Kiln Wall Research Articles

Temperature Field Simulation Model for Rotary Kiln of Iron Ore Oxidized Pellet

Based on conduction, convection and radiation heat transfer among the flue gas, kiln wall, and the pellet bed material, and on the basis of the coal combustion and analysis of reaction heat of pellet induration in the rotary kiln, the temperature field model of rotary kiln was established. Using visual studio net, matlab and open source computer vision library as development tools, combining with the ActiveX data objects database technology, the temperature field simulation system for rotary kiln of iron ore oxidized pellet production was developed. Temperature distribution of pellet and flue gas in rotary kiln was dynamically displayed.

Development of a Prototype Pots and Potsherds Kilns for Facilitating Ceramic Wares Firing in Tertiary Institutions in Nigeria

The purpose of this research is to design and produce a gas and wood fired kilns with waste pots and potsherds that are as efficient as electricity and gas operated kilns which are built using conventional refractory bricks. Waste pots and potsherds were collected from two different pot producing communities, that is, Ojah in Akoko Edo and Imiegba in Etsako Central Local Government Ares of Edo State. To determine the suitability of the sample pots and potsherds collected for the construction of the kilns, the following tests were carried out: shrinkage, porosity and insulating tests. Two kilns were designed and constructed, a gas and wood fired kilns. The firing space and the outer wall of the gas kiln were designed to be circular with one burner port using only potsherd and mortar without using whole pots. The wood kiln was designed to have circular internal firing chamber, two fire boxes and a chimney. The kilns were subjected to series of gloss firing with wood and gas as sources of fuel and the maturing temperatures were recorded. The efficiency of the kilns constructed revealed that they were capable of firing to temperature above 1200°C that was originally planned for it to be attained coupled with uniform heat distribution experienced without any indication of cold spot. These kilns are capable of sustaining the deficiency arising from lack of imported kilns that could be used to accomplish finished ceramic productions as it is being currently encountered in Nigerian tertiary institutions and cottage level industries.

Numerical and experimental thermal analysis of an industrial kiln used for frit production

This paper describes a methodology for the study and modeling of the thermal energy in ceramic frit melting kilns with an oxy-fired combustion process through the development of a numerical simulation in CFD software. Ceramic frits are vitreous compounds that provide glazes with specific properties for use in the coating of other ceramics, especially those of the ceramic tile industry. The aim of this study is to generate technical subsidies in order to support economically viable proposals for the ceramic industry. The CFD modeling is performed using the commercial software Ansys CFX 11.0, which is based on the method of finite volumes. The geometric domain of resolution consists of the internal cavity of the kiln. The CFD resolution is coupled to a three-dimensional heat conduction code along the kiln walls to determine the external temperature distribution. The thermal problem is composed of the combustion of natural gas with oxygen, the internal turbulent flow of exhaust gases, the energy loss by convection and radiation to the environment through the walls and the radiation within the kiln cavity with participating media. Data collected in an operating kiln are used to verify the numerical solution, achieving a good agreement in the general analysis of the kiln. The numerical solution provides physically consistent results, making it possible to predict the behavior of the kiln as a whole in similar cases with changes in the parameters of the manufacturing process or in the geometry. Other specific results, such as heat flux inside the kiln, are presented and discussed.

Weathered Ilmenite: Diverse Mechanisms of Sintering and Association with Contaminants

We briefly review the nature and provenance of extremely weathered ilmenite, then investigate its fate when it is 10 % of a blended feed in the reduction kilns of the Becher process. There it is bound, unintentionally and intermittently, in sinter, which is discarded. It takes with it discrete aluminosilicate grains as well as contaminants, adsorbed and occluded within the ilmenite. Two distinct sintering mechanisms are identified. A layered wall accretion forms purely by solid state reaction, and is thickest early in the kiln. It occasionally detaches under its own weight or is eroded, and is tolerated between scheduled shutdowns for maintenance. However, if the weathered ilmenite and accompanying silica escape earlier wall accretion, a transitory aluminosilicate melt may later promote sintering of this material within the bed, adhering catastrophically to constrictions and obstructions on the kiln wall. The mechanisms and controlling factors are discussed.

Dynamic modelling of a rotary kiln for calcination of titanium dioxide white pigment

Abstract A rigorous one-dimensional dynamic model of a rotary kiln for calcination of titanium dioxide white pigment is developed. The regenerative heat transfer in the kiln wall is described by a new mixed numerical/analytical approach. The model is validated by means of a dynamic test case representing a 15-day period of plant operation. The required process data are captured within a measurement campaign on a kiln run by TRONOX Pigments GmbH, Krefeld-Uerdingen, Germany. The predictive accuracy of the model is estimated by means of a sensitivity analysis considering uncertainties of model parameters and measured input values. The actual agreement between simulation and measurement results is significantly better than indicated by the sensitivity analysis.

Trace gas and particle emissions from domestic and industrial biofuel use and garbage burning in central Mexico

Abstract. In central Mexico during the spring of 2007 we measured the initial emissions of 12 gases and the aerosol speciation for elemental and organic carbon (EC, OC), anhydrosugars, Cl−, NO3−, and 20 metals from 10 cooking fires, four garbage fires, three brick making kilns, three charcoal making kilns, and two crop residue fires. Global biofuel use has been estimated at over 2600 Tg/y. With several simple case studies we show that cooking fires can be a major, or the major, source of several gases and fine particles in developing countries. Insulated cook stoves with chimneys were earlier shown to reduce indoor air pollution and the fuel use per cooking task. We confirm that they also reduce the emissions of VOC pollutants per mass of fuel burned by about half. We did not detect HCN emissions from cooking fires in Mexico or Africa. Thus, if regional source attribution is based on HCN emissions typical for other types of biomass burning (BB), then biofuel use and total BB will be underestimated in much of the developing world. This is also significant because cooking fires are not detected from space. We estimate that ~2000 Tg/y of garbage are generated globally and about half may be burned, making this a commonly overlooked major global source of emissions. We estimate a fine particle emission factor (EFPM2.5) for garbage burning of ~10.5±8.8 g/kg, which is in reasonable agreement with very limited previous work. We observe large HCl emission factors in the range 2–10 g/kg. Consideration of the Cl content of the global waste stream suggests that garbage burning may generate as much as 6–9 Tg/yr of HCl, which would make it a major source of this compound. HCl generated by garbage burning in dry environments may have a relatively greater atmospheric impact than HCl generated in humid areas. Garbage burning PM2.5 was found to contain levoglucosan and K in concentrations similar to those for biomass burning, so it could be a source of interference in some areas when using these tracers to estimate BB. Galactosan was the anhydrosugar most closely correlated with BB in this study. Fine particle antimony (Sb) shows initial promise as a garbage burning tracer and suggests that this source could contribute a significant amount of the PM2.5 in the Mexico City metropolitan area. The fuel consumption and emissions due to industrial biofuel use are difficult to characterize regionally. This is partly because of the diverse range of fuels used and the very small profit margins of typical micro-enterprises. Brick making kilns produced low total EFPM2.5 (~1.6 g/kg), but very high EC/OC ratios (6.72). Previous literature on brick kilns is scarce but does document some severe local impacts. Coupling data from Mexico, Brazil, and Zambia, we find that charcoal making kilns can exhibit an 8-fold increase in VOC/CO over their approximately one-week lifetime. Acetic acid emission factors for charcoal kilns were much higher in Mexico than elsewhere. Our dirt charcoal kiln EFPM2.5 emission factor was ~1.1 g/kg, which is lower than previous recommendations intended for all types of kilns. We speculate that some PM2.5 is scavenged in the walls of dirt kilns.

Temperature distribution within the moving bed of rotary kilns: Measurement and analysis

Inadequacies in the temperature measurement within the moving bed have hindered a thorough understanding of the processes occurring within rotary kilns. A new measuring system, consisting of thermocouple arrays, a radio-transmitter, a radio-receiver and a computer monitor is introduced in this paper. With it, the 3D temperatures within the moving bed, as well as the temperatures of the freeboard gas and the kiln wall, can be measured and saved automatically. Experiments with sand on a co-current pilot kiln demonstrated that, in the passive layer of the moving bed, the temperatures were approximately constant in the circumferential direction. In the radial direction, however, large temperature difference was observed within the bed near the feed end of the kiln, and the difference became smaller as the bed went progressed through the kiln. This temperature measuring system can be used to obtain data over a wide range of operating conditions for use in engineering design. The obtained results may give new thoughts in theoretical modeling of heat transfer within the moving bed of rotary kilns.

In situ Raman study of mineral phases formed as by‐products in a rotary kiln for clinker production

AbstractPortland clinker production consists essentially in the burning of material with defined composition in a rotary kiln at temperatures around 1450 °C. The main fuel used in this process is coal, even though in the last few years the use of alternative fuels has been increasing. Four main minerals are formed, namely, tricalcium and dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite. Along with these main phases, variations in burning conditions of fuels or in the local composition of raw materials can lead to the formation of relatively high amounts of secondary by‐products, which can negatively affect the quality of the final material. Characterization of these by‐products allows not only optimization of the process of clinker production but also the design of special refractory materials for the wall of kilns and preheaters. Being found as particles included in (or alternating to) a hard solid clinker matrix, a detailed characterization of these extra phases could be achieved only via microscopic techniques. In this work, micro‐Raman spectroscopy has been successfully tested as a highly selective method for characterization and localization of included minerals that formed as overlapped crusts deposited on the internal wall of a conventional rotary kiln for cement production, without any manipulation of the sample. Understanding the chronological order of deposition of these overlapped layers is extremely important, as it is the only way to go back up to the production process and to individuate the problem. Copyright © 2008 John Wiley & Sons, Ltd.

Archaeomagnetic study of a lime kiln at Bazzano (northern Italy)

An archaeomagnetic study was carried out as part of a rescue operation on a lime kiln discovered during the exploitation of a gravel quarry at Bazzano, near Bologna (northern Italy). Based on very poor archaeological information the kiln is dated around 3rd–4th century AD but no other structures have been found in the area to support this age. A hierarchical sampling process has been followed; twelve independently oriented bricks were collected from the circular wall of the baking room from which 35 cylindrical specimens were cut and measured. Demagnetization procedures reveal a single-component, stable remanent magnetization. The dispersion of the mean direction is low, even though some deviations in the remanence direction as a function of the position of the samples in the kiln wall are observed. The archaeomagnetic age of the kiln has been obtained using recent advances on data elaboration involving Bayesian statistics and the preliminary secular variation (SV) curve of Italy. For comparison, the kiln has been also dated using the French SV curve. The ages obtained are in good agreement and suggest that the last firing of the kiln could have occurred as late as at the end of 6th century AD.

Improvements in Pyrolysis of Wastes in an Externally Heated Rotary Kiln (Measurements of the Overall Heat Transfer Coefficient from the Wall to Wastes)

The effects of rotating speed and internal structure on the performance of an externally heated rotary kiln for waste pyrolysis were investigated. A newly developed method was adopted to evaluate the overall heat transfer coefficient km-w from the inner wall to the wastes for this purpose. The experimental results revealed that km-w monotonically increased with the number of lifters and their height. When six lifters 200 mm in height were attached to the inner wall of the kiln, the mean value of km-w increased from 38.6 W/m2K to 45.3 W/m2K at 2.7 rpm. In addition, km-w increased to 50.1 W/m2K when the rotating speed was increased to 4.0 rpm. In the water vaporization phase during the course of the pyrolysis process, the height of the lifters had a significant influence on km-w. However, the number of lifters had a significant impact on km-w in the pyrolysis phase of the plastic-based wastes. According to measurements, a 10 % increase in km-w could be obtained when installing lifters to attain a ratio of lifter height Hl to the thickness of the waste layer Hw larger than 0.45 or when arc length between two lifters Ll to the arc length of the interface between the wastes and the kiln wall Lw was larger than 1.

Energy Saving in Industrial Wood Drying Addressed by a Multiscale Computational Model: Board, Stack, and Kiln

This article proposes a multiscale computational model able to calculate energy consumption in a batch lumber kiln. A dual-scale computational model of wood drying deals with the boards/stack interaction and serves as a basis for the present work. A new module was added here that calculates heat losses through kiln walls (convection, condensation) and the energy used by each kiln component (fans, heating elements, humidifier, vacuum pump, etc.). The corresponding mathematical formulation is presented and then theoretical results are compared to those collected in an industrial vacuum kiln. As application example, the effect of air reversal, air velocity, and kiln insulation are exhibited, which depicts the great potential and prospects of this new tool for energy savings in relation to the product quality.

Investigation of nodule formation in lime kilns using batch kilns

Causes for nodule formation in lime kilns were investigated using rotary batch kilns. The results show that the size of the mud lumps and the sodium content in the mud are important factors in determining the final lime nodule size. Under the test conditions, lumps smaller than 13 mm appear to agglomerate to form larger nodules, while lumps larger than 19 mm do not agglomerate and, therefore, do not form larger nodules. The melting of sodium compounds in lime mud appears to be responsible for particle agglomeration once the sodium content exceeds 5%. Passing air through the bed material in the batch kiln prevented particles from agglomerating and adhering to the kiln wall.

Estimating baking temperatures in a Roman pottery kiln by rock magnetic properties: implications of thermochemical alteration on archaeointensity determinations

SUMMARY Absolute past geomagnetic field intensity determinations requiring laboratory heating are labourious and the success rate is rather low, mostly because of induced thermochemical magnetic mineral alterations. Archaeomagnetic intensity determinations are mainly limited to displaced ceramics produced in kilns. In this study, the suitability of an in situ baked structure is investigated. Different magnetic properties of baked material taken from the combustion chamber wall and floor of a Roman pottery kiln, with variable colouring, are examined in dependence on the distance to the combustion chamber. The temperature distribution is re-constructed based on rock magnetic experiments after stepwise heating. The rock magnetic temperature estimates agree fairly well with a mathematical heat conduction model demonstrating the penetration of heat into the combustion chamber wall. The rock magnetic results show that blackish- and greyish-coloured kiln parts, that had been in close contact with the fuel, during ancient kiln operation, are not suitable for intensity determinations. Although sufficiently baked, they strongly alter during laboratory heating and new remanence-carrying minerals are formed. The brownish-coloured material at a distance 65–80 mm away from the combustion chamber seems to be most suitable as its magnetic properties remain nearly unchanged during laboratory heating. Rock magnetic and modelled temperature estimates for this material consistently indicate ancient baking temperatures of about 600°C. The model demonstrates that cooling takes longer in the inner parts of the combustion chamber wall. Retarded cooling affects the blocking temperatures and hence the strength of the thermoremanent magnetization. The variability of cooling rates should be taken into account when investigating archaeointensities of specimens cut from large samples, or of samples taken from different parts of a kiln.

Modelling low-temperature carbonisation of solid fuels in a heated rotary kiln for clean fuel production

A numerical simulation of the physico-chemical processes occurring inside a heated rotary kiln reactor, where coal, lignite or biomass are treated in vacuum for the production of clean solid fuel, has been performed with FLUENT6 Computational Fluid Dynamics (CFD) code. The model accounts for the rotation of the kiln walls and mixing blades, multiphase flow modelling of the solid (fuel) and gaseous (mixture of gases) phases, heat transfer between phases and the heated kiln walls and mass transfer due to chemical reaction between species of different (heterogeneous) phases. The objective is to contribute towards a reliable numerical methodology as a design tool with reference to the fuel feed properties (e.g. solids size, volatile, carbon and moisture content, feed rate) and process requirements (e.g. desired residence time). Kiln wall erosion is also assessed.

Origin of deviations between the remanent magnetisation and inducing geomagnetic field direction in kilns and implications on archaeomagnetic dating

Standard secular variation curves of the geomagnetic field direction for the last few millennia for different countries in Europe, based mainly on baked materials discovered in archaeological sites, are reaching sufficient accuracy and reliability that archaeomagnetic dating within this timespan in these areas is becoming feasible now. Orientation errors during sampling and sample preparation can be kept to a minimum and measurement errors of baked materials are in general very small. Nevertheless, even when the secular variation in the site to be dated is similar to that in the reference site, systematic or regular deviations between the remanence vector and geomagnetic field direction in kilns, due to internal and external factors, may result in biased average magnetisation directions and consequently in diverging archaeomagnetic dates. In more or less circular kilns, important non-random deviations of the remanence direction in the walls, in function of the relative azimuth as seen from the centre of the kilns, have been noticed in spite of precise and highly reliable average kiln magnetisation directions. The effect was revealed in the walls of the combustion chambers of roman pottery kilns and of mediaeval brass melting and working kilns, of different shape, lined with refractory bricks. Several hypotheses for the origin of these deviations were examined and anisotropy and/or magnetic refraction are unlikely to be the principal causes. The regular component of these deviations may be responsible for a strongly biased average magnetisation direction when only part of the kiln wall is preserved or when sampling is limited to certain parts of it and consequently result in unreliable dates when applying the archaeomagnetic dating method.

On the suitability of refractory bricks from a mediaeval brass melting and working site near Dinant (Belgium) as geomagnetic field recorders

Directional field archaeomagnetic data from two oval shaped kilns, of which still one was lined with refractory bricks, unearthed in a brass melting and working site in Bouvignes-sur-Meuse in Belgium, confirm the archaeologic dating as 14–15th century A.D. for the main site activities. The archaeomagnetic dates, obtained using reference secular variation curves of the geomagnetic field direction for France and Great Britain, lead to better time constraints for the cessation of kiln operations. Refractory bricks (firebricks) that are used for their chemical and thermal properties, and in particular for their resistance to high temperatures and temperature changes, are not unusual in metal melting and working sites. The firebricks from the examined site are coarse-grained and very porous inside but possess a very stable remanent magnetisation and revealed to be suitable magnetic field recorders. Although the firebricks have a single-component remanent magnetization, non-random deviations in remanence direction in function of the relative azimuth from the centre of the kiln or with the position of the bricks in the kiln wall, were observed. Several hypotheses for the origin of the deviations were considered: anisotropy, refraction, magnetic interaction, magnetic field distortion and the presence of a local disturbing magnetic source.

Salt damage to brick kiln walls in Japan: spatial and seasonal variation of efflorescence and moisture content

To clarify the mechanism of salt fretting of a brick building, monthly observations were made over one year at a two-storey brick kiln in central Japan. Products of weathering that had fallen were collected and weighed; salts were identified using XRD and the moisture content of the brick was measured at its surface using a portable infrared optical moisture meter. Gypsum (CaSO4·2H2O) was found at the bottom of the first floor wall in the warm and humid season. Thenardite (Na2SO4) is dominant on the first floor wall; it is abundant in the cold and dry season but sparse in the warm and humid season. Magnesium sulphate is dominant on the second floor wall; epsomite (MgSO4·7H2O) was observed in the dry-to-wet season and hexahydrite (MgSO4·6H2O) in the wet-to-dry season. Seasonal changes in salt abundance result from the temperature dependence of the solubilities and equilibrium relative humidities (ERH) of each salt. The amount of brick decay material due to salt weathering is much greater from the second floor wall than from the first floor wall and is greater from spring to the end of summer. These seasonal and spatial variations of the rate of brick decay can be explained by a combination of factors: (1) the types of salt, (2) efflorescence or sub-florescence and (3) salt deliquescence.

Curing starch based adhesives: microwave or conventional

The field of microwave material processing is inherently multidisciplinary linking electromagnetism and material science. There are a variety of manufacturing industries utilising microwave power as heating drying source, several cases incorporating hybrid-heating technologies in processes such as paper, rubber, polymers, foodstuff and brick. In reference to starch based adhesive bonding, microwave processing produced improved adhesive joint properties due to the incorporations of dielectric heating methodologies. Relative to the ageing steam heated hot plate, which has been plagued with inconstancies such as; operational efficiency, economics of scale, factory floor requirements and throughput, the science of microwave curing of wheat base starch adhesive is based on the relationship between the interaction of electromagnetic energy and the dielectric properties of the materials. Microwave heating possesses some unique characteristics, which are not found in other types of heating. In volumetric heating, heat is generated principally in the product and not on the kiln walls or atmosphere. Hence the heat losses from the oven walls to the surroundings are much lower and results in reduced running costs. The objective of this article is to establish a comparative material characterisation between microwave and conventionally cured wheat base starch adhesives, also to provide a bonding strength analysis. All references made to microwave heating also apply to microwave curing.

高濃度塩化ビニル脱塩素技術の開発

To utilize waste polyvinyl chloride (PVC), the removal of chlorine in PVC has been studied by newly designed rotary kiln. Coarse coke was simultaneously supplied to prevent an agglomeration of PVC particle and sticking to an inner wall of kiln during PVC dechlorination reaction. The heat for dechlorination was supplied from the outer tube of the rotary kiln so as to minimize the amount of processed gas containing HCl. Basically, it was verified that this rotary kiln could be smoothly operated due to the presence of coke particle. It was observed that dechlorinated residue was a porous materials formed along with the removal of HCl and was coated with coke particle. Dechlorination efficiency of PVC increased with an increase in the processing temperature and retention time in kiln. Dechlorination reaction of soft PVC was a little different from that of rigid PVC because of containing plasticizer in soft PVC. It was considered that plasticizer in soft PVC was inhibited dechlorination reaction. From the above results, it was concluded that an optimum reaction conditions to give 95% of dechlorination efficiency were the processing temperature of 350°C, the retention time of over 15min and the PVC/Coke weight ratio of 1.0. Yield of the dechlorinated residue for the use of blast furnace was 40% for rigid PVC and 20 to 40% for soft PVC. It was estimated that the application of this process enable to utilize effectively industrial and municipal waste plastics containing PVC in the blast furnace.

AN ARCHAEOMAGNETIC STUDY OF POTTERY KILNS FROM BRÜHL‐PINGSDORF (GERMANY)*

Four pottery kilns from Brühl‐Pingsdorf (Germany) were dated by comparing their characteristic remanent magnetization with a curve of the palaeo‐secular variation of the geomagnetic field. Archaeomagnetic results suggest last heating events between AD 775 and 1020. The archaeological evidence generally supports the relative temporal succession and the duration of use, but indicates that the kilns are about 150 years younger on average. Hence, a systematic offset between these independently developed chronologies must be considered. Rock magnetic parameters display radial variations through the kiln walls. These variations are controlled by the maximum temperature the rock was exposed to. These parameters were used to identify specimen which acquired a thermoremanent magnetization.