Simulation operating modes for enhancing the efficiency of a shaft limestone kiln

Abstract

Analysis of performance by various shaft lime stone kilns with distributed central and peripheral gas fuel supply, applied in metallurgical industry, shows that the major disadvantages of these units are caused by poor gas mixing conditions and incomplete burning of fuel. To avoid over burning the lime due to the high heat capacity of natural gas, primary fuel for these furnace, the mixing and combustion must occur directly in the moving packed bed of material. That results in low quality of end product.
However, the way this problem can be partially resolved is the development and optimization of justified and efficient operating modes based on advanced technical solutions for gas fuel mixtures. To reduce fossil fuel consumption, one of the possible solutions for metallurgical plants is application of waste combustible gases like blast furnace gas combined with optimal fuel and air distribution between all levels of kiln burners.
For this purpose, the mathematical model of a shaft counter flow lime-stone kiln with central and peripheral natural gas supply was developed. The model took into account gas dynamics in the moving bed of lime-stone material, convection, fuel combustion, external and internal heat transfer.
To reduce the consumption rate of natural gas in lime stone calcining, the optimization of operating modes was conducted. as working conditions there were examined fuel, air and recycling gas distribution between central and peripheral burners.
As a result, the efficient operating conditions of the kiln were determined. In average, the reduction of natural gas consumption rate comprised 20 ÷ 25 % with enhanced performance of the whole unit, in terms of product quality and productivity.
According to the obtained results, switching the kiln to firing with mixtures of natural and blast furnace gases can lead to economy of natural gas by 30%.