Improving Kraft Pulp Mill Energy Efficiency through Low-Temperature Hydrothermal Carbonization of Biological Sludge

Of the various waste and side streams created in a kraft pulp mill, biological sludges from wastewater treatment plant are some of most problematic to handle. Incineration is becoming common solution as landfilling no longer permitted by legislation many countries, but this also due high moisture content, poor drying characteristics, ash content solids. This study evaluates technical potential mild hydrothermal carbonization (HTC) at 160 °C for 3 h improve energy efficiency on-site incineration biosludge handling method. HTC transforms wet organic substrates into hydrophobic carbonaceous material (hydrochar). The heating value elemental composition both sludge hydrochar product were analyzed. Based on this, model developed earlier was adjusted feedstock, process integration modelling performed evaluate performance impact power heat generation mill. results indicate that if alternative combustion boiler, pre-treatment could allow significant increase generation. If combusted recovery practice often avoided order not introduce non-process elements chemical cycle sometimes necessary to, e.g., absence much smaller obtained. smallest freed evaporator capacity cannot be utilized increasing firing liquor dry solids content.