Waste to Wealth Strategy: Preparation and Properties of Lightweight Al2O3-SiO2-Rich Castables Using Aluminum Dross Waste

Aluminum dross is a well-known industrial waste generated in the aluminium industry, and its recycling and reuse is still a worldwide issue. Herein, aluminum dross waste (ADW) was recycled to progressively replace the aggregate fraction of clay at 70, 75, 80, 85, and 90 wt% for the fabrication of Al2O3-SiO2-rich porous castable refractories. Their physical properties and mechanical behavior were assessed by the measurement of linear shrinkage rate, bulk density, apparent porosity, cold crushing strength, and thermal conductivity. The microstructure and phase evolutions were analyzed via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The incorporation of 85 wt% of ADW allowed the development of a waste-containing conventional refractory castable with improved properties as compared to those of the other samples. The sustainable refractory castable exhibited decent thermal conductivity and physical and mechanical characteristics, and is suitable for application as reheating furnace lining. It is a “green” practice to partially replace the traditional raw materials with industrial waste in the manufacture of conventional refractory castables and provides environmental and economic benefits.

Physical and mechanical characteristics of composite briquette from coal and pretreated wood fines

Melina wood torrefied at 260 °C for 60 min was agglomerated with lean grade coal fines into composite briquettes using pitch as binder. Torrefied biomass (3%–20%) and coal fines (80%–97%) were blended together to produce the composite briquettes under a hydraulic press (28 MPa). The briquettes were cured at 300 °C. Density, water resistance, drop to fracture, impact resistance, and cold crushing strength were evaluated for the composite briquettes. The proximate, ultimate, and calorific value analyses were carried out according to different ASTM standards. Microstructural studies were carried out using scanning electron microscope and electron probe microanalyzer equipped with energy dispersive x-ray. Fourier Transform Infrared Spectrophotometer (FTIR) was used to obtain the functional groups in the raw materials and briquettes. The density of the composite briquettes ranged from 0.92 to 1.31 g/cm3 after curing. Briquettes with < 10% torrefied biomass has good water resistance index (> 95%). The highest cold crushing strength of 4 MPa was obtained for briquettes produced from 97% coal fines and 3% torrefied biomass. The highest drop to fracture (54 times/2 m) and impact resistance index (1350) were obtained for the sample produced from 97% coal and 3% torrefied biomass. The fixed and elemental carbons of the briquettes showed a mild improvement compared to the raw coal. The peaks from FTIR spectra for the briquettes shows the presence of aromatic C=C bonds and phenolic OH group. The composite briquettes with up to 20% torrefied biomass can all be useful as fuel for various applications.

Analisis Pengaruh Perubahan Beban Terhadap Kondisi Refraktori Boiler Pembangkit Listrik Tenaga Uap Punagaya

Penelitian ini menganalisa kerusakan yang terjadi pada Refraktori Boiler Pembangkit Listrik Tenaga Uap di PLTU Punagaya. Tujuan penelitian ini adalah untuk mengetahui mengapa pola pembebanan unit yang berubah-ubah dapat menyebabkan kerusakan pada refractory boiler. Metode yang digunakan pada penelitian ini ialah Failure Mode and Effect Analysis (FMEA) dan Root Cause Failure Analysis (RCFA) serta pembuktian perhitungan Cold Crushing Strength (CCS). Hasil penelitian menunjukan bahwa data kecepatan aliran flue gas masuk cyclone yang melebihi spesifikasi (<35 m/s) dan data kekuatan CCS refractory aktual yang menunjukan nilai 43 MPa menjadi penyebab dari pembebanan yang tidak stabil yang merupakan salah satu faktor penyebab dari kerusakan refractory boiler.

Effect of Binders on the Crushing Strength of Ferro-Coke

Ferro-coke, as a new burden of blast furnace (BF), can not only greatly reduce the energy consumption and CO2 emission, but also promote the resource utilization by using the low-quality iron ore and low-grade coal. However, the strength of ferro-coke decreased with the increasing amount of iron ore powder. In order to maintain the strength of ferro-coke while increasing the amount of iron ore powder, it is necessary to add binder during the coking process to enhance the strength of ferro-coke. In this paper, phenolic resin, silicon metal powder, corn starch, and coal tar pitch were used as binder for the fabrication of ferro-coke. I-type drum machine (I 600), scanning electron microscope (SEM), and X-ray diffraction (XRD) were applied to test the crushing strength, morphology, and microcrystalline structure of the ferro-coke. The results showed that the increasing amount of iron ore powder resulted in lower crushing strength, higher porosity, and the worse macroscopic morphology of ferro-coke. When the amount of iron ore powder reached 40%, obvious cracks appeared on the surface of ferro-coke. When the amount of iron ore was 30%, the crushing strength of ferro-coke dropped to 18.15%. Among the four binders, coal tar pitch could significantly enhance the cold crushing strength of ferro-coke through decreasing the porosity of ferro-coke and improving the bonding effect between carbon matrix particles. In the case of the 10% coal tar pitch addition, the cold crushing strength of ferro-coke was increased from 18.15% to 76.41%; meanwhile, its hot compression strength during gasification improved by 100N.

Preparation of high-strength biochar composite briquette for blast furnace ironmaking

In this research, using iron-oxide fines (average size: 2.5 μm) and biochar fines (average size: 50.0 μm), the biochar composite briquette (BCB) for blast furnace (BF) application was prepared by cold briquetting followed by heat treatment. The preparing conditions were optimized regarding its cold crushing strength. Anti-pulverization capability, reaction development, and structure evolution of the optimally-designed BCB under simulated BF conditions were then examined. Results of optimizing BCB preparation conditions showed that a heating temperature of 1073 K was optimal for preparing the BCB. The optimally-designed BCB contained 11.10 wt.% carbon, 72.21 wt.% Fe3O4, 11.25 wt.% FeO, and 0.77 wt.% Fe, 6.44 wt.% gangue, and had a cold crushing strength of 1800 N/briquette. Results of BCB behavior under simulated BF conditions showed that the cold crushing strength after partial reaction of the BCB ranged from 1500 N/briquette to 5500 N/briquette and its maximum volume shrinkage degree was 0.45. The high anti-pulverization capability of the BCB was supported by the slag matrix or the iron network. Under the simulated BF conditions, the BCB underwent five stages of reduction by atmosphere, partial self-reduction and reduction by atmosphere, full self-reduction, partial self-reduction and gasification by atmosphere, and gasification by atmosphere. It is inferred from the experimental findings that, by charging the BCB in BF, an increase of top gas utilization efficiency could be realized, and a favorable influence on lowering the temperature level of the thermal reserve zone could be obtained.

Influence of an addition amount of a new type of alumina on the properties of ramming mullite-corundum mixes and samples from them

Effect investigation of an addition amount of spherical alumina on the properties of ramming mullite-corundum mixes of the MMK-90 (on a binder of an aqueous solution of orthophosphoric acid) and MMKPBF (with a MgO addition on a borophosphate binder) brands, as well as samples from them, have been carried out. As a result of the carried out studies, it was found that the use of an optimal amount (4 %) of spherical alumina in the composition of ramming mullite-corundum mixes provides an increase in by 30 % in the cold crushing strength of samples made from them, fired at a temperature of 1580 °C, while maintaining at sufficiently high level indicators of their thermal shock resistance and slag resistance. The indicated alumina use in the composition of the MMK-90 mix during high-temperature firing of samples leads to an intensification of the mullite synthesis process. In fired samples from the MMKPBF mix, the spherical alumina forms a dense intergrowth of "felt-like" structure, which reinforces the structure, increasing the strength and thermal shock resistance of the samples. Indicators of physical and chemical properties of ramming mullite-corundum mixes of improved composition and samples made from them (for MMK-90 and MMKPBF mixes, respectively): chemical composition, wt. %: Al2O3 — not less than 90.0 and 85.0; SiO2 — within 3.2-5.0 and no more than 2.5; Fe2O3 — no more than 1.0 and 0.6; P2O5 — in the range of 2.5-3.5 and 0.5-1.0; grain size composition, mm — 3-0; cold crushing strength after firing at a temperature of 1580 °С — 110 and 70 N/mm2; thermal shock resistance — > 20 thermal cycles 950 °С — water. Ramming mullite-corundum mixes of improved composition are recommended for use in various heating units with high specific mechanical loads on the lining.

Researches on development of alumina-chromia-zirconium silicate refractories containing 60 % Cr2O3

Researches of a branch composition and firing atmosphere influence on structure and properties of pressed alumina-chromia-zirconium silicate refractories with 60 % Cr2O3 content were carried out. The optimal branch composition which after firing in oxidizing atmosphere provides obtaining of samples with open porosity 24.8 %, apparent density 3.46 g/cm3, cold crushing strength 78 N/mm2 and thermal shock resistance by 950 ºС — water — 7 thermal cycles was established. The phase composition of samples was determined. It has been shown that, firing in a reducing atmosphere, as well as titanium oxide addition, have no significant effect on samples properties. Corrosion resistance comparative researches of alumina-chromia-zirconium silicate refractories with 60 % Cr2O3 content and refractory brand KHTSS-30 with 30 % Cr2O3 content to glass «E» and basalt melts by crucible method at a temperature of 1580 °C with an exposure time of 8 hours were carried out. It has been established that, glass «E» and basalt impregnate refractories, moreover for samples with the developed optimal composition the impregnation depth was the smallest in comparison with samples of other compositions. The corrosion mechanism has been established, which consists in the penetration of glass «E» and basalt melts into refractory with further dissolution of corundum grains in them. Sintered Cr2O3 and solid solutions based on it in the composition of samples prevent corrosion, reducing the interaction area of melts with corundum grains, and when exposed to basalt melt, also forming spinelid with its components, which slows down further penetration of melt into refractory structure, thereby reducing its corrosive effect on the refractory. Based on the obtained results, a technology of a new domestic type of product (alumina-chromia-zirconium silicate refractories with 60 % Cr2O3 content manufactured by semi-dry pressing method) was developed.

Effect study of an amount of active alumina addition on the properties of alumina refractories with a complex additive of chromium oxide and zirconium dioxide

An effect of active alumina amount introduced into a batch (7.5 - 22.0 %) on the properties of alumina samples containing a complex additive of chromium oxide (10 %) and zirconium dioxide (3 %) was studied. The optimal amount of introduced active alumina (12.5 %) was established, which ensures the production of samples fired at a temperature of 1580 ºС, with the lowest open porosity (18.2 %), the highest apparent density (3.25 g/cm3) and the highest cold crushing strength (117 N/mm2), refractoriness under a load of 0.2 N/mm2 > 1700 ºС, thermal shock resistance (in the mode of 1300 ºС — water) not less than 7 thermal cycles.The results of carried out studies were used in the development of production technology of domestic refractory products based on fused corundum, α-form alumina, active alumina, containing the complex addition of chromium oxide and zirconium dioxide, by semi-dry pressing method. These refractory products characterized by high properties and intended for service at a temperature of 1850 ºС in the combustion chamber of carbon black production reactors.The use of these refractories in the lining of above mentioned high-temperature industrial units will allow to increase a duration of their operation due to an increase in the refractory durability in service, as well as to save material and energy resources associated with a relining of the reactors.

Influence research of an α–form alumina type on the properties of samples from vibrocasting mullite corundum granular masses

The technology of refractories vibrocasting was developed by JSC "URIR named after A. S. Berezhnoy" in particular highly refractory mullite corundum crucibles for melting of heat-resistant alloys in induction furnaces. At manufacturing of highly refractory vibrocasting mullite corundum refractories a-form alumina, as a dispersion binder, which milling to a particles size of less than 10 μm (the content of particles less than 4 μm in such alumina is more than 50 %) is used. For improvement the casting characteristics of vibrocasting masses dispersants are used. At research milling kinetics alumina of all brands was milling in a vibration mill for a specified time. For this research a certain amount of the investigated alumina of each brand was loaded into a vibration mill, and after a specified grinding time (30, 45, 60, 75 and 90 min), a sample of alumina after milling was taken in a specified amount. In this work, the kinetics of changes the dispersion of alumina (S, N and NR brands) during their milling was studied. The dispersion of alumina which were needed (the content of particles less than < 10 μm in such alumina is not less than 90 %, the content of particles less than < 4 μm — not less than 50 %) was achieved in almost the same milling time was found (~ 45 min). With a further increase of milling time to 60, 75 and 90 minutes, the dispersion of alumina N and NR brands increases in comparison with alumina S brand and after 90 minutes of milling, the content of particles < 4 μm in alumina, respectively, is ~ 60, ~ 75 and ~ 80 %. After fired at a temperature of 1580 °C the properties of vibrocasting mullite corundum samples, which contain alumina S, N and NR brands, are characterized by a high level of apparent density (above 3 g/cm3), open porosity (less than 16 %) and cold crushing strength (above 140 N/mm2). The high properties make it possible to use a-form alumina N and NR brands along a-form alumina S brand in the technology of vibrocasting mullite corundum refractories, including the highly refractory mullite corundum crucibles.