Experimental Furnace Research Articles

Influences of the Introduced O-Containing Functional Groups on the Gaseous Pyrolysis Product of Superfine Pulverized Coal

An O-containing structure in coal can affect the pyrolysis process; however, the influence of the introduced O-containing functional groups has rarely been investigated. To study this issue, two kinds of representative coal were selected for superfine pulverization and chemical oxidation. The 13C-NMR and FTIR experiments demonstrated that O-containing functional groups, such as carboxyl, could be added into the carbon skeleton after 5 wt% peracetic acid modification. It was found that 1 wt% and 5 wt% hydrogen peroxide solutions had no such ability, but the 1 wt% solution could expand the pore structure and increase the specific surface area. Thermogravimetric experiments in the air showed that peracetic acid oxidation could increase the weight loss rate below 400 °C and reduce ignition temperatures. Pyrolysis experiments in the tube furnace proved that the amount of CO released increased and the commencing temperature decreased by 50 °C after the modification of peracetic acid. The generation paths of C2H4 and C6H6 changed; new generation peaks appeared near 200 °C. It has been strongly confirmed that superfine pulverization and chemical oxidation modification has obvious synergistic effects on the introduction of O-containing functional groups, especially for anthracite samples.

CO2 gasification of dry quenching dust ash catalyzed in situ by soot

It's imperative to reduce the CO2 emissions in iron and steel manufacturing and improve the reaction rate of the CO2 gasification of dry quenching dust ash (DQDA). In this study, a new technology is proposed in which the CO2 gasification of DQDA is catalyzed by high-temperature soot (HS) in the high-temperature flue gas of a converter. In the experiments, a composite catalyst (FeO: Fe2O3 = 5:2) was used to stimulate the main Components of HS. The influence of the main components of HS (FeO, Fe2O3) on DQDA gasification with CO2 was evaluated by thermodynamic simulation calculation (FactSage 6.1), thermo-gravimetric analysis, and drop-tube furnace experiments at high temperatures. In addition, the catalytic efficiency was quantitatively evaluated by the α and β values, LHVs, and kinetic analyses using homogeneous and shrinking-core models. The results indicated that the HS has significant catalytic effects on the CO2 gasification of DQDA, and exhibited differing characteristics. The catalytic efficiency increased with temperature. At 1200 °C, the consumption of CO2 was increased from 24.13% without a catalyst to 30.76% with the HS composite catalysts. As a result, Fe, FeO, and Fe3C were the most common solid products catalyzed by HS. Experiments proved the new technology's practicality.

Study on crack healing performance of Al2O3/SiCw/TiSi2 new ceramic tool material

In consideration of the crack sensitivity in ceramics, a new alumina-based ceramic material with excellent crack healing ability was successfully fabricated by adding SiC whiskers and TiSi2 particles. Different sizes of cracks were prefabricated on the surface of the material with the diamond indenter, and corresponding crack healing behavior was studied by high temperature oxidation experiments in a muffle furnace under air. The influences of healing temperature, healing time, and crack size on the surface morphology and flexural strength of the material were investigated in detail. When the crack width was 0.68 μm, the appropriate temperature and duration time for crack healing and full-strength recovery were 800 °C for 60 min or 1000 °C for 30 min, respectively. The maximum crack size capable for self-healing of the ceramic material was 2c = 250–300 μm and w = 0.68 μm, and the corresponding healing condition was of 800 °C/60 min. The crack healing of Al2O3/SiCw/TiSi2 ceramics was primarily driven by the high temperature oxidation reactions of Ti5Si3 and SiCw. Ti5Si3 was a new phase formed during sintering, and its formation could be described by thermodynamically feasible reactions. The new crack healing mechanism was revealed deeply, including both the local crack bridging generated by the in-situ development of TiO2 and the liquid phase filling of SiO2 intermediate oxides (Si2O3 and SiO). This research conclusion has great significance for the repairing and remanufacturing of ceramic materials with crack defects.

Dust removal ash coupled with high-temperature exhaust gas to produce energy gas CO and remove the heavy metals synchronously

In order to solve the utilization problem of dry quenching coke dust removal ash (DRA) and high-temperature exhaust gas (HTEG) at the same time, this study proposes a new technology that combines DRA and high-temperature exhaust gas to produce energy gas CO and realize the removal of heavy metals in dust removal ash. The reaction properties of DRA and high-temperature exhaust gases, as well as the migration law of heavy metals, are preliminarily evaluated using thermodynamic simulation software (FactSage) and a combination of thermogravimetric mass spectrometry (TG-MS). The dropper furnace (DF) experiments are used to verify the feasibility of the new technology by simulating the high-temperature flue gas environment. The findings reveal that as pressure rises, the content of gas products namely CO2 and CH4 rises while the content of gas products CO and H2 falls. At the same time, when the temperature rises, the CO and H2 contents rise. Heavy metals such as Cd, Pb, and Zn are also more volatile, whereas heavy metals such as Ni, Cr, and Cu, require higher temperatures to volatilize. As the temperature increases from 800 to 1200 °C, the Pb removal rate climbs from 34.6% to 92.5%, the Cd removal rate increases from 46.5% to 95.6%, and the Zn removal rate increases from 13.4% to 80.5%. The new technology captures CO2 from high-temperature exhaust gases and converts them into CO energy gases, simultaneously realizing the removal of heavy metals. This provides an innovative solution for the treatment of organic solid waste.

Development of Iron Recovery Technique from Steelmaking Slag by Reduction at High Temperature

In order to develop a new recycling process of steelmaking slag, reduction of (FetO) and (P2O5) in steelmaking slag at high temperature have been investigated. In this work, 50 kg-scale experiments which simulated rotary kiln were conducted to investigate the separation behavior between slag and metal. Main results are as follows. (1) Molten iron was tapped out from the experimental furnace under the condition that more than 86% iron was reduced. (2) Weight of reduced iron did not affect the undefined ratio of phosphorus. (3) Common logarithm of phosphorus distribution ratio (logLP), which was used as an index to explain the effect of slag composition, temperature and oxygen potential, correlates to the undefined phosphorus ratio. (4) In the experiments which simulated rotary kiln treatment, calculated phosphorus distribution ratio (LP) was smaller than that from experimental results. It can be said that the phosphorus transfer into the metallic phase decreased because the smaller interface between slag phase and metallic phase was obtained due to the slag/metal separation.

Size- and temperature-dependent oxidative pyrolysis and auto-ignition of spherical beech and spruce wood

Abstract Opposed to piloted ignition, where a substance is ignited by an external flame or spark, the term auto-ignition describes the onset of combustion by spontaneous ignition without an external source. In this study, the influence of the size of spherical wood samples and the temperature surrounding the samples was investigated by performing ignition experiments in a muffle furnace with beech and spruce wood. On a specially constructed rig, spheres with four different diameters (8 mm, 12 mm, 18 mm, and 25 mm) were put into a preheated furnace at five isothermal temperatures (240 °C, 270 °C, 300 °C, 330 °C, and 360 °C). For every temperature, diameter, and wood species, the experiments were repeated eight times, and positions of the spheres on the rig were changed for every measurement. Temperatures inside the samples were recorded with thermocouples (TC) positioned in holes drilled to the middle of the spheres. With rising size and temperature, samples were more prone to auto-ignition in a glowing mode, due to a larger, highly reactive pyrolyzed surface and internal overheating. During heating and oxidative pyrolysis, isothermal phases were present at approximately 360 °C in the recorded temperature curves. The comparison to simultaneous thermal analysis (STA) measurements shows decomposition of hemicelluloses, and cellulose is highest around 360 °C. It is concluded that pyrolysis and disintegration of the main wood constituents use up all arising energy. Due to differences in the composition of the wood polymers, beech wood samples already ignite at lower temperatures compared to spruce wood samples with the same diameter. It can be concluded that the size is a critical factor for auto-ignition at the used temperatures. Larger samples will produce more volatile compounds during pyrolysis and have a larger pyrolyzed, porous surface area where heterogenous oxidation reactions can happen. The influence of the size is already critical at differences on the millimetre scale.

A pilot-scale experimental study on MILD combustion of sawdust and residual char solid waste blend using low-temperature preheating air

The treatment of solid waste through incineration has become an important development trend. A solid waste blend (sawdust and residual char) is studied experimentally in a tubular-furnace reactor and a 200-kW pilot-scale furnace under moderate or intense low-oxygen dilution (MILD) combustion conditions. The effects of temperature and oxygen concentration on NO release characteristics are examined in the tubular-furnace reactor. The pilot-scale furnace experiments include the conventional flame combustion using a swirl nozzle (CFC-S), MILD combustion using symmetrical dual straight nozzles (MILDC-SD), and MILD combustion using an asymmetrical single straight nozzle (MILDC-AS). The tubular-furnace reactor results indicate that the NO released from solid waste blend mainly originates from fuel-NO under medium temperature and low oxygen environments. The pilot-scale furnace results demonstrate that stable combustion of the solid waste blend can be achieved under three co-combustion conditions. Compared to CFC-S, the MILDC-AS combustion of solid waste blend inhibits the fuel-NO and PM2.5 emissions by 54% and 50%, respectively. The burnout rates of solid waste blend MILD combustion exceed 95%. This study not only extends the fuel adaptability of MILD combustion to solid waste blend, but also proves the suppression influence of MILD combustion on fuel nitrogen and PM2.5 emissions.

Trace element partitioning in silica-undersaturated alkaline magmatic systems

Alkaline magmatism is an important chemical end-member of magmatic activity that typically occurs in response to small volume melting of asthenospheric- and/or lithospheric mantle material in intra-continental settings. Understanding trace element partitioning and phase equilibria during alkaline magmatism can therefore provide constraints on intra-continental geodynamic settings. However, the partitioning of trace elements between alkaline melts and their dominant equilibrium mineral phases remains poorly constrained. Feldspathoids in particular have received limited attention with regards to their trace element contents, hampering our ability to interpret geochemical trends in alkaline magmatic systems. In this study, we performed a series of 1 atmosphere experiments in a gas-mixing furnace using a variety of highly alkaline (Na2O + K2O = 4.15–14.97 wt%) and silica-undersaturated (SiO2 = 36.73–45.96 wt%) lava compositions from Nyiragongo, Democratic Republic of Congo, in order to investigate the partitioning behaviour of trace elements in minerals from alkaline magmas. Experimental runs were performed with oxygen fugacity buffered at both QFM (quartz-fayalite-magnetite equilibrium) and QFM + 1 and cover a range of geologically-relevant temperatures (1025–1200 °C). The quenched products of these experiments contained leucite, nepheline, melilite, clinopyroxene, olivine, and rhönite crystals, of which glass-crystal pairs were analysed for rare earth elements, large-ion lithophile elements, and high-field-strength elements. Leucite and nepheline host considerable quantities of large-ion lithophile elements but take up negligible amounts of more highly charged cations. Åkermanitic melilite readily incorporates mono- to trivalent cations with a preference for light over heavy rare earth elements, but incorporates only select divalent cations. Rhönite and clinopyroxene have analogous partitioning behaviours, with a strong preference for heavy over light rare earth elements. Fractionation modelling using the reported partitioning behaviours reproduces the 2021 eruption products of Nyiragongo, with 48% fractionation from an olivine-melilitic parental melt composition. Crystallization of trace-element poor feldspathoid amplifies pre-existing high LREE/MREE ratios of the parental magma and progressively increase trace element abundances for all but monovalent cations.

CFD Modeling and Validation of Blast Furnace Gas/Natural Gas Mixture Combustion in an Experimental Industrial Furnace

The use of residual gases from steel production processes as fuel for steel treatment furnaces has attracted great interest as a method for reducing fossil fuel consumption and the steel footprint. However, these gases often have a low calorific value, and a direct substitution can lead to low temperatures or combustion instability issues. CFD simulations of the combustion of these gases can help steel producers forecast the results of the substitution before real testing and implementation. In this study, a CFD model of an industrial experimental furnace in the steel sector is developed and validated. The results are calculated using the combustion, radiation, and heat transfer models included in the software Ansys Fluent. The validation of the simulated results is performed with data acquired from experimental tests under the same simulated conditions at three air-to-fuel equivalence ratios, which vary from an excess of 0% to an excess of 5% oxygen at the outlet. The model is adjusted to the results, capturing the trends of the measured physical variables and pollutant concentrations. In the case of the combustion temperature, the differences between the simulated and measured values vary from 0.03% to 6.9. Based on the simulation results, the use of blast furnace gas as fuel produces temperatures inside the chamber between 1004 °C and 1075 °C and high stream velocities because of the high flow needed to keep the power constant. Flames exhibit straight movements since the high flows absorb the effect of the swirling flames. The addition of natural gases increases the combustion temperature up to 1211 °C and reduces the flow and length of the flames. Finally, temperatures up to 1298 °C and shorter flames are reached with natural gas enriched with a stream of oxygen, but in this case, NOx emissions need to be controlled.

Modification of Inclusions by Rare Earth Elements in a High-Strength Oil Casing Steel for Improved Sulfur Resistance

Steel casing pipes used in the construction of deep oil wells usually require both high strength and corrosion-resistant behavior. Due to the exploration of deep H2S-bearing oil reservoirs, sulfide stress cracking (SSC) is becoming an increasingly serious concern for casing steel. The nonmetallic inclusions in the steel are among the key reasons for its service failure. The rare earth element Ce can be used to modify the inclusions in casing steel and improve its SSC resistance. Here, taking C110 grade casing steel (the highest class currently in service) as the investigated object, the modification behavior of Ce inclusions in the steel and the effect of the addition of Ce in varying amounts (0.01, 0.024, and 0.042 wt.%) on the modified products were studied through high-temperature tube furnace experiments and thermodynamic calculations. The results showed that Ce had an obvious modification effect on the CaO·Al2O3 inclusions in casing steel, and the diffusion of dissolved Ce in the steel was the limiting step of the modification reaction. With the extension of reaction time, the sequence describing the modification of inclusions in the steel was determined as follows: CaO·Al2O3 → CeAlO3 → Ce2O3/Ce2O2S. The final stable product after modification depended on the amount of Ce added. With 0.01 wt.% Ce, the stable phase in molten steel was Ce2O3; on the other hand, upon adding ≥0.024 wt.% Ce, the stable phase became Ce2O2S. In addition, the thermodynamic stability of Ce2O3 decreased, and it was transformed into CeAlO3, Ce2O2S, Ce2S3, and CeS during solidification. On the basis of our results and the considerations for smooth casting, the addition of a proper amount of a rare earth element is suggested for industrial trials, following the achievement of a significant and surprising improvement in the qualified rate of SSC resistance for the final steel products. The relevant mechanism is also analyzed.

Evaluation of combustion characteristics in biomass residues open burning

Open burning of biomass residues is known as major source of atmospheric pollutant in agricultural areas. Biomass open burning released several toxic compounds that endanger not only human health but also enhance global warming effect. This paper aims to evaluate the characteristics of combustion in bagasse, rice straw and leaf litter open burning. Experimental furnace is designed to mimic the open burning condition with controlled observation system of combustion parameters i.e., temperature, gas composition, and particulate concentration. It is obtained that bagasse produced the lowest emission factor compared to other biomasses combustion i.e., 35 g CO/kg biomass and 0.2 g PM/kg biomass. High temperature level is obtained to be the main factor of low emission emitted in open burning.

Transformation of mineral matter during pyrolysis, gasification and combustion of biosolid chars

During thermochemical processing of biosolids in sewage sludge, different forms of phosphorus-containing compounds are generated in biosolid chars (biochars). This study examines the effects of biochar processing conditions on the mineral compounds produced during the pyrolysis, gasification, and combustion of biosolids, and the major determinants of phase formation kinetics. Our results show identified phase transformations through experiments in a laboratory tube furnace followed by X-ray diffraction analysis (XRD). Additionally, a synchrotron powder diffraction study was conducted to verify XRD results of the laboratory processed samples and to observe in situ phase transformations in biochars. It was found that under a neutral atmosphere, crystalline oxide phases are formed at lower temperatures and much faster than iron phosphide, while gasification and combustion conditions led to the formation of crystalline phases in phosphate forms. These forms of phosphorus compounds in by-products of biosolids thermochemical treatment can be used as agricultural fertilizers.

Effects of core air gaps and steel inserts on thermal response of GFRP-balsa sandwich panels subjected to fire

Sandwich systems composed of combustible glass fiber-reinforced polymer (GFRP) face sheets and balsa cores must fulfill fire resistance requirements if used, for instance, in bridge or building construction. Air gaps and steel inserts in the balsa core, the latter to suspend external pipes below bridge decks for example, may therefore present critical zones where heat ingress is facilitated, and fire resistance is therefore reduced. The thermal responses of such GFRP-balsa sandwich panels comprising through-thickness air gaps or steel inserts, and subjected to a one-sided external fire, were thus investigated by furnace experiments and fluid-structure interaction simulations. Through-thickness air gaps and steel inserts between the face sheets cooled the surrounding zones close to the hot face and heated those located towards the cold face. In T-shape steel inserts penetrating the bottom face sheet, the fire-exposed flange collected the heat and the whole section around the insert was significantly heated. The results revealed that the remaining cross section might be considerably reduced by char formation around the air gaps and steel inserts. Although the effect is quite local, it may be significant if slabs are unidirectional or if it occurs at critical locations, e.g., in the vicinity of supports.

Design and evaluation of a light-field multi-wavelength pyrometer.

This letter describes the design and implementation of a multi-wavelength light-field pyrometer, where six-channel radiation images were captured with one CMOS sensor. Such capability is achieved by placing a 2 × 3 filter array in front of the main lens of an unfocused light-field camera, such that discrete wavelength and radiation intensity can be simultaneously recorded. It demonstrates that through black-body furnace experiments, how multi-channel radiation images can be extracted from one raw light-field multispectral image, and how accurate 2D temperature distribution can be recovered by optimization algorithms.

Experimental investigation of structural failure during the cooling phase of a fire: Timber columns

AbstractThis paper describes fire tests on loaded glued laminated timber columns in which the structural response was measured during the heating and cooling phases. Identical columns with 280 × 280 mm2 cross‐section and 3.7 m length were tested under various heating durations in a standard furnace to investigate integrity to full burnout. Two of the columns were subjected to ISO 834 heating until failure and their measured fire resistance was 55 and 58 min, respectively. Two columns were subjected to 15 min of ISO 834 heating followed by controlled cooling; these columns failed during the cooling phase, respectively after 98 and 153 min. Flame self‐extinction occurred after approximately 40 min while smoldering continued locally. Two columns tested under 10 min of ISO 834 heating both survived the defined heating–cooling exposure. Thermocouples inside the columns show sustained temperature increases for hours after the end of the heating phase. These full‐scale furnace experiments show that timber columns may fail during the cooling phase after exposure to standard heating for about 25% of the standard fire resistance duration. These results, in line with previous numerical predictions, highlight the need for further investigation into fire safety until full burnout for timber structures.

Carbon balance analysis of sewage sludge biochar-to-soil system

Converting sewage sludge (SS) into biochar via pyrolysis is proposed as a prospective strategy for recycling nutrients and reducing environmental risks. Yet, from the perspective of carbon (C) balance the viability of pyrolyzing SS still remains unclear. Here we quantified the C footprint of the whole process from raw SS pyrolysis to final disposal of SS-derived biochar (SSB) using life cycle assessment based on a 20-tonne industrial pyrolysis furnace and field experiments. Results indicated that about 0.101 tonnes of direct CO2 equivalent (CO2e) (from N-containing organic compounds in SS) plus 1.506 tonnes of indirect CO2e (from energy consumption and dewatering agents) were emitted for each tonne of dry SS treated during its dewatering and pyrolysis processes, and at least 0.252 tonnes of CO2e were sequestered as stable C in SSB, depending on the final application route of SSB. In contrast, the net C emissions from traditional SS treatments amounted to at least 2.432 tonnes of CO2e per tonne of dry SS under the similar scenarios. Converting SS into SSB thus showed great advantages in C balance over the traditional treatments of SS. Sensitivity analyses indicated that the moisture and C contents of SS and the usage of dewatering agents were the key factors affecting C balance in the SSB-to-soil system. These findings highlight the C sequestration potential of pyrolysis and provide important support for the optimization and management of SS treatment.

Influence of nozzle design parameters on exhaust gas characteristics in practical-scale flameless hydrogen combustion

Considering the trend toward decarbonization, hydrogen is expected to be used as a fuel in industrial furnace burners. One of the challenges in using hydrogen as a fuel is the increase in thermal-NOx emission compared to hydrocarbon fuel owing to its high flame temperature. This study experimentally evaluated the combustion characteristics of flameless combustion, which is a low-NOx combustion technology, with hydrogen as a fuel in a practical-scale experimental furnace as well as the effect of nozzle design parameters on the combustion characteristics. Through comparative tests with city gas by considering parameters, such as the fuel gas velocity, combustion air velocity, and air nozzle pitch, the low-NOx effect of flameless combustion was confirmed in hydrogen combustion with appropriate nozzle design parameters. The optimal nozzle design parameters to achieve this effect differ from those for city gas, and the design guidelines are summarized.

An experimental and theoretical study of NO heterogeneous reduction in the reduction zone of ammonia co-firing in a coal-fired boiler: Influence of CO

The co-firing of ammonia (NH3) and coal in boilers and furnaces has attracted increasing attention worldwide. However, only a few studies have been reported on the mechanism of NO reduction in the reduction zone of coal and ammonia co-firing. This work adopted theoretical calculations and experiments to explore the mechanism of NO reduction by char and NH3 and the role of CO. Theoretical results indicated that CO exhibits a synergistic effect with the amino agent on NO reduction. In char/NH/CO/NO system, the hydrogen-rich environment created by H atoms weakens the energy of N-C bond, thereby promoting NO heterogeneous reduction. However, CO occupies the active sites on the char surface and slightly inhibits the NO heterogeneous reduction in char/NH/CO/NO system. Experimental results revealed that CO improves the NO reduction efficiency in the NH3/char/NO system. CO plays different roles in the heterogeneous reduction of NO by NH on the char surface in high-temperature furnace experiments as well as in theoretical calculations. These results are attributed to the fact that the homogeneous reduction rate of NO by the amino and CO in the ammonia and coal co-firing is greater than the heterogeneous reduction rate of NO by CO-coordinated char.

Material evaluation for engineering a novel crucible setup for the growth of oxygen free Czochralski silicon crystals

For manufacturing of several high performance electronic devices, e.g. insulated-gate bipolar transistors (IGBT), single crystalline silicon crystals with high purity and minimum oxygen (in the range of 1015 at/cm3) concentration are required. Such silicon crystals are typically grown by the Floating Zone technique (Fz), as the more common and cheaper Czochralski technique (Cz) uses silica crucible, which leads always to a relatively high oxygen concentration in the silicon crystals (>1017 at/cm−3). Therefore, in this work potential materials were evaluated with respect to the development of a novel oxygen-free crucible system, which should enable a cost effective growth of oxygen free Cz silicon ingots. For that purpose different graphite materials as well as nitride bonded silicon nitride (NSN) were tested in contact with liquid silicon due to their infiltration behaviour and occurrence of crack formation. Functional silicon nitride (Si3N4) coatings were applied by powder based spray coating of reaction bonded silicon nitride (RBSN) and chemical vapour deposition (CVD) on graphite and NSN crucibles. Characterization of the crucible/coating systems before and after crystal growth experiments in a lab-scale casting furnace reveal information about morphology, infiltration behaviour and adhesion strength on the crucible. Further, investigations on the grown silicon crystals give information about impurity incorporation coming from the novel crucible systems. The results indicated, that especially graphite materials with low porosity and a high mechanical strength as well as NSN with polysilazane sealing in combination with a CVD Si3N4 coating have definitely a potential for application as crucible system in silicon growth processes.

Study on the dynamic evolution law of spontaneous coal combustion in high-temperature regions

In regard to coal spontaneous combustion (CSC) in the goaf, it is difficult to determine the high temperature regions due to its hidden fire source, while effective prevention and control of CSC in the goaf have become increasingly difficult. COMSOL Multiphysics was adopted to conduct theoretical calculations and numerical simulation analysis of the dynamic evolution of high temperature regions in CSC process. The results indicated that the general trend of the high-temperature regions in the experimental furnace involved movement from the middle and upper parts to the lower air inlet. The high-temperature regions in the goaf was mainly concentrated on the air inlet side. Both the advancing speed and air supply rate at the working face impacted the dynamic evolution of the high-temperature regions. With the increase of the advancing speed, the heat and mass transferred process in the goaf became more and more intense, so that the caving coal and rock entered the suffocation zones after a short period of oxidation and temperature rise. Moreover, the temperature difference between the suffocation zones and the deep goaf was small, so there was some uncertainty in the high-temperature area. With the increase of air supply, the heating rate of high-temperature point increased, and the material migration speeds in the goaf also increased, which made the high-temperature regions move towards the deep part of the goaf, which was more unfavorable to the prevention and control of CSC.