Mathematical modelling and experimental study of straw co-firing with gas using electric field control of combustion characteristics

The main aim of the research is to provide wider and more efficient use of a renewable fuel - straw for energy production with reduced GHG carbon and polluting NO_x emissions during co-firing straw pellets with gas (propane) und using the electric field control of thermochemical conversion of straw. A pilot plant with a combined biomass gasifier and combustion chamber with the heat power up to 4 kW has been used to provide the thermochemical conversion of straw pellets during co-firing with gas, which is supplied at the outlet of the gasifier with average heat input 0.8 kW. A positively charged electrode was inserted axially into the flame base for electrical control of the thermal decomposition of straw pellets and combustion of volatile compounds (CO, H₂, C_xH_y). The field-induced electric body force enhanced the mass transfer of combustible volatiles from the axial reaction zone toward the water-cooled walls of the combustor providing radial expansion of the reaction zone and enhancing the heat output from the device. The electric field effect on the combustion characteristics and heat output from the device was estimated from the results of the complex measurements of the flow velocity components, flame temperature of the produced heat energy per mass of burned volatiles and the composition of emissions by varying the bias voltage of the electrode in the range from 0 up to 2.4 kV and the ion current in the range from 0 to 6 mA. For the calculation and solving a system of 9 parabolic type PDEs for the 2D compressible laminar axisymmetric flow in a coaxial cylindrical pipe with the electric field between the axially inserted electrode and the grounded walls of the pipe and with the simple exothermic reaction the mathematical modelling is developed. The maximal values of the temperature, flow velocity components and the mass fraction of the products (CO₂) were estimated.