Tunnel Furnace Research Articles

Coke and Blast Furnace Gases: Ecological and Economic Benefits of Use in Heating Furnaces

ABSTRACT Currently, the metallurgical industry in Poland is struggling with the problem of the energy use of process by-products. Coke oven gas (COG) or blast furnace gas (BFG) in accordance with the latest directives should not be a side effect troublesome to manage. They should become an energy carrier that improves the economic and ecological efficiency of the steelworks. The easiest way to manage them is combustion or co-combustion with natural gas directly in the place of production. In the article, simulations of process gas combustion were carried out in the actual operating conditions of a roller-hearth tunnel furnace for sheet hardening, using the Directed Relation Graph with Error Propagation aided Sensitivity Analysis (DRGEPSA) method. The main objective of the analyses was to determine the optimal solution for the use of COG and BFG gases in a heating furnace in the ecological and economic aspect. The conducted analysis shows that co-firing COG and BFG in appropriate proportions is the most advantageous solution. The presented savings resulting from the use of process gases and the heating of the sheet metal in the hardening furnace constitute a remarkable economic aspect of the furnace operation. Considering the growing competition on the steel market, the presented savings are a more advantageous technological solution for Polish steelworks, ensuring a lower price of the final product.

Non-destructive tests of fibre-cement materials structure with the use of scanning electron microscope

The article presents the NDT results of research on the influence of high temperature on the destruction of the structure of fiber-cement board as a result of the failure of a tunnel furnace. Two fiber cement boards were tested. There was a plate in a tunnel furnace during a failure, and reference plate dried in normal conditions. The research used acoustic emission method in combination with artificial neural networks.Interesting research results were obtained, which allowed to observe visible changesin the structure of the tested panels under the influence of high temperature. An important application from the point of view of building practice was formulated.

Research into the impact of structural features of combustion chamber in energy-technological units on their operational efficiency

The experimental studies of the influence of the degree of masonry development (geometry) and aerodynamics of the combustion chambers (circuits of combustion products removal) on the energy-technological indicators of the processes in the system gas-solid (in combustion chambers) were carried out. The experimental research into the influence of geometry and aerodynamics of the combustion chamber on the energy-technological indicators in the system gas – solid body was conducted at the industrial large-scale fire bench. It was shown that a decrease in the height of the working space of the combustion chamber, equipped with flat flame burners, affects the use of fuel due to heat exchange intensification, including direct convection. The dependence is caused by a decrease in heat losses with flue gases and due to a decrease in losses through the masonry. It was established that at the height of the working space of 800÷1,000 mm of the combustion furnace, fuel consumption decreases by 20÷30 %. The design of the combustion space of the furnace of continuous operation mode was developed. The distinctive feature of the furnace of the developed design is the elimination of discreteness and implementation of the stable continuous operation mode of the heating unit. The longitudinal channels were made on the lateral surfaces of the cars and the furnace along the entire length of the latter, which makes it possible to implement the continuous removal of combustion products from the combustion space through canalized hearth of the cars into the longitudinal lateral channels, made in the walls of the furnace. Additional aerodynamic compaction of the working space of the furnace is ensured at any speed of the motion of the cars. It was found that energy-technological efficiency at the arch heating of the combustion units with flat flame burners and combustion products removal under the workpiece (lower smoke removal) is on average by 1.3 times higher than at use of the circuit of products removal above the workpiece (lateral smoke removal), which is used in currently operating furnaces. The design was developed and the tunnel furnace was put into operation. It was for chemical and thermal treatment of metallic and non-metallic materials and products during their heating by the assigned schedule.

Comparative study on interfacial microstructure and cutting performance of tunnel furnace and vacuum furnace brazed diamond core-drill

The diamond core-drills were brazed with NiCr filler alloy in the tunnel furnace with the characteristics of the continuous heating and in the vacuum furnace, respectively. The surface morphology and interfacial microstructure between diamond and filler alloy, and filler alloy and substrate were characterized using scanning electron microscopy, energy spectrometer and X-ray diffraction. The effect of different cooling methods on the microstructure and micro-hardness of the filler alloy and substrate was investigated. Furthermore, the drilling tests were conducted, and the cutting efficiency, service life and wear behavior for both tools were comparably analyzed. The results demonstrated a layer of CrC compound formed at the interface of diamond and filler alloy, and a diffusion band composed of Ni and Fe solid solution or compound formed at the interface between filler alloy and substrate regardless of fabricating technique. The thickness of the CrC compound, the width of the diffusion band, the micro-hardness of the substrate and the molten solidified filler alloy for the tunnel furnace brazed diamond core-drill were greater than that of vacuum brazed tool. After drilling polished tiles using diamond core-drill, the cutting efficiency and service life of the tunnel furnace brazed core-drill were close to that of the vacuum brazed core-drill. The attrition wear was the main wear mode for both kinds of tools, and neither the pullout nor the fracture of the abrasive grains occurred during the machining.

Effects of process parameters on interfacial microstructure, residual stresses, and properties of tunnel furnace brazed diamonds

Diamonds were brazed on the substrate with nickel‑chromium (NiCr) filler alloy at a certain temperature for three different mesh belt speeds in the mesh belt continuous tunnel furnace, respectively. In this study, a different perspective involving the exploration of the new processes was used that could allow for the mass production of brazed diamond tools. The interfacial microstructure between the diamonds and filler alloy was analyzed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The residual stresses and mechanical properties of the brazed diamonds were determined through the laser Raman spectrum and the compressive strength or impact toughness testing equipment for superabrasives, respectively. The results illustrated the occurrence of chemical reaction at the interface of the filler alloy-diamond followed by the formation of the CrC compound. Moreover, the thickness of the interfacial reaction layer increased with the decrease in the mesh belt speed. The brazing high temperature and development of the CrC layer were found to be responsible for the residual stresses in the diamonds. The mechanical properties of the brazed diamond grits strongly depended on the resultant thickness of the diamond surface and the residual stresses produced during brazing.

Study of the Heat Transfer of a Large-Scale Tunnel Furnace Based on Numerical Modeling

The aim of this work is to perform a thermal analysis of the operational conditions of a large-scale roller conveyor furnace in a ceramic factory. The entire furnace was divided into three subzones according to the combustion conditions, and the temperature and gas (CO2, H2O vapor, and O2) distributions of each subzone were evaluated. The computational fluid dynamics (CFD) approach was employed to simulate the flow, temperature profile, and heat transfer. The realizable k–ε model was applied for turbulence simulation of the fluid flow coming from the burners. The discrete ordinates method (DOM) and weighted sum of gray gases (WSGG) model were used for simulation of the radiative heat transfer of the furnace. The high accuracy of the simulation methods was validated with the temperature data of the furnace measured by an infrared thermal camera. From the comparisons between the furnace's operating conditions and the numerical simulations, it was concluded that the simulation methods yielded successful results, and relative deviations of up to 22% were observed in the side wall.

Whiteness and Gloss Evaluation of Porcelain

The influence of the firing conditions on the color characteristics and surface gloss of glazed porcelain after firing in a tunnel furnace is shown for a concrete example. The whiteness of glazed porcelain is determined according to the values of two indices: whiteness WI and tint T w . It is shown that the whiteness index WI of porcelain is closely associated by an inverse relation with the yellowness b * CIE L * a * b * and the tinting T w with the coordinate –a * (green) right up to inadmissible values. The gloss corresponds to a shiny or highly shiny surface of porcelain glaze.

Модернизация туннельных печей для производства стройкерамики с целью снижения расхода теплоносителей

Модернизация туннельных печей для производства стройкерамики с целью снижения расхода теплоносителей

Development of Microalloyed Steels Through Thin Slab Casting and Rolling (TSCR) Route

Thin slab casting and rolling (TSCR) route of hot rolled strip production is identified with certain hurdles in the processing of microalloyed steels of different levels of strength. First of all, precipitates formed during casting may undergo partial dissolution in tunnel furnace, leaving the valuable microalloying elements out of solution prior to commencement of hot rolling. Secondly, difficulty in complete recrystallization may lead to microstructural inhomogeneity in the form of mixed grain structures which is detrimental to strip performance. Such difficulties are not typically encountered in conventional casting and hot rolling of thick slabs. This paper summarizes the studies of various researchers about microalloying behaviour during production of strips through TSCR route. Along with this, the experiences of developing microalloyed steels of different strength levels through TSCR route of TATA Steel, Jamshedpur have been discussed.

Mechanical properties of diamond grinding discs brazed in a continuous-belt tunnel furnace or vacuum furnace

A new method for brazing diamond grains is presented. The brazing was conducted in a continuous-belt tunnel furnace under a dissociated ammonia atmosphere, which allows for a continuous large-scale production and greatly enhances productivity. To compare the brazing quality, identical samples were also brazed in a traditional vacuum oven. The surface morphology and interfacial microstructure were characterized, and the residual stresses, the static compressive strength, and the impact toughness were determined for both types of brazed diamond samples. Furthermore, grinding tests were conducted using the brazed diamond grinding discs. The results revealed that graphitization did not occur on the surface of the diamond grits. Cr3C2 and Cr7C3 were found at the interface between the diamonds and the Ni-Cr filler alloy brazed in the tunnel furnace. The residual stresses in the tunnel-brazed diamond grits were smaller than the stresses in the vacuum-brazed diamond grits in case of an identical measuring height, and the static compressive strength and the impact toughness of the etched tunnel-brazed diamond grits were 2316.7 MPa and 66.5 %, respectively, which was higher than the values obtained for the vacuum-brazed diamond grits (1865.6 MPa and 59.3 %). After grinding a granite test sample using the brazed diamond grinding discs, the fraction of abrasive grains pulled out from the surface of the tunnel-brazed grinding disc was slightly higher than the fraction of grains pulled out from the surface of the vacuum-brazed disc, whereas the overall abrasive grain fracture rate was lower at the same grinding length.

Improving the Lining of Cars Used in Short Tunnel Furnaces

An improved design of lining has been developed for the cars of short PG-30 tunnel furnaces, which are used to fire ceramic tooling: crucibles, cores, and molds for casting products made of heat-resistant alloys. The top part of the refractory layer that is installed on the heat-insulating layer consists of two superimposed panels. All of the panels except for the top panel contain interrupted holes (a total of 44 such holes) that are arranged in staggered fashion and open onto the panels’ main surfaces. The top panel contains blind holes (totalling 22). In assembling the refractory layer, the ends of the panels are connected to one another in such a way that the holes their surfaces are coaxial. The top panel is positioned so that the surface without holes faces upward and the holes on the other surface face downward. The box-inserts that hold the ceramic products which are to be fired are placed on the top panel. Such a design of car significantly reduces its weight while also increasing its service life. Durability is improved in particular for high-speed operation of the cars, such as in the firing of foundry molds for casting nickel alloys.

Developing an Energy-Efficient Lining for the Firing Zone of a High-Temperature Tunnel Furnace

Boundary conditions and a method of calculation are examined for determining parameters that characterize heat transfer through the lining of a tunnel furnace. An energy-efficient structure is conceived for the linings of the roof and walls of the furnace and the floor of the cars used in the furnace. It is established that the improvements made in the structure of the furnace’s protective elements make the production process more energy-efficient and create the conditions necessary for also improving the quality of heat treatment of the raw materials/semifinished products. The author determines the amount heat loss and the temperature of the outside surface of the lining for which the temperature gradients from the tunnel axis to the furnace walls and roof and the car floor are no greater than 17, 25, and 43°C, respectively.

Avaliação das propriedades físicas de revestimentos cerâmicos produzidos com resíduo da indústria cerâmica (cinza pesada de carvão mineral)

A cinza resultante da queima do carvão mineral pulverizado é um dos resíduos gerados pelas empresas produtoras de materiais cerâmicas. Quimicamente, é constituída de uma ampla mistura de óxidos, sendo os majoritários Al2O3, SiO2 e Fe2O3 e outros menores como CaO, MgO, sulfatos e outras combinações. Atualmente, em muitas empresas, a cinza produzida é aterrada em áreas licenciadas por órgãos ambientais. Com o ritmo acelerado de produção de revestimentos cerâmicos e em virtude da sua limitada vida útil é necessário a utilização de outros locais, adequados, para deposição das cinzas, medida que provoca um gasto mensal elevado. Diante deste cenário, a adição de cinza à matéria-prima, além de diminuir o impacto ao meio-ambiente, pode propiciar uma redução geral de custos, tanto pelo barateamento da produção, como pela diminuição daquantidade de cinzas a serem aterradas. Desta forma, o objetivo deste trabalho foi avaliar as propriedades físicas de revestimentos cerâmicos produzidos com a adição de cinza pesada de carvão mineral. Para sua realização, corpos de prova foram confeccionados com adição de 1 a 30% de cinza em base mássica. Os corpos de prova foram armazenados dentro de placas refratárias e queimados em forno túnel a uma temperatura de 1084ºC em um ciclo de 29 horas. Foram analisados parâmetros físicos para a barbotina e corpo de prova pós-queima. Os resultados obtidos foram comparados com os padrões estabelecidos pela norma NBR 13818. Foi demonstrado que os experimentos realizados com adição de 1 a 10 % de cinza apresentaram-se dentro dos padrões estipulados pela norma. Para porcentagens de cinza adicionada acima de 4 %, alguns valores estiveram fora dos padrões, sendo a formação de "coração negro" o parâmetro que mais se afastou das exigências da norma em questão.

Towards Robust Neural-Network-Based Sensor and Actuator Fault Diagnosis: Application to a Tunnel Furnace

The paper shows a unified approach for designing both sensor and actuator fault diagnosis with neural networks. In particular, a general scheme of the group method of data handling neural networks is recalled. Subsequently, a unscented Kalman filter approach for designing the network and determining its uncertainty is briefly portrayed. The achieved results are then used to obtain the so-called robust sensor fault diagnosis scheme. The main contribution of this paper is to show how to use the above-mentioned results for actuator fault diagnosis. In particular, the obtained neural model is used to obtain the input estimates. The achieved estimates are then compared with the original input signals to formulate the diagnostics decisions. The input estimation scheme is based on a chain of robust observers, which guaranties that the input estimates are obtained with a prescribed disturbance attenuation level while ensuring the convergence of the observers. The final part of the paper shows a comprehensive case study regarding the laboratory tunnel furnace, which exhibits the performance of the proposed approach.

Туннельная печь для обжига керамических изделий как объект автоматического управления по разрежению продуктов горения

Туннельная печь для обжига керамических изделий как объект автоматического управления по разрежению продуктов горения

Reconstruction of a Small Tunnel Furnace for Firing Refractory Products

A tunnel furnace which is being used to fire heat-insulating and refractory products internally recirculates gases between the stacks of the products inside the furnace. The gases’ movement is due to the kinetic energy imparted by high-speed jets of the combustion products. The jets are formed by high-speed GNB-80 burners designed by the Gas Institute of the Ukrainian National Academy of Sciences. Thanks to the faster and more uniform heating of the products, the protective muffles that were previously installed around the stacks have been dismantled, the productivity of the furnace has increased 25 – 67%, and unit fuel consumption has decreased 15 – 25%.

Characterization on The Mode of The Surface Combustion of Organic Building Materials in Madison-type Small Tunnel Furnace (II). Factors Dominating the Flame-Spread Patterns and Evolution of the Smoke for the Organic Building Materials

Characterization on The Mode of The Surface Combustion of Organic Building Materials in Madison-type Small Tunnel Furnace (II). Factors Dominating the Flame-Spread Patterns and Evolution of the Smoke for the Organic Building Materials

An unscented Kalman filter in designing dynamic GMDH neural networks for robust fault detection

This paper presents an identification method of dynamic systems based on a group method of data handling approach. In particular, a new structure of the dynamic multi-input multi-output neuron in a state-space representation is proposed. Moreover, a new training algorithm of the neural network based on the unscented Kalman filter is presented. The final part of the work contains an illustrative example regarding the application of the proposed approach to robust fault detection of a tunnel furnace.

Analysis of Radiative Heat Transfer in an Indirect-Fired Strip Annealing Furnace based on Integral Equations

A dynamical model of a tunnel furnace for strip annealing is proposed. The continuous furnace has a uniform cross section and is divided into several heating zones, where the local temperatures are used as model inputs. The presented model is tailored to control and optimization applications and takes into account the most important underlying physical phenomena, i.e., the energy balance of the strip and the heat transfer due to radiation. For determining the radiative heat transfer, radiation balances in the form of integral equations are used. Approximate solutions of these equations are obtained by means of the method of weighted residuals. To facilitate an accurate representation of the strip temperature, the strip motion is described based on Lagrangian coordinates, which is especially useful for capturing the temperature transition at welded joints between consecutive strips. The capabilities of the model are explored in simulation studies.

Occupational exposure assessment of magnetic fields generated by induction heating equipment—the role of spatial averaging

Induction heating equipment is a source of strong and nonhomogeneous magnetic fields, which can exceed occupational reference levels. We investigated a case of an induction tempering tunnel furnace. Measurements of the emitted magnetic flux density (B) were performed during its operation and used to validate a numerical model of the furnace. This model was used to compute the values of B and the induced in situ electric field (E) for 15 different body positions relative to the source. For each body position, the computed B values were used to determine their maximum and average values, using six spatial averaging schemes (9–285 averaging points) and two averaging algorithms (arithmetic mean and quadratic mean). Maximum and average B values were compared to the ICNIRP reference level, and E values to the ICNIRP basic restriction. Our results show that in nonhomogeneous fields, the maximum B is an overly conservative predictor of overexposure, as it yields many false positives. The average B yielded fewer false positives, but as the number of averaging points increased, false negatives emerged. The most reliable averaging schemes were obtained for averaging over the torso with quadratic averaging, with no false negatives even for the maximum number of averaging points investigated.