Scholarly article on topic 'Effect of Sintering Performance of the Utilization of Blast Furnace Solid Wastes as Pellets'

Effect of Sintering Performance of the Utilization of Blast Furnace Solid Wastes as Pellets Academic research paper on "Materials engineering"

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{"Blast furnace flue dust" / "Blast furnace sludge" / Pellets / Sintering / Recycling}

Abstract of research paper on Materials engineering, author of scientific article — Prince Kumar Singh, P.K. Katiyar, A. Lava Kumar, Bharava Chaithnya, S. Pramanik

Abstract The present research paper discussed the utilization of plant waste materials such as blast furnace flue dust and sludge as macro pellets and use of these macro pellets in the production of sinter. Wastes addition as pellets to the sinter modifies the productivity of the laboratory grade sinter machine as well as the better mechanical strength of sinter. At the same it also decreases the coke rate for sinter production. The maximum productivity achieved is 5t/m2/day at basicity 2.2(super fluxed sinter). Microstructure of the sinter of basicity 2.2 revels that it consists of re-oxidized hematite (Fe2O3) and few magnetite (Fe3O4) phases with some slag phase of calcium silicate(CaSiO3). X-ray diffraction also confirms the presence of hematite and magnetite as the main constituents of the sinter. Although using these waste made pellets in the sintering process leads to decrease the coke consumption, simultaneously it is used as secondary raw material and at the same time it is eco-friendly also due to recirculation of hazardous wastes.

Academic research paper on topic "Effect of Sintering Performance of the Utilization of Blast Furnace Solid Wastes as Pellets"

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Procedia Materials Science 5 (2014) 2468 - 2477

International Conference on Advances in Manufacturing and Materials Engineering,

AMME 2014

Effect of sintering performance of the utilization of blast furnace

solid wastes as pellets

Prince Kumar Singha*, P K Katiyara, A Lava Kumarb, Bharava Chaithnyab, S Pramanikc

"Department ofMSE, Indian Institute ofTechnlogy, Kanpur,208016, India bDepartment of MSME, Maulana Azad National institute ofTechnology, Bhopal, 462051, India ""Department of MME, National Institute ofTechnology, Durgapur, 713209, India

Abstract

The present research paper discussed the utilization of plant waste materials such as blast furnace flue dust and sludge as macro pellets and use of these macro pellets in the production of sinter. Wastes addition as pellets to the sinter modifies the productivity of the laboratory grade sinter machine as well as the better mechanical strength of sinter. At the same it also decreases the coke rate for sinter production. The maximum productivity achieved is 5t/m2/day at basicity 2.2(super fluxed sinter). Microstructure of the sinter of basicity 2.2 revels that it consists of re-oxidized hematite (Fe203) and few magnetite (Fe304) phases with some slag phase of calcium silicate(CaSi03). X-ray diffraction also confirms the presence of hematite and magnetite as the main constituents of the sinter. Although using these waste made pellets in the sintering process leads to decrease the coke consumption, simultaneously it is used as secondary raw material and at the same time it is eco-friendly also due to recirculation of hazardous wastes.

© 2014ElsevierLtd.Thisisanopenaccessarticleunder the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of Organizing Committee of AMME 2014

Keywords:Blast furnace flue dust; Blast furnace sludge; Pellets; Sintering; Recycling

* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . E-mail ö^^re55:author@institute.xxx

2211-8128 © 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer-review under responsibility of Organizing Committee of AMME 2014 doi: 10.1016/j.mspro.2014.07.498

1. Introduction

Blast furnace sludge and flue dust are a hazardous metallurgical waste generated in the iron making process [1]. These Iron making plant wastes are mainly composed of oxides of iron, calcium, silicon, magnesium, aluminium, as well as carbon in the form of coke breeze [2]. In this work, these two different types' wastes such as flue dust and sludge are used to make pellets by using the three types of binders, bentonite, molasses and dextrin. Among these binders, bentonite provides the best quality of pellets having high shatter strength, high tumbler index as well as good compressive strength. Therefore bentonite based pellets are used in sintering of iron ore fines with fluxes to reduce the coke breeze consumption as well as increase better productivity of sinter machine. Therefore, utilization of these fine wastes as aggregates is a great opportunity to recycle of blast furnace wastes. So blast furnace flue dust and its sludge can be used as secondary raw material for the production of hot metals [16-28] in this way. Many research works have been carried out in the recycling of blast furnace flue dust and sludge. Hussiny et al. describes the effect of sintering of blast furnace flue dust and sludge after pellitisation in a disc pelletiser using molasses as a binder through the sintering process as a substitute of coke breeze due to high price [3]. Owing to the comparatively high price of binders the only interest becomes feasible is that of using waste products such as molasses that is both cheap and locally available [5-8]. Almost all types of ferrogenous wastes available in iron and steel plant can be utilized in appropriate proportion to produce quality sinter [10]. Approximately 6.7% of the total energy consumed in iron and steel production is required for the sinter operation [11, 12]. As a result of the growth of iron and steel industries all over the world, prime coking coal with adequate properties that yield metallurgical coke is becoming difficult to procure, and hence this trend is becoming progressively more severe and therefore more expensive [13]. Most research has been done in the sintering area includes energy consumption and production process control. Significant reduction in energy has already been achieved in the sintering plant as a result of improving raw material characteristics of ores and coke breeze as size and composition [14]. Sintering of BOF dust without coke breeze (fuel) was investigated by the sintering pot test. The coke breeze less sintering has an advantage in investment, as a sintering machine is more economical than a rotary kiln or other reduction facilities [15]. Gupta et al. investigated the process of recirculation of ferrogenous waste materials along with the iron ore fines to produce a quality sinter as percent trends in the international arena [25]. In the present work, blast furnace sludge and its flue dust are used as substitutes of primary raw materials in the form of pellets in sintering. Processing waste fines and utilized these fines in sinter helps to eliminate raw material flux and improves furnace productivity. This recycling method provides the optimum sized of the sinter, greater than 10mm.

2. Materials and Methods

2.1. MaterialusedforSintering

The raw materials used for sintering were iron ore fines, limestone fines, coke breeze and pellets of waste ferrogenous materials. Iron ore fines coke breeze and waste material were obtained from SAIL-DSP. The chemical and sieve analysis of raw material other than wastes have been shown in table land 2.

Table 1. Chemical Analysis of raw material for sintering process.

Material Fe(t) CaO Si02 MgO AI2O3 LOI Ash V.M. F.C.

Iron ore Lime stone Coke breeze 53.2 48.64 2.81 7.03 2.05 3.23 1.23 2.92 40.28 25.51 4.97 68.50

Table 2. Sieve analysis of raw material.

Sieve size(mm) Iron ore % Coke% Limestone %

+9 7 6 -

-9+6 35 20 -

-6+3 20 20 13

-3+1 25 20 40

-1+.5 5 10 15

-0.5 8 24 32

100 100 100

Additionally a table 3, 4 shows the chemical composition of blast furnace flue dust, sludge and bentonite binder, which is used as a binding agent during pelletisation process, was obtained from Sugar Company.

Table 3. Chemical composition of Blast furnace sludge.

Element Weight %, by mass

Fe 30.82

CaO 8.95

Si02 11.59

MgO 3.83

A1203 3.6

Na20 0.09

K20_0.29

Table 4. Chemical composition of Blast furnace flue dust.

Element Weight %, by mass

Fe 39.92

CaO 6.28

Si02 6.95

MgO 2.01

A1203 4.0

Na20 0.51

K20_0.29

The sample contains high level of carbon and iron, showing the abnormal accumulation of these two elements. X-ray diffraction of blast furnace flue dust and sludge as shown in Figuresl, 2 indicates that iron ore mainly consists of hematite and limonite while the main phases in the blast furnace flue dust and sludge are hematite (Fe203), magnetite (Fe304), silica (Si02), limestone (CaC03) and carbon respectively.

2-Theta 2-Theta

Fig. 1. X-ray diffraction pattern of blast furnace flue dustFig 2 X-ray diffraction pattern of blast furnace sludge

2.2. Experimental

A disc pelletiser was used for the preparations of pellets which has a diameter of 56 cm. The angle of inclination of disc pelletiser was 36.21° with rotating speed 29 rpm and the residence time was 10 minutes. The sintering experiments were conducted in a laboratory down draft sinter machine. It was a pot-type, consists of pan, exhaust pipe, suction fan with cooling arrangement having the facilities of suction valves. The machine was overhauled fully and arrangements were made to attach thermo couples and manometer in the sintering pan. The suction valve have four notches for 0%, 33.33%, 62.66%, 100% opening. Suction of air is provided by a suction fan which is capable of producing a suction pressure of 1120 Pa. The water based manometer was used to measure the differential pressure across the bed and pressure difference between bed and outlet pipe. Thermocouple was required to measure the temperature of wind box. The most suitable pellets of waste material of size (3-5 mm) having highest mechanical property (by using 4% bentonite binder) were collected from pelletisation laboratory. The green pellets were dried in open air for 2 days and then fired at 900oC for 1 h. These pellets were mixed with iron ore fines, coke breeze and lime stone with an optimum amount of moisture (8-10% of the charge mix). The moistened charge-mix was kept inside the experimental pan thereafter, wooden sticks, cotton fibres soaked and kerosene oil was used for the initial ignition of the upper layer bed in the pan sintering machine. After putting the experimental pan on top of the machine, the joints are sealed with fireclay to stop suction of air from the joints. Thermocouple and manometer was fixed to the experimental pan. Afterthat the upper surface was ignited by a torch and the fan was put on. The flame gradually travelled to the bottom of the bed. After few minutes the walls of pan became red hot. At the end of the experiments, composite of iron ore fines, limestone, coke breeze and flue dust with sludge sinter were obtained. The hearth layer of 306 m2 was filled with returned sinter of 8-10 mm fraction about 15 mm height of the pan. The bed height was maintained at 100 mm. the ignition was done under suction pressure of 750 Pa while sintering was performed under three value of suction pressure. The suction was regulated by means of a valve which was manually controlled. The sintering time was determined by the time elapsed from the start of ignition until the exhaust gas temperature reached its maximum value.

2.3. Sintering Charge Calculation

Basic assumptions for calculation of charge mix for sinter was produced in pilot sinter plant with basicity (Ca0/Si02) was 1.5, 1.73 and 2.2. Whereas, amount of coke breeze and iron ore was used in each experiments 300gm and 3kg simultaneously. By mass balance the raw material mixes was calculated for three grades of sinter.

The sinters produced in experiments have been graded as Si, S2, S3.....Si5 by varying lime stone fines i.e. flux, and

addition of flue dust and sludge pellets amount.

Raw Materai Basicity = 1.5 Basicity=1.73 Basicity = 2.2

I.D. No. Si S2 S3 S4 S5 s6 S7 Ss S9 Sio Su Sl2 Si3 S14 Sl5

Iron ore fines(kg) 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

Coke breeze (gm) 150 150 150 150 150 150 150 150 150 150 150 150 150 150 150

Lime stone fines(gm) 335 383 400 432 465 400 445 471 490 535 550 660 697 770 843

dust+sludge pellets (gm) 0 300 400 600 800 0 300 400 600 800 0 300 400 600 800

2.4. Productivityof sintering machine

At the end of sintering experiment, the produced sinter was screened over a sieve of 10 mm to determine the productivity of the machine by using the formula.

Productivity of the sintering machine P = LSKH—^/day

Whereas

S Amount greater than 10 mm.

H Height of the charge / time of sintering K Bulk density of the sinter L Machine constant Reducibility of sinter:

Reducibility of the sinter was measured by weight loss method by carbon mono oxide, at the rate of 1.5 1/min and the gas was blown at in the ratio of 70:30 of nitrogen to carbon monoxide at temperature 900 °C and reduction time 90 min.

% Weight loss = (Initial weight - Final weight) / Initial weight x 100

Testing of sinter:

The sinter strength was measured by Shatter test, Tumbler test and Abrasion test, 3. Results and Discussion

3.1. Effect of different parameter on the sintering time

The sintering time was determined by the time elapsed from the start of ignition until the exhaust gas temperature reaches the maximum as shown in the fig.2.

Time (min)

Fig 2 Temperature of wind box vs. time for a typical sintering experiment

A typical suction pressure versus time plot is shown in figs. 3, 4 and 5 at different opening of valve as 33.33%, 62.66% and 100% respectively.

Time (min)

Fig. 3 Suction pressure vs. time for sintering experiment at 33.33% valve open

0 2 4 6 8 10 12 Time(min)

Fig 4 Suction pressure vs. time for sintering experiment at 62.66% valve open

Time(min)

Fig. 5 Suction pressure vs. time for sintering experiment at 100% Value open

The above figures show that the suction was regulated by a valve. All the above figures (3-5) show nearly the same behaviour as pressure increase with time in initial span and then decreases. Whereas, fig. 5 illustrated that the high suction pressure was achieved at minimum time, when the valve was opened at 100%. After reaching the maximum temperature, the hot sinter was allowed to cool. The time to reach maximum temperature is taken as sintering time.

3.2. Behavior of waste on coke rate (kg/t) of sinter:

Figure.6 shows the effect of waste addition on coke rate (kg/t of sinter). It is seen that coke rate decreases with increase in waste. The waste contains some fixed carbon in flue dust (9.6%) and sludge pellets (12.34%) which reduces the coke requirement during actual sintering. With the increase in waste percentage more carbon is available during sintering which in turn decreases the coke rate. The coke rate was (above 60 kg/t of sinter) calculated on the basis of amount of coke breeze added in sintering charge and produced sinter of size above 10mm.

Fig. 13 illustrates the XRD pattern of typical sinter sample containing 20% waste and of basicity 2.2. Analysis of the sinter indicates that the sinter consists of mainly hematite phase and other is magnetite with slag (CaSi03) phase. Among the above phases, hematite phase is the main phase and very few peaks of magnetite are observed.

The most suitable pellets(3-5 mm) of wastes(Blast furnace flue dust and sludge) is obtained with 4 % bentonitebinder, effectively used as one of the raw material for sintering which confirms the recirculation of wastes of plant efficiently utilized without deteriorating the quality of sinter. Use of wastes made pellets decreases the coke rate in sintering operation due to the presence of some fixed carbon in wastes (Flue dust 9.60 % and in Sludge 12.34%).Higher waste addition to the sinter mix also facilitates the enhancement in mechanical property of sinter as well as the productivity of the laboratory grade pot type sintering machine. Productivity of the sintering machine is also increased with the increment in waste addition percentage. Maximum productivity is reported as 5 t/h m2 at basicity 2.2 for nearly 27 % waste addition to the chrage mix. The total iron content in the sinter is marginally low which can be enhanced by with high grade ore. Deterioration regarding reducibility of sinter comes in to account with increase in waste addition due to the presence of Calcium ferrite (CaO. Fe203) and CaSi03 slag phase in the

The author wishes to express his sincere thanks to the Department of MME National Institute of Technology Durgapur for using the facilities. Authors are also thankful to Mr. S. K. Dubey, Dupty General Manager, Blast Furnace operation, DSP-SAIL, for providing the waste as well as other raw materials to carry out research work.

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