Baosheng Jin

Computational Fluid Dynamics Modeling of Chemical Looping Combustion Process with Calcium Sulphate Oxygen Carrier

To concentrate CO2 in combustion processes by efficient and energy-saving ways is a first and very important step for its sequestration. Chemical looping combustion (CLC) could easily achieve this goal. A chemical-looping combustion system consists of a fuel reactor and an air reactor. Two reactors in the form of interconnected fluidized beds are used in the process: (1) a fuel reactor where the oxygen carrier is reduced by reaction with the fuel, and (2) an air reactor where the reduced oxygen carrier from the fuel reactor is oxidized with air. The outlet gas from the fuel reactor consists of CO2 and H2O, while the outlet gas stream from the air reactor contains only N2 and some unused O2. The water in combustion products can be easily removed by condensation and pure carbon dioxide is obtained without any loss of energy for separation.Until now, there is little literature about mathematical modeling of chemical-looping combustion using the computational fluid dynamics (CFD) approach. In this work, the reaction kinetic model of the fuel reactor (CaSO4+ H2) is developed by means of the commercial code FLUENT and the effects of partial pressure of H2 (concentration of H2) on chemical looping combustion performance are also studied. The results show that the concentration of H2 could enhance the CLC performance.

Flow Behaviors of Non-spherical Granules in Rectangular Hopper

Abstract Flow behaviors of four kinds of granular particles ( i . e . sphere, ellipsoid, hexahedron and binary mixture of sphere and hexahedron) in rectangular hoppers were experimentally studied. The effects of granular shape and hopper structure on flow pattern, discharge fraction, mean particle residence time and tracer concentration distribution were tested based on the visual observation and particle tracer technique. The results show that particle shape affects significantly the flow pattern. The flow patterns of sphere, ellipsoid and binary mixture are all parabolic shape, and the flow pattern shows no significant difference with the change of wedge angle. The flowing zone becomes more sharp-angled with the increasing outlet size. The flow pattern of hexahedron is featured with straight lines. The discharge rates are in increasing order from hexahedron, sphere, binary mixture to ellipsoid. The discharge rate also increases with the wedge angle and outlet size. The mean particle residence time becomes shorter when the outlet size increases. The difference of mean particle residence time between the maximum and minimum values decreases as the wedge angle increases. The residence time of hexahedron is the shortest. The tracer concentration distribution of hexahedron at any height is more uniform than that of binary mixture. The tracer concentration of sphere in the middle is lower than that near the wall, and the contrary tendency is found for ellipsoid particles.

Experimental Analysis of Heavy Metals Behavior during Melting Process of Fly Ashes from MSWI under Different Atmospheres

Fly ashes from municipal solid waste incinerator were melted using a micro-scale furnace at 1100 to 1400 °C. The behaviors of several heavy metals had been systematically measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). This study investigated leaching characteristics of melted slag. Experimental results showed that the fixation rates of Cr, Ni, Cu and As in melted samples would increase with the elevation of their melting point at oxidizing atmosphere. Several volatile heavy metals are readily emitted during melting process. The volatilization rates of lead, cadmium and mercury with low boiling points reached over 95% at oxidizing atmosphere. The reducing atmosphere would be propitious to enhancing the fixation rates of chromium, nickel, copper and arsenic. It is confirmed that mercury, cadmium, and zinc are more easily vaporized under reducing atmosphere, but the volatilization of lead would be inhibited at the same condition. The volatilization rate of zinc was very low due to easily forming the nonvolatile compounds, like Zn2SiO4, ZnSiO3, and ZnAl2O4. Due to the volatilization rate of lead being inhibited, it was less than 50% at 1100-1400 ℃. The leaching test on all the melted slag samples showed that the fly ashes were successfully detoxified to meet of the limits toxicity characteristic leaching procedure (TCLP) in China and United States.

Modeling of heavy metals behavior based on fly ash from MSWI in a swirling furnace

Based on the experimental results and existent states of heavy metals in fly ashes and slag, the gas-solid reaction theory during the melting process, heat and mass transfer of particles in fly ashes, chemical dynamics theory such as volatile heavy metals diffuseness, the plentiful experimental datum were analyzed. Theoretical simulated results from the predicted model are basically consistent with experimental data concerning Co, Cu, Ni, Cr, and Mn fixed rates from in swirling furnace. Results indicate that this approach permits to predict the extent of heavy metals vaporization from a glassy matrix, such as As, Cd, Pb, Zn, and Hg, when heavy metals in swirling melting. The model of heavy metals melting reaction and the volatility in particles during fly ashes melting process has been constructed.

Characteristics of Heavy Metals Partition during Melting Process of MSWI Fly Ash

The partition characteristics of heavy metals during melting process of MSWI fly ash was carried out using a microscale furnace between 1100 and 1400°C under different melting time and basicity conditions. Experimental results indicated that the fixation rates of Ni, Cr, Cu and As were up to the maximum at 1200°C. This is attributed to inorganic materials in solid residue took place chemical reaction and transformed into the salt layer. The produced crystal prevented the evaporation of heavy metals and their volatile chlorides. Temperature changes had slimly impact on the volatilization rates of Pb, Cd and Hg with the exception of Zn. There are marked differences that the melting time affects the behavior of various heavy metals. The fixation rates of Ni and Cr increase with increasing melting time prolonging in duration. On the contrary, the proportion of Cu and As in the slag was decreasing. With melting time increasing, the fixation rate of Ni, Cr, Cu and As in samples tended to level off after melting for 90 min. The volatilization rates of Pb, Cd, Hg were on a high level above 95% and nearly complete volatilization in 30 min. The proportions of heavy metals remaining in the melted slag were affected by the basicity (CaO/SiO 2 ). High basicity redounded to fixation of Ni, Cr, Cu and As. There were slightly impacts on volatilization of Pb, Cd, Hg and Zn with the basicity changes of fly ash. Low basicity produced a remarked effect on volatilization of Zn. The leaching test on melted slag samples showed that the fly ashes were successfully detoxified to meet of the limits toxicity characteristic leaching procedure (TCLP) in China and United States.

Operation of a Pressurized CFB Gasification for Bituminous Coal

The effect of furnace pressure on bituminous coal gasification was studied on laboratory-scale pressurized circulating fluidized bed (CFB) gasifying furnaces. Within the scope of this paper this test facility as well as its operation behavior is described. Furthermore the parameter pressure has been investigated regarding to its influence on the producer gas composition, carbon conversion, carbon content of fly ash, yield of dry gas, efficiency of cold gas and low heat value (LHV) of coal gas are presented and discussed in the following. The study results showed that the gasification quality was improved at elevated pressure because of the better fluidization in the reactor. Coal gasification at a higher pressure shows advantages in LHV, and carbon conversion. The dry gas yield and efficiency of cold gas increased little with the increase of the furnace pressure. For a certain CFB coal gasification process, when the pressure is 0.3~0.4 MPa, this parameter had an optimum operating figure.

Numerical Simulation of Boiler Implosion

Mathematical model of a 300 MW boiler was created including furnace, super-heater, economizer, air pre-heater, ESP, and ID fan. Furnace implosion simulation was accomplished at 100% load during MFT and ID fan maloperation. The pressure changing process was summarized into three steps and flow character of each step was analyzed in detail. It is pointed out that furnace implosion is caused by many factors, such as air flowing-into, gas flowing-out, ID fan pressure, resistance of the gas duct, gas combustion, and so on. Such analysis is helpful for both theoretical and application purposes. Simulated values of steady combustion agree well with designed ones.

Flow Regime Distinguish in a Circulating Fluidized Bed Gasifier Based on Wavelet Modulus Maxima

Pressure fluctuation is often used to analyze the dynamic changes of the gas-solid fluidized beds. In this paper, cold tests were carried out to study the gasification system of circulating fluidized beds gasifier, to find out the change law of the solid circulation rate Gs and the holdup by altering such parameters as air velocity, particle size and integrated particle, and recognize the flow regime in the boiler through analysis of the differential pressure fluctuation signals with wavelet transform modulus maximum method. Results indicate that Gs increases with the increase of the superficial gas velocity. When the superficial gas velocity is higher than 2m/s, the three kinds of particles with higher distribution concentration of particle size exhibit characteristics of fast fluidization at the bottom of the riser, and the number of modulus maxima lines is almost the same as that in the top area. Change the distribution range of particle sizes of bed materials, and the larger particles in the riser after particle separation exhibit characteristics of both the turbulence region at the bottom and the fast region on the top, prolonging their residence time in the bed. There are more modulus maxima lines for the differential pressure fluctuation signals at the bottom than on the top. The regime recognition method based on modulus maximum and its experimental results will help us learn more about the design, enlargement and operation of circulating fluidized beds.

Feasibility of the Thermal Treatment of Printworks Solid Waste

To study the feasibility of the thermal treatment of solid waste contained 2-naphthol from the printworks, the performance of the pyrolysis and combustion character of the solid waste was tested on the TG-DTA 92 thermogravimetric analyzer. This apparatus can perform experiments such as TG and DTG at the same time. The experiments were carried out at four different atmospheres. High purity nitrogen was used as the carried gas at a flow rate of 65 mL/min. The samples were heated up to 383 K at a heating rate of 10 K/min in order to dry the sample. After a drying period of 10 minutes, the samples were heated up to the desired temperature (1173 K) at the heating rate of 10 K/min. The experimental results indicate that the solid waste contained 2-naphthol is unstable and is easy to be decomposed at high temperature in the presence of oxygen. The weight loss rate of the solid waste was affected by the oxygen content of the carried gas. Pyrolysis kinetics parameters of the solid waste were obtained and a proper kinetics model was proposed.