Endothermic Gasification Research Articles

Thermal pattern formation and process intensification in chemical reaction engineering

This contribution contains an overview on process analysis and process development in the field of fixed-bed processes for gas–gas and gas–solid reactions. The examples are mainly taken from the work performed during the last 20 years at the Institut für Chemische Verfahrenstechnik in Stuttgart. Its main intention is to show how process analysis and process intensification can benefit from the simplified representation of typical thermal reaction front patterns which evolve in such reactors. Favourable patterns should be used as natural building blocks for the robust design of integrated processes. The processes considered include heat integrated processes for exothermic and endothermic gas–gas reactions as well as exothermic gas–solid reactions, with a special view on automotive Diesel exhaust purification.

Hydrodynamics of an endothermic gas with application to bubble cavitation

The hydrodynamics for a gas of hard spheres which sometimes experience inelastic collisions resulting in the loss of a fixed, velocity-independent, amount of energy Delta is investigated with the goal of understanding the coupling between hydrodynamics and endothermic chemistry. The homogeneous cooling state of a uniform system and the modified Navier-Stokes equations are discussed and explicit expressions given for the pressure, cooling rates, and all transport coefficients for D dimensions. The Navier-Stokes equations are solved numerically for the case of a two-dimensional gas subject to a circular piston so as to illustrate the effects of the energy loss on the structure of shocks found in cavitating bubbles. It is found that the maximal temperature achieved is a sensitive function of Delta with a minimum occurring near the physically important value of Delta approximately 12,000 K approximately 1 eV.

Gasification of Kentucky bluegrass (Poa pratensis l.) straw in a farm-scale reactor☆

A novel gasification reactor was designed for conversion of grass straw to synthesis gas. Our design goal was to improve synthetic gas yield and thermal stability at a scale suitable for on-farm use at a cost similar to that of a combine harvester. The reactor that was constructed and tested in this study follows the newly emerging design technique whereby the endothermic pyrolysis or gasification and exothermic char combustion co-exist in the same reactor. It operates in a dual mode where straw gasification occurs in the annulus of an outer tube and an inner (draft) tube. Our trials established that the dual-mode operation could be performed without material flow problems. Sustained tests demonstrated reactor stability at gasification temperatures up to 650 °C and successful gasification of Kentucky bluegrass straw utilizing combustion heat from the inner tube. Calculated equivalence ratios of combustion in the inner tube ranged from 0.3 to 0.78 indicating fuel lean combustion of residual char without slagging. Carbon conversion ranged between 35.4 and 44.8%. Energy recovery, estimated as the ratio of the heat of combustion of the gas to that of the dry-ash-free feedstock, ranged from 14.7% to 30.92%. The estimated heating value for the synthesis gas ranged from 1.27 to 2.85 MJ m−3. Although these conversion parameters are low, a proof of the design concept was established. They can be improved with little modification by increasing the residence time in the draft tube and complete isolation of the gaseous products of combustion and the gasification. More tests are required to evaluate the economic feasibility of the farm-scale unit.

A Novel Process of Biomass Gasification for Hydrogen-Rich Gas with Solid Heat Carrier: Preliminary Experimental Results

A new process of biomass gasification with a catalytic solid heat carrier is proposed that is called the ECCMB (external circulating concurrent moving bed) gasification system. The system is composed of a moving-bed gasification zone and a combustion zone. A circulation loop of bed material, which acts as catalyst and heat carrier, is achieved between these two zones. The char circulated with the bed material and the cokes deposited on the catalyst are burned off in the combustion zone to regenerate the catalyst and provide the energy for the endothermic gasification reactions with steam in the gasification zone. A lab-scale facility was established to demonstrate this process concept, where steam gasification of biomass and combustion of the produced char can occur simultaneously. The H2 content of 53.3 mol % in dry gas and the tar yield of 0.7 g/Nm3 dry gas can be obtained at a bed height of 400 mm and an S/B ratio (steam/biomass mass ratio) of 0.4 g/g at 800 °C with calcined olivine as the catalyst. Th...

Transient radiative heat transfer within a suspension of coal particles undergoing steam gasification

Transient radiative heat transfer in chemical reacting media is examined for a non-isothermal, non-gray, absorbing, emitting, and Mie-scattering suspension of coal particles, whose radiative properties vary with time as the particles undergo shrinking by endothermic gasification. A numerical model that incorporates parallel filtered collision-based Monte Carlo ray tracing, finite volume method, and explicit Euler time integration scheme is formulated for solving the unsteady energy equation that couples the radiative heat flux with the chemical kinetics. Variation of radiative properties, attenuation characteristics, temperature profiles, and extent of the chemical reaction are reported as a function of time. It is found that radiation in the visible and near IR spectrum incident on a cloud of coal particles greater than 2.5μm is more likely to be forward scattered than absorbed, but the opposite is true as the particles shrink below 1.3μm. The medium becomes optically thinner as the particles shrink and this effect is more pronounced for smaller initial coal particles because these offer higher volume fraction to particle diameter ratio and, consequently, attain higher temperatures, reaction rates, and shrinking rates.

1020 AISI-SAE steel Austenitic Nitrocarburising with alcohol and triethanolamine

The present work shows AISI-SAE 1020 steel’s nitrocarbide layer’s microstructure and micro-hardness profile following 4 hours at 700°C using methanol, isopropanol and triethanolamine. The steel was then hardened by quenching it in water and then tempered at 350°C for 1 hour. Its surface had been partially oxidized by heating it at 400°C for 1 hour. An example is given of other researchers analyzing microstructure and properties in steel having 0.5% C, using endothermic gas and different amounts of ammoniac.

The role of endothermic gasification in propellant ignition

This study explores a reactor model designed to describe the decomposition, ignition and combustion of energetic materials in combination with real experimental data for these energetic materials. Spatial uniformity is initially assumed which reduces the system of partial‐differential‐equations to a system of ordinary‐differential‐equations that can be easily solved numerically. The phase‐plane is explicitly presented and examined to illustrate how chemistry and temperature evolve in time. The computations provide an understanding of the vast different timescales that exist and illustrate the singularity structure. Following this the effect of including this chemical regime in an environment typically induced by the combustion of these materials, that is within a compressible fluid flow, is pursued.

04/00710 Conversion of coal to hydrogen by integrating the exothermic and endothermic gas production and separation reactions in gasifier: Lin, S. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2003, 48, (1), 462–463

04/00710 Conversion of coal to hydrogen by integrating the exothermic and endothermic gas production and separation reactions in gasifier: Lin, S. et al. Preprints of Symposia — American Chemical Society, Division of Fuel Chemistry, 2003, 48, (1), 462–463

Improvement in delubrication by addition of endothermic gas nitrogen-hydrogen atmosphere

Improvement in delubrication by addition of endothermic gas nitrogen-hydrogen atmosphere

Convection Effects on the Endothermic Gasification and Piloted Ignition of a Radiatively Heated Combustible Solid

A study is presented on the effect of convective conditions on the endothermic gasification and subsequent ignition of a slab of solid material heated by a radiant flux. A simple solid-phase thermal model is numerically integrated to approximately reproduce results of a previous experimental study of piloted ignition. The model is formulated in terms of the transient energy equation including endothermic Arrhenius-type pyrolysis and Beer-law in-depth absorption of the radiant flux. Temperature evolution curves are obtained for different values of the heat flux and convective coefficient, and are shown to accurately predict experimental surface temperature measurements prior to ignition. Material gasification rates are calculated and used in conjunction with the experimental ignition results to show that the piloted ignition delay closely corresponds to the time required by the solid to reach a critical value of the gasification rate. The critical gasification rate is nearly constant and independent of the heat flux for given convective conditions, and increases linearly with the convective coefficient. It is shown that the graphs of piloted ignition delay vs. heat flux may be accurately determined from this critical gasification criterion. Finally, a non-dimensional parameter that represents the relative amount of gasified fuel transported by the oxidizer stream is presented as a suitable measure of the flammability of the material.

Gas exchange potential in reptilian lungs: implications for the dinosaur–avian connection

The theory that birds evolved from a group of small terrestrial theropod dinosaurs has created much controversy. One argument proposed against this theory is that the lungs of early theropods were incapable of sustaining endothermic gas exchange requirements and could not have given rise to the lungs of birds. A reexamination of the comparative physiological and morphological literature combined with a theoretical analysis of gas exchange potential indicates that non-avian lungs would not constrain the gas exchange requirements of early endotherms. Furthermore, our analysis suggests that factors besides diffusive gas exchange were important in the evolution of the distinct morphology of the highly effective avian and mammalian lungs.

Betriebserfahrungen bei der Nutzung hoher Kohlenstoffübergangszahlen und deren sinnvolle Einsatzgrenzen bei der Gasaufkohlung

The speed of the carburization process depends very strongly on the atmospheric system used. Endothermic gases and synthetic endothermic gas substitution systems (e.g. N 2 -methanol) have proven their worth in the past and won general acceptance. These systems have a carbon transfer rate β of 1.2-1.3.10 -5 cm/sec. A significant prerequisite for an increase in the speed of carburization at identical temperature and carbon levels lies in an increase in the carbon transfer rate β. Theoretically it can be raised to 3.1.10 -5 cm/sec. The possibilities and limits of application of such atmospheric systems are examined more closely below with regard to generation and the system technology used. Experiences by practical operation show that, subject to the necessary boundary conditions, using high β-values in many cases leads to the results already known from theory (reduction in the carburizing time required). The potential time gain is sometimes considerable, especially in the case of small carburization depths.

Sintering of steel parts in endothermic gas and nitrogen-hydrogen atmospheres: J.G.Marsden et al. (Air Products and Chemicals Inc, USA.)

The design and testing of a new isothermal flow gas calorimeter is described. The calorimeter achieves complete combustion of the natural gas at temperatures from 400 to 500°C using a bed packed with a proprietary catalyst. The catalyst is 100% efficient for mixtures containing all of the typical natural gas components (C1-C6). The calorimeter assembly consists of a flow reactor that is suspended in a high temperature air bath. The temperature sensors for both reactor and shield temperature measurement or control are Pt RTDs. The gas is delivered by a cycling sample loop with constant volume and a lean gas/air mixture is supplied to the reactor. The gas sample net heating value (NHV) is determined from the gas flow rate required to maintain a constant reactor temperature. The water content in the exhaust is measured to obtain the gross heating value (GHV). All operations of the calorimeter including periodic calibration and reporting of heating values, specific gravity, and compressibility data are automated.The calorimeter makes energy measurements with an accuracy of ±1 BTU ft−3 and a precision of 0.5 BTU ft−3 for gas samples having gross heating values ranging from 800 to 1200 BTU ft−3. The calorimeter measures both the net and gross heating values. The mol. percent inerts, specific gravity, and compressibility are calculated by use of empirical correlation equations relating these properties to the net and gross heating values. The gas calorimeter has been packaged for field operation and operation in areas with potentially combustible atmospheres. The field performance of the gas calorimeter is compared with both an on-line gas Chromatograph and a Cutler-Hammer calorimeter.

Feasibility assessment of an endothermic gas generator-built-in fluidized bed furnace

Advantages of the fluidized bed furnace are claimed to be the rapid heating rate, fast atmosphere purging speed and good temperature uniformity. However, it consumes enormous amounts of fuel gas and the atmosphere composition in the bed is unstable because of direct boosting of fuel gas and air from the bottom of the bed. As a result, the effective treating zone of the bed is too narrow for applying the fluidized bed to high-quality carburization or bright heat treatment of steel. An endothermic gas generator-built-in fluidized bed furnace constructed with a catalytic zone in the lower part of the furnace was studied in this research. The fuel gas and air were stoichiometrically mixed and endothermically reacted in the catalytic zone before the product gases were guided upwards into the bed so as to acquire a stable endothermic atmosphere. The results showed that it substantially enlarged the effective working zone of the furnace, which made the precise carburization and/or bright heat treatment of steels possible in the fluidizing bed furnace. In order to simulate the high humidity season of the year in subtropical settings, the incoming air for reforming the endothermic atmosphere was further moistened according to the humidity of the rainy season and the results were compared with those of the theoretical computer calculations.

Using a catalyst in natural-gas conversion for preparing endothermic gas in the volzhskii automonile plant

Special catalysts are used to accelerate the conversion of natural gas in the converter of the generator for preparing protective endothermic atmospheres. VAZ has tested and introduced a catalyst of protective atmospheres (KZA) produced by the Novomoskovsk Branch of the State Institute of the Nitrogen Industry (GIAP) instead of the GIAP-25 catalyst used previously. The KZA catalyst is a promoted lower nickel oxide deposited on a large-pore carrier (cubic particles 17 mm in size) made of a chamotte-pearlite lightweight refractory of grade ShL-04 produced by the Vnukovskii Refractory Plant. During the eight years of employing this catalyst in VAZ its stability decreased from 1.5 years to 1.5 -4 weeks. The operating capacity of a catalyst usually decreases due to its break up into a dust-like state, which markedly decreases the penetrability of the process gases through the converter. The present paper is devoted to the causes of the low stability of the KZA catalyst and suggests ways to improve it.

分解アンモニア雰囲気下における鉄系圧粉体の寸法変化におよぼす焼結条件の影響

dimensional change behavior of the system Fe-2wt%Cu-0.8wt%C-0.75wt% zinc stearate was investigated under an atmosphere of dissociated ammonia and the results were compared with those of endothermic gas. sintering process was divided into three stages ; delubricating, heating and cooling, and the sintering conditions were varied in each stage.The decrease in the heating or cooling rate and the increase of dew point in an atmosphere caused shrinkage at all the stages. These behaviors in dissociated ammonia were very simple and in numerous cases differed from those in endothermic gas. shrinkage was mainly caused by the decarburization, which began soon after reaching maximum temperature. The modified carbon transfer theory can be also considered to be appliciable to other sintering atmospheres. This theory is that the carburization during temperature rise contributes to the shrinkage but after reaching maximum temperature it contributes to the expansion and that the decarburizing have an opposite action of the carburizing.

鉄系圧粉体の脱ろう過程における異状膨張機構

In order to investigate the mechanism of abnormal expansion observed during delubrication of Fe-Cu-C-Zn-st compacts above 500°C, two extreme conditions were selected. Delubricating condition at a dew point of -35°C, a heating rate of 10°C/min and a holding time of 600°C×60 min in endothermic gas, in which specimen has shown the largest expansion, was compared with the same condition in argon, in which no expansion has been observed.Abnormal expansion was not caused by vapour pressure of zinc stearate nor deposition of soot but by a lot of fine cementites formed on the surface of iron powders in compacts. The carbon for cementite is supplied by Boudouard reaction and decomposition of methane in endothermic gas. The de-composition residue of zinc stearate, such as zinc oxide plays an important role as a catalyst in this process. The cementite is directly formed as equilibrium phase, because the carbon solubility in ferrite phase is little.

鉄系圧粉体の焼結時の寸法変化におよぼす脱ろう条件の影響

The influence of delubricating conditions on dimensional change of the compacts of the system Fe-2wt%.Cu-0.8wty.C-0.75wt%.Zn-st was examined under an atmosphere of endothermic gas. An abnormal expansion, which increases under slower heat pattern and atmosphere of lower dew point, occurred above about 500°C. As this expansion becomes larger, copper growth decreases, the shrinkage becomes larger and carbon content after sintering becomes higher.The diffusion of carbon is greatly influenced by delubricating conditions but that of copper is little. The delubrication in Ar, N2, H2 and dissociated ammonia atmosphere makes the sintering behaviors and sintered properties stable. In the case of endothermic gas, the similar tendency is observed at the rapid delubrication under the high dew point atmosphere.

鉄系圧粉体の焼結時の寸法変化におよぼす加熱，冷却条件の影響

The dimensional changing behavior of the system Fe-2wt%.Cu-0.8wt%C-0.75wt% zinc stearate under an atmosphere of endothermic gas was investigated. The decrease of heating rate causes shrinkage and the decrease of cooling rate causes expansion. On the other hand, the influence of the dew point on dimensional change is also in accordance with tendency of heating and cooling rate. It became clear by two model experiments that the compacts shrink with carburizing during heating and expand during cooling.In this way, dimensional change depends on carburization, but the behavior observed during heating differs from that during cooling. Authors proposed the new transfer theory . When this theory was applied to various sintering phenomena, experimental results could be explained well. In order to solve problems during the sintering process, it must be important to consider the stage where carbon transfer occurrs.

Corrosion of Sic Materials in N2–H2–CO Gaseous Environments: I, Thermodynamics and Kinetics of Reactions

Two sintered SiC materials and a siliconized SiC materials were exposed to two gas compositions in the N2–H2–CO system at 1000°–1350°C, 133 Pa and 98.7 kPa for 8–1000 h. The two gases were a nitrogen‐based gas which contained 98.2% N2, 1.2% H2, and 0.6% CO; and an endothermic gas which contained 37.8% N2, 41.1% H2, and 21.1% CO by volume. Thermodynamics of reactions were modeled using the program SOLGASMIX. Kinetic studies were based on weight change measurements obtained from vacuum TGA and long‐term tube–furnace experiments. In the case of a siliconized SiC, reactions were complex, owing to its two phase composition and to the presence of impurities. Under many conditions, silicon was rapidly etched from the surface of the siliconized SiC during a short initial period due to the formation of SiO and carbon or SiO and β‐SiC. In the case of sintered mateials (and the siliconized material during the later stages of corrosion), etching of SiC was observed under many of the conditions studied, due to the apparent formation of SiO, HCN, and/or carbon. Corrosion in an endothermic gas was typically more severe than in a nitrogen‐based gas, due to its higher Pco.