Xuetao Wang

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.

Biomass gasification-gas turbine combustion for power generation system model based on ASPEN PLUS

ASPEN PLUS is an important tool for process design. But in the biomass gasification-gas turbine combustion field, ASPEN PLUS has not been extensively studied. In this paper, the operation unit in the biomass gasification-gas turbine combustion power generation system was introduced. Based on ASPEN PLUS, an integrated system model for power generation by biomass gasification-gas turbine combustion was developed. The model consists of biomass gasification and gas-cleaning system, gas turbine combustion system, and power generation system. The main aim of this research was to develop an integrated power generation system model, to predict the gasifier performance and power generation under various operating conditions. Parameters such as temperature, equivalence ratio (ER), and catalyst affected the syngas composition and heating value. The results show that the simulated data are consistent with the experimental data. Considering M701F gas turbine as the research object, the process of integrated power generation system was described. The simulation of biomass gasification-gas turbine combustion integrated power generation system can simulate the integrated system and obtain the main parameters of gas turbine. The system model based on ASPEN PLUS can be used to predict power generation capacity from biomass gasification-gas turbine combustion system.

Effect of CaO additive on formation of PM 2.5 under O 2 /CO 2 atmosphere during coal combustion

The influence of CaO additive on the emission characteristics of PM<inf>2.5</inf> (particulates with aerodynamic diameter less than 2.5µm) was studied with a tube furnace. The combustion tests were carried out at 1123K under O<inf>2</inf>/CO<inf>2</inf> atmosphere. The PM<inf>2.5</inf> generated from coal combustion was collected and analyzed with an Electrical Low Pressure Impactor (ELPI). The results indicate that CaO is an important factor for the formation of PM<inf>2.5</inf> during coal combustion under O<inf>2</inf>/CO<inf>2</inf> atmosphere. The number and mass concentrations of PM1 diminish, but the number and mass concentrations of PM<inf>1–2.5</inf> enhance slightly after CaO is added. The size distributions of PM<inf>2.5</inf> are similar, which display two peaks around 0.2µm and 2.0µm, respectively. With increasing the additive weight ratio of CaO, the concentrations of S, Pb, Cu, Na and K decrease. The submicron-size ash particles smaller than 0.317µm are formed via nucleation of vaporized ash components, and the supermicron-size ash particles are formed by coagulation and coalescence of the submicron-size ash, and fragmentation and coalescence of mineral matter.

Characteristics of Pd-Rh/CeO 2 /Al 2 O 3 TWC for NO x and PAHs removal in flue gas of MSWI

Pd-Rh/CeO<inf>2</inf>/Al<inf>2</inf>O<inf>3</inf> three-way catalysts by sol-gel method were investigated by catalytic performance test for simultaneous removals NO<inf>x</inf> and PAHs. The experiments were carried out in a laboratory scale incineration system equipped with a catalyst reactor. The catalysts were characterized with BET, SEM, and XRD. The sol-gel way prepared carrier CeO<inf>2</inf>/Al<inf>2</inf>O<inf>3</inf>, characterization results showed that, CeO<inf>2</inf>/Al<inf>2</inf>O<inf>3</inf> the specific surface area is 207m²/g, average pore size is 88.76 Å, pores volume is 0.67 cm³/g. In addition to surface roughness, the surface also appeared in many small crystal particles, suggesting that these small crystals may be Pd crystals. Experimental results showed that the removal efficiency of NO<inf>x</inf>, and PAHs in Pd-Rh/CeO<inf>2</inf>/Al<inf>2</inf>O<inf>3</inf> TWC was generally greater than 80%. The bimetallic catalyst with a Pd/Rh ratio of 1/0.10 was found to have a best activity for highest removal efficiency.

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.