total mass loss, especially at the heating rate of 5℃min-1. By FTIR analysis, the functional groups including NH, C-H, C=C and so on, are all found in the sewage sludge. Comparing the FTIR spectra of sludge heated to 350℃(temperature associated to maximum devolatilization rate in the second stage) and heated to 730℃(temperature associated to maximum devolatilization rate in the third stage), In the second stage, the alcohols, ammonia and carboxylic acid in the sludge has been mostly decomposed into gases, and only a little bit compounds contained CH and OH of COOH exist. The pyrolysis kinetic parameters of second stage are as follows: the reaction orders are in the range of 1.5～1.8 and the activation energy is about 48 kJ/mol. The combustion kinetic parameters of second stage and third stage are as follows: the reaction orders are in the range of 0.3～1.4 and 1.1～1.3, the activation energy is about 33 kJ/mol and 176kJ/mol respectively. The sewage sludge particles sizes have small influence to stage two of sewage sludge pyrolysis and stage three of sewage sludge combustion, however, it has big influence to stage two of sewage sludge combustion.