Vapor Removal Research Articles

Study on Reactivity of HgO over Activated Carbon with HCl and SO2 in the Presence of Moisture by Temperature-Programmed Decomposition Desorption Mass Spectrometry

Reactivities of mercury compounds over mercury sorbents with HCl and SO2 are very important to the design of a solid sorbent for mercury vapor removal from coal-derived flue gases. However, presently available data on the reactivity of mercury oxide over mercury sorbent is insufficient. This study investigated the reactivity of mercury oxide with HCl and SO2 using a temperature-programmed decomposition and desorption technique and a mass spectrometer (TPDD-mass) method. Mercury desorption from HgO over activated carbon (HgO/AC) was observed at the same temperature range as from HgO/SiO2, but the mercury desorption peak from the HgO/AC was observed at a higher temperature than from the HgO/SiO2, indicating that some of the HgO was stabilized by the AC surface. When the HgO/AC was pretreated with HCl–H2O, the formation of HgCl2 was suggested by the mass spectra of m/z = 272 and 270. The mercury desorption temperatures in the TPDD spectra were lower than those of nonpretreated samples. On the basis of the sh...

Increasing Boiling Heat Transfer using Low Conductivity Materials

We report the counterintuitive mechanism of increasing boiling heat transfer by incorporating low-conductivity materials at the interface between the surface and fluid. By embedding an array of non-conductive lines into a high-conductivity substrate, in-plane variations in the local surface temperature are created. During boiling the surface temperature varies spatially across the substrate, alternating between high and low values, and promotes the organization of distinct liquid and vapor flows. By systematically tuning the peak-to-peak wavelength of this spatial temperature variation, a resonance-like effect is seen at a value equal to the capillary length of the fluid. Replacing ~18% of the surface with a non-conductive epoxy results in a greater than 5x increase in heat transfer rate at a given superheat temperature. This drastic and counterintuitive increase is shown to be due to optimized bubble dynamics, where ordered pathways allow for efficient removal of vapor and the return of replenishing liquid. The use of engineered thermal gradients represents a potentially disruptive approach to create high-efficiency and high-heat-flux boiling surfaces which are naturally insensitive to fouling and degradation as compared to other approaches.

Flow boiling and critical heat flux in horizontal channel with one-sided and double-sided heating

This study explores flow boiling of FC-72 along a 5-mm high by 2.5-mm wide rectangular channel that is fitted with top and bottom heating walls. By activating one wall at a time, the opposing influences of gravity are examined for inlet velocities from 0.11 to 2.02m/s. Results for top wall and bottom wall heating are then compared to those for double-sided heating. For top wall heating, high speed video imaging proves gravity effects are dominant at low velocities, accumulating vapor along the heated wall and resulting in low critical heat flux (CHF) values. For bottom wall heating, buoyancy aids in vapor removal and liquid replenishment of the heated wall, resulting in higher CHF values. Higher velocities result in fairly similar interfacial behavior for top wall and bottom wall heating, and double-sided heating exhibiting greater symmetry between interfacial behaviors along the opposite walls. Overall, CHF values for all three configurations converge to one another above 1.5m/s. This convergence is clearly the result of high inertia negating the influence of gravity. It is shown that interfacial instability theory provides an effective means for assessing the influence of velocity on CHF for top wall versus bottom wall heating. For top wall heating, a stable interface at low velocities causes vapor accumulation against the top wall resulting in very low CHF. Instability theory shows that top wall heating becomes unstable above 1.03m/s, allowing liquid contact with the wall and improved wall cooling. For bottom wall heating, the interface is always unstable and favorable for liquid contact. Instability theory also shows that inertia dwarfs gravity around 1.5m/s, where critical wavelengths for top wall and bottom wall heating converge. Convergence of the CHF values for top wall and bottom wall heating also occurred at a similar value.

Experimental investigation on compressed air drying performance using pressurized liquid desiccant

ABSTRACTAs a new compressed air-drying method, the compressed air dehumidification using a pressurized liquid desiccant was proposed in our previous study. The pressurized dehumidifier is a complex and core component of the drying system. The mass transfer performance between the compressed air and LiCl aqueous solution is experimentally studied in a counter-flow pressurized dehumidifier filled with structured packing. The humidity ratio of outlet compressed air, vapor removal of processed compressed air, moisture removal rate, and dehumidification efficiency were selected as the performance indices. The results show that the minimum humidity ratio of processed compressed air could reach 0.23 g/kg under 0.71 MPa. Compressed air-drying performance could be remarkably enhanced through increasing the air pressure and liquid desiccant inlet concentration while the influence of liquid desiccant temperature is negative. Furthermore, in order to ensure high compressed air-drying performance, reduce the power consumption of the air compressor and liquid desiccant pump, and the possibility of carryover, the optimum ratio of liquid to compressed air flow rate is recommended to be around 1.5 under pressure around 0.50 MPa. Meanwhile, the energy consumption for per-gram moisture removal of a liquid-desiccant-based compressed air-drying system can reach 1.42 kJ/g lower than cooling dehumidification under 0.3 MPa, which is 16.0% lower than a compressed air-cooling dehumidification system.

Air dehumidification by hollow fibre membrane with chilled water for spacecraft applications

A novel hydrophobic membrane-based dehumidification technology with chilled water is proposed to substitute the traditional dew point method for humidity control in spacecraft, which fulfils the tough tasks of air/water separation and water reuse under low gravity at the same time. A prototype hydrophobic membrane module was designed and fabricated by packing 853 hollow fibres in the shell-and-tube configuration, which could prevent the leakage of the tube-side chilled water to the air side. Theoretical models concerning conjugated heat and mass transfer have been established for the explanation and prediction of the moisture migration across the membranes. Experiments were conducted to validate the theoretical models and the feasibility of water vapour removal under various operating conditions. Although undesirable dewing occurred on the outer membrane surface due to the slow mass transfer relative to heat transfer across the membranes, it was verified by the water increase in graduated cylinder that some water vapour actually transferred through the membrane pores under partial pressure difference. A maximum net dehumidification rate (excluding dewing) of 45 g/h has been achieved by the experiment.

Influence of packing columns starting modes on effectiveness of processes of water rectification and detritiation of gases by the method of phase isotopic exchange

The results of the comparative study of the effect of the method for structured packing pretreatment (CY-type Sulzer packing and rolled ribbon-screw packing) on the effectiveness of mass exchange in the course of hydrogen isotope exchange in water rectification and its phase isotope exchange (PIE) are given. The latter process is used for the removal of tritiated water vapors from gases and its difference from rectification involves that the irrigation density of packing by water is 50–150 times less under other comparable process conditions. This difference leads to the fact that, for the packings prepared from stainless steel, the coefficient of mass transfer ratio for two boundary cases, namely, its preliminary flooding by water or launch of column with dry packing, is nearly 50 for PIE and 2 for rectification. The use of CY-type Sulzer packing for PIE process prepared from oxidized copper yields that this ratio for PIE becomes identical with rectification. Based on the obtained results, the recommendations for the optimization of PIE column startup are given.

Technical Note: A fully automated purge and trap GC-MS system for quantification of volatile organic compound (VOC) fluxes between the ocean and atmosphere

Abstract. The oceans are a key source of a number of atmospherically important volatile gases. The accurate and robust determination of trace gases in seawater is a significant analytical challenge, requiring reproducible and ideally automated sample handling, a high efficiency of seawater–air transfer, removal of water vapour from the sample stream, and high sensitivity and selectivity of the analysis. Here we describe a system that was developed for the fully automated analysis of dissolved very short-lived halogenated species (VSLS) sampled from an under-way seawater supply. The system can also be used for semi-automated batch sampling from Niskin bottles filled during CTD (conductivity, temperature, depth) profiles. The essential components comprise a bespoke, automated purge and trap (AutoP & T) unit coupled to a commercial thermal desorption and gas chromatograph mass spectrometer (TD-GC-MS). The AutoP & T system has completed five research cruises, from the tropics to the poles, and collected over 2500 oceanic samples to date. It is able to quantify >25 species over a boiling point range of 34–180 °C with Henry's law coefficients of 0.018 and greater (CH22l, kHcc dimensionless gas/aqueous) and has been used to measure organic sulfurs, hydrocarbons, halocarbons and terpenes. In the eastern tropical Pacific, the high sensitivity and sampling frequency provided new information regarding the distribution of VSLS, including novel measurements of a photolytically driven diurnal cycle of CH22l within the surface ocean water.

Scavenging of radioactive soluble gases from inhomogeneous atmosphere by evaporating rain droplets

We analyze effects of inhomogeneous concentration and temperature distributions in the atmosphere, rain droplet evaporation and radioactive decay of soluble gases on the rate of trace gas scavenging by rain. We employ a one-dimensional model of precipitation scavenging of radioactive soluble gaseous pollutants that is valid for small gradients and non-uniform initial altitudinal distributions of temperature and concentration in the atmosphere. We assume that conditions of equilibrium evaporation of rain droplets are fulfilled. It is demonstrated that transient altitudinal distribution of concentration under the influence of rain is determined by the linear wave equation that describes propagation of a scavenging wave front. The obtained equation is solved by the method of characteristics. Scavenging coefficients are calculated for wet removal of gaseous iodine-131 and tritiated water vapor (HTO) for the exponential initial distribution of trace gases concentration in the atmosphere and linear temperature distribution. Theoretical predictions of the dependence of the magnitude of the scavenging coefficient on rain intensity for tritiated water vapor are in good agreement with the available atmospheric measurements.

Experimental and modeling analysis of membrane-based air dehumidification

In this work, a membrane cross flow filtration is studied specifically for the purpose of air dehumidification. A flat sheet composite membrane comprising ceramic and polymeric layers with varied water vapor permeability and selectivity has been developed. Effects of the feed air velocity and humidity, the membrane permeability and selectivity, and the permeate pressure on dehumidification performance (i.e. water vapor removal) and resulting COP (Coefficient of Performance) under a cross-flow flat-sheet setting is systematically studied. Results have shown that the membrane dehumidification performance does not depend on the feed air humidity while its COP does not dependent on the membrane’s permeability and the feed air velocity. There exists a tradeoff between the membrane’s ability to dehumidify and its achievable COP when both selectivity and permeate pressure are varied.

Styrene vapor biodegradation in single- and two-liquid phase biotrickling filters using Ralstonia eutropha

This study examined the use of a bacterial culture of Ralstonia eutropha in biotrickling filters (BTFs) for styrene vapor removal in the absence and presence of silicone oil (5%v/v). Removal was carried out at 40°C using styrene inlet concentrations of 0.8–3.3gm−3 and empty bed residence times (EBRTs) of 1 and 2min. For single-phase BTF, a removal efficiency (RE) of 95% was achieved at inlet concentrations of <2.5gm−3 and at an EBRT of 1min. The addition of oil to the recirculating solution enhanced styrene elimination under all operating conditions and increased maximum elimination capacity (ECmax) from 70 to 110gm−3h−1. Results of elemental analysis of microorganisms isolated from the bed of the BTFs and biodegradation equations showed that the ratios of CO2 generation to styrene consumption were 2.60 for single-phase and 4.85 for two-phase BTFs. A comparison of results at 35°C and 40°C showed that the presence of oil decreased the effect of operating temperature on RE.

A Study on Toxic Acidic Vapor Removal Behaviors of Continuously Nanostructured Copper/Nickel‐Coated Nanoporous Carbons

Nanostructured copper (Cu)/nickel‐ (Ni‐) coated nanoporous carbon sheets (NCS) were prepared to improve the toxic acidic vapor (hydrogen chloride, HCl) removal efficiency of NCS using a continuous bimetal electroplating method at various metal content ratios. The surface morphology and nanostructure of Cu/Ni‐NCS were observed by scanning electron microscopy and X‐ray diffraction, respectively. N2/77 K adsorption isotherms were investigated using the Brunauer‐Emmett‐Teller equation. HCl vapor removal efficiency was confirmed using two types of detection techniques: a gas detecting tube for low concentrations and gas chromatography for high concentrations. HCl removal efficiency was improved mainly in the copresence of nanostructured Cu/Ni clusters compared to the efficiencies of the as‐received and single‐metal‐plated NCS. In particular, the removal efficiency of Cu/Ni‐3 was increased by 270% compared to that of as‐received sample, but Cu/Ni‐5 showed lower efficiency than Cu/Ni‐3, indicating that suitable metal composition on NCS can accelerate HCl removal behaviors of the NCS.

Investigations into a thiol-impregnated CaCO3-based adsorbent for mercury removal: a full factorial design approach

We demonstrated removal of Hg0 vapor by adsorbing it on thiol-impregnated calcium carbonate and assessed the significance of temperature and thiol mass in Hg0 removal.

Performance evaluation of a scoria-compost biofilter treating xylene vapors.

The removal of xylene vapors was studied in a biofilter packed with a new hybrid (scoria/compost) packing material at various inlet loads (IL) and empty bed residence times (EBRT) of 90, 60, and 40s. The best performance was observed for EBRT of 90s, where a removal efficiency of 98% was obtained under steady state condition for inlet xylene concentration of 1.34 g m−3, while a maximum elimination capacity of 97.5 g m−3 h−1 was observed for IL of 199.5 g m−3 h−1. Carbon dioxide production rates and the microbial counts for xylene-degraders followed xylene elimination capacities. Overall look to the results of this study indicates that the scoria/compost mixture could be considered as a potential biofilter carrier, with low pressure drop (here <4 mm H2O), to treat air streams containing VOCs.

Bone char surface modification by nano-gold coating for elemental mercury vapor removal

The present work was done to develop a novel nanocomposite using bone char coated with nano-gold for capture of elemental mercury (Hg0) from air. The morphologies, structures, and chemical constitute of the prepared nanocomposite were evaluated by UV–VIS–NIR, dynamic light-scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infra-red (FTIR) spectroscopy, and energy dispersive X-ray spectroscopy (EDS). The capture performance of nanocomposite was evaluated in a needle trap for mercury vapor. An on-line setup based on cold vapor atomic absorption spectrometry (CVAAS) was designed for Hg0 determination. Dynamic capacity of nanocomposite for Hg0 was shown high efficient operating capacity of 586.7μg/g. As temperature increases, the dynamic adsorption capacity of the nanocomposite was decreased, which are characteristics of physicosorption processes. It was found that the surface modification of bone char with nano-gold has various advantages such as high operating dynamic adsorption capacity and low cost preparation. It was also demonstrated that the developed nanocomposite is suitable for on-line monitoring of Hg0. It could be applied for the laboratory and field studies.

Modeling, Simulation, and Economic Assessment of Membrane-Based Gas Dehydration System and Comparison with Other Natural Gas Dehydration Processes

An economic assessment of natural gas dehydration using polymeric membranes was made through modeling and simulation and the results were compared with those conducted through absorption and adsorption. A diagram of the economic boundaries between different natural gas dehydration processes was also introduced. The effects of the membrane properties, membrane module cost, feed pressure, and natural gas wellhead price on the cost of water vapor removal were examined. It has been concluded that at low feed pressures and at feed flow rates more than 0.85 MMSCMD the membrane-based gas dehydration system is not competitive with the absorption process. An increase in the feed pressure increases the cost of the absorption and adsorption processes, while decreases that of the membrane system. At feed flow rates higher than 3.4 MMSCMD and inlet pressures less than about 4100 kPa, the total separation cost of the adsorption unit was lower than that of the membrane system.

Micro- and mesoporous poly(Schiff-base)s constructed from different building blocks and their adsorption behaviors towards organic vapors and CO2gas

Four porous poly(Schiff-base)s, PSN-DA, PSN-TAPB, PSN-TAPA and PSN-TAPM, are synthesized via one-pot condensation from 1,3,5,7-tetrakis(4-formylphenyl)adamantane with rod-like m-phenyldiamine, triangular 1,3,5-tris(4-aminophenyl)benzene and tris(4-aminophenyl)amine as well as tetrahedral tetrakis(4-aminophenyl)methane, respectively. It is found that the variation of the geometrical shape of the building blocks significantly alters the surface areas, pore sizes and distributions of the resultant porous polymers and thereby remarkably influences their adsorption behaviors towards organic vapors and CO2 gas. PSN-DA, PSN-TAPB and PSN-TAPA are microporous materials with pore sizes of 0.72, 0.95 and 1.04 nm, whereas PSN-TAPM is a micro- and mesoporous material with the major pores centered at 0.86 and 2.62 nm, respectively. Their BET surface areas are in the range from 419 to 1045 m2 g−1. At P/Po = 0.9 and 298 K, PSN-DA possesses high uptakes for both aromatic vapor (benzene, 86.1 wt%) and aliphatic vapor (cyclohexane, 77.9 wt%). In addition, the adsorption and desorption isotherms of CO2 gas in the four porous polymers are reversible – a characteristic which is convenient for the regeneration of CO2 adsorbents. Their adsorption capacities of CO2 are up to 15.0 wt% (273 K/1 bar) with the ideal selectivities of CO2/N2 and CO2/CH4 up to 71 and 14, respectively. showing potential applications in the removal of toxic organic vapors and capture of CO2 from air.

A parametric analysis of periodic and coupled heat and mass diffusion in desiccant wheels

Solid sorbents are frequently adopted for gas component separation in the chemical industry. Over the last decades, solid sorbents have also been applied for the benefit of indoor air quality and humidity control in modern building design. Adsorptive rotors have been designed for the removal of water vapor, CO and VOCs from indoor environments. Although the adsorption of water vapor by a specific adsorbent (particularly silica-gel) has been extensively studied, a non-dimensional parametric analysis of humidity adsorption on a nonspecific hygroscopic material appears to be an original contribution to the literature. Accordingly, a mathematical model using non-dimensional parameters is built from energy and mass balances applied to elementary control volumes. The periodic nature of the cyclic adsorption/desorption processes requires an iterative solution, which is carried out by comparing temperature and mass distributions at the onset to the distributions by the end of the cycle.

Creating internal conductivity in dry biological SEM samples by a simple vapour treatment.

Internal sample conductivity in scanning electron microscopy can be a valuable alternative to metal coating. Proton conductivity may be used for this purpose. Many solid materials with active hydrogen atoms, such as hydrogen- and ammonium-salts, organic acids, and even ice, are protonic conductors or semiconductors. Here we present a method to generate proton conductivity in dry biological materials. A simple treatment with hydrogen chloride gas or hydrochloric acid vapour for a few minutes provides sufficient conductivity for many samples. After a removal of excess hydrogen chloride vapour with a vacuum desiccator, the objects may be examined in the SEM without metal coating. The use of internally conductive samples extends the range of easy-to-perform SEM preparation techniques. It is advantageous for material contrast imaging of uncoated samples, and it can be used in combination with metal coating to enhance conductivity on difficult samples with complex overlapping surfaces, where simple metal coating does not reliably eliminate charging problems.

Oxidation of trichloroethylene, toluene, and ethanol vapors by a partially saturated permeable reactive barrier

The mitigation of volatile organic compound (VOC) vapors in the unsaturated zone largely relies on the active removal of vapor by ventilation. In this study we considered an alternative method involving the use of solid potassium permanganate to create a horizontal permeable reactive barrier for oxidizing VOC vapors. Column experiments were carried out to investigate the oxidation of trichloroethylene (TCE), toluene, and ethanol vapors using a partially saturated mixture of potassium permanganate and sand grains. Results showed a significant removal of VOC vapors due to the oxidation. We found that water saturation has a major effect on the removal capacity of the permeable reactive layer. We observed a high removal efficiency and reactivity of potassium permanganate for all target compounds at the highest water saturation (Sw=0.6). A change in pH within the reactive layer reduced oxidation rate of VOCs. The use of carbonate minerals increased the reactivity of potassium permanganate during the oxidation of TCE vapor by buffering the pH. Reactive transport of VOC vapors diffusing through the permeable reactive layer was modeled, including the pH effect on the oxidation rates. The model accurately described the observed breakthrough curve of TCE and toluene vapors in the headspace of the column. However, miscibility of ethanol in water in combination with produced water during oxidation made the modeling results less accurate for ethanol. A linear relationship was found between total oxidized mass of VOC vapors per unit volume of permeable reactive layer and initial water saturation. This behavior indicates that pH changes control the overall reactivity and longevity of the permeable reactive layer during oxidation of VOCs. The results suggest that field application of a horizontal permeable reactive barrier can be a viable technology against upward migration of VOC vapors through the unsaturated zone.

Erratum to: Evaporation Removal of Boron from Metallurgical-Grade Silicon Using CaO-CaCl2-SiO2 Slag

YE WANG, Second-Year Ph.D. Student, and KAZUKI MORITA, Professor, are with the Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan. Contact e-mail: wangye@iis.u-tokyo.ac.jp, wangye2003@163. com XIAODONG MA, Postdoctoral Research Associate, is with the School of Chemical Engineering, The University of Queensland, Brisbane, St Lucia, QLD 4072 Australia. The online version of the original article can be found under doi: 10.1007/s11663-014-0031-1. Article published online June 10, 2014.