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This paper reports on the recent experimental and numerical results from a 35 MW front wall-fired large pilot boiler. The boiler features a first-of-its-kind compatible design of oxy-fuel combustion and conventional air combustion (air-combustion). A sub-bituminous coal is used as fuel in the experiment. Wet and dry flue gas recycle oxy-fuel conditions are investigated, while air-combustion is also examined for reference. Measured in-furnace temperature, species concentration, exhaust emission, and transferred heat to membrane-wall and superheater are compared between oxy-fuel and air-combustion. Detailed numerical studies of combustion and heat transfer are performed using in-house developed sub-models for oxy-fuel condition, including a radiative property model and a global reaction mechanism. The predicted results agree well with the experimental data. The experimental and numerical results show that stable oxy-fuel combustion is achieved in the 35 MW large pilot boiler. Importantly, the oxy-fuel combustion and air-combustion can operate well with the especially designed burner system at similar heat loads in the experiment. Moreover, similar average temperatures and heat flux distributions are achieved under wet and dry flue gas recycle oxy-fuel conditions with an initial O 2 concentration of 28% in the oxidant. Transferred heat to membrane-wall and superheater in oxy-fuel combustion is slightly greater than in air-combustion. Furthermore, the flue gas recycle ratio significantly influences the heat transfer in oxy-fuel combustion. Increasing the recycle ratio from 0.71 to 0.73 reduces the transferred heat to membrane-wall by approximately 6%, while that of superheaters increases by approximately 4%. The selection of the optimized recycle ratio is a trade-off between boiler performance and flame stability of the burner system. [ABSTRACT FROM AUTHOR]

• A certain amount CaCO 3 exists under oxy-fuel combustion. • The viscosity of fly ash particles was higher under oxy-fuel combustion. • The particles were stickier and more easily coalesced under oxy-fuel combustion. • The slagging trend under oxy-fuel combustion was greater. Global warming has attracted extensive attention due to increasing CO 2 emissions. Oxy-fuel combustion has become an important topic in the domain of energy saving and emission reduction due to its high efficiency in CO 2 reduction. The slagging characteristics of coal ash under oxy-fuel combustion conditions are the premise for the successful application of this technology. In this study, we relied on a tubular furnace and flat flame-assisted entrained flow reactor to test coal ash under different atmospheres. The slagging trend of Shenhua coal under oxy-fuel combustion, including its melting point, mineral species, particle size, and morphology, was analyzed. A comparative analysis of different ash samples obtained from different experimental platforms was also conducted. Results showed that the oxy-fuel combustion atmosphere exerted a minimal effect on the melting point of Shenhua coal ash. Moreover, a high oxygen concentration corresponded to a relatively high melting point of ash. Ca existed in the form of CaO under air combustion, and a certain amount of undecomposed CaCO 3 appeared under oxy-fuel combustion. Given the same oxygen concentration, the average particle size under oxy-fuel combustion was smaller than that under air combustion. Moreover, particle adhesiveness was stronger and particles more easily gathered under oxy-fuel combustion than under air combustion. Particle aggregation was also more obvious under oxy-fuel combustion than under air combustion. Therefore, the slagging trend under oxy-fuel combustion was obviously higher than that under air combustion. [ABSTRACT FROM AUTHOR]

Abstract: The emission of mercury by coal-fired power plants has become a recent concern on the part of the electric utility industry. Knowledge of mercury kinetic mechanisms is imperative for the research of predicting mercury transformation and finding its effective control methods in coal combustion flue gas. Near the end of the flue gas path, mercury exists as a combination of elemental vapor and HgCl2 vapor. HgCl2 is more likely to be removed from the flue gas. Thus, the degree of oxidation is considered to be a critical factor that tends to reduce emission. In the present work, the microcosmic kinetic mechanisms of reactions between mercury and oxidizing species were investigated by ab initio calculations of quantum chemistry. The geometry optimizations of reactants, transition states, intermediates and products were made by the quantum chemistry MP2 method at SDD basis function level. All molecule energies were calculated at QCISD(T)/SDD level and corrected with zero point energy. The activation energies and heat of reactions were calculated. The reaction rate constants were calculated from transition state theory (TST). The performance of the ab initio calculations of quantum chemistry was assessed through comparisons with the literature data. The comparisons showed that the ab initio calculations of quantum chemistry were in agreement with the literature data. The results showed that quantum chemistry was an effective means for investigating kinetic mechanism of mercury interaction with combustion-generated flue gas. [Copyright &y& Elsevier]

The catalytic hydrogasification of coal char was investigated in a high-pressure fixed-bed tube reactor using CaO, CaCO 3 , Na 2 CO 3 , and K 2 CO 3 as catalysts. Experimental results showed that the char reactivity could be greatly improved with the addition of catalysts. Analysis of char structural evolution was performed to further explore the catalytic mechanism by employing Raman spectroscopy and scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX). The results revealed that CaO catalyst inhibited the aromatic ring condensation of the char structure during hydrogasification. The catalytic reaction of CaO only occurred on the char surface. Na 2 CO 3 or K 2 CO 3 was reduced to metallic Na or K and diffused into the char under hydrogen atmosphere, enhancing the cracking of large aromatic ring systems into small ones, which were the active species for hydrogasification. The catalytic reaction of alkali catalyst occurred simultaneously on the surface of and inside the char. Therefore, the Na 2 CO 3 and K 2 CO 3 displayed higher catalytic activities than CaO in hydrogasification. [ABSTRACT FROM AUTHOR]

• CFD results of a swirl oxy-coal flame are compared with detailed experiment. • Nonlinear variation particle radiative property is first used in oxy-coal modeling. • Contributions of gas and particle radiation are illustrated in oxy-coal flame. • Constant model ten times over-predicts the particle absorption after burnout. This paper reports a comprehensive computational fluid dynamics simulation of the IFRF's swirling oxy-fuel flame with pulverized coal using wet flue gas recycle. Special attention is given to the influence of particle radiative property model. Based on the burnout rate of pulverized coal, a recent proposed nonlinear conversion-dependent particle radiative property model (Guo et al., 2018) is used in the simulations. The influences of the high CO 2 concentration on the sub-models are also considered in detail. The gas-phase global reaction mechanism, kinetic parameters of char oxidation and gasification, and gas radiative property model are modified for oxy-fuel condition. The results show the prediction results agree well with the measurements, in terms of the temperature and composition of the flue gas. The particle radiation has an important effect on the flame temperature. Even in the small furnace studied here (optical length is approximately 1.6 m), the radiation in the flame zone is still dominated by particle radiation. Linear variation assumption (Yin et al., 2015) under-predicts the particle absorption in combustion zone. Ignoring the effect of burnout rate on particle radiative property will 10 times over-predict the particle absorption after burnout. [ABSTRACT FROM AUTHOR]