Hancai Zeng

Flexibility of a 300 MW Arch Firing Boiler Burning Low Quality Coals

Abstract Experimental investigations on the flexibility of a 300 MW Arch Firing (AF) coal-fired boiler when burning low quality coals is reported. Measurements of gas temperature and species concentration and char sampling using a water-cooled suction pyrometer were carried out along the furnace elevation. The carbon content and the size distributions of the char samples were obtained. The char morphology was examined using a field emission scanning electron microscope (FESEM). The char sampling was performed on this type of boiler for the first time. The results indicate that the flexibility of this boiler burning low quality coals under a moderate boiler load is better than its flexibility under a high boiler load. Because of the insufficient capacity of the coal pulverizers used, in case of low coal quality the pulverized coal fineness will drastically decrease under high boiler loads. This causes an increase in the loss due to incomplete mechanical and chemical combustion. This is the main cause of a low burnout degree of the pulverized coal and the decrease of the flexibility of this AF boiler under a high boiler load.

Determination of Optimum Blending Ratio During Coal Blends Combustion

Abstract This paper reports the experimental research on combustion and pollution properties of several typical Chinese individual coals and coal blends and the methods determined optimum blending ratios. Thermogravimetry analysis technique and a drop-tube furnace were used to investigate the ignition and burnout behavior and NOx emission characteristics. Ash chemical composition and fusion temperature was also measured. The effects of the blending ratios on ignition, burnout, slagging and NOx emissions have been analyzed. The fuzzy logic approach has been used to determine the optimum blending ratios based on experimental data which provide a scientific basis for design and operation of power station blending coal. Calculation results were comparable with that of results obtained from combustion test carried out in a boiler simulator furnace.

Effects of SO2 and NO on removal of VOCs from simulated flue gas by using activated carbon fibers at low temperatures

Abstract Volatile organic compounds (VOCs) have serious detrimental effects on the environment and the health of human beings. The removal of pollutants from coal-fired power plants by activated carbon fiber (ACF) adsorption is a promising method. In this study, hydrogen peroxide (H 2 O 2 ) was used to modify ACF samples and the methods of N 2 adsorption isotherm and XPS (X-ray photoelectron spectroscopy) were utilized to characterize the ACF samples. The adsorption tests of VOC (toluene as a typical representative) based on ACF were conducted and the effects of SO 2 and NO on the adsorption of toluene were investigated. It was found that H 2 O 2 modification had no impact on the BET surface and pore volume of the ACF sample, although it increased the oxygen groups on the ACF surface. The results also indicated that SO 2 or NO inhibited the adsorption of VOC on ACF, and this inhibition strengthened with an increase in the concentration of SO 2 or NO. It is also found that the coexistence of SO 2 and NO deteriorates the adsorption of VOCs on ACF more seriously than the single existence of SO 2 or NO.

Grey Clustering Prediction for Slagging Potential of Coal Blends Combustion

The ash behavior and slagging characteristics of several individual coals, different in rank and ash content, and of their two-component blends, were studied by measuring chemical composition, ash fusion temperature, viscosity, and mineral transformation. The experimental results indicate that ash fusion temperatures for various percentages of two different coal blends illustrate non-arithmetic averaging. The fusion slag of base coals affects the viscosity of coal blends. Temperature and atmosphere affect mineral species vaporization. Considering the limitation of single slagging index for prediction, an overall grey clustering model that takes into account the main related parameters such as ash characteristics, mineral transformation, and combustion parameters is proposed to predict the slagging propensity of the blends. The results suggest that the slagging propensity of coal blends from two coals of similar reactivity and slagging potential was similar to that of the individual coals. However, when one coal was blended with another coal with widely different reactivity or slagging potential, the slagging grade of the coal blends changed significantly. The results of slagging experiments in a combustion test furnace were in agreement with those from model prediction. It implies that the proposed overall grey clustering model can predict slagging tendency more accurately than conventional index. Moreover, the predicted results are comparable with that from a practical boiler slagging test.

Effect of surface oxygen/nitrogen groups on hydrogen chloride removal using modified viscose-based activated carbon fibers

Activated carbon fibers (ACFs) can effectively remove pollutants including nitrogen oxides, sulfur oxides and trace metals due to their rich micropores and large specific surface area. This work aims to investigate the roles of surface carbon–oxygen and nitrogen–oxygen species on the removal of hydrogen chloride (HCl) using viscose-based ACFs. To evaluate the effect of surface carbon–oxygen and nitrogen–oxygen groups, commercial viscose-based ACFs were treated by thermal treatment (900 °C) and chemical impregnation using H2O2, HNO3 and Cu(NO3)2. Pore volumes, average pore sizes and specific surface areas were separately characterized by t-plot method, density functional theory and Brunauer–Emmett–Teller theory. The surface morphology of the ACFs was observed by a scanning electron microscope. An X-ray photoelectron spectroscopy (XPS) technique was applied to determine the specific ratios of surface oxygen and nitrogen groups. Temperature programmed desorption was performed to investigate HCl adsorption behaviors over the ACFs. As experimental results, the thermal process decreased the carbon–oxygen groups while H2O2 impregnation increased the carbon–oxygen groups (especially carbonyl and carboxyl). Nitroso and nitro groups were introduced onto the carbon surface after HNO3 and Cu(NO3)2 treatments. The removal efficiency of HCl was improved slightly by H2O2 modification due to the increase of carbon–oxygen groups, and significantly by HNO3 and Cu(NO3)2 treatments because of newly formed nitrogen–oxygen groups. Nitroso and nitro groups show significant promotion of HCl retention ability over the ACFs surface. Moreover, HCl removal efficiency was much more influenced by nitroso than nitro groups.

Adsorptive Removal of SO2 from Coal Burning by Bamboo Charcoal

Bamboo charcoal (BC) is an environmentally friendly, low-cost and renewable bioresource with porous structure. The adsorption property of bamboo charcoal for sulfur dioxide was investigated through a parametric study conducted with a bench-scale bed and mechanism study by BET, XPS, and temperature pro-grammed desorption (TPD). The varying parameters investigated include particle size of BC, moisture, oxygen, nitric oxide. The experimental data suggest that BC has a good adsorption potential for SO2, which removal efficiency is greatly dependent upon the operation conditions. This study provides a good reference for BC to be used for SO2 removal in the actual flue gas over a wide range of conditions and further provided the preliminary experimental studies and theoretical discussion for bamboo charcoal to be used in multiple pollutants removing.