Gongcheng Kexue Yu Jishu/Advanced Engineering Science

Surface quenching of the rail steel using the laminar plasma jet can increase its service life, but the treatment parameters can only be determined by the experimental methods currently, which is time-consuming and laborious. If a simulation model for the surface quenching process can be established to quickly predict the variation of the temperature field in the surface quenching process and the hardness distribution within the hardened zone, the optimal treatment parameters can then be obtained rapidly. A numerical simulation model was firstly established by the finite element method to obtain the temperature distribution. Then the limit value of the carbon diffusion was determined by the hardness distribution obtained from the surface quenching experiment. After that, the Austenite transformation rate at each heating rate was determined using JMATPRO. Finally, a model for predicting the metallographic structure was proposed. With the numerical simulation model, the variation of the temperature field during the surface quenching process could be obtained. By selecting the nodes greater than the phase transition temperature (for example, 745 ℃ for the U75V rail steel), the width and depth of the hardened zone could be predicted. The prediction error was found to be within 8% errors compared with experimental results. By extracting the temperature change curve of the nodes in the hardening zone and substituting into the metallographic structure prediction model, the transformation of the austenite and martensite at each node position in the hardening zone could be calculated, and the hardness at the hardening zone could be predicted. A series of surface quenching experiments with different surface quenching parameters, e.g. including arc current, anode diameter, scanning speed, etc., were carried out. It was found that the hardness predicted by the proposed simulation model was in good agreement with the actual hardness, which verified the effectiveness of the proposed simulation model for the laminar plasma jet surface quenching of rail steel.

Transition metal Fe2+ is the most economical, effective and environmentally friendly PS activation substance, but Fe2+ is prone to be oxidized and loses its activation ability, resulting in poor continuous effect of the Fe2+/PS system. In order to improve the efficiency of the Fe2+/PS system in oxidizing and degrading organic pollutants, iohexol, a commonly used iodinated X–ray contrast media in medical field, was taken as the target pollutant，and its degradation in four advanced oxidation proeesses such as UV/PS，Fe(C2O4)3 3–/PS，UV/Fe(C2O4)3 3–/PS and Fe2+/PS was studid. The effects of Fe(C2O4)3 3– concentration, ultraviolet light intensity and pH on the degradation of iohexol and PS decomposition in UV/Fe(C2O4)3 3–/PS system were examined, and then the Fe2+ concentration change and its conversion rate in the system were analyzed. The results verified that the oxidation decomposition rates of iohexol in the four advanced oxidation systems were 83.8%, 7.0%, 98.8%, and 69.9% respectively, among which the UV/Fe(C2O4)3 3–/PS system could promote the reduction of ferrous irons through ultraviolet light, Fe2+ that activates PS in the solution was gradually released, and the degradation of iohexol was the most efficient and complete. As the concentration of Fe(C2O4)3 3– increased, the decomposition rate of PS in the UV/Fe(C2O4)3 3–/PS system increased, while the degradation rate of iohexol first increases and then decreases. Under four different initial Fe(C2O4)3 3– concentrations (20, 50, 100, 200 μmol/L), the degradation rate of iohexol is in the order of 100>200>50>20 μmol/L. In the UV/Fe(C2O4)3 3–/PS system, the Fe2+ concentration first increases rapidly and then slowly decreases, the degradation rate of iohexol, the decomposition rate of PS and the highest conversion rate of Fe2+ are all positively correlated with ultraviolet light intensity and negatively correlated with pH. Therefore, the use of ultraviolet light to reduce iron ions can greatly improve the Fe2+ activation efficiency, and the system has strong adaptability to influencing factors such as light intensity and pH, and has great application prospects in the field of advanced oxidation in water treatment.

The secondary fly ash problem in the application process of fly ash of municipal solid waste incineration (shorter form, fly ash) melting treatment technology has become a constraint. It is beneficial to the development of harmless and resource utilization technology of secondary fly ash by mastering the distribution law of salt in the gas phase product of fly ash melting, and it can be used as a reference for the design of tail gas purification equipment and operation. The fly ash released from one municipal solid wastes incineration plant in Jiangsu Province was adopted. The fly ash melting experiments were performed in a self-designed high-temperature pilot-scale plasma arc furnace system. The weight subtraction method, X–ray fluorescence spectroscopy, atomic absorption spectrometry and electrochemical process were used to analyze melting fly ash and slag during melting and to abtain gaseous phase migration rate of Na, K, Ca, Mg and Fe. The thermodynamic model was used to simulate the distribution rules of gaseous phase salts at 1000～1600 ℃, with 0～50% auxiliary material, at different atmosphere (without gas, nitrogen or air) and 0～12% water content of fly ash. The simulation results showed that NaCl, (NaCl)2, KCl, (KCl)2, CaCl2, KCaCl3, KMgCl3, FeCl2 etc. were main compositions of gaseous phase salts during fly ash melting. These compositions distribution was greatly effected by melting temperature and was little effected by melting atmosphere, auxiliary material amount and water content of fly ash. At atmosphere, there were new product Na2SO4 in gaseous phase salts. The simulation values and the experimental values of gaseous phase migration ratio of Na and K fitted well, and the simulation values were largely smaller than the experimental ones of Ca, Mg and Fe. It is suggested that the distribution law of gaseous product salt should be used to develop the technology of salt separation or chloride salt utilization, so as to realize the comprehensive utilization of secondary fly ash, change the current situation that the secondary fly ash is mainly landfill, and thoroughly realize the harmless and resource utilization of fly ash.