Olena Zhyriakova

Goals. Objectives. Tasks
It is necessary to develop viable projects for the neutralization of toxic gases from sintering process because of the environmental crisis situation in the Donbass, Krivbass, and Pridneprovye.
In a market economy, competitive environment and the general trend of energy cost rise in prices, the product quality and energy cost become priorities. Progressive changes in these characteristics are inextricably linked to environmental performance improvement. It is especially important for sinter production.general directions of energy savings for sinter plants include the charge preparation, increase the layer height; optimization of parameters and design characteristics of ignition furnace; use the heat of hot sinter and flue gases from the sinter machine; increasing the equipment tightness and reducing the pressure loss; optimization mode of the exhauster.
Level of significance of these directions is different for each sinter plant. The content of harmful gaseous components (carbon, sulfur and nitrogen oxides) in the off gases is determined by the charge composition and characteristics of technological process.
Consider modern trends of sinter production development, determine technological methods and organizational-technical measures to suppress the emission formation before exit the process are the solutions of the problem.


Relevance. Motivation
Sinter plants in Ukraine were built more than 40-70 years ago. 70-90% of them obsolete. There is no modern technological schemes, efficient equipment for homogenization and accurate proportioning of raw materials, charge mixing and granulation, cooling, crushing and screening of sinter. For this reason, for many years the sinter quality improving, especially on the content of undesirable fines, was not possible.
It should be noted, that in 2005, in All-Ukrainian project "Metallurgiya, mashinoobrabotka, machinostroyeniye" "the improvement of the quality of raw materials and coke for the blast furnace" have been declared as a primary measure. But nothing concrete and constructive for sinter production came of this proposition.
The technical policy of the head at privatized enterprises - general managers of financial-industrial corporations - focuses mainly on the production of the desired quantity of sinter. The supporting repairs of sinter machines were made for this without performing major reconstructive work to improve the main thing - the quality of sinter.
As a result, the sinter production in Ukraine is lagging behind the achievements of the best world analogues 5-7 times.
Therefore, the modernization of sinter plant is necessary in general as well as for individual components and devices.

Europe's largest sinter plant of
OJSC "Ilyich Iron and Steel Works of Mariupol"
(satellite imagery, Google Earth)

Scientific novelty
There are many developments in this field for individual elements of the process.
Ongoing work is the systematization of experience the best-known global and national developments. It reflects the impact of sinter production technological factors at specific consumption of solid fuels, raw materials and the quantity of emissions.


Expected results
After analysis of general technological and environmental conditions at sinter plants, research of new and upgraded processes, some generalizations and recommendations to reduce dust and gas emissions during the processes of preparation, sintering, crushing and screening are suggested for the sinter plants in Ukraine.
In sum, after studies of existing and proposed ways of "greening" a table is obtained. It shows the energy saving results and toxic emissions reduce for every method.


Research. Developments
There are lots of researches concerned to improvement of technology, energy savings, environment protection for sinter production. Japanese researchers from «Nippon Steel» do a lot of works in this area. Russian companies as machine-building corporation OJSC «Uralmash», «TOREKS», OJSC «Uralmechanobr», as well as the German «Siemens VAI» are well-known sinter plant designers.
At the national level, «Ukrgipromez», «Energostal», «Doniks» solve the problems of reconstruction and upgrade of sinter plant. In the last 3-4 years for the group of companies (OJSC «Alchevsk Iron & Steel Works», OJSC «EMZ», OJSC «DMKD», OJSC «Azovstal») technological tasks and feasibility studies for the construction of new modern sinter plants are preliminarily developed. Old sinter plants should be demolished.
At the Donetsk National Technical University PhD, associate professors Arkadiy S. Bondar and Ivan M. Mishchenko research a problem of sinter plants.

My own results
In the light of increased environmental requirements and considering socio-economic impact of the proposed processes, some generalizations and recommendations on the integrated development of sintering technology have been obtained after the analysis of the overall state of technology and environmental conditions at sinter plants in Ukraine, the results of studies of new and upgraded processes. Priorities for sintering should be determined taking into account their impact on the environment.
The object of study of this work is sinter plant in Ukraine where sintering machines were built in the 30-60's, and where the problem of improving working conditions and the environment protection is particularly relevant.
Initial operations in sinter production - unloading, storage and homogenization of charge materials are implemented mainly in open storages. The equipment of storages have limited averaging ability and is not suitable for recycling of dust containing materials. And does not provide enough power margin in many cases.
According to the methods of mixture averaging sinter plant can be divided into two groups, distinguished by simultaneous and distributed average of components.
In a simultaneous scheme of averaging all components of iron ore (concentrate, ores, waste) and lime at OJSC «Azovstal», OJSC «ArcelorMittal Kriviy Rih», CJSC «MMZ», OJSC «DMKD» is stored in a stack. In a distributed scheme components are stored in two stacks: concentrate stack and ores stack. Wastes are stored in the concentrate stack (OJSC «Alchevsk Iron & Steel Works») or in the ores stack («Ilyich Iron & Steel Works»). The separate storage (for example, flue dust at «Zaporizhstal Integrated Iron & Steel Works JSC» and OJSC «EMZ») is also possible. Usually lime is added in concentrate stacks. According to the point of lime addition sinter plants are divided into three groups: lime is added only at storage, only to the flow of iron ore or charge and addition of lime to the storage and in the flow of charge materials.
These schemes of raw materials processing influence in different ways to the sinter charge quality as well as to the environment. For example, the forced add of lime to the open averaging storage without any dust control measures provoke high dust conditions at the storage and also far beyond. The use of lime and dry waste for drying of concentrate and for make it free-flowing have a major drawback: iron concentrate – the component of charge with the most stable chemical composition – loses its stability because of imperfect add of supplements without weighing scale dosing. Besides, the absence of normative technological reserves and spasmodic delivery of charge materials negatively influence the processes of averaging and further charge preparation at the sinter plant. That makes the stationary regime impossible and process is accompanied by dust and often by additional gas emissions.

Crushing of limestone, fuel, and sintered iron ore return fines to optimal size
Sintering practice and research proved that the optimal size of these components provides not only increase productivity and improve the strength of sinter, but also a significant reduction of the solid fuel consumption:

• iron ore and sintered return fines - about 5-6 mm;
• concentrate - 0,07-0,1 mm;
• flux - 0-3 mm (2 mm);
• fuel - 0,5-3 mm.

Limestone is crushed in special hammer crusher to size 0-3 or even 0-2 mm. Solid fuel (coke waste and anthracite) are crushed in roll crusher to size <3 mm. What is more, additional methods, which guarantee the exclusion of small fuel classes <0,5 mm, that burn quickly, have less convective heat transfer and emit more CO during the burning process, are used. With total removal of fractions 0-0,5 mm fuel consumption is reduced by 15,2%, the concentration of CO in the exhaust gas is reduced by 17.6%. Remove of 0-0,5 mm fraction from the fuel is possible by its pneumatic classification or intermediate screening. Classification, screening and gravity-inertial method of separation are used abroad.
The Japanese are using the fuel particle size of 1-2 mm, and consume it on a 20,2% lower than with using fuel size of 0-3 mm.
At the recommended optimum size 5-6 mm of iron ore and return fines, in fact, size is 15-20 mm. Implementation of additional crushing of iron ore and return fines can reduce the consumption of solid fuel by 7%, increase the strength of sinter by 6% and increase the productivity of the sintering process by 10%.

Averaging of charge materials
Real iron content and basicity fluctuations of charge are approximately three times more than necessary:

• ± 0,5 for iron;
• ± 0,05 for basicity.

In fact, iron content fluctuations of charge are 1,5-2%. The reduce of fuel consumption in sintering and blast furnace by 7-10% is possible by reaching the level of global developments on the chemical composition stability of the ore material.

Lime production and use in the sintering process
The use of lime in sintering allows to:

• ensure transportability - the free-flowing of such moist materials as ore concentrates, sludges - excludes their freezing during transport and storage, ensures the quality of dosage by maintaining a steady flow of;
• good charge granulation, sufficient strength of granules during the charge transportation to sinter machine, as well as in the process of sintering with large static loads;
• 50-70 kg/t of sinter of fresh lime specialists receive a gas permeable structure of layer and can increase its height up to 400-600 mm, with 1-2% savings of solid fuel at every 20 mm, and also increase the strength of sinter by 0,5-0,7% at every 20 mm of layer height increasing. Additional fuel consumption for the production of lime (about 150 kg of standard fuel per 1 ton of lime) paybacks due to achieved improvements of blast furnace production indices.

The «greening» of lime production must include a reliable localization of dust issue places and effective cleaning of gas flows from lime, with a maximum concentration of lime dust in the exhaust gas 10-50 mg/m cubic.

Dosing charge materials
A composition of charge in accordance with its calculation guarantees the required productivity, the uniform chemical composition and strength of sinter. The influence of the dosing accuracy on the solid fuel consumption can be 25-50%. Charge is composing in the automatic mode, i.e. by continuously weighing of material flows and by controlling the issuance of doses in kg per linear m of the dosing or assembly conveyor.
For high-quality dosing with issuance accuracy of each component ± 0,3-0,5% of the maximum value on the scale the following conditions are necessary:

• construction of dosing bins should have a conical shape with an inner surface of hydrophobic materials;
• avoid hanging of materials vibrating or pneumatic systems are needed;
• sensors, measurers of consumption and weight of charge in the form of load sensors and conveyer scales;
• steady flow of materials is a condition of compliance with dose accuracy;
• control the accuracy of weighing in modern automatic dosing systems span devices are provided.

Charge mixing and granulation
The dispersing of crushed fuel and flux (limestone, lime) in the amount of ore material is the main purpose of the charge mixing. Each macro amount of charge should get some fuel particles for allocated heat after his burning, for the processes of melting and crystallization. In poorly mixed charge some volumes have excessive fuel, and in some there is no fuel at all. Charge without fuel doesn’t sinter and returns to the process as return fines. And excess of fuel provokes melting to such silicate modification as β-2 CaO·SiО2, which restructures crystal lattice during the cooling with a volume increase by 10-12%, and converts the sinter to dust.
Drums are mainly used as mixers. They are simple to use, reliable, have sufficient efficacy (if the diameter and length correspond to the properties of mixing materials). Elongation of mixers are often accompanied by a reduction in fuel consumption.
Charge granulation in the optimal mode lets to obtain the charge with a relatively high gas permeability.
The main operational parameters of granulation include:

• speed of drum granulator (u <4-6 rpm), keeping the charge rolling mode;
• charge filling degree of the drum should not exceed 5-10%;
• charge wetting degree must be stable 7,5-8%;
• diameter and length of the drum, combined with the speed of rotation should provide formation and the growth of grains, but also sufficient tightening for a durable structure of granules capable withstand the load during transport to sinter pallet cars.

There are several ways of charge granulation where the main objective is to reduce fuel consumption and increase the strength of sinter. It is a process of separate granulation. In the world practice the granulation technology with roll up of solid fuel to ready-made charge granules is used. With separate feeding of solid fuel (20-30% in charge dosing and 70-80% in granulation) the consumption of solid fuel is possible to reduce by 8-10%, and gas (natural gas, as a rule) by 7-12%.

Charge feeding on palettes of sinter machine
This operation ends the cycle of charge preparation to the sintering.
Sinter machine feeding station should provide:

• optimum degree (maximum is desirable) of charge segregation, which means the separation of its mass by virtue of differences in the size, density, shape and other properties of particles of which they are composed in the height layer;
• destruction degree of charge granules during the charging from mixer-drum to pallets of sinter machine;
• same height to the width of the layer, and thus to the length of the sintering area of sinter machine;
• grain size and chemical properties of charge to the width and height of the layer.

Due to the segregation of the solid fuel temperatures equalize in height layer, and solid fuel savings can reach 8-10% or more due to improved segregation. Soft charging mode with maintaining its fenestration provides an opportunity to improve the process productivity, to create conditions for economic high-layer sintering.
Searching of upgrading ways for technology and equipment for charging continues to be a challenge, because such a unique feeding station, that would meet all the requirements of modern technology about creating a layer with optimum temperature, thermal and gas dynamic characteristics, is not yet developed.
Feeding stations at the Ukrainian sinter plant unable to meet the requirements of specific technologies: preparation and sintering of charge consisting of iron ore concentrate and waste. These systems are less advanced than some foreign analogues, and basic modernization is required as minimum. While the Japanese experts have proposed several new constructions of two-stage feeding stations, some of which have been used successfully not only in Japan but also in China, Brazil and other countries.

High-layer sintering
This is the main direction of upgrade the sintering technology in the world, because the best indices of the sinter strength and the solid fuel savings have been achieved.
The increase in the layer height at 20 mm reduces the solid fuels consumption by 2%, reduces emissions into the atmosphere:

• Dust by 7%;
• CO by 3,6%;
• NO2 and NOx by 2-3%.

The increase in the height of the layer is possible to add three conditions:

• granulated charge qualitative preparation with the use of modern equipment and binders;
• of sinter machines with powerful exhauster, able to create a large vacuum (15-30 kPa) under the sintered layer;
• system of sinter machines should have a high tight.

High-layer sintering uses the following thermotechnical advantages: the higher layer, the more inflow of heat regeneration and sufficient temperature for melting and forming of stable sinter.

Combined heating in the charge layer
High-layer sintering creates uniform temperature conditions of sinter formation. However, the problem remains that it is heat deficit in upper sinter layer. For this purpose (providing approximately the same temperature in layer height) is a combined heating, comprising:

• heat from the combustion of fuel inside the layer;
• from external heat source by blowing air or products of fuel gases combustion (natural gas, coke, blast-furnace gas, converter gas) through the layer.

Sinter gas recirculation
The purpose is after-burning or decomposition of CO and complex hydrocarbons, as well as some absorption in the layer of sulfur dioxide.
Usually waste gas of last wind boxes with temperature of 150-200 °C returns in the process of sintering. The optimum degree of waste gas recycling for Ukrainian sinter plants is about 25%. At the same time emissions of CO into the atmosphere reduce by 25% and the consumption of solid fuels reduce by 2 kg/ton sinter.
For long machine, where about 40% of the area is used for sinter cooling, air blow of almost ready-made sinter and lodge of the air with temperature of about 600 °C to the sintering process. In this case, the consumption of solid fuels can be reduced by 20%.
Composition of sinter gas:

• CO = 0,5-3%;
• CO2 = 14%;
• SO2 = 0,3%;
• NOx = 0,05%;
• N2 = 60%;
• PCDD/PCDF.

Sinter cooling and mechanical treatment
Sinter is cooled in special coolers for ensure normal working conditions in a cycle of transport, dosing and feeding of sinter in blast furnace. The heat of sinter is 38% in the overall heat balance of the sintering process. Heat recovery provides 20% of fuel savings.
During the cooling the strength and particle size of sinter stabilize, that the maximum number of fines is possible to separate and good stable sinter size is possible to get. This is a base for fuel saving in blast furnaces.


Results. Prospects
Higher cost of fuel and electricity should encourage to more active work on technical upgrading and renovation of sinter plants.
Sinter plants in Ukraine now are morally and physically obsolete, produce low-quality sinter, especially on the particle size. This is the main reason for the insufficient efficiency and high energy-consuming production of blast furnaces.
The technical level of sinter production in Ukraine can be significantly improved by the introduction of effective processes and equipment at all stages - from averaging of raw materials to the screened sinter. For this the construction of new sinter plants and the upgrade of old sinter plants are required.
The cardinal improvement of basic indices of the sinter quality contributes for the heat and fuel saving, for the introduction of effective processes: the intensification of pig iron smelting and improving the pig iron quality (the use of pulverized fuel (PF), modern feeding station, improving the parameters of the combined blast, etc.), net cost reducing and improving the competitiveness of the blast furnace products.
Improving the blast furnace ironmaking process on a base of a radical improving of the sinter quality can increase pig iron production and reduce the consumption of coke. The coke consumption reduce gives a great opportunity to the coke production modernization, removal from service and dismantling of coke-oven batteries. In this regard, besides growth in economic performance, the positive changes in the ecological situation are expected.
For reduce capital and operating costs it is necessary to make maximum use of equipment of specialized engineering machine-building factories in Ukraine and near abroad.



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NB! The Master's work is not yet complete. Final completion date: December 2009. Full text of the work and materials on the topic can be obtained from the author (or her scientific adviser) after that date


e-mail: zhiryakova'at'yahoo'dot'com