S. V.PRAKASH1, Dr. S.R. SHANKAPAL2

1. Sr. Lecturer, MSRIT, MECH. DEPT., Bangalore-560054, yagprash@hotmail. com

2. Director, MSRSAS, Bangalore-560054, srspal@msrsas. org,

ABSTRACT:

An existing oil fired furnace was modeled to obtain the maximum swirling of biomass based slurry fuel and air to achieve better combustion of the biomass fuel present in the slurry. For analysis a computational model of the furnace was constructed with a swirl burner placed at the bottom of the furnace using commercially available CFD preprocessing software (GAMBIT). The boundary conditions were set so as to allow biomass slurry and air with different swirl angles with respect to horizontal and vertical planes, with constant velocities of the mixtures. This research work studied the effect of different inlet angles of the fuel at constant velocity into the furnace for maximum combustion efficiency. Using Fluent code, the post process results shows the increase in residence time by 40 % with inlet angle of 45 deg with respect to the x and z-axis, 75 deg from positive y-axis and top partially opened, compared to the initial position of the swirl burner placed directly at 0deg.

1.INTRODUCTION:

The Biomass slurry fuel considered in this research work is a combination of coconut shell powder, light diesel oil, water and air. Since a long time lot of research work has been done to replace the fossil fuels by certain ecofriendly fuels, initially the diesel oil was tried to replace by coal-oil fuel combination so that they could save the oil at the same time control the pollution to certain extent, but there was lots of problem associated with the combustion of the coal oil slurry because of the presence of the ash, highly viscous and particles size [1]. However, by utilizing biomass with fossil fuels as external input fuels, we would get about 10-15 times more electric energy per unit fossil fuel, compared with a 100% fossil power system. All this past research motivated to the present work, which involves combustion of biomass slurry in oil fired furnaces, which can be use for either power generation, melting purposes or as a fuel in I. C.engine. Coal water slurries and coal-methanol studies were developed over the last 20 years as an alternative to liquid fuel mainly in industries and power generation furnaces [2-3]. Determination and improvement of combustion characteristics of coal-water slurries are as important as the preparation of the suitable slurry. Suspended single droplet combustion technique was the method used in the investigation of combustion characteristics of liquid fuel droplets. The
study includes the study of the droplet lifetime history, ignition delay, flame structure, center and surface temperature of the droplet and burning rate [4]. Later the problems involved in using the coal were overcome by using a novel technique by superfine grinding the coal and selective separation of the coal particles and other inorganic ingredients and finally combustion of the fine fraction coal in slurry droplets [5]. Based on the same principles in 1995 investigation on combustion of biomass-based fuel slurries were successfully done and the solid fuel particles were dispersed in a liquid medium and the resultant slurry fuel was burnt like a liquid fuel [6]. The biomass slurry considered were pulverized coconut shell powder, light diesel oil and water, the solid fuel was directly mixed with the liquid medium and was burnt in an oil-fired foundry furnace without adding any chemicals and no problems were encountered during the combustion process, since most of the study was concentrated on the combustion of the droplet of fuel burnt and its characteristics like droplet lifetime history, ignition delay, flame structure, center and surface temperature of the droplet and burning rate[7-10], now with the advent of the commercially available software like CFD with preprocessor(GAMBIT), postprocessor(FLUENT) and the solvent, the required properties for biomass slurry were developed and combined with the commercially available Fluent software to study the flow analysis of the fuel in the furnace and the problems that were encountered in the droplet study were easily overcome and a complete flow analysis of the fuel in the furnace was done. A pulverized biomass slurry combustion simulation involves modeling a continuous liquid phase flow fluid and its interaction with a discrete phase of biomass particles. The biomass particles traveling through the gas devolatalize and undergo char combustion, creating a source of fuel for reaction in the gas phase. Reaction can be modeled using either the species transport model or the non-premixed combustion model. The non-premixed combustion model uses a modeling approach that solves transport equations for one or two conserved scalars, the mixture fractions. Multiple chemical species, including radicals and intermediate species, may be included in the problem definition and their concentrations will be derived from the predicted mixture fraction distribution. Property data for the species are accessed through a chemical database and turbulence chemistry interaction is modeled using a beta or double beta probability density fraction (PDF). With relevant data as in annexure-1, the computational model and flow analysis was carried out.