Techno-economic And Environmental Assessment Of Biomass Torrefaction, Hydrothermal Carbonization, And Steam Explosion Pretreatment Technologies

As a renewable energy source,biomass has received great attention and rapid development over the past decade.After pretreatment,the physical and chemical properties of biomass have been improved,such as increased calorific value and grindability.Biomass pretreatment technologies include torrefaction,hydrothermal carbonization and steam explosion.Up to now,the production of fuel pellets by torrefaction pretreatment has been developed to the industrial scale,while hydrothermal carbonization and steam explosion are still in the pilot stage.Performing energy,economic,and environmental assessments of the three pretreatment technologies can properly understand the development and market potential of those technologies.In this study,a random forest kinetic prediction model was constructed by collecting kinetic data and python programming.The kinetic prediction model can be used to generate data as Aspen Plus input to establish process simulation models for three pre-treatment methods.The simulation models can help to calculate the mass balance and heat balance of the three pre-treatment processes.Life cycle boundaries were defined and life cycle assessment models were established to calculate the energy consumption and carbon dioxide emissions of the three processes.The capital cost,operating cost of the pellet plants and the minimum selling price,delivery cost of pretreated pellets were estimated to evaluate the economic performance of different pre-treatment methods.At the pellet plant level,with an annual output of 100,000 tonnes of pellets,the energy consumption of the torrefaction pretreatment process is 0.0383GJ/GJ pellet,followed by hydrothermal carbonization（0.0587 GJ/GJ pellet）and steam explosion（0.0662 GJ/GJ pellet）.The torrefaction pretreatment process has the lowest carbon dioxide emission,596 g CO_2-eq/GJ pellet.914g CO_2-eq/GJ pellet for hydrothermal carbonization,and 1031 g CO_2-eq/GJ pellet for steam explosion.The production cost of torrefaction pretreated pellets is the lowest,at 6.82$/GJ pellet,followed by steam exploded pellets at 7.81$/GJ pellet,and hydrothermal carbonized pellets at 8.6$/GJ pellet.The most sensitive factor in the production cost of the three types of fuel pellets is the cost of raw materials.At the entire supply chain level,with an annual output of 100,000 tonnes of pellets,the supply chain energy consumptions for torrefaction,hydrothermal carbonization,and steam explosion were 0.1064,0.1453,and 0.1506 GJ input/GJ pellet output,respectively.Supply chain carbon emissions were 2056,2762,and 2837 g CO_2-eq/GJ pellet,respectively.The delivery costs were 13.91,15.33,and 18.69$/GJ pellet,respectively.