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ГИАБ. Горный информационно-аналитический бюллетень / MIAB. Mining Informational and Analytical Bulletin, 2019;(9):122-130
УДК 622.788.32 DOI: 10.25018/0236-1493-2019-09-0-122-130
экспериментальные исследования технологии брикетирования железосодержащих отходов металлургического производства
А.Н. Корчевский1, H.A. Звягинцева1
1 Донецкий национальный технический университет, Донецк, e-mail: [email protected]
Аннотация: Цель настоящей работы заключалась в подборе рационального режима брикетирования железосодержащих отходов металлургического производства. Были выполнены лабораторные исследования по определению оптимального состава компонентов шихты и подбору оптимального связующего при невысоких давлениях прессования с минимумом технологических операций. Были исследованы отходы металлургического производства — колошниковая пыль, доменный шлак, вторичная окалина, пыль газоочистки. Были проведены опыты по получению брикетов с использованием в качестве связующего известковой муки, жидкого стекла, лигносульфоната, доменного шлака, шлака производства силикомарганца, связующего СБ, угольного пека. В результате выполненной работы отработана методика исследования технологии брикетирования и оценки прочности полученных брикетов. Из опробованных связующих выделено связующее СБ (продукт из отходов нефтепереработки), которое позволяет брикетировать мелкодисперсные материалы с высоким содержанием коксовой мелочи (до 18% содержания углерода), поскольку является эффективным связующим для углеродсодержащих материалов. Определена возможность получения брикетов из мелкодисперсных железосодержащих отходов со связующим СБ в количестве 10% с прочностью на раздавливание 100—130 кг/см2. Высокотемпературные испытания полученных брикетов показали, что брикет сохраняет форму после отжига при температуре 1240 °С; степень металлизации железа при этом составляет 68,7—91,2%; степень восстановления — 74—87,6%.
Ключевые слова: брикет, железосодержащие отходы, связующее вещество, брикетирование, прочность, термообработка, прессование, исследование.
Для цитирования: Корчевский А. Н., Звягинцева Н. A. Экспериментальные исследования технологии брикетирования железосодержащих отходов металлургического производства // Горный информационно-аналитический бюллетень. - 2019. - № 9. - С. 122-130. DOI: 10.25018/02361493-2019-09-0-122-130.
Experimental study of briquetting technology for iron-bearing metallurgical waste treatment
A.N. Korchevskii1, N.A. Zviagintseva1
1 Donetsk National Technical University, Donetsk, e-mail: [email protected]
Abstract: The study was aimed to select an efficient briquetting mode for iron-bearing metallurgical waste. The laboratory tests determined the optimal composition of batch and the optimal binder for low-temperature pressing with minimum process stages. The tested metallurgical waste was blast furnace dust, furnace slag, mill scale and gas cleaning dust. The binders in the briquetting
© А.Н. Корчевский, H.A. Звягинцева. 2019.
tests were lime powder, liquid glass, lignosulphonate, furnace slag, silicomanganese manufacture slag, binder SB and coal tar. The studies have allowed refinement of the testing technique for briquetting technologies and the briquette strength. From among the examined binders, we select binder SB (refinery waste product). Binder SB enables briquetting finely dispersion materials with high content of coke fines (to 18% of carbon content) as this binder is efficient with carbon-bearing materials. According to the tests, it is possible to manufacture briquettes with crushing strength of 100-130 kg/cm2 from finely dispersion iron-bearing waste with binder SB at its consumption of 10%. The high-temperature tests show that these briquettes keep their shape after annealing at 1240 °C at metallization of 68.7-91.2% and iron recovery of 74-87.6%.
Key words: briquette, iron-bearing waste, binder, briquetting, thermal treatment, pressing, analysis.
For citation: Korchevskii A. N., Zviagintseva N.A. Experimental study of briquetting technology for iron-bearing metallurgical waste treatment. MIAB. Mining Inf. Anal. Bull. 2019;(9):122-130. [In Russ]. DOI: 10.25018/0236-1493-2019-09-0-122-130.
Introduction
Experimental investigations undertaken recently in the area of recycling of iron-bearing waste are reflective of a considerable concern exhibited by the industry and researchers both in Russia and abroad [1—5]. Agglomeration factories treat waste mostly using agglomeration belts. However, when agglomeration circuit involves fines (less than 0.08 mm in size), such as slimes, blast furnace dust, lime powder, gas permeability of such batches is reduced and productivity of agglomeration machines drops.
For this reason, efforts are persistently made to find alternative approaches to iron-bearing waste treatment [6—8]. One of the most promising and increasingly wider applied techniques is iron waste briquetting on revolving and ram pressing machines [9—11].
Iron-bearing waste (except for furnace scale) features fine dispersion (fraction < 0.08 mm) and presence of coke dust, which governs application of [12, 13]:
• Briquetting under high pressure (above 100 MPa) without binders;
• Briquetting with binders which ensure sufficient strength at minimum consumption;
• Combination of the two methods above.
High-pressure briquetting uses complex and low-productive equipment, while the process is very expensive. Accordingly, the optimized solution to the problem of fine iron-bearing waste briquetting is selection of an efficient binder for briquetting under low pressure with minimum number of process steps [14—18].
Materials and procedure
The experimental tests were carried out using laboratory equipment and instrumentation.
Before the briquetting tests, the optimal distribution of particle size was calculated in order to ensure maximum density packing of grains in batches.
The theoretical quantities of the briquetting batch components were mixed in a certain order until an indiscrete mass was produced, which was then pressed on a rolling press under pressure of 25 MPa. In some case, the pressing pressure was increased.
The test procedure involved three experimental series of briquetting magnetic and nonmagnetic fractions with different binders.
Metallurgical waste to be treated was batched at ratios fitting the waste generation at plant. The reference briquetting mix (batch 1) was composed of:
Table 1
Physical properties of iron-bearing waste Физические свойства отходов
No. Material Moisture content, % Density, g/cm3
1 Lime powder 4.5 1.25
2 Blast furnace dust 2.5 1.2
3 Furnace slag 27 1.39
4 Bucket furnace dust 1.3 0.46
5 Mill scale 21 1,74
Table 2
Chemical composition of iron-bearing waste and briquettes Химический состав железосодержащих отходов и брикетов
Material Fe total Fe O 2 3 FeO C CaO SiO2 S P Content in batch, %
Batch 1: 42.1 54.9 5.6 14.6 9.4 8.0 0.36 0.075 -
including blast furnace dust 38.2 52.6 3.1 18.1 10.3 9.1 0.24 0.08 56.3
furnace slag 45.2 58.6 5.5 10.5 8.9 7.2 0.55 0.07 39.5
mill scale 66.0 50.6 39.5 5.77 1.82 1.27 0.17 0.05 4.2
Briquette (composition): batch 1 — 83.4%; lime — 8.3%; SB — 8.3% 33.9 40.1 7.58 19.1 11.5 8.2 1.04 0.02
Table 3
Comparative strength of different composition briquettes after pressing (16 MPa) and hand molding
Сравнительная прочность брикетов различных составов, отпрессованных (16,0 МПа) и отформованных вручную
Composition of briquette Strength, kg/cm2
Pressing and curing for 3 days Hand molding and curing for 3 days Hand molding and carbonization for 2 h under 200 °C in C02
100 g batch 1, 20 g furnace slag (0-3 mm), 20 g liquid glass not manufactured 0.68 briquette falls to pieces
100 g batch 1, 20 g slag SiMn, 20 g liquid glass 37 21 14.7
100 g batch 1, 20 g bucket furnace dust, 20 g liquid glass 31 3.4 4.4
100 g batch 1, 20 g cement 500, 30 g liquid glass 11 10.4 5.3
100 g batch 1, 20 g power lime, 20 g liquid glass not manufactured not manufactured 3.7
100 g slag SiMn, 20 g liquid glass 55.6 not manufactured not manufactured
80 g furnace slag (0—3 mm), 40 g liquid glass not manufactured 283.4 not manufactured
• blast furnace dust — 56.3%;
• furnace slag —39.5%;
• oily mill scale — 4.2%.
The average iron content of batch 1 was 42%.
Binders in the experimental briquetting process were lime powder, liquid glass, lignosulfonate, furnace slag, silicomanga-nese manufacturing slag, binder SB and coal tar. The properties of the waste are described in Tables 1 and 2.
Results
Aimed to select efficient mode for briquetting iron-bearing waste, different compositions and binders were tested. The test results are compiled in Table 3.
From the analysis of the obtained data, the strength of the briquettes is governed by the pressing force (Table 3): the pressed briquettes possess much higher strength than the briquettes after hand molding.
Table 4
Test data of binders for briquetting batch 1 Результаты исследований связующих веществ
Carbonization shows no influence on the properties of the briquettes within the testing period (24 h). The mix of furnace slag and liquid glass has the strength of 283.4 kg/cm2, while the same composition used as a binder offers the minimal strength. This implies that this composition is inapplicable as a binder for batch 1 containing coke fines.
The obtained results were verified in the tests of binders for briquetting batch 1. These test data are given in Table 4.
These results prove the earlier made conclusion that these binders are useless for batch 1 as they lack strength in the raw state while annealed briquettes fall to pieces (except for the sample composed of 20% of cement and 20% of emulsion as a binder).
Then, the strength of the briquettes manufactured by pressing under 160 kg/cm2 was tested as function of curing time. Table 5 presents these test data.
для брикетов смеси 1
Components Content, %
mix 1 mix 2 mix 4 mix 4 mix 5
Batch 1 60 B0 BS 74 7S
Cement 20 - BS 4 7.S
Curing agent (liquid glass) - - 0.4 0,S6
Water - - BS 9 B.7
Emulsion: 20 20 - 1S 10.64
including reclaiming agent 1.BB 1.BB - 1.22 1.0
clay 0.4 0.4 - 0.26 0.21
surfactant 0.52 0.52 - 0.S4 0.2B
water 17.2 17.2 - 11.1B 9.15
Briquetting parameters
Density, kg/m3 2230 2270 1B70 2050 2090
Manufacturing mode Pressing 150 kg/cm2 Vibro-molding Pressing 150 kg/cm2
Compression strength in 7 days, kg/cm2 107.37 7.13 S0.0 SS.67 54.6-64.3
Curing under 900°C for 3 h surface scaling, briquette maintains shape briquette falls to pieces maintains shape, has cracks
Table 5
Strength of mixtures versus curing time
Прочность различных составов в зависимости от времени выдержки
Composition, % Curing time, days
0 14 22
Compression strength of briquettes, kg/cm2
100 g batch 1, 20 g slag SiMn, 20 g liquid glass 5.1 11 63
100 batch 1, 25 g liquid glass 7.1 18.9 14
100 g batch 1, 25 g liquid glass without water 12.8 35.7 22.7
100 g batch 1, 1.5 g sodium carbonate 22 g liquid glass 5.8 48.5 50.7
100 g batch 1, 10 g powder lime, 10 g milled coal tar 108.9 118.8 (3 days) 75 (9 days)
100 g batch 1, 10 g powder lime, 10 g liquid glass 175.6 244.1 (3 days) 250 (9 days)
The data display a trend of strengthening, especially observable in the first 14 days, though strength is yet insufficient even after curing.
The compression strength of the briquettes manufactured with binders appeared to be lower by an order of magnitude than the required value of 200 kg/cm2 and averaged less than 50 kg/cm2. That low strength can be explained by the high content of coke fines in blast furnace dust, which prevents binding by the ma-
250
terials at the mentioned consumption (not more than 10%).
The strength of the briquettes made with the binder composed of coal tar and modified liquid glass (density of 1.5 g/cm3) approached the required value. However, the compression tests ended with brittle failure of the briquettes into fractions smaller than 5—8 mm in size.
Therefore, particular attention was imposed on binder SB commonly used in bri-quetting coke fines and small coal. Briquet-
o 200 15>
£ 150
100
50
Amount of binder SB = 5 % Amount of binder SB = 7 % Amount of binder SB = 10 %
100
200
600
700
300 400 500
Pressing effort, kg/cm2
Fig. 1. Compression strength of briquettes versus binder consumption and pressing force
Рис. 1. Зависимость прочности брикетов на сжатие от количества связующего и усилия прессования
Maturing, hours
Fig. 2. Compression strength versus time of drying under temperature of 150 °C Рис. 2. Зависимость прочности на сжатие от времени просушки при температуре 150 °С
tes manufactured from coal slack exhibited the crushing strength of 20—35 kg/cm2 in the raw state and 79 kg/cm2 after curing for 14 days. Thus, application of SB allows partial elimination of the adverse effect exerted by small coal and coke fines on the strength of iron-bearing briquettes.
The tests of binder SB in the reference batch briquetting and in the thermal processing mode were aimed to:
• Find optimal consumption of the binder (in the range of 5—10%);
• Determine the influence of the briquetting force on the compression strength of briquettes (in the range of 140— 700 kg/cm2);
• Develop a temperature—time processing pattern for briquettes after briquetting.
With this end in view, a series of briquettes were made with different contents of binder SB (5%, 7%, 10%) by pressing under various unit pressures. The test results are depicted in Fig. 1.
The results obtained with SB consumption of 10% approach the required compression strength; thus, for the further research, this composition (10% SB) was assumed as reference.
The temperature—time processing mode was determined using a series of briquettes manufactured with SB 10% and
dried under 150 °C within different time periods. The heat treat process data are demonstrated in Fig. 2.
The optimized heat treat mode found from the experimental result is curing for 4 h under the temperature of 150 °C (for a briquette with diameter of 32 mm and 15 mm high).
At the same time, the reference batch briquettes with SB binder at the consumption of 10% were subjected to curing under 20 °C. The results are presented in Fig. 3.
According to the test data, strengthening takes place in the first 10 days and, then, grows insignificantly. Curing for 10 days under the temperature of 20 °C increases the strength of the briquettes from 42 to 108 kg/cm2.
In the high-temperature processing tests, batches of different compositions were melted in a Tamman furnace.
The first test series A consisted of melting with blast furnace dust without any reducing agent (owing to the presence of coke fines at the content C = 18.1%). The feed mass of the dust was 100 g, and the melting temperature was 1500 °C. As a result, the yield was 34 g of metal (34% of the batch) and 32 g of slag (32% of the batch).
►-Sample 1 ■-Sample 2
О 5 10 15 20 25
Maturing, twenty-four hours
Fig. 3. Strength dependence of briquette on curing time under 20 °С Рис. 3. Влияние выдержки брикетов при температуре 20 ° на прочность
From the test results, it is possible to make a conclusion that at the content of Fetotal = 38.2%, the yield of iron is 34%, which makes 89% of recovery. Thus, coke fines in the composition of blast furnace dust allow iron recovery of 89% from the dust.
The second series B was the same melting of the reference batch with the content of 10% of SB as a binder in a Tam-man furnace. The feed mass was 74.5 g, and the melting temperature was 1500 °C. The yield was 24 g of metal (32.2% of the briquette weight) and 19.5 g of slag (26.1% of the briquette weight).
Accordingly, at the content of Fetotal = = 34%, the yield of iron is nearly 94°7%, which implies that the carbon of the binder works as a reducing agent (the carbon content of the briquette is C = 19.1%, including the binder carbon).
Conclusions
The authors have reached some conclusions based on the implemented research findings:
1. In the tests of binders, binder SB (refinery waste product) stands out; it enables
briquetting finely disperse materials with high content of coke fines (to 18% content of carbon) as it is an effective binder for carbon-bearing materials.
2. It is possible to manufacture briquettes from fine-disperse iron-bearing waste using binder SB at consumption of 10% with the crushing strength of 100-130 kg/cm2 (the laboratory briquette made under the pressing force up to 700 kg/cm2).
3. The high-temperature tests of the manufactured briquettes show that the start and end temperatures of the briquette softening is 880 and 1000°C, respectively; the briquette maintains its shape after annealing under 1240°C; metallization of iron makes 68.7—91.2% while recovery reaches 74—87.6%.
Based on the accomplished research, specifications are developed for iron-bearing briquettes meant for use in blast furnaces. The mechanical and thermal strengths of the briquettes comply with the standards of metallurgical recycling.
The process flow chart and equipment have been developed for finely disperse iron waste briquetting and recommended for semi-commercial testing.
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информация об авторах
Корчевский Александр Николаевич1 - канд. техн. наук, доцент, зав. кафедрой, Звягинцева Наталья Анатольевна1 - старший научный сотрудник, 1 Донецкий национальный технический университет, Донецк. Для контактов: Звягинцева Н.А., e-mail: [email protected].
INFORMATION ABOUT THE AUTHORS
A.N. Korchevskii1, Cand. Sci. (Eng.), Assistant Professor, Head of Chair, N.A. Zviagintseva1, Senior Researcher, 1 Donetsk National Technical University, 83000, Donetsk. Corresponding author: N.A. Zviagintseva, e-mail: [email protected].
