Numerical Simulation Of Mixed Combustion Of Pulverized Coal & Blast Furnace Gas In A 200mw Utility Boiler

To decrease discharge of blast furnace gas while at the same time save the energy , part of utility boilers are retrofitted for the mixed combustion of coal and blast furnace gas. Nevertheness, the large fuel characteristics differences make design and operation adjustment of the new type of boilers more difficult, and problems such as flue gas deviation, tube explosion ,high exhaust gas temperature and high carbon content of of fly ash are more severe. Therefore, to solve the problems, it is important to study the combusiton and pollutant production process when blast furnace gas and coal are mixed firing. This paper is provided for the purpose on the basis of numerical simulation.A WGZ670/13.7-8 2.1 tangential firing boiler in the Wuhan steel electric limited company is studied in the thesis. Firstly, design condition with full load of the boiler is simulated. During the process, grid comparison and models and the according models parameters are analyzed respectively. Compared with certain design operation parameters and experiment data, the result shows to be reasonable and errors are within the allowance.With the same grid system and models, influence of various amount of blast furnace gas on the combustion and pollutant production process under the same load condition of 180MW is studied. The result shows that, with the increase of amout of blast furnace gas, temperature level decreases significantly and the worsening combustion condition caused by the blast furnace gas leads to reduction of burnout of coal. The result also presents that, for the retrofit on the upper burners with tilting downwards and arc tangent of tertiary air, flame center occurs in the upper burners region, and the less rotation residual is useful to avoid severe thermal deviation.Finally, the influence of different air distribution modes on combustion and particularly NOx emissions condition is discussed. Within the process, the frequent practical operation condition of 90,000 standard cubic meter per hour under 180 MW load is chosen, on the basis of equal air distribution mode, another three distribution modes such as shrinked-middle, waist drum and pagoda are also calculated. The result shows that, the difference of emissions of NOx is significant under various air distribution moded, with the largest differcence of 120 ppm. NOx output under the waist drum air distribution mode is the lowest, which is the same as condition that coal is the only fuel, 25 percent less than that under equal air distribution mode, while the burnout is reduced by 0.3%.However, the lowest NOx ouput still does not meet emission standard of NOx, and more methods should be used to further reduce NOx emissions.