Robert J. Stirling
University of Nottingham, UK
Title: Hydrothermal carbonisation of biomass to produce reduced-ash fuel
Biography
Biography: Robert J. Stirling
Abstract
Hydrothermal carbonisation (HTC) is potentially an attractive option as a pre-treatment process to produce an energy dense, friable, reduced-ash, chlorine free solid biofuel (also referred to as biocoal) from biomass. It is particularly attractive for waste feedstocks with a high moisture content, which would not require drying before treatment. HTC experiments have been conducted on a range of biomasses, including wood pellets, olive cake, miscanthus pellets, and sewage sludge over the temperature range of 200-300oC with residence times up to 4 hours, using a Parr reactor. The resultant char was then subjected to proximate analysis with the alkali and alkaline earth metal contents of the process water being determined by ion chromatography and induction-coupled plasma (ICP) analysis. To complete the mass and carbon balance, gas chromatography was used to analyse the gas generated by the process and the dissolved organic carbon content of the process water was determined. The biocoals produced had considerably higher fixed carbon contents than the feedstocks with the HTC process generating additional quantities of fixed carbon compared to the feedstocks. At 200oC, the biocoal represented 82% (dry, ash free basis) of the wood, which corresponds to over 90% of the initial carbon. Although increasing temperature increases fixed carbon content further, the yields of biocoal were reduced markedly. HTC was also shown to reduce ash content considerably through extraction of alkali and alkaline earth metals.