Hot Inert Gas Research Articles

A Hybrid Windowless Dual Tube Solar Reactor for Continuous Volumetric Natural Gas Dissociation

Solar natural gas thermal dissociation, producing both hydrogen and solid carbon, appears as a promising way for progressive decarbonization of the world energy mix. Three main challenges remain to be tackled: carbon deposition issue, continuous round the clock operation of the solar reactor with an intermittent energy resource, and technology scale-up. The present work proposes a new windowless scalable solar reactor enabling volumetric gas-phase (i.e., not at the walls) methane cracking with possible hybridization. CFD simulations demonstrate the advantage of the new concept as compared to conventional tubular reactors. The proposed system uses a hot inert gas to generate a high temperature fluid zone similar to a combustion flame where the methane decomposition occurs. Based on the numerical model developed, a sensitivity study is carried out in order to optimize the reactor design enabling both high methane conversion and low carbon deposition. For methane flow-rates of 4.6 × 10 −6 kg.s −1 and 2.3 × 10 −6 kg.s −1 (argon flow-rate of 9.3 × 10 −5 kg.s −1), methane conversion reached 46 and 73% for maximum fluid zone temperatures of 1676 and 1750 K, respectively. Furthermore, electric hybridization is investigated in order to highlight the potential for day and night continuous operation. Indeed, since an inert carrier gas is used as heat transfer medium, it can be heated by different energy sources to maintain the thermal power input during low irradiation periods. Thus, the solar flame concept that we previously patented proves to be of interest for practical implementation to introduce solar heat into high temperature processes.

Evaporation Rate of Colloidal Droplets of Jet Fuel and Carbon-Based Nanoparticles: Effect of Thermal Conductivity

Adding nanoparticles to liquid fuel is known to promote its combustion characteristics through improving several thermo-physical properties. This study investigates the effects of adding carbon nanoparticles on thermal conductivity and evaporation rate of liquid jet fuel. Multi-walled carbon nanotubes, activated carbon nanoparticles, and graphene nanoplatelets were added to jet fuel at different concentrations to prepare colloidal suspensions. Thermal conductivity is determined by passing known amounts of heat through a very thin layer of fuel and measuring temperature difference across its thickness. A fiber-supported droplet technique is also used to evaluate evaporation rate due to force convection of a hot inert gas. It is observed that both thermal conductivity and evaporation rate increase as a result of nanoparticle addition. Since there is no radiation heat transfer mechanism, the increase in evaporation rate is concluded to be only due to enhanced thermal conductivity.

Mathematical and Numerical Modeling for Energy Valorization of Sugarcane

This study concerns the numerical modeling of the pyrolysis of sugarcane waste. The potential application of pyrolysis products obtained (fuel) is in use in domestic or industrial combustion plants. To facilitate the digital modeling of the process of pyrolysis, the waste particles are assumed arranged in a vertical cylindrical enclosure (fixed bed). Their heating is provided by an ascending vertical stream of hot inert gas. Solving the equations of the balances on a two-dimensional flow and nonstationary provides the axial development of the temperature, the solid concentration of the carbonaceous residue (coke) and the pyrolysis gas. The method of finite differential was used for spatial discretization of the equation system, and method of Rang-Kutta order4. After validation, this model was applied to a configuration of a fixed bed. The results are in good agreement with the experimental results reported in the literature.

Production of light oil by injection of hot inert gas

Hot inert gas, when injected into an oil reservoir is capable of generating a vaporization–condensation drive and as a consequence, a preferential movement of the lighter components to the production well. This form of displacement is an important unit mechanism in hot flue-gas injection, or in thermal recovery from a watered-out oil reservoir. This article presents the movement of heat front vis-a-vis the changes in the saturation profile, and the gas-phase composition. The plateau in the temperature profile due to the exchange of latent heat, and the formation of water bank at the downstream are elaborated. The broadening of the vaporization–condensation zone with continued progression is discussed. The effect of inert gas temperature on the cumulative production of oil is reviewed. The results provide insight to the vaporization–condensation drive as a stand-alone mechanism. The paper underscores the relative importance of this mechanism, when operated in tandem with other processes in improved oil recovery and CO2 sequestration.

Transient thermal protection of film covering circular aperture by sublimation and weak decomposition

Unwanted heating of sensitive surfaces in harsh thermal environments can be prevented by precise application of sacrificial materials such as sublimation layers and pyrolyzing films. The use of sublimation for the protection of circular polyimide membranes subjected to brief (∼100ms) heating by infrared radiation and hot (6000K) inert gas convection is analyzed. Selection of sublimation material and sublimation layer and membrane thickness is considered with emphasis on providing sufficient thermal protection yet negligible unwanted material remaining at the end of a specified heating period. Though the analysis here is general, the motivation is protection of the polyimide films covering the laser entrance holes on IFE (inertial fusion energy) hohlraums being injected into the hot gas (xenon) protecting IFE reactor chambers. Both one and two dimensional thermal models are used to develop a robust thermal concept. Sensitivity analyses (SA) methods are exercised to show where the design may be vulnerable and which input parameters have the greatest effect on performance and likelihood of success. For the design and conditions considered, methane sublimating layers are probably preferred over xenon or pentane.

The Interplay of Heat Transfer and Endothermic Chemistry Within a Ceramic Microchannel Reactor

Ceramic microchannel heat-exchanger and reactor technology is capable of achieving high performance while operating under high-temperature, corrosive, and/or oxidative environments. This work describes two computational fluid dynamics (CFD) modeling studies which examine the coupling of heat transfer and endothermic methane-steam-reforming chemistry within a ceramic microchannel reactor. These modeling tools are then applied to improve microchannel-reactor design and performance. Within the reactor, methane is converted to syngas through steam reforming; the thermal requirements for this endothermic chemistry are provided by heat transfer from hot-inert gas on adjacent layers. Fluid flow, heat transfer, and complex elementary surface chemistry are all simulated using the ANSYS FLUENT models. CFD studies reveal the substantial chemical contribution of reforming on thermal gradients across and within the reactor. Improved control of the reforming temperature is also discovered through stack-design analysis, where an odd number of inert-gas layers are found to create more-uniform reactive wall temperatures. Model results provide insight on the interplay of conjugate heat transfer and chemical kinetics in reactor design.

Air Regeneration of a Silicalite Column Loaded with Ethanol: Modelling and Energy Estimation

Concentration-thermal swing adsorption (CTSA) using an ethanol-selective adsorbent can be an attractive option to reduce the energy costs associated with the separation of ethanol from water. In this process, ethanol regeneration is the only step with significant energy consumption, in which the adsorbent column saturated with liquid ethanol is purged with a hot inert gas to recover ethanol by condensation. Despite many showing interest in applying CTSA, the method has received little attention in the open literature, and consequently little information is available about its energy requirement. In this work, we experimentally measured the regeneration dynamics of a heated silicalite column saturated with liquid ethanol by air purge using different column wall temperatures and purge gas flow rates. Using a theoretical model based on conservation equations, the mass and heat transfer kinetics in this process are adequately reproduced. The proposed model has been used to estimate the overall energy requirem...

Microwave Swing Regeneration vs Temperature Swing Regeneration—Comparison of Desorption Kinetics

This paper presents a comparison of microwave swing regeneration (MSR) and temperature swing regeneration (TSR) of acetone and toluene from 13X molecular sieves in terms of desorption kinetics and desorption efficiencies. The experiments were performed for two forms of the adsorbent: adsorbent bed consisting of spherical beads and adsorbent pressed in the shape of pastilles to allow for precise temperature measurement of the solid adsorbent. In TSR the adsorbent is heated by means of a hot inert gas stream whereas in MSR the adsorbent dissipates microwave energy into heat. It was found that MSR runs faster even when the adsorbent temperature is much lower than the gas temperature in TSR. This implies more efficient desorption due to less energy waste in the form of heat losses and less sensible enthalpy of purge gas stream since the total gas consumption is considerably decreased. The observed enhancement of microwave-driven desorption is more pronounced for the polar adsorbate (acetone) or high heat transfer resistances (pastilles). Finally, it was verified that microwaves do not affect the adsorption capacity of the molecular sieves after several consecutive adsorption–desorption cycles.

Generalized flame balls

We consider generalized flame balls which correspond to stationary spherical flames with a flow of hot inert gas, either a source or a sink, at the origin. Depending on the flow, these flames can have positive, zero, or negative burning speeds, with zero speeds characterizing the Zeldovich flame balls. A full analytical description of these structures and their stability to radial perturbations is provided, using a large activation energy asymptotic approach and a thermo-diffusive approximation. The results are also complemented by a numerical study. The number and stability of the generalized flame balls are identified in various regions of the l-M-h 0 space, where l is the (reduced) Lewis number, and M and h 0 the flow rate and its enthalpy at the origin, respectively. It is typically found that, when the flow is a source, there is a maximum value of the flow rate M ax depending on l and h 0, above which no stationary solutions exist, and below which there are two solutions characterizing a small stable flame ball and a large unstable flame ball; the implications of these results to the problem of ignition by a hot inert gas stream are discussed. When the flow is a sink, however, there is typically a single unstable solution, except for sufficiently large values of the Lewis number and large negative values of M, where three flame balls exist, the medium one being stable. Finally, the relation between the flame speed, positive or negative, and the flame curvature, small or large, is discussed.

Direct patterning of organic light-emitting devices by organic-vapor jet printing

We demonstrate small molecular weight, fluorescent organic light-emitting devices directly patterned by organic-vapor jet printing (OVJP). In OVJP, a hot inert carrier gas picks up a molecular organic vapor that expands when passed through a nozzle, resulting in physisorption of the molecules onto a cooled substrate. A (1cm)2 flat organic semiconductor thin film is achieved by sweeping the nozzle over the substrate to print closely spaced lines. Using an array of nozzles, multiple parallel stripes are simultaneously printed at a growth rate of 3.4Åcm2∕s. Organic heterostructure fluorescent-light-emitting devices consisting of a broad area hole transport layer, followed by a striped electron transport layer, both printed by OVJP, yield an external quantum efficiency of (0.84±0.03)%, which is comparable to that of similar devices deposited by vacuum thermal evaporation.

Direct mask-free patterning of molecular organic semiconductors using organic vapor jet printing

We demonstrate the solvent-free, high-resolution direct printing of molecular organic semiconductors for use in low cost optoelectronic applications. In this method, called organic vapor jet printing, hot inert carrier gas picks up the molecular organic vapor and expands it through a microscopic nozzle, resulting in physisorption of the molecules onto a cooled substrate. Pattern resolution and printing speed are determined by the nozzle shape, nozzle-to-substrate distance, downstream pressure, and molecular mass of the carrier gas. Quantitative models are developed using a combination of scaling analysis, direct simulation Monte Carlo modeling, and printing experiments. Pattern resolutions of up to 1000dpi and local deposition rates exceeding 2300Å∕s are achieved. Pentacene channel thin film transistors are printed at a local deposition rate of 700Å∕s at both low and atmospheric pressures, resulting in a field-effect mobility of 0.25cm2∕Vs and a current on/off ratio of 7×105 for devices grown at a background pressure of 0.24Torr. The high directionality of the molecular jets and well-defined shape of the deposits enables combinatorial printing of structures and devices, while affording considerable control over film morphology. The method is also readily applicable to document printing using solvent-free inks.

Control of carbon disulfide emissions from viscose processes

AbstractThe U.S. Environmental Protection Agency (EPA) has issued a proposed rule for control of hazardous air pollutants from cellulose manufacturing operations. Both the hydrogen sulfide and carbon disulfide emissions must be controlled.An activated carbon‐based process has been developed which effectively removes both of these hazardous compounds with high efficiency. An impregnated activated carbon is used to remove hydrogen sulfide by converting it to sulfur on the interior surface of the activated carbon. The resulting waste is minimal and can be land filled at relatively low cost. A unique type of activated carbon is used to remove the carbon disulfide from the air stream, and periodic regeneration of the carbon, using hot inert gas, recovers the carbon disulfide for reuse. This type of system has operated for several years with no safety problems associated with the low auto‐ignition temperature of carbon disulfide.Extensive laboratory tests have been conducted to optimize this process and the results are presented. A large system has been designed and installed, and typical operating information is provided. Capital costs for systems of various sizes and configurations are given.

Zur Desorption von mit leichtflüchtigen chlorierten Kohlenwasserstoffen (LCKW) beladenen Adsorberpolymeren

To verify the regeneration of novel crosslinked polymeric adsorbents the desorption of VCHC loaded polymeric adsorbents was investigated and compared to activated carbons. Desorption methods used were thermal analysis, steam regeneration, hot inert gas and solvent regeneration. It was proven that the novel crosslinked polymeric adsorbents were effectively desorbed both by thermal desorption methods and by organic solvents. Thereby, the desorption of the polymeric adsorbents proceeds faster and more complete than of the activated carbons.

Zur Desorption von mit leichtflüchtigen chlorierten Kohlenwasserstoffen (LCKW) beladenen Adsorberpolymeren

To verify the regeneration of novel crosslinked polymeric adsorbents the desorption of VCHC loaded polymeric adsorbents was investigated and compared to activated carbons. Desorption methods used were thermal analysis, steam regeneration, hot inert gas and solvent regeneration. It was proven that the novel crosslinked polymeric adsorbents were effectively desorbed both by thermal desorption methods and by organic solvents. Thereby, the desorption of the polymeric adsorbents proceeds faster and more complete than of the activated carbons.

Design and optimisation of temperature cycled adsorptive reactors

This work describes a novel process in which reaction, separation and heat-exchange are combined within a single unit operation. Thermal and concentrations swing steps are considered in the theoretical design and optimisation of the process configurations, and include co- and counter-current configurations. The operation is carried out over a fixed bed of an admixture of catalyst and adsorbent which selectively removes the primary product from the reaction zone. The adsorbent is periodically regenerated using hot inert gas, which also acts as an energy supply step for the endothermic reaction. An optimisation strategy is used to seek the optimal operating policy that enables the process to separate the primary product, and outperform an optimal PFR in terms of production yield and energy consumption.

Desorption Kinetics of A N, N-Dimethylformamide Vapor from Granular Activated Carbon and Hydrophobic Zeolite

Abstract Such thermodynamic properties as enthalpy, free energy, and entropy of adsorption have been computed for N,N-dimethylformamide (DMF) vapor on two commercial adsorbents: coconut shell Type PCB of activated carbon and Type DAY of hydrophobic zeolite. The computation is based on the Langmuir adsorption isotherms obtained at 293, 303, and 313 K as reported by Tsai et al. The laden adsorbents were regenerated with hot inert nitrogen gas and studied by thermal gravimetric analysis at three different heating rates. The apparent activation energies (E des) of thermal desorption were determined by using the Friedman method. The zeolite DAY has an adsorption potential higher than that of activated carbon PCB as indicated by the more negative value of the adsorption enthalpy of DMF vapor. The average value of E des of zeolite DAY is larger than that of activated carbon PCB.

Wall-Less Like Reactor : Simulation and Experimental Results

The formation of thin films in the conventional thermally activated chemical vapour deposition process is based on heterogeneous reactions involved in surface nucleation and growth. Nevertheless, the influence of homogeneous reactions has often been underestimated, and the intermediate species that are formed from homogeneous reactions may have a great influence on the deposition mechanism. In order to study the formation of these species, a specific reactor has been designed, in which the effects of gas-phase and surface reactions can be separated and so clearly identified. In order to limit the influence of surface phenomena, a so called wall-less reactor has been developed. In such a reactor, the reactive gas mixture is heated by mixing with a hot inert gas. Two basic configurations have preliminary been optimized by simulation modelling using the Si-H chemical system. A reactor has been designed according to these calculations. Comparison of the calculated flow pattern with that visualized by the laser sheet method shows an excellent agreement, that partially validates our model. The reactor is coupled with Raman spectroscopy, that allows both the determination of the local temperature of the gas phase and the detection of gaseous species.

An asymptotic analysis of branched-chain ignition of cold combustible gas by hot inert gas

An asymptotic analysis of large activation energy with regard to ignition or flame initiation of a cold combustible gas stream coming into contact with a hot inert gas stream is presented. Two-step reaction kinetics, that is, a first-order chain-branching reaction and a second-order chain-termination reaction, responsible for ignition is adopted, and the dependence of ignition time (or flame attachment distance) on the second-order recombination reaction is examined. Equations for ignition delay are given by means of elementary functions, which show that ignition time increases with an increase in recombination reaction rate.

Steaming of activated carbon beds

When activated carbon is used in a thermal swing adsorption process, it may be regenerated by a hot inert gas or by steam. Preliminary experiments with steam (and without removal of an adsorbate) showed intermediate axial temperatures to be higher than inlet or exit temperatures. It was concluded that the heat of adsorption of water is the primary source of energy for the regeneration step of thermal swing adsorption involving steaming.

A model for simultaneous heating and devolatilization of a single coal particle in a hot gas stream in the presence of a thermal radiative field

The devolatilization of coal is a complex process (Lowry, 1963; Kobayashi et al., 1977). A simple approach has been employed to develop a theoretical model required for the prediction of simultaneous heating and devolatilization of a single coal particle entrained in a hot inert gas stream in the presence of a thermal radiative field. Reidelbach and Algermissen (1978) have described a single coal particle heating model that predicts the temperature of the particle as a function of time. Their model, however, does not account for the effect of loss of mass of the coal solid phase on the particle temperature during devolatilization. The model described in this note accounts for this deficiency.