A Novel Application of Biochar Produced from Invasive Weeds and Industrial Waste in Thermal Backfill for Crude Oil Industries

The application of biochar in agricultural practices and vegetative slopes has been rigorously recommended in previous literature. However, its potential application in other industries is scarcely explored. Biochar is a chemically stable material with a low thermal conductivity, which makes it a perfect fit for blending with soil to use as thermal backfills. A thermal backfill is an essential component for maintaining the ambient temperature around the underground pipelines and storage tanks of crude oil industries. This study investigates the potential application of eighteen soil-biochar blends as thermal backfill. Highly plastic silt and clayey sand (SC) soil were amended with three different biochar types viz. hardwood biochar, water hyacinth biochar, and sugarcane bagasse biochar (SBBC), at three biochar contents of 2.5%, 5%, 7.5% (w/w). Thereafter, their compaction characteristics, thermal and physicochemical properties were investigated. The thermal conductivity ( K ) and volumetric heat capacity ( C ) of MH soil were reduced by 22%, 29%, 33%, and 16%, 24%, 26% with 7.5% amendment of hardwood, water hyacinth, and SBBC. Similarly, K and C values of SC soil decreased by 22%, 34%, 37%, and l2%, 18%, and 20%. The micrographic analysis of soil-biochar blend reveals that the entrapped air in biochar particles governs the heat transfer in biochar-amended soil. An inverse correlation of thermal conductivity with pH and electrical conductivity was also observed for the soil-biochar mixes. This study extends the domain of biochar application highlighting the engineering properties of different blends, which would be helpful for its field-scale application. Graphical Abstract