As a renewable non-food resource, biomass has great potential as an energy source or feedstock for further conversion. However, potential problems exist with transportation and storage of this geographically widely scattered and perishable resource. As a precursor to further thermochemical conversion, wet torrefaction treats any kind of biomass in 200 to 260°C compressed water under a nitrogen atmosphere for a period of less than 20 minutes.. It is also known as hydrothermal carbonization or hot compressed water (HCW) treatment. The pretreated solid is about 60 – 80% of the mass of the originating solid, and has 80 – 95% of the fuel value of the original biomass feedstock. Byproducts include carbon dioxide, volatile organic acids such as acetic acid, precipitates of glucose and 5-hydroxymethyl furfural. Regardless of the initial form of biomass, the solid product has decreased equilibrium moisture content for longer “shelf life,” and increased fuel value. The solid product is friable, and resembles charcoal.
In this study, acetic acid addition to the wet torrefaction process when run at 230°C has been shown to increase the energy densification of the solid product. A maximum in higher heating value (HHV) was found at a level of 0.4 g acetic acid added per g of biomass. With recycling of acetic acid produced in the reaction system, the pretreated biomass product could be enhanced at minimal cost. Another possibility to enhance the wet torrefaction of lignocellulosic biomass is the addition of lithium chloride. Energy densification can be improved with the addition of LiCl to the wet torrefaction process. Another benefit of LiCl addition is the reduction of the reaction pressure necessary to maintain liquid water at reaction temperatures. Lower reaction pressure reduces reactor cost and decreases safety risks.
See more of this Group/Topical: Engineering Sciences and Fundamentals