Hydrothermal Carbonization of Crude Oil Tank Bottom Sludge for Energy Applications

Hydrothermal carbonization (HTC) is a promising technology for the conversion of waste biomass into an energy-dense coal-like product known as hydrochar. This study evaluated the application of HTC to generate a renewable solid fuel resource from hazardous oily sludge. The influence of process parameters on the energy characteristics of hydrochar was investigated. A design matrix of 20 experimental HTC runs was used as input for response surface methodology (RSM). The central point for this HTC operation was at a temperature of 200°C, with a duration of 75 min and a concentration of 5.5%. The higher heating value (HHV) increased from 18.18 to 28.7 MJ/kg. A linear correlation was derived between yield and HHV. The influence of process parameters on energy densification and energetic retention properties revealed that energy storage properties were enhanced. In total, 66.6%–80% of energy was retained in hydrochar. The enhancement of the fuel characteristics of hydrochar was demonstrated by the elevated fuel ratio of 0.31 obtained at a temperature of 250°C, thereby indicating the improvement brought about by the HTC process. The quantification of energy losses due to convection and radiation yielded 309 and 1,854 kJ/h, respectively. Maximizing the efficiency of internal heat sources is crucial to conserving energy and reducing costs in HTC.