An orthogonal experimental study on solid fuel production from sewage sludge by employing steam explosion

► The steam explosion is confirmed to improve sludge dewaterability effectively. ► The energy consumption of SE was 22.02% of that of conventional drying. ► Increasing the holding time improves the net heating value of sludge derived fuel. ► The holding time and pressure of SE process are the most significant factors. The treatment and disposal of sewage sludge have been one of the most significant environmental problems in China. Production of solid fuel from sewage sludge could be an effective way to work out this problem as it can realize the harmlessness treatment and recycling of these wastes simultaneously. This study proposed a novelty process, including the steam explosion (SE) pretreatment, mechanical dewatering, natural drying and pelleting, to produce solid fuel from sewage sludge. Dewatered sewage sludge with moisture content about 80% and the leaves of Chinese parasol were used as raw materials. A L16(45) orthogonal table was employed to arrange the experiments to investigate the feasibility of the proposed process and optimize the operating parameters such as the ratio of sludge to leaves α and size of leaves S, pressure P and holding time H of the SE process. The range analysis and Analysis of Variance (ANOVA) were carried out to detect the optimal level within the observed range and the predominance of each factor. The thermogravimetric (TG) method was also adopted to characterize the combustion behaviors of these sludge derived fuel (SDF). The results show that no important factor has been omitted from the orthogonal design and the experimental results are consequently reliable. Considering only the SE operating parameters, the holding time H with a percentage contribution φH of 31.75% is the main influencing factor on the dewaterability of the SE treated products. With a holding time of 55s, the moisture of all the solid product is lower than 46.5% after mechanical dewatering with a press pressure of 1.0MPa for 1.5h. Moreover, the dewaterability of the SE products becomes better with the increase of the SE pressure. The optimal parameters to produce solid fuel from sewage sludge and leaves were α=2:1, H=70s, P=2.4MPa, and S=40mm within the range observed in this study. The wet base heating value of these fuels is more than 4000kJ·kg−1, which are capable of self-sustaining combustion. The TG analysis results show that these fuels have a good combustion performance with a low ignition point, narrow range of combustion temperature. The combu