Kinetic Modeling of Hydrothermal Carbonization for a Waste-to-Energy Economy

DATE: JANUARY 2023
UNIVERSITY OF EDINBURGH | UK BIOCHAR RESEARCH CENTRE
ELOISE BEVAN, PhD STUDENT

I am studying the biomass waste-to-energy conversion process known as Hydrothermal Carbonization (HTC). Unlike other thermo-chemical conversion processes, HTC operates in an aqueous medium of water, where, under high temperatures and pressures, wet organic materials such as plant matter, sewage sludge, and food waste are efficiently converted to valuable end-products. HTC produces three product streams: a solid material (hydrochar), a liquid (hydrolysate), and a gaseous stream. Hydrochar has a range of applications, including bio-coal, soil amendment- a super-capacitor material, filler in tires, and activated carbon. The aqueous liquid, hydrolysate, can be used as a fertilizer or for ethanol production. The gaseous stream has the potential to be directed through a carbon capture system if paired with the technology. When applying hydrochar as a bio-coal, HTC has a net positive energy balance making this waste-to-energy process a very promising technology for developing a sustainable and circular economy.

I have developed a lab-sized rig where I will be performing HTC experiments on components of lignocellulosic biomass (cellulose, hemicellulose, and lignin), which comprise all organic plant material. Where, for a range of process conditions, I will be measuring the product yields and percentage of carbon in each product stream. At present, the UK Biochar Centre has only one viable method to quantify the amount of gas produced and the carbon recovery in this phase. Which is to be collected in a gas bag, submerged in water, and dispensed for analysis in the mobile gas analyzer. However, the submerging method is not the most accurate way to measure the volume of gas produced. A more accurate method to measure the volume of gas would be to collect the gas in an inverted volumetric cylinder released for collection through a water basin, where the gas can displace the water within the cylinder. However, this method means that the gas cannot be collected for subsequent analysis. With a Gas-Tigh Super Syringe, I can be the first to produce an accurate kinetic model that can be applied to the HTC of any type of biomass and does not neglect the gas phase.