As the largest source of iron in North America, and as the largest energy consumer in the modern integrated steel mill, the blast furnace is a critical part of modern ironmaking. Any improvements that can be made to the efficiency or emissions of the blast furnace can have far reaching environmental impacts as the production of one ton of steel results in 1.85 tons of carbon dioxide emissions. Given the concerted push to reduce greenhouse emissions, novel technologies are needed to improve efficiency. In this study the injection of preheated natural gas, precombusted syngas from a variety of feedstocks, and hydrogen injection were all modeled using computational fluid dynamics, from the tuyere through the shaft of the furnace. The impacts of these various operational changes were evaluated using CFD calculated analogs for Raceway adiabatic flame temperature (RAFT), top gas temperature (TGT), and coke rate (CR). Results indicate that a reduction of 3% to 12% in CO2 emissions is possible through the implementation of these technologies, with each possessing distinct benefits and drawbacks for industrial implementation.

This thesis deals with development of shrinkage reducing admixtures designed for alkali activated materials based on blast furnace slag. The main task of this work is to select the most suitable shrinkage reducing admixture based on experiments, in which can be observed minimal shrinkage and at the same time it will not adversely affect the properties of alkali activated blast furnace slag. In the experimental part of the work, test beams containing shrinkage reducing admixtures were prepared, in which the shrinkage and loss of weight were measured. Moreover, the mechanical properties of individual beams, such as tensile strength and compressive strength, were measured. Next, the surface tension of individual shrinkage reducing admixtures was measured in a mixture with pore solution. The hydration process of alkali activated materials under the action of reducing shrinkage admixtures was monitored by calorimetric analysis. The microstructure of the prepared samples was observed by scanning electron microscopy.

This diploma thesis is focused on methods of using cement kiln by-pass dust in building materials technology. By-pass dust was treated to remove chlorides and could then be used as other constituent to various types of cements in the amount of 0–5 wt. % according to ČSN EN 197-1. The properties of dusts before and after chloride removal were examined and after incorporating modified by-pass dust into the cement, the properties of fresh and hardened cement pastes and mortars were studied. It was found that modified by-pass dust after incorporation into cement fulfill requirements of ČSN EN 197-1.

Alkali-activated materials (AAM) are construction materials with great potential, especially for their environmental friendliness, but also due to their mechanical properties. Therefore, it is appropriate to pay further attention to these binders. This diploma thesis deals with monitoring the effectiveness of plasticizers in connection with the surface chemistry of the alkali-activated slag system. Sodium hydroxide and sodium water glass were used as alkaline activators for the preparation of alkali-activated blast furnace slag-based systems. To study the effectiveness of the lignosulfonate plasticizer, yield stress, heat flow, adsorption and zeta potential were monitored depending on the amount and time that the plasticizer was added to the system. The results show that the type of activator used in the mixtures plays an important role. NaOH-activated samples revealed the best efficiency of lignosulfonate plasticizers. A key factor in studying the behavior of the studied mixtures was the measurement of the zeta potential, which provided insight into the surface charge of blast furnace slag particles related to the ability of lignosulfonate to adsorb on grains of alkali-activated slag.

The topic of this thesis is the calculation of the steam-boiler. The begining of the thesis deals with stoichiometric calculations. In the second chapter is performed the heat balance of the boiler. In the fourth and fifth chapter are defined dimensions of the fire and is established the temperature of a combustion gas in the outlet from the fire. The fifth chapter includes the balance calculations of the particular heating surfaces of the steam-boiler. As a conclusion of the calculations of the steam-boiler is performed the total balance. In the last chapter are proposed the methods for a reduction of the quantity of NOx contained in the combustion gas.

The aim of a diploma thesis is design of draft boiler for co-firing blast furnace gas and natural gas. In the first part is made the stoichiometric calculation for the gas mixture. Next is the proposal of combustion chamber and proposal of individual heating surfaces of boiler. Next part contains the thermal calculation and control of individual heating surfaces. Part of the work is also drawing documentation of boiler.

Aluminosilicate refractory grog are being manufactured by firing refractory clays, claystone and shale. Firing takes place mainly in rotary or blast furnaces. However, when adjusting the raw material before firing in blast furnaces, the formation of the fine clay particles takes place. It is not possible to fire the fine particles in blast furnaces the usual way, which leads to the generation of waste. There is a possibility, however, to form briquettes of these particles, which can be fired in blast furnaces. This solution also brings the possibility of adjusting the mixture by using correction raw materials or other types of clay. Using this method, it is possible to produce a special refractory grog with specific properties.

Alkali activated materials could be suitable alternative to construction materials based on ordinary Portland cement (OPC). Therefore, it is advisable to pursue these binders further on. Aim of this thesis is to clarify the effect of lignosulfonate-based plasticizer and polycarboxylate-based superplasticizer on the behaviour and nature of alkali activated materials. For the purposes of studying the efficiency of plasticizing additives, the change of workability of alkali activated blast furnace slag in dependence on time, effect of additives on mechanical properties as well as, with usage of isothermal calorimetry, their impact on kinetics of solidification and hardening had been observed. The stability of the plasticizing admixtures in a high alkaline environment such as water glass and sodium hydroxide had been studied using infrared spectrometry. As a last step, X-ray photoelectron spectroscopy (XPS) had been used while clarifying the chemical changes in the structure of plasticizing additives after adsorption to blast furnace slag.

Une étude expérimentale de l'influence des mélanges gazeux sur le régime de combustion sans flamme a été menée sur l'installation pilote du CORIA, en collaboration avec GDF SUEZ. La première partie de cette étude a été consacrée à la caractérisation détaillée de ce régime de combustion particulier au méthane pur avec et sans préchauffage de l'air comburant. Des mesures locales de température et concentrations d'espèces stables ont été réalisées à l'aide de thermocouples à fil fin et sonde de prélèvement. Une attention particulière a aussi été portée au développement et l'adaptation de techniques d'imagerie sur ce type de four : l'imagerie de chimiluminescence OH* pour la visualisation des zones de réaction et la PIV endoscopique afin d'obtenir des champs de vitesse de grandes dimensions malgré le fort confinement à haute température. L'analyse des résultats obtenus a permis de mettre en évidence le rôle principal de l'aérodynamique des jets turbulents de réactifs dans le four assurant l'obtention et la stabilisation de ce régime de combustion massivement diluée. Dans la seconde partie de cette étude, la faisabilité de l'utilisation d'hydrogène dans un four pilote fonctionnant en régime de combustion sans flamme a été démontrée. On retrouve toutes les caractéristiques intrinsèques à ce régime de combustion en termes de forte efficacité énergétique (lors du préchauffage de l'air) et très faibles émissions polluantes (CO et NOx) de ce régime massivement dilué, associé à la réduction des émissions de CO2 avec l'augmentation de la teneur en hydrogène dans le combustible. En fonctionnement à l'hydrogène pur et sans préchauffage de l?air, le four n?émet plus aucune espèce carbonée et quasiment pas de NOx ; on se rapproche d'un four à "zéro émission". / An experimental study of the influence of the aerodynamic mixing on flameless combustion regime has been carried out on the CORIA lab-scale facility with the collaboration of GDF SUEZ. A detailed characterisation of this innovating combustion mode, using pure methane as fuel, with and without air preheating is the first part of this study. Temperature and stable species concentrations measurements have been performed with fine wire thermocouple and sampling probe. Imaging techniques have been developed and adapted for in-furnace measurements: OH* chemiluminescence imaging for reaction zone visualization and endoscopic PIV in order to obtain large dimensions velocity fields in spite of the confinement. The results enable us to put in evidence the leading role of aerodynamic of the turbulent jets to ensure the stabilisation of this massive diluted combustion regime. The second part of this study concerns the use of hydrogen as fuel in the pilot furnace operating in flameless combustion regime. The main characteristics of this combustion regime have been found again: high efficiency and very low pollutant emissions (CO and NOx) associated to CO2 emissions reduction while increasing content of hydrogen in the fuel. With pure hydrogen and without air preheating, the furnace produces no carbon-species and nearly no NOx, condition close to a “zero-emission” furnace.

Direct Reduced Iron (DRI) is used as an alternative feedstock in electric arc furnaces, making up 50% or more of the total iron charge. DRI produced with coal based reductants (for example in rotary kilns) make up roughly 25% of DRI produced in the world. It was found that SL/RN DRI samples from a kiln cooler had high nitrogen contents (50-250ppm, depending on particle size), higher than DRI from gas-based reduction. The higher nitrogen content of SL/RN DRI would increase the levels of nitrogen of liquid steel produced in the EAFs. The problem is exacerbated by the fact that the SL/RN DRI contains virtually no carbon (which would aid in preventing nitrogen pickup). The proposed mechanism of nitrogen pick-up by the SL/RN DRI is one where nitrogen present within the atmosphere of the rotary cooler (where hot DRI, discharged at 1000°C from the rotary kiln, is cooled to approximately 100 °C in ca. two hours) penetrates the solids bed and nitrides DRI particles. Possible rate-determining steps for nitriding in the cooler have been evaluated. Nitriding of DRI particles is predicted to be rapid: the most plausible location for rapid nitrogen pickup is the first 5 meters of the rotary cooler, where the high temperature, nitrogen-rich gas atmosphere and rapid solids bed mixing are conducive to nitriding; solid-state and pore diffusion of nitrogen into DRI particles are predicted to be rapid too. The most plausible rate determining step for nitriding of DRI particles is that of nitrogen dissociation on the DRI surface, which can be further retarded by the presence of sulphur. A strong correlation was found between the amount of “melt-in” carbon in the liquid steel and the final tap nitrogen content, with 0.3% C resulting in nitrogen levels as low as 50 ppm (80 ppm or less is desired on the plant in question) at tap, even with DRI material that is high in nitrogen and contains virtually no carbon. Proposals to increase the melt-in carbon are included. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Materials Science and Metallurgical Engineering / unrestricted