| In this study, firing brick tunnel kilns was examined, gas-solid two-phase flow along the cooling zone of a tunnel kiln and the process of firing zone combustion are performed using numerical simulation. Research achievement can be utilized in the theoretical guidance of reducing the dust and NOx pollution emissions of firing bricks tunnel kiln.This research is based on FLUENT, using natural gas top-combustion tunnel kiln as the research object, geometrical model and numerical model of cooling zone and firing zone has been established. The air flow rate and particle concentration in cooling zone, distribution of NOx concentration field in the firing zone based on different technological parameters have been determined from the calculation using numerical simulation.The work have been done in this research list below:1. Investigations on air velocity field along the cooling zone and particle concentration field inside firing bricks tunnel kilns have been carried out. Cooling air has faster air flow rate, stronger convection along the longitudinal channel of tunnel kiln and brick packages, while has slower air flow rate and weaker convection along the width channel of tunnel kiln. particle mainly aggregate in the gap of tunnel kiln along the width direction, which will gather together positioned downstream of the cooling air, and the particle concentration increases along the longitudinal direction of the tunnel kiln. Along the height direction of tunnel kiln, as the height increases, the dust concentration becomes lower and lower.2. Investigations of how the cooling air rate affects the particle concentration in the cooling zone. On the conditions of high air flow rate, accelerated gas flow rate has been found on each section of tunnel kiln, which results in enhanced particle transportation and reduced particle concentration inside the kiln. Therefore, increasing cooling air rate can reduce the dust pollutant emission of firing bricks in tunnel kilns.3. Investigation on the effects of different brick arrangement on the particle concentration along the cooling zone. Sparse arrangement cause smaller air flow resistance, higher air flow rate, easier particle diffusion, lower concentration of particle in the cooling zone. As a consequence of that, decreasing the stacking density of the bricks can reduce the dust pollutant emission of firing bricks tunnel kilns effectively.4. Investigation of firing zone temperature field and NOx concentration field inside firing bricks tunnel kilns. The firing zone temperature increases along the height direction of kiln, additionally, high temperature zone primarily concentrates at the roof gap. The type of NOx inside kiln is mostly as Prompt NOx, concentration gradually decreases along the height direction of kiln and slowly decreases from the centre to both sides of kiln wall along the width direction of kiln.5. Investigation on impact of brick packages porosity on temperature field distribution inside kiln. High porosity means sparse bricks arrangement, so the smaller resistance within the fluid zone will be. Thus, fuel and air can be mixed uniformly and complete combustion can be achieved. As the porosity increases, temperature of the bricks increases and temperature in the roof gap gradually decreases. Hence, higher porosity can decrease the temperature difference inside kiln, which benefits higher quality of products.6. Investigation on porosity of brick packages effect on NOx concentration in the firing zone. With the increasing porosity, average NOx concentration of the section which along the height direction of kiln and gas outlet gradually decrease. So NOx pollutant emission can be reduced by higher porosity of brick packages.The results of this research indicate: increase cooling air velocity can reduce the dust pollutant emission of firing bricks tunnel kilns; decrease the density of the bricks arrangement is beneficial to improved quality of products, and decreased NOx and dust pollutant emission. |
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