Inlet Gas Concentration Research Articles

Effects of gas flow‐rate and inlet concentration on nitric oxide removal in an autotrophic biofilter

AbstractThe effects of inlet gas concentration and gas flow‐rate on the NO elimination process were studied in a laboratory‐scale biofilter and the removal process is discussed. Various pollutant inlet concentrations and gas flow‐rates were tested in the biofilter. The results showed that the removal efficiency increased with increase in the empty bed residence time (EBRT) and finally reached a steady state. The mass transfer process became the limiting step of NO removal when the EBRT was less than 2 min. A removal efficiency of ∼73% was obtained in the biofilter at an inlet concentration of 107.1 mg m−3. The removal efficiency decreased with increase in inlet concentration, whereas the removal capacity increased. The removal process consisted of chemical oxidation and bio‐nitrification in the biofilter. The bioprocess mainly contributed to the removal. Copyright © 2006 Society of Chemical Industry

PDMS-바이오 멤브렌인을 이용한 용해성과 비용해성 휘발성유기화학물질의 가스 제거에 관한 연구

An experimental study on the removal of VOCs gas using a biomembrane reactor were carried out at various inlet gas concentration, specific loading rate, retention time and gas flow rate of volume. The variations of efficiency and various parameters, which are relevant to gas removal, with mixing of soluble gas and without have been discussed. More than 95% of the toluene and methanol present in the feed was successfully removed in each study. The elimination of methanol with mixture of soluble compound of about 300 mg/h corresponds to a portion of 21% if there is a feed stream of 1400 mg/h. On the contrary the maximum efficiency of about 72% of toluene was reached. This is to be rated as a treatment of sorption that the limiting factor of the dismantling speed could be represented by this difficult degradable component. Nevertheless the elimination capacities for this reactor for toluene were on a very high level. For substances which show a very high solubility in silicon rubber an advantage of a bio membrane is clearly shown. Therefore a similarly good result is expected for n-hexane, because of its relatively good permeability which was distinguished during permeation experiments.

Simulation of Catalytic Combustion of Methane in a Monolith Honeycomb Reactor

Abstract Catalytic combustion of CH 4/air in monolith reactor is simulated using a commercial computational fluid dynamic code. The user subroutines to describe the heterogeneous reaction at the channel wall in a single channel and at the channel walls in the whole reactor are incorporated into the program. The correctness of the method is verified by comparing the simulation results with the experimental data for the whole reactor. Furthermore, it is observed that the model based on the whole reactor is more reasonable than that based on a single channel. Therefore, using the former, the effects of operating conditions such as inlet gas velocity, temperature, concentration and catalyst loading on methane conversion are investigated.

Can a membrane oxygenator be a model for lung NO and CO transfer?

To model lung nitric oxide (NO) and carbon monoxide (CO) uptake, a membrane oxygenator circuit was primed with horse blood flowing at 2.5 l/min. Its gas channel was ventilated with 5 parts/million NO, 0.02% CO, and 22% O2 at 5 l/min. NO diffusing capacity (Dno) and CO diffusing capacity (Dco) were calculated from inlet and outlet gas concentrations and flow rates: Dno = 13.45 ml.min(-1).Torr(-1) (SD 5.84) and Dco = 1.22 ml.min(-1).Torr(-1) (SD 0.3). Dno and Dco increased (P = 0.002) with blood volume/surface area. 1/Dno (P < 0.001) and 1/Dco (P < 0.001) increased with 1/Hb. Dno (P = 0.01) and Dco (P = 0.004) fell with increasing gas flow. Dno but not Dco increased with hemolysis (P = 0.001), indicating Dno dependence on red cell diffusive resistance. The posthemolysis value for membrane diffusing capacity = 41 ml.min(-1).Torr(-1) is the true membrane diffusing capacity of the system. No change in Dno or Dco occurred with changing blood flow rate. 1/Dco increased (P = 0.009) with increasing Po2. Dno and Dco appear to be diffusion limited, and Dco reaction limited. In this apparatus, the red cell and plasma offer a significant barrier to NO but not CO diffusion. Applying the Roughton-Forster model yields similar specific transfer conductance of blood per milliliter for NO and CO to previous estimates. This approach allows alteration of membrane area/blood volume, blood flow, gas flow, oxygen tension, red cell integrity, and hematocrit (over a larger range than encountered clinically), while keeping other variables constant. Although structurally very different, it offers a functional model of lung NO and CO transfer.

05/02872 Microwave technology for energy-efficient processing of waste

Two kinds of macroalgae biochars were prepared through pyrolysis of typical macroalgae (enteromorpha and sargassum), and were used to adsorb gaseous hydrogen sulfide (H2S) from biogas for the first time. Effects of several key technological parameters on H2S adsorption over two typical macroalgae (enteromorpha and sargassum) biochars were evaluated. The physical and chemical properties of two kinds of macroalgae biochars were analyzed using several characterization tools. The adsorption kinetics of H2S on two kinds of macroalgae biochars were also studied. The results show that the optimal calcination temperatures for two kinds of macroalgae biochars are 800 °C. The adsorption of H2S is reduced via raising temperature, gas flow rate or inlet concentration of H2S. An increase in moisture concentration enhances at first, and then reduces H2S adsorption. Some key oxidative and alkaline functional groups that were beneficial to H2S removal were found. The kinetic model with pseudo-first-order can describe the adsorbing process of H2S on two kinds of macroalgae biochars well. Thermodynamic analysis exhibits that the physical adsorption plays a dominant role in the H2S adsorption process.

RESPIRATION RATE MEASUREMENT OF FRESH PRODUCE USING AN AUTOMATED FLOW-THROUGH SYSTEM

This study was conducted to develop an automated measuring system for the respiration rates of fresh produce held under various gas compositions. This system was based on the flow-through measurement method. The system has two main parts; gas mixture generation, and gas analysis. The gas mixture generator consisted of precision pressure regulators and metering valves. The flow rate of O 2 , CO 2 and N 2 (balance gas), which were supplied from cylinders, was controlled by the precision pressure regulator and metering valve to obtain the desired gas mixture. The gas analysis part consisted of a multi-position valve, sample loop and gas chromatograph. The gas flow line was connected to the multi-position valve, which separated inlet and outlet from the gas mixture chamber. Therefore, it was possible to analyze gas samples by gas chromatography using the flow-through method. The gas concentration generated by the gas mixing system was within ± 0.2% of the target concentrations. In an empty chamber, the difference of inlet and outlet gas concentration was 0.1%. When gas samples were analyzed three times at each gas flow line (inlet and outlet), the measuring reproducibility was ± 0.03%. The system successfully measured the respiration rates of tomato fruit.

Restaurant emissions removal by a biofilter with immobilized bacteria.

Pseudomonas sp. ZD8 isolated from contaminated soil was immobilized with platane wood chips to produce packing materials for a novel biofilter system utilized to control restaurant emissions. The effects of operational parameters including retention time, temperature, and inlet gas concentration on the removal efficiency and elimination capacity were evaluated. Criteria necessary for a scale-up design of the biofilter was established. High and satisfactory level of rapeseed oil smoke removal efficiency was maintained during operation and the optimal retention time was found to be 18 s corresponding to smoke removal efficiency greater than 97%. The optimal inlet rapeseed oil smoke loading was 120 mg/(m(3) x h) at the upper end of the linear correlation between inlet loading and elimination capacity.

Effect of gas velocity and influent concentration on biofiltration of gasoline off-gas from soil vapor extraction

This study was conducted to evaluate the effects of gas inlet concentration and velocity on the biofiltration of gasoline vapor. Gasoline vapor was treated using a compost biofilter operated in an upflow mode for about 3 months. The inlet concentration of gasoline total petroleum hydrocarbon (TPH) ranged from about 300 to 7000 mg m −3 and gas was injected at velocities of 6 and 15 m h −1 (empty bed residence time (EBRT) = 10 and 4 min, respectively). The maximum elimination capacities of TPH at 6 and 15 m h −1 found in this research were over 24 and 19 g m −3 of filling material h −1, respectively. TPH removal data was fit using a first-order kinetic relationship. In the low concentration range of 300–3000 mg m −3, the first-order kinetic constants varied between about 0.10 and 0.29 min −1 regardless of gas velocities. At TPH concentrations greater than 3000 mg m −3, the first-order kinetic constants were about 0.09 and 0.07 min −1 at gas velocities of 6 m h −1 and 15 m h −1, respectively. To evaluate microbial dynamics, dehydrogenase activity, CO 2 generation and microbial species diversity were analyzed. Dehydrogenase activity could be used as an indicator of microbial activity. TPH removal corresponded well with CO 2 evolution. The average CO 2 recovery efficiency for the entire biofilter ranged between 60% and 70%. When the gas velocity was 6 m h −1, most of the microbial activity and TPH removal occurred in the first quarter of the biofilter. However, when the gas velocity was 15 m h −1, the entire column contributed to removal. Spatial and temporal variations in the biofilter microbial population were also observed. Nearly 60% of the colonies isolated from the compost media prior to biofiltration were Bacillus. After 90 days of biofiltration, the predominant species in the lower portion (0–50 cm) of the filter were Rhodococcus, while Pseudomonas and Acinetobacter dominated the upper portion (75–100 cm).

MATHEMATICAL AND EXPERIMENTAL INVESTIGATION ON NOX RECOVERY IN FLUIDIZED BED ADSORBERS FOR EXHAUST GASES OF NITRIC ACID PLANTS

A mathematical model for sorption of NOx from exhaust gas of nitric acid plants by activated carbon (AC) in a fluidized bed is proposed based on two-phase flow theory of fluidization. To solve the proposed model a computer program has been developed. The output of this program reveals the effects of various parameters such as temperature, inlet gas velocity, particle diameter, and inlet gas concentration on the rate of adsorption. To evaluate the proposed model, a pilot-scale plant was erected and the obtained experimental data were compared with the values predicted by the model. A good agreement is observed between these values. Once the validity of the proposed model is checked, it could be used for obtaining the optimum operating condition for this type of bed.

Experiment and Analysis on the Treatment of Gaseous Benzene Using Pulsed Corona Discharge Plasma

An experiment and analysis on removal of gaseous benzene by pulse corona induced-plasma is presented in this article. Important parameters effecting removal efficiency have been investigated, such as pulse peak voltage, pulse frequency, gas inlet concentration, gas flow rate and reactor temperature. The result shows that the removal efficiency increases with the increase in pulse peak voltage, pulse frequency and reactor temperature, but decreases in the rise of gas inlet concentration and gas flow rate. On the condition of Vp = 36 kV, f = 80 Hz, C = 1440 mg/m3 and Q = 640 ml/min, the largest removal efficiency is 98%. Finally, the reacted products are qualitatively analysed and the reaction processes are deduced in combination with plasma-chemistry theory.

Dimethyl sulfide removal from synthetic waste gas using a flat poly(dimethylsiloxane)-coated composite membrane bioreactor.

The reduction of volatile organic sulfur emissions should be completely as they cause odor nuisance, even when they are emitted in very small amounts. In general, biofilters are applied for odor reduction, but their operational control is limited. A new biotechnique for the treatment of complex emissions is the use of membranes integrated within bioreactors (MBRs). In this study, the reactor performance of MBRs for removal of dimethyl sulfide (DMS) as a model compound is presented. Composite membranes with a poly(dimethylsiloxane) (PDMS)-coating layer were used. The MBRs were inoculated with the sulfur-degrading culture Hyphomicrobium VS or a suspension of Hyphomicrobium VS, ammonium-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) to colonize the PDMS-coating layer. Although inoculation with AOB and NOB might give rise to competition for space on the membrane, their presence in the MBRs appeared to be positive as they co-oxidize DMS. Dimethyl sulfide elimination depended on the inoculum type, DMS inlet concentration, gas residence time, and membrane polymer. For equal loading rates, the elimination capacity (EC) increased at larger gas residence times and inlet concentrations. The maximum EC obtained with the MBRs was 4.8 kg of DMS x m(-3) x d(-1). This value is higher than any reported figure for biofilters and biotrickling filters.

Hydrogen Sulfide Gas Treatment by a Chemical‐Biological Process: Chemical Absorption and Biological Oxidation Steps

In order to remove high concentrations of hydrogen sulfide (H2S) gas from anaerobic wastewater treatments in livestock farming, a novel process was evaluated for H2S gas abatement involving the combination of chemical absorption and biological oxidation processes. In this study, the extensive experiments evaluating the removal efficiency, capacity, and removal characteristics of H2S gas by the chemical absorption reactor were conducted in a continuous operation. In addition, the effects of initial Fe2 + concentrations, pH, and glucose concentrations on Fe2 + oxidation by Thiobacillus ferrooxidans CP9 were also examined. The results showed that the chemical process exhibited high removal efficiencies with H2S concentrations up to 300 ppm, and nearly no acclimation time was required. The limitation of mass‐transfer was verified as the rate‐determining step in the chemical reaction through model validation. The Fe2 + production rate was clearly affected by the inlet gas concentration as well as flow rate and a prediction equation of ferrous production was established. The optimal operating conditions for the biological oxidation process were below pH 2.3 and 35°C in which more than 90% Fe3 + formation ratio was achieved. Interestingly, the optimal glucose concentration in the medium was 0.1%, which favored Fe2 + oxidation and the growth of T. ferrooxidans CP9.

Influence of the Presence of CO2 in the Feed of an Indirect Heating TSA Process for VOC Removal

This work deals with an experimental study of an indirect temperature swing adsorption process for VOC removal from air or for gas purification. A 1 m long and 70 mm diameter column with an internal heat exchanger has been filled with Ambersorb 600 carbonaceous adsorbent. This column is equipped with sensors to measure temperature at several points inside the bed, as well as the inlet and outlet gas concentration, pressure, temperature and mass flow. In a first step, CO2 or ethane/dry nitrogen mixtures were used to simulate a single VOC in air, with different concentrations (350 ppm, 1% and 10%). As a first results very effective gas purification was obtained and an advantage of this process is the high pollutant concentration during the regeneration phase. Experiments were performed with various ethane/CO2 mixtures. The influence of the presence of CO2 on the ethane concentration breakthrough curves and on the ethane concentration during regeneration is reported. The IAS theory was used, as a first approach, to predict the adsorbed pollutants amount. Relatively good prediction is obtained with a maximum error in the order of 10%. An energy balance study is reported as well.

Silicon oxide gas barrier films deposited by reactive sputtering

Transparent silicon oxide thin films were deposited on polyethylene terephthalate substrates by means of reactive sputtering in oxygen and their gas barrier properties were evaluated. The SiO x film sputtered in 10% oxygen/90% argon mixture of inlet gases showed the lowest oxygen transmission rate, and this rate increased with an increase of inlet oxygen concentration. In addition, the oxygen contents of SiO x films increases rapidly within the range of small value of the inlet oxygen gas concentration (0–10%), and gently for oxygen gas concentration larger than 10%. The SiO x films sputtered at high oxygen concentration had more micro-defects than the films prepared at low oxygen concentration. The annealing at 120 °C in vacuum improved the gas barrier properties of the SiO x films sputtered at high oxygen concentration.

Removal of dimethyl sulfide from waste air in a membrane bioreactor

Long-term experiments with a membrane bioreactor to remove dimethyl sulfide (Me 2S) from waste air are reported for the first time. The membrane bioreactor contained a polydimethylsiloxane/Zirfon® composite membrane and was inoculated with Hyphomicrobium VS, a methylotrophic micro-organism. The optimal conditions of pH (6–7) and sulfate contents (< 8 g SO 4 2−-S.L −1) for maximum Me 2S-degradation were determined in batch studies and applied during membrane biofiltration. Dimethyl sulfide conversion depended both on gas residence time and inlet concentration. The removal efficiency of air contaminated with 38 mg Me 2S.m −3 was found to be 99% at 24 s, 90% at 12 s and 85% at 8 s gas residence time. At a gas residence time of 24 s, removal efficiencies of 99%, 93% and maximum 87% were observed for Me 2S concentrations of 33 mg.m −3 116 mg.m −3 and 375 mg.m −3, respectively. The maximum elimination capacity was 4.82 kg Me 2S.m r −3.d −1 (efficiency of 74%) which is higher than ever obtained with the conventional biofilters and biotrickling filters.

Effects of gas flow rate, inlet concentration and temperature on biofiltration of volatile organic compounds in a peat-packed biofilter

The effects of incoming gas concentration, empty bed residence time (EBRT), and column temperature on the removal efficiency of volatile organic compounds (isoprene, dimethyl sulfide, chloroform, benzene, trichloroethylene, toluene, m-xylene, o-xylene and styrene) were studied for 101 d in a biofilter comprising two glass columns (I.D. 5.0 cm × height 62 cm) packed with peat. At an EBRT of 3 min the removal efficiency increased up to 90% 34 d after start up at both 25°C and 45°C when the incoming gas concentration was raised stepwise to 65 g · m −3. When the incoming gas concentration increased to 83 g · m −3, the removal efficiency was 93% at 25°C, but dropped to 74% at 45°C. At an incoming gas concentration of 92 g · m −3 and an EBRT of 1.5 min, the removal efficiencies were 91% and 94% at 25°C and 32°C, respectively. However, at 1 min of EBRT, the removal efficiencies decreased to 68% and 81% at 25°C and 32°C, respectively. The removal rate per unit time and per unit volume of the biofilter was proportional to the incoming gas rate up to 3483 g VOC · m −3 · h −1. Further increase of the incoming gas rate lowered the removal rate as compared to that predicted by the proportionality. The maximum removal rate was 3977 g · m −3 · h −1 at 32°C. At an EBRT of 1.5 min, the removal efficiency was highest for isoprene (93%), and lowest for chloroform (84%). Aromatic compounds (benzene, toluene, and xylene) were removed by 93–94%. The cell concentration increased 100-fold from the initial value, and reached 1.12 × 10 8 cells · (g of dry peat) −1. At 32°C, 67% of the incoming VOC was removed in the first quarter of the column.

Effects of Gas Flow Rate, Inlet Concentration and Temperature on Biofiltration of Volatile Organic Compounds in a Peat-Packed Biofilter

The effects of incoming gas concentration, empty bed residence time (EBRT), and column temperature on the removal efficiency of volatile organic compounds (isoprene, dimethyl sulfide, chloroform, benzene, trichloroethylene, toluene, m-xylene, o-xylene and styrene) were studied for 101 d in a biofilter comprising two glass columns (I.D. 5.0 cm x height 62 cm) packed with peat. At an EBRT of 3 min the removal efficiency increased up to 90% 34 d after start up at both 25 degrees C and 45 degrees C when the incoming gas concentration was raised stepwise to 65 g.m(-3). When the incoming gas concentration increased to 83 g.m(-3), the removal efficiency was 93% at 25 degrees C, but dropped to 74% at 45 degrees C. At an incoming gas concentration of 92 g.m(-3) and an EBRT of 1.5 min, the removal efficiencies were 91% and 94% at 25 degrees C and 32 degrees C, respectively. However, at 1 min of EBRT, the removal efficiencies decreased to 68% and 81% at 25 degrees C and 32 degrees C, respectively. The removal rate per unit time and per unit volume of the biofilter was proportional to the incoming gas rate up to 3483 g VOC.m(-3).h(-1). Further increase of the incoming gas rate lowered the removal rate as compared to that predicted by the proportionality. The maximum removal rate was 3977 g.m(-3).h(-1) at 32 degrees C. At an EBRT of 1.5 min, the removal efficiency was highest for isoprene (93%), and lowest for chloroform (84%). Aromatic compounds (benzene, toluene, and xylene) were removed by 93-94%. The cell concentration increased 100-fold from the initial value, and reached 1.12 x 10(8) cells.(g of dry peat)(-1). At 32 degrees C, 67% of the incoming VOC was removed in the first quarter of the column.

Simultaneous removal of benzene, toluene and xylenes mixture by a constructed microbial consortium during biofiltration

A bacterial consortium with complementary metabolic capabilities was formulated and specific removal rates were 0.14, 0.35, 0.04, and 0.39 h−1 for benzene, toluene, o-xylene, and m,p-xylene, respectively. When immobilized on a porous peat moss biofilter, removal of all five (= BTX) components was observed with rates of 1.8–15.4 g m−3 filter bed h−1. Elimination capacities with respect to the inlet gas concentrations of BTX and airflow rates showed diffusive regimes in the tested concentration range of (0.1–5.3 g m−3) and airflow (0.55–1.82 m3 m−2 h−1) except for o-xylene which reached its critical gas concentration at 0.3 g m−3.

The reduction of recycled-NO x in coal combustion with O 2/recycled flue gas under low recycling ratio

The emission and reduction of NO x in coal combustion with O 2/recycled flue gas were investigated in an electric heated up-flow-tube combustor with a high volatile bituminous coal. The recycling ratio of flue gas ranged from 0 to 0.4, and the concentrations of recycled-NO in inlet gas were 0, 500 and 1000 ppm. Reduction efficiency of the recycled-NO x changed both with equivalence ratio and recycling ratio. More than 60% recycled-NO was reduced when equivalence ratio ϕ>1.4. Less recycled-NO was reduced under lower recycling ratio than that under higher recycling ratio. HCN and NH 3 were also detected with GC-FTD. The results indicated that HCN emissions decreased with the increase of recycled-NO concentration in inlet gas. No obvious influence of temperature on the reduction of recycled-NO was found. The experiments on recycled-NO 2 demonstrated a consistent trend similar to the NO recycle tests.

An in vitro study of the effects of isoflurane on oxygen transfer.

A common anesthetic technique utilized during cardiopulmonary bypass (CPB) includes the use of various inhalation agents, such as isoflurane. The purpose of this study was to evaluate the effects of this agent on oxygen transfer during CPB. An in vitro model was designed using bovine blood. Blood flow was held constant at 2 l/min, while gas flow was manipulated at 1 and 3 l/min. The percentage of inspired oxygen (FiO2) was set at 50 and 100%, and isoflurane was manipulated to 1.0, 3.0 and 5.0%. Blood gas analysis, oxygen transfer, and inlet and outlet isoflurane concentrations were measured at each of the given conditions. A total of 12 trials with four oxygenators were conducted. In the four oxygenators used in our study, no significant differences in oxygenator performance were found. At conditions of 1 I/min gas flow, 50% FiO2 and 1% isoflurane, there were no significant changes in O2 transfer between baseline and measurements taken during isoflurane administration (100.18 +/- 12.49 vs 102.35 +/- 10.99 ml O2/min, p=0.8031). At 3 I/min gas flow, 100% FiO2 and 5% isoflurane, no significant differences were found (142.35 +/- 10.76 vs 154.04 +/- 8.95 ml O2/min, p=0.1459). The only significant differences found for oxygen transfer were between 50 and 100% FiO2, all other conditions being set equal (102.35 +/- 10.99 vs 137.68 +/- 8.62 ml O2/min, p=0.0023). In conclusion, increasing concentrations of isoflurane up to 5% does not affect the efficiency of oxygen transfer in an in vitro circuit. Further studies are necessary to evaluate the effects in an in vivo setting.