Kiln Wall Research Articles

Transient mathematical modelling of a gas rotary furnace for melting slag

A 2D transient mathematical model is proposed to analyse a gas rotary furnace intended for melting a CaO-SiO2 slag, a crucial component to be used in the aluminothermic reduction for silicon production. The research, conducted in the framework of the EU SisAl Pilot project, aims to assess the feasibility of the industrial process of these furnaces and to recommend potential scale-up strategies. The mathematical model addresses two distinct but related issues. First, one problem is dedicated to the evaluation of the gas combustion characteristics, including the simulation of the natural gas flame as well as the heat transfer by convection and radiation. Secondly, the temperature data computed on the inner wall of the rotary kiln is used as a boundary condition to solve the problem of melting the solid material, thus determining the required melting time. The model is validated against experimental data for the melting of iron, the material currently used in the plant.

An interdisciplinary approach to the study of kiln firing: a case study from the Campus Galli open-air museum (southern Germany)

Pottery kilns are a common feature in the archaeological record of different periods. However, these pyrotechnological installations are still seldom the target of interdisciplinary investigations. To fill this gap in our knowledge, an updraft kiln firing experiment was run at the Campus Galli open-air museum (southern Germany) by a team consisting of experimental archaeologists, material scientists, geoarchaeologists, and palaeobotanists. The entire process from the preparation of the raw materials to the firing and opening of the kiln was carefully recorded with a particular focus on the study of the raw materials used for pottery making, as well as on fuel usage. The temperatures were monitored by thermocouples placed at different positions in the combustion and firing chambers. In addition, thermocouples were installed within the kiln wall to measure the temperature distribution inside the structure itself. Unfired raw materials as well as controlled and experimentally thermally altered ceramic samples were then characterised with an integrated analysis including ceramic petrography, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and portable X-ray fluorescence (pXRF). Our work provides data about mineralogical and microstructural developments in both pottery kiln structures and the ceramics produced in this type of installations. This is helpful to discuss the limits and potential of various scientific analyses commonly used in ancient ceramic pyrotechnological studies. Overall, our work contributes to a better understanding of updraft kiln technology and offers guidelines on how to address the study of this type of pyrotechnological installations using interdisciplinary research strategies.

DEM-CFD coupled simulation of limestone calcination and fuel combustion in beam type lime shaft kiln

This paper presents the development and simulation analysis of a coupled DEM-CFD model of the gas–solid heat and mass transfer process in an industrial-scale beam lime shaft kiln, which uses Computational Fluid Dynamics (CFD) to simulate the combustion of gaseous fuels and the three-dimensional transport of mass, momentum and energy in the gas, and the Discrete Element Method (DEM) to simulate the movement of limestone particles and calcination reactions in the kiln are simulated using the Discrete Element Method. A beam lime kiln uses five burner beams staggered up and down to provide heat for the decomposition of limestone particles in the kiln, and natural gas is injected as fuel from the burners on the burner beams into the limestone bed of the kiln for combustion, while cooling air enters the kiln from the bottom air cap to cool the calcined products and then enters the calcination zone as secondary air to participate in the combustion. In this paper, a 250 m3 beam lime shaft kiln in normal production is used as the research object to simulate and analyze the data of temperature, gas and solidity field and limestone decomposition rate in the kiln. The simulation results show that the overall limestone calcination temperature in the kiln is low and the temperature distribution is uneven, and the decomposition degree of limestone near the kiln wall is higher than that in the center of the kiln. It's caused by the wall effect, the particle porosity is larger near wall, and combustion gas penetration is therefore enhanced in the vicinity. Meanwhile, the simulation results are in good agreement with the actual measured data, which verifies the reasonableness of the model for application in industrial-grade lime kiln.

Two- and Three-Dimensional Benchmarks for Particle Detection from an Industrial Rotary Kiln Combustion Chamber Based on Light-Field-Camera Recording

This paper describes a benchmark dataset for the detection of fuel particles in 2D and 3D image data in a rotary kiln combustion chamber. The specific challenges of detecting the small particles under demanding environmental conditions allows for the performance of existing and new particle detection techniques to be evaluated. The data set includes a classification of burning and non-burning particles, which can be in the air but also on the rotary kiln wall. The light-field camera used for data generation offers the potential to develop and objectively evaluate new advanced particle detection methods due to the additional 3D information. Besides explanations of the data set and the contained ground truth, an evaluation procedure of the particle detection based on the ground truth and results for an own particle detection procedure for the data set are presented.

Combined Effect of Brick Surface Roughness and Lattice Setting Density on Brick Firing in Tunnel Kilns

This paper investigates the combined effect of the kiln or brick surface roughness and the brick lattice setting density on the fluid flow and heat transfer characteristics in tunnel kilns. The flow uniformity, pressure drop, convective heat transfer coefficient (CHTC), and pumping power are studied. A high-density setting (HDS), which comprises 768 bricks, and a low-density setting (LDS), which comprises 512 bricks, are tested for kiln boundaries and brick surface roughness levels of 0, 1, 2, 3, and 4 mm. The investigation is conducted using a 3D-CFD model with the k-ω turbulence model. The surface roughness changes from 0 to 4 mm for either kiln walls or bricks while fixing the other. The results show that increasing the tunnel kiln surface roughness from 0 to 4 mm increases the pressure drop of both the HDS and LDS by about 13.5%. It also increases the established CHTC value of the LDS more than the HDS by about 23% for all tested roughness levels. Changing the brick surface roughness from 0 to 4 mm increases the pressure drop and CHTC value for the LDS more than for the HDS by about 10% and 12%, respectively. Additionally, the total heat transfer rate-to-pumping power ratio for the LDS is larger than for the HDS by 17.4% for smooth bricks and 23.1% for the brick roughness of 2 mm, i.e., the brick roughness provides a greater advantage to the LDS. The results confirm that the LDS for rough and smooth bricks loaded in tunnel kilns attains a better brick quality, a higher heat transfer rate, and a lower pumping power than the HDS.

Decline of Lanna ceramic group production in northern Thailand (Ban Bo Suak site) confined by radiocarbon and luminescence dating

The Lanna group is a traditional ceramic production style from Southeast Asia, with several kiln sites found distributed all over present northern Thailand. However, its origin and development are considered controversial and chronological constraints are scarce. Applied here are radiocarbon dating to charcoal remains and luminescence dating to ceramics, kiln wall material, and fluvial sediments from the Ban Bo Suak archaeological site near Nan, northern Thailand. The site has been suspected to have been abandoned due to destruction by a flood. Unexpectedly, the ceramic samples lack proper thermoluminescence signal properties and only two samples could be dated using optically stimulated luminescence (OSL). These ages in combination with published radiocarbon ages point towards a ceramic production around AD 1700. The kiln wall material and fluvial sediments reveal evidence for partial resetting of the OSL signal, which is unexpected for heated material. Supported by some radiocarbon ages, the OSL ages imply a temporal connection between the last use of the kilns and the flood deposits, during the fifteenth century AD. Besides general methodological considerations, the data reported here indicates that while a flood apparently dismantled several kiln sites, this did not stop the production of Lanna style ceramics in the region.

A Medieval Stonepaste Ceramic Production Site in Moshkin Tepe, Iran: Ceramics, Wasters, and Manufacturing Equipment

ABSTRACT Stonepaste (or fritware) is an artificial ceramic body, generally thought to have been produced from the eleventh/twelth century in the Islamic lands. Stonepaste production radically transformed the development of medieval Islamic ceramics and was eventually used for all high-quality pottery in central and eastern Islamic lands until the modern period. Despite the significance of stonepaste ceramics, archaeological evidence for their production is extremely rare and most propositions of provenance are based on art historical evidence alone. This paper reports evidence for stonepaste ceramic production from the medieval site of Moshkin Tepe in Central Iran, including stonepaste ceramic sherds, wasters, and a large collection of manufacturing equipment (i.e. hand mills, kiln rods, saggars, and remnants of kiln walls). Through field surface collection and laboratory analyses of the finds, this paper identifies the distinctive characteristics of Moshkin Tepe stonepaste ceramics. It also discusses the manufacturing equipment used and compares the material finds with the descriptions in the medieval Persian textual account by Abu’l Qasim Kashani on the production of stonepaste wares. The results presented here could pave the way to trace and study the manufacture of stonepaste ceramics and to compare different productions across the broader context of medieval Islamic lands.

Transient operation effects on the thermal and mechanical response of a large-scale rotary kiln

Rotary kilns are central equipment in material processing operations such as oxide ore reduction, clinker manufacturing, and hazardous waste incineration. This work focuses on an industrial-scale rotary kiln for Ferronickel production via the Rotary Kiln-Electric Furnace (RKEF) process. Rotary kilns are prone to mechanical failure exacerbated by thermal effects, mainly during transient operation, such as preheating and cooling. However, few studies have tackled the impact of the transient operation on the stress state in the rotary kiln wall. Therefore, we evaluate the thermal and mechanical behavior of the rotary kiln wall during preheating. Actual operation data and a thermal model enable to obtain the temperature distribution along the kiln length. This temperature distribution is the starting point for calculating the stress state of the shell and refractory. The maximal thermal gradient occurs at 10 m from the hot end, with temperatures at the outer and inner surfaces of 200 °C and 820 °C, respectively. The von Mises stress shows a maximum of 121 MPa at the wheel position in the hot region of the refractory and a range of 30–60 MPa in the shell. In addition, the compressive stress is higher than the ultimate compressive strength of the refractory. However, it does not necessarily represent refractory detachment due to the plastic deformation undergone by the refractory under high temperatures. This work paves the way towards developing a tool for accurately predicting rotary kiln mechanical failure, which can help optimize operating conditions and assist in programming maintenance.

Coloring zirconium oxide for novel energy saving industrial applications

White conventional zirconium oxide was mixed to black or rust coloring second phase additives to increase the absorptance and thermal emittance with the aim of exploring novel oxide-based ceramics for energy exploitation and saving, like solar absorbers or even industrial refractory kiln walls. The variation of the optical properties of the colored samples was evaluated as a function of the amount, dopant type and co-doping and it was found that notable changes to the optical spectrum occur already upon introduction of 0.05 wt% pigment. The absorptance of ZrO2 passed from 0.1, in the white ceramic, to 0.75, for the rust-colored ones, and up to 0.82, for black colored materials containing Co-oxide as additive. The thermal emittance and solar absorptance of the black/rust-shaded specimens were calculated for temperatures from 400 to 1500 K and compared to commercial white, black and brown reference to identify the most appropriate composition for the two proposed applications and operating temperatures.

Enhancement of heat transfer during rubber pyrolysis process

Pyrolysis can transform the waste rubber into high value oil, gas and solid carbon, which is a green and environmental protection treatment method. However, due to the poor thermal conductivity of rubber and easy to bond to the reactor wall when heated, the heat transfer efficiency of rubber is low, which has seriously affected the industrialization process of waste rubber pyrolysis. In order to solve this problem, Internal Circulational Thermal Dispersion Technology (ICTDT) was proposed in this study. A certain number of spherical heat-conducting media made of alumina oxide was added into the rotary kiln, forming more high temperature heat source, making the heat transfer efficiency of the rubber in the rotary kiln greatly increase. Besides, the friction between heat-conducting media and the wall of rotary kiln or rubber inhibited the formation of the coking center, thus reducing coking production to a certain extent. The improvement of coking also improved the heat transfer efficiency of pyrolysis process. Through experiments and numerical simulations, the influence of diameter and filling rate of the heat-conducting media on the distribution of pyrolysis products and the temperature rise of the rotary kiln was analyzed, which is expected to provide a feasible method and scientific guidance for the industrialization of waste rubber pyrolysis.

Energy evaluation of clay firing process and combustion gases in an intermittent kiln

The recording of temperatures in different positions in the firing process in an intermittent kiln to produce ceramic materials is presented, which led to the energy evaluation, determining the heat used for the clay firing process and the heat losses. In addition, a study of the emissions of pollutant gases released into the environment was carried out, as stipulated in the protocol of control, and monitoring of stationary source. In the energy balance, large energy losses were detected in heat accumulation in the masonry of 7.20×106 KJ of the energy supplied, representing 16.99%, and in the kiln walls of 5.20×10 KJ, representing 12.17%. As a result, it is necessary to make constructive and operative changes in the operation of the kilns, which will lead to the recovery of residual heat in the use of drying of parts, drying, and preheating of combustion air, reducing energy consumption and emissions of pollutants into the atmosphere. The average concentration of particulate matter released into the environment was 1056.60 mg/m3, 422% higher than the standard, affecting people’s health.

The archaeomagnetic field recorded in ancient kiln walls in Si Satchanalai, Sukhothai

Archaeological dating is crucial in archaeology as it is a key to understand human history. However, traditional dating methods used by archaeologists such as potassium-argon dating and luminescence dating can provide ambiguous age results, e.g., argon loss during the dating returns young apparent ages. Therefore, I plan to establish an archaeomagnetic secular variation (ASV) curve to resolve this problem and use the ASV curve as an alternative tool to date archaeological artefacts. However, archaeomagnetic data in Thailand are absent from literature. Therefore, the ASV curve cannot be constructed from the archaeomagnetic data for this locality. To provide archaeomagnetic data to construct the ASV curve, the directions of the Earth’s magnetic field recorded in kiln walls from Ban Ko Noi (KN123, age 1,370 ± 100 A.D.), Si Satchanalai were measured. The mean declination and inclination of 49.6° and 32.6° with 95% confidence limit of 5.4° were determined from 10 samples from kiln KN123. Mean directions from this study were also compared with the directions of the Earth’s magnetic field in Thailand during 1,370 A.D. from the global archaeomagnetic field model ARCH3k.1. Declination and inclination from this study show significant departure from the field predicted by the ARCH3k.1 model.

Recording of temperatures and heat accumulation in masonry in a continuous kiln used to produce ceramic materials

In Ocaña, Colombia, a traditional ceramic industry has been developed using low efficiency kilns without controls in the combustion processes, which generate large heat losses. As a result, it was necessary to implement a virtual instrument to monitor temperatures in the firing process. For the study, a continuous Hoffman kiln, and the temperature acquisition was carried out in two combustion chambers and lasted twenty-four hours. In the kiln firing process, the energy supplied due to coal combustion was 22198×106 KJ, while the heat accumulated in the kiln roof, walls and floor was 14452.6×106 KJ, 1085.71×106 KJ and 164.72×106 KJ respectively. The total heat stored in the masonry was 15703.03×106 KJ, representing 70.73 % of the energy supplied. Due to the material used in the construction of the kiln, the accumulated heat is high, and it is necessary to implement coatings using ceramic fibers on the kiln walls, keeping the temperature constant in the firing process and leading to a decrease in heat accumulation of about 20 %. Also, air, fuel, temperature, and pressure injection systems should be implemented.

Determination of physical properties and chemical composition of clay from intrusive and extrusive igneous formation

In the mixtures used to produce ceramic materials in Ocaña, Colombia, clays from the intrusive and extrusive igneous formation are used, to which grain size, chemical composition, and thermal conductivity are determined. Scanning electron microscopy tests at 700x magnification were applied to the prepared clay sample to find grain size and chemical composition. The results of the chemical composition of the clay indicate that the major component present is silicon with 27.96%, followed by 13.81% of aluminum, 3.29% of potassium and 58.95% of oxygen. Also, the grain size is in the range of 82701 nm to 96980 nm, density of 1.0705 g/cm3 and average thermal conductivity of 1.78 W/m×°C. The morphological and physical-ceramic properties of the clays are within the admissible ranges to be used in technological applications in the wastewater treatment plants, in designs of clay filters for water purification; they can also be used as refractory material for kiln walls in the ceramics sector.

Efek Zeolit untuk Produksi Tar dan Char pada Pirolisis Rotary Kiln

<p class="00textwithtab">This study aims to investigate the effect of zeolite as a catalyst to enlarge biomass decomposition in the pyrolysis process. It absorbs a high water content in the biomass, besides it makes the easier breaking of biomass molecules to maximize the biomass decomposition into the expected pyrolysis products; tar and char. In addition, to decompose the biomass molecules, the zeolite also stimulates the rate of heat transfer due to its ability to hold and release the heat. If the previous research pyrolysis was conducted in a fixed bed reactor, in this study, it will be carried out rotary kiln as a pyrolysis furnace. If the fixed bed reactor the heat transfer was dominated by conduction, the heat transfer in the rotary kiln is more controlled by the convection and radiation transfer due to stirring and turning of biomass by the kiln. In the study, the biomass used was mahogany with an initial weight of 150 grams. The rotary kiln rotated at 10 rpm and the heating rate during the pyrolysis process was around 0.1483°C/s. The pyrolysis temperatures used were varied as 250°C, 350°C, 450°C. Meanwhile, the percentage of zeolites used from 0% to 60% with a mesh size of 80. The results showed that zeolites were able to increase tar production and maximize the reduction of char as an effect of the Bronsted-Lowry and Lewis reaction in the process of catalytic cracking. The maximum production of tar and char production was also supported by the process of convection and radiation from the rotary kiln wall increasing the rate of heat transfer to decompose the biomass.</p><p class="02abstracttext"> </p>

Effect of Surface Roughness on Fluid Flow and Heat Transfer Characteristics of Lattice Brick Setting in Tunnel Kilns

Abstract This paper presents the effect of brick and kiln wall roughness on the fluid flow, pressure drop, and convection and radiation heat transfer in tunnel kilns. The surface roughness of 0–4 mm is investigated for bricks and tunnel boundary. Another wall roughness of 10 mm is considered to explore the effect of significant defects in the tunnel boundary. The study is conducted using a three-dimensional computational fluid dynamics (CFD) model based on the finite volume method with the k – ω turbulence model. The convective heat transfer coefficients enhance by 45% and 97%, and the pressure drop increases by 25.1% and 80.4% as the brick roughness is increased from 0 to 1 mm and 0 to 4 mm, respectively. The ratio of heat transfer rate to pumping power reaches its maximum at a brick roughness of 2 mm. These results provide essential knowledge about the acceptable range of brick roughness for manufacturers. As the tunnel boundary roughness is increased from 0 to 1 and 0 to 10 mm, the heat transfer rates increase by 1.34% and 3.88%, while the pressure drops increase by 7.5% and 18.2%, respectively. These results are supportive of scheduling the maintenance of tunnel kilns’ interior structure. Moreover, the enhancement of the radiation heat transfer depends on the brick emissivity and the area ratio of rough to smooth surfaces.

Numerical analysis of the thermal profile inside the wall of a rotary cement kiln

Abstract The present study aimed to evaluate the temperature profile along the inside of the wall of a clinker kiln from a cement industry. The problem was modeled by the equation of transient heat conduction in cylindrical coordinates, considering radial symmetry. Being the wall composed of different materials, even adopting constant physical properties, there is no analytical solution to the problem. The method of the lines was used, being the radial and axial directions discretized by finite differences and the resulting system of ordinary differential equations integrated in time until obtaining the temperature field in steady state. The obtained field was compatible with heat transfer fundamentals and presented a good fit in relation to industrial data. The main limitations of the modeling performed in this study include the fact that the gases and solids contained in the kiln have not been modeled, and the variation in thicknesses of the layers of the kiln wall has not been considered. The program developed in this study can be used to evaluate the performance of different refractories or to infer the refractory wear level from experimental kiln surface temperature profiles.

Temperature acquisition and heat loss on the wall of an intermittent kiln

In the research the temperature acquisition was carried out inside and outside the wall an intermittent furnace and the evaluation of the energy loss on the wall during baking process, the first phase begins with the design, programming and implementation of an virtual instrument for data temperature acquisition and generation of temperatures profiles then, heat loss due to conduction on the furnace wall was determined considering one-dimensional heat flow, in radial direction and in a transitory state. The virtual instrument was programmed every 5 minutes and 1596 data were recorded, the input heat supplied to the furnace was 49.2x106 KJ and the energy losses due to the furnace wall were 5.2x106 KJ indicating the 10.57 percent of the supplied energy. Results of research have made it possible to establish trends in the temperature distribution, as well as identify thermal energy entering and leaving the furnace to propose improvements in performance of the furnace that increase its energy efficiency, reduce fuel consumption and gas emissions to the environment avoiding acute respiratory diseases.

Carbonization temperature and charcoal properties at different positions in rectangular kiln

To increase production and decrease the heterogeneity of charcoal produced in rectangular kilns, the control of carbonization must be carried out based on the kiln internal temperature. The objective of this work was to analyze the maximum carbonization temperature and the time of thermal degradation at temperatures above 290 °C based on the internal kiln wall temperatures, in addition to evaluating charcoal properties in different positions of a rectangular kiln. Wood from the hybrid Eucalyptus urophylla x E. grandis at seven years of age was used for carbonization in rectangular kiln where temperature was monitored and controlled. Process parameters and charcoal quality were evaluated in seven positions in the rectangular kiln. Positions 1 and 7 had higher maximum temperature values and thermal degradation time at temperatures above 290 °C in comparison with the other positions, which presented similar values. There was no significant effect of kiln position on the characteristics of charcoal, which presented average values of 234.61 kg m-3 of bulk density; 55.87% of pieces with size greater than 30 mm; 19.77% of fines (granulometry < 9.5 mm); and 20.80% of friability, 75.39% of fixed carbon, 24.37% of volatile materials, and 0.24% of ash. It was concluded that the kiln position affects the temperature and time of thermal degradation; however, the control of temperature guarantees the production of homogeneous charcoal throughout the kiln, presenting satisfactory quality for steel industry usage.

Numerical investigation of the impact of coating layers on RDF combustion and clinker properties in rotary cement kilns

The formation of regions of solid coating, where agglomerated clinker material adheres to the refractory lining of the kiln wall, is very common during cement clinker production. While a thin coating layer protects the refractory lining, strong deposit formation can impair the material flow through the kiln. In this study, the impact of these coating layers on the clinker production process within a rotary kiln is investigated with CFD simulations. The fuel injected at the main burner is a mixture of pulverized coal and refuse derived fuel (RDF). Advanced models were developed to accurately describe the trajectories and thermal conversion of non-spherical RDF particles in the gas phase. These models are based on a detailed fuel analysis of major RDF fractions. A blocked-off region approach is used to consider different coating profiles within the simulation domain. The thermochemical processes in the clinker bed of the kiln are approximated with a one-dimensional model that calculates heat and mass exchange with the gas phase, the incorporation of fuel ashes into the bed and the chemical-mineralogical reactions of the clinker. The blocked-off region approach is also employed to account for the clinker bed geometry in the kiln, which greatly depends on the considered coating profile. Two cases, one with a thin and evenly distributed coating profile and one with a thick and locally concentrated coating, are simulated. The resulting impact on RDF conversion, gas phase properties and clinker phase formation are assessed and compared to a reference case without any coating. Results show that the insulation effect of a thin coating profile increases the gas phase temperature in the kiln and helps to reduce the free lime content of the final clinker product. In the case of heavy coating, a temperature shift towards the solid material inlet of the kiln occurs, which outweighs the beneficial insulation effect of the coating in the sintering zone and leads to lower local gas phase temperatures. In combination with reduced clinker residence times, this results in a slight increase of the free lime content in the clinker.