Outlet Gas Stream Research Articles

The influence of Metal Dusting on gas reactions

AbstractGas composition analysis measurements have been performed in the outlet gas stream of a laboratory metal dusting test furnace in order to study the influence of metal dusting on gas reactions. This analysis has shown that carbon deposition is associated with metal dusting, i.e. the material most severely attacked by metal dusting, catalyses the formation of carbon to the largest extent. Also, metal dusting has not been seen to influence the methanation reactions. A kinetic model has been used to interpret the obtained data with respect to the catalytic activity of several high temperature materials showing that the catalytic activity of the material can vary by orders of magnitude for different reactions.

Low-temperature SCR of NO x with NH 3 over carbon-ceramic supported catalysts

A new method for preparing vanadium oxide supported on carbon-ceramic cellular monoliths is described. This includes a support oxidation step with HNO 3, followed by ionic exchange with a NaOH solution, equilibrium adsorption impregnation of VO 2+ and thermal treatment. As a result an active catalyst for low-temperature selective catalytic reduction (SCR) reaction is obtained. The V-catalyst is more resistant to SO 2 poisoning than the previously developed Mn-catalyst. Inhibition by water is reversible for both types of catalysts. Testing of the vanadium catalyst after subjecting it to the outlet gas stream of a power plant shows fast deactivation until constant residual activity is reached. Deactivation seems to be caused by arsenic poisoning and the formation of superficial sulphates.

Application of biofiltration to the degradation of hydrogen sulfide in gas effluents.

A laboratory scale bioreactor has been designed and set up in order to degrade hydrogen sulfide from an air stream. The reactor is a vertical column of 7 litre capacity and 1 meter in height. It is divided into three modules and each module is filled with pellets of agricultural residues as packing bed material. The gas stream fed into the reactor through the upper inlet consists of a mixture of hydrogen sulfide and humidified air. The hydrogen sulfide content in the inlet gas stream was increased in stages until the degradation efficiency was below 90%. The parameters to be controlled in order to reach continuous and stable operation were temperature, moisture content and the percentage of the compound to be degraded at the inlet and outlet gas streams (removal or elimination efficiency). When the H2S mass loading rate was between 10 and 40 g m(-3) h(-1), the removal efficiency was greater than 90%. The support material had a good physical performance throughout operation time, which is evidence that this material is suitable for biofiltration purposes.

Experimental evidence for electrochemical nature of the reaction between iron oxide in calcia-silica-alumina slag and carbon in liquid iron

The electrochemical nature of the reaction between iron oxide in calcia-silica-alumina slag and carbon in liquid iron has been studied by measuring the kinetics of the slag-metal reaction. A base slag (48 pct CaO-40 pct SiO2-12 pct Al2O3) containing iron oxide (≤8 wt pct FeO t ) was reduced by an Fe-C metal bath (∼4 wt pct C) at 1400 °C. The reaction rate was calculated from measurements of the total inlet gas flow rate and the CO concentration in the outlet gas stream. The slag was “internally short circuited” by dipping an iron plate through the slag layer, and this resulted in an increase in the rate of CO evolution. An external circuit was produced by dipping a graphite rod (shielded from the slag) into the metal bath and a steel or molybdenum rod into the slag layer; the open-circuit voltage and short-circuit current were measured when iron oxide was added to the base slag layer. The reaction rate was enhanced by applying a voltage across the slag layer, and an electric arc cathode was employed in some of these “electrolysis” experiments.

Organic compound destruction and removal efficiency (DRE) for plasma incinerator off-gases using an electrically heated secondary combustion chamber

The United States Department of Energy (DOE) sponsored a series pilot-scale plasma incineration tests of simulated mixed wastes at the MSE Technology Applications, Inc. technology development test facility in Butte, MT. One of the objectives of the test series was to assess the ability of an electrically heated afterburner to destroy organic compounds that may be present in the off-gases resulting from plasma incineration of mixed wastes. The anticipated benefit of an electrically heated afterburner was to decrease total off-gas volume by 50% or more, relative to fossil fuel-fired afterburners. For the present test series, feeds of interest to the DOE Mixed Waste Focus Area (MWFA) were processed in a plasma centrifugal furnace while metering selected organic compounds upstream of the electrically heated afterburner. The plasma furnace was equipped with a transferred-mode torch and was operated under oxidizing conditions (10–15% oxygen at the stack). Feeds consisted of various mixtures of soil, plastics, Portland cement, silicate fines, diesel fuel, and scrap metals. Benzene, chloroform, and 1,1,1-trichloroethane were selected for injection as simulates of organics likely to be present in DOE mixed wastes, and because of their relative rankings on the US Environmental Protection Agency (EPA) thermal stability index. The organic compounds were injected into the off-gas system at a nominal concentration of 2000 ppmv. The afterburner outlet gas stream was periodically sampled, and analyzed by gas chromatography/mass spectrometry. For the electrically heated afterburner, at operating temperatures of 1800–1980°F (982–1082°C), organic compound destruction and removal efficiencies (DREs) for benzene, chloroform, and 1,1,1-trichloroethane were found to be >99.99%. The electrically heated afterburner was also operated at temperatures well below the design operating temperature, in order to assess the sensitivity of the afterburner to temperature swings. At 1300–1320°F (704–716°C) DREs for benzene and 1,1,1-trichloroethane were still >99.99%, while the DRE for chloroform was slightly degraded to 99.977%. At 820–850°F (438–454°C) the DRE for 1,1,1-trichloroethane remained >99.99%, while the DREs for benzene and chloroform were substantially degraded, in the order expected from the EPA thermal stability index. For comparison, analogous tests were performed using a conventional natural gas fired afterburner, with similar results. The natural gas fired afterburner yielded DREs greater than 99.99% for 1,1,1-trichloroethane, chloroform, and benzene, when operated at 1600–1820°F (871–993°C) and ∼1350°F (∼732°C). Similarly to the electrically heated afterburner, at ∼850°F (∼454°C) DREs were substantially degraded for chloroform and benzene. At normal operating temperatures both the electrically heated afterburner and the natural gas fired afterburner gave acceptable DREs (>99.99%), for the three injected organic compounds. DREs remained acceptable for both units even when operated at substantially reduced temperatures.

Bioventing of hydrocarbon ‐ contaminated soil and biofiltration of the off ‐ gas: Results of a field scaleinvestigation

Bioremediation through venting, biodegradation and biofiltration was considered to be a feasible approach to remediate a hydrocarbon‐contaminated soil from a site underneath a paint factory. Before the field‐scale treatment process was designed, a microbial enumeration study was performed to estabilish the existence of an indigenous population of microorganisms capable of degrading naphtha in the impacted soil. A significant remediation of a limited area contaminated with approximately 100 Kg of naphtha, toluene and xylenes was achieved in a 2 month treatment in which the soil was remediated to conform with local soil quality regulations. The bulk of soil removal of contaminants was achieved by vapour extraction (about 70 kg). Biodegradation also provided a significant contaminant removal (about 18 Kg). The hydrocarbons removed from the vent system were successfully biofiltered and outlet gas stream concentrations were acceptable under Italian national law. The biodegradative capacity of a mixed culture of microorganisms selectively isolated from the soil was tested in vial culture experiments. After 1 day of incubation, four of the seven most important naphtha components were completely degraded; the remaining constituents were slowly degraded.

Photosynthetic performance of a helical tubular photobioreactor incorporating the cyanobacterium spirulina platensis

The photosynthetic performance of a helical tubular photobioreactor ("Biocoil"), incorporating the filamentous cyanobacterium Spirulina platensis, was investigated. The photobioreactor was constructed in a cylindrical shape (0.9 m high) with a 0.25-m(2)basal area and a photostage comprising 60 m of transparent PVC tubing of 1.6-cm inner diameter (volume = 12.1 L). The inner surface of the cylinder (area = 1.32 m(2)) was illuminated with cool white fluorescent lamps; the energy input of photosynthetically active radiation(PAR, 400 to 700 nm) into the photobioreactor was 2920 kJ per day. An air-lift system ncorporating 4%CO(2) was used to circulate the growth medium in the tubing. The maximum productivity achieved in batch culture was 7.18 g dry biomass per day [0.51 g . d biomass/L . day, or 5.44 g . d biomass/m(2)(inner surface of cylindrical shape)/day] which corresponded to a photosynthetic (PAR) efficiency of 5.45%. The CO(2) was efficiently removed from the gaseous stream; monitoring the CO(2) the outlet and inlet gas streams showed a 70% removal of CO(2) from the inlet gas over an 8-h period with almost maximum growth rate. (c) 1995 John Wiley & Sons, Inc.

Measurement of kLa by dynamic pressure method in pilot‐plant fermentor

The dynamic pressure method (DPM) is used for measurement of k(L)a in a 1-m(3) pilot scale fermentor in coalescing (distilled water) and noncoalescing (0.3 M Na(2)SO(4) aqueous solution) batches. The method consists in recording oxygen concentration in a batch after a small pressure change (20 kPa) in the fermentor. The upward pressure change is brought about by temporary closing and subsequent throttling of outlet gas stream and the downward change by full reopening of the gas outlet. Absorption of pure oxygen yields the same k(L)a values as absorption of air. In noncoalescing batch, the downward k(L)a values are always higher than the upward values owing to spontaneous nucleation of bubbles. The experiments performed in a stirred cell confirm this behavior. Thus, only upward pressure change should be used for measurement. The correlation of k(L)a data measured in small (18-L) and large (1000-L) vessels based on power dissipated and superficial gas velocity are in a good agreement. Unlike the DPM, the classical dynamic methods yield, under the same conditions, excessively low values of k(L)a (the dynamic startup method) or fail to produce data at all (the dynamic method with interchange of air for N(2)). (c) 1994 John Wiley & Sons, Inc.

Growth ofCatharanthus roseus cell suspensions in bioreactors: On-line analysis of oxygen and carbon dioxide levels in inlet and outlet gas streams

Catharanthus roseus cells (C87N) grown in a 30 litre airlift vessel achieved a growth rate of 0.366 day−1. The maximum biomass yield (9.13 gl−1) was recorded after 168 hours (7 days). On-line analysis of the composition of inlet and outlet gas streams during the growth cycle allowed calculation of the metabolic activity of the cultures. Oxygen uptake on a dry weight basis reached a maximum of 4.5×10−4 Moles O2 g dry weight−1 h−1 after 96 hours (during the mid-logarithmic phase of growth) and a maximum of 2.7×10−3 Moles O2 l−1 h−1 on a volume basis (towards the end of the logarithmic phase). Carbon dioxide production ran in parallel with oxygen use with maxima at 4.2×10−4 Moles CO2 g dry weight−1 h−1 and 3.4×10−3 Moles g l−1 h−1 respectively.

Influence of carbon dioxide solubility on the accuracy of measurements of carbon dioxide production rate by gas balance technique

AbstractThe total amount of carbon dioxide (CD) produced by a microbial culture is evolved via an outlet gas stream, outflowing broth, and can lead to a rise of the CD content in broth. To analyze relations among the three amounts, the equilibrium is considered between different ionic forms of carbon dioxide at different pH values as well as between the gaseous and disolved CO2. Dependences of the equilibrium constants on temperature are found by a thermodynamic analysis. Numerical estimation of an error of the CD production rate measurement, originating from the neglect of dissolved CD, is developed. The gas analysis technique alone provides a sufficient accuracy at pH lower than 6. At higher pH the error can be estimated using equations presented below.

Preparation of uranium trifluoride and studies on its disproportionation

The reduction of UF 4 to UF 3 by molecular hydrogen has been studied. At hydrogen flow rates which yield a constant H 2/HF ratio in the outlet gas stream, the optimum conversion temperature range is 1070–1125 K. Disproportionation studies on UF 3 have also been carried out in the temperature range 1169–1360 K. The variation of specific disproportionation rate ( k) with temperature can be represented by ▪

Interaction of sulfur dioxide with active carbon

The interaction of SO 2 with a well-outgassed active carbon surface has been studied over the temperature range 50–650°C. SO 2 (0.5 volume %) in He was passed through a packed bed of carbon, the outlet gas stream being monitored by a thermal conductivity cell and a mass spectrometer. Chemisorption of SO 2, and/or its dissociation products, between 50 and 300°C was small, amounting to about 1% of the total surface area. Essentially complete regeneration of the carbon could be achieved by heating at 950°C in flowing He. At 650°C, SO 2 reacted with the carbon rapidly forming CO, CO 2, and elemental sulfur. Significant amounts of the sulfur left the bed and deposited in cooler parts of the reactor. Under these conditions, active carbon is most efficient at removing SO 2.

Automatic control of dissolved oxygen levels in fermentations

AbstractDissolved oxygen levels in fermentation systems are affected by (a) gas flow rate, (b) degree of agitation, and (c) oxygen partial pressure in the gas. Since the first two variables cannot easily be separated, a method for dissolved oxygen control has been devised based on the variation of oxygen partial pressure in the gas. Oxygen and nitrogen are fed to a special mixing valve capable of varying the proportions of the two gases while keeping the total flow rate constant. A dissolved oxygen electrode and control system adjust the valve setting to automatically maintain a preset oxygen level. Oxygen analyzers, monitoring the inlet and outlet gas streams, provide additional information from which oxygen absorption and uptake rates may be determined. The system provides a means for the quantitative and independent study of aeration and agitation effects. In addition, it offers a basis for routine control of oxygen levels in plant fermentation equipment.

Modified Chromatograph to Record Helium Content of Natural Gas Streams

The construction and procedure for use of a special-purpose chromatograph designed to analyze small amounts of helium in natural gas streams are described. The successful use of ordinary solenoid valves for column switching is unique. Automatic-zero circuitry is also mentioned. The instrument has proved to be useful in the reduction of wasted helium in the outlet gas streams from helium extraction plants.