Use of Mixed Fuel Based on Brown Coal and its Thermal Processing Products in Energy Boilers

The work investigated the thermal behavior of Borodino coal, brown coal coke and mixed fuel, consisting of 80 % Borodino brown coal and 20 % brown coal coke during the combustion process using thermogravimetric analysis. The chemical composition of the samples is presented. When analyzing the TG-DTG curves, combustion characteristics were determined, such as: ignition temperature (Ti) and coke burnout temperature (Te), flammability index, integral combustion parameter. To determine Ti and Te, the technique of crossing the TG and DTG curves was applied and justified. An electron microscopic study of the cross-section of a lignite coke particle has been carried out. The results of the study showed that the addition of lignite coke to brown coal has a positive effect on its combustion characteristics

Evaluation of the Porosity of a Coke Particle According to Its Combustion Data

The dependence of the density of a porous coke particle on its diameter at the particle combustion in the external diffusion mode is analyzed. It is shown that, for the large values of the internal diffusion-kinetic ratio, Sev > 5, the required dependence can be obtained in the analytic form. The analytic formulas are found to be different for the bulk and Knudsen diffusion modes inside the pores. A graphical comparison of the obtained dependences with the empirical power-law dependence is carried out to evaluate the power exponents in the analytic dependences. The corresponding results make it possible to evaluate the effective specific surface area of the pores.

Influence of Mass Transfer on the Critical Conditions and the Time of the Coke Particle Ignition

The time evolution of the temperature in a coke particle during its ignition in a heated gas has been analyzed in order to analytically determine the induction period with regard for the mass transfer of oxygen to the particle surface. It is shown that the ignition process can be divided into characteristic stages. But the inflection points in the time dependence of the particle temperature do not coincide with the stage boundaries and, hence, cannot be used for their identification. When determining the end of the heating stage analytically, it is better to associate it with a temperature that is lower than the inflection temperature by one characteristic interval. When considering the further heating of the particle during the chemical reaction, the mass transfer has to be taken into account. A new method for the analytical determination of the ignition time is proposed, which makes allowance for chemical reactions and the mass transfer that simultaneously run in the transition and diffusion combustion regions.

Fundamental Research on Gasification Dephosphorization with Coke Powder Reducing Converter Molten Slag

In order to realize the gasification dephosphorization process in converter slag splashing stage for avoiding the P enrichment, and the dephosphorized slag can be left for recycling in subsequent furnaces. The experiment of reduction of converter slag by coke powder in laboratory was carried out, The results show that with the increase of the experimental temperature, the gasification dephosphorization rate of coke powder gradually increases, and the gasification dephosphorization rate reaches up to 82.35% at 1900K. The gasification dephosphorization rate decreases with the increase of slag basicity. When the coke powder is added in a sufficient amount, increasing properly the FeO content of slag is favorable for the gasification dephosphorization reaction; when the coke particle size is between 0.5 and 2.5 mm, the gasification dephosphorization rate changed little, about 58%, but when the coke particle size between 2.5 and 3.5mm, the gasification dephosphorization rate dropped to 52%. The results provide some theoretical guidance for industrial development.

Computational fluid dynamics investigation on the effect of co-firing semi-coke and bituminous coal in a 300 MW tangentially fired boiler

In this paper, the effect of co-firing semi-coke in a 300 MW tangentially fired boiler was numerically investigated. The results indicate that the incomplete combustion heat loss and NO x emission both increase with semi-coke co-fired ratio. Semi-coke may be injected into the furnace at a different height, which can lead to different thermal efficiency and NO x emission. It is suggested that semi-coke should not be fed from the top or bottom layer burners, since this could give rise to high carbon content respectively in fly ash and bottom slag. In addition, injecting semi-coke from the top burners could significantly increase the NO x emission. Under 1/2 co-firing ratio, the optimal fuel allocation is that feeding semi-coke from the B, D, and E layer burners. The growth in semi-coke particle size could increase the unburned carbon loss and NO x emission. It is highly recommended to reduce the unburned carbon loss under semi-coke co-fired condition by increasing the stoichiometric ratio of primary air for semi-coke. As it is increased from 0.25 to 0.3, the combustion efficiency of the co-fired condition is 99.47%, the same as when only firing bituminous coal, and the NO x emission is about 30% higher.