Dynamic Adsorption of Heavy Metals under Various Incineration Temperatures

Previous studies have indicated that an effective control technology, for heavy metal emissions from incinerators, is to use solid sorbents to capture metals by physical deposition and chemical adsorption. The controlling efficiency is affected by the kind and size of sorbents, the operating temperature, and the specific compositions of the waste. However, the dynamic adsorption behavior of heavy metals on sorbents during incineration is rarely discussed, because it is difficult to analyze and identify trace metals at high temperatures. The main objective of this study is to investigate the dynamic adsorption behavior of Cr, Cu, Pb, and Cd on sorbents (silica sand with limestone) at different operating temperatures (600, 700, and 800°C) and to find the adsorption saturation point of the sorbents during fluidized bed incineration. This will help us to determine when the sorbents should be renewed and investigate the adsorption mechanism. The results show that the adsorption saturation points of three of the four metals were: (1) Cr, 1.4 mg∕g at 600°C, 1.04 mg∕g at 800°C; (2) Pb, 16.08 mg∕g at 600°C, 12 mg∕g at 800°C; and (3) Cu, 10.6 mg∕g at 600°C, 5.34 mg∕g at 700°C. The adsorption capacity follows the sequence of Pb > Cu > Cr > Cd.     

Control of Incinerator Organics by Fluidized Bed Activated Carbon Adsorber

Adsorption on activated carbon of organic compounds from a particle-free and low temperature gas stream has been investigated previously. However, the adsorption processes in a fluidized bed adsorber of particles interfacing with high temperature flue gas has rarely been studied. The major objective of the work was to demonstrate the performance of a fluidized activated carbon adsorber for removal of organic compounds [polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylene (BTEX)] and particulate from flue gas of an incinerator at selected fluidized velocities, fixed bed heights, and bed temperatures. The particle-size distribution of particulate prior to and after flowing through the fluidized adsorption bed were also analyzed. The results indicate that the fluidized bed activated carbon adsorber has a high removal efficiency of PAHs and BTEX. Three evaluated parameters show different effects on PAHs, BTEX, and particles. That the fluidized bed activated carbon adsorber has the ability to filter coarse particles due to the inertia collision is also identified.     

Control of PAHs from Incineration by Activated Carbon Fibers

The aim of this research was to use activated carbon fibers (ACFs) to adsorb 16 polycyclic aromatic hydrocarbon (PAH) species from flue gas emissions during incineration. The operation conditions included the presence of three activated carbon fibers, the adsorption temperature (200, 300, and 340°C), and the weight of the ACFs. The removal efficiencies of the gaseous and solid-state PAHs were evaluated respectively. It was found that the BET surface area did not affect PAH removal when the BET surface area was enough for PAH removal and micropore volume was the determinant parameter for PAHs removal. The best adsorption temperature in this study was 300°C. The removal efficiency of PAHs was proportional to the weight of ACFs.     

Adult height, stroke, and coronary heart disease

Trace toxic metals in municipal solid waste may escape from the incineration process in flue gas, in dry collected ash, in wet scrubbed ash, or as a suspended aerosol. Therefore, understanding the behavior of heavy metals in the flue gas and the best controls in the air pollution control equipment are important and necessary. The control conditions of water cooling and spray dryer systems during incineration processes significantly influence the formation of heavy metal compounds. The formation of chromium (Cr), lead (Pb), and cadmium (Cd) species under various control conditions (water cooling tower and spray dryer reactor) was investigated in this study. The object of the experiment is to understand the effects of water cooling and spray dryer systems individually on the formation of heavy metal species. The operating parameters that are evaluated include different control systems, control temperatures, and chlorine content. A thermodynamic equilibrium model was also used to evaluate experimental data. In order to match real incineration conditions, a two-stage simulation was performed in this experiment. The results showed that the relationship of speciation between the simulation prediction and X-ray diffraction (XRD) analysis is consistent for Cr compounds; both indicated that Cr2O3 is the major species. The relationship is almost the same for Cd compounds, but not for Pb compounds.     

Microwave Technology for Treatment of Fume Hood Exhaust

CHA Corporation installed a fume hood adsorber (scrubber) unit onto an operating fume hood and microwave regeneration system in the Safety and Risk Management Building at the Advanced Technology Park in Bozeman, Montana. The microwave-based fume hood exhaust purification process is designed to capture hazardous air pollutants in the fume hood exhaust using granular activated carbon (GAC) and natural zeolite, and subsequently either recover or destroy desorbed pollutants by microwave energy during regeneration of the saturated adsorbents. Onsite testing of this prototype microwave system was conducted using a variety of air borne pollutants including toluene, ethyl acetate, methylene chloride and hydrochloric acid. Test results showed that microwave energy, at a frequency of 2,450 MHz, restored the original adsorption capacity of saturated GAC and saturated natural zeolite. The results also demonstrated that microwave-induced catalytic oxidation was capable of providing oxidation efficiencies greater than 99% with oxidation temperatures below 100°C.     

Modeling the Temperature Dependence of Adsorption Equilibriums of VOC(s) onto Activated Carbons

In order to optimize the efficiency of the removal of volatile organic compounds (VOCs) by adsorption onto activated carbon beds, process simulations taking into account exothermicity effects are helpful. Significant temperature increases may arise in the bed during the VOC adsorption cycle, especially when high concentrations have to be treated. Consequently, reliable and easy-to-handle isotherms remain a key hurdle to build realistic models. In this study, adsorption models were tested to describe a set of experimental data obtained for three VOCs (acetone, ethyl formate, and dichloromethane) adsorbed onto five commercial activated carbons at four different temperatures (20, 40, 60, and 80°C). A new expression of the Freundlich equation [qe = (a1T+a2T2)Ce(1/nf)] was shown to be statistically the most efficient to describe the adsorption isotherms of VOCs, single or in mixtures. A second-order polynomial temperature-dependence was introduced in this expression. The so-adapted Freundlich relationship gave a mean coefficient of determination of 0.97 for single-component adsorption and a correlation coefficient of 0.98 for binary mixtures.     

Applications of Low-Temperature Regenerative Thermal Oxidizers to Treat Volatile Organic Compounds

A series of plant scale low temperature regenerative thermal oxidizers (LTRTOs) equipped with heating wires were constructed to treat volatile organic compounds (VOCs) laden gas streams. All regenerative beds were packed with gravel (approximate particle size 1.25 cm, specific area 205 m2/m3, and specific heat capacity 840 J/kg?°C) and equipped with K-type thermocouples for measuring gas temperatures. Test gas streams were extracted from manufacturing sections of varnishing, semiconductor packing, and petrochemical plants, representing a variety of gas-phase pollutants, including several commercial solvents. Experimental results indicate that 98% or greater treatment of VOCs with concentrations between 100 and 7,000 ppm as methane. Analysis of gas temperature variation with time at various bed depths confirm that VOC degradation occurs at temperatures ranging from 300 to 440°C, which are much lower than autoignition points of tested compounds. A 1.0 s gas residence time in the oxidation zone of regenerative beds is required for successful LTRTO operation.     

Determination and Correlation of Binary Gas Adsorption Equilibria of VOCs

Highly porous activated carbon is used in the removal of volatile organic compounds (VOCs) and the purification of room air. Since the activated carbon must be capable of removing VOCs at low concentrations through adsorption, studies on the adsorption equilibrium of trace-level concentrations of VOCs are essential. To determine the adsorption isotherm, a headspace gas chromatography (HSGC) method was used, with analysis carried out using gas chromatography or gas chromatography-mass spectroscopy. The reliability of this method was confirmed by comparison of the adsorption isotherms of methanol measured by the HSGC method with those measured by the volumetric method. Isotherms for three different types of activated carbon and eight types of VOCs were determined over a wide range of concentrations. Furthermore, the results of the HSGC method for two systems of binary adsorption equilibria (dichloromethane+trichloroethylene) and (benzene+toluene), were found to be correlated with those of the ideal adsorbed solution theory.     

Catalytic Oxidation of Volatile Organic Liquids

Metal oxide and supported-Pt catalysts were developed for complete oxidation of volatile organic compounds (VOCs) and other solvent-derived organic vapors (OVs) in air at relatively low temperatures. The goal for this work is to produce a simple, cost-effective technology for reducing the concentration of organic contaminants in air to acceptable levels before the air is released into the atmosphere or recirculated. Specific applications include ventilated work spaces for spray painting and engine maintenance, indoor air decontamination, dry cleaning, food processing, fume hoods, residential use, and solvent-intensive industrial processes. Catalyst powders and monolith-supported catalysts were screened for conversion of 1-butanol, toluene, and methyl ethyl ketone to carbon dioxide and water. The concentration of OVs in the feedstream was maintained at approximately 100 ppmv, and the space velocity was between 6,000 and 18,000 h?1. Metal oxide catalysts without Pt generated complete conversion of 1-butanol to CO2 at 150°C, 69% conversion at 100°C, and 15% conversion at 80°C. For toluene, complete conversion was achieved at 200°C, and greater than 75% conversion at 150°C. Addition of Pt to the metal oxide compositions typically lowered the temperature for a given OV oxidation rate by at least 20–50°C. Catalysts deposited onto standard commercial cordierite monoliths retained their composition and activity, and were stable in humid air, as well as nitrogen- and chlorine-containing OVs. However, the catalysts quickly deactivated in the presence of sulfur and phosphorus.     

Study on Pb and PAHs Emission Levels of Heavy Metals- and PAHs-Contaminated Soil during Thermal Treatment Process

The objective of this study was to use thermal treatment to treat soil contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). The emissions of lead (Pb) and PAHs during the thermal treatment process were evaluated. The parameters included pretreatment, temperature, and speed of the rotary kiln. Cadmium (Cd) had a higher mobility in thermally treated contaminated soil slag than other heavy metals because the primary fraction of Cd was the exchangeable fraction (90%). Of the temperatures tested in this study, the highest emission concentration of Pb occurred at 700°C. The Pb emission concentrations in the gas phase and solid phase were 44?μg/N?m3 and 138.35?μg/N?m3, respectively. In PAHs emissions, naphthalene, acenaphthene (Acp), and fluorene were the main species in the gas phase, at different operating temperatures. The concentrations of these species ranged from 615.5 to 2,002.3?μg/N?m3. Acp and chrysene were the main species in the solid phase at different temperatures, and the concentrations of these species ranged from 25.5 to 113?μg/N?m3.     

Equilibrium Adsorption of Phenol-, Tire-, and Coal-Derived Activated Carbons for Organic Vapors

Adsorption isotherms for alkane, aromatic, and ketone vapors were determined for activated carbon fiber cloth, tire-derived activated carbon and coal-derived activated carbon adsorbents. Physical and chemical properties of the vapors and adsorbents were used to interpret these results that were obtained from 20 to 50°C, with a more limited data set at 125 and 175°C and relative pressures between 0 and 0.99. Fitted isotherms using the Freundlich and Dubinin–Radushkevich adsorption models had mean total relative errors <5.6 and 9.2% for the microporous and mesoporous/macroporous adsorbents, respectively, at the temperature range from 20 to 50°C. The predictive direct quantitative structure activity relationship model had mean total relative errors <9.7 and 61% for the microporous and mesoporous/macroporous adsorbents, respectively, at the temperature range from 20 to 50°C without requiring experimental input.     

Thermal Behavior of Activated Carbon Cloths Heated by Joule Effect

Activated carbon cloths (ACC) are promising adsorbents for the treatment of air loaded with volatile organic compounds (VOC). Their characteristics and properties allow them particularly high adsorption capacities and useful handling. Moreover, the Joule effect regeneration of these media may be used as a regeneration process. These peculiarities make it possible to design and size ACC filters for a wide range of industrial applications: low VOC concentration and flow for indoor air quality as well as high concentration and flow in some industrial effluents. Hence, innovating reactors could be equipped with such an adsorption-desorption process which permit us to recover the condensed compounds. The heating of ACC by Joule effect (between 20 and 250°C) is generally highly homogeneous, and the spatial distribution of the temperatures is directly connected to the activation level distribution in the material. A characterization method and a modeling approach are proposed to describe the ACC thermal behavior and to compare and select the best media in term of regeneration process. This allows sizing of future industrial processes.     

Catalytic Incineration of C2H5SH and Its Mixture with CH3SH over a Pt/Al2O3 Catalyst

Catalytic incineration is one of the cost-effective technologies to solve troublesome volatile organic compounds. However, some sulfur containing volatile organic compounds, such as ethyl mercaptan, may deactivate the Pt catalyst that is commonly used in the catalytic incineration process. This paper provides information on the poisoning effect of ethyl mercaptan. The catalytic incineration of ethyl mercaptan, typically emitted from the petrochemical industry, over a Pt/Al2O3 fixed-bed catalytic reactor was studied. The effects of operating parameters including inlet temperature, space velocity, C2H5SH concentration, O2 concentration, and catalyst size were characterized. Catalytic incineration on a mixture of C2H5SH with CH3SH was also tested. The results show that the conversions of C2H5SH increase as the inlet temperature increases and the space velocity decreases. For the temperature from 200–260°C, the higher the C2H5SH concentration is, the lower its conversion. The O2 concentration has a positive effect on the conversion of C2H5SH. C2H5SH has a poisoning effect on the Pt/Al2O3 catalyst, especially at lower temperature. The existence of CH3SH has no effects on the conversion of C2H5SH.     

载体对二氧化钛光催化降解苯的影响

研究了以活性炭、沸石、膨润土和硅藻土为负载的TiO2对空气中苯的光催化降解性能，并与无负载的TiO2进行了比较，结果表明，选择合适的载体可以起到吸附与催化氧化的协同作用，提高催化效率。     

Wet Air Oxidation of Solid Waste Made of Polymers

Wet air oxidation was attempted on synthetic (mixture of plastics of various compositions) and natural (cellulose substances) solid polymers. The temperature was maintained at 270°C and the oxygen pressure varied from 0 to 2 MPa (from understoichiometric conditions to oxygen excess). No valorizable compounds were found, even in runs carried out under an oxygen deficit. Suitable conditions for the total destruction of the initial polymers were temperatures above 270°C, an excess of oxygen, and a residence time of less than 1 h. Only such degradable compounds as acetic and benzoic acids are found at low concentrations. Formation of chlorine and gaseous hydrochloric acid can be limited by adding CaCO3 as a neutralizing agent.     

Injection Nozzle for Ultraviolet Light-Enhanced H2O2 Oxidation of Air Pollutants in Flue Gas

Injecting aqueous solutions of hydrogen peroxide (H2O2) into hot flue gases can split the peroxide into OH and HO2 radicals. These reactive radicals readily oxidize air pollutants such as CO, VOCs, NO, mercury, and others. H2O2 is thermally “activated” (split into free radicals) rapidly at temperatures of 500°C and above. At lower temperatures, such as found in boiler exhaust flue gases, ultraviolet (UV) light can be used to activate the peroxide molecules. However, placing the UV lamps directly in the flue gases can lead to operating and maintenance problems, and “dilutes” the UV energy due to absorption by other gases. A “UV nozzle” has been developed that produces H2O2 radicals and delivers them into a flowing stream of boiler flue gases. Using a previously constructed pilot scale system at NASA's Kennedy Space Center, experiments were run to prove the concept of the nozzle, measuring the oxidation of NO as an indicator of radical formation and delivery. Data were taken at three temperatures, with none, one, or two UV lamps on, and with various injection rates of peroxide. Flue gas temperatures ranged from 85 to 304°C (186 to 580°F), and the molar ratios (inlet peroxide to inlet NOx) ranged from about 1.5 to over 15. Conversions of NO varied from 0% (at the lowest temperature tested) to above 50% (at highest temperature). Although increasing temperature had a marked effect on conversion, the activation of hydrogen peroxide by UV light was demonstrated in the temperature range of final flue gas exhaust gases (290–350°F). These results indicate that radicals can be created from hydrogen peroxide at reasonable temperatures using UV light, and that the radicals can be delivered into a flue gas stream where they can oxidize pollutants.     

Capacity of Activated Carbon Derived from Peach Stones by K2CO3 in the Removal of Acid, Reactive, and Direct Dyes from Aqueous Solution

The present research deals with the production of activated carbon by chemical activation using peach stones and its adsorption behavior. The prepared activated carbon was used for the adsorption of three kinds of textile dyes, acid, reactive, and direct dyes, from aqueous solution. The results indicated that the overall adsorption process followed the pseudo-second-order kinetic model. The equilibrium data were found to be well represented by the Langmuir adsorption isotherm model. The calculated adsorption capacities for Reactive Orange 16, Acid Yellow 11, and Direct Red 23 onto activated carbon were 667, 539, and 427?mg?g?1 at 50°C, respectively. Thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were also calculated and indicated that the adsorption of dyes onto activated carbon was spontaneous and endothermic in nature.     

Capture of Organic Vapors Using Adsorption and Electrothermal Regeneration

Activated-carbon-fiber cloth (ACFC) is an alternative adsorbent to granular activated carbon (GAC) for removing and recovering organic vapors from gas streams. Electrothermal desorption (ED) of ACFC provides rapid regeneration while requiring less energy compared to traditional regeneration techniques used with GAC. This paper provides proof-of-concept results from a bench-scale ACFC adsorption system. The automated system captured 1,000 ppmv of hazardous air pollutants/volatile organic compounds (HAPs/VOCs) from air streams and demonstrated the use of ED, using ac voltage, to recover the HAP/VOC as a pure liquid. The desorbed HAP/VOC condensed onto the inner walls of the adsorber and was collected at the bottom of the vessel, without the use of ancillary cooling. Seventy percent of the HAP/VOC was collected per cycle as condensate, with the balance being retained in the regenerated adsorber or recycled to the second adsorber. ED with in-vessel condensation results in minimal N2 consumption and short regeneration cycle times allowing the process to be cost competitive with conventional GAC-based adsorption processes. This technology extends the application of carbon adsorption systems to situations that were previously economically and physically impractical.     

煤基活性炭改性及其甲烷吸附能力

针对无烟煤制备成的煤基活性炭,采用酸式改性、碱式改性和联合改性的方法对其进行改性处理。通过低温液氮吸附实验、傅里叶红外光谱技术、高压甲烷吸附实验,分析了煤基活性炭的表面物理、化学结构、甲烷的吸附能力。借助Langmuir吸附等温模型、Freundlich模型进行数据拟合,研究了吸附热力学和动力学特征。结果表明,联合改性后的煤基活性炭比表面积和孔容均明显增大,其中比表面积增大66.66%,总孔容增大30.89%;煤基活性炭的甲烷吸附能力明显提高,甲烷吸附量提升25.686%。煤基活性炭的孔隙结构和表面官能团共同决定了其对甲烷的吸附作用,且较于孔隙结构,表面官能团的极性对甲烷吸附量起主要作用。      

Removal and Destruction of Organic Compounds in Water Using Adsorption, Steam Regeneration, and Photocatalytic Oxidation Processes

A treatment strategy is examined whereby organic compounds in the aqueous phase are first removed by fixed-bed adsorption, followed by off-line regeneration of spent adsorbent using saturated steam (160°C) and cleanup of steam condensate using fixed-bed photocatalysis. This treatment strategy is examined with the following organic compounds: Tetrachloroethylene (PCE), carbon tetrachloride (CCl4), p-dichlorobenzene (p-DCB), o-chlorobiphenyl (o-PCB), and methyl ethyl ketone (MEK). For six cycles of adsorption and regeneration, the steaming process is effective to regenerate the adsorbent exhausted with PCE, p-DCB, CCl4, or MEK. In the case of o-PCB, there is about 20% loss in adsorbent capacity after the first cycle; however, the adsorption capacity for Cycles 2–6 is almost the same. Fixed-bed photocatalysis is examined for decontamination of steam condensate carrying the desorbed organics, and it is observed to be effective for mineralization of aqueous phase PCE, p-DCB, CCl4, and o-PCB. In the case of MEK, although 97% of the compound was removed, only 16% removal of total organic carbon was observed, thereby suggesting that some by-products were produced that were refractory to oxidation.