Showing papers on "Charring published in 2002"

Cone Calorimeter Combustion and Gasification Studies of Polymer Layered Silicate Nanocomposites.

Abstract: Polymer composites based on organically modified phyllosilicates (organoclay) and poly(ethylene-co-vinyl acetate) (EVA) were prepared by melt processing to study their combustion behavior. Their degrees of dispersion and intercalation spacings as determined by transmission electron microscopy (TEM) and X-ray diffraction (XRD) were typical of either a microcomposite or an exfoliated nanocomposite, depending on the type of organoclay. Combustion experiments showed that the microcomposite burns in the same way as pure EVA, whereas the heat release is reduced by 70−80% when nanocomposites with low silicate loadings (2−5%) are burned, because a protective charred ceramic surface layer is formed as a result of reassembly of the clay layers and catalyzed charring of the polymer. A chemical mechanism for this charring is proposed.

Rapid pyrolysis of agricultural residues at high temperature

Abstract: This paper deals with rapid pyrolysis of agricultural residues such as olive waste and straw at high temperature (800 -1000degreesC) in a free-fall reactor at pilot scale. The conditions are of interest for gasification in fluidized beds where rapid pyrolysis plays an important role as first stage. The objective of the work is to study the effect of the process conditions such as heating rate, temperature and particle size on the product distribution, gas composition and char reactivity. A higher temperature and smaller particles increase the heating rate resulting in a decreased char yield. The cracking of the hydrocarbons with an increase in the hydrogen content is favoured by a higher temperature and by using smaller particles. Wood gives more volatiles and less char than straw and olive waste. The higher ash content in agricultural residues favours the charring reactions. The higher lignin content in olive waste results in a higher char yield in comparison with straw. Chars from olive waste and straw are more reactive in gasification than chars from birch because of the higher ash content.

Charring characteristics of atmospheric organic particulate matter in thermal analysis

Abstract: The charring of organic materials during carbon analysis bythermal methods makes it difficult to differentiate elemental carbon (EC) from organic carbon (OC). Failure to correct for charring results in the overestimation of EC and the underestimation of OC. The charring characteristics andthermal behaviors of aerosol OC are studied by subjecting hexane and water extracts of ambient aerosols to various analysis conditions. The complete evolution of water-soluble organic carbon (WSOC) aerosol materials is found to require a temperature as high as 850 degrees C and the presence of oxygen. EC would be oxidized under these thermal conditions as well. As a result, thermal methods relying only on temperature for the differentiation of EC and OC would give unreliable OC and EC concentrations. Our investigation also reveals that WSOC accounts for a large fraction (13-66%) of charring, while hexane extractable organic compounds produce little charring. The extent of charring from WSOC, defined as the ratio between pyrolytically generated EC to the total WSOC, is found to increase with the WSOC loading in each analysis when the loadings are below a certain value. This ratio remains constant when the loadings are above this value. This may account for the high variability in the extent of charring among aerosol samples from different locations as well as among samples from a single location collected at different times. Charring is reduced if the residence time at each temperature step in a helium atmosphere is sufficiently long to allow for maximum C evolution at each step. Charring is also influenced by the presence of inorganic constituents such as ammonium bisulfate. For the few tested organic materials, it is observed that ammonium bisulfate enhances the charring of starch and cellulose but reduces the charring of levoglucosan.

Post-flashover fires in light and heavy timber construction compartments

Abstract: A series of fire experiments was performed to study the gas temperature development and charring behaviour of timber construction compartments. The measured gas temperatures were 300-500 C lower th...

Update for combustion properties of wood components

Abstract: The combustion properties of various biomass and wood materials from various references and from our laboratory were reanalysed. The net heat of combustion for cellulosic materials was found to be 13.23 kJ/g times the ratio of stoichiometric oxygen mass to fuel mass, r(0), regardless of the material composition. Bomb calorimeter data for original, charred and volatilized material components provide gross heating values, while elemental analysis of the materials for carbon hydrogen, oxygen and ash provide direct evaluation for r(0). We corrected these data as provided in various references by converting gross heating values to lower heating values and converting elemental compositions, char fractions and r(0) to a moisture-free and ash-free basis. Some existing formulae were found to disagree with data from vegetation, charred wood with high ash content, and with volatiles from cellulose treated with the fire retardant NaOH. We also established various functional correlations of r(0) with elemental compositions, or volatization fractions of untreated and treated materials, or material fractions for cellulose, lignin and extractives, or volatile fractions for tar, combustible gases and inert gases in pure nitrogen carrier gas. An interesting predictive result provides nearly constant heat of combustion while the volatile tar fraction is decreasing and combustible and inert gas fractions are increasing with time during the charring of Douglas-fir wood. Language: en

Food remains from Bronze Age-Archondiko and Mesimeriani Toumba in northern Greece?

Abstract: Finds of fragmented cereal grain from the sites of Mesimeriani Toumba and Archondiko in Macedonia, northern Greece, dated to 2100-1900 cal. B.C. provide the basis for the experimental investigation of the effects of a) fragmentation before and after charring, b) treatment of grain with water and c) charring conditions, on the morphology of the fracture surface. The experiments indicate that it is possible to distinguish fragmentation before and after charring and, with low charring temperatures, it is possible to distinguish prior treatment of grain with hot water. Comparison of the archaeological grain with the grain produced experimentally suggests that both archaeologieal finds represent ground grain, and at least those from Mesimeriani correspond to some type of wheat bulgur, probably intended for human consumption. These finds mark the prehistoric origins of a foodstuff widely used in Mediterranean cuisine. Further experimentation along the lines followed here would be desirable.

Coupled Aeroheating/Ablation Analysis for Missile Configurations

Abstract: A method for high-fidelity surface temperature and thermal transient calculations for missile configurations is described. The key technical requirements for these predictions are accurate heat transfer coefficient distributions as functions of time and a coupled, transient thermal solution. These requirements have been met by integrating the capabilities of two computer codes. The Maneuvering Aerotherm Shape Change Code is used to determine the convective boundary conditions based on a prescribed trajectory. At each time step, these boundary conditions are applied to the surface nodes. The Charring Material Thermal Response and Ablation Program is used to determine the conduction of heat into the body, the charring of the materials, and ablation from the surface during the time step. This explicit coupling is continued throughout the entire flight. The methodology is verified with comparisons to the arc heater and flight-test data. A final demonstration of the code's capability is shown with a lethality sled test on an airframe prototype subjected to multiple environmental mediums (air/helium).

A model of opposed-flow flame spread over charring materials

Abstract: This paper presents a theoretical description of a diffusion flame spreading against the wind on a semiinfinite charring solid. It extends the previous flame spread models on “vaporizing” solids to charring materials like wood and provides a realistic description of the gas phase. To make the problem analytically tractable, a mixture fraction approach is used in the gas phase and the no-slip boundary condition is satisfied only for x >0. In the solid phase, the charring solid is assumed to decompose abruptly (endothermically or exothermically) into char and fuel gases at a specified pyrolysis temperature. The steady-state coupled elliptic equations for conservation of energy, mixture fraction, and momentum in the gas phase and conservation of energy in the char and the pristine solid are solved by using orthogonal parabolic coordinates. A general analytical solution is presented that reduces to de Ris's flame spread formula in the limit of zero char thickness and with similar assumptions. The growing char layer in the solid phase has considerable influence on the flame spread rate. It is seen that formation of a thicker char layer significantly retards the spread rate. Unique steady-state solutions for the parabolic char-material interface were found to exist only for Stefan number >−1. For Stefan number=−1 (i.e., exothermic), two solutions were found. One of these solutions corresponds to the location of the char-solid interface at infinity, indicating the likelihood of a thermal runaway. This happens regardless of the property values.

Numerical Analysis of Charring Ablation for Ablative Materials of Re-Entry Capsules.

Abstract: A computer code for charring ablation and thermal response analysis has been developed for simulation of one-dimensional transient thermal behavior of multi-layer stack of isotropic charring ablation materials used for re-entry capsules. Mathematical model of charring ablation including governing equations is summarized. Analytical solutions of several thermal response problems with or without ablation agreed very well with numerical results that are obtained with the charring ablation analysis code. Arc-heated tests of CFRP ablator models were carried out and measured results including temperature response data were compared with the simulation results of the ablation analysis code. Test results and the simulation results agreed very well. These results show that the analysis code based on the present mathematical model are available for the thermal response prediction of CFRP ablator used in the re-entry capsules such as USERS/REM.

Energetic utilization of used tires

Abstract: In this study, used tire pyrolysis experiments were performed in a captive sample reactor, at atmospheric pressure, under a helium atmosphere. The effects of temperature on the yields and composition of the pyrolysis products were investigated. Char yield decreased with the temperature of pyrolysis, while total gas yield increased. Tar and liquid hydrocarbons increased slightly with temperature. Experiments combined with a first-order kinetic model allowed the estimation of the kinetic parameters for total weight loss. The char produced by pyrolysis was burned and its reactivity was measured as a function of pyrolysis temperature. It was found that there was a decline in reactivity for charring temperatures above 650°C and that char produced at low pyrolysis temperature is preferable for medium heating value solid fuel uses.

A moving grid model for the pyrolysis of charring materials

Abstract: This paper describes a one dimensional moving grid model for the pyrolysis of charring materials. In the model, the solid is divided by a pyrolysis front into a char and a virgin layer. Only when the virgin material reaches a critical temperature it starts to pyrolyse. The progress of the front determines the release of combustible volatiles by the surface. The volatiles, which are produced at the pyrolysis front, flow immediately out of the solid. Heat exchange between those volatiles and the char layer is taken into account. Since the model is used here as a stand‐alone model, the external heat flux that heats up the solid, is assumed to be known. In the future, this model will be coupled with a CFD code in order to simulate fire spread. The char and virgin grid move along with the pyrolysis front. Calculations are done on uniform and on non‐uniform grids for the virgin layer. In the char layer only a uniform grid is used. Calculations done with a non‐uniform grid are about 3 times faster than with a uniform gird. The moving grid model is compared with a faster but approximate integral model for several cases. For sudden changes in the boundary conditions, the approximate integral model gives significant errors.

Analyses of TeflonTM Surface Charring and Near Field Plume of a Micro-Pulsed Plasma Thruster

Abstract: : The Teflon(TM) ablation in a micro-Pulsed Plasma Thruster is studied with an aim to understand the charring phenomena. Microscopic analysis of the charred areas shows that it contains mainly carbon. It is concluded that the carbon char is formed as result of carbon flux returned from the plasma. A simplified model of the current layer near the Teflon(TM) surface is developed. The current density and the Teflon(TM) surface temperature have peaks near the electrodes that explain preferential ablation of these areas as was observed experimentally. The comparison of the temperature field and the ablation rate distribution with photographs of the Teflon(TM) surface shows that the area with minimum surface temperature and ablation rate corresponds to the charring area. This suggests that the charring may be related to a temperature effect. Electron densities predicted by the plume model are compared with near field measurements.

Portable kiln for making charcoal from forestry wood waste

Abstract: A portable kiln is transported to a site of logging where there is significant wood waste. At the site, wood waste is collected. The portable kiln is assembled as it is being loaded with wood waste. Once the portable kiln is assembled it is lit with all air intakes open. When combustion is complete and charring begins, some of the air intakes are closed. When charring ends, all of the air intakes and exhausts are closed to permit the kiln to cool down.

Process for preparing activated carbon from bamboo

Abstract: An activated bamboo carbon is prepared from choosing raw material, loading raw material in kiln, smoking for dewatering, dry distilling for charring it, refining, spraying steam and sealing kiln. Itsadvantages are physically activating it thoroughly, high adsorbability and electric conductivity, high output rate and no environmental pollution.

Performance Analysis of Thermal Protection System of a Solid Rocket Nozzle

Abstract: A coupled approach is adopted to solve the conjugate problem of fluid flow and heat transfer in solid rocket nozzles in order to achieve an optimum thermal protection system (TPS). The computational fluid dynamics (CFD) code to solve the Navier-Stokes equations for fluid flow in a rocket nozzle is coupled with the charring material ablation code through an energy balance at the active surface of the wall material. The present analysis compares well with the test results generated in-house as well as those reported in the literature.

Side-jetting non-recovering coke oven

Abstract: The utility model discloses a side jet-type non-recovery coke oven and is characterized in that a combustion chamber is provided beneath the bottom plate of a charring chamber; the combustion chamber is a four-cavity arch-shaped one with an air passage longitudinally provided at the bottom, the air passage being communicated with the combustion chamber; each two combustion chambers are combined in pair and isolated by a partition and a coal gas hole is provided at the end of the partition; an air cooling passage is arranged beneath the bottom plate of a charring chamber; walls are provided respectively at two sides of he charring and combustion chambers; a lateral U-shaped passage for raw coal gas is arranged inside the wall and communicated with the charring and combustion chambers; and the coke oven body is positioned on a coke oven body base plate. The utility model has the advantages that the charring chamber works under a negative pressure condition and raw coal gas and volatile substances produced in the charring chamber are all burned, thereby avoiding the recovery of coking byproducts and the pollution to water. The utility model realizes pollution-free coke production.

Installation used for continuous destructive distillation and carbonization

Abstract: A device of continuous carbonization and charring belongs to the industrial furnace field and is characterized in that carbonization and charring can be conducted continuously. The device adopts a carbonization chamber (1) with a channel feed inlet (5) and the top adopts a connecting pipeline to send carbonized air into a heating and cooling system. The bottom of the carbonization chamber (1) is a tilted rectangle and the terminal of the bottom is connected with an outlet leading to a charcoal-receiving chamber (4) or a combustion chamber (2). The bottom of the combustion chamber (2) is an upside-down trapezoid inclining towards a plant-ash receiving container (3) and the rear of the combustion chamber (2) is connected with a flue (9) and a chimney (10).

Method and device for manufacturing activated charcoal

Abstract: PROBLEM TO BE SOLVED: To provide a method and a device for efficiently manufacturing activated charcoal, which is an inexpensive charcoal having high surface activity suitable for environmental clean-up or the like. SOLUTION: This method comprises detecting by a thermocouple a centrosphere temperature of a treated material 21 which is a raw material for charcoal and changing or controlling the volume of combustion emission gas supplied to a carbonizing furnace 2 as heat source so that the detected centrosphere temperature meets the programmed characteristics of temperature change set separately in respective processes for drying, thermal decomposition, charring, carbonization/activation and forcibly cooling. In the carbonization/activation process, combustion emission gas is supplied together with activation gas such as air and steam to simultaneously carry out carbonization and activation treatments. In the forcibly cooling process, cooling gas is repeatedly supplied into the carbonizing furnace to forcefully lower the treated material's temperature. When the treated material's temperature is lowered to about 150 deg.C, cooling water is sprayed in the carbonizing furnace while supplying cooling gas to accelerate cooling speed and shorten the time required for cooling.

Grain base medicine active carbon

Abstract: A medical activated carbon is prepared from non-polluted grains (corn, millet, yellow rice, rice, wheat, etc) through screening raw material, charring or calcining by isolating air, activating with steam, and post treating.

Device against overflow and burning of cooker

Abstract: A device for household cookers which can avoid spilling and charring comprises a thermoelectric generator, a power supply processing circuit, a spill adjusting and signal processing circuit with a spill avoiding sensor and a charring adjusting and signal processing circuit with a charring avoiding sensor which are arranged on the cooker in seal. The spill avoiding sensor is arranged in the cooker and is connected with the spill adjusting and signal processing circuit by a conductor. The utility model is characterized by safety, convenience, spilling and charring avoiding. When in use, traditional operations need not to be changed and to be watched by people, and automatic alarming is available when unusual cases appear, and the utility model need no battery or power supply and has water-proofing and high temperature resistant performance and reliable and durable structure.

Method for charring agricultural product material

Abstract: PROBLEM TO BE SOLVED: To provide a method that an agricultural product material can be well charred so as to effectively use agricultural products such as bamboo shoot. SOLUTION: An agricultural product material is housed in a refractory container 38 which is made of a mesh-like plate material or of a plate material having many small holes and which can be closed. The refractory container is then closed and located in a combustion kiln 10. The agricultural product material is charred in the combustion kiln as sealed while air is supplied into the kiln in a controlled supply amount. COPYRIGHT: (C)2004,JPO