Tank Furnaces Research Articles

A Glimpse of the Evolutionary Studies on Glass Tank Furnace in Terms of Raw Materials, Melting Process, Refractories, and Energy Efficiency

This paper discusses the raw materials used in ancient glasses. Following a consideration of some archaeological reasons for studying glass, the discussion concentrates on the evidence provided by the chemical analysis of the glass and focuses on glass from later prehistoric Western Europe. Consideration of the major, minor, and trace components of the glass leads to the conclusion that prehistoric glass artisans were able to closely control the addition of small quantities of colorants, opacifiers and clarifiers to the glass melt. Some possible ways of introducing such small quantities of these substances are suggested. Reduction of fuel consumption in glass melting furnaces can cut the cost of production, and tackle the global warming. The paper presents three independent solutions to reduce the fuel consumption in industrial glass melting furnaces. The solutions include air preheating, raw material preheating, and improving the insulation of combustion space refractory. Energy balance equations are derived and used to identify the effects of each solution. The results indicate that the three solutions reduce the fuel consumption by 9.5%, 17%, and 34% respectively. An insight into the refractory usage is shown for different sections of the glass tank furnace.

Metal prills in primary glass: A puzzling aspect of the production process

Primary glassmaking in the first millennium CE during Roman and post Roman periods was conducted in large heating installations, the so-called tank furnaces, in two main regions of the East Mediterranean, namely the Levant and Egypt. Especially in Israel, a large number of tank furnaces in various sites such as Apollonia, Bet Eli’ezer (Hadera) and Jalame have been discovered, giving new insights regarding the technology of glassmaking in the first millennium CE.In this paper, we investigate the existence of metal prills embedded in raw glass at the contact layer with a tank furnace floor. The glass chunks were found in a refuse pit at Umm ez-Zinat, southern Carmel, Israel, and are dated to the Late Roman-Early Byzantine periods (fourth-early fifth centuries CE) based on glass vessels found with the debris of primary and secondary production. Another three prills from Bet Eli’ezer, the massive glass industry dated to the seventh-early-eighth centuries CE, were also analysed to compare any similarities/differences between the prills from the two sites.Results show that the prills vary greatly in shape and composition. Their morphology ranges from rounded spheres to asymmetric ellipses, all showing inclusions indicating the source material was chemically heterogeneous. The prills from Umm ez-Zinat are mainly lead, with minor contribution of copper, tin, antimony and silver as inclusions. Two of the three prills from Bet Eli’ezer are copper alloyed with lead, and one has a lead matrix with various copper inclusions. We investigate possible scenarios to understand the nature of the metal in the glass, how and when it was added to the glass melt, and possible technological and ritual interpretations for its presence.

Recycling of exhausted dust from regenerator of glass furnace in glass batch melting

In soda-lime glass manufacturing, evaporation of volatile compounds from glass melt is the origin of the dust emission from glass tank furnace. The exhausted dust then is deposited on the regenerator and is needed to be removed. Thus, this study focuses on using the dust from melting glass in glass production. The glass batches were prepared from 0 wt% to 10 wt% of the exhausted dust from soda-lime glass production as a substitution of the total raw materials. The analysis of phase and chemical composition of the dust by x-ray powder diffraction (XRD) and x-ray fluorescence technique (XRF) indicated that it consisted mainly sodium sulphate. Thermal analysis (TG/DSC) revealed that the addition of exhausted dust reduced the temperature of the melting reaction of the glass batches. The optimum amount of the exhausted dust, which made it possible to obtain the glass with the lowest number of remaining bubbles, was 2 wt%. From CIE lab and dilatometry results revealed that up to 2 wt% replacement of total raw materials by the exhausted dust in the glass batch did not affect the glass color, thermal expansion coefficient, glass transition temperature and dilatometric softening point of glass samples.

Calculated estimation of influence of convection rate of molten working and heating medium during hardening of restored parts

The paper presents a computational and mathematical assessment of the convection rate of the molten working and heating medium during the strengthening of the restored parts. The calculated estimate is based on the theory of multidimensional heat and mass transfer processes occurring in the electrode furnace during the strengthening of the restored parts. Computational modeling is carried out based on the choice of initial data and characteristics. The calculation results made it possible to establish the effect of the convection rate of the molten working and heating medium on the hardening of the restored parts. The theoretical description of the conditions for the onset of convective motion of a molten continuous medium is based on the Rayleigh–Bénard, Navier–Stokes, and Lorenz equations for the flow of a viscous continuous medium using the Oberbeck-Boussinesq approximation. The description of the internal space of the tank furnace is carried out by a system of differential equations of the balances of elementary volumes into which it is divided. Transformations into a system of differential equations are carried out on the basis of the Galerkin method. The use of this transition method leads to the fact that the sought functions are represented in a variable-separated form that exactly satisfies the boundary conditions. The introduction of assumptions and boundary conditions made it possible to obtain the equations of motion of mass forces and a viscous medium in a polar coordinate system. A formula describing the configuration of the temperature field is obtained.

Characterisation of Byzantine and early Islamic primary tank furnace glass

In order to improve the understanding of glass production and provenance, we present trace element and Sr, Nd and B isotope ratio data for 15 samples of raw natron glass from a single tank furnace in Apollonia (6th–7th century CE) and eight glass samples from two tank furnaces in Bet Eli'ezer (8th century CE) in Israel. This data provides information about the geochemical homogeneity within a single batch of raw glass and about the differences and/or similarities between different tank furnaces on a single site. Four glasses from a secondary workshop at Tell el-Ashmunein, Egypt (8th–9th century CE) are analysed for comparative purposes.All raw glass samples have uniform trace element patterns and ratios. Because of poor mixing of the glass batch before and during firing, absolute concentrations however can vary significantly within a single tank furnace. The concentrations of trace elements commonly associated with (de)colouring are very low and can be attributed to background concentrations in the sand raw materials. This indicates that there was no obvious recycling of glass cullet at this stage of the production process and that the tank furnace glass is primary glass in the true sense of the word. The isotopic compositions of Sr, Nd and B in the tank furnace glasses are relatively homogeneous. This confirms their potential as provenance indicators. The isotopic composition of Sr in tank furnace glass from Apollonia and Bet Eli'ezer indicates that the lime was derived from seashell, suggesting the glass was produced from beach sand. Glass from Tell el-Ashmunein contains Sr with lower 87Sr/86Sr ratios, pointing to the use of limestone as the source of lime. All primary glasses from Israel analysed have Nd isotopic compositions typical for an Eastern Mediterranean origin. δ11B indicates that natron used in the tank furnaces in Apollonia and Bet Eli'ezer was most likely imported from Egypt.

Selection of the Optimal Air Heating Temperature for Glassmaking Tank Furnaces

The required level of heating of the air, securing in the combustion zone the maximum admissible temperature of the products of combustion of a tank furnace, is determined by a computational method. It is shown that recuperative heating of air up to superhigh temperatures is not expedient.

Structure of the Tuyere Zone of A Tank Furnace with A Bubbling Layer and Gas Delivery Through A Tuyere Located on the Side Wall Below the Level of the Molten Glass

Possible regimes of gas efflux into a layer of molten glass through a horizontal tuyere as well as the structure of the blowing zone formed in the process are investigated using a physical model of a glass furnace with a bubbling layer. The initial data required for uniqueness are obtained in a mathematical model of mixing of molten glass in a tank furnace.

Composition of Byzantine glasses from Umm el-Jimal, northeast Jordan: Insights into glass origins and recycling

Abstract Twenty glass samples collected from four structures at Umm el-Jimal, northeast Jordan were analysed using the electron probe microanalysis (EPMA). Except one ash-soda-lime-silica glass, all were natron soda-lime-silica glasses of Levantine origin. Most of the glasses compositionally resemble glass from the Byzantine tank furnaces at Apollonia-Arsuf (Arsuf), but four with lower lime are closer to Umayyad period production at Bet Eli’ezer (Hadera). The paper presents diagnostic information indicating recycling in a diagnostic recycling table (DRT) in which the analyses are ranked in a descending order of K 2 O, a key contaminant in the recycling process. This allows the comparison of a range of contaminant elements and it is observed that in general glass contaminated with fuel ash components K 2 O, P 2 O 5 and CaO are also richer in transition metal oxides CuO, PbO, FeO and MnO, confirming that both sets of elements are important in identifying recycled glass. Chlorine is also identified as a component modified by recycling. The results ascertain that Umm el-Jimal was part of a major system of glass recycling in the Byzantine period, and emphasise the importance of recycled glass in its supply, in spite of its relative proximity to the location of raw glass production on the Syro-Palestinian coast.

Efficient Control Regimes for the Thermal and Technological Process of Glassmaking in Tank Furnaces for Float-Glass Production

The basic principles for controlling the thermal and technological regimes of the glassmaking process in furnaces used for sheet-glass production by the float method are presented. Fuel delivery is redistributed above the melting zone in order to improve the operating efficiency of the glass furnace. The technical results of using an efficient distribution of the thermal loads over the burners in the furnace is lower energy consumption in the melting process and higher product quality. It is important to maintain the prescribed level of iron oxides in the glass and to monitor the oxidation-reduction potential during the glass melting process.

A XANES study of chromophores in archaeological glass

We applied X-ray absorption near edge spectroscopy (XANES) to obtain information on the origin of glass colour of several archaeological samples and on the oxidation conditions employed during their production. We studied a series of selected glass fragments—mainly from excavated primary and secondary production centres and dated to the first millennium AD—containing iron and manganese in a wide compositional range. In most of the studied samples iron is rather oxidised, while Mn K-edge XANES data show that, in all the studied glasses, Mn is mainly present in its reduced form (predominantly 2+), with the possible subordinate presence of Mn3+. The most oxidised samples are the HIMT (high iron manganese titanium) glasses, while the less oxidised ones belong to the primary natron glass series from the early Islamic tank furnaces at Bet Eliezer (Israel), and to the series coming from a Roman glass workshop excavated in Basinghall Street, London. In these glasses, iron is approximately equally distributed over the 2+ and 3+ oxidation states. The XANES analyses of two glasses which had been deliberately decolourized using Sb- and Mn-based decolourizers demonstrate that Sb is more effective than Mn as oxidant.

SEM-EDS analysis of ancient gold leaf glass mosaic tesserae. A contribution to the dating of the materials

Metal leaf (gold, silver or their alloys) glass tesserae began to be used in wall mosaics in the first century AD (the first examples are in Rome) and their use has been uninterrupted up to day.The metal leaf could be obtained from circulating coins, jewellery or refining. According to various techniques that have changed over the centuries, the leaf was hot fixed between two glass layers.From an archaeological point of view, it is interesting to know when and where these tesserae were made, if they were new made or if they were reused tesserae recovered from earlier dismantled mosaics.The determination of the glass composition of the tesserae is not of great help in this connection, for the same kind of glass was used over long periods. Available information is still scanter for glasses produced between the 1st to 8th centuries when the batch of raw materials (a natural soda called natron and a silica-lime sand) was melted in large tank furnaces and chunks of raw glass were transported all over the Mediterranean to be remelted and shaped into manufacts in small pot furnaces.The SEM-EDS analysis is proposed in this study as a useful tool to investigate the composition of both the glass and the gold alloy in leaf tesserae from mosaics of the 1st - 9th centuries. The comparison of the composition of the gold leaf of the tesserae with that of circulating gold coins (for which an important analytical data base is available), adds further information to the glass analysis, allowing us to improve the dating of the tesserae and increase the knowledge that may result from scientific analyses. The results demonstrate that good quantitative analyses of the metal leaf can be performed and that metal leaves made of pure gold or gold-silver alloys were used.

Numerical Simulation of Heat Transfer and Fluid Flow in Glass Tank Furnace after Bubbling

Numerical method to simulate the effect of air bubblers on glass melt flow and heat transfer in glass tank furnace is presented in this paper. The numerical simulation is preformed by using Gambit and Fluent software. Results of numerical simulation for glass melt flow and heat transfer with and without air bubbling technology are compared. The roles of stirring air bubblers installed in different locations played are discussed. The results show that mathematical model established in this paper can better simulate the glass melt circulation and heat transfer in glass tank furance, and air bubbler has a significant effect on glass melt circulation and heat transfer, and the best installation locations should be chosen by calculating in order to make full use of the air bubblers. Air bubbling technology will improve the quality of glass obviously if it is used properly. The results obtained can provide reference for engineering design of glass tank furnaces.

Chemical characterisation and manufacturing technology of late Roman to early Byzantine glass from Beit Ras/Capitolias, Northern Jordan

The finding of considerable collections of glass artefacts, together with considerable lumps of glass chunks, fuel ash slag and kiln fragments related to glass processing strongly suggests a local secondary production (working) of glass at the Beit Ras/Capitolias archaeological site in northern Jordan from the late Roman to the early Byzantine period. The chemical analysis of ancient glasses can provide important information regarding the manufacturing technology of the glass made during a specific period. The aim of this study is to characterise the chemical and technological aspects of late Roman to early Byzantine glasses excavated from this main archaeological site. Furthermore, the present paper aims to provide incontrovertible evidence that this site must be considered as a major centre for the secondary production of glass during a period between the 3rd and the 6th centuries. For this purpose, a considerable group of raw glass chunks and vessel fragments of different colours and typologies were collected. The results of chemical analyses indicated that the glass did not show a clear difference in chemical composition between late Roman and early Byzantine times. All the glasses (artefacts and chunks) are of the soda-lime-silica type and correspond to the previously defined Levantine I glass group. The chemical composition of the glass chunks, identical to that of contemporary glass of the same colour, strongly suggests that these chunks were used for the manufacture of late Roman to early Byzantine glass at Beit Ras. The observation of technological features indicates that glass chunks were produced in massive tank furnaces in other primary production centres elsewhere, and were meant for local reworking. According to the microscopic examination, it can also be observed that mould-blowing was the main technique used for forming glass.

Modeling of Redox Reaction in Glass Melt and Its Effect on Glass Flow

A new mathematical model is developed to solve transport of FeO with an apparent redox reaction coupled with a model of thermal convection in a glass tank furnace. A numerical method is proposed to calculate the distribution of FeO with a non-equilibrium reaction in a flow field. Computer simulation enables prediction of the FeO concentration, thermal conductivity, and optical characteristics. It is apparent that chemical homogeneity is attained by residence time and temperature, and that it is more uniform than the mechanical homogeneity by glass flow.

Method for Evaluating Thermal Convection in Molten Glass Flow in a Glass Tank Furnace

Various computer simulations of molten glass flow have been used for the design, operation and trouble shooting of glass tank furnaces. It is necessary to predict the degree of thermal convection of molten glass, whose viscosity is affected by the major composition of glass and thermal conductivity of which varies with the ferrous oxide (FeO) content. The thermal conductivity decreases as the FeO content increases. Thermal convection is characterized by the Rayleigh number, Ra, and the Prandtl number, Pr. Typically, Ra is expected to be large for a small thermal conductivity, but the actual thermal convection is weaker in this case than when the thermal conductivity is large. To elucidate the underlying convection mechanism, a two-dimensional mathematical flow model is developed in this study. Non dimensional formulation of the governing equations shows that Pr–1 affects the degree of thermal convection. The effective value of Ra, Raeff, is introduced to evaluate the influence of temperature-dependent properties on thermal convection. An evaluation method of thermal convection is proposed and extended to glasses with different thermal conductivities.

Mathematical model of bubble number density in glass tank furnace

There have been innumerable contributions to clarify bubble behaviour in glass melt, where various approaches have been carried out. Experimental results show bubble quality is represented by bubble number density, bubble diameter, and standard deviation of the diameter, which depend on time and temperature. The latest experiment implies growth of bubble is strongly dependent on temperature, and the standard deviation is independent of time and temperature. Not only appeared location but also number density of small bubble (seeds) is of major concern for manufacturers to produce high quality glass. A new mathematical model is developed to predict bubble number density, which quantifies effect of both fining and refining on the density by introducing an exhausting effect of bubbles from upstream of the highest temperature area, i.e. hot spot, and the downstream in melter, i.e. stagnant. Inlet bubble number density with melting down is extrapolated from the published data. Monitored diameter obtained in experiment is applied to calculation. Calculated bubble number density is compared with measured one in an actual flat glass furnace, which makes it clear that the mathematical model is valid to predict order of the density in the glass melt. Numerical simulation gives reasonable suggestion about fining effect.

Mathematical Modeling of Sulfate Fining in a Glass Melting Furnace

In this study, we propose a new mathematical model of dissolved SO3 transport in a glass melting furnace, considering secondary decomposition of sulfate. The calculated concentration of SO3 agrees with measured data near the maximum temperature area, hot spot, in an actual glass tank furnace. The effect of onset temperature of secondary decomposition, the maximum solubility of SO3 and concentration of inlet SO3 on sulfate fining is quantified by simulation.

The trend toward development of tank furnaces in production of sheet glass

The cardinal changes in the design of sheet glass tank furnaces that significantly improve the technical and economic indexes are examined. The most effective technical solutions are the change in the design of the feed pocket, burners, regenerators, and knuckle and equipping them with modern process equipment and highly stable refractories.

Dynamics of the redox state of the melt in the continuous production of clear glass

The effect of a set of external factors on the redox equilibrium of iron and sulfur, changes in melt properties, and light transmission of clear sheet glass is investigated for continuous production of glass. A quantitative estimate of trends in the variations of the redox potential of glass melt is proposed. Practical measures improving the efficiency of a tank furnace by correcting the oxidation state of the melt are considered.

Effect of an overflow sill on heat and mass transfer in the glass-melting tank of a furnace with horseshoe-shaped flame

A numerical model is used to study the effect of the height and position of an overflow sill on glass melt hydrodynamics and heat transfer in a glass-melting tank furnace. A differentiated effect of the overflow sill on the formation of convection flows and heat and mass transfer in various parts of the tank is established. It is demonstrated that the considered parameters of the sill have virtually no effect on the intensity of the charge convection cycle. At the same time, they have a significant effect on melt hydrodynamics past the sill. The quantitative correlations between the design parameters of the sill and certain characteristics of heat and mass transfer in the melting tank are identified.