Refractories, Furnaces and Thermal Insulations
The Faculty of Metallurgy of the Technical University of Košice has regularly organized the international scientific conference on “Refractories, Furnaces and Thermal Insulations” in Tatras/SK, in a two-year periodicity. The 10th conference on the subject was held in April 2018 at the Congress Center of Hotel Grand in Jasná, Low Tatras. Introduction Nearly 200 experts from 11 countries took part in the professional and social program of the conference. In the technical program, 24 papers were presented. The scientific contributions can be divided into following main thematic groups: development of refractory products, new and innovated refractories and their properties, application of refractory materials, thermal engineering and recycling of refractories. Next, there will discussed briefly the papers content (in case that the paper has more co-authors, only the presenting author will be indicated). Development of refractory products J. Vlcek/CZ dealt with the development of non-cement bonding systems. He described the preparation and the properties of a sol-gel binder from high-purity raw materials (SiO2 and Al2O3). The efficiency of binder was verified by the addition to a bauxite-based refractory castable, the properties of which were compared to the refractory castable with a calcium-aluminate cement binder. After the thermal treatment of casta-bles with the sol-gel bond the formation of final phases was completed at 1000 °C, resp. 1200 °C, and the strength reached 27 MPa. The sol-gel bond can be consid-ered being a possible alternative of cement bonding. D. Chudíková/SK referred to the latest trends in RMS A.S. Košice in the development of insulation refractory ma ter ials with higher refractoriness under load. She presented the portfolio of innovated insulation products that included several types of the lightweight castables and bricks based on advanced lightweight aluminosilicate materials (Al2O3 content in the range 36–42 %). A new product line of lightweight bricks KOLAS with bulk densities 500–1200 kg·m-3 and T0,5 value of 1190–1422 °C was developed for applications in thermal aggregates with continuous operation. The basis of this brick consists of lightweight aluminosilicate, perlite, shale and a binder providing a cer am ic bond. Insulating castable KOPORO, based on spherical alumina, is suitable as insulation layer of thermal aggregates, such as supports of annealing furnaces, doors of pusher furnaces and other applications, where insulation of lining and avoidance of heat leaks is required. The newly developed lightweight products extend the application of products in the thermal aggregates with higher operating temperature. A. Kudžma/LT reported on the results of experimental work on the influence of Nano-Graphene Oxide Solutions (GOS) on the hydration of Calcium Aluminate Cement (CAC) at 20 °C. The studies have shown that the addition of GOS had an accelerating effect on the ion release in CAC (Gorkal 70) suspension. Measurements of the ultrasonic wave velocity revealed the differences in the formation of cement paste structure during hardening. The mixture with the addition of GOS forms denser structure compared with the mixture without GOS. The content of non-hydrated CA and CA2 is lower, while the content of hydration product CAH10 is higher in the mixture with the addition of GOS. The authors could conclude that the use of GOS as the additive to CAC enables controlling the hydration of the cement pastes and provides with a positive influence on the formation of the structure and the properties of CAC pastes. O. Orišenková/SK presented MgO–C refrac-tory materials manufactured in Slovmag AG. These materials use two environmentally friendly (low benzo [a] pyrene) bonding systems: synthetic novolac resin and CAR-BORES® (Rütger). Technological advantages (+) and disadvantages (–) of both binding systems are cited. Resin bond: simple manufacturing process (+), without polyaromatic hydrocarbons (+), higher strength after annealing at 200 °C (+), lower strength after carbonization at 1000 °C [(-), low residual carbon (–)]. CARBORES bonding: more complicated manufacturing process [(-), lower strengths after tempering at 300 °C (–)], higher strengths after carbonization at 1000 °C (+), highly organized structure of carbon bond (+), higher residual carbon (+). Properties of MgO–C materials based on fused magnesia (97 % MgO) with both binders and with the residual carbon content of 5 %, 10 % and 15 % are quoted. K. Lang/CZ reported on the situation in the production and application of aluminosilicate raw materials for the production of refractory materials. Attention was focused mainly on the production of chamotte grains at the largest manufacturer in Czech Republic, P-D Refractories CZ. He described the quality of individual raw materials and the production technology of fired granular raw materials in the broad range of Al2O3–SiO2. In the current shortage of these raw materials in the market, the investigation was mainly focused on the complex exploitation of available raw materials, especially on the use of fine-grained old stocks. The production of mixed grog and insulating grog are planned. New and innovated refractories and their properties A. Davies/GB introduced Isofrax®1400 and Insulfrax®LTX-AES Wools of new generation. The Fiberfrax Ceramic Fibre products (alumino-silicate fibres) have been complimented recently with the Isofrax and the Insulfrax (AES – Alkaline Earth Silicate) product groups. These AES insulation materials exhibit good thermal efficiency and low biopersistence that meet European regulatory requirements for man-made vitreous fibres. Isofrax is based on unique patented silica-magnesia chemistry, and is capable of withstanding continuous operating temperatures to 1400 °C. Blankets, modules, papers, and boards are available. Insulfrax is based on calcium, magnesium, silica chemistry and is capable of continuous oper ation to 1200 °C. The enhanced LTX fibre performance helps companies reduce their energy costs and meet increasingly strict carbon emission targets, without increasing the amount of insulation required. V. Wagner/DE introduced advanced materials, developed by Calderys/DE, for energy savings by optimised lining concepts. The developed refractory materials applied in linings of cement production lines can play an important role in terms of a cost and energy efficient plant operation. By providing low thermal conductivity (0,8 W/m·K at 1000 °C) and simultaneously showing a good alkali resistance co-existing with a high strength, now it is possible to line cyclones with just one layer. The name of this new product is CALDE™ GUN R 50 A, and can be applied easily by gunning. This new solution results in excellent energy efficiency and additionally increases the safety range during operation.
P. Ermtraud/PL discussed the possibilities of replacing Refractory Ceramic Fibre (RCF) in iron and steel forging furnaces without any drop in performance. Recently, RCF which widely replaced asbestos, has been classified as a category 1B carcinogenic in Europe. Morgan Thermal Ceramics has now developed and introduced a new product called Superwool®XT. It is a potassia aluminosilicate type of fibres, its melting point exceeds 1650 °C. Both in lab and industrial trials at temperature ranges from 900–1400 °C have proven its properties being capable to substitute a 1430 °C RCF blanket. This new material is suitable for continuous use up to 1300 °C even in harsh conditions in forging furnaces and many other applications, as for example reformers and crackers in petrochemical industry, specific annealing furnaces in heat treatment plants, steel industry, foundries, blast furnace plants and many others. S. Dvorák/CZ informed about the recent development of ilica bricks for the crowns of glass furnaces. Silica refractory is the preferred material for the crowns of most glass furnaces. The newly developed high-density silica brick, in comparison with commercial silica brick, has low porosity and low permeability, and thus also higher resistance to alkaline corrosion. Based on the results of corrosion tests, the predicted durability of this brick is expected to be 3–4 times higher. Technical parameters of the developed products were not specified. Application of refractory materials L. Dˇ urík/SK has presented a brief overview of a tundish working lining with refractory products of the company Žiaromat in Železiarne Podbrezová (ŽP). At present, there are two methods of making working lining in ŽP: 1. wet mixes applied by spray; 2. self-hardening dry mixes. Wet mix KAL-MAG 70T, which is commonly used in ŽP, is based on olivine and sintered magnesia with fibres and additives. Typical chemical compositions are: MgO 69,1 %, SiO2 24,9 %, Fe2O3 4,2 %, CaO 0,4 %. The self-hardening dry mix, in development, KALTUN 70D, has a similar composition to the wet mix. The aim of the first test was to find out the optimal chemical and granular com pos ition from the point of view of installation parameters and the performance of dry working lining in the operation conditions. The preliminary tests were promising and will continue. I. Priesol/SK reported on the optimisation of the ladle well filler sands for ladle slide gate system of casting ladles and their influence on the high free opening rate. The so-called filler sands are heterogeneous mixtures consisting of fillers – usually quartz sands, ceramic grains – especially chromite and zircon and separators – graphite or carbon black. The composition of filler sands must always be adapted to the metallur gical conditions in steelmaking, i.e. heating of the pan before tapping, convection of the steel in ladle during tapping, the holding time of steel in the ladle, the steel treatment processes in ladles and the level of molten steel in the ladle. Also important is the cleanness of the slide gate refractory assembly, prior to filling the filler sand, and its precise in-corporation into the nozzle, usually through a pipe. J. Klempai/SK described the replacement of refractory lining of casting ladles in conditions of OFZ A.S. (Orava Ferroalloy Industries). Ferroalloys, especially FeSi75 %, are transported in these ladles. Insulating boards Intoisol are installed on the shell of ladles. In the monolithic anchored working lining, products made by INTOCAST – In-toval TK 80 T with 80 % Al2O3 and gunning mixes Intomag VS16 or VS14 based on MgO are used. To repair the refractory lining, GUN 80 REPA is used. Technical data of the products were not listed. P. Kovárˇ/CZ dealt with refractory ma ter ials in aggregates for thermal processing of biomass and biowaste. The development was oriented primarily to the improvement of corrosion resistance, at operating tem-peratures of 1200 °C in the incinerators, with a possibility of short time exposure up to 1400 °C. New refractory products were pres ented: high-density materials based on andalusite (60 % Al2O3, porosity below 13 %) having high corrosion resistance, high-alumina based refractories (80 %Al2O3) with SiC addition, and refractories with high content of corundum (98 % Al2O3) with high resistance in reducing con-ditions (CO and H2). In addition, a SiC-based (70 % SiC) slip-casting material, with high resistance against thermal shock, has been developed for the fabrication of complicated formats and large moulded parts. V. Petrov/SK discussed the optimisation and design of torpedo ladle lining in U.S. Steel Košice. The aim of the new proposal of zonal lining is to achieve an even wear of working lining of torpedo ladle. By us-age of high alumina firebricks and refrac-tory mastic the corrosion resistance of the slag line increases. Another alternative of increasing the corrosion resistance is the application of bricks ALKO BSC (Al2O3–SiC–C brick based on bauxite) and ALKO ASC (Al2O3–SiC–C brick based on fused alumina). The disadvantage of ASC bricks with resin bond is higher thermal conductivity (thus higher transfer to torpedo shell) and higher permanent linear change. Economically it is more beneficial to use such zonal lining where the costs per ton of transferred hot metal are the lowest. P. Šíma/CZ described the thermal insulation of the torpedo ladles in the steelworks Trinec. With the intention of reducing the heat losses by the three-layer lining (total thickness 455 mm) of the 350 t torpedo ladle, the working lining was made of high-alumina bricks, with firebrick in safety lining, and with insulating boards PROMATON and PROMALIGHT in insulating lining (technical data not stated). The benefits of this design of lining have been proven by thermal measurements and calculations. Compared to the previously used layout of refractory lining with the commercially available in-sulating boards, the new arrangement allowed decreasing the surface temperature of the steel shell from 167 °C to 133 °C, and reducing the heat flow through the shell from 2230 W·m–2 to 1503 W·m–2. N. Priesolová/SK described the possibilities of geometrical changes of the impact area in various types of tundishes. Innovation represents the spherical shape of the impact pads. This system, which was developed for tundishes of different shape, minimises the dead zones when casting the steel, secures the optimal flow, wide metal-slag interface, thereby assisting the refining of steel and achieving higher purity of steel. D. Chudíková/ SK discussed the recent trends in the development and application of refractory castables in the working lining of blast furnace runners in U.S. Steel Košice. KOFOND ZH and KOTOR ZH castables installed in the blast furnace tilting runner have very good assumptions to handle at least 900 000 t of hot metal under proper treatment conditions. KOFOND ZH (Al2O3 65 %, SiO2 8 %, CaO 1 %, SiC 21 %, C 7 %) is a castable made of brown alumina with additive of silicon carbide and carbon with low cement content. It is a vibratable castable for installation in tilting slag runner. KOFOND ZH is resistant to corrosion and erosion by slag melt. KOTOR ZH is a castable designed for gunning, used for local repairs. This material is made from bauxite and 14 % SiC and 1,5 % C. Both castables have excellent resistance to thermal shocks. A. Aksamit/PL compared in his paper the properties of the most popular materials used as the working lining of the coke wharfs. He discussed the advantages and disadvantages of the tested materials and special attention was paid to the mechanical strength, abrasion resistance and thermal shock resistance. Basalt bricks (fused cast basalt) are characterised by outstanding mechanical strength and abrasion resistance, but are not resistant to the temperature changes even under mild conditions. Super-duty low alumina bricks have moderate physical properties, abrasion resistance and thermal shock resistance. ABRAL ZRMK (alumina-zirconia-silica) fired refractory bricks are characterised by high mechanical strength and high abrasion resistance. Due to the outstanding thermal shock resistance, this material is perfectly suited for application as the working lining of coke wharfs. Thermal engineering J. Šuška/SK spoke about the installation of two Oxipyr® air burners in the anode furnace MAERZ. In order to increase the efficiency of the combustion process, two burners with adjustable enrichment of the combustion air with oxygen were installed in the 250 t anode furnace for the refining of copper.
The parameters of the installed equipment were: Oxipyr® air burners with the power of min. 0,4 MW, nominal 8 MW, max. 12 MW per burner; – temporary oxygen control (2 × 2000 Nm3/h); – air control (8000 Nm3/h). As a positive economic result, the reduction of the cycle from 30 h to 24 h, and the reduction in the flue gases by more than 50 % could be mentioned. Z. Veselý/CZ addressed the subject of the emissivity of materials as a key property in furnace heat transfer processes. The first part of the paper dealt with the influence of the emissivity on heat transfer processes inside the furnace. Modifications of the emissivity of internal surface of the furnace may result in a combination of these effects: increasing the efficiency of heat transfer, reducing heat losses and reducing the heating times of the furnace charge. The emissivity depends on the surface of materials, on the reactions with the surrounding atmosphere, on the temperature and wavelengths. As it is difficult to include all of these factors to a mathematical simulation, the experimental tests seem to be the most reliable solution. The 2nd part of the contribution presents the methods of measurement of emissivity at room and high temperatures, respectively. The representative results of measurements are presented. Recycling of refractories P. Vadász/SK evaluated the recycled MgO from worn MgO–C refractories. The basis of recycling process lies in the removal of carbon from the MgO–C grain by oxidation. The investigations of annealing MgO–C aggregates (6,3–15 mm) in a laboratory furnace showed insufficient burnout of the carbon. The annealing of the size fraction below 6,3 mm resulted in brittle disintegrating ag-glomerates. The pilot-scale experiments of the burnout of carbon were carried out in a rotary kiln. The oxidation of MgO–C material was accelerated by addition of oxygen to the fuel gas. A batch of MgO–C aggregates 1–12 mm was fired in the rotary kiln at max 1250 °C.
The value of L.o.I. <0,5 % was achieved in the product. From the results of evaluations of recycled magnesia grain, it was possible to conclude that the produced mateial was satisfactory regarding its chemistry, and physical properties, as well. However, in comparison to sintered magnesia the strength of grains is lower. The recycled MgO grain is suitable for applications as a raw material for undemanding applications. M. Pytloun/CZ described the issue of recycling refractory and other waste products from foundries and steel mills. It is possible to state, that the contemporary condition of recycling and utilisation of wastes is unsatisfactory. The authors discussed the reasons and ways to increase the processing of waste into products that can be reused in the manufacturing process with positive economic results. From recyclable refractory materials the following are cited: refractory plates of sliding gate systems, carbon electrodes, graphite crucibles and monobloc stopper rods. The available Proceedings have 156 pages, and contain all presented papers, part in English, and part in Slovak or Czech; for ordering, contact: email@example.com F. Tomšů