Numerical Simulation Of Biomass Briquette Heating Stove With Swirl Grate

It is studied how to organize better combustion flame, enhance combustion in biomass briquette heating stove with narrower space and lower temperature, in order to reduce pollutant emissions and improve stove thermal efficiency in this article.The combustion experiments and analysis of thermal balance for the biomass briquette heating stove are studied. Some problems such as combustion of the incomplete biomass fuel, ash blockage the air channel, a hypoxia combustion zone, uneven mixed between volatile and secondary air, bigger exhaust smoke loss are found in biomass briquette heating stove. Then, a grate optimization program——Swirl grate burner is proposed.Cold state test of biomass briquette heating stove is studied. Cold velocity field of the biomass briquette heating stove with cyclone and non-cyclone grate is analyzed, proved that the cyclone grate can produce swirl velocity field.Based on FLUENT software, according to the characteristics of biomass briquette heating stove, employing RNG k-ε turbulence model and wall function method, non-premixed combustion model and the P-1radiation model coupled multi-field of the furnace, using the prePDF program calculated chemical reaction equilibrium, built a numerical simulation system of the biomass briquette heating stove. Numerical simulation study of different excess air coefficient, secondary air inlet angle and grate length-width ratio combination in the heating stove is considered, aiming to solve the velocity, temperature and concentration field changes in the furnace and flue gas composition changes on furnace exit. The main conclusions are drawn as follows:(1) When the simulation model using Swirl grate burner, exhaust temperature is decreased obviously, flue gas temperature distribution is uniformly distributed, the range of temperature fluctuation is narrowed. Thermal efficiency between flue gas and heat exchange tube is improved, and the problem of large heating grate smoke loss is solved. Indicated that the simulation model is accurate and reliable, superior to use square non-cyclone grate;(2) With the increase of excess air coefficient, the swirl strength increased gradually, the recirculation zone upward displacement, flame transverse area increased and close to the furnace wall gradually, until the wall-attach combustion phenomenon generated. When the excess air coefficient is1.5, furnace exit flue gas temperature distribution is uniformly distributed, the range of temperature fluctuation is narrowed and fuel burnout rate is higher and pollutant emission is lower. The conclusion is that the optimal choice of excess air coefficient is1.5.(3) With the increased of secondary air inlet angle, the swirl strength decreased, the swirling flow region closed to furnace wall and disappeared gradually. When the angle of secondary air inlet is30°, furnace exit flue gas temperature distribution in the most homogeneous, the range of temperature fluctuation is narrowed and fuel burnout rate is higher and pollutant emission is lower. The conclusion is that the optimal choice of secondary air inlet angle is30°.(4) When the grate length-width ratio is1.6, furnace exit flue gas temperature distribution is uniformly distributed, the range of temperature fluctuation is narrowed and fuel burnout rate is higher and pollutant emission is the lowest. The conclusion is that the optimal choice of grate length-width ratio is1.6.