Experimental Study On Bio-oil Production From The Municipal Sewage Sludge By Pyrolysis In Supercritical Water

With the rapid development of social economy and the improvement of urbanization level,municipal sewage emissions are increasing.The production of sludge as a by-product in the process of wastewater treatment plant also increased sharply.Supercritical water pyrolysis of sludge is a technology that the sludge was pyrolysis out of bio-oil under supercritical conditions which used water in wet sludge after mechanical dewatering as solvent.The bio oil can replace fuel,and can aiso reduce the emission of greenhouse gas.It has the role of sludge treatment,energy recycling and ease of energy shortage.It solves the two major problems of energy shortage and environmental pollution.The experimental of supercritical water pyrolysis of sludge process was designed and the experimental system was constructed.The sludge sample was direct pyrolysis with supercritical water.By changing the pyrolysis temperature,sludge moisture rate,catalyst,catalyst and dry sludge quality ratio(R),observed the influence on the yield of bio-oil,and made corresponding analysis with the pyrolysis gas,solid residue and bio-oil.It was found that the pyrolysis temperature is the most important factor affecting the reaction of sludge.The pyrolysis temperature was 385℃,the water content of the sludge was 85%,and no catalyst was added.The yield of the bio oil produced by the reaction residence time of 0min was 37.23%.Na2CO3 catalyst had a good effect on the yield of bio oil.When R is 0.10,the highest bio-oil yield was 41.27%.Under this condition,the calorific value of pyrolysis gas generated is lower about 6.16 MJ/m3.For the solid residue,the proportions of mineral elements were very high,and the hazardous heavy metals also had relatively high proportions.Therefore the solid residue should be pretreatment to reduce heavy metals before it could be used as soil amendment to improve the utilization of solid residue.In this paper,the reaction path of supercritical water pyrolysis of sludge was explored.The final pyrolysis products of protein were amines,nitrogen heterocyclic compounds(indole,pyridine,pyrrole,pyridine,etc.),aromatic hydrocarbons,aldehydes,dioxopiperazene and so on.The cellulose was final decomposition to 1,6-anhydroglucose,1,2,4-hydroxyhydroquinone,angelica lactone,acids and so on.Esters in supercritical water were pyrolysis to carboxylic acids and alcohols.Hydroxyl compound had the dehydration reaction and generated to other organics.In this paper,the energy consumption of the municipal sewage sludge pyrolysis in supercritical water was analyzed,which found it needed 1235 k J/kg energy consumption.Economic analysis was calculated that 1 kg of sludge costed 0.94 yuan,and the profit was 0.47 yuan.It has to technology research and development to reduce energy consumption and improve efficiency.