Effect Of Gas Residence Time Research Articles

Prediction of pyrolysis product yield of medical waste based on BP neural network

Predicting pyrolysis product yields becomes more and more important for the realization of harmless, reduction, and resource disposal of medical waste. Based on the gray correlation analysis, this study predicted the three-state yield of medical waste pyrolysis products by building a BP neural network model. A database of pyrolysis product yields distribution of multivariate organic solid waste was established by selecting 225 sets of literature data in the existing research on rapid pyrolysis of organic solid waste and 18 sets of experimental data obtained from independent experiments. By the combination of the S-type tansig function of the hidden layer with the linear transfer purelin function of the output layer, the transfer function was created to construct the mapping between input and output variables. The results showed that when the number of hidden layer neurons was 14 and the learning rate was 0.04, the predicted yields and experimental yields were in good agreement with the R2 of neural network training and testing samples were 0.943 and 0.889, respectively. Increasing temperature and prolonging solid residence time were beneficial to the conversion of solid phase products to gas and liquid phase products. The effect of gas residence time on the three-phase yield distribution was less than that of temperature and solid residence time.

Decomposition of xylene in strong ionization non-thermal plasma at atmospheric pressure

A large amount of volatile organic compounds (VOCs) produced by industry have caused serious environmental pollution. In this paper, the removal effect of simulated xylene by strong ionization dielectric barrier discharge (DBD) plasma at atmospheric pressure and its degradation mechanism and pathway were studied. The effect of gas residence time, and initial xylene concentration was studied. The results showed that higher voltage caused an increase in discharge power, and with the increase of voltage, the concentration of ozone and nitrogen oxide in the reactor increased. The degradation efficiency decreased from 98.1% to 80.2% when xylene concentration increased from 50 ppm to 550 ppm at 4kV. And with the increase of residence time from 0.301s to 1s, the degradation efficiency increased from 78.5% to 98.6%. According to GC-MS analysis, the degradation products were ethyl acetate and n-hexylmethylamine at 4kv. And the main intermediates are 2,4-2-tert-butylphenol, 2-aminopentane, 2-methyl-5 - (2-aminopropyl) - phenol and propionamide at 1.5kV.

Effects of gas residence time of CH4/H2 on sp2 fraction of amorphous carbon films and dissociated methyl density during radical-injection plasma-enhanced chemical vapor deposition

Quadruple mass spectrometric measurements of CH3 density during radical-injection plasma-enhanced chemical vapor deposition to consider the sp2 fraction of amorphous carbon (a-C) films were performed. The sp2 fraction of the a-C films reached a minimum of 46%, where the CH3 density was maximum for a residence time of 6 ms. The sp2 fraction of the a-C films was tailored with the gaseous phase CH3 density during the deposition. This knowledge is useful for understanding the formation mechanism of bonding structures in the a-C films, which enables the precise control of their electronic properties.

Singlet delta oxygen production in a 2D micro-discharge array in air: effect of gas residence time and discharge power

The production of singlet delta oxygen (O2(a1Δg)) is of growing interest for many applications. We report on the measurement of O2(a1Δg) and ozone (O3) in a room temperature atmospheric pressure discharge in dry air. The plasma source is a 2D array of micro-discharges generated by an alternating current voltage at 20 kHz. The study focuses on the effect of gas flow through the discharge. The maximum investigated flow rate allows reducing the gas residence time in the discharge zone to half the discharge period. Results indicate that the residence time and discharge power have a major effect on the O2(a1Δg) production. Different O2(a1Δg) density dependencies on power are observed for different flow rates. Effects of collisional quenching on the as-produced and measured O2(a1Δg) densities are discussed. The flow rate also allows for control of the O2(a1Δg) to O3 density ratio in the effluent from 0.7 to conditions of pure O3.

Discharge dynamics and plasma density recovery by on/off switches of additional gas

Measurement of the plasma density is investigated to study plasma dynamics by adding reactive gas (O2) or rare gas (He) in Ar plasmas. When the O2 or He gas is added, plasma density is suddenly decreased, while the plasma density recovers slowly with gas off. It is found that the recovery time is strongly dependent on the gas flow rate, and it can be explained by effect of gas residence time. When the He gas is off in the Ar plasma, the plasma density is overshot compared to the case of the O2 gas pulsing due to enhanced ionizations by metastable atoms. Analysis and calculation for correlation between the plasma density dynamics and the gas pulsing are also presented in detail.

Effect of gas residence time on near-edge X-ray absorption fine structures of hydrogenated amorphous carbon films grown by plasma-enhanced chemical vapor deposition

In hydrogenated amorphous carbon films, deposited using a radical-injection plasma-enhanced chemical vapor deposition system, the chemical bonding structure was analyzed by near-edge X-ray absorption fine-structure spectroscopy. With a change in the residence times of source gases in a reactor, whereby total gas flow rates of H2/CH4 increased from 50 to 400 sccm, sp2-C fractions showed the minimum value at 150 sccm, while H concentration negligibly changed according to the results of secondary ion mass spectroscopy. On the other hand, widths of σ* C–C peaks increased with decreasing gas residence time, which indicates an increase in the fluctuation of bonding structures.

Effects of gas residence time on microwave plasma enhanced CVD of ultrananocrystalline diamond in mixtures of methane and argon without hydrogen or oxygen additives

For low-power and low-temperature microwave plasma CVD of UNCD in gas mixtures of methane and argon without hydrogen and oxygen additives, excessive carbon containing species often induce gas phase synthesis of non-diamond carbon phases, which fall on diamond growing surfaces to become part of the deposited diamond films. To prevent undesirable gas phase reactions, effects of gas residence time, or equivalently, the total gas flow rate at a fixed gas pressure and compositions, on the microwave plasma and its deposition of UNCD are studied. The gas residence time is increased by by-passing an increasing amount of a pre-set mixture of methane and argon at a fixed total flow rate through a mass flow controller to a vacuum pump while allowing the rest of the gas feed to flow through the reaction chamber. The gas composition, gas pressure, microwave power, and substrate temperature are kept constant. Optimization of the UNCD growth is, thus, achieved by increasing the gas residence time to deposit UNCD of high phase purity.

Effect of gas residence time on the morphology of silicon surface etched in SF 6 plasmas

This paper describes the effect of the SF 6 gas residence time on the morphology of silicon (1 0 0) samples etched in a reactive ion etching system. Profilometry and atomic force microscopy techniques were used to characterize the etching process focusing attention on the evolution of the surface morphology. Under the condition of variable pressure and gas flow rate, the decrease of the residence time leads to an increase of the silicon etch rate concomitantly with an increase of the surface roughness. Contrary fact is observed when the gas flow is fixed and the pressure is varied. Here, the increasing of residence time leads to a constant increase of silicon etch rate with small variations in final surface roughness. To better understanding this resident time effect, mass spectrometry analyses were realized during the discharge for both gas flow conditions.

Producer gas conditioning from a rice husk gasifier for engine application

The producer gas generated from an open core throatless down draft gasifier even after passing through a gas conditioning unit comprising of a water scrubber, dry filter, a cyclone separator and a fabric filter, contains about 200 mgINm3 of tar. This was specially the case during rainy season i.e periods of high relative humidity and temperature. The tar after condensing stick to the engine valves and connecting pipe lines causing problems in smooth operation of the engine. The tar content in the gas is a function of gas residence time in the dry scrubber once the gas is cooled to ambient temperature in water scrubber. A series of experiments were conducted to study the effect of gas residence time and the superficial gas velocity in the dry scrubber on tar reduction in producer gas keeping the water scrubber and fabric filter as such. With a gas residence time of 12-15 seconds and superficial gas velocity of 0.03 m1s in dry filter the tar content can be brought down to around 50 mg/Nm3.

Control of Trichloroethylene Emissions from Sparging Systems by Horizontal Bio- and Chemo- Barriers

The scope of this study was to develop a continuous system to clean-up a trichloroethylene (TCE) contaminated gas stream, where biotic and abiotic removal mechanisms are undertaken sequentially simulating the horizontal bio- and chemo-barriers proposed for the in-situ remediation of the contaminated sites. The bio- and chemo-barriers were simulated by using glass columns packed with granular anaerobic mixed culture and Fe(0) filings, respectively. The effect of gas residence time, which is adjusted by the gas flowrate, on the TCE removal efficiency of the reactor system was investigated. TCE removal efficiency of over 90% was achieved at gas residence times above 1hr. Furthermore, the effluent of reactor system contained only ethane and ethylene, which are non-toxic by-products of TCE reduction reactions, along with trace amounts of TCE.

Gas Residence Time Effects on Plasma Parameters: Comparison between Ar and C4F8

The effects of gas residence time on the plasma parameters such as the ion current density (ICD) and hot-electron population have been studied in an inductively coupled plasma (ICP) system employing Ar and C4F8, separately. The fluorocarbon ionic and radical compositions with respect to the residence time have also been studied in the case of C4F8 ICP. The ion current density with the gas residence time shows a totally opposite behavior in Ar and C4F8 discharge. To elucidate this phenomenon, the hot-electron population with the gas residence time was investigated. The measurement of hot electron population reveals that the energetic electrons are generated much more in Ar discharge but they become less in the case of C4F8 with the decrease of the residence time. Moreover, hot electron population is 3–6 times higher in Ar discharge than in C4F8. In the C4F8 ICP system, the number of all CFx (x=1–3) radicals increases but the intensity of the fluorocarbon ionic species [CFx+ (x=1–3)] except for the high-order molecular ions decreases with the decrease of the residence time. All of the diagnostic results show that the effects of the gas residence time must be considered by the characteristics of the plasma parameters as well as the effect of the adsorption and the desorption rate in the etch process.

Low Temperature Pyrolysis of an Australian Brown Coal in a Fluidised Bed Reactor

AbstractThe pyrolysis of Loy Yang coal was investigated under rapid heating conditions in a fluidised bed with a feed rate of 10g/h. Nitrogen was used as the fluidising gas operating at fives times the minimum fluidising velocity. The yields of tar, total volatile matter and C1‐C3 hydrocarbons are obtained for pyrolysis temperatures between 300 to 600°C. A maximum tar yield of 24.3% w/w (dry ash‐free coal) was achieved at 550°C and 1.82 s gas residence time. Fourteen fractions were identified in the tar dissolved in methanol. Yields of C1‐C3 hydrocarbons increased with increasing temperature to 3% w/w at 600°C. Elemental analysis showed that the composition of char and the tar yields were strongly dependent on temperature. The effects of gas residence time and feed particle size were also investigated.

96/05248 Flash pyrolysis of brown coal for obtaining liquid and gaseous hydrocarbons. III. Effect of gas residence time

96/05248 Flash pyrolysis of brown coal for obtaining liquid and gaseous hydrocarbons. III. Effect of gas residence time