Xiaojia Tang

Kinetics and mechanism of ultrasonic-assisted magnesium oxide hydration

The kinetics of ultrasonic-assisted magnesium oxide (MgO) hydration was investigated in the present paper. The degree of hydration at different temperature (298-338K) and reaction time (0.25-3h) was determined by thermal gravity analysis (TGA). And the products of the hydration were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectrometer (FT-IR) and Particle Size Distribution analysis (PSD). A coupling model based on characteristic equations for chemical reaction control and inward diffusion control was employed to describe the hydration process. The experimental data indicated that the degree of hydration at 2h under ultrasound reaction condition was 18-25% higher than that of mechanical stirring reaction condition. However, the value was nearly the same at the first hour. Combined with the analysis results of degree of hydration, characterization of products and model fitting, the hydration process was supposed to be a mixed model, which controlled by both chemical reaction and inward diffusion. A reaction mechanism emphasized on the physical effect of ultrasound was proposed, assuming that the hydration product layer was broken and regenerated during the process. The calculated activation energy of 24.2kJmol-1 corroborated the mechanism proposed in this study.

Adsorption Characteristics of Macroporous Resin for Oil Removal from Desulphurization Wastewater on Board

According to our previous results on the magnesium-based exhaust gas cleaning system (Mg-EGCS), PAHs and total oil content were the main factors affecting the COD in the wastewater. In this work, three kinds of adsorption materials were investigated and macroporous resin was selected for oil removal. The effects of the dosage of macroporous resin, adsorption time and the flow rate were studied, and thermodynamics equation was used to characterize the adsorption process. The results showed that macroporous resin is a good candidate for oil removal from desulphurization wastewater on board, and the COD after treatment can meet the discharge criteria set by the International Maritime Organization (IMO).

Pilot scale experiments of magnesia hydration under gas-liquid-solid (three-phase) reaction system

Pilot scale experiments were conducted to prepare magnesium hydroxide by magnesia hydration under gas-liquid-solid (three-phase) reaction system. The effect of reaction pressure, reactivity and particle size of magnesia and the concentration of the pulp on the degree of hydration was investigated. The results indicated that the hydration reaction occurred at the first 30min mainly. During the set reaction condition, degree of hydration of 68% could be obtained at the reaction pressure of 0.2MPa, concentration of pulp of 5%w/w with high reactivity and fine powder. The promotion effect on the degree of hydration caused by the three-phase reaction system was mostly attributed to the exfoliation of steam.

Study on jet aeration oxidation of magnesium sulfite from magnesium-based exhaust gas cleaning system

ABSTRACT Oxidation of magnesium sulfite in washing water is essential for the treatment of by-product of shipboard magnesium-based exhaust gas cleaning systems. The purpose of this study is to obtain a highly efficient magnesium sulfite oxidation technology by using the jet aeration process. Response surface methodology and central composite design were used to investigate the effects of major variables on oxidation of magnesium sulfite and optimize the oxidation conditions. The predictions of the two response functions agree well with the experimental data. The optimum oxidation conditions for ship are temperature 318 K, liquid flow rate 4.04 m3/h, and pH 7.70. Under optimal conditions, 12 moles of magnesium sulfite were oxidized by 90% over 15 minutes at an energy consumption of 0.220 kw h.

Study on Marine Bacteria Inactivation by UV Radiation Combined with Multi-pore Ceramic Filtration

Abstract UV is one of well-established ways to deal with bacteria in water. However, when applying on marine bacterium inactivation in ballast water, it shows low efficiency due to the existence of large amounts of plankton. To recover high transmission rate of seawater, plankton are required to be removed before UV radiation. Considering technical and economic feasibility, a novel method of multi-pore ceramic filtration (MPCF) is used as a primary treatment before UV radiation. The study compared UV treatment with MPCF & UV treatment at different flow rates and alga concentrations. The results showed that less than 40% marine bacteria can be inactivated by single UV radiation for the existence of large amounts of algae, while up to 100% inactivation rates were observed by MPCF & UV treatment at high alga concentration. According to the results of orthogonal tests, optimal experimental conditions including UV dose were detected. With the combination of MPCF, lethal UV dose for marine bacteria inactivation can reduce to 8 mW·s·cm-2 even at alga concentration of 15000~20000 cells·mL-1 if alga can be completely removed in advance.

Industrial Test of Energy Saving on Combustion of Watered Fuel Oil

A Self-made micro-mixing device was employed to produce watered fuel oil. Fuel oil and water in a certain ratio entered into the mixer through each channel respectively. Mixed with water fuel was formed under the action of shear force, convective impact and friction. The watered fuel oil was online applied to a steam boiler in an oilfield. The results of the industrial test show as follows: the thermal efficiency of the boiler was increased from 84.1% to 88.6% and the energy saving rate was 5.1% when the fuel oil was mixed with 3.49% water, meanwhile, CO emissions was decreased to 12.0×10-6 from the previous 26.6×10-6.

Promotion of catalytic ozonation of aniline with Mn-Ce-O x /γ-Al 2 O 3

In this study, Mn-Ce-Ox/γ-Al2O3 supported catalysts were adopted to promote the removal efficiency of aniline in simulated wastewater with ozone. Mn-Ce-Ox/γ-Al2O3 catalysts were prepared by the impregnation-calcination method. Its phase structure, specific surface area, loading amount and distribution of active units were analyzed by XRD, BET, ICP-AES and TEM/SEM respectively. The characterization results demonstrated that the catalysts had a good dispersion of Mn-Ce-Ox active sites and an abundant porous structure from the γ-Al2O3 support. The catalytic ozonation results showed that with Mn3-Ce1-Ox/γ-Al2O3(1.0), the aniline removal efficiency was highly improved, 15.0% higher than that of ozonation without a catalyst. Furthermore, from the variation in loading amounts of Mn and Ce, it can be seen that the molar ratio of Mn and Ce within the Mn-Ce-Ox plays a key role in accelerating the ozonation of aniline in simulated wastewater with ozone, while Mn:Ce = 1.9:1 showed the best performance. More importantly, the catalysts showed high recycling performance and could be reused at least 12 times without obvious loss of activity.

Modeling and prediction of desulfurization efficiency for magnesium-based seawater exhaust gas clean system:

The desulfurization efficiency is a major parameter of magnesium-based seawater exhaust gas clean system, which is one of the important means to control the sulfur dioxide emission from marine diesel engines. In this work, the RFlow, a computational fluid dynamics software, was used to analyze the flow field and sulfur dioxide absorption rate in the desulfurization tower of magnesium-based seawater exhaust gas clean system. The subdomain technology was applied for physics modeling and mesh generation of the desulfurization tower, and total number of the mesh is 2.25 million. The flow field model was set up by coupling the multi-fluid model with the dispersive k-ε turbulence model. Based on flow field model, the prediction model for desulfurization efficiency of magnesium-based seawater exhaust gas clean system was programmed in user-defined module of the RFlow software, according to the two-film theory and sulfur dioxide absorption reaction equations. The simulation results predicted a desulfurization efficiency of 97.9%, which agrees well with the practical result. In order to study the effect of gas and liquid flow rate on the desulfurization efficiency, the computational fluid dynamics prediction model was applied. And the verification tests were conducted on a container vessel. Comparing the predicted results with the experimental data, the maximum error is less than 2%. It is proved that the prediction model is reliable and useful for the magnesium-based seawater exhaust gas clean system.

Modeling and prediction for the oxidation efficiency of magnesium sulfite in aeration tank of magnesium-based seawater exhaust gas clean system

In magnesium-based seawater exhaust gas clean system, the desulfurization by-product, magnesium sulfite (MgSO3), has a negative impact on the ecological environment, which needs to be treated to make harmless. Due to the limited space on board, the aeration oxidation method is used to convert it to magnesium sulfate. Because of the variable size, shape and flow field of aeration tank, it is difficult and expensive to design and verify the oxidation efficiency of the aeration tank by experimental method. In this work, in order to predict the oxidation efficiency accurately, RFlow, a computational fluid dynamics software, was used to analyze the flow field and MgSO3 oxidation reaction in aeration tank. The subdomain technology was adopted for physics modeling and mesh generation of the aeration tank, and the total number of meshes was 285,000. The multi-phase flow field model was set up using the multi-fluid model and dispersive k-ε turbulence model. Under the given initial conditions, the predicted oxidation efficiency was 94.2%. Compared with the results of the actual ship test, the prediction model for MgSO3 oxidation efficiency of the aeration tank is reliable.

Research on Water Droplet Size Influencing Factors in Watered Fuel Oil Prepared by Mechanical Agitation

Water droplet size of disperse phase of watered fuel oil, which was prepared by a self-made mechanical micro-mixing device, was inspected under optical microscope. The effects of agitation speed, oil temperature and water content on water droplet size were investigated in this research. The experimental results showed that: water droplet size decreases with the increase of agitation speed and oil temperature at 1000-1300 r/min and 60-80°C, respectively. The lower the water content is, the smaller the size of water droplet will be, and the water content is better to be 3-5%.