Acetylene Concentration Research Articles

Study on the inhibition of methane production from anaerobic digestion of biodegradable solid waste

The inhibition effects and mechanisms of chlorinated methane, anthraquinone and acetylene on methanogenesis in the anaerobic digestion process of biodegradable solid wastes were investigated. It was found that both chloroform and acetylene could effectively inhibit methanogens. Acetylene inhibited the activity of methanogens, while chloroform inhibited metabolic process of methanogenesis. A central composite design (CCD) and response surface regression analysis (RSREG) were employed to determine the optimum conditions and interaction effects of chloroform and acetylene in terms of methane and hydrogen production. Acetylene promoted the inhibition efficiency (F = 31.14; P < 0.01) more effectively than chloroform (F = 2.46; P > 0.05). In addition, a maximum hydrogen production of 1.6 ml was estimated under the optimum conditions of chloroform concentration of 6.69 mg kg(-1) and acetylene concentration of 3.08 x 10(-3) (v/v). Chloroform had a significant effect on enhancing the production of propionic acid and a minimum molar ratio of acetic acid to propionic acid of 0.707 was reached with the chloroform concentration of 9.24 mg kg(-1) and acetylene concentration of 4.0 x 10(-3) (v/v). Hence, methanogens can be inhibited while the stabilization process of solid wastes can still work well. Moreover, co-inhibition technology practice at landfills was feasible and the environmental damage was negligible, according to the analysis and experimental results.

Thermodynamic analysis of coal pyrolysis to acetylene in hydrogen plasma reactor

A systematic re-examination of the thermodynamic study on the process of coal pyrolysis to acetylene in a hydrogen plasma reactor was performed with referenced pilot-plant data at the scale of 2-MW plasma. At the ultra-high temperature conditions, the gas phase composition may reach thermodynamic equilibrium immediately no matter whether the solid carbon exists or not. The mass ratio of C/H in the gaseous phase plays a significant role in the acetylene concentration at the thermodynamic equilibrium states. It is demonstrated either in thermodynamics calculation or in hot tests that a mass ratio of C/H near or above 2 is essential to gain an acceptable concentration of acetylene in the mixed gases, which indicates that the mixing efficiency between gas and coal particles near the coal injection point becomes pivotal to the yield of acetylene for its direct influence on the devolatilization of coal, i.e., the gaseous C/H ratio. Being consistent with the hot test experience, the extra amount of water added into the system may inhibit the production of acetylene. However, the addition of methane might impose a positive effect on the yield of acetylene and therefore on the overall reactor performance.

Numerical Study on the Acetylene Concentration in the Hydrogen-Carbon System in a Hydrogen Plasma Torch

Effects of the hydrogen/carbon mole ratio and pyrolysis gas pressure on the acetylene concentration in the hydrogen-carbon system in a plasma torch were numerically calculated by using the chemical thermodynamic equilibrium method of Gibbs free energy. The calculated results indicate that the hydrogen concentration and the pyrolysis gas pressure play crucial roles in acetylene formation. Appropriately abundant hydrogen, with a mole ratio of hydrogen to carbon about 1 or 2, and a relatively high pyrolysis gas pressure can enhance the acetylene concentration. In the experiment, a compromised project consisting of an appropriate hydrogen flow rate and a feasible high pyrolysis gas pressure needs to be carried out to increase the acetylene concentration from coal pyrolysis in the hydrogen plasma torch.

Acetylene measurement in flames by chirp-based quantum cascade laser spectrometry

We have designed and characterized a mid-IR spectrometer built around a pulsed distributed-feedback quantum cascade laser using the characteristic frequency down-chirp to scan through the spectral region 6.5 cm(-1) spectral region. The behavior of this chirp is extensively measured. The accuracy and detection limits of the system as an absorption spectrometer are demonstrated first by measuring spectra of acetylene through a single pass 16 cm absorption cell in real time at low concentrations and atmospheric pressure. The smallest detectable peak is measured to be approximately 1.5 x 10(-4) absorbance units, yielding a minimum detectable concentration length product of 2.4 parts per million meter at standard temperature and pressure. This system is then used to detect acetylene within an ethylene-air opposed flow flame. Measurements of acetylene content as a function of height above the fuel source are presented, as well as measurements of acetylene produced in fuel breakdown as a function of preinjection fuel temperature.

Towards practical gas sensing with micro-structured fibres

In this work we realize a compact, low volume gas sensor utilizing commercially available hollow core photonic band-gap fibre (PBGF) guiding at around 1550 nm. The device is demonstrated for the detection of methane and acetylene gas. Hollow core PBGF offers near free-space beam guidance. This gives an advantage for gas sensing applications providing a longer interaction length than conventional gas cells and the potential to detect very low analyte concentrations whilst also being inherently safe for operation in remote or hazardous environments. However, one difficulty with such a device is filling a long fibre core with the test gas. Allowing the test gas to enter by diffusion alone can be a lengthy process and forced gas flow may be undesirable. A compact sensor has been designed and built to provide gas detection in an enclosed environment. Standardized connectors incorporating single mode fibre are used to couple light to and from the device. This is spliced to PBGF which has been arranged in sections connected by specially designed splices allowing gas into the fibre and therefore reducing the diffusion length. The fill time by diffusion is minimized while maintaining a long (∼1 m) interaction length. Results from demonstration gas concentration measurements are presented and the performance of the device is evaluated. Results are limited by the presence of interferometric noise which is believed to arise from the interaction between core and surface modes within the PBGF; despite this, acetylene concentrations down to 0.05% are measured.

Analysis of acetylene in blood and urine using cryogenic gas chromatography–mass spectrometry

A method for quantitative analysis of acetylene in blood and urine samples was investigated. Using cryogenic gas chromatography–mass spectrometry (GC–MS), acetylene was measured with isobutane as the internal standard in the headspace method, which revealed a linear response over the entire composite range with an excellent correlation coefficient, both in blood ( R = 0.9968, range = 5.39–43.1 μg/ml) and urine ( R = 0.9972, range = 2.16–10.8 μg/ml). The coefficients of variation (CV) for blood ranged from 2.62 to 11.6% for intra-day and 4.55 to 10.4% for inter-day. The CV for urine ranged from 2.38 to 3.10% for intra-day and 4.83 to 11.0% for inter-day. The recovery rate as an index of accuracy ranged from 83 to 111%. The present method showed good reliability, and is also simple and rapid. In actual samples from a charred cadaver due to acetylene explosion, the measured concentrations of acetylene by this method were 21.5 μg/ml for femoral vein blood, 17.9 μg/ml for right atrial blood, 25.5 μg/ml for left atrial blood and 7.49 μg/ml for urine. Quantification of acetylene provides important information, because the acetylene concentration is a vital reaction or sign. For example, when acetylene is filled in a closed space and then explodes, in antemortem explosion, the blood acetylene concentration of the cadaver might be significant. On the other hand, in postmortem explosion, acetylene is not detected in blood. Furthermore, when several victims are involved in one explosion, comparison of the sample concentrations can also provide useful information to establish the conditions at the accident scene; therefore, the present method is useful in forensics.

Oxidation of Acetylene in Atmospheric Pressure Pulsed Corona Discharge Cell Working in the Nanosecond Regime

Combined experimental and modeling studies of acetylene oxidation in pulsed corona discharges working in the nanosecond regime are presented. The corona cell was characterized in term of power deposition to provide input data for the model. The concentrations of ozone, CO, CO2 and residual acetylene were systematically measured for model validation purposes. The model used allows describing the detailed chemistry in the discharge and the mass transfer between the microdischarges and the discharge free regions in the corona cell. Results showed that the model allows a satisfactory prediction of the acetylene residual fraction, CO and CO2 yields and O3 concentration for a wide range of conditions. They enabled a precise identification of the product distribution and confirmed the central role of O-atom in the oxidation process. They also revealed that ketene, H2CCO, plays an important role in the oxidation mechanism and allowed drawing some conclusions on the optimization of the oxidation process.

Coal pyrolysis to acetylene using dc hydrogen plasma torch: effects of system variables on acetylene concentration

In order to unveil the inner mechanisms that determine acetylene concentration, experimental studies on the effect of several parameters such as plasma torch power, hydrogen flux and coal flux were carried out from coal pyrolysis in a dc plasma torch. Xinjiang long flame coals including volatile constituents at a level of about 42% were used in the experiment. Under the following experimental conditions, namely plasma torch power, hydrogen flow rate and pulverized coal feed speed of 2.12 MW, 32 kg h−1 and 900 kg h−1, respectively, acetylene volume concentration of about 9.4% was achieved. The experimental results indicate that parameters such as plasma torch power and coal flux play important roles in the formation of acetylene. Acetylene concentration increases inconspicuously with hydrogen flux. A chemical thermodynamic equilibrium model using the free energy method is introduced in this paper to numerically simulate each experimental condition. The numerical results are qualitatively consistent with the experimental results. Two parameters, i.e. the gas temperature and the ratio of hydrogen/carbon, are considered to be the dominant and independent factors that determine acetylene concentration.

Process Development and Reactor Analysis of Coal Pyrolysis to Acetylene in Hydrogen Plasma Reactor

Coal pyrolysis in hydrogen plasma opens up a direct means for producing acetylene. This process is operated under high temperature conditions (e. g., ~3000 K) with the residence time in milliseconds. To better understand the complex reaction behavior in a 2 MW pilot-scale reactor, a comprehensive CFD model was established to describe the gas–particle reacting flows for the process of coal pyrolysis in hydrogen plasma. Equilibrium chemistry in the gas phase was introduced and the mixture fraction approach with β-shape probability density function was used. The coal particles were modeled by discrete phase model approach so that the heating and devolitilization processes of coal particles can be well quantified in the reactor. The 3-dimensional simulations revealed the detailed flow field, temperature field, devolitilization process of coal and the spatial distribution of product gases. The unique structure of the V-shape plasma torch leads to the non-uniformity of temperature distribution in the reactor as well as the dissimilar courses of devolatilization of coal particles injected from different inlets. The results indicated that coal released its volatile matter in the first third of the reactor. Increasing the coal feeding rate results in the temperature drop of the reactor and an increase of the concentration of methane. The concentration of acetylene may reach its maximum in a good match between the plasma power input and the feeding rate of coal. All the results showed good accordance with the operation experience on the 2 MW pilot-plant reactor.

Co-inhibition of methanogens for methane mitigation in biodegradable wastes

The inhibition effects and mechanisms of chlorinated methane and acetylene on methanogenesis in the anaerobic digestion process of the biodegradable wastes were investigated. It was found that both chloroform and acetylene could effectively inhibit methanogens while the biodegradability of the wastes was not affected. Acetylene inhibited the activity of methanogens, while chloroform inhibited metabolic process of methanogenesis. A central composite design (CCD) and response surface regression analysis (RSREG) were employed to determine the optimum conditions and interaction effects of chloroform and acetylene in terms of inhibition efficiency, production of volatile fatty acids (VAF) and molar ratio of propionic acid to acetic acid. Chloroform had significant effect on enhancing the production of VFA ( F = 121.3; p < 0.01), and acetylene promoted the inhibition efficiency ( F = 99.15; p < 0.05) more effectively than chloroform ( F = 9.72; p > 0.05). In addition, a maximum molar ratio of propionic acid to acetic acid of 1.208 was estimated under the optimum conditions of chloroform concentration of 9.05 mg/kg and acetylene concentration of 3.6×10 −3 ( V/ V). Hence, methanogens in the wastes can be inhibited while the stabilization process of the biodegradable wastes can still work well, as propionic acid generated during the inhibition process could hardly be utilized by methanogens.

TDLAS-based in situ measurement of absolute acetylene concentrations in laminar 2D diffusion flames

We report the first quantitative and calibration-free in situ C2H2 measurement in a flame environment using direct Tunable Diode Laser Absorption Spectroscopy(TDLAS). Utilizing a fiber-coupled Distributed Feedback diode laser near 1535nm we measured spatially resolved, absolute C2H2 concentration profiles in a laminar non-premixed CH4/air flame supported on a modified Wolfhard–Parker slot burner with N2 purge slots to minimize end flames. We developed a wavelength tuning scheme combining laser temperature and current modulation to record with a single diode laser a mesh of 37 overlapping spectral windows and generate an ∼7nm (30cm−1) wide, high-resolution absorption spectrum centered at 1538nm. Experimental C2H2 spectra in a reference cell showed excellent agreement with simulations using HITRAN2004 data. The enhanced wavelength coverage was needed to establish correct C2H2 line identification and selection in the very congested high temperature flame spectra and led to the P17e line as the only candidate for in situ detection of C2H2 in the flame. We used highly efficient optical disturbance correction algorithms for treating transmission and background emission fluctuations in combination with a multiple Voigt line Levenberg–Marquardt fitting algorithm and Pt/Rh thermocouple measurements to achieve fractional optical resolutions of up to 4×10−5 OD (1σ) in the flame (T up to 2000K). Temperature dependent C2H2 detection limits for the P17e line were 60 to 480ppm. By translating the burner through the laser beam with a DC motor we obtained spatially resolved, absolute C2H2 concentration profiles along the flame sheet with 0.5mm spatial resolution as measured with a knife edge technique. The TDLAS-based, transverse C2H2 concentration profiles without any scaling are in excellent agreement with published mass spectrometric C2H2 data for the same flame supported on a similar burner, thus validating our calibration-free TDLAS measurements.

Enhancing the measurement accuracy of a cavity-enhanced fiber chemical sensor by an adaptive filter

Amplified spontaneous emission (ASE) noise, induced by an erbium-doped fiber amplifier (EDFA), is always a key problem for the measurement accuracy in a cavity ring-down (CRD) fiber amplified loop gas sensing system. A digital least-mean-square (LMS) adaptive filter is proposed to reduce the ASE noise in a CRD acetylene-sensing fiber loop for improving the measurement accuracy in terms of concentration. The simulation and experimental results show that the measurement accuracy in terms of concentration of acetylene could achieve about 15 ppm.

Fibre optical sensor for C2H2 gas using gas-filled photonic bandgap fibre reference cell

We present results from the first optical fibre correlation spectroscopy gas sensor which uses no lenses other than in the measurement gas cell. The sensor measures acetylene (C2H2) gas concentration. A 1-m length of photonic bandgap fibre (PBGF) was filled with acetylene at atmospheric pressure, then fusion spliced to standard, solid-core, single-mode SMF-28 fibre to form a compact, coilable, reference cell without the need for any lenses or bulk optics. As the cell contained a gas volume <5μL, it presents a greatly reduced hazard even when filled with explosive or harmful gases. Acetylene concentration measurements were made by comparing the absorption spectrum of this reference cell with that of a bulk optics measurement cell containing test gases, using a simple sensing topology requiring no spectrally selective components. Our sensor had a noise-limited sensitivity of 100ppm acetylene using 4s averaging time. Pure carbon dioxide gave a cross-sensitivity equivalent to 150ppm acetylene.

Stable kilohertz spark discharges for high-efficiency conversion of methane to hydrogen and acetylene

Stable kilohertz spark discharges with a unique waveform of discharge current were studied for high-efficiency conversion of methane to hydrogen and acetylene at atmospheric pressure for the first time. Discharge stability was confirmed by the concentration variation in the product streams with 220 min discharge time using pure methane as the feed gas. Utilizing the stable kilohertz spark discharges, the hydrogen concentration in the product stream could be as high as 72.1 vol% at an energy cost of 6.7 eV per H2 molecule produced and 81.5% of methane conversion. The acetylene concentration could reach 18.4 vol% at an energy cost of 21.2 eV per C2H2 molecule produced and 70.3% of methane conversion. For methane conversion ranging from 51.9% to 81.5%, the energy costs were 6.6–10.7 eV per CH4 molecule converted, 4.4–6.7 eV per H2 molecule produced and 16.9–27.6 eV per C2H2 molecule produced. This study showed the high-concentration production of COx-free hydrogen and acetylene from methane at a low energy cost by stable kilohertz spark discharges.

The control of diameter of carbon nanotube over Co-loaded Zeolite Y

This study examined carbon nanotubes (CNTs) with various outer diameters produced by the catalytic decomposition of acetylene over Co-loaded zeolite Y. The CNTs were grown at differed reaction temperatures, reaction times, and acetylene concentrations. In addition, the effect of the amount of Co dispersed over zeolite Y used as a support was determined. The shape and diameter of the synthesized CNT were identified by SEM and TEM analyzers. As a result, CNTs with various outer diameters were synthesized successfully. The average outer diameter of the synthesized CNTs increased with increasing amount of Co dispersed over zeolite Y regardless of the reaction temperature and reaction time. The outer diameter did not change with acetylene concentration, and the acetylene concentration was fixed to 10 cm3/min. Most of the CNT had large surface areas, >400 m2/g. The surface area increased with increasing outer diameter of the CNT until the outer diameter reached 60 nm but decreased with further increases in outer diameter.

Advanced Quartz-Enhanced Photoacoustic Trace Gas Sensor for Early Fire Detection

A spectroscopic trace gas sensor using a distributed feedback diode laser at λ=1.53 μm and based on quartz enhanced photoacoustic spectroscopy technique is described. The sensor is capable of quasi-simultaneous quantification of trace ammonia, hydrogen cyanide, and acetylene (NH3, HCN, and C2H2, respectively) concentrations at ~100 ppbv levels with a 4s integration time. The sensor design, responsivity, noise, and crosstalk characteristics are reported.

Inlet effect on the coal pyrolysis to acetylene in a hydrogen plasma downer reactor

AbstractCoal pyrolysis to acetylene in hydrogen plasma is a clean process for the coal utilization. A gas–solid downer reactor was employed to facilitate the high temperature reactions of coal pyrolysis in milliseconds. The effect of the inlet design on the coal injection was studied using CFD simulations, which were qualitatively compared with the cold model experiments in the prototype of a 2 MW hydrogen plasma reactor. The results revealed that the distribution of the coal particles near the inlet nozzles was significantly influenced by the layout of the flat‐shaped nozzles and the operating conditions. Accordingly the heating efficiency of the particles by the hot gas showed strong dependence on the inlet design. The hot model tests demonstrated that the reactor performance characterized by the concentration of acetylene in the product gas increased from ∼7.6 to 9.6% by optimizing the nozzle design, which indicated the critical role of the nozzle design in the coal pyrolysis process.

Effect of Fuel Spray Angle on Soot Formation in Turbulent Spray Flames

Results are presented from a combined experimental and modeling study undertaken to understand the effect of fuel spray angle on soot production in turbulent liquid spray flames. The experimental work was conducted in a cylindrical laboratory furnace at fuel spray cone angle of 30o, 45o and 60o. Soot concentrations inside the combustor are measured by filter paper technique. The soot concentration is modeled by using the soot particle number density and the mass density based acetylene concentrations. Soot oxidation occurred by both hydroxide radicals and oxygen molecules. The comparison of calculated results against experimental measurements shows good agreement. Both the numerical and experimental results show that the peak value of soot and its location in the furnace depend on fuel spray cone angle. An increase in spray angle enhances the evaporating rate and peak temperature near the nozzle. Although peak soot concentration increase with enhance of fuel spray angle but soot emission from the furnace decreases. Keywords—Soot, spray angle, turbulent flames, liquid fuel.

Formation of carbon clusters in deflagration and detonation waves in gas mixtures

Numerical and experimental results of studying the formation of carbon clusters due to propagation of deflagration and detonation waves in enriched acetylene-oxygen and acetylene-air mixtures are described. Experiments are performed in tubes of different diameters (including tubes filled by a porous medium) with wide-range variations of the initial pressure and the fuel-to-oxidizer ratio. A large variety of carbon clusters formed in different regimes of burning of the mixture is found. A typical size of condensed carbon particles is 15–100 nm. In the case of detonation in a porous medium, the size of carbon particles is 15–45 nm; in some tests, large individual fullerene-type particles 150, 400, and 950 nm in size are formed. The fraction of condensed carbon in the total amount of carbon in the initial mixture is found to depend on the wave type; detonation is characterized by the minimum “yield” of condensed carbon. The amount of condensed carbon increases with increasing acetylene concentration in the mixture and initial pressure. The size of carbon particles in the case of deflagration is greater than that in the case of detonation. Cooling of reaction products decelerates condensation and interrupts the growth of carbon particles.

Method and Detailed Analysis of Individual Hydrocarbon Species From Diesel Combustion Modes and Diesel Oxidation Catalyst

An undiluted exhaust hydrocarbon (HC) speciation method, using flame ionization detector gas chromatographs, is developed to investigate HC species from conventional and low-temperature premixed charge compression ignition (PCI) combustion pre- and postdiesel oxidation catalyst (DOC) exhaust. This paper expands on previously reported work by describing in detail the method and effectiveness of undiluted diesel exhaust speciation and providing a more detailed analysis of individual HC species for conventional and PCI diesel combustion processes. The details provided regarding the effectiveness of the undiluted diesel exhaust speciation method include the use of a fuel response factor for HC species quantification and demonstration of its linearity, detection limit, accuracy, and precision. The listing of individual HC species provides not only the information needed to design surrogate exhaust mixtures used in reactor tests and modeling studies but also sheds light on PCI combustion and DOC characteristics. Significantly increased engine-out concentrations of acetylene, benzene, and toluene support the theory that net soot reduction associated with PCI combustion occurs due to the reduction of soot formation (as opposed to increased soot oxidation). DOC oxidation behavior differs depending on the combustion characteristics, which change exhaust species and temperature.