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Rovin S.L.,
Ph.D.,
Belarusian National Technical University, Minsk, Belarus
Kalinichenko A.S., D.Sc,
Belarusian National Technical University, Minsk, Belarus
A NEW METHOD OF RECYCLING OF PARTICULATE IRON-CONTAINING WASTES - THE WAY TO CREATION OF NON-WASTE PROCESSING AND UTILIZATION OF METALS IN INDUSTRY.
Summary: The article presents an alternative method for recycling ferrous-containing waste. Method based on a continuous solid-liquid phase reduction of iron oxides in rotary tilting furnaces (RTF). The new method allows the processing of waste from virtually any composition and state from metal to oxide and multicomponent (shavings, scales, sludges, etc.) contaminated with moisture, oils, organic impurities without their preliminary preparation (purification, homogenization, pelletization, etc.). The final product of method is a cast iron or steel ingot or specified casting alloys.
Key words: recycling, reduction, disperse iron-containing wastes, rotary tilting furnaces
Introduction
Efficient use of recourses including wastes utilization and recycling is a matter of universal significance. In response to the growth of deficit of qualitative charge materials and their prices the recycling of disperse iron-containing wastes, such as chips, scale, aspiration and abrasive dust, sludge etc., and which accumulation in dumps today comparable with ore mining is a matter of great significance.
At present in metallurgy methods of direct ore oxides reduction are rapidly on the rise along with a traditional blast-furnace practice of iron production. It seems that these methods may be also used for processing of industrial metal wastes. But at the formal resemblance of the processes it is practically impossible
to use the engineering solutions existing in metallurgy for recycling dispersed iron-containing wastes.
The main problem is that all the methods of iron direct reduction, as well as blast-furnace practice, maintain the differential process characteristic - charge must be in the form of lumps (pellets, agglomerates, briquettes). Lower size limit is 10 - 15 mm, while the upper one doesn't have practically any restrictions. The lower limit is conditioned by a layer mode of furnaces working technology and their sizes. Herewith not only size limitations but also strict requirements to the charge density and strength are attributed to operational and technological characteristics [1].
It is known that the rate of heat exchange and all heterogeneous processes at the gas-solid interface, including solid-phase reduction, depends on the reagents
specific surface area. As well the rate of reduction (oxidation) is a direct function of material dispersion and porosity, first of all, open porosity [1, 2].
Such technological conflict in metallurgy is solved by increasing the furnace size both in two-stage and one-stage methods of iron production. Profitability of metallurgical units may be reached only by production of about a million tons per year or even to higher values. Herewith, requirements for stability and uniformity of the charge stock, its composition, size, mechanical properties etc., become prevalent ones.
However, dispersion and porosity of the original charge substance are considered to be negative characteristics. The above characteristics are aimed to be lowered by various approaches - the stock is pelletized, that results in the increase of the expenditures and the cost of the final product.
Centralized collection and processing metal wastes lead to uncontrolled mixing of dissimilar materials resulting in worsening their quality as metallurgical iron source. Moreover, it requires well developed material handling and logistic systems, sophisticated equipment for cleaning and preparation, melting, control and realization of the product. It makes the above product uncompetitive in comparison with traditional charge materials. So, the recycling of the industrial metal wastes must be organized on a different basis.
It is necessary to provide maximum intensity and the flexibility in creating recycling technology that must be oriented on processing of disperse technogenic metal wastes obtained from relatively small amounts on hundreds of sources (machine-building, metal-working and metallurgical enterprises).
This technology should allow the use of different raw materials without preliminary preparation and organization of profitable production with the application of small power units at minimal capital cost.
Small-tonnage recycling on a national scale does not mean a low-powered production but this means decentralized flexible production, organized directly at the enterprises-sources of waste generation.
Results and discussions
Developed small-tonnage recycling is based on closed ecological system of metal recovery. Herewith, the material porosity and dispersion are positive characteristics since processing is carried out in principally new facilities - rotary tilting furnaces (RTF).
Alternatively to traditional installations working with fixed bed of lump materials dispersed materials in RTF are within a dynamic continually stirred layer being influenced by high-speed high-temperature looplike gas flow with 25-35 m/s circulation speed. Forward speed in the axial direction does not exceed 1-3 m/s. Constant renewal (mixing) of the layer and its intensive blow increase manifold the processes of mass and heat transfer: in RTF volumetric heat transfer coefficient (av) reaches 2000-3000 W/m3, while in a fixed bed of the material it is at the level of (3-4) W/m3 [2].
In order to implement high-temperature and highspeed processes of heating, reduction and melting of dispersedB materials it was necessary to study character of gas flow and movement of dispersed materials in RTF and to develop methods to control these processes.
For the research, a specially developed technique for simulation modeling and computer modeling using high-level programs were used.
Facilities modeling was carried out for furnaces of different types: for traditional short drum-type furnaces with rectilinear translation of the gas flow and for rotational tilting furnaces with loop rotational motion of gas (Fig.1.).
Fig. 1. -RTF General Drawing
The results of numerical simulation are the fields of temperatures, velocities and trajectory of the gas flow, an example of the solution is shown in Fig. 2.
Fig. 2. - Trajectories and velocities of gas motion and temperatures in RTF.
Aerodynamics of the flow and its interaction with material depend on the burners disposition, their number and incidence angle, layer configuration, spinning speed, spinning axis tilting angle, etc., which makes such furnace the facility with controlled vector of heat carrier flow.
High velocities gradient in the layer section and the pulse nature of the material motion in RTF provide high intensity of mixing and, as a consequence, that of heat exchange in the layer. According to the results of simulation and computerized modeling, equalizing of the composition and thus the temperature in the material layer in RTF takes 5-10 turnovers of the furnace body.
The results of simulation and computerized modeling made the basis for development of engineering solutions which have been successfully realized in practice.
Time of dense agglomerates reduction process, including pellets and agglomerates, amounting to 20 hours and more in the processes of direct nonblast-fur-nace iron-making is conditioned, first of all, by inside dffusion, and is proportional to the size of the reduced material.
As a basic model, accepted in iron and steel industry, describing the mechanism of agglomerates reduction process, the model with "unreacted core" is used [3, 5]. In compliance to the above model reactions of the reduction from highest oxide to metal (Fe2O3-Fe3O4-FeO-Fe) go at the reaction zone surface; reduced lower oxides (or metal) develop a particular barrier round the unconverted core - shell.
As the reaction zone moves deep into agglomerate the reduction speed decreases rapidly due to, first of all, the growth of route of the reducing gas molecules, diffusing through the layer (shell) of the reduced material and that of the re-diffusion of reaction products, and secondly, reaction surface area decreases proportionally to a squared radius of the unconverted core.
When describing the reduction processes of porous disperse materials, such as scale, aspiration dust and metallurgical sludge, etc., the use of the model with "unconverted core" does not reflect the actual conditions and is unacceptable.
Oxide particles have the sizes tens and hundreds times smaller than pellets, much less briquettes. Porosity of scale, aspiration dust and sludge, as a rule, is apparent, and is by two or three orders of magnitude greater than the agglomerate porosity, which during the process of reduction provides similar conditions of the
exchange process practically throughout the whole depth of the reduced particle. Studies have found that during the process of scale reduction in a dynamic layer at the temperature of 1100-1200°C the degree of metallization reaches 75-80 % yet in 30 minutes.
In such conditions the "quasi-homogeneous" model of the reduction process, based on the fact that reducing agent gets inside and simultaneously interacts with oxides throughout the whole mass, operating speed is equal and metallization goes on throughout the whole volume of the particle (layer element) simultaneously [2].
Adequacy of the "quasi-homogeneous" model use for description of the processes of solid-phase reduction (SPhR) of disperse materials in a dynamic blown through layer as well as high operational rates have been supported also during reduction smelting of scale in RTF pilot furnace at Belarusian Steel Works, where SPhR-process did not exceed 2.0 - 2.5 hours [2].
Interaction nature of iron oxides with gas reducing agents and carbon is adsorptive-catalytic, which is promoted by fast-renewing surface: in RTF the material is in continuous spiral reciprocating motion actively being mixed, both in the section perpendicular to the rotation axis and longitudinally. Fixed contact of dynamic layer with high-speed turbulent gas flow with CO/CO2 ratio is not less than 2/1, being in looping motion in furnace operating space also facilitates mass-exchanging processes.
There has been growing the role of direct reduction at the expense of solid Carbon (C), that is present within the material layer both in the form of carbon soot and disperse and ultra-disperse particles: specific developed surface of reagents up to 1,5-2,5 m2/g contributes to the direct carbon interaction with iron oxides. Appearance of the excess CO amount over the material layer and also heavy frothing of slugs at the transition into the stage of liquid-phase reduction that finalizes the process of oxides recycling in RTF is the evidence of process described.
Hydrogen also plays an active role in reduction of porous (microporous) material. Hydrogen originating due to H2O conversion from the products of natural gas combustion easily penetrates into micropores, which size are commensurate with molecule free path of ~ 0.5-0.7^. Pores with size <1 ^m make up 30-50% of the total surface of slag plates and sponge iron obtained. The presence of hydrogen accelerates the recovery process by 10-20%.
All the known methods of nonblast-furnace iron-making from ore and industrial iron-containing wastes may be divided into two groups, differing from each other by the method of oxides reduction and final product: methods of solid-phase reduction (SPhR), which final product is sponge iron, and liquid-phase reduction (LPhR), the final product of which is liquid iron [3,4].
Solid-phase oxides reduction and sponge iron production is the most developed and efficient processes, though rather time-consuming and do not solve the problem of complete replacement of the primary charge materials. Producing of high-quality dense materials, pig and casting alloys, is possible only by the method of their further re-melting in furnaces of different type, mainly in electric arc or induction ones, or in cupola installations.
High-rate LPhR-processes are rather energy-intensive, thus using such methods for reduction, starting from original composition, without first solid-phase reduction of oxides results in cost increase of the final product - cast iron and steel [4].
It seems that the most rational is the process of continuous two-stage reduction in one installation without overloading and transient heat loss.
Herewith, heating, drying, oil burning-out and first materials reduction are carried out in solid state.
and then after the optimal metallization level (70-80 %) has been reached and solid-phase reduction has been slowed down, the above process transits into high-temperature mode of liquid-phase reduction to produce liquid iron or steel. Exactly such two-stage process was realized on the basis of the designed technology with use of RTF.
One of the main factors, hindering continuous two-stage process with transition from SPhR to LPhR, is bloom processing (agglomeration of reduced iron with slag and under-reduced material). Lumps (blooms) formation terminates the reduction process, hinders material smelting and liquid-phase reduction.
Due to high technological mobility RTF makes it possible to overcome the above difficulty. The main part herewith is the rate of material heating during the transition period from 1100-1200°C (temperature of SPhR conduct up) to 1700-1800 °C, which is temperature of LPhR realization. During experimental melting 5-6 minutes transition time was reached while the heating rate was 2-3 K/sec.
Characteristics of the developed method of recycling in RTF, based on continuous solid-liquid-phase reduction process that differ from the known technologies of direct iron production may be presented using Fe-C diagram (Fig. 3).
Fig. 3. - Technological interval of producing iron carbon alloys in RTF.
Technology of processing oxide iron-containing wastes in RTF may be divided conditionally into two main stages, realized successively and continuously in one facility:
I - loading and heating of initial materials, solidphase reduction of iron oxides in recovering atmosphere (may be reached by gas burning with oxygen deficiency a = 0.6 - 0.7) with reducing agent (undersized coke, lignin, crushed electrodes, etc.) at 1000-12000 °C. Such long process taking about 2.5-3.0 hours depending on oxidation level of the original material.
Metallization degree at the end of solid-phase reduction is 70-80 %.
II - smelting, final liquid-phase reduction, melt carbonization, if necessary; equalizing till boiling stops and mold casting; or melt ladle pouring and transfer for chemical composition adjustment into electric furnace (duplex-process). Furnace temperature at melting rises up to 1700-1800°C, which is achieved by oxygen enrichment up to the general content of (27-29 %). The duration of the above stage is 30-50 minutes.
Specific temperature - time recycling mode of scale is presented in Fig.4.
The process of recycling of unoxidized metal wastes (chips, metal dust, fine scrap) in RTF is limited to remelting. Metal oxidation during heating is pre-
vented due to high heating rate (60-80 K/min) and furnace reducing atmosphere. At melting 5-7 % contaminated iron chips (moisture, oils, non-organic compounds) metal yield made up 95-93 %. The presence of oil in chips reduces specific fuel (natural gas) consumption.
OJj 0J
■a
= 1000
S
o
h
400 200
/
Heating SI 1 // / LPhR JL
/
y
r /
F / ? 00 n rs
2 r \ / "rz V© M o c_ g = & 13 ©XI «o
•a « i c .1 / e .ç n a t£ 11 1 F s C£ 9 -3 e «
H K « M \ v O Q is c % Di"2" a '3c S 4» E o
I c o -= H -= H c « s
100
12 17 22 28 33 40 50 60 70 77 84 92 100 110 132 138 148 158 170 188
Time, min
Tn - furnace temperature; TM - materials temperature; n - metallization rate Fig. 4. - Mode of scale reduction melting in RTF.
Metal, produced in RTF, depending on the original task, my be casted into ingots (pigs) with further use as charge stock in traditional melting facilities, or transmitted to electric furnaces for adjusting chemical composition in accordance with branded alloys or for its bringing up to the set composition directly in RTF.
Besides recycling of iron-contaning wastes, technological processes and rotary furnaces for processing
disperse aluminum, copper and lead-bearing wastes have been developed and introduced into production.
In total 8 technological recycling processes and 15 rotary facilities have been developed and introduced into production at 12 Works in the Republic of Belarus and in Russia (some of the installations are presented in Fig.5).
a -processing of iron turnings("Centrolit", City of Gomel, Belarus); b - lead recycling ("KPVR SPLAV", City of Riazan, Russia); c - recycling of iron scale and sludge ("BMZ", City of Zhlobin, Belarus) Fig. 5. -Rotary furnaces for the recycling of dispersed metal waste.
a
Conclusion
For the first time in the world, the process of obtaining iron from oxides (oxide and multicomponent iron-containing wastes) with the metal yield (cast iron or steel) to 90% of the theoretically possible by continuous solid-liquid phase reduction in one unit (RTF) without overloads and stops at intensive mode with rates exceeding the recovery rates in known SPhR-pro-cesses, and with lower specific energy costs than in the LPhR-processes has been realized. The new process allows for batch processing of materials, which makes it
p ossible to carry out decentralized low-tonnage recy-c ling of disperse metal waste without their preliminary preparation and directly at machine-building, metallurgical and metalworking enterprises - sources of this waste.
The introduction of the developed technology and equipment allows creating a new raw material base for foundry production, reducing dependence on primary charge materials, organizing the non-waste turnover of metals in industry, eliminating accumulated metal waste, using waste of solid carbonaceous materials,
thus obtaining significant economic and environmental benefits.
References
1. Yusfin Yu.S., Himmelfarb A.A, Pashkov N.F. New processes of metal production (iron metallurgy). (Novye protsessy polucheniya metalla (metallurgiya zheleza)). M.: Metallurgy, 1994. 320 p. (in Russian)
2. Rovin S.L. Recycling metal wastes in rotary furnaces. (Retsikling metallootkhodov v
rotatsionnykh pechakh) Minsk: BNTU, 2015. 382 p. (in Russian)
3. Tulin N.A., Kudryavtsev V.S. and others. Development of non-coke metallurgy (Razvitiye beskoksovoy metallurgii) / Ed. N.A.Tulina, K.M. Mayer. M.: Metallurgy, 1987. 328 p. (in Russian)
4. Bondarenko B.I., Shapovalov V.A, Garmash N.I. Theory and technology of non-coke metallurgy (Teoriya i tekhnologiya beskoksovoy metallurgii) / Pod.red. B.I.Bondarenko.
K.: Naukova Dumka, 2003. 506 p. (in Russian)
5. Die Reduktion der Eisenerse. L. von Bogdandy, H-J. Engel / - Verlag Stahleisen mbH, Dusseldorf, 1967. 520 p.
Brazhenko V.N.
assistant of the department of gidrogas system, National Aviation University Браженко Владимир Николаевич
асистент кафедры гидрогазовых систем, Национальный авиационный университет
THEORETICAL RESEARCH OF THE EFFICIENCY OF A FLUID MECHANICAL CLEANING
BY A ROTARY FILTER
ТЕОРЕТИЧЕСКОЕ ИССЛЕДОВАНИЕ ЭФФЕКТИВНОСТИ МЕХАНИЧЕСКОЙ ЧИСТКИ ЖИДКОСТИ РОТАЦИОННЫМ ФИЛЬТРОМ
Summary: The main task of this work is to research the efficiency of the hydraulic fluid cleaning by the rotary filter with a discrete perforated filter element and a storage bin for sediment at various modes of a fluid flow. According to the results of the numerical simulation a analysis of liquid's motion has been performed. The unequal motion of particles at the surface and through holes of a filter element has been noted. The influence of the tangential and radial components of the particle velocity on the filtration efficiency of the rotational filter is has shown. The results of separation efficiency of mechanical particles by discrete perforated filtering baffle on the basis of numerical simulation is has presented.
Key words: rotary filter, mechanical impurities, numerical simulation, discrete perforated filtering baffle, storage bin.
Аннотация: Основная задача данной работы - исследование эффективности очистки гидравлической жидкости с помощью ротационного фильтра с дискретно перфорированным фильтрующим элементом и бункером для осадка при её различных режимах течения. По результатам численного моделирования проведен анализ движения жидкости. Отмечено неравномерное движение механических частиц на поверхности и через отверстия фильтрующего элемента. Показано влияние тангенциальной и радиальной составляющих скорости частицы на эффективность фильтрации ротационного фильтра. Представлены результаты эффективности сепарации механических частиц дискретной перфорированной фильтрующей перегородкой на основе численного моделирования.
Ключевые слова: ротационный фильтр, механические примеси, численное моделирование, дискретная перфорированная фильтрующая перегородка, бункер.
Постановка проблемы.
Перспективным направлением для большинства современных отраслей промышленности является применение фильтров, конструкция которых позволяет выполнять длительное непрерывное восстановление фильтроэлемента без прекращения рабочего процесса в гидросистеме и непосредственно фильтрации. Реализация самовосстановления или самоочистки поверхности фильтроэлеме-нта потенциально реализована в относительно не дорогих гидродинамических полнопоточных фильтрах, а именно ротационных фильтрах. При их эксплуатации осуществляется вращательное движение перфорированного фильтроэлемента относительно жидкости. Таким образом, реализуется её очистка с помощью проницаемой перегородки и наблюдается явление гидродинамической действия инерционных сил потока жидкости на загрязнения, которые непрерывно удаляются с поверхности
этого фильтроэлемента (использование принципа гидродинамической очистки).
Однако, на сегодняшний день применение полнопоточных гидродинамических фильтров, а именно ротационных фильтров, с вращающимся фильтроэлементом ограничено из-за реализации эффекта гидродинамической очистки в неполной мере.
Таким образом, актуальной задачей при совершенствовании гидродинамических устройств фильтрации является исследование потока несущей жидкости между корпусом и вращающимся филь-троэлементом и движения в рабочей жидкости механических частиц загрязнений, особенно у вращающейся поверхности и в её отверстиях.
Анализ последних исследований и публикаций.
Обзор теоретических и экспериментальных работ в области исследования ротационных фильтров
