Chemical production on a deforming substrate

The interplay between chemical reaction and substrate deformation is discussed by adapting Ranz's formulation for scalar mixing to the case of a reactive mixture between segregated reactants, initially separated by an interface whose thickness may not be vanishingly small. Experiments in a simple shear flow demonstrate the existence of three regimes depending on the Damköhler number $Da=t_s/t_c$ where $t_s$ is the mixing time of the interface width and $t_c$ is the chemical time. Instead of treating explicitly the chemical cross-term, we rationalize these different regimes by globalizing it as a production term involving a flux which depends on the rate at which the reaction zone is fed by the reactants, a formulation valid for $Da>1$ . For $Da<1$ , the reactants interpenetrate before they react, giving rise to a ‘diffusio-chemical’ regime where chemical production occurs within a substrate whose width is controlled by molecular diffusion.

Простая теория многокомпонентной диффузии и моделирование горения стехиометрической смеси H-=SUB=-2-=/SUB=-/O-=SUB=-2-=/SUB=-

A theory of multicomponent diffusion based on Fick's law is proposed, where, when writing the Maxwell-Stephen equations, a multicomponent mixture is represented as consisting of two components: the isolated substance and all the others with average characteristics. The number of diffusion coefficients is significantly reduced, the method for their calculation is indicated, and they strongly depend on the concentration of the mixture components. Based on the results of this theory, the combustion of an H2/O2 mixture with an equivalence ratio equal to unity was simulated. For each component, great chemical work is carried out with alternating signs, but in total they partially destroy each other. Also, in the chemical reaction zone, there is a strong change in the stoichiometric ratio of the H2 and O2 components.

Comparison of Tar Samples from Reaction Zone and Outlet in Ex-Situ Underground Coal Gasification Experiment

Tar remaining in the gasification cavity during underground coal gasification (UCG) is an important pollution source, while the reported studies only focus on the tar behavior at the outlet. The present work aims to compare the tar properties from the reaction zone and the outlet, analyze the tar evolution during gasification, and discuss possible measures to control tar pollution. Tar was sampled with a self-developed equipment from an ex-situ underground coal gasification experimental system and analyzed by GC-MS. The gas composition, temperature, and PM10 were also compared for the reaction zone and the outlet. Compared with the tar from reaction zone, the tar from outlet has a smaller percentage of high boiling point content, PAHs, C, O, N, S, Cl, Si, and a larger percentage of H. The PAHs percentage in tar at the outlet in this work is closer to the field data than the lab data from literature, indicating the experimental system gives a good simulation of tar behavior in underground coal gasification. Condensation due to a fast temperature drop is one of the main reasons for PAHs decreasing. Tar cracking and soot formation also cause the decrease of heavy tar, proven by the light gas and particulate matter results.

Video registration of physicochemical processes in BOF cavity at bath top blowing at application oxygen lances of various designs. Report 3. The picture of bath blowing at application two-level oxygen lances

Further increase of resources- and energy-saving efficiency of BOF processes is unthinkable without development of new methods of blowing and designs of blowing devices. It requires information on the real physicochemical phenomena in the converter cavity accompanying the blowing of the converter bath using new designs of oxygen lances in order to assess the possible risks in the mastering of the proposed developments in industrial conditions. The paper presents the results of video filming of the top blowing of a 80-kg converter bath by groups of multi-pulse supersonic and sonic oxygen jets formed, respectively, by Laval and cylindrical two-level nozzles of two designs equipped with double-row tips with a circular arrangement of Laval nozzles and cylindrical ones and upper block with cylindrical nozzles. Previously unknown information was obtained on the picture of the bath blowing with the formation of a reaction zone of interaction of supersonic and sonic oxygen jets with a metal melt with a flow of carbon monoxide going out the bath and afterburning of CO to CO2 under conditions of a counter-directed double curtain of sonic oxygen jets at different levels of location of the foamed slag-metal emulsions. It was established that in the initial period of blowing during slag formation most of the thermal energy of CO to CO2 combustion flares is transferred to the surface of the bath with lumps of added lime, and the rest is transferred by forced convection to the converter walls and gases escaping from the bath to the neck. In the case of the location of the foamed slag level at the upper tier of the cylindrical nozzles of the lance, heat transfer from high-temperature flares of localized afterburning of CO to CO2 within a limited in size near-lance flow of exhaust gases from the reaction zone is carried out according to the laws of submerged combustion and is completed completely in foamed slag-metal emulsion with the prevention of aggressive action of afterburning flares and volumes of overheated slag on the converter lining. Revealed and recorded by video recording modes of blowing the converter bath, contributing to the development of such undesirable phenomena during smelting as the appearance of intense emissions of slag-metal suspension from the facility, coagulation of the slag with the cessation of dephosphorization of the metal melt, the development of intense dust formation and the removal of small metal particles and slag with the formation of crust on the lance barrel. A variant of the final stage of blowing with a transition to supplying nitrogen instead of oxygen through cylindrical nozzles of two-level lances was experimentally tested, which provides an effective reduction in the level of foamed slag-metal emulsion before the converter turning down. The data obtained were used in the development of an industrial design of a two-level lance with a double-row tip, blowing and slag modes of blowing a converter bath with its use.

Video registration of physicochemical processes in BOF cavity at bath top blowing at application oxygen lances of various designs. Report 1. Facility and methodology of the study

Interaction of the upper oxygen jets with the BOF bath considerably effects the hot metal refining flow. To optimize the lances designs and methods of BOF bath blowing, information is needed on the actual physical and technical phenomena taking place during top blowing of BOF bath by groups of ultrasonic and sonic oxygen jets. It was shown that obtaining the information is possible at high temperature simulation of the BOF bath blowing by application oxygen lances of various designs and video registration. Results of previous studies by filming of the blowing in a BOF and OHF presented. Description of modern facilities of high temperature simulation within a multi-purpose 160 and 60‒80 kg BOFs, equipped by special manholes for observation and registration by video camera the physicochemical processes taking place on the surface of the bath presented. In particular the manholes made it possible to observe the processes taking place at various methods of top and combined blowing of the BOF bath by application regular, two-circuit and double-flow oxygen lances. A methodology of test heats carrying out presented, which ensured obtaining important practical information on forming and variation of dimensions of the reaction zone. In particular, information was obtained about the interaction of ultrasonic and sonic oxygen jets with the metal melt, development of afterburning, emission out of reaction zone C to CO2 in the subsonic and sonic oxygen jets with forming high temperature flares directed on the BOF bath surface or penetrated in the foamed slag, emissions of slag-metal suspension out the BOF, forming of metal-slag sculls on the lance tube during the blowing with various level of foamed slag-metal emulsion.

Reactive Structures of Ammonia MILD Combustion in Diffusion Ignition Processes

Reactive structures have been analyzed, when ammonia is used as a fuel, in a steady 1D counterflow diffusion flame layer, mimicking diffusion ignition processes. The characterization has been carried out in a wide range of feeding parameters under Moderate or Intense Low-oxygen Dilution (MILD) combustion conditions. Both the Hot-Fuel-Diluted-Fuel (HFDF) and Hot-Oxidant-Diluted-Fuel (HODF) configurations were studied to analyze the main effects of the inlet feeding conditions on the oxidative structures. The reaction zone has been analyzed in terms of temperature and heat release profiles in the mixture fraction space for various ranges of inlet parameters, using a standard code and a validated chemical kinetic scheme. Several features of the reaction zone have been recognized as reported also in previous works for hydrocarbon flames. They were used as discriminative for the achievement of various combustion regimes. In particular, the flame thickening process and the absence of correlation between the maximum heat release and the stoichiometric mixture fraction were analyzed to build maps of behaviors. The latter were reported on an inlet preheating level-temperature increase plane for fixed values of the bulk strain rate and system pressures. Another relevant feature previously reported with hydrocarbons in the literature, in Hot Diluted Diffusion Ignition (HDDI) processes under MILD conditions, was the pyrolysis depression. The latter characteristic has been not observed when ammonia is used as a fuel, for the operative conditions here investigated. Indeed, the heat release profiles do not show the presence of negative heat release regions. The results obtained for the HFDF configuration are strongly dependent on the system pressure level. Finally, the HODF condition has been also analyzed for ammonia at the atmospheric pressure. Boundaries of the combustion regimes and reactive structure features showed several differences between HFDF and HODF cases with respect to the inlet parameters.

Video registration of physicochemical processes in BOF cavity at bath top blowing at application oxygen lances of various designs. Report 2. The picture of bath blowing at application two-circuit lances

To elaborate blowing and slag modes, a clear picture of BOF bath blowing in various periods of heat is needed. It can be obtained by video registration of physicochemical processes in a BOF cavity. Results of video filming of BOF bath blowing with application two-circuit oxygen lances of five designs presented. Reliable information was obtained on rational form of organization of reaction zone of interaction of ultrasonic and sonic oxygen jets with BOF bath. The picture of physicochemical processes within the reaction zone of interaction of oxygen jets with metal, slag and gas phases of the cavity, preceded to a stable “ignition” of a heat and in the process of the whole heat. A possibility was revealed to accelerate the processes of lime dissolving and slag formation and phosphor removal intensification. The intensification can be accomplished by increase of the number of reaction zones of interaction of ultrasonic and sonic oxygen jets on bath surface and forming of foamed slag-metal emulsion, being stable within the basic part of blowing time. It was shown that at initial period of a heat, it is necessary to ensure consolidation of supersonic oxygen jets, coming out of different reaction zones of interaction. It will enable to oncoming jets to create a curtain on the way of metal and slag drops taking away, to form a flare of CO afterburning to CO2 and ensure heat energy transfer from them to mainly the bath surface. It was established that at the location of the foamed slag-metal emulsion level higher the head end of the lance, the high-temperature products of CO to CO2 afterburning reaction transfer the heat of CO surrounding macro bubble to the shell of slag-metal emulsion. An additional control effect of “hard” supersonic oxygen jets on the bath was also established when replacing the subsonic and sonic oxygen jets by nitrogen ones. At that the flow rate of nitrogen should be big enough to prevent the sealing of cylinder nozzles of the lance head by metal and slag drops during final stage of blowing. The variant of the final stage of blowing was checked experimentally by transfer to the “hard” supersonic oxygen blow, contributing to final metal and slag oxidation decrease.

DIRECT OBSERVATION OF HIGH-TEMPERATURE AREAS OF METAL MELT AT OXYGEN CONVERTER BLOWING WITH LOW VOLTAGE APPLICATION

Introduction. The process of oxygen conversion, despite the existing improvements, can be supplemented by physical methods of influence, including the unconventional method of applying low-voltage potential developed at the Iron and Steel Institute of the NAS of Ukraine.Problem Statement. The studies of the method of low-voltage potential application on 60, 160 and 250 ton converters have shown that the technology intensifies thermophysical and hydrodynamic processes in the gasslag-metal system and increases the converter process efficiency.Purpose. The purpose of this research is to study the features of the influence on the reaction zones of the low voltage potential application at four blowing options with the use of high-temperature physical model.Materials and Methods. A physical model that simulates the top, bottom and combined oxygen blowing under low-voltage potential application of different polarity on the lance has been used. An insert of a transparent quartz plate is made in one of the walls for visual observation and video recording. The top blowing is conductedwith two nozzle lance (nozzle diameter 1.7 mm with an angle of 30 ° to the lance). The bottom blowing is conducted with a bottom tuyere with a 1.5 mm diameter central nozzle. Combined blowing is realized by a combination ofthese options.Results. The visual observation of the reaction zones with different blowing options has shown that the highest temperature and the largest dimensions of the brightest parts of the bath correspond to the combined blowing, while the lowest ones are reported for the bottom blowing. While applying the low-voltage potential method it has been established that the reaction zone is longer at the positive polarity on the lance, during the period of silicon oxidation, and at the negative polarity on the lance, during the period of intense carbon oxidation. The video of gas bubbles flotation, probably CO, has shown that the bubbles are formed more intensively in thecase of negative polarity on the lance.Conclusions. The applied technique has allowed estimating the influence of low-voltage potential application on the geometric parameters of the reaction zone.