Firing Technology Research Articles

Numerical simulation of oxygen-enriched combustion in industrial processes

Industrial processes using fossil fuels have to meet stricter environmental requirements and improve energetic efficiency without compromising product quality. Oxygen-enrichment, and/or full oxygen firing technology addresses all these requirements, and leads to an increase in productivity in a variety of industrial applications. While the concept of oxygen enrichment has been around for a long time, its large-scale implementation has been postponed due mostly to the advances in air separation. The successful implementation of oxy-combustion has been largely based on state-of-the-art simulation tools, given the complexity of the process. As most of the oxy-combustion solutions have been implemented in existing air-fired furnaces, detailed design analysis has been required, in order to secure on-the-fly retrofit, without perturbing the furnace operation. This article presents the state-of-the-art in the simulation of industrial high temperature processes, with specific emphasis on oxygen-enriched combustion. A focus of the effort relates to the appropriate treatment of the combustion space, the load, and the interactions between them. Thus, different codes are implemented for each side, with information being exchanged between them, in a technique termed as numerical coupling. Examples of industrial systems such as glass melting, steel reheating and cement making are provided. Although the 3-D CFD coupled simulations are very helpful in designing improved processes, they require important computing resources, limiting the use of detailed chemistry, radiative transport properties, etc. One way to overcome this limitation is to use less complex models, such as one-dimensional models during the initial process design phases, allowing selection of a first set of operating conditions such as the power distribution along the furnace. The article also presents an on-going model development, namely the NOx = NOx production from oxy-fired systems, a topic of great interest in the design of new generation burners.

Analysis of Mesoamerican Plumbate Pottery Surfaces by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a highly sensitive microprobe technique with many potential applications in chemistry-based archaeological provenance research. Laser sampling makes it possible to characterize individual components of heterogeneous matrices or to characterize surface materials, such as pigments, slips, and glazes on ceramics. Quantifying the analytical data poses a significant challenge, but an approach suggested by Gratuze et al. (2000) seems to perform well if the major oxides are measured. In the present study, LA-ICP-MS is used to characterize the slipped surfaces on specimens of a famous Mesoamerican tradeware known as Plumbate. First, systematic chemical variation with depth in the slipped surface layer is investigated in order to determine how much material to remove by pre-ablation before taking measurements for provenance determination. Slip-compositional subgroups are found to coincide well, but not completely, with paste-compositional subgroups identified in a separate study that employed instrumental neutron activation analysis (INAA). Comparison of LA-ICP-MS data on raw materials from the presumed source region (Pacific coastal southern Mesoamerica near the present border between Mexico and Guatemala) to the slip-compositional groups yields highly specific source attributions that agree with provenances determined for the INAA paste groups. This evidence indicates that the distinctive Plumbate paste preparation and firing technology was shared by two groups of potters who exploited two distinct ceramic resource bases within the Pacific coastal source region. The dominance of Plumbate at sites outside these two source areas indicates the importance of intra-regional commercial interaction during the Late Classic through Early Postclassic periods.

The influence of shaping and firing technology on ceramic properties of calcareous and non-calcareous illitic–chloritic clays

Two very different illitic–chloritic clays (calcareous and non-calcareous), both currently used in the Italian brickmaking industry, were used. Technological testing consisted in a simulation of the industrial processing performed at a laboratory scale. The pieces were obtained by three shaping techniques, pressing, extrusion and moulding, and fired at 1000 and 1100 °C, in fast and slow heating cycles. In each case their technological properties were studied. The microstructure and technological parameters of the ceramic pieces vary greatly, depending on the clay composition and the processing techniques. Pressing always produces pieces made from non-calcareous clay with the lowest drying and firing shrinkage, open porosity and water absorption. As it regards the calcareous clay, the lowest values of drying and firing shrinkage and water absorption are obtained by extrusion and moulding, respectively. The mechanical resistance, pore size distribution and critical pore diameter do not reflect clearly the influence of shaping techniques. Independently from the shaping technique adopted, all non-calcareous bodies show higher Maage's indexes than the calcareous ones. In any case, the Maage's durability factor is higher in extruded samples.

Medieval pottery kilns in the Carpathian Basin

This article discusses tenth–sixteenth-century pottery kilns in the Carpathian Basin in the territory of medieval Hungary. Kilns are classified on the basis of their structure, building technique and firing technology and these characteristics are examined using archaeological evidence, ethnographical sources and also technological and pyrotechnical analysis. The archaeological and stratigraphical features and some methodological problems of medieval pottery kiln study are also discussed and a topographical analysis of the pottery kilns in relation to the workshops and settlements on the basis of archaeological and historical evidence is presented. The history of the development, origin and distribution of the types of medieval pottery kilns in the Carpathian Basin is also presented. There is a brief discussion of the contribution that pottery kiln studies can make to the understanding of workshop organization.

Comments On ‘Technological Choices in Ceramic Production’, Archaeometry, 42(1), 1–76, 2000

Sillar, B., and Tite, M. S., 2000, The challenge of ‘technological choices for materials science approaches in archaeology, Archaeometry42, 2–20. Livingstone Smith, A., 2000, Processing clay for pottery in northern Cameroon: social and technical requirements, Archaeometry42, 21–42. Sillar, B., 2000, Dung by preference: the choice of fuel as an example of how Andean pottery production is embedded within wider technical, social, and economic practices, Archaeometry42, 43–60. Pool, C. A., 2000, Why a kiln? Firing technology in the Sierra de los Tuxtlas, Veracruz (Mexico), Archaeometry42, 61–76.

Technological features of the ‘Cotto Variegato’: a petrological approach

The ‘Cotto Variegato’ are tiles used in Lombardy, between the XVII and XIX centuries as flooring for several historical buildings. Tiles are produced by the processing of two compositionally distinct clays. The main stylistic character of these tiles is a banded texture producing a veined aspect, in which white and red bands are also folded. The artefacts were hand crafted using two clayey raw materials of different composition, that are only partially mixed before the firing. The colour differences are produced during the firing. In all samples white and red portions are always composed of Ca-rich and Ca-poor clay, respectively. The multi-layered texture was obtained by a multiple folding and pressing process of the mixture. The interference of fold limbs with the tile surface gives the ‘variegato’ style to tiles. The paper explains how basic petrological knowledge can be applied to the study of ceramic artefacts in order to define provenance of the raw material, firing technology and how ancient craftsmen transformed the natural clayey materials into floor tiles. The methodological approach is that commonly applied to the study of the rocks and consists of textural analyses, at a different observational scale, combined with X-ray powder diffraction, X-ray fluorescence and microprobe analyses.

Infra-red Spectroscopy of Ceramics from Tell Brak, Syria

Infra-red microspectroscopy (IR), in both reflectance and transmission geometries, can be successfully applied to archaeological ceramics. This non-destructive technique provides constraints on the mineralogic make-up of both ceramic bodies and coatings. Using a combination of IR, X-ray diffraction, and inductively coupled plasma analysis, we examine select samples from Tell Brak, Syria, from three periods, the Halaf/Ubaid, Akkadian and 2nd millennium, in terms of their mineralogy and thus firing temperature. Utilising this technique, “local” and “imported” categories of samples are proposed, and developments in firing technology can be identified.

00/02024 Heat and firing engineering concept of the steam boiler for Unit K of the Niederaussem brown coal power plant with optimized firing technology

00/02024 Heat and firing engineering concept of the steam boiler for Unit K of the Niederaussem brown coal power plant with optimized firing technology

WHY A KILN? FIRING TECHNOLOGY IN THE SIERRA DE LOS TUXTLAS, VERACRUZ (MEXICO)*

The benefits of one ceramic firing technology over another are not absolute, but depend upon the interaction of multiple environmental, economic and social factors, as well as the specific design of firing facilities. The coexistence of updraft kilns and open firing methods in the Sierra de los Tuxtlas, Veracruz, Mexico, for over 1700 years provides a case‐in‐point. Evaluation of the performance characteristics of ancient and modern firing technologies in relation to their natural and behavioural contexts offers a more secure basis for understanding this specific historical instance of long‐term polymorphism than explanations based in the generalized technological advantages of kilns or their cross‐cultural association with intensive modes of production.

Glazed Majolica Articles Produced by Single-Stage Firing

Results of synthesis of ceramic mixtures for producing glazed majolica articles employing single-stage firing technology are presented. The features of gas formation and formation of the structure of the crock and a clear glaze layer are studied. Criteria for selection of the mixture composition and the time/temperature parameters of the heat treatment are determined.

98/02190 Co-combustion of biomass pretreated in a fluid bed pyrolysis unit

An attractive option for reducing the net CO2 emissions is to substitute coal with biomass in large power plant boilers. However, the presence of chlorine (Cl) and alkali metals (K, Na) in biomass may induce large operational problems due to ash deposit formation on the superheater tubes. The aim of this study was to investigate ash transformation and deposition behavior in two biomass-fired boilers, firing wheat straw and/or wood. The influence of straw firing technology (grate and suspension) on the ash transformation, deposit formation rate and deposit characteristics has been investigated. Bulk elemental analysis of fly ashes revealed that fly ash from suspension firing of straw has high contents of Si, K and Ca, while fly ash from straw firing on grate was rich in the volatile elements K, Cl and S. Investigations of deposit formation rates were made in the superheater and convective pass regions of the boilers by use of an advanced online deposit probe. During straw firing on grate, the measured deposit formation rate was close to 38 g/m2/h. Data from straw suspension firing showed a deposit formation rate of 41 g/m2/h. The deposit formation rates during straw suspension firing and straw grate firing were on similar levels. This was observed even though the concentration of fly ash in the flue gas was significantly higher during straw suspension firing. The influence of co-combustion of wood with straw on deposit formation rate, probe heat uptake and deposit characteristics was also investigated during suspension firing conditions. Data from 35% straw suspension firing with wood showed a deposit formation rate of 33 g/m2/h for the first 12 h. The deposit formation rate increased to 41 g/m2/h with 100% straw firing. The probe heat uptake reduction up to 40 h of exposure time was 3.0, 7.3, 8.4 and 16.5 kW/m2 during 35, 65, 80 and 100% straw firing, respectively.

Characterisation of the surface conductivity of glassy materials by means of impedance spectroscopy measurements

Abstract The phenomenon of tin dioxide doping by antimony, Sb(V), atoms in semiconductive glazes is discussed. In particular, the impedance spectra of the glaze surface at room temperature were experimentally determined, and the results were analysed in terms of equivalent circuits. The parameters resulting from the fitting procedure were related to the SnO 2 Sb(V) relative content, the SnO 2 Sb (V) percentage in the glaze, and the microstructure as observed by SEM. It is proposed that the addition of SnO 2 and Sb 2O 3 to a common glaze for ceramic tile results in a semiconductive continuous phase, whose electrical characteristics fulfil the antistatic floor regulation, as far as surface conductivity is concerned. As a whole the obtained results suggest that the thermal cycle used in fast firing technology is capable to promote the oxidation of Sb 2O 3 to Sb 2O 4, resulting in a sufficient amount of Sb(V) capable of generating a semiconductive behaviour of the SnO 2 crystalline phase dispersed in the glaze.

97/03980 System designs to convert a package boiler to fire coal-based fuels

The Energy and Environmental Research Corporation (EER) and the Pennsylvania State University are engineering the conversion of an existing heavy fuel oil and natural gas-fired watertube boiler at a US Department of Defense (DOD) facility to fire either micronized coal-water slurry fuel (MCWSF) or dry, micronized coal (DMD). The retrofit is being conducted as part of a program for DOD and the US Department of Energy in which coal-based technologies are being evaluated to determine the technical and economic viability of replacing heavy fuel oil with coal in industrial-sized boilers. Retrofit options currently being evaluated are the direct firing of MCWSF and DMC, and coal precombustion technologies. The status of the evaluations and designs of the MCWSF and DMC direct firing technologies is presented.

Pottery Kilns of Ancient Ejutla, Oaxaca, Mexico

In contemporary Mesoamerica, traditional methods of ceramic production are highly variable. Tracing this diversity to its prehispanic antecedents has been limited by a major empirical difficulty: the identification of production sites, especially kilns and other firing features, in archaeological contexts. As a consequence, Mesoamerican archaeologists have rarely recognized technological variation in firing methods, thereby limiting their capacity to discern spatio-temporal variation in ceramic production. The discovery and excavation of relatively ephemeral ceramic firing features at the Ejutla site in Oaxaca, Mexico, offers an archaeological perspective into the variability of pottery production techniques that were employed in ancient Mesoamerica. The excavated firing features and associated indicators of ceramic production at Ejutla are described and compared to similar features at other sites. An experimental study was conducted to understand how these firing features worked and the nature of the remains that they would have left. Our research suggests that impermanent methods of ceramic firing were more common in ancient Mesoamerica than previously supposed. The ephemeral nature of these firing procedures may contribute to the overall scarcity of excavated firing features to date. Consideration of ceramic firing technologies is argued to be a significant research concern since variation in firing methods may indicate prehispanic differences in the intensity of ceramic production.

Thermomechanical analysis of fired ceramic materials

A thermomechanical analysis of fired clay specimens is carried out and empirical equations are derived for dilatation (shrinkage) as a function of temperature. The experimental results obtained can be used in designing optimum firing technology for preparing ceramics from polymineral clays.

Utilisation of straw and similar agricultural residues

Considerable straw resources and the wish for a reduction of the CO 2 emission by substitution of fossil fuels with biomass are the basis for a still growing European interest in production of power based on straw or co-firing of straw and fossil fuels. However, straw is an expensive fuel, and 15 years of experience have shown that straw is rather problematic as a fuel for heat- and power production. To obtain reasonable power efficiencies, stable operational and environmental conditions, as well as an acceptable economy, it is important to know more about the characteristics of the straw and straw ash in relation to energy, to develop better firing and combustion technologies, and to optimise the logistics system for gathering and delivery of straw. Compared with the coal firing technology, the extent of research and development within power production based on straw, is modest so far. Political agreements on straw-based power production at big power plant units in Denmark and the UK will during the years to come contribute essentially to a higher degree of know-how on utilisation of straw for energy purposes.

Mössbauer study of the firing technology of the moon-white Jun porcelain in Chinese Yuan Dynasty

The moon-white Jun porcelain glaze contains Fe2O3, Fe3O4 and structural iron. The firing atmosphere of ancient Jun kilns was modestly reductive. The firing temperature was slightly above 1250 ‡C. The glaze color appears moon-white, and is related to the low concentration of Fe2+. The coordination numbers of Fe2+ and Fe3+ are both 4.

Development of as-fired aluminium nitride substrates with smooth surface and high thermal conductivity

As-fired aluminium nitride (AIN) substrates with smooth and uniform surface have been developed by green sheet and firing technology. The effect of setting for firing on surface roughness was investigated. AIN substrates were fabricated by pressureless sintering of green sheets piled up and sandwiched between AIN plates in an AIN crucible. The thermal conductivity, surface roughness and bending strength of the substrate sintered at 1770 °C for 2 h under a pressure of 1 MPa nitrogen were 194 Wm−1 K−1, 0.15 (μm and 353 MPa, respectively.

Review: Burning Refuse-Derived Fuel in a Rotary Cement Kiln

In cement kilns, combustion takes place under very high flame temperatures and relatively long residence times. These conditions are favourable for the burning of refuse waste. The purpose of this note is to review the combustion and pollutant emission implications of using such a fuel as a supplementary source of heat in a cement kiln. Based on technical and environmental considerations, the analysis of burning refuse-derived fuel (RDF) in a cement kiln shows that no special firing technology has to be installed except that of the RDF handling system, that there is an upper limit to the total fuel consumption (no more than 30 per cent) for firing RDF and that there is no increase in the emission levels of air pollutants (including acid gases, dioxins, furans, etc.). At present, there seems to be no economical advantage in burning RDF. However, if municipal solid waste (MSW) is generated in large amounts and financial support is provided by the local authority to cover the investment/operating costs, burning RDF in cement kilns will become economically attractive as well as feasible.

Research on the Techniques of Making Pottery Figurines of the Qin Army

AbstractA description of the excavations of the Qin pottery army is given first. Analyses of the raw materials are reported. The construction techniques of the soldiers and horses are detailed separately. Lastly, analysis and reconstruction of the firing technology and post-fire paints are presented.