Papers by Keyword: Pulverized Coal

Abstract: By rapid pyrolysis of pulverized coal in oxygen and steam atmosphere, powder activated coke (PAC) nanostructured carbon material was derived by one step. Then, nitrogen adsorption measurement, scanning electric measurement (SEM) and Fourier transform infrared spectroscopy (FTIR) test were conducted to analyse the detail characteristic of the obtained PACs. The results showed that the one-step pulverized coal rapid pyrolysis process was an effective method for the production of PAC powders. The mixture of oxygen and steam as the activating agent was essential during the pyrolysis progress. Oxygen act as the most important fast activating agent for the pore formation, while steam activation protected the material matrix and weakly affected pore growth. The composition and concentration of oxygen and steam had a great effect on pore structure, surface micromorphology and functional groups of PACs. The mixed oxygen and steam atmosphere exhibited a tightly tailored micropore structure. By further optimizing activating oxygen and steam composition, the PAC products could have considerable pore structures, respectable surface morphology and functional groups.

Abstract: Chlorine additives are often used to improve the combustion performance of pulverized coal injection (PCI) in blast furnace. The influence of chlorine additives on pulverized coal combustion rate was analyzed and the micrograph of unburned pulverized coal (UPC) was observed by SEM in order to analyze the influence mechanism of chlorine additives. The results show that proper addition amount of CaCl₂, NaCl, MgCl₂ and FeCl₃ respectively promotes pulverized coal combustion in different degrees. The average size of UPC is smaller and the micrograph becomes irregular when the chlorine additives are increased. While beyond the appropriate addition amount, the combustion rate of PCI reduces. During the combustion process of pulverized coal with chlorine additives, HCl is produced which prevents the combustion process.

Abstract: Methane and carbon dioxide of different pressures were absorbed by the anthracite coal for 5 hours in high pressure reactor. When adsorption experiment was completed, pressure is reduced quickly. The content of pulverized coal which was produced by releasing gas quickly, was used to reflect capacity of gas adsorption. The result showed that the content of pulverized coal which was produced by adsorbing CH₄ was higher than that was produced by adsorbing CO₂ on the same coal under the same pressure. Langmuir isotherm and Freundlich isothermal can describe coal methane adsorption. Freundlich isothermal can be a good description of coal carbon dioxide adsorption.

Abstract: In the present research work, adding a certain amount of coke dry quenching(CDQ) dust to pulverized coal used in blast furnace is proposed for efficient utilization of resources and reducing smelting cost. The properties of coal blends and coal/dust blends were investigated by using long tube tester and the device of thermogravimetry (TG). Important results were obtained by experimental researches about explosibility and combustion performance. According to optimum blending ratio of coal B in coal blend (around 50%), burnout of coal/dust blends decreases after adding CDQ dust in the range 5% to 10% to blends. However, all of them are more than 80%, which can meet production requirements. In the case of adding about 8% of CDQ dust to coal blend, combustion efficiency is better and safety injection can be realized.

Abstract: The effects of Ca-based sulfur catcher on sulfur fixing were investigated by experiments. The results indicate that sulfur capture efficiency of CaO is the maximum when n(CaO)/n(S) ratio is equal to 2.5. Moreover, the influences of Cr₂O₃ on sulfur-fixing of CaO were studied when n(CaO)/n(S) ratio is equal to 2.5. The results indicate that addition of Cr₂O₃ can improve the sulfur capture efficiency of CaO, and efficiency of CaO is the best when Cr₂O₃ is added to 0.5%. This is because that Cr₂O₃ can be oxidized to CrO₂. On the one hand, the oxides of chromium can catalyze the reaction of sulfur-fixing. On the other hand, CrO₂ can react with SO₂ to form Cr₂(SO₄)₃. These also can improve the sulfur capture efficiency of Ca-based sulfur catchers.

Abstract: Reduction of high-phosphorus titanomagnetite was studied for future comprehensive utilization of resource. Experimental temperature (T), burden alkalinity (CaO/SiO₂) and carbon-oxygen ratio (C/O) had an influence on the content of [P] and [S] in hot metal. Highest dephosphorization rate in hot metal appeared at C/O=1, high temperature was beneficial to desulphurization, but not for dephosphorization. High CaO/SiO₂ may decrease the content of [P] and [S]. C/O and CaO/SiO₂ had great influence on the content of [P] and [S] in hot metal.

Abstract: The combustion stability of pulverized coal is very essential for utility boilers. That is the key issue to keep the operation of the whole power-generation unit in a safe state. The amount of volatile matter is used to anticipate the combustion state of pulverized coal. As a widely accepted concept, higher volatile matter content would result in more stable combustion state. But in some cases, the coal with high volatile matter content led to poor combustion states, even resulted in the flameout of the burner. More method is needed to judge the coal and to predict the combustion stability. With research on the approximate analysis of the coal composition, the heat value of volatile matter was calculated. Such heat value varies obviously for different kinds of coal. The ratio of the heat value of volatile matter to the heat value of fixed carbon is supposed to describe the combustion stability of pulverized coal. The application of the method judges the coal better than using the amount of volatile matter alone.

Abstract: In the present research work, volatile matter, influences of reaction temperature and particle size on combustion performance were investigated. Important results were obtained by experimental researches. Ignition point of anthracite coal/bituminous coal blends decreased with volatile matter in blend and combustion was improved. Burnout of coal blends decreased as a function of particle size. However, similar effects were gained when particle size less than 0.074mm accounted for 70%, 60% and 50%, respectively. By contrast, the ratio of 50% was a better choice for good effect and low cost.

Abstract: The optimum temperature within the reagent injection zone is between 900 and 1150°C for the NO_X reduction by SNCR (selective non-catalytic reduction) in coal-fired utility boiler furnaces. As the load and the fuel property changes, the temperature within the reagent injection zone will bias from the optimum range, which will reduces significantly the de-NO_X efficiency, and consequently the applicability of SNCR technology. An idea to improve the NO_X reduction efficiency of SNCR by regulating the 3-D temperature field in a furnace is proposed in this paper. In order to study the new method, Computational fluid dynamics (CFD) model of a 200 MW multi-fuel tangentially fired boiler have been developed using Fluent 6.3.26 to investigate the three-fuel combustion system of coal, blast furnace gas (BFG), and coke oven gas (COG) with an eddy-dissipation model for simulating the gas-phase combustion, and to examine the NO_X reduction by SNCR using urea-water solution. The current CFD models have been validated by the experimental data obtained from the boiler for case study. The results show that, with the improved coal and air feed method, average residence time of coal particles increases 0.3s, burnout degree of pulverized coal increases 2%, the average temperature at the furnace nose decreases 61K from 1496K to 1435K, the NO emission at the exit (without SNCR) decreases 58 ppm from 528 to 470 ppm, the SNCR NO removal efficiency increases 10% from 36.1 to 46.1%. The numerical simulation results show that this combustion adjustment method based on 3-D temperature field reconstruction measuring system in a 200 MW multi-fuel tangentially fired utility boiler co-firing pulverized coal with BFG and COG is timely and effective to maintain the temperature of reagent injection zone at optimum temperature range and high NO_X removal efficiency of SNCR.

Abstract: The comparative study of numerical results on pulverized coal combustion process with CFD has become an important measure for direct engineering practice. In this paper, a combustion facility was simulated numerically with the Fluent code to investigate the process of coal combustion. Firstly, geometric models, grid and boundary type were established in the Gambit. Secondly, required models, physical properties and working conditions were chosen in the solver. Then, the important diagrams of each component displayed distinctly in the post professor. The simulation results showed that the rules of the volatile releasing and combustion processes of coke could provide important references to improve the combustion of the pulverized coal.