Characteristics And Mechanisms Study On Co-pelletization Of Sewage Sluge And Typical Biomass

Biomass densification technology can be squeezed into a granular, briquette and cubic. Thus, it can significantly improve the volume density, reduce the storage, transportation and handling costs. The biomass products after densification had uniform size and shape, which can be applied to the standard processing and storage equipment. They also can be more convenient for direct combustion, co-combustion with coal, gasification, pyrolysis or other thermal conversion method. At the same time, incineration is one of the most effective treatment s for the large amount of municipal sludge coming from sewage treatment plant.This paper mainly studies the influence of different process parameters on the energy consumptions and pellet properties of sludge-biomass pellets. The process parameters included pressure(28-110MPa), temperature(30-150oC), moisture content(5-25%), sludge mixing ratio(0-100%) and raw materials(Chinese fir sawdust, camphor sawdust and straw). This paper analyzes compression energy consumption, extrusion energy consumption, pellet density, expansion rate, Meyer hardness and water absorption. The effects of various process parameters on the energy consumption and pellet properties were identified. The pressure was applied to provide the necessary power for the material in the mold, which made the loose biomass become dense and improved the briquette strength. With the increase of pressure, pellet density increased. The Meyer hardness of pellets was found to be independent with applied pressure and biomass materials. The die temperature is an important factor affecting co-pelletization of sludge and biomass. High pellet density, high hardness and low expansion sludge-biomass pellets could be obtained under the temperature of 90~150oC. However, the high temperature meant more energy consumption. Water can serve as binder and lubricant in pelletization. Excess and low content of water in raw materials was not suitable for pelletization. Experimental results showed that high pellet density, high Meyer hardness, low energy consumption and low expansion of pellet can be obtained u nder the moisture content of raw materials mixture in the range of 10%~15%. Hemicelluloses and cellulose with a certain degree of viscosity characteristics can play as reinforced frame in co-pelletization of sludge and biomass. Sludge particle filled in the void and served as cement, which led to good bonding. Therefore, with the increase of the proportion of sludge, pellet density and hardness of sludge-biomass pellets increased while water absorption decreased.Through the comprehensive investigate of energy consumption and pellet properties under different process parameters, the appropriate sludge-biomass pelleting conditions were 55~83MPa for the pressure, 110~130 oC for the temperature, 10~15% for the moisture content, and 50% for the sludge ratio. The combustion process of the pellet has four characteristics stages, namely water evaporation, combustion of volatile matter, fixed carbon combustion and burnout. With the increase of the proportion of the pellet sludge, weight loss rate of volatile decreased, while the combustion rate of fixed carbon increased.