Experimental Study On Production Of A Solid Fuel Using Sewage Sludge And Spent Cooking Oil

In recent years, more waste water treatments have being established due to the fast urbanization in China, which result in a large amount of sewage sludge needed be disposed safely. Thermal drying is an effective and environment-friendly sludge treatment method. Dried sludge can be land filled, manufactured into agricultural fertilizer, used for landscape and building materials, or burned directly, fulfilling four requirements of sludge disposal:volume reduction, stabilization, safe treatment and resource. The hot air convective drying is wildly applied to dry sewage sludge nowadays. This drying method has the merits of simple structure and easy operation but its limitations are the long drying time, high operation coast due to a high energy consumption and the risk of explosion.To overcome the shortcomings of the hot air convective sludge drying, a new type of sludge drying technology was proposed in this project:the sludge was immersion frying dried by the spent cooking oil and through immersion frying, the fresh sludge was converted simultaneously into a useful solid fuel. Some benefits are expected for the sludge frying drying technology: the immersion frying drying has a short drying time, low energy consumption and no explosion risk. Due to water removal and the oil incorporation in the sludge frying drying process, the fresh sludge was converted into a fuel with high calorific value. In addition, the new technology provided a new possibility for massively disposal of another municipal waste-spent cooking oil.The main research objectives are to provide some basic knowledge and technical data for a better understanding of this new sludge drying technology and thus, more research effort are put on studying of the sludge immersion frying process and its parametric study, properties evaluating of the solid fuel made by the frying process, the combustion performance of the solid fuel in a pulse combustion burner. The main works conducted in this project include:(1) Investigating of the frying drying characteristics of the sewage sludge. The frying experiments of sewage sludge were carried out in a self-made sludge immersion frying drying dehydration experimental setup, to study the drying characteristics and effects of operation parameters on the drying process. Experimental results showed that comparing with the hot air sludge drying, the drying time in the sludge frying process is shorten largely. Oil temperature is an important parameter of the drying process.(2) Evaluating the physics, chemistry, pyrolysis and combustion properties of the solid fuel. The fuel physical structure and chemical composition were determined by scanning electron microscopy (SEM) method and element analysis, respectively. The pyrolysis and combustion characteristics of the solid fuel were determined by thermogravimetric analyzer in the nitrogen and air atmosphere respectively. It was found that the fried sludge fuel has two combustion stages: gas combustion and residual carbon combustion, merits of easy ignition and complete combustion.(3) Testing the combustion performance of the solid fuel in a pulse combustion burner. The pulse combustion of fried sludge and hot air dried sludge were carried out in a self-made Rijke pulse combustion burner. Experimental results showed that the improved combustion stability and intensity was observed on the fried sludge due to its higher calorific value.