Bingtao Zhao

Simulation of mercury capture by sorbent injection using a simplified model

Mercury pollution by fossil fuel combustion or solid waste incineration is becoming the worldwide environmental concern. As an effective control technology, powdered sorbent injection (PSI) has been successfully used for mercury capture from flue gas with advantages of low cost and easy operation. In order to predict the mercury capture efficiency for PSI more conveniently, a simplified model, which is based on the theory of mass transfer, isothermal adsorption and mass balance, is developed in this paper. The comparisons between theoretical results of this model and experimental results by Meserole et al. [F.B. Meserole, R. Chang, T.R. Carrey, J. Machac, C.F.J. Richardson, Modeling mercury removal by sorbent injection, J. Air Waste Manage. Assoc. 49 (1999) 694-704] demonstrate that the simplified model is able to provide good predictive accuracy. Moreover, the effects of key parameters including the mass transfer coefficient, sorbent concentration, sorbent physical property and sorbent adsorption capacity on mercury adsorption efficiency are compared and evaluated. Finally, the sensitive analysis of impact factor indicates that the injected sorbent concentration plays most important role for mercury capture efficiency.

Evolution and comparative assessment of ambient air quality standards in China

Abstract Ambient air pollution has become one of the key issues in China because it is highly associated with economic development, energy consumption, the atmospheric environment, and public health. Ambient air quality standards are guidelines of environmental management and fundamentals of air pollution emission control. To adapt to the changing environmental situation, China’s ambient air quality standard GB 3095 was established in 1982, amended in 1996, again in 2000, and most recently in 2012. This article presents a historical analysis on the evolution of China’s ambient air quality standards focusing on the critical pollutants and their concentration thresholds, as well as a comparative analysis that illustrates the differences to important developed countries and international organizations. The results show that the ambient air quality standard in China features a progressive update in pollutant items, more stringent concentration thresholds, and more scientific planning. Although there are differences in the economic, technological, and environmental development levels, China’s latest ambient air quality standard GB 3095-2012 is found to be comparable with other important standards. However, the support of macro policies and technical measures are necessary to ensure the standard is implemented more effectively.

Modeling mercury speciation in combustion flue gases using support vector machine: Prediction and evaluation

Mercury emission from coal combustion has become a global environmental problem. In order to accurately reveal the complexly nonlinear relationships between mercury emissions characteristics in flue gas and coal properties as well as operating conditions, an alternative model using support vector machine (SVM) based on dynamically optimized search technique with cross-validation, is proposed to simulate the mercury speciation (elemental, oxidized and particulate) and concentration in flue gases from coal combustion, then the configured SVM model is trained and tested by simulation results. According to predicted accuracy of indicating generalization capability, the model performance is compared and evaluated with the conventional multiple nonlinear regression (MNR) models and the artificial neural network (ANN) models. As a result, it is found that, the SVM provides better prediction performances with the mean squared error of 0.0095 and the correlation coefficient of 0.9164 for testing sample. Moreover, based on the SVM model, the correlativity between coal properties as well as operating condition and mercury chemical form is also analyzed in order to deeply understand mercury emissions characteristics. The result demonstrates that SVM can offer an alternative and powerful approach to model mercury speciation in coal combustion flue gases.

Development of a Dimensionless Logistic Model for Predicting Cyclone Separation Efficiency

To predict the cyclone separation efficiency, a semi-empirical dimensionless multivariate logistic model is developed by stepwise multiple regression based on dimensional analysis. The model can be expressed as a simple explicit function of characterized dimensionless numbers for cyclone geometries, the dimensionless number for gas flow called Reynolds number and the dimensionless number for particle dynamics called Stokes number. The model coefficients are regressed according to the experimental data reported by Iozia and Leith (1990), which includes the effects of cyclone geometrical parameters, gas-particle physical parameters and operating parameters. The result indicates there is an agreement between the experimental data and model prediction with the mean squared error (MSE) of 0.62 and the efficient of determination (COD) of 0.90. Further, by the comparison with the additional experimental data as well as several popular theoretical models, it is found that although the present model can not reveal detailed mechanism and process of the gas-particle flow and separation in cyclones, it still is demonstrated to be useful and applicable to predict the cyclone separation efficiency.

CFD Simulation of High Temperature Air Combustion of Coal Gas at Different Air Straddle Angle

Numerical simulation was carried out on the High Temperature Air Combustion of coal gas in an industrial furnace with a multi-jet burner. A Beta-function PDF (Probability Density Function) combustion model was selected to simulate the gas combustion combined with the standard k- turbulent model. The radiation was simulated by a Discrete Ordinates method. Thermal NOx model was used to calculate NO emission. The effect of the straddle angle of the preheated air jets on the combustion characteristics was discussed. The results showed the smaller the straddle angle of the preheated air was, the better the mixing of the fuel, oxygen and the flue gas became, which resulted in a stable flame, an enlarged low-oxygen zone, an equable temperature distribution and a suppressed local high temperature. At 15% O2 condition, when the straddle angle of the preheated air is 120°, the final NOx emission can be reduced about 65% compared with that when the straddle angle of the preheated air is360°.

Cyclone performances depend on multiple factors: comments on "A CFD study of the effect of cyclone size on its performance parameters" by Mehdi Azadi et al. (2010).

In the manuscript published by Azadi et al. [1], the authors invesigated the effect of cyclone size on its performance parameters. n their work, the authors used the CFD approach to simulate the as-particle flow inside cyclones with three different sizes, and hen determined the effect of cyclone size on the particle cut-off iameter and pressure drop. As interested yet critical readers of the article, we would like to hare some understanding and comments on the effects of cyclone imensions and physical properties of particles on the particle cutff diameter, the effect of cyclone size on the pressure drop, and herefore the major conclusions derived from their work.

Pyrolysis of Waste Tire and Its Model

A TG/DTG experiment was conducted to study the pyrolysis process of waste tire powder. The results showed that the first stage of weight loss during tire pyrolysis corresponded to the thermal decomposition of the mixture of oils, moisture, plastifiers and other additives. The second stage was due to the decomposition of the natural rubber and the polybutadene (BR) and polybutadene-styrene (SBR). A simple model for the mass loss rate of tire pyrolysis was developed based on TG data and the parameters including the activation energy and frequency factor were calculated. The function of weight loss rate was determined by an integral method for the low and high temperature stages. The model results and experimental data agreed well.

Experimental study on selective catalytic reduction of NO with propene over iron based catalysts supported on aluminum pillared clays

Abstract Iron based catalysts supported on aluminum pillared clays (Fe/Al-PILC) was prepared by impregnation method and the selective catalytic reduction of NO with propene by the Fe/Al-PILC catalysts was investigated in a fixed bed reactor. The physical and chemical properties of the catalysts were characterized by N2 adsorption/desorption, XRD, H2-TPR, UV-Vis, Py-IR, etc. Results showed that 9% Fe/Al-PILC reduced 98% of NO at 400-550°C. SO2 and water vapor slightly influenced the catalytic activity of the catalysts. XRD and N2 adsorption/desorption characterization results revealed that the iron oxides in the catalyst were highly dispersed on the surface of the carrier and the catalyst has a large specific surface area and pore volume. H2-TPR results indicated that the activity of the catalysts was mainly determined by the reduction performance of Fe2O3 phase. UV-Vis results showed that the activity of the catalysts was positively correlated with the iron oxide oligomer FexOy. Py-IR results indicated that both Lewis acid and Bronsted acid were formed on the catalyst surface and the Lewis acid sites were the main catalytic activity center of NO and C3H6 reaction.

Numerical modelling of effect of channel width on heat transfer and ventilation in a built-in PV-Trombe wall

The heat transfer and air flow rate in a built-in PV-Trombe wall with vertical inlet were numerically simulated based on CFD method. Effect of channel width on heat transfer and air flow rate was discussed. As the channel width increased, the natural convective heat transfer was enhanced and the PV surface was better cooled by the air which improved the PV electricity efficiency slightly. The ventilation rate through the built-in PV-Trombe wall reached its maximum at an optimal ratio of the channel width to the channel height, (b/H)opt=1/5. Dimensionless expressions to calculate the averaged heat transfer coefficient, Nusselt number, and the air flow rate in term of a Reynolds number were correlated according to a modified Rayleigh number by multivariable regression analysis.

CO2 Emission Reduction from Power Plant Flue Gas by Micro-Algae: A Preliminary Study

CO 2 fixation by marine micro-algae cultivation has the potential to diminish the emission of CO 2 . To select the proponent micro-algae species this is vital to realize workable biological CO 2 fixation systems, three kinds of candidate energy marine algal strain were cultivated and tested for bio-fixation of CO 2 from power plant flue gas. It was found that Chlorella was the most appropriate strain for CO 2 fixation in high level CO 2 gas, with the maximum CO 2 fixation rate of 2979 mg/L-week.