ENVIRONMENTAL TOBACCO SMOKE REMOVAL CAPABILITY OF ACTIVATED CARBON

Removal of gaseous and vapor constituents of environmental tobacco smoke (ETS) by activated carbons in a packed bed arrangement was studied under dynamic conditions and was compared with that by silica gel and molecular sieve 13X. ETS is a mixture of sidestream smoke and exhaled mainstream smoke, and it consists of various organic and inorganic compounds, trace heavy metals, and particulate matters. Due to the complex nature of ETS-air mixture, its removal from indoors is a challenging task. For experimentation in a laboratory, the ETS was produced from a specially designed smoking apparatus that simulated the puffng of a cigarette by a person. Air containing ETS was passed through a bed containing about 25 grams of activated carbon at room temperature. The flow rate of air-ETS mixture through the bed was 4000 cm3/min. The relative humidity of the air was 50% and contained about 35 to 40 ppm of hydrocarbons as measured as methane-equivalent. The number of particles in the inlet air stream were in the range of 30,000 to 35,000 particles/cm3. About 60% of hydrocarbons present in ETS were removed at these operating conditions for a period of about 70 hours. Based on 15 adsorption and regeneration cycles, it was noted that the carbon bed did not loose its capacity for ETS significantly as indicated by the BET surface area and water adsorption data. At the beginning of an adsorption cycle, the carbon bed captured a significant number of particles. However, the bed rapidly lost its particle capture effciency as the experiment progressed. The number of particles in the outlet air stream was found to be the same as that of the inlet stream within five minutes.     

IMPORTANCE OF DISPERSED SOLIDS IN BUBBLES FOR EXOTHERMIC REACTIONS IN FLUIDIZED BEDS

Ignition of activated carbon particles were measured in a vertical tube reactor of 4 cm ID, where single particles fell consecutively through a gas mixture containing oxygen.

A two dimensional fluidized bed reactor 24 cm wide, 51 cm high and 2.5 cm in thickness was used for visual observation through a wide front window 24 cm × 35 cm covered with a silica glass plate 1 cm thick. Activated carbon particles were fluidized incipientiy by air, and a gas mixture containing oxygen was injected upwards into the bed through a nozzle positioned 5 cm above the distributor, forming single bubbles intermittently.

It was observed that carbon particles dispersed in rising bubbles were ignited abruptly at emulsion phase temperatures above 550°C. Experimental findings from the fluidized bed were compared with those from the tube reactor, suggesting that the igniting conditions for particles dispersed in bubbles are nearly the same as for single particles falling in the tube reactor.     

IMPORTANCE OF DISPERSED SOLIDS IN BUBBLES FOR EXOTHERMIC REACTIONS IN FLUIDIZED BEDS

Ignition of activated carbon particles were measured in a vertical tube reactor of 4 cm ID, where single particles fell consecutively through a gas mixture containing oxygen.

A two dimensional fluidized bed reactor 24 cm wide, 51 cm high and 2.5 cm in thickness was used for visual observation through a wide front window 24 cm × 35 cm covered with a silica glass plate 1 cm thick. Activated carbon particles were fluidized incipientiy by air, and a gas mixture containing oxygen was injected upwards into the bed through a nozzle positioned 5 cm above the distributor, forming single bubbles intermittently.

It was observed that carbon particles dispersed in rising bubbles were ignited abruptly at emulsion phase temperatures above 550°C. Experimental findings from the fluidized bed were compared with those from the tube reactor, suggesting that the igniting conditions for particles dispersed in bubbles are nearly the same as for single particles falling in the tube reactor.     

The rate of gas adsorption by activated carbon

A study was made of the rate of gas adsorption by activated carbon in terms of the functional dependence of the pseudo first order adsorption rate constant. Benzene was used as the adsorbate vapor and a packed bed column of a Pittsburgh activated carbon as the adsorbent. Benzene at a concentration of 2 × 10^?6 g/cm³, equivalent to a relative pressure of 0·005 at 25°C, was flowed into the carbon bed at superficial linear velocities ranging from 2 to 50 cm/sec. The time at which 1% of the inlet concentration appeared in the exit stream of the bed was the breakpoint time. By applying the Wheeler adsorption kinetic equation to the experimental plot of breakpoint time vs bed weight pseudo first order adsorption rate constants at various linear velocities were determined. Using a presumed mathematical model and an overdetermined set of six equations the Univac 1108 computer provided the coefficients for an expression showing the dependence of the adsorption rate constant on the linear flow velocity.     

Experimental breakthrough curves determined under carefully controlled conditions for the adsorption of water vapour on alumina in adiabatic fixed beds

The adsorption on activated alumina of water vapour from an air stream is studied experimentally in an adiabatic fixed bed. The experimental set-up which provides accurate results is described. The influence of particle size, gas inlet concentration and temperature, linear gas velocity and bed length on concentration and temperature at bed outlet is investigated.     

回料流入口高度对循环流化床提升管流动特性的影响

The axial pressure drop profile and the radial solids distribution were measured in a circulating fluidized bed for evaluating the effects of return gas-solids stream position on the riser flow properties.The saturation carrying capacity of gas for Geldart B typed particles and the flow mode of return gas-solids stream in the bed were discussed.It was found that arranging the inlet at a higher position of the riser would make the bottom bed leaner when U₀ was high and G_s was low.When G_s increased,the longer influenced region of return particles and a small air-staging through lifting the loosening air injection position made the bottom bed become denser significantly.The deceleration and residence of return particles caused a relatively denser but asymmetrical region in the vicinity of inlet.But much more symmetrical solids distribution profile was found in the upper and lower regions far away from the inlet.The effects of inlet height on the flow properties of the riser with air-staging also were analyzed.The secondary air injection below the solids inlet could not cut off the solids exchange in the bed.The bed solids concentration increased when the particles inlet moved to a higher position of the bed when air-staging was adopted.Using CO₂ as tracer,the dispersion of the loop-seal-fluidizing air for transmitting the return particles was investigated.It was found that the loop-seal fluidizing air dispersion rate was low but can be enhanced by the secondary air injection.     

Comparison of vapor adsorption characteristics of acetone and toluene based on polarity in activated carbon fixed-bed reactor

Adsorption characteristics according to polarity of acetone and toluene vapors on coconut based activated carbon were investigated by using a fixed bed reactor. Single vapor and binary vapor adsorption of acetone and toluene were conducted. In the single vapor system, the equilibrium adsorption capacity of toluene vapor on activated carbon was five times higher than that of acetone vapor because of polarity difference between adsorbent and adsorbate. The breakthrough curve of acetone vapor in the binary vapor was quite different from that of single acetone vapor. Acetone adsorbed in the binary vapor was substituted with toluene due to the affinity difference during adsorption process and its outlet concentration increased to 1.6 times than inlet concentration. The temperature changes in activated carbon bed during adsorption of acetone vapor and toluene vapor occurred in the time ranges of 10–30 min. The temperature change for acetone vapor adsorption was about 3 °C; however, that for toluene vapor adsorption was increased to 33 °C maximally.     

低浓度甲苯和对二甲苯在微纤包覆活性炭结构化固定床上的竞争吸附

通过湿法造纸技术制备了微纤包覆活性炭复合材料,研究了甲苯和对二甲苯在基于微纤复合材料结构化固定床上的吸附透过行为. 结果表明,颗粒活性炭被很好地包覆在烧结锁定的三维网络中,活性炭包覆前后的比表面积分别为976和955 m2/g,微孔体积分别为0.261和0.247 cm3/g;甲苯和对二甲苯在单一颗粒碳固定床和结构化固定床上的吸附均展示出竞争吸附特性,在两床层中均是甲苯先透过. 在5%透过浓度下,甲苯和对二甲苯在结构化固定床上的透过时间较在颗粒碳固定床上分别延长了20和30 min,甲苯和对二甲苯分离时间增加了10 min. 采用Yoon-Nelson模型对透过曲线进行拟合,相关系数R2>0.98,甲苯和对二甲苯在结构化固定床上的吸附速率常数分别为颗粒碳固定床的3和1.6倍.     

Adsorption of elemental mercury vapor by impregnated activated carbon from a commercial respirator cartridge

In order to protect workers from the harmful effects of mercury vapor, adsorption technology using impregnated activated carbon is currently in use in respirator cartridges to capture mercury vapor in breathing air. Adsorption onto the activated carbon can be improved through the modification of the carbon surface by impregnation with certain reagents that enhance the bonding of mercury either physically or chemically. The first objective of this study was to characterize the chemisorption behavior of a commercial adsorbent (3M-6009) by measuring the mercury breakthrough using a bench-top apparatus. The second objective was to develop a kinetic model describing the breakthrough behavior. Dynamic breakthrough concentrations were measured using a fixed bed to study the effects of the following adsorption parameters at room temperature: air flow-rate, adsorbent amount, inlet mercury concentration, and bed diameter. A model was developed in which, the rate of irreversible chemisorption was proportional to the concentration of mercury in the airflow, and the concentration of active sites of the surface of the carbon. A model incorporating two different types of the active sites was applied in an effort to differentiate the high initial adsorption rate mediated by readily accessible open sites from the lower adsorption rate mediated by the availability of hindered sites within micro-pores. The model developed herein was superior to a traditional isotherm model for describing the chemisorption behavior of impregnated activated carbon.     

铁水脱硫渣-生物质活性炭的烟气脱硫性能研究

以农业废弃物核桃壳为原料,以及炼钢副产品铁水脱硫渣作为添加剂,采用共混法制备铁水脱硫渣-生物质活性炭。采用固定床反应器对铁水脱硫渣-生物质活性炭进行脱硫实验,考察入口SO2含量、床层温度、水蒸气含量、空速和氧气含量等工艺参数对其脱硫性能的影响。结果表明,随着入口SO2含量和空速的增加,铁水脱硫渣-生物质活性炭的穿透硫容和脱硫穿透时间均减小,床层温度是显著因素,水蒸气和氧气有利于铁水脱硫渣-生物质活性炭的化学吸附,铁水脱硫渣-生物质活性炭的脱硫最优工艺参数：即入口SO2含量、空速、床层温度、水蒸气含量和氧气含量分别为0.25%、750 h-1、85℃、9%和12%,其穿透硫容为274.1 mg/g和脱硫穿透时间为31 h。     

The Wheeler-Jonas equation: a versatile tool for the prediction of carbon bed breakthrough times

This paper gives an overview of the recent developments in the use of the Wheeler-Jonas equation. Extensive experimental work has been done by measuring breakthrough times of different types of activated carbon beds, under different experimental conditions, for a large variety of gases and vapours. This includes the use of activated carbon fibre beds, the presence of moisture on the carbon and in the air stream, non-constant flow patterns and adsorption of chemisorbed species. In all cases the applicability of the Wheeler-Jonas has been demonstrated, i.e. one can use this equation to extrapolate single laboratory breakthrough results by simply varying the independent variables of the equation (amount of adsorbent, flow rate, inlet and breakthrough concentrations). In most cases it is even possible to perform ab initio breakthrough calculations for a well-defined carbon bed. To achieve this new supporting equations had to be derived to allow the estimation of the dependent variables, W_e (the equilibrium adsorption capacity) and k_v (the overall mass transfer coefficient), under different circumstances. In conclusion, the scope of the Wheeler-Jonas (or Reaction Kinetic) equation extends largely beyond its commonly accepted boundaries. This is primarily due to its apparent simplicity: the combination of a single capacity term and an overall kinetic effect strongly enhances its applicability to different adsorption circumstances. In this way it is far more potent than many of the more modern equations that require the exact knowledge of several, not readily available, input parameters.     

Three-dimensional numerical simulation of a circulating fluidized bed reactor for multi-pollutant control

Circulating fluidized bed adsorber (CFBA) technology is regarded as a potentially effective method for simultaneously controlling emissions of sulfur dioxide, fine particulate matter, and trace heavy metals, such as mercury vapor. In order to analyze CFBA systems in detail, a gas mixture/solids mixture model based on the three-dimensional Navier-Stokes equations is developed for particle flow, agglomeration, physical and chemical adsorption in a circulating fluidized bed. The solids mixture consists of two solids, one with components of CaO and CaSO₄, and the other being an activated carbon. The gas mixture is composed of fine particulate matter (PM), sulfur dioxide, mercury vapor, oxygen and inert gas. Source terms representing fine particulate matter agglomeration onto sorbent particles, sulfur dioxide removal through chemical adsorption onto calcined lime, and mercury vapor removal through physical adsorption onto activated carbon are formulated and included into the model. The governing equations are solved using high-resolution upwind-differencing methods, combined with a time-derivative preconditioning method for efficient time-integration. Numerical simulations of bench-scale operation of a prototype CFBA reactor for multi-pollutant control are described.     

Residual adsorption capacity of carbon beds

The retention time of a small (0.3 cm³) ethane pulse, to which various dry weights (1–3 g) of activated carbon were exposed, was studied as a nondestructive method of determining the residual adsorption capacity of the bed. Carbon beds, partially saturated with CCl₄ or water, adsorbed the ethane from and then desorbed the ethane into the nitrogen carrier gas stream. At a fixed flowrate and fractional carbon saturation the retention time in the bed varied linearly with carbon weight. A critical bed weight existed, below which the retention time of ethane in the bed was zero. The logarithm of a dimensionless time parameter, normalized with respect to the effective bed weight (total weight minus critical weight), was a linear function of the percentage carbon saturation (or the percentage residual adsorption capacity) of the bed. This approach constitutes a nondestructive, in situ method for determining the residual adsorption capacity of an activated carbon bed that is independent of bed weight.     

吸附法回收油气的研究

分别以活性炭和活性炭纤维为吸附剂吸附回收油气,比较了两者油气吸附性能的差异,研究结果表明:在相同的吸附条件下,活性炭纤维对油气的穿透吸附量为114.0mg/g,明显大于活性炭对油气的穿透吸附量(71.8 mg/g),而且活性炭纤维床层的最高温升仅为4.7℃,低于活性炭床层温升(12.0℃);活性炭纤维对油气的吸附速率快、穿透时间短,但是能处理的油气的浓度小;活性炭重复利用18次后失活,活性炭纤维利用20次后失活.     

颗粒直径对吸附分离影响的数值模拟

基于Fluent的多孔介质模型,建立了变压吸附制氧发生器的立式填充床模型。采用用户自定义函数功能,以反映吸附传质、传热,并将多孔介质单相模型整合为更精确的气固两相耦合模型。在此基础上,模拟了吸附颗粒直径对气相压力、速度、床层压降以及氧气分离浓度、回收率等参数的影响情况。结果表明：床层压降随颗粒直径的增大而减小;床层对入口急流的抗穿透性能随颗粒直径的增大而减小;相同条件下,采用较小颗粒直径能够提高氧气分离浓度、回收率,原因在于小颗粒直径降低了床层内气体的流速,增加了吸附时间,促进了吸附的进行。     

Simulation of mercury emission control by activated carbon under confined-bed operations

Mercury emissions from coal-fired power plants have been a great environmental and regulatory concern due to the toxic nature of mercury and the significant amount of emissions from these plants. An effective method for controlling mercury emission is to employ activated carbon to adsorb mercury from the combustion flue gas. In this study, an activated carbon mercury sorption model was applied to simulate a confined-bed mercury emission control process. Model simulations were performed to generate dynamic mercury concentration profiles and the corresponding profiles of mercury uptake by activated carbon at various bed locations under various process conditions. The simulation parameters included flue gas flow rate, inlet mercury concentration, and adsorption bed temperature. The study has demonstrated the applicability of the model for simulating the process and provided insights into the mercury control process especially the effects of flue gas flow rate, inlet mercury concentration, and activated carbon bed temperature on the process. Such information is critically needed in the design and operation of a mercury emission control process involving activated carbon adsorption.     

Studies on the Effects of Certain Non‐dimensional Groups on Dynamic Simultaneous Adsorption Behaviour of Carbon Dioxide and Moisture in Molecular Sieve, 5A

A non‐isothermal model based on linear driving force approximation for a system like CO₂ – moisture – N₂ – molecular sieve, 5A predicted the experimental results satisfactorily for simultaneous adsorption of CO₂ and moisture in a fixed bed. Moisture being the strongly adsorbed component forces carbon dioxide (weakly adsorbed component) to be rolled up. The thermophysical and transport properties of moisture mainly governs the dynamics of the process, control or manipulation of which could give better separation by adsorption of one component from the other lying together in a stream. The major parameters are inlet adsorbate concentration, particle Reynolds number, bed diameter to bed length ratio, Schmidt number, Equilibrium Distribution coefficient, Sherwood number, and Kutateladze number.     

Tracer experiments in fixed beds: effects of flow maldistribution on the estimation of transport kinetic parameters

A systematic study of liquid phase axial dispersion was conducted in glass columns (inner diameters, 1 cm and 1.6 cm), packed randomly with granular sand, by varying the fluid flow rate, particle size and bed height. Pulse and step response techniques, with KCl as an inert tracer, were used. The resultant data, covering the Reynolds number range from 1 to 50, are presented as plots of the Peclet number based on particle diameter against Reynolds number.Inert tracer experiments were also carried out in a column (inner diameter, 1.6 cm) packed with activated carbon granules, using different particle sizes, fluid flow rates and bed heights, in order to estimate the effective intraparticle diffusivity. We show that flow maldistribution produces pulse response curves with sharp, narrow peaks which, when compared with theoretical curves, result in small intraparticle diffusivities.We illustrate how the outer-phase transfer function can be obtained from the overall transfer function of the activated carbon bed and we compare it with the transfer function obtained directly using impermeable particles similar to the activated carbon granules.     

活性炭吸附法脱除双酚A反应液中残留催化剂

采用活性炭吸附法脱除双酚A反应液中的残留催化剂,用丙酮对活性炭进行再生。考察了活性炭的粒径、吸附温度、空速等对双酚A反应液中残留催化剂脱除效果的影响。结果表明,最佳操作条件为:10～20目活性炭,床层体积5 cm3,吸附温度65℃,空速1.0 h-1。在此条件下,对酸度为0.014 mmol/L的双酚A反应液进行了连续脱除残留催化剂处理,双酚A反应液的酸度能符合要求(≤0.001 mmol/L)。该方法具有不引入碱性杂质、不影响产品质量、操作简单的优点。     

Surfactant‐Enhanced Carbon Regeneration in a Vapor‐Phase Application

Abstract

Coal‐based granular activated carbon (GAC) is saturated with trichloroethylene (TCE) by passing air through a fix bed adsorber. In surfactant‐enhanced carbon regeneration, an aqueous solution of anionic surfactant, sodium dodecyl sulfate (SDS), is passed through the bed to induce desorption of TCE. More than 95% of the sorbed TCE was removed in the desorption operation with a 0.1 M SDS solution at a superficial flow rate of 1 cm/min. The desorption rate of TCE from pores of GAC is limited by pore diffusion and not significantly affected by either the concentration of SDS in the regenerant (when well above the critical micelle concentration) or its flow rate. From the breakthrough curve of a subsequent adsorption cycle without a flushing step following the desorption, only 7% of the virgin carbon effective adsorption capacity is observed for the regenerated carbon. With a water flushing step following the regeneration step, the effective adsorption capacity is significantly improved to about 15% of that of virgin carbon. Increased temperature of the flushing water also enhances the effective adsorption capacity of the regenerated GAC. Separate batch adsorption‐desorption isotherms of SDS on GAC support the enhanced desorption of SDS at elevated temperatures. The drastic reduction in the effective adsorption capacity of regenerated GAC results from the residual SDS remaining in the pores of GAC as confirmed by thermal gravimetric analysis. Both the regeneration and water flush steps are rate limited under conditionsused here.