Gasification of silicone fluids under external thermal radiation. Part 2. Gasification products — characterization and quantitation

The gasification behavior for a wide range of polydimethylsiloxane fluids in a nitrogen atmosphere was investigated. Part 1 of this study addressed the measurement of the energy (global heat of gasification) required for the gasification of a wide range of dimenthylsiloxanes. Several significant corrections were required to reconcile measured gasification energy(s) with calculated heat(s) of gasification based on fundamental thermochemical data. The identification of the dominant mode(s) of gasification via the characterization of pyrolysis products provided a firm basis and rationale for understanding and directing efforts at quantifying these correction factors. In Part 2, the gasification products were identified and quantified at various stages of the gasification process corresponding to ignition, fire growth, and steady-state burning. Pyrolysis of methylated siloxanes occurs via two modes: (1) the volatilization of short chain and intermediate chain length species native to the polymer, and (2) the volatilization of short chain and intermediate chain length species resulting from thermal degradation via siloxane rearrangement. The former process is the dominant gasification mechanism for short chain oligomers and low viscosity fluids (η<10 cS) and the latter process is dominant in all higher molecular weight polymers (η>100 cS). Both gasification mechanisms are evident in all polymers (η>20 cS); the dominant mechanism is dependent upon polymer size and distribution thereof, the gasification stage, and the presence of trace catalysts in the polymer. Because of their structural similarity, the combustion of all gasification products emanating from PDMS regardless of the stage of the pyrolysis process or the dominant mode of gasification will result in virtually identical combustion products, i.e. SiO₂, CO₂, and H₂O. Copyright © 1998 John Wiley & Sons, Ltd. This paper was written under the auspices of the US Government and is therefore not subject to copyright in the US.     

Time-dependent mass loss rate behavior of wall materials under external radiation

External radiation in enclosure fires can significantly enhance flame spread and fire growth. One of the effects of external radiation is to increase the mass loss rate of the fuel, which in turn produces larger flames. In this work, a measurement of mass loss with and without applied radiation was made as a function of time for three types of materials: a plastic (polymethylmethacrylate), wood-based products (particle board and hardboard), and a paper-based product (cardboard). The levels of applied radiation ranged from 0 to nearly 12 kWm^?2. The purpose of the investigation was to (1) quantitatively determine the effect of external radiation on the mass loss of various materials,(2) measure various parameters which may be used to characterize the mass loss rate history of the materials and (3) determine a method for expressing the mass loss rate as a function of time for input into numerical models. Higher levels of external radiation resulted in higher peak mass loss rates and quicker consumption of the material. Quantities which are useful for ranking the flammability of materials have been measured for the samples tested and are tabulated.     

Experimental study on fire behaviors of external thermal insulation composite system under vertical radiation

Using a vertical thermal radiator, we perform a set of experiments on the external thermal insulation composite system (ETICS) and pure extruded polystyrene (XPS). Several important parameters, including time to ignition, mass loss, and sample temperature, were measured. The combustion degree of XPS used during the experiments was B1 and B2. Results show that the whole burning process can be divided into 3 typical stages. Because of the protection effect of the outer layer of ETICS, the burning process of ETICS was noticeably different from that of pure XPS. The experimental results indicated that the protection effect of the outer layer weakened the difference between B1 and B2 flame‐retardant XPS. The time to ignition was increased under the effect of outer layer, while the core material (XPS) was easier to be ignited when the outer layer falls out. The research results are useful to the theoretical and numerical study on the fire characteristics of foamed polymer under vertical thermal radiation condition.     

Non-dimensional heat of gasification measurements in the intermediate scale rate of heat release apparatus

Wall-fire spread models require heat of gasification or non-dimensional heat of gasification to calculate mass loss rate or rate of heat release from the wall material. An intermediate scale rate of heat release apparatus was used to measure all the parameters needed to calculate non-dimensional heat of gasification for wood materials. An infra-red pyrometer was used to measure surface temperature. The results of measurements on six wood materials indicate that non-dimensional heat of gasification, if plotted against mass remaining, does not change significantly with external heat flux, but is material dependent.     

硅橡胶防热涂层隔热与耐热性能研究

本文系统研究了自制DMGQ-2硅橡胶防热涂层的热物理性能。结果表明，固化剂用量对热化学参数无显著影响，热化学参数随温度的变化而变化，通过拟合方程，可以对特定温度下DMGQ-2涂层的导热系数λ、比热容Cp、热扩散系数α进行预估。采用有限元分析，相比于X涂层，DMGQ-2涂层的隔热性能更优。TGA分析了DMGQ-2涂层的热分解温度。200℃热空气老化性能表明，DMGQ-2涂层具有较好的抗热空气老化性能。     

Coal gasification studies: Part I. Single stage complete gasification of coal using water as the hydrogen source

The complete gasification of coal to low molecular weight hydrocarbons has been achieved in a single stage process using water as the source of hydrogen. Reaction times of one hour, and a temperature of 600°C were required. The reactions were carried out in a stainless steel reactor with iodine or FeI₂ as a catalyst. It is shown that FeI₂ is a catalyst for the reaction Stainless Steel + H₂O → H₂ + Metal Oxide and also for the coal hydrogenation reaction. The apparent excellent reduction efficiency is probably a consequence of the good contact between the coal sample and the catalyst, which at the reaction temperature has a significant vapor pressure.     

Support studies for the U-GAS coal gasification process. Part I: Fluidization

This is the first part of a series of papers providing the details of support studies conducted as part of the development of the U-GAS fluidized-bed ash-agglomerating coal gasification process. The fluidized-bed gasifier in the U-GAS process behaves much like a conventional well-mixed bed, having a uniform bed composition and temperature in the bulk of the region, but it exhibits some departure in a small localized area confined to the proximity of the central spout, where a somewhat higher temperature is maintained for producing ash agglomerates. Extensive cold-flow experimental studies have been conducted to predict the solids discharge rates and agglomerates classification from the venturi/classifier system in the gasifier; these studies have resulted in a generalized analytical expression in terms of operating velocities, gas properties, and venturi/classifier configuration for the gasifier scale-up.Large-scale U-GAS gasifiers can have single-cone or multiple-cone grid configurations. X-ray cinematographic studies have been conducted in a program at University College London to compare the fluidization behaviors in the one-cone and three-cone grid configuration systems. The objective of this test program was to visually examine the solids circulation and study the bubble dynamics in the fluidized beds with these different configurations.     

Impingement heat transfer under a confined slot jet. Part I: Effect of surface throughflow

Local and average heat transfer coefficients were measured for a confined turbulent slot jet impinging on a permeable surface at which there may be throughflow. Local Nusselt number was obtained using a unique porous sensor designed for measurement of local heat transfer at a permeable surface which is subjected to rapidly and widely varying heat transfer. Measurements were performed for a wide range of jet Reynolds number and throughflow rates. Convective heat transfer coefficients was found to be enhanced by throughflow, and the enhancement factor in terms of Stanton number to be independent of jet Reynolds number and of extent of heat transfer area.     

Improving heat ageing and thermal properties of silicone rubber using montmorillonite clay

Heat ageing and thermal stability of a silicone rubber (SR) filled with montmorillonite clay (MMT) was investigated. Three types of rubber nanocomposites were prepared with highly exfoliated Cloisite 30B (SR/C30B), intercalated/exfoliated Cloisite Na⁺ (SR/Na⁺MMT), and highly intercalated Cloisite 20A (SR/C20A). This study showed that the SR/C30B nanocomposite exhibited excellent heat resistance in comparison to the other two nanocomposites and neat SR as revealed by higher retention strength. The thermal stability of the rubber in air was strongly dependent on the clay morphology and increased in the following order: highly intercalated/exfoliated SR/Na⁺MMT < highly intercalated SR/C20A < highly exfoliated SR/C30B. The thermogravimetric analyses of the SR/C30B nanocomposite showed a substantial increase in the final residue in comparison with the neat SR. This indicated a major improvement in the thermal stability of the rubber containing the exfoliated clay, which was also supported by the higher activation energy of decomposition measured for the nanocomposite. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41061.     

Heat transfer in a fluidized bed. Part I. The effect of thermal driving force on the heat transfer coefficient

The influence of the thermal driving force on the coefficient for heat exchange between a fluidized bed (diam. 30 cm) and part of a submerged vertical cylinder (diam. 7 cm) is described. In the experiments both negative and positive driving forces have been applied (the heat flow being considered positive if directed towards the bed).

Beds of glass beads, quartz sand and silica-alumina catalyst powders have been used to cover a range of particle size and density. For powders exhibiting dense phase expansion, heat transfer coefficients are found which are significantly affected by the driving force. At driving forces of about − 70°C heat transfer coefficients in a 40 μm catalyst bed were only half of those at driving forces approaching zero.

The behaviour of a transparent ‘two-dimensional’ fluidized bed showed that this might be the result of a reduction of solids mobility in the vicinity of the relatively cold surface. In an attempt to explain this reduction three mechanisms were considered; of these the decrease of the dense phase expansion due to a temperature gradient proved to be the most important one.

Powders not exhibiting dense phase expansion show heat transfer coefficients which are only slightly affected by the driving force, the differences resulting entirely from changes in physical properties with temperature.     

四苯基苯基多乙烯基硅油对高温硫化硅橡胶耐辐射性能的影响

通过Diels—Alder反应合成了四苯基苯基多乙烯基硅油（C2胶）。研究了在真空下经受总辐照剂量为500kGy和1000kGy、辐照剂量率150Gy／min的γ-射线辐照后C2胶对高温硫化硅橡胶耐辐射性能的影响。讨论了辐照前后硅橡胶相邻两交联点间有效链平均分子量^-Mc和力学性能的变化。结果表明C2胶能有效地提高硅橡胶的耐辐射性能，并且其辐射保护效果随着其浓度的增加（从2份到14份）而增加。     

影响有机硅热防护涂层的热导率的因素

以硅树脂为基料,配合中空玻璃微球等填料,制备了有机硅热防护涂层;研究了填料的组合、添加量、规格以及溶剂体系等对有机硅热防护涂层热导率的影响。结果表明,采用表面经过处理的中空玻璃微球和气相法白炭黑A380的组合填料、中空玻璃微球的用量选择60份、并使用酮类溶剂和芳香类溶剂的混合溶剂制成的热防护涂层,其热导率≤0·1W/(m·K),密度≤0·55g/cm3,拉伸强度≥2·0MPa。     

功能热流体强化脉动热管的热输送特性

考察了以水为工质,在不同的加热功率和不同的充液率情况下,脉动热管在不同加热方式（垂直底部加热和水平一侧加热）时的热输送特性。固定充液率,对比了脉动热管采用不同工质（微胶囊流体、氧化铝纳米流体、水）在不同加热功率、不同放置加热方式下的热输送特性。结果发现：功能热流体（微胶囊流体、氧化铝纳米流体）作为脉动热管的工质都起到强化热输送能力的作用,均优于水。垂直底部加热时,1%微胶囊流体作为工质的脉动热管的热输送能力较优,水平一侧加热时,0.1%氧化铝纳米流体较优,但微胶囊流体稳定性要比氧化铝纳米流体好。     

Electrical insulation properties of silicone rubber under accelerated corona and thermal aging

A contactless method based on energy shift of high-energy cut-off of the x-ray bremsstrahlung, the so-called Duane Hunt Limit and a conventional low voltage electrical technique (three-probes technique) is applied on thermal and corona aged silicone rubber (SiR) to measure, respectively, the surface potential, V_s, and the surface resistivity, ρ_s. The effect of aging on these quantities, representing the dielectric properties, is studied. The results are highly reproducible and highlight a good correlation between V_s and ρ_s. It was observed that thermal aging combined with electrical aging deteriorates more the electrical properties of the polymer than thermal aging alone. Explanations for electrical characteristics (V_s, ρ_s) change with aging are supported by attenuated total reflection Fourier transform infrared spectroscopy spectra analysis and a chemical mechanism of aging in three steps (i.e., oxidation-polycondensation, degradation, and thermal cracking). The surface degradation of the polymer is revealed by images of surface morphology obtained by using scanning electron microscopy (SEM). Roughness is greater for combined thermal and corona aging mode compared to thermal aging alone. In addition, the surface degradation of SiR polymer is confirmed by the loss of its hydrophobicity.     

Studies on catalytic gasification of coal chars. Part 1. Development of pores during gasification

Chars prepared from three coals were impregnated with nickel catalyst and gasified with hydrogen at 850°C and 10 atm. The surface area and porosity of gasified residues at several conversions were measured. Blair Athol char, which had a relatively large surface area, showed a unique gasification pattern, i.e., the rate increased with time until a maximum was attained. Catalytic gasification resulted in an increase in the volume of macropores of a given diameter range, which was characteristic of the catalyst system used. In non-catalytic gasification and in cases when activity of the catalyst was low, mainly pores smaller than 6 nm were enlarged. Possible explanations of the acceleration of the rate are discussed and some consequences of the porosity measurements for this explanation are indicated. As the macropores are enlarged during catalytic gasification, the kinetic pattern could be modified when intraparticle diffusion comes into play.     

煤气化技术工业应用概况及工艺选择(上)

煤气化技术是煤化工产业发展的核心技术,我国庞大的煤化工市场促进了煤气化技术的研发和应用。根据国内、外煤气化技术的实际情况,评述了固定层、流化床、气流床煤气化工艺的主流技术路线及其工艺特点和发展概况,介绍了各种煤气化技术在国内的技术研发和产业化现状。     

Gasification reactivity of charcoal with CO2. Part I: Conversion and structural phenomena

The gasification reaction of fir charcoal with CO₂ was studied by isothermal thermogravimetric analysis under kinetic control. The derived reaction rate (r=dX/dt) as a function of the converted carbon mass (X) was compared with random pore model predictions and found to be much higher at elevated conversion levels than predicted by theory. Similar enhanced reaction rate behaviour was evidenced after removing the natural alkali catalyst from the charcoal by acid washing, suggesting that with untreated charcoal the late reaction rate contribution stems from both, catalytic and additional structure effects. Literature attributes the unpredicted late reaction rate behaviour to the disintegration of the porous char particle into small fragments, which, in line with percolation theory predictions, seems to occur only after a critical conversion level has been reached. However, our gasification data reveal a gradual rise in the charcoal reactivity thereafter, suggesting a breaking up (embrittlement) of the solid phase accompanied by the exposure of fresh surface area from fracturing. The original random pore model derivation given by Bhatia and Perlmutter is extended to account also for these peculiarities and the resulting kinetic relation described our reaction rate data well over the entire conversion range.     

Separation of alkanes and alcohols with supercritical fluids. Part I: Phase equilibria and viability study

The chemical conversion of detergent range alkanes (12-14 carbon atoms) to alcohols is often incomplete and results in a large amount of residual alkane. This paper shows that these alkanes and alcohols can be separated by supercritical fluids. Ethane, propane and carbon dioxide were selected as possible supercritical solvents while n-tetradecane and 1-dodecanol were selected to represent the alkane-alcohol mixture, as these would be the two most difficult compounds to separate in a C12 to C14 alkane-alcohol mixture. A phase behaviour study and relative solubility analysis revealed that both ethane and carbon dioxide show promise in separating n-tetradecane and 1-dodecanol. Propane was eliminated as possible solvent because the phase behaviour of n-tetradecane and 1-dodecanol in supercritical propane is too similar. A pilot plant study showed that both supercritical ethane and carbon dioxide can be used to separate n-tetradecane and 1-dodecanol, with indications that supercritical ethane may affect a superior separation. An economic analysis, considering the energy requirements, revealed that the most important parameter with regard to energy consumption is the solvent-to-feed ratio. The process utilising ethane is more energy intensive, yet the energy requirements for both processes compare well with other petrochemical separation processes using supercritical fluids. Further investigations with both ethane and carbon dioxide should be conducted to determine which of these two solvents are superior and to optimise the operating parameters.     

Gasification of waste biomass chars by carbon dioxide via thermogravimetry. Part I: Effect of mineral matter

A series of carbon dioxide gasification tests of waste biomass chars were performed in a thermogravimetric analysis system, at non-isothermal heating conditions. The effects of the inorganic constituents of the fuels on thermal conversion characteristics were examined. Reaction rates were determined by developing a power law model.The bulk of char gasification process occurred between 800 and 950 °C. Maximum reaction rate and conversion were exhibited by waste paper char, due to its higher surface area.Inherent alkaline and alkaline earth carbonates and sulphates acted as catalysts, by increasing the reactivity of the fuels in carbon dioxide and causing their degradation to start at lower temperatures (60-75 °C).The kinetic model fitted the experimental results accurately. Activation energy values and reaction order ranged from 180 to 370 kJ/mol and 0.4 to 0.6, respectively, among the chars, indicating a chemically controlled process.