Tube Furnace Experiments Research Articles

Determination of coal gasification kinetics from integral drop tube furnace experiments with steam and CO2

Lab scale drop tube furnace reactors with conditions similar to large-scale gasification reactors are able to generate applicable reaction-kinetic expressions for reactor simulation and dimensioning. In the present work, a method is introduced to determine reaction kinetic parameters from integral drop tube furnace experiments. A one-dimensional model of the gasification process was developed incorporating the influence of reaction gas composition, char particle structure change, pore diffusion and gas phase reaction. Suitable kinetic parameters were determined by fitting the gasification model to experimental data. Gasification experiments with gas mixtures of steam, carbon dioxide, carbon monoxide and hydrogen were carried out in an isothermal pressurized drop tube furnace reactor at 6 bar total pressure and temperatures of 900–1100 °C. It was shown that the determined kinetic expressions fit the experimental data. The best fit to the experiments was achieved by application of a Langmuir-Hinshelwood type rate expression with respect to product gas inhibition. Integrating a pore diffusion model did not improve the fitting quality.

Utilization of semi-dry sintering flue gas desulfurized ash for SO2 generation during sulfuric acid production using boiling furnace

To effectively solve the problem of reutilizing semi-dry sintering flue gas desulfurized ash (SSFGDA) from steel plants, a new technology is proposed in this paper in which ash is added to a boiling furnace to obtain SO2 during sulfuric acid production. Using thermodynamics and simulation calculations, the high-temperature characteristics of CaSO3 in the ash were preliminarily investigated. By using Kissinger method and the models of Achar and Coats-Redfer, the decomposition kinetics equation of CaSO3 in the ash were obtained. The decomposition characteristics of CaSO3 in the ash were further investigated by thermogravimetric analysis (TGA) and drop tube furnace (DTF) experiments. The results show that at temperatures below 400°C, free water is lost and Ca(OH)2 decomposes, whereas at approximately 460°C, part of the CaSO3 is oxidized. Above 680°C, CaCO3 begins to decompose, with the decomposition process terminating at 790°C. The remaining CaSO3 continues to decompose at approximately 810°C. The activation energy of CaSO3 decomposition is 261.45±77.93kJ/mol; the pre-exponential factor is expressed as ln(A/s−1)=26.13±7.29, and the kinetics equation is dα/dt=2.19×1011×exp(−3.11×104/T). Pressure, temperature and oxygen content are the key factors affecting the decomposition of CaSO3 in the ash. A lower pressure and oxygen content and a higher temperature can facilitate the decomposition of CaSO3 and can be achieved in actual sulfuric acid processing plants. Therefore, in this study, the feasibility of preparing SO2 by adding desulfurized ash during the production of sulfuric acid using a boiling furnace was preliminarily examined and verified.

Migration and Distribution of Heavy Metals During Co-combustion of Sedum plumbizincicola and Coal

Co-combustion is considered one of the most promising disposal techniques for Sedum plumbizincicola and coal. However, the distribution of heavy metals (Cd, Zn and Pb) in this incineration is still not determined. Tube furnace experiments were conducted to investigate the effects that burning temperature, atmosphere and mixing ratio impacted on the distribution of heavy metals. XRD analysis was performed to study the speciation characteristics of heavy metals in bottom ash. The results indicate that high temperature is beneficial to the volatilization of heavy metals with the order of Pb > Cd > Zn. With increasing oxygen content, the distribution of Zn and Cd in bottom ash is more, while Pb concentration is initially increased and then decreases. Increase in the proportion of S. plumbizincicola is not conducive to the stabilization of Zn and Pb, but is conducive to the disposal of Cd. The calculation results of HSC Chemistry demonstrate that increasing temperature significantly increases the volatilization of Cd and Pb in the form of Cd (g) and PbO (g). In oxygen atmosphere, Zn exists in the form of heavy metal oxides, not easy to volatilize. Under anaerobic condition, Zn begins to volatilize as Zn (g) and oxygen is not conducive to the volatilization of Zn. The co-combustion in air condition is proved to be beneficial to the disposal of heavy metals.

Detailed kinetic modelling of H2S oxidation with presence of CO2 under rich condition

This paper presents a detailed kinetic study of H2S oxidation with presence of CO2 under fuel rich condition. Effect of CO2 reactivity on the partial oxidation of H2S was particularly studied via tube furnace experiment and detailed kinetic analysis with CHEMKIN-PRO software. A detailed kinetic model involving 90 species and 596 reactions was developed and validated using experimental data with respect to production of H2, and conversions of CO2 and H2S under different conditions by altering the initial gas composition temperature and residence time. In the tube furnace experiment, it was found that decomposition of H2S and conversion of CO2 were promoted by increase in temperature while H2 production decreased and CO concentration evidently increased at temperature higher than 1450K, which could be explained by CO2+H=CO+OH. The degree of this reaction as features the major reactivity of CO2 is obviously dependent on residence time whilst H2S partial oxidation proceeds much swiftly at 1473K or higher temperature. In addition to the experiment, rate of production (ROP) analysis for H2S, H and OH were performed by CHEMKIN-PRO. It was found for the partial oxidation of H2S, reactions S+SH=S2+H and SH+SH=H+HSS are important in H producing while H2S+O=SH+OH and H2O2(+M)=OH+OH(+M) are key steps for OH producing. Presence of CO2 prolonged the OH production process via CO2+H=CO+OH to the whole residence time which definitely differed from the condition without CO2. Thereby production selectivity of SO2 and H2O was promoted while that of H2 and S2 were degraded when CO2 was considerably present in the H2S partial oxidation scenario.

Kinetics of Poplar Short Rotation Coppice Obtained from Thermogravimetric and Drop Tube Furnace Experiments

This article concentrates on the kinetics of poplar short rotation coppice obtained from thermogravimetric and drop tube furnace (DTF) experiments. Three poplar samples were studied, specifically, clone AF8 from two different plantations, one located in Italy (AF8-I) and another located in Portugal (AF8-P), and clone AF2 from a plantation located in Portugal. Initially, the combustion behavior of the three clones was evaluated by thermogravimetry. For the devolatilization zone, the thermogravimetric experiments yielded apparent activation energies of 109.7, 117.7, and 118.6 kJ mol–1 for clones AF8-I, AF8-P, and AF2, respectively. For the char oxidation stage, the apparent activation energies were 267.4, 252.0, and 264.3 kJ mol–1 for clones AF8-I, AF8-P, and AF2, respectively. Subsequently, the combustion behavior of the clone AF8-I was examined in a DTF. The data reported includes gas temperature and particle burnout measured along the DTF for five wall temperatures (900, 950, 1000, 1050, and 1100 °C). Th...

Study on the Incineration Experiment to Dispose <i>Ptreis vittata</i> L<i>.</i>

Phytoextraction of heavy metal polluted environment generates large quantities of hyperaccumulators. How to dispose hyperaccumulators safely has been one of the most important issues in the phytoextraction field. In this paper, incineration technology was studied in order to investigate the feasibility of incineration technology on disposal of the arsenic-containing hyperaccumulator Pteris vittata L.. The tube furnace experiment examined the changes of arsenic in Pteris vittata L., studied the effects of factors including temperature, time, percentage of CaO on the incineration state. The results show that the most appropriate incineration condition was temperature of 400°C, time of 30min, percentage of CaO of 10%, which solved the problem to reduce biomass of Pteris vittata L. and volatilization of arsenic. The result provide insight into developing harmless disposal or resource-reuse-oriented methods for disposal of the plants used for large scale phytoremediation application.

Thermochemical reaction mechanism of lead oxide with poly(vinyl chloride) in waste thermal treatment

Poly(vinyl chloride) (PVC) as a widely used plastic that can promote the volatilization of heavy metals during the thermal treatment of solid waste, thus leading to environmental problems of heavy metal contamination. In this study, thermogravimetric analysis (TGA) coupled with differential scanning calorimeter, TGA coupled with Fourier transform infrared spectroscopy and lab-scale tube furnace experiments were carried out with standard PVC and PbO to explicate the thermochemical reaction mechanism of PVC with semi-volatile lead. The results showed that PVC lost weight from 225 to 230°C under both air and nitrogen with an endothermic peak, and HCl and benzene release were also detected. When PbO was present, HCl that decomposed from PVC instantly reacted with PbO via an exothermal gas–solid reaction. The product was solid-state PbCl2 at <501°C, which was the most volatile lead-containing compound with a low melting point and high vapor pressure. At >501°C, PbCl2 melted, volatilized and transferred into flue gas or condensed into fly ash. Almost all PbCl2 volatilized above 900°C, while PbO just started to volatilize slowly at this temperature. Therefore, the chlorination effect of PVC on lead was apt to lower-temperature and rapid. Without oxygen, Pb2O was generated due to the deoxidizing by carbon, with oxygen, the amount of residual Pb in the bottom ash was significantly decreased.

Simulation of entrained flow gasification with advanced coal conversion submodels. Part 2: Char conversion

CFD modeling results for entrained flow coal gasification using advanced submodels for coal conversion are presented and compared to detailed experimental data. The focus of this investigation is on the accurate modeling of the char conversion process. The CBK/E and CBK/G models are used for calibrating a simplified Single Nth-Order Reaction (SNOR) kinetic model, which is suitable for CFD calculations. The kinetics of the CBK/G model are fitted using char gasification data obtained from drop tube furnace experiments. CFD simulations are performed for the BYU entrained flow gasifier fired with four different coals varying significantly in rank ranging from bituminous coal to lignite. The comparison with the experiments generally gives good agreement in terms of flame stand-off, gas composition and carbon conversion when the kinetics of the CBK/G model calibrated with drop tube experiments is used. On the other hand, lower carbon conversion is obtained using the default correlation of the CBK/G model, which only allows to depict the overall tendency of the gasification reactivity with coal rank.

Transformation of aluminum-rich minerals during combustion of a bauxite-bearing Chinese coal

Abstract Samples of two high-aluminum coals and an associated fly ash were collected from a coal-fired power plant and a coalfield in Inner Mongolia, China. The mineralogy and physicochemical characteristics of low-temperature ash (LTA), high-temperature ash (HTA), and fly ash from those coals were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), and field scanning electron microscopy with energy dispersive X-ray spectroscopy (FSEM-EDX). The transformation of typical aluminum-bearing minerals at high temperature was investigated by systematic drop tube furnace (DTF) experiments and thermogravimetric analysis. The results show that the aluminum-bearing minerals in the high-Al coal are mainly boehmite and kaolinite. High temperature treatment transforms the aluminum-rich minerals to gamma alumina (γ-Al 2 O 3 ), corundum (α-Al 2 O 3 ), and an amorphous phase. γ-Al 2 O 3 is the main mineral in the HTA (17.4 wt.%), while α-Al 2 O 3 and mullite are the main minerals in the fly ash. The high-aluminum fly ash particles are irregular and their shapes are related to their compositions. The degree of irregularity of the high-aluminum fly ash particles is proportional to their aluminum content. The phase transformation of boehmite in the coal during high temperature treatment appears to have involved four stages including: boehmite dehydroxylation, transitional θ-Al 2 O 3 formation, crystal nucleation and α-Al 2 O 3 formation, and growth of α-Al 2 O 3 crystals. The DTF experimental results indicated that the growth of α-Al 2 O 3 crystals has a significant impact on PM emissions. Understanding the mineral transformation mechanism is therefore helpful in reducing PM emissions.

A generalized relationship between the normalized yields of carbon monoxide and hydrogen cyanide

Experimental studies have demonstrated that there are close correlations between the normalized yields of carbon monoxide (CO) and hydrogen cyanide (HCN) from the combustion of materials containing nitrogen. In this paper, a generalized relationship using the stoichiometric oxygen to fuel mass ratio (SOFMR) is derived to represent these correlations. Using this generalized relationship, the predicted yields of HCN for nylon in tube furnace experiments and HCN concentrations in full-scale cable fire tests are in good agreement with the corresponding measured data. The derived relationship is used to analyse the contributions of CO from different materials in a complex fire reconstruction. The generalized relationship is then used to predict HCN concentrations in two full-scale nylon fires and the predicted concentrations are compared with both experimental data and predictions from a flamelet model. Finally, a method to incorporate the generalized relationship within CFD fire simulations to determine HCN (or CO) concentrations based on measurements of CO (or HCN) yields is presented. Copyright © 2010 John Wiley & Sons, Ltd.

Identification of Compounds Formed During Low Temperature Thermal Dispersion of Encapsulated o-Chlorobenzylidene Malononitrile (CS Riot Control Agent)

U.S. Army chemical mask confidence training is conducted in an enclosed chamber where airborne o-chlorobenzylidene malononitrile (also known as CS or “tear gas”) is generated using a low temperature (150–300°C) dispersal method. CS capsules are placed onto a flame-heated aerosol generator that melts the capsules and disperses CS into the chamber. To instill confidence in chemical protective equipment, trainees are required to break the seal of their chemical protective mask, resulting in the immediate irritation of their eyes, nose, throat, and lungs. Solid phase micro extraction (SPME) sample collection techniques were used inside the chamber, followed by gas chromatography and mass spectrometry (GC/MS) to identify unintended thermal degradation products created during the CS dispersal process. The temperature of the aerosol generator averaged 257°C, and 17 thermal degradation products were identified. To characterize the relationship between temperature and the types of CS thermal degradation products formed, CS was dispersed in a tube furnace at controlled temperatures from 150–300°C and analyzed using the same method. There was a graded response between temperature and the number of thermal degradation products formed, with one product formed at 150°C and 15 products formed at 300°C. Two additional products were identified in the chamber experiment when compared with the tube furnace experiment. These products are likely the result of molten CS dripping directly into the aerosol generator's flame, which averaged 652°C. To prevent undesirable degradation products during thermal dispersion of CS, a delivery system designed to contain the molten CS and maintain a consistent temperature near 150°C is recommended.

Development of a sampling train for arsenic in pyrolysis vapours resulting from pyrolysis of arsenic containing wood waste.

In the present study a sampling and analysis method for arsenic emissions during pyrolysis of arsenic containing wood, such as chromated copper arsenate (CCA) treated wood, has been developed. The procedure is based on the NIOSH (National Institute for Occupational Safety and Health) standard for arsenic trioxide sampling. Validation for this specific application is needed since pyrolysis of arsenic containing wood leads to a gas stream containing sticky tar compounds and aerosols. Validation was carried out through tube furnace experiments using both CCA treated wood and arsenic trioxide powder as input. The outlet of the tube furnace was coupled to a cooling section and sampling train. The sampling train consisted of one or more filter sections and impingers. Different combinations of filters (untreated or impregnated) and impingers, as well as different combinations of washing solutions were tested. The different units of the sampling train were analysed by inductively coupled plasma mass spectrometry (ICP-MS) in order to determine the distribution of arsenic over the different units. For the working conditions considered (pyrolysis at 350 degrees C for 20 minutes with a nitrogen flow rate of 100 Nl h(-1)) the combination of a quartz cooling tube and a cellulose ester membrane filter impregnated with a Na2CO3-glycerol solution was sufficient to capture the arsenic. Two extra impingers (the first one containing 50 ml HNO3 1 M in the case of CCA treated wood and 50 ml NaOH 0.1 M in the case of As2O3 and the second one containing 50 ml NaOH 0.1 M) were added downstream of the filter section as backup either in case of filter failure or to check whether all the arsenic released is captured by the cooling tube and filter.

An investigation into the decomposition and burning behaviour of Ethylene-vinyl acetate copolymer nanocomposite materials

Ethylene-vinyl acetate copolymer (EVA) is a widely used material, particularly as a zero-halogen material in the cable industry. It is frequently formulated with large quantities of inorganic filler material, such as aluminium trihydroxide (ATH). Used alone, EVA is known to form a protective layer which can inhibit combustion under well ventilated conditions, though this effect is not observed when used in formulations with ATH. The incorporation of nanoscale clay fillers into EVA appears to reinforce the protective layer. The stages of the decomposition under different conditions is described both for the 10 mg (TGA) and 200 mg (small tube furnace) scales. The latter allows the residues formed to be subjected to further analysis, to elucidate the mechanism of the reduction of decomposition and flammability. Enhancements in the thermo-oxidative stability of the EVA clay material were evident from both tube furnace and TGA experiments. The polymer-organoclay materials, prepared on a two-roll mill, showed poor dispersion when studied by SEM, suggesting that a significant portion was present as a microcomposite. However, when the char was analysed by SEM, layers of protective material were clearly evident on the char surface. From XRD spectra, there was no evidence of order within the polymer-organoclay, but ordering of the outer layer of char was demonstrated. This suggests that for EVA, which melts before burning, organoclay layers become nanodisperse at the surface of the burning polymer. These materials have also been studied in the Purser furnace, designed to replicate the conditions found in fully developed fires. This allows effluent yields, such as O 2, CO 2 and CO to be determined as a function of fire condition, by controlling the rate of burning and the ventilation rate. The effect of both the nanofillers and the protective layers are reported and discussed, under different ventilation conditions. Specifically, the relationship between equivalence ratio and hydrocarbon and carbon monoxide yield is focussed upon.

Decomposition and combustion of EVA and LDPE alone and when fire retarded with ATH

Conventional thermogravimetric analysis (TGA) and a controlled atmosphere horizontal tube furnace have been used to study thermal degradation, in air and nitrogen, of ethylene–vinyl acetate copolymer (EVA) and low-density polyethylene (LDPE). The addition of aluminium oxide trihydrate (ATH) as a fire retardant was investigated. At 400 °C and at 450 °C, in both air and nitrogen, LDPE showed greater thermal stability in conventional TGA than the EVA copolymer. However, in the tube furnace experiments, at both temperatures, EVA showed comparable thermal stability to LDPE in nitrogen, and superior thermal stability to LDPE in air. This is thought to be the result of the formation of a protective layer, which is more effective at 400 °C than at 450 °C. In combination with approximately 55% ATH, the rate of mass loss of LDPE is significantly reduced at 400 °C, but the rate of mass loss of EVA is significantly increased. This may result from the evolution of water disrupting the protective layer. At 450 °C, ATH reduces the rate of mass loss of both LDPE and EVA to a similar extent in the absence of a coherent protective layer. © 2000 Society of Chemical Industry

Waste minimization pretreatment via pyrolysis and oxidative pyroylsis of organic ion exchange resin

Pyrolysis and/or oxidative pyrolysis of organic ion exchange resins and other combustible waste may be effective pretreatment processes before vitrification. To further examine these processes, organic ion exchange resins were pyrolyzed or oxidatively pyrolyzed with the use of a small-scale, commercial TGA. Volatilization of the anionic and cationic resins was observed separately for each resin as a function of temperature for pyrolysis and oxidative pyrolysis conditions. The quantity of remains or residue was found to be dependent on the method employed. Three different methods were examined with the TGA to pretreat the resins: pyrolysis; oxidative pyrolysis; and oxidative pyrolysis of ash remaining after the pyrolysis of resin. The latter two methods were found to provide better volume reduction than the pyrolysis-only process. Between the two types of resins, cationic and anionic, the cationic exchange resin was less volatile. Pyrolysis and oxidative pyrolysis of mixed resin (50% cation and 50% anion by wt.) showed volatilization at the temperatures where volatilization was observed for each of the separate resins. Because of certain limitations of the commercial TGA, tube furnace experiments were performed, generally, to examine the pyrolysis of larger quantities of cationic, anionic, and mixed resin, and to examine off-gas characteristics. The cationic resin-only and anionic resin-only gravimetric results showed good agreement with the smaller-scale TGA results. SEM pictures of the different variants of the resin (cationic, anionic, and mixed) show a different morphology for each. Off-gas data showed the presence of H 2S, SO 2, CO, and NO during the pyrolysis of cationic resin. CO was observed during the pyrolysis of anionic resin. The mixed resin trials showed the presence of the gases approximately at the temperatures where the gases would evolve if the results of the two different resins (cationic and anionic) were superimposed. However, the amount of hydrogen sulfide relative to the sulfur dioxide was found to increase significantly compared to the results of the cationic resin-only trials.

Distributed activation energy model of heterogeneous coal ignition

We present a model that simulates the conventional tube-furnace experiment used for ignition studies. The Distributed Activation Energy Model of Ignition accounts for particle-to-particle variations in reactivity by having a single preexponential factor and a Gaussian distribution of activation energies among the particles. The results show that the model captures the key experimental observations, namely, the linear increase in ignition frequency with increasing gas temperature and the variation of the slope of the ignition frequency with oxygen concentration. The article also shows that adjustments to the model parameters permit a good fit with experimental data.

Reduction of tungsten oxides with carbon. Part 2. Tube furnace experiments

Further information on the kinetics and mechanism of the reduction of WO 3 with carbon (in the form of graphite and of lamp black), complementing the results obtained in Part 1 using isothermal thermogravimetry in the temperature range 935–1100°C, was obtained using larger sample masses (up to 5 g) heated isothermally in flowing argon in a tube furnace (935–1060°C). The amounts of CO and CO 2 in the evolved gas were determined using infrared gas detectors. Results obtained supported the proposed two-stage reduction to W metal, via WO 2. The rate of reduction was influenced by the flow rate of argon, the CO CO 2 ratio in the product gases, the form of the carbon used, and the WO 3 carbon ratio. From kinetic data obtained from tube furnace experiments, an activation energy of 374 ± 2 kJ mol −1 was calculated for the diffusion-controlled first stage of the reduction with graphite. Lamp black was less reactive than graphite at the temperatures studied. Activation energies of 386 ± 9 kJ mol −1 and 465 kJ mol −1 were calculated from TG experiments for the reduction with graphite and lamp black, respectively. The gravimetric measurements from the tube furnace experiments were insufficient to analyse the kinetics of the second stage of reaction.

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.