Chang’an Wang

Experimental study on interaction and kinetic characteristics during combustion of blended coals

The combustion behaviors and kinetic parameters of three parent coals (A1, A2, and A3) and their blends (A1/A2 and A2/A3) have been evaluated under oxidizing atmosphere (O2 and N2 mixtures), using a non-isothermal thermo-gravimetric analyzer. The aim of this study is to investigate the interaction between the blended components during the process of co-combustion, and the effects of blending ratio and oxygen concentration (10, 15, and 21%) on combustion performance of blended coals. When high reactivity and low reactivity coals are co-combusted, double peaks are observed in the DTG curves, and significant interaction occurs in the temperature range between the two peaks (Tp1 and Tp2). The activation energies obtained by Coats–Redfern method indicate that the activation energies of blended coals are lower than that of parent coals. The combustibility index S is used to evaluate the combustion performance of blended coals, and the results show the non-additive effects of the combustion characteristics of blended coals. The increased oxygen concentration results in a significant improvement of combustion performance of blended coals. In addition, as the blending ratio of high reactivity coal is increased, the oxygen can greatly enhance the combustion stability of blended coals.

Ignition and Kinetics Analysis of Coal Combustion in Low Oxygen Concentration

Abstract The combustion of coals in low oxygen concentration, which exists widely in industry combustion, was investigated by the use of thermogravimetry. Experimental results show that thermogravity/differential thermogravity/differential scanning calorimetry curves of four studied coals shift to a higher temperature zone in lower oxygen concentration. The ignition temperature is almost constant for each coal and increases with the increased coal rank. The burnout temperature and peak temperature increase with the decreased oxygen concentration. The kinetic parameters were calculated using the Coats-Redfern method for coal combustion in low oxygen concentration. The apparent activation energy increases linearly with oxygen concentration, and high rank coal has a high apparent activation energy. An intensive compensation effect exists between the apparent activation energy E and pre-exponential factor A, and the corresponding compensation coefficients are obtained.

Effect of ashing temperature on physical-chemical features of high-sodium ashes of Zhundong coals

ABSTRACT Ash analysis provides useful information for better understanding the serious ash-related issues during utilization of Zhundong coals, while the influence of ashing temperature on exploration of ash properties of high-sodium coals is still unclear. Here, we focused on the effect of ashing temperature on physical-chemical properties of high-sodium ashes. The ash yields of high-sodium coals decrease obviously with an increase of ashing temperature, while the decrease extent is closely related to content and occurrence mode of alkali metals. Partial properties of high-sodium ashes of Zhundong coals are strongly influenced by the ashing temperature, and an appropriate ashing temperature is necessary.

Diffusional effects on differences of coal char reactivity between air and oxy-fuel combustion in thermogravimetric experiments

Oxy-fuel combustion can realize large-scale CO2 capture and low NOx emission from coal-fired power plants, while the evaluation of coal reactivity differences between air and oxy-fuel conditions is of importance for retrofitting existing conventional boilers to oxy-fuel ones. Here, two sets of specially designed experiments were contrastively conducted to assess the diffusional limitation effects on differences of coal char reactivity between air (O2/N2) and oxy-fuel (O2/CO2) combustion in non-isothermal thermogravimetric (TG) experiments, which were seldom investigated previously. Experimental results show that the TG/DTG curves of char combustion present distinct differences before and after reducing diffusional limitation. The differences of char combustion measured in non-isothermal TG experiments between O2/CO2 and O2/N2 conditions are shrinking with the reduction of diffusion resistance. Compared with conventional air combustion, change of combustion atmosphere in oxy-fuel condition mainly exhibits influence on diffusion process, while it has no observable effect on char-O2 chemical reaction in TG experiments. Obviously different results between air and oxy-fuel combustion can be obtained when the diffusional limitation in TG tests is significant, while the change of combustion atmosphere has negligible influence on char reactivity under minimized inhibition of heat and mass transfer. Knowledge of the respective influence of intrinsic reaction and diffusion resistance on the measured TG experiments is of considerable significance for the exploration of reactivity and kinetics differences between air and oxy-fuel combustion.

Pyridine and pyrrole oxidation under oxy-fuel conditions

ABSTRACT In this article, a study on pyridine and pyrrole oxidation under oxy-fuel conditions has been carried out. The experimental results indicate that when the temperature is above 800°C, concentration of N2O in the offgas quickly destructs mainly into N2 with the increase of temperature. Both NO and N2O concentrations can be enlarged, obviously due to the increase of oxygen concentration. In addition, the effect of gas atmosphere on pyrrole oxidation is quite different from that on pyridine oxidation. Introduction of high content CO2 in oxy-fuel combustion can lead to a certain migration change of fuel nitrogen.

Energy analysis of a lignite predrying power generation system with an efficient waste heat recovery system

ABSTRACT Lignite has been extensively used for electricity generation in many regions worldwide. However, its high water content has obviously negative effect on plant thermal efficiency. Performance of lignite-fired power plant can be improved by predrying the lignite before combustion. In addition, recovery of waste heat from the dryer and the power generation system will enhance the plant thermal efficiency further. In the present study, a new lignite predrying power generation system integrated with an efficient waste heat recovery system was proposed. Both dryer exhaust waste heat and steam turbine exhaust latent heat were recovered to heat boiler feed water. Energy analysis indicates that system performance is improved significantly. The plant thermal efficiency increases linearly with drying degree and then increases at a lower rate. The generation of unused dryer exhaust changes the variation tendency of system performance with drying degree.

Effect of Volatile-Char Interaction on Nitrogen Oxide Emission during Combustion of Blended Coal

AbstractUtilization of blended coal has been a great issue due to the increasing off-specification coals received in power plants, while the reduction of nitrogen oxide is also attracting extensive...

Optimization Design and Thermal Economy Analysis of the Flue Gas Treatment System in Power Plant

A novel flue gas treatment system was proposed in this paper. The system integrates the low pressure economizer (LPE) with the desulphurized flue gas heater (DFGH) for both waste heat recovery of the exhaust gas and the desulphurized flue gas heating. A model for the system was established based on the equivalent enthalpy drop theory. The thermal economic comparisons among 5 feasible connection schemes for the flue gas treatment system of a 300 MW unit were executed. The parametric analyses were also performed to evaluate the effects of the outlet flue gas temperature and the condensate temperature of the DFGH. Results indicate that the optimized flue gas treatment system can improve the thermal economy and heat the desulphurized flue gas. Better thermal economy is achieved when the LPE is connected with the high energy level feed water heater, and the low pressure extraction steam is extracted for heating desulphurized flue gas. The thermal economy decreases with the increase of the outlet flue gas temperature of the DFGH while it increases slightly with the decrease of the condensate temperature of the DFGH.Copyright

Effects of silicoaluminate oxide and coal blending on combustion behaviors and kinetics of zhundong coal under oxy-fuel condition

Oxy-fuel combustion of high-alkali coal is beneficial for near-zero emission of pollutants in power plants and has the potential for extensive, efficient, and safe utilization of Zhundong coal in future. The present work was performed on oxy-fuel combustion of Zhundong coal, while the effects of silicoaluminate oxide and coal blending on oxy-fuel combustion characteristics and kinetics of high-alkali coal were further studied using thermogravimetric analysis. The thermogravimetric curves of Zhundong coals present two obvious stages but the contrastive coals are different. The increase in oxygen content weakens the impact of coal property on oxy-fuel combustion behavior of high-alkali coal. The addition of Al2O3 and kaolin results in a slight decline of the peak combustion rate, while the influences of SiO2 and diatomite additives are negligible. The additive fraction of silicoaluminate oxide gives rise to a non-monotonic impact on combustion characteristics of Zhundong coal. The interaction effect within blended coal could cause a reduction in reaction rate during the intense combustion stage, while its influence on kinetics is intensified during the later stage of oxy-fuel combustion. The impact extent of silicoaluminate oxide and coal blending on oxy-fuel combustion kinetics of high-alkali coal is highly associated with additive species and individual coals.

Thermodynamic and economic analysis on a two-stage predrying lignite-fueled power plant

ABSTRACT In this study, an improved configuration of lignite-fueled power plant integrated with a two-stage predrying system was proposed. The predrying system mainly consists of two fluidized-bed dryers and an additional feed water heater. Lignite is dried successively in the exhaust gas dryer and steam dryer. With boiler exhaust gas being the heat source of the first stage dryer, waste heat of a fraction of the boiler exhaust gas can be used. The exhaust gas of the second stage dryer was considered to be water vapor and its latent heat can be recovered by the additional feed water heater. The thermodynamic and economic analysis show that with the lignite drying degree being 0.1, 0.2, and 0.3 kg/kg, the power generation efficiency of the proposed power plant is 1.45, 2.12, and 2.81% higher than that of the conventional lignite power plant, respectively. Moreover, the annual net economic benefit will be 1.34, 2.03, and 1.60 M