Mechanisms Of Sludge Pyrolysis Process And Its Carbon Emission

With the booming construction of urban wastewater treatment plants in China, the problem of sludge treatment and disposal emerged. Sludge safe disposal and utilization is the trend of sludge treatment and disposal. Sludge pyrolysis is one of the research hotpots, as sludge can produce both useful materials and fuels in this process, meanwhile, part of carbon in sludge can be storage in sludge-char to mitigate greenhouse gases emission.In this study mechanisms of sludge pyrolysis, modeling of carbon emission in sludge process and assessing carbon emission of different sludge treatment and disposal process were conducted via experiments and reviewing others'research in this field. First, gas and solid products in sludge pyrolysis process were analyzed to investigate the mechanisms of sludge pyrolysis. Second, the quantity of stable carbon in sludge-char was analyzed with (13)^C NMR and Raman Spectral. The results indicated that the stable carbon accounted for 92.43% of all the carbon in sludge-char made at 650℃,and the main form of carbon was aromatic carbon and amorphous graphite with the aromaticity f_a=93.94%. Through investigating the pyrolysis mechanisms of the main components of sludge such as lignin, protein, fat, cellulose and semi cellulose, the pathways of forming pyrolysis products can be deduced. The main reactions in pyrolysis are free radical creation reaction, aliphatic chains'and Oxygen-contained function groups'broking down reactions, hydrogenation reactions, dehydrogenation reactions, condensation reactions and condensation polymerization.Carbon emission and sequestration in sludge drying-pyrolysis process can be divided into three stages: drying, pyrolysis and sludge-char utilization.When treating 1 ton of 20% DS sludge,sludge heat drying-pyrolysis process'carbon emission is 501.98 kgCO_2e; since the carbon in sludge is neutral, the emission is 106.213 kg CO_2e.Sludge heat drying-inceration process'carbon emission is 486.586 kgCO_2e; since the carbon in sludge is neutral, the emission is 49.583 kg CO_2e.Sludge sludge aerobic fermentation process'carbon emission is 28.083 kgCO_2e; since the carbon in sludge is neutral, the emission is 24.083 kg CO_2e.In the comparison of sludge aerobic fermentation, sludge drying-inceration, and sludge pyrolysis:the carbon emission of sludge aerobic fermentation was far less than drying-inceration.Take the utilization potential of sludge-char into consideration, sludge pyrolysis process is a promising sludge treatment process.