Study On Sewage Sludge Pyrolysis Kinetics And Energy Balance In Pyrolysis

Recently sewage sludge treatment and disposal have become urgent environmental problems to be solved. In our research group, two inorganic composite conditioners have been developed for the deep-dewatered process of sewage sludge, i.e. Fenton reagent + red mud composite conditioners and Fenton reagent + lime composite conditioners. In this thesis, the pyrolysis of the dewatered sludge after conditioning with these two inorganic composite conditioners has been investigated. The content of the thesis includes:1. Pyrolysis of sludge with two compsite conditioners and their kinetics analysisThe raw sludge and two conditioned dewatering sludges were studied experimentally by using TGA(Thermogravimetric analysis) thermal analysis technique, obtaining different heating rates sludge TG(Thermogravimetric) and DTG(Differential Thermogravimetric) curves of weightlessness. And the M-KAS(Kissinger-Akahira-Sunose) model and Discrete DAEM(Discrete distribute activation energy model) were used to study the pyrolysis kinetic parameters of sludge cakes dewatered by two conditioning systems. The results showed that sludge pyrolysis can be divided into three zones, the first zone temperature ~ 120 oC is the dewatering stage. The second zone 120 ~ 720 oC is the main volatile pyrolysis stage, pyrolysis temperature of sludge cakes dewatered by two conditioning systems has a difference. The third zone 720 ~ 900 oC is inorganic salt decomposition stage; Heating rate plays an important role in the pyrolysis process, affecting the initial temperature pyrolysis stage(Ti), end temperature(Tf) and peak temperatures(Tp) of various types. The pyrolysis weight loss curve of two conditioning systems is different, the impact of red mud on pyrolysis exists entire pyrolysis stage, and the impact of lime exists mainly at 800 ~ 1000 oC temperature range. In this temperature range, the pyrolysis curve of raw sludge + Fenton + Lime exists a clear lime decomposition peak. The average activation energies of raw sludge, raw sludge + Fenton, raw sludge + red mud, raw sludge + Fenton + red mud and raw sludge + Fenton + lime pyrolysis reactions are 218.99, 181.27, 187.35, 176.04 and 175.83 k J mol-1, respectively2. Pyrolysis mechanism of sludge inhanced by red mudRed mud can increase pyrolysis efficiency of sludge, improve pyrolysis weight loss rate, and pyrolysis conversion fullment of organic matter in the sludge; At the same time, red mud can improve sludge pyrolysis conditions, reduce sludge pyrolysis temperature termination, reduce energy consumption, shorten the reaction time, especially the Fe2O3 components in red mud played a key role; And red mud can catalyze the pyrolysis reaction of sludge, reducing the apparent activation energy of pyrolysis reaction in high temperature pyrolysis stage, making organic matter pyrolysis reaction easier, in which the Fe2O3 and Al2O3 components played a catalytic role in this part.3. Energy and material balance of sludge pyrolysisSludge pyrolysis energy consumption including the two parts of sludge pre-drying and pyrolysis reaction energy. For the pyrolysis reaction energy consumption, analysis of different organic content of sludge pyrolysis system, since the raw sludge in organic content changes, carbon content has changed; with the increase of organic matter pyrolysis residue lower yields, corresponding to pyrolysis gas yield higher. Mechanical sludge dewatering depth moisture content of about 60 % of the entire energy of pyrolysis system about ~ 5.5 MJ/kg, and most of the energy consumed in the drying and sample pre-heating stage, and the main sludge pyrolysis reactions heat is relatively small, accounting for less than 10 %. The energy consumption of sludge drying depends mainly on the initial moisture content of sludge. 80 wt% initial moisture content sludge drying to 5 wt% moisture content required termination 10.3 MJ·kg-1dried, ss energy; If the initial moisture content is reduced from 80 wt% to 60 wt%, the same drying to 5 wt% only required 3.8 MJ·kg-1dried, ss, reduce energy consumption by 63 %. However, the same initial moisture content of the sludge, drying the moisture content from 45 wt% to terminate reduced to 5 wt%, the required energy consumption are just 1.6 MJ·kg-1dried, ss, far lower than 10.3 MJ·kg-1dried, ss. Improve the efficiency of sludge dewatering, sludge control the initial moisture content is the primary means of controlling sludge drying energy consumption.This paper can provide theoretical guidance for efficient pyrolysis to energy utilization of municipal sewage sludge.