Wenyi Deng

Moisture distribution in sludges based on different testing methods.

Moisture distributions in municipal sewage sludge, printing and dyeing sludge and paper mill sludge were experimentally studied based on four different methods, i.e., drying test, thermogravimetric-differential thermal analysis (TG-DTA) test, thermogravimetric-differential scanning calorimetry (TG-DSC) test and water activity test. The results indicated that the moistures in the mechanically dewatered sludges were interstitial water, surface water and bound water. The interstitial water accounted for more than 50% wet basis (wb) of the total moisture content. The bond strength of sludge moisture increased with decreasing moisture content, especially when the moisture content was lower than 50% wb. Furthermore, the comparison among the four different testing methods was presented. The drying test was advantaged by its ability to quantify free water, interstitial water, surface water and bound water; while TG-DSC test, TG-DTA test and water activity test were capable of determining the bond strength of moisture in sludge. It was found that the results from TG-DSC and TG-DTA test are more persuasive than water activity test.

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.

Effect of calcium oxide (CaO) and sawdust on adhesion and cohesion characteristics of sewage sludge under agitated and non-agitated drying conditions

Stickiness phenomenon is widely observed in sewage sludge drying practices. This paper is aimed at demonstrating and comparing the sticky properties of sewage sludge through non-agitated and agitated drying tests specially designed for sewage sludge. Special attentions were paid to the effects of additives, i.e. CaO, fine sawdust (FSD) and coarse sawdust (CSD), on the adhesive and cohesive characteristics of sewage sludge. The results indicated that the sticky properties of the sludge were markedly different under the different testing methods, and was also greatly influenced by CaO or sawdust addition. For instance, in the non-agitated drying tests, CaO can significantly enhance the maximum adhesive and cohesive stresses of the sludge, whereas in the agitated drying tests, the torque of agitation, which strongly correlated with the cohesive stress of the sludge, was lowered by CaO addition. During agitated drying process, sludge lump with CaO addition started to break up at higher moisture content than that of original sludge. On the other hand, sawdust also affected the sticky properties of sludge in a way that was totally different with CaO. After sawdust addition (at 5-10%WS (wet sludge basis)), the cohesive stress of the sludge was markedly increased due to strengthening of mechanical interlocking inside the sludge, whereas the adhesiveness of the sludge was lowered by sawdust addition. The influencing mechanisms of CaO and sawdust under the different testing methods were detailedly discussed in the paper.

Experimental study on selective catalytic reduction of NO by C 3 H 6 over Fe-Ag/Al 2 O 3 catalysts

Abstract Sol-gel and impregnation methods were used to prepare the Fe-Ag/Al2O3 catalysts supported on the monolithic cordierite with different Fe/Ag loading ratios. The catalytic performance to reduce NO with C3H6 was evaluated in a one-dimensional electrically heated temperature programmed ceramic tubular reactor in simulated flue gas atmosphere at 200–700°C. The results show that the NO reduction efficiency on 7.2Fe/1.9Ag/20Al2O3/CM with C3H6 is more than 90% and reaches about 100% at the temperatures of 500°C and 550°C respectively. Iron can effectively improve the ability of Ag/20Al2O3/CM catalysts to resist SO2 and H2O in flue gas. When SO2 and H2O are 0.02% and 8% in the flue gas, the NO reduction efficiency is almost not influenced on 7.2Fe/1.9Ag/20Al2O3/CM at 500°C. The 90% NO reduction efficiency is maintained during 6 h without decrease. However, the catalytic activity of 2Ag/20Al2O3/CM without iron modification is strongly influenced by SO2 and H2O in the flue gas. The NO reduction efficiency on Ag/20Al2O3/CM decreases rapidly from about 70% to 46% and 25% respectively, when the SO2 and H2O are 0.02% and 8% in the flue gas. The results of XRD and SEM of the catalyst show that AgFeO2 and Fe3+ are formed in the 7.2Fe/1.9Ag/20Al2O3/CM catalyst after the modification by iron, and the surface of the catalyst become loose and porous, forming Fe3O4-based needle-like and flaky crystals. H2-TPR results show that 7.2Fe/1.9Ag/20Al2O3/CM has better reduction properties than Ag/20Al2O3/CM in the wider temperature range. Pyridine adsorption Infrared Spectroscopy (Py-FTIR) experimental results show that Fe increases the Lewis acid sites in the catalyst surface.

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.

Second Law Optimization of Pin Fin Heat Exchangers with Lateral Ejection Holes

The authors theoretically studied the entropy generation during heat transfer of a pin fin array in channels with lateral ejection holes for a turbine blade. The entropy generation model was established based on the second-law analysis. The distribution of the entropy generation due to heat transfer and fluid friction irreversibility respectively was analyzed and a comparison was made for three typical short pin fin channels. The entropy generation number component due to heat transfer decreases while Red increases, while the component due to fluid friction increases with the increase of Red. The entropy generation number takes its minimum value when the two components meet and the corresponding Reynolds number is optimal. The ejection holes influence the energy lost of the working fluid. For the three cases studied in the paper, case b with short ejection holes gives the best comprehensive thermal performance with comparison to cases with no and long ejection holes. The results would be helpful for the design of the heat dissipation of pin fin heat exchangers.

Numerical Study of Effect of Burner Jet Parameters on High Temperature Air Combustion of Coal Gas

A numerical simulation was carried out on the High Temperature Air Combustion of coal gas in an industrial furnace with a multi-jet burner. The effect of jet parameters on NOx emission, temperature and oxygen distribution was investigated. A Beta function PDF(Probability Density Function) combustion model was selected to simulate the gas combustion combined with the standard k-ƒÕ model to simulate the turbulent flow. The radiation was simulated by a Discrete Ordinates method. The NOx emission was simulated by thermal NOx model. The effect of jet parameters, i.e., the velocity ratio of fuel jet and air jet and the fuel jet inclined angle on the combustion characteristics was discussed. The simulated results showed that the jet parameters changed the recirculation of flue gas in the furnace leading to different mixing of the fuel, air and hot flue gas which determined the local temperature, oxygen concentration and NOX production. As the velocity ratio of fuel jet and air jet and the fuel jet inclined angle increased, the flue gas recirculation was enhanced and the low oxygen zone enlarged. The maximum and mean temperature both decreased and NOX emission decreased.