Chuguang Zheng
Huazhong University of Science and Technology
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Featured researches published by Chuguang Zheng.
Fuel Processing Technology | 2004
Minghou Xu; Rong Yan; Chuguang Zheng; Yu Qiao; Jun Han; Changdong Sheng
Several important aspects are described in this paper. The occurrences of trace elements (TEs) in coal are introduced. Four main groups of trace element content level, say, >50, 10–50, 1–10 and <1 ppm, can be drawn. Trace elements partitioning in emission streams; enrichment in submicron particles; vaporization and emission in flue gas; and the mobility and leaching behavior of trace elements in coal and combustion waste are summarized. The mechanisms of trace element transformation during combustion are illustrated as following: the vaporized metals at high temperature near the combustion flame will subsequently nucleate or condense at a lower temperature downstream. These metals form a suspended aerosol along with particles. The conversion of vaporized components into various solid and/or liquid forms is the key factor influencing the final trace elements transformation/partitioning behavior. Finally, current trace element emission control technologies are briefly introduced. To control trace elements in particle phase, electrostatic precipitators and fabric filters are mainly used. To control trace elements in vapor phase, spray dryer absorbers, wet scrubbers, condensing wet scrubbers, wet scrubbers and solid sorbent injection should mainly be used. Research needs are identified and potentially promising research topics on trace elements emission are proposed as following: (1) trace element speciation and enrichment in coal and coal ash. (2) Trace elements partitioning in combustion process. (3) Mechanisms of transformation and control technologies for easily vaporized TEs during combustion.
Combustion and Flame | 2003
Minghou Xu; Yu Qiao; Chuguang Zheng; Laicai Li; Jing Liu
Abstract Homogeneous mercury speciation in combustion-generated flue gases was modeled by a detailed kinetic model consisting of 107 reactions and 30 species. This kinetic model includes the oxidation and chlorination of key flue-gas components, as well as six mercury reactions involving HgO with new reaction rate constants calculated neither from experimental data nor by estimated, which was commonly used by other investigators before, but directly from transition state theory (TST). An important and previously unrecognized pathway of homogeneous Hg oxidation mechanism including Hg reactions involving HgO was proposed. Among those reactions involving HgO, the progress of reaction HgO + HCl → HgCl + OH is HgO + HCl → TS 1( HgClOH )→ M ( HgClOH )→ TS 2( HgClOH )→ HgCl + OH , in which the controlling step is HgO + HCl → TS 1( HgClOH )→ M ( HgClOH ). The progress of reaction HgO + HOCl → HgCl + HO 2 is HgO + HOCl → M ( HgClOOH )→ TS ( HgClOOH )→ HgCl + HO 2 , in which the controlling step is M ( HgClOOH )→ TS ( HgClOOH )→ HgCl + HO 2 . Four other reactions are one-step, with no intermediates formed. The performance of the model was assessed through comparisons with experimental data conducted by three different groups. The comparison shows that model calculations were in agreement with only one set of all the three groups experimental data. The deviation occurs due to the absence of accurate rate constants of existing mechanism, the adding of reactions involving HgO, as well as the exclusion of heterogeneous Hg oxidation mechanism. Analyses by quantum chemistry and sensitivity simulations illustrated that the pathway Hg + ClO = HgO + Cl is more significant than some of the key reactions in the kinetic mechanism proposed in the literature, which indicates the necessity of including reactions involving HgO in the mercury speciation kinetic mechanism. Studies on the effects of oxygen show that O 2 weakly promotes homogeneous Hg oxidation, especially under the condition of low Cl 2 concentration. In all cases, 1.5–6.0% of the mercury is predicted to be present as HgO.Keywords: Mercury speciation; Reaction mechanism; Quantum chemistry; Kinetic modeling
Journal of Quantitative Spectroscopy & Radiative Transfer | 2002
Huai-Chun Zhou; Shu-Dong Han; Feng Sheng; Chuguang Zheng
In this paper, the possibility of visualization of three-dimensional (3-D) temperature distributions in large-scale boiler furnaces from radiative energy images captured by multiple charge-coupled device (CCD) cameras mounted around the furnace is studied numerically. For the calculation of the radiative energy image formation, a fast algorithm proposed by the authors for pinhole imaging is used in this paper, which is based on the Monte Carlo method and combined with a concept of angular factor effective for image formation. This algorithm is applicable for the emitting, absorbing, and isotropic scattering medium. For the inversion of the 3-D temperature distributions which is an ill-posed problem, a modified Tikhonov regularization method is improved, where the finite difference regularizer is defined and can be used in 3-D cases, and the optimal regularization parameter is suggested to be selected by using a post-treatment method. For a 3-D unimodal temperature distribution, the numerical simulation results show that the reconstruction errors for the 3-D temperature distribution can be maintained at levels similar to the measurement error and the visualization quality of the temperature distribution is satisfactory. For a kind of bimodal temperature distribution, the reconstruction errors are higher than those for the unimodal distribution, but the bimodal feature of the temperature distribution can also be reproduced clearly.
Journal of Quantitative Spectroscopy & Radiative Transfer | 2002
Huai-Chun Zhou; Yu-Bo Hou; Dong-Lin Chen; Chuguang Zheng
Abstract A parallel-plane space filled with absorbing, emitting, isotropically scattering, gray medium is studied in this paper. The boundary intensity and boundary temperature profiles are calculated for the inverse analysis. For the simultaneous estimation of temperature, absorption and scattering coefficient profiles in the medium, the sum of residuals of boundary intensity and temperature after being weighted by a balance factor is minimized through using a Newton-type iteration algorithm and the least-squares method. To avoid over-updating for the parameters, the relative updating magnitude during the iteration process is constrained not to be >0.5. It is shown that the boundary intensity measurement alone is not enough to estimate simultaneously the temperature (source) and the radiative properties (both absorption and scattering coefficients) when the measurement data contain sensitive random errors. The boundary temperature measurement can serve as a necessary supplementation to the boundary intensity to make this kind of inverse radiative transfer problem resolvable. It was shown that a compensation relationship between absorption and scattering coefficients makes it difficult to fix them accurately. Parabolic profiles for the three parameters are used to validate the estimation method. When the optical thickness approaches 4.0, the results for the radiative properties are not acceptable, although the result for temperature profile is reasonable. This means the method needs further improvements.
Energy | 2002
Rong Yan; Haijing Zhu; Chuguang Zheng; Minghou Xu
This paper provides a general investigation of the emissions of organic hazardous air pollutants (HAPs) during the combustion of several typical Chinese coals. First, the distribution of four types of HAP, i.e., aliphatics, cyclic hydrocarbons, monoaromatic compounds and PAHs, in the CH2Cl2 extracts of six Chinese coals were studied and the influences of the extractive times and coal varieties were also evaluated. Second, the partitioning of these HAPs in the flue gas during coal combustion in a small-scale reactor were investigated, depending on oven temperatures (500 °C, 600 °C, 700 °C, 800 °C, 900 °C) and coal varieties. The behaviors of HAP in the combustion flue gas were compared with those in the CH2Cl2 extracts. Finally, combustion was conducted at given conditions in two laboratory-scale reactors: a fluidized bed and a fixed bed. Two coals (Shengmu bituminous coal and Xunhuan anthracite coal) and one coke were considered in this case. The HAP partitioning both in flue gases and in ashes were evaluated and compared between the two combustors.
Journal of Molecular Structure-theochem | 2003
Lai-Cai Li; Ping Deng; Anmin Tian; Minghou Xu; Chuguang Zheng; Ning-Bew Wong
Ab initio MP2 method was performed to study the reaction mechanism and kinetic of mercury oxidation by chlorine species during the process of coal combustion. Seven channels were detected by calculations, the geometric configurations of reactants, products, intermediates and transition states were optimized and energies were computed at QCISD(T)/SDD level. Besides, we used the classic transition state theory to compute the rate constants of the seven channels. Compared with the experimental values, the results show that the rate constants are in good agreement with experimental datum. So our study is believable.
Proceedings of the Combustion Institute | 2002
Zhaohui Liu; Chuguang Zheng; Lixing Zhou
A new joint-probability density function (PDF) method is proposed for modeling turbulent gas-spray flows, with special effort in considering the influence of gas turbulence on droplet dispersion, evaporation, and combustion. By taking the droplet velocities, temperature, diameter, and droplet-seen gas velocity, temperature, and mass concentration as stochastic variables, a joint-PDF evolution equation for the properties of droplets and gas eddies seen by droplets is derived. To close the turbulent dispersion model of droplets, the Langevin equation proposed by Simonin for simulating the gas velocity seen by particles, is taken to account for the crossing trajectory effect and the continuity effect. The turbulent head and species transport were modeled accordingly by a Langevin equation model with isotropic drift coefficients. The PDF model combined with the second-order moment (SOM) model of gas turbulence was used to simulate well-specified spray evaporation in a sudden-expansion chamber. The predicted droplet mean velocities, velocity fluctuations, mean diameter, root-mean-square (rms) diameter, and droplet axial mass flux profiles are in good agreement with the measurement results. The PDF model can give good predicted droplet properties even in the recirculation zone, where the droplet concentration is low and the stochastic particle trajectory (SPT) method always fails to give good results. The proposed method provides a sound basis for simulating turbulent spray combustion.
Powder Technology | 2001
Zhaohui Liu; Chuguang Zheng; L.X. Zhou
Abstract A second-order moment (SOM) gas-phase turbulence model, combined with a Monte-Carlo (MC) simulation of stochastic particle motion using Langevin equation to simulate the gas velocity seen by particles, is called an SOM–MC two-phase turbulence model. The SOM–MC model was applied to simulate swirling gas–particle flows with a swirl number of 0.47. The prediction results are compared with the PDPA measurement data and those predicted using the Langevin-closed unified second-order moment (LUSM) model. The comparison shows that both models give the predicted time-averaged flow field of particle phase in general agreement with those measured, and there is only slight difference between the prediction results using these two models. In the near-inlet region, the SOM-MC model gives a more reasonable distribution of particle axial velocity with reverse flows due to free of particle numerical diffusion, but it needs much longer computation time. Both models underpredict the gas and particle fluctuation velocities, compared with those measured. This is possibly caused by the particle–wall and particle–particle interaction in the near-wall region, and the effect of particles on dissipation of gas turbulence, which is not taken into account in both models.
Numerical Heat Transfer Part A-applications | 2000
Huai-Chun Zhou; Feng Sheng; Shu-Dong Han; Chuguang Zheng
In the fast algorithm, the total energy received by pinhole image-formation elements is divided into two parts: the direct part and indirect part. The indirect energy was related to the direct part, and the latter was calculated through a concept of effective angle factor for image formation. For 2-D systems filled with emitting, absorbing, isotropically scattering medium and surrounded by diffusely reflecting wall surfaces, the results through using the fast algorithm approached the statistical average values of those calculated using the Monte Carlo method, and the computation time can be nearly 50 times faster.In the fast algorithm, the total energy received by pinhole image-formation elements is divided into two parts: the direct part and indirect part. The indirect energy was related to the direct part, and the latter was calculated through a concept of effective angle factor for image formation. For 2-D systems filled with emitting, absorbing, isotropically scattering medium and surrounded by diffusely reflecting wall surfaces, the results through using the fast algorithm approached the statistical average values of those calculated using the Monte Carlo method, and the computation time can be nearly 50 times faster.
Fuel | 1995
Minghou Xu; Jianwei Yuan; Caiyuan Han; Chuguang Zheng
Mean and fluctuating velocity components and turbulence characteristics of the flow in the outlet of a cavity bluff-body burner were measured using three-dimensional laser particle dynamics anemometry (3D PDA). Results are also given on the choice of model particles, particle diameter distribution in and out of the recirculation zone, particle number density and volume flux distribution, and the combustion process for low-volatile coals. The experimental results not only provide an explanation of the mechanism of flame stabilization of the cavity bluff-body burner, but also demonstrate the potential of this kind of flame stabilization in industrial use.