Ya Li Wang

Effect of CaO on SNCR Reaction with NH3 as Reducing Agent

Selective non-catalytic reduction (SNCR) is a denitration method in the high temperature area, and NH3 or urea is used for SNCR as reducing agents to react with NOX to produce N2 in the flue gas in the temperature ranged from 850°C to 1100°C. The SNCR deNOx technology has been well used in utility boiler, but compared with it, the lower denitration efficiency and the larger consumption of ammonia indicate a more complex process in cement pre-calciner. Unlike in utility boiler, the presence of high concentrations of cement raw materials may influence SNCR denitration reaction process in cement kilns. Therefore, studying the effect of CaO which occupy the major composition of cement raw material is very important in SNCR process. In this study the influence of CaO on the SNCR deNOx process was investigated by simulating SNCR reaction at temperature that ranges from 750°C to 1100°C with different normalized stoichiometric ratio. The experimental results demonstrate that the addition of CaO increases the optimum denitration temperature to 1100°C, but it has no effect on normalized stoichiometric ratio. In the whole reaction process NH3 not only restores NO to O2 but also reacts with O2 to NO. Since the adsorption of NH3 on CaO surface, in the temperature range of 750°C-850°C the addition of CaO promotes the reaction of NH3 and O2 and increases NOX concentration. However, in the temperature range of 850°C-1000°C it not only promotes NH3 oxidation but also inhibits the reduction reaction of NH3, thereby the denitration reaction is inhibited. In the temperature range of 1050°C-1100°C the denitration reaction is promoted due to the NH3 desorption from CaO surface.

Effects of Preparation of Cement Raw Meal with Carbide Slag on the Environment and Equipments

Based on the physical and chemical properties of carbide slag, the contents of heavy metals in effluent came from carbide slag drying process were studied, and then the composition of exhaust gas emitted from the carbide slag drying process and calcinations process of raw materials prepared with carbide slag was detected, in order to know whether there are harmful or corrosive gases released and the effect of the emissions on the environment and related equipments. The results indicate that the exhaust gases emitted from the calcination process of raw meal prepared with carbide slag is mainly composed of CO2 and water vapor, and is free from harmful gases. However, a lot of water in carbide slag during the pre-heat and decomposition process under high temperature would accelerate the corrosion of equipments. Simultaneously, a small number of heavy metal ions contained in the carbide slag can cause environmental pollution and sulfides would be adverse to the cement calcination process resulting in the crust blockage of kiln.

Influence of Catalysts with Different Templates on Direct Decomposition of NO in Cement Kiln Exhaust

The influence of catalysts with different templates on direct decomposition of NO in cement kiln exhaust was studied in this paper. The NO direct decomposition rate of porous catalyst materials with different templates was determined by infrared spectrometer. And pore structure and the microstructure of the catalysts were characterized by BET surface area, nitrogen adsorption-desorption. The results show that the catalytic performance of porous catalyst without any template is better than catalysts with other templates at low temperature. When the temperature reached 550 °C, NO decomposition rate of porous catalyst with CTAB could reach to more than 80%. And meanwhile, the catalysts with organic template reagent have higher BET surface area than those with inorganic template agent. With the increasing of the reaction time, the NO decomposition rate decreases. After reaction for 3 hours, the decomposition rate decreases from 80% to 40%.

Different Precipitant Preparation of Nickel-Doped Mn/TiO2 Catalysts for Low-Temperature SCR of NO with NH3

The Mn-Ni/TiO2 catalyst was prepared by co-precipitation method and investigated for the low-temperature selective catalytic reduction (SCR) of NO with NH3 in this work, and Mn-Ni/TiO2 catalysts were prepared by different precipitants respectively such as sodium hydroxide, carbamide, ammonia or hydrogen peroxide. The microstructure and performance of catalysts were investigated. The activitiesof catalysts prepared by different precipitants were studied in the temperature range 90°C-350°C. The results show that Mn-Ni/TiO2catalyst prepared by CO(NH2)2-NH3·H2O-H2O2 compound precipitant has an extraordinary performance even at the low temperature of 120°C. H2-TPR results show the peak positions shift to lower temperatures, standing for the reduction potential of MnOx species is increased compared to those of Mn/TiO2 catalysts. The interaction of Ni and Mn atoms is beneficial to an enhancement of the oxygen mobility due to CO(NH2)2-NH3·H2O-H2O2 as precipitant. It is worth noting that the low temperature peak area increased by adding hydrogen peroxide as precipitant. NH3-TPD results illustrat that for the Mn/TiO2 and Mn-Ni/TiO2 catalysts which are attributed to NH3 desorbed by weak acid sites and Brønsted acid sites.

Effect of Cement Raw Material and Oxygen Concentration on SNCR Reaction

As the selective non-catalytic reduction denitration(SNCR denitration) was used in cement decomposition furnaces under the high concentration cement raw materials and complex flue gas composition , the denitration efficiency is poor and the reducing agent is largely consumed.In order to meet the more stricter requirements of environmental protection, there is an urgent need to improve the denitration efficiency of SNCR and reduce the escape of reducing agentsin order to prevent the unnecessary waste caused by excessive use of reducing agents and secondary atmospheric pollution.Therefore, studying the effect of cement raw materials and O2 concentration on SNCR process is very important. In this paper, the initial concentration of NO and the ammonium to nitrogen ration (CNH3/CNO) was 800ppm and 1.5, respectively. The effects of cement raw material and oxygen concentration on the reaction process of NH3+NO+O2 in the temperature range of 750°C -1100°C were investigated by means of denitration rate, in Situ DRIFTS analysis.The results demonstrate when O2 concentration was 5% and denitration temperature was 950°C, the deNOx rate reached a maximum of 89.64%, which due to O2 promoted NH3 and NO to react with O2 to produce N2 and H2O. However,under the effect of cement raw material, O2 can promote NH3 which was adsorbed on the surface of cement raw material to react with O2 and produce NO and H2O, and the reaction of oxidation of NH3 is dominant, therefore, the denitration reaction is inhibited. .When O2 concentration was 5% and temperature was 850°C, the deNOx rate reached a minimum value of -109.09%. the high concentration cement raw material and flue gas composition reduce the denitration efficiency of cement kiln.

Thermal Decomposition Characteristics and Drying Process of Municipal Sludge

Using cement kiln dispose sludge from sewage plants can achieve the sludge stabilization, harmless, reduction and resource comprehensive utilization purposes. This is Not only to solve the problem of sludge treatment which is difficult to solve by sewage treatment plant, but also to make full use of the sewage treatment plant sludge to replace part of cement clinker production materials. And it makes full use of sludge incineration emitted in the process of low calorific value. Municipal sludge contains more moisture. It is necessary to dry the sludge outside the kiln before entering kiln process. As cement kiln co-processing, it should be combined with the characteristics of NSP clinker production, it is necessary to not only consider the total energy consumption of the drying process, but also the re-use of dried sludge heat value, as well as consider the total of water into the kiln by drying sludge affecting the whole clinker production process. In this paper, with the initial solid content 20%, dry heating value 3400 cal/g sludge as a research object, the moisture morphology, thermal characteristics, drying technological parameters and composition of water after drying in sludge were analysed. This issue combines sludge drying with cement kiln disposal, which can not only solve the heat and odor problem during the individual sludge drying process, but also provide a theoretical basis for cement kilns co-disposal of municipal sewage sludge to achieve the purposes of sludge stabilization, harmless, minimization and resource utilization.

A Novel Way to Modify PTFE Membrane into Hydrophilicity

Polytetrafluoroethylene (PTFE) membrane, with high resistances to acid, alkali and other chemical corrosion, is the ideal filter material in water treatment, which can be used in a variety of harsh environment. However, the hydrophobictity of PTFE membrane limits its wide application in water treatment. Thus, the hydrophilic modification of PTFE membrane attracts much attention. In this work, the microporous PTFE membrane was treated by a novel strategy for enhancing its hydrophilicity. The pristine microporous PTFE membrane was modified by assembly of fluorocarbon surfactant. The structure and morphology of the membranes were characterized by attenuated Fourier Transform Infrared spectroscopy (ATR-FTIR) and scanning electron microscope (SEM). The variation of wettability was evaluated by the change of water contact angle (WCA). And the influences of the concentration of fluorocarbon surfactant and modification time on PTFE WCA were also investigated as well. The WCA of the pristine PTFE membrane is 156°. After modified by 5.0 g/L of fluorocarbon surfactants, the WCA reduced to 4.3°, indicating that the hydrophobic PTFE membrane was transformed into a hydrophilic one. FTIR and SEM results indicated that there were hydrophilic groups, such as carbonyl (-C=O) and hydroxyl (–OH) existing on the surface of PTFE membrane after modification. And WCA of the hydrophilic membrane showed a slight increase from 4.3°to 8° after a week, indicating that the hydrophilic PTFE membrane exhibiting a persistent durability.

Removal of NOx by Cement Raw Meal and Biochar Admixture

Many studies have indicated that carbon can be reduced to nitric oxide. This paper reports an experimental study of NO reduction by mixed materials of biochar or active carbon with cement raw meal. The proportion of mixed materials was 95 wt.% cement raw meal and 5 wt.% biochar or active carbon. A mixture loading amount and gas flow rate study quantifying the effect of carbon amount and gas residence on the reduction of nitric oxide was carried out. The experiment was performed in a fixed bed reactor at the temperature of 800°C, with O2 concentration of 1%. The inlet NO concentration was 1000 ppm. The characterization of structure and properties of biochar and active carbon was conducted by SEM-EDS, BET. The results show that different carbon materials have different NO reduction effect. The NO conversion rate increases with the increase of the amount of mixture loading. This method of removing NO is practically feasible.

Effect of Testing Factors on Rietveld Quantitative Analysis of Cement-Matrix Materials

For cement-matrix materials, the microstructure plays a vital important role in the research. Recently, quantitative phase analysis of cementitious materials can be performed using the Rietveld method by fitting the calculated X-ray diffraction (XRD) profile with the observed one. The aim of this paper is to further perform the quantitative analysis by the Rietveld method and discuss the influence of testing factors on the Rietveld quantitative phase analysis. The factors included the collection range of pattern, step size and the scan time of per step. In this study, the chemical composition of the samples was determined by X-ray fluorescence (XRF) spectrometry. And their phase composition was calculated by X-ray powder diffraction and Rietveld analysis. The results showed that the collection range of pattern depended on the tested materials , and the scanning range should include the main diffraction peak of the sample. Smaller step size and longer scan time of each step made the fitting factor smaller, also the calculated pattern coincided with the measured pattern, better enhance the precision of the analyses.

Effect of Fly Ash Composition and Structure on the Formation of Cement Clinker

In the view of scarce of natural mineral resources and requirement of energy-saving/emission-reducing for cement industry, the natural silicon-aluminum clay as one cement raw material has been gradually replaced by silica-rich industrial wastes, such as, fly ash, a principal solid waste discharged from coal-fired power plants, composed mainly of silica- and alumina-rich glass bead-shaped mineral. Using fly ash to produce cement raw materials, the formation and chemical reactions of cement clinker are affected by the chemical and mineral composition as well as the texture of the fly ash and the paper was focused on it. The empirical formula for formation heat of fly ash-doped cement clinker is revised on the basis of chemical thermodynamics. The results show that with the use of fly ash, in contrast with the traditional ingredients, the formation of varieties of clinker minerals as well as the formation sequence and types of intermediates varied little, while the maximum decomposition temperature of carbonate was lowered by 50 °C approximately, so that both the solid phase reaction temperature and liquid phase sintering point were decreased, which is favorable to the reduction of clinker formation heat. The revised formation heat empirical formula of fly ash-doped clinker could facilitate the thermal calculation of furnaces and the evaluation of thermal efficiency.