AbstractsPhysics

Verge grass is being considered to replace expensive wood pellets (thus reducing imports) as potential bio-energy resources for use in co-firing. However, drying of these verge grass resources is very important because of its high moisture content (almost 60 % wt.) and also results in an increased heating value for the fuel. Drying is the first process which occurs before torrefaction of biomass (which serves as an important pre-treatment step before co-firing with coal). Though fixed bed drying models have been studied in the past, development of drying models for drying verge grass have so far not been investigated. The drying of verge grass in fixed bed using a system of coupled differential equations in the gas phase and algebraic equations in the solid phase have been used to setup mass and energy balances has been investigated. The system of differential and algebraic equations has been solved by the Runge-Kutta method using ordinary differential equation solvers available in MATLAB® and by using finite difference techniques. The behaviour of the process variables (air humidity, air temperature, solid moisture content and solid temperature) with time and height has been investigated. Further a sensitivity analysis has been performed to study the effect of the influence of varying process parameters such as inlet air flow rate and temperature on the drying process. To validate the model, data from experiments performed with grass on a lab-scale drying and torrefaction setup were used at the Energy Technology research group have been used. With increase in the inlet air flow rate and the air temperature the drying time period was reduced due to an increase in the drying rate. Under certain conditions the model was insensitive with regard to increase in the number of grid points used in modelling in space and time. The simulation results however weren’t in agreement with experimental results and need to be further to investigate the validity of the assumptions or correlations used in the process of modelling.