Jyh-Cherng Chen

The adsorption of heavy metals by different sorbents under various incineration conditions

The emission of heavy metals can be controlled by adding solid sorbents into the combustion chamber during incineration processes. The objective of this work was to experimentally study the adsorption efficiency of different sorbents for heavy metals under various incineration conditions. Each sorbent has its optimum operating temperature. Kaolinite and aluminum oxide have the best adsorption efficiency at 800 degrees C, and bauxite is at 700 degrees C. The adsorption efficiencies of the three sorbents for the four heavy metals all follow the sequence of Pb > Cu > Cr > Cd. The presence of inorganic chloride (NaCl) and sulfate (Na2SO4) increases the adsorption efficiency of the sorbents, but organic chloride PVC decreases the adsorption efficiency.

The simulation of hexavalent chromium formation under various incineration conditions

The formation of hexavalent chromium Cr(VI) during waste incineration processes is of interested because its carcinogenic characteristic. The objective of this study is to simulate the formation of Cr(VI) species under various operating temperatures and input waste compositions during incineration by a thermodynamic model. The results show that the major hexavalent chromium species are CrO2Cl2(g) and CrO3(g). Chlorine and oxygen can increase the formation of Cr(VI) species; while hydrogen, sulfur, sodium, and calcium can inhibit. The input waste composition has greater effect on the formation of hexavalent chromium species than operating temperature.

Two-stage simulation of the major heavy-metal species under various incineration conditions

Abstract A thermodynamic equilibrium model was used to determine the major species of chromium, lead, cadmium, copper, and zinc formed under various incineration conditions. The effects of temperature and oxygen, chlorine, sulfur, and hydrogen content on the speciation were established by the minimum Gibbs free energy method. Sixty-seven compounds of five metallic species were determined in this study. The simulation conditions included: 1) single metal with oxygen, chlorine, and sulfur system; 2) different chlorine and hydrogen content; and 3) comparisons of a single combustion chamber and a two-stage combustion chamber. The simulation results indicated that the oxides were the dominant forms in a single metal-oxygen system, while the metallic chlorides were the major species in a metal-chlorine-oxygen system. When sulfur was present, in the case of all metals other than Pb, the metallic sulfates were the major species at temperatures below 1000 K, and metallic oxides were the dominant species above 1000 K. Increasing the temperatures caused a decrease of lead chloride, but increased the formation of other metallic chlorides. The concentrations of metallic chlorides decreased significantly as the hydrogen moles were 2∼3 orders higher than those of chlorine. The level of difference between one-stage and two-stage simulations depends on the species formed in the one-stage simulation.

Stability of heavy metals in bottom ash and fly ash under various incinerating conditions

Abstract High chloride concentrations are normally found in municipal waste. Most chloride resources are originally derived from organic chlorides, e.g., PVC and inorganic chlorides, or chloride salt from kitchen waste. Heavy metals can easily react with chlorides during incineration, thus, producing related metallic chlorides. These factors make the combustion products more complicated (such as metallic chloride, metallic oxide, or heavy metal). This study evaluates the effects of operating conditions on the stability of heavy metals (Pb, Cd and Cr) in bottom ash and fly ash. The parameters evaluated include (1) the additives of inorganic chloride (CaCl 2 and NaCI) and organic chloride (PVC), and (2) various operating temperatures. The experimental results indicate that adding organic chloride (PVC) increased the leaching rates of Cr, Pb and Cd in bottom ash, but decreased this rate in fly ash. The addition of sodium chloride (NaCl) increased the leaching rates of the three metals in fly ash, but only Cr and Cd increased in bottom ash. The other inorganic chloride (CaCl 2 ) increased the leaching rate of Cr in bottom ash and fly ash, but for Pb and Cd decrease. In addition, the TCLP leaching rates of these three metals did not have an obvious relation between the total amount of original metals existed in bottom ash and fly ash and operating temperatures of incinerator, but did relate to the chemical species of the formed products.

The Relationship between the Quantity of Heavy Metal and PAHs in Fly Ash

Heavy metal and polycyclic aromatic hydrocarbons (PAHs) in flue gas have received considerable attention in recent years due to their mutagenic or carcinogenic properties. The present study is carried out to investigate the influence of the quantity of heavy metals on PAHs formation in fly ash. A fluidized bed incinerator was used in this experiment to obtain fly ash of chemical similarity by incinerating various compositions of waste. The obtained fly ash, both with and without heavy metal, were used to adsorb the PAHs in the flue gas and to investigate the formation of PAHs in fly ash. The results indicate that carbon and heavy metals most greatly influence the formation of PAHs in the fly ash. Carbon is absorptive; heavy metals encourage not only absorption of PAHs but also catalyze PAHs formation.

The effect of operating conditions on the capture of metals with limestone during incineration

Abstract The objective of this work was to experimentally study the effect of different operating conditions on sorbent (limestone) to capture metals and the formation of hexavalent chromium during fluidized bed incineration of wastes containing Pb, Cd, Cu, and Cr. The operating parameters evaluated included: 1) addition of organic chloride (PVC); 2) addition of inorganic chloride (NaCl); 3) addition of sulfide (Na2S); 4) size of sorbent; and, 5) air factor. The experiments were carried out in a pilot scale fluidized bed incinerator with air pollution control devices of two consecutive cyclones and a wet scrubber. Experimental results indicated that limestone could effectively capture most heavy metals Pb, Cr, and Cd in the sand bed. The addition of organic chloride (PVC) and inorganic chloride (NaCl) in feedstock caused different consequences. The former decreased the adsorption efficiency, while the latter increased the adsorption efficiency of limestone in the sand bed. Moreover, the presence of sulfide (Na2S) was helpful in controlling metals during incineration. Little hexavalent chromium is formed during incineration, but the presence of organic chloride PVC produced more Cr(VI) than inorganic chloride NaCl.

Study of Ambient Air Particle-Bound As(p) and Hg(p) in Dry Deposition, Total Suspended Particulates (TSP) and Seasonal Variations in Central Taiwan

This study investigated the ambient air particle-bound As(p) and Hg(p) levels and compositions in dry deposition and total suspended particulates (TSP) at five sampling sites in Central Taiwan (suburban/coastal, downtown, residential, industrial and wetland) during the years of 2009 and 2010. The main industrial sources of studied metals in various investigated sites include: steel, electronic, plastic, and chemical industries, the Taichung thermal power plant (TTPP), fossil fuel combustion, a science park, transportation, and waste incineration. The samples were digested with hydrochloric acid (HCl) and nitric acid (HNO3), then they were analyzed for metals by ICP-MS. The mean As(p) levels in dry deposition were the highest at Quan-xing site (industrial) and the lowest at Chang-hua site (downtown). Moreover, the mean Hg(p) levels in dry deposition were the highest at Gao-mei site (wetland) and the lowest at He-mei site (residential). In addition, the mean As(p) levels in TSP were the highest at He-mei site (residential) and the lowest at Gao-mei site (wetland). The mean Hg(p) levels in TSP were the highest at Quan-xing site (industrial) and the lowest at Gao-mei site (wetland). Regarding seasonal variation, the lowest levels in dry deposition for both particles As(p) and Hg(p) occurred in spring and summer. Finally, the lowest levels of As(p) and Hg(p) in TSP were observed in fall and winter.

Effects of sodium modification, different reductants and SO2 on NO reduction by Rh/Al2O3 catalysts at excess O2 conditions

Although many catalysts of NO reduction have been developed, the presence of excess O(2) and SO(2) significantly inhibits their performance when they are used to treat the incineration flue gas. To solve such problem, this study prepared new Rh/Al(2)O(3) catalysts and investigated the effects of Na modification, SO(2) and different reductants. Experimental results indicated that the average removal efficiency of NO at such high O(2) concentrations exceeded 80% when the Rh/Al(2)O(3) catalysts were used. CO was a better reductant than C(3)H(6) and the best concentration ratio of reductant/NO was equal to 1. Adding Na to modify Rh/Al(2)O(3) catalysts significantly enhanced the removal efficiency of NO from 80 to 99% at 250-300 degrees C, especially at relative high SO(2) concentrations. Unfortunately, Rh-Na/Al(2)O(3) catalysts do not have long-time activities for NO reduction, possibly because of the formation of NaNO(3). Both Rh/Al(2)O(3) and Rh-Na/Al(2)O(3) catalysts have good performance for NO reduction, they can feasibly be used to reduce NO in the flue gas from waste incineration.

Effects of particulates, heavy metals and acid gas on the removals of NO and PAHs by V2O5–WO3 catalysts in waste incineration system

This study investigated the activities of prepared and commercial V(2)O(5)-WO(3) catalysts for simultaneous removals of NO and polycyclic aromatic hydrocarbons (PAHs) and the influences of particulates, heavy metals, SO(2), and HCl on the performances of catalysts. The experiments were carried out in a laboratory-scale waste incineration system equipped with a catalyst reactor. The DREs of PAHs by prepared and commercial V(2)O(5)-WO(3) catalysts were 64% and 72%, respectively. Increasing the particulate concentrations in flue gas suppressed the DRE of PAHs, but increasing the carbon content on surface of catalysts promotes the NO conversions. The DRE of PAHs by the catalysts was significantly decreased by the increased concentrations of heavy metal Cd, but was promoted by high concentration of Pb. The influence level of SO(2) was higher than HCl on the performances of V(2)O(5)-WO(3) catalysts for PAHs removal, but was lower than HCl for NO removal. Prepared and commercial V(2)O(5)-WO(3) catalysts have similar trends on the effects of particulates, heavy metals, SO(2), and HCl. The results of ESCA analysis reveal that the presence of these pollutants on the surface of catalysts did not change the chemical state of V and W.

Removals of fly ash and NO in a fluidized-bed reactor with CuO/activated carbon catalysts.

This study investigates the effects of fly ash compositions (SiO(2) and Al(2)O(3)), particle sizes (4-10 μm and 40 μm), and concentrations on the simultaneous removals of fly ash and NO using a fluidized-bed catalyst reactor. Experimental results show that the removal efficiencies of fly ash and NO at particle concentrations of 968-11,181 mg m(-3) are 71-97% and 42-57%, respectively. SiO(2) particles have more influences than Al(2)O(3) particles on the performances of fluidized-bed CuO/AC catalyst. As the concentration of fine particle increases, the pores and active sites on catalyst surface are obstructed and therefore the activities of catalysts are depressed.