Dry Slag Research Articles

Crystallization dynamics of the post-cooling molten slag against temperature rise

Turning molten slag into a solid state involves a complex cooling history that significantly influences the quality of the final product. It is crucial to unveil the crystallization dynamics of molten slag during practical cooling, particularly in the post-cooling course with temperature rise. In this work, we employed the single hot thermocouple technique to visually investigate the crystallization behavior of blast furnace slag. A series of control experiments were conducted to quantify the effects of temperature rise features and chemical composition on incubation time (τo-τl), crystallization temperature region (To ∼ Te), and the average crystal growth rate (Vα). The results proved that the governing factor of Vα changed from nucleation growth rate to nucleation rate, resulting in a significant difference in crystallization phenomena between the continuous cooling condition and temperature rebounding condition. Considering the post-peak temperature, temperature rise rate, and corrected optical basicity exerted remarkable effects on the crystallization behaviors, we established correlations for predicting τo-τl, To, Te, and Vα by fitting experimental data. These correlations offer valuable insights for optimizing cooling parameters in dry slag treatment, contributing to a comprehensive understanding of crystallization dynamics in high-temperature slag subjected to intricate cooling histories.

Strength and deformation characteristics of slag crushed stone of coal thermal power plants

Mechanical properties of the slag crushed stone (coarse-grained ASM), formed in the course of coal combustion at Kansk-Achinsk, Kuznetsk coal deposits (in boilers equipped with liquid and dry slag removal facilities) and the application of the slag crushed stone in roadbuilding are considered. In the course of the research, the crushability and the deformation modulus of particular fractions of slag crushed stone samples taken from the dumps of Novosibirsk TPP-3 (that consumes the coal of the Kansk-Achinsk coal mining field) and from Novosibirsk TPP-2 and Seversk TPP (that consume the coal of the Kuznetsk coal mining field) were identified. To assess the factors influencing the mechanical strength of the slag crushed stone, ignition losses, the content of flaky and acicular particles, dust and clay particles and clay lumps was made. The difference in the mechanical strength of samples having different genesis was identified. The graphs obtained in the course of testing were assessed and deformability characteristics were calculated (for materials having different fineness values). The factors influencing the mechanical strength of slag crushed stone were determined. Dependencies between deformation parameters and crushability of the slag crushed stone were obtained. Some mechanical and physical parameters of the slag crushed stone were identified; they were applied to outline potential areas of the slag crushed stone application in road building. The mathematical relationship needed to project the deformation modulus of the slag crushed stone was identified. This relationship will be used to design structures to be made of this material.

Design of a Dry Slag Granulation Plant for Blast Furnace No. 5 of Severstal

Design of a Dry Slag Granulation Plant for Blast Furnace No. 5 of Severstal

Steel slag-bonded strand board as a carbon-negative building product

The feasibility of using carbonation-activated steel slag as the exclusive binder for the production of slag-bonded strand boards was studied in an attempt to replace the cement-bonded fiberboards and resin-bonded strand boards. After 12-hours of carbonation curing, the developed slag-bonded strand board displayed excellent compatibility and enhanced performance owing to the slag chemistry. Carbonated boards successfully met International Standard requirements for mechanical strength and physical performance. Durability of the composite was examined through accelerated ageing by warm water test and soak-dry cycles. Microstructure development was monitored through X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The study demonstrated that carbonation curing successfully reduced the production time, activated the dormant γ-C2S, contributed towards superior dimensional stability, and sequestered almost 10.8 % of CO2 by dry slag mass. A further 28 days of hydration improved the mechanical characteristics of the composite and contributed towards a superior end-product. It was found that slag-bonded strand boards are resistant to ageing owing to carbonation-induced precipitation and are carbon-negative with higher carbon storage capacity and lower production cost.

Application of Pre-Wetted High Titanium Heavy Slag Aggregate in Cement Concrete.

High titanium heavy slag is one kind of solid waste that exists in large amounts in the southwest of China. In this paper, this high titanium heavy slag is used as natural pre-wetted material in concrete because of its porous structure. Three kinds of aggregates are used in this concrete. The first one is natural limestone and river sand. The second one is dry slag fine aggregate and coarse aggregate. The third one is pre-wetted coarse slag aggregate and dry slag fine aggregate. The strength, dry shrinkage, autogenous shrinkage, relative humidity, pore size distribution, stress–strain relationship, micro-hardness and chloride penetration of concrete composed of the above three aggregates are tested in this study. The results show that pre-wetted slag aggregate is a suitable internal curing material. The concrete with pre-wetted slag aggregate shows higher strength, lower shrinkage and smaller porosity. The water absorbed in the slag aggregate can be released effectively to increase the relative humidity, accelerate hydration, improve porosity and increase the interface strength.

Determination of Geometric and Operating Parameters of Device for Spraying Molten Slag in a Dry Slag Granulation Plant

Determination of Geometric and Operating Parameters of Device for Spraying Molten Slag in a Dry Slag Granulation Plant

Definition Of Puzzolanic Properties Active Mineral Additives In Portlandcement

The article presents the results of testing the use of Angren dry remote active ash and slag in Portland cement as an active mineral additive. It was found that Portland cement with the addition of Angren dry remote active ash and slag renders karrazastoy, ekanomet clinker and it is proved that hydro removed ash and slag (2011 year) does not recommend as an active mineral additive. Therefore, dry remote active ash and slag is recommended for use as an active mineral additive in the production of cement, improving its construction and technical properties. The possibility of using Angren dry remote active ash and slag as an active mineral component for producing cements with low corrosion resistance is shown. Angren dry remote active ash and slag contributes to the formation of the structure of the cement stone, increases its density and strength against aggressive ions, causing increased resistance in aggressive environments. And save up to 30% of cement. It has been established that Portland cement with the addition of Angren dry remote active ash and slag has an intensifying effect on the formation of clinker minerals. Therefore, the Angren dry remote active ash and slag is recommended for use as a mineralizing additive in the production of cement. Use of chemical industry waste with replacement of expensive natural production and consumption waste. At the same time, an environmental problem is being addressed.

Experimental investigation on granulation characteristics and waste heat recovery of molten slag in gas quenching dry granulation technique

The gas quenching dry slag granulation technique is one of the most promising slag treatment methods due to realize efficient waste heat recovery as well as high value-added resource utilization. To better understand the granulation characteristics and to achieve high waste heat recovery efficiency in the gas quenching granulation technique, high temperature experiments were performed with different airflow velocity and different molten slag mass flow rate. Particle average diameter, particle size distributions, and fiber mass fraction were in-depth studied for the granulation characteristics. The results indicated that the average diameter decreased with increasing airflow velocity and with decreasing the mass flow rate. The dimensionless diameter empirical formula was presented according to the experimental data. The particle size distributions were mainly concentrated in 1–3 mm. The fiber mass fraction decreased with increasing airflow velocity, but it increased when the airflow velocity exceeds 550 m·s−1 at lower mass flow rate. The higher waste heat recovery rate can be obtained with smaller particle diameter and lower fiber mass fraction. The maximum of waste heat recovery rate can reach 59.55% with the airflow velocity of 550 m·s−1 at the mass flow rates of 4.2 kg·s−1, which is the most ideal working condition.

Numerical investigation of breakup process of molten blast furnace slag through air quenching dry granulation technique

Molten slag is broken up by supersonic air into droplets through the air quenching dry slag granulation technique. The breakup process of blast furnace slag directly determines the droplet diameter and the waste heat recovery. In order to gain deep insight into the granulation mechanism and visualize the breakup process, three-dimensional unsteady numerical simulation based on the k-ω based shear stress transport turbulence model was conducted to simulate the transient breakup process of molten slag (k is the turbulent kinetic energy, and ω is the specific dissipation rate). The coupled level-set and volume-of-fluid method was utilized to capture the sharp air–liquid interface. The results show that a flat film is formed firstly under the effects of air impingement, recirculation zone and pressure gradients. Then, the axial wave and the spanwise wave appear simultaneously and the film is broken up into ligaments owing to the generation of vortex and hole structure at the intersection of axial trough and spanwise trough. Finally, the ligaments are broken up into droplets owing to Rayleigh–Taylor instability at the air–liquid interface. The droplets smaller than 3.00 mm account for 80%, with the average diameter of 1.95 mm.

Simulation of primary breakup of molten slag in the gas quenching dry granulation process

Gas quenching dry slag granulation process is an energy-saving environmental protection method for waste utilization and waste heat recovery of molten slag, and the molten slag is broken up by supersonic airflow into droplets in this process. This paper performed the numerical investigations on the breakup behavior of slag by the coupled level-set and volume of fluid (CLSVOF) methodology and gain a deep insight into the breakup mechanism of the primary breakup and influence of gas Weber number (We) and liquid Reynolds number (Re) on the primary breakup. The results indicated that the primary breakup include flat film breakup and spherical cap film breakup, the both are typical perforation breakup; Aerodynamic force cause K-H (Kelvin Helmholtz) instability, K-H surface waves are the root cause of film breakup; The wavelength and the film thickness decrease with increasing We which is conducive to reducing the ligament diameter; The wavelength and the film thickness decrease first and then increase with increasing Re which is optimum in the range of 1068–1280; The empirical formula of the ligament diameter is obtained. The ligament diameter decrease with increasing airflow velocity and slag density and increase with increasing slag mass flow rate and slag viscosity.

Mechanical strength of slag crushed stone generated at coal-fired thermal power plants

Introduction. Production waste is used in the construction industry worldwide as it helps to cover a considerable portion of the industry’s demand for building materials. Coarse-grained slag deposits (slag crushed stone and sand), formed in the slag washout zone, have more potential for application than other ash and slag mixtures (coarse ASM), but they need more research. Mechanical properties of the slag crushed stone (coarse-grained ASM), formed in the course of coal combustion at Kansk-Achinsk, Kuznetsk coal deposits (in boilers equipped with liquid and dry slag removal facilities) and the application of the slag crushed stone in roadbuilding are considered.
 Materials and methods. In the course of the research, the crushability and the deformation modulus of particular fractions of slag crushed stone samples (in dry and water-saturated conditions) taken from the dumps of Novosibirsk TPP-3 (that consumes the coal of the Kansk-Achinsk coal mining field) and from Novosibirsk TPP-2 and Seversk TPP (that consume the coal of the Kuznetsk coal mining field) were identified. To assess the factors influencing the mechanical strength of the slag crushed stone, ignition losses, the content of flaky and acicular particles, dust and clay particles and clay lumps was made.
 Results. The difference in the mechanical strength of samples having different genesis was identified. The graphs obtained in the course of testing were assessed and deformability characteristics were calculated (for materials having different fineness values). The factors influencing the mechanical strength of slag crushed stone were determined. Dependencies between deformation parameters and crushability of the slag crushed stone were obtained.
 Conclusions. Some mechanical and physical parameters of the slag crushed stone were identified; they were applied to outline potential areas of the slag crushed stone application in road building. The mathematical relationship needed to project the deformation modulus of the slag crushed stone was identified. This relationship will be used to design structures to be made of this material.

Heat Transfer in Fluidized Beds in a Dry Slag Granulation Unit

The world’s leading countries develop dry slag granulation units that are capable of producing solid slag granules and recovering the sensible heat of slag. The main element of such units is a granulation chamber where molten slag is atomized and solidified. In this chamber, up to 30% of the sensible heat of the molten slag is extracted. To recover more heat, the solid granules from the granulation chamber should be fed to fluidized beds. The more there are such beds, the better the granulated slag can be cooled and, therefore, the more heat can be recovered. Foreign publications on dry slag granulation do not provide methods for designing fluidized beds for dry slag granulation units. A method for analyzing the heat transfer in fluidized beds during cooling of slag granules by counter airflow is presented. The method allows determining the heat flow from the slag to the air in fluidized beds and the temperatures of the slag and air exiting the fluidized beds. Recommendations on choosing the airflow velocity, the rational mass of slag in one fluidized bed, the number and dimensions of beds and evaluating air pressure losses in fluidized beds are formulated. It is shown that three fluidized beds in a dry slag granulation unit are sufficient to recover up to 92% of the sensible heat of slag.

Experimental Study on Recovery of Cyanide Tailings Slurry by Membrane Separation in a Gold Mine

In view of the difficulty in recovering valuable metals and cyanides from cyanide tailings pulp in gold mines, the laboratory exploratory test of recovering gold and silver from the tailings pulp produced by a CIP process was carried out by using the technology of “solid-liquid separation + membrane separation and purification + adsorption and recovery of gold and silver by activated carbon”. The results showed that the cyanide tailings slurry was separated by solid-liquid in the laboratory and stabilized by chemicals, and the dry slag was identified as a general solid waste according to the results of the identification standard for hazardous waste leaching toxicity GB5085.3-2007. The screened reverse osmosis membrane test showed that 95% of the permeate water recovery rate were obtained. The concentration of cyanide in membrane concentrate water reached 807.9 mg/L, the concentration of copper, gold and silver reached 0.43 mg/L and 3.91 mg/L respectively after being concentrated from below the detection limit, and the concentration was 19.9, 14.3 and 18.6 times respectively. The adsorption test of membrane concentrate water by activated carbon showed that gold, silver and copper were absorbed in membrane concentrated water, the adsorption rates reached 99.76%, 96.16% and 9.09% respectively, which facilitated the subsequent selective recovery of gold and silver. The recovery of valuable metals and cyanide from cyanide tailings slurry by the process of “solid-liquid separation + membrane separation and purification + adsorption and recovery of gold and silver by activated carbon” had a good effect.

RecoDust\u2014An Efficient Way of Processing Steel Mill Dusts

RecoDust is believed to be an efficient way of processing steel mill dusts to produce reusable secondary raw material resources. The rising costs of the steel production process and the increasing public attention towards environmental protection have caused steel plants worldwide to focus on emission-reduction processes and circular economy. As a reusable secondary raw material resource, the steel mill dust contains a high amount of iron and zinc. Nowadays, most of the steel mill dusts are processed under the Waelz-Process. However, this process is limited or impossible without additional dust treatment and can only be operated economically with zinc contents over 20 wt%. In the future, RecoDust in combination with dry slag granulation will become an efficient technique for processing lower zinc-containing materials of a steel mill. A challenging area in the field of RecoDust is the melting/reduction phase to separate volatile components and the slag treatment. A previous study was limited to the recovery of zinc. This paper compares the energy consumptions of the primary metal production to the recycling and of the RecoDust process to the Waelz-Process and outlines a new approach to RecoDust slag treatment.

Design and Operation of Dry Slag Granulation Pilot Plant

CSIRO has been working on a dry granulation process, integrated with heat recovery, since 2002. It involves a rotary disc that atomizes molten slag to produce liquid droplets, which are rapidly quenched to become solid granules. The hot granules are fed to a counter-current moving packed bed heat exchanger, where they are further cooled and finally discharged at close to ambient temperature. Air is used in both units to recover the heat. Development has proceeded through proof-of-concept tests, a prototype and now a pilot plant, capable of processing 100 kg/min of slag. Extensive CFD modeling was used to predict disc and granulator performance as a function of design and operating parameters. Experimental results on the dry slag granulator pilot plant have demonstrated that the process can effectively produce glassy slag granules from molten iron blast furnace slag, and recover significant heat, and that the CFD model can be used to predict process performance. Work continues to scale-up the process and extend the operation to other metallurgical materials, such as non-ferrous slags and mattes.

Visualization of the heat transfer character of dry slag discharge system

Visualization of the heat transfer character of dry slag discharge system

Life cycle and economic assessment of multi-stage blast furnace slag waste heat recovery system

Abstract In order to utilize the waste heat of blast furnace slag more effectively, the multi-stage slag waste heat recovery system was proposed. This study employed the life cycle assessment to evaluate the environmental performance of the proposed system. Meanwhile, the economic feasibility of the system was analyzed in terms of capital cost and return analysis. Based on the current status of the environment, CO2 tax was also referred in the net explicit profit and net implicit profit calculation of the system. The energy consumption and resource consumption of the system were 268.84 kg coal-eq/tslag and 1213.60 kg/tslag, respectively. The main environmental impact came from the slag production process. Under the consideration of CO2 tax, the net explicit profit and net implicit profit of the proposed method were 13.40 $/tslag and 135.14 $/tslag when the CO2 tax were 33.00 $ per ton. In this process, the evaluations of the proposed system were done in comparison with the conventional water quenching method-open circuit process and latest dry slag granulation method by the main energy, environmental and economic indicators. As results suggested, the multi-stage slag waste heat recovery system had a good application potential in the aspect of energy conservation and emission reduction for iron and steel industry.

Cleaner and effective process for extracting vanadium from vanadium slag by using an innovative three-phase roasting reaction

The traditional industrial practice for extracting vanadium from vanadium slag involves a Na2CO3-Na2SO4-NaCl-added pellet roasting at 800 °C followed by a water leaching. Some chlorine and hydrogen chloride are emitted by this process. About 80% of vanadium and 5% of chromium can be extracted in this case. The disposal of this leaching residue containing high contents of chromium and vanadium is still an unsolved environmental problem so far. A complete extraction of vanadium and chromium from vanadium slag might be an ultimate solution. In order to efficiently extract vanadium from vanadium slag, an innovative NaOH-added pellet was applied in this work to replace traditional Na2CO3-Na2SO4-NaCl-added pellet. It was found that the volume of NaOH-added pellet increased by 144% and many cavities were formed spontaneously throughout the pellet during the roasting at 700 °C. A solid phase (dry slag minerals), a liquid phase (molten liquid drops of NaOH with low viscosity) and a gas phase (O2) were involved in a three-phase reaction occurred inside the pellet. The spontaneously formed cavities created good kinetic conditions for the three-phase reaction. The V extraction was thus increased from traditional 80% at 800 °C to current 99% at 700 °C. The V extraction was increased by 39% when a NaOH-added pellet sample was used instead of a NaOH-added powder sample. The roles of porous pellet and liquid NaOH drops were explored. The V extraction dramatically increased with increasing temperature in the temperature range of 400 °C to 600 °C and reached a maximum at 700 °C. The V extraction dramatically increased with time within the first 15 min at 700 °C. The optimal roasting temperature, time and R(Na/Cr) value for the V extraction were 700 °C, 15 min and 7.67, respectively. The V extraction was 99.2% under the optimal conditions. The cooling rate of the roasted pellet had no significant effect on V extraction. The vanadium from the vanadium slag was mainly contained in a vanadium-containing spinel phase (Mn, Fe)(V, Cr, Ti)2O4. The oxidation of V3+ probably went through the following process: (Mn, Fe)(V, Cr, Ti)2O4 →(Cr0.15V0.85)2O3→NaVO2→Na3VO4. This process avoided the emission of toxic gas.

Blast Furnace Ironmaking – A View on Future Developments

Within many industries there is a constant drive to reduce environmental impact and energy costs thereby ensuring maximum energy re-use. Within the iron and steel industry the ironmaking processes are acknowledged to be the focus area when the topic of energy saving arises.A lot of attention has been applied to the ironmaking processes with regards to environment and energy saving, with established technologies being in place to reach these goals such that the process per se, is now at or very close to theoretical limits.The following areas of the blast furnace process are currently the focus of Primetals activity with regards the target to further improve energy saving with incremental improvements:•Flue gas recycling within blast furnace stoves•MERIM dry gas cleaning process•Dry slag granulation including heat recoveryThis paper will present the concepts and latest status of the above technologies. The paper will review the progress to date of these development activities and thus present ideas on options for energy saving and re-use within the ironmaking system.

Experiment study on entrained flow gasification technology with dry slag by second-stage water supply

Experimental system of a new entrained flow gasifier with second-stage water supply (20kg/h) was set up in this paper, and effect of molar ratio of O/C on temperature distribution, syngas composition, carbon conversion and effective syngas were analyzed with a typical high AFT coal (Guizhou LJ coal). The results of non-second-stage water and second-stage water with changing molar ratio of O/C indicate that, when the molar ratio of O/C is larger than 0.96, gasification efficiency with dry slag by second-stage water would become better than non-second-stage water. Specifically, when the molar ratio of O/C was 1.1, the effective syngas fraction and carbon conversion of second-stage water gasification were 80.2% and 93.24% respectively. Correspondingly, the effective syngas fraction and carbon conversion of non-second-stage water gasification were 78.5% and 91.67% respectively. Furthermore, the gasification temperature was lower than the ash fusion temperature of test sample, the slag was non-melt during all the gasification experiments. The optimal gasification was conducted with the process temperature under 1450°C, which was lower than the ash fusion temperature of LJ coal. These experimental results prove the applicability of entrained flow gasification technology with dry slag by second-stage water supply on using high AFT coals, which is helpful to generalize the large-scale gasification technology using abundant high AFT coals in China.