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This article was downloaded by: [Dalhousie University] On: 12 November 2014, At: 11:28 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of Coal Preparation and Utilization Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gcop20 Methodology to Improve the Mean Size of Coke for Stamp Charge Battery Debjani Nag a , Bidyut Das a , P. K. Banerjee a , S. K. Haldar b & V. K. Saxena c a Raw Material and Coke Making Research Group, Research and Development, Tata Steel , Jamshedpur , Jharkhand , India b Coke Plant, Tata Steel , Jamshedpur , Jharkhand , India c Indian School of Mines , Dhanbad , Jharkhand , India Accepted author version posted online: 28 Feb 2013.Published online: 20 Apr 2013. To cite this article: Debjani Nag , Bidyut Das , P. K. Banerjee , S. K. Haldar & V. K. Saxena (2013) Methodology to Improve the Mean Size of Coke for Stamp Charge Battery, International Journal of Coal Preparation and Utilization, 33:3, 128-136, DOI: 10.1080/19392699.2013.769436 To link to this article: http://dx.doi.org/10.1080/19392699.2013.769436 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

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Page 1: Methodology to Improve the Mean Size of Coke for Stamp Charge Battery

This article was downloaded by: [Dalhousie University]On: 12 November 2014, At: 11:28Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

International Journal of Coal Preparationand UtilizationPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/gcop20

Methodology to Improve the Mean Size ofCoke for Stamp Charge BatteryDebjani Nag a , Bidyut Das a , P. K. Banerjee a , S. K. Haldar b & V. K.Saxena ca Raw Material and Coke Making Research Group, Research andDevelopment, Tata Steel , Jamshedpur , Jharkhand , Indiab Coke Plant, Tata Steel , Jamshedpur , Jharkhand , Indiac Indian School of Mines , Dhanbad , Jharkhand , IndiaAccepted author version posted online: 28 Feb 2013.Publishedonline: 20 Apr 2013.

To cite this article: Debjani Nag , Bidyut Das , P. K. Banerjee , S. K. Haldar & V. K. Saxena (2013)Methodology to Improve the Mean Size of Coke for Stamp Charge Battery, International Journal ofCoal Preparation and Utilization, 33:3, 128-136, DOI: 10.1080/19392699.2013.769436

To link to this article: http://dx.doi.org/10.1080/19392699.2013.769436

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &

Page 2: Methodology to Improve the Mean Size of Coke for Stamp Charge Battery

Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

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Methodology to Improve the Mean Sizeof Coke for Stamp Charge Battery

DEBJANI NAG1, BIDYUT DAS1, P. K. BANERJEE1,S. K. HALDAR2, AND V. K. SAXENA3

1Raw Material and Coke Making Research Group, Research andDevelopment, Tata Steel, Jamshedpur, Jharkhand, India2Coke Plant, Tata Steel, Jamshedpur, Jharkhand, India3Indian School of Mines, Dhanbad, Jharkhand, India

Coke physical properties like mean size and distribution are very important for blastfurnace operation. Coke properties mainly depend upon parent coal characteristicsand carbonization conditions. Some additives were found to influence the cokeproperties. This article presents the influence of pyroxenite as an additive and effecton operating parameter on coke size.

Keywords Additives; Coke size; Operating parameter

Introduction

Coke plays three types of role in a blast furnace: chemical, thermal, and physical.Coke acts as a reducing agent and supplies heat for the reduction reaction. Cokephysical properties are also of great importance for the blast furnace operation.The importance of coke physical properties is linked to the need to support the fer-rous burden and to give a permeable matrix through which reducing gases can flowand molten material can percolate in the lower part of blast furnace. These physicalproperties are related to its size (mean and distribution) and its resistance to breakageand abrasion. Proper sizing of furnace coke can contribute to the increase in pro-duction of a blast furnace and to the lowering of coke rates. Too small coke entailsthe formation of an impermeable inert central core in the blast furnace whereas largemean size with a narrow size distribution maintains adequate permeability [1–2].

The parameters that are affecting coke size can be divided mainly in three factors:coal factor, operational factor, and additives. The coke size during carbonization isgoverned by the bulk density, rank, and ash content of the coal charge [3]. By a properchoice of the coal varieties in the blend, it is possible to control the size of coke to agreat extent. Stamping of an oven charge is well known to bring about markedimprovement in the bulk density of the coal charge and cohesion of coke. On theother hand, stamp charging also tends to increase the fissuring tendency in the coke

Received 12 December 2012; accepted 21 January 2013.Address correspondence to Debjani Nag, Raw Material and Coke Making Research

Group, Research and Development, Tata Steel, Jamshedpur, Jharkhand, Pin: 831001, India.E-mail: [email protected]

International Journal of Coal Preparation and Utilization, 33:128–136, 2013Copyright # Taylor & Francis Group, LLCISSN: 1939-2699 print=1939-2702 onlineDOI: 10.1080/19392699.2013.769436

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mass resulting in the reduction of lump coke size. The rank in terms of vitrinite reflec-tance of coal charge has been reported not to bring about any marked change in thesize of stabilized coke reaching blast furnaces; however, the size of wharf coke tendsto somewhat increase with the increase in the rank-of-coal charge. The ash content isthe most important quality parameter of the coal charge influencing the coke size [4].

Conditions of carbonization have a great effect on coke physical properties.Charging temperature, coking rate, duration of coking, and final coking temperatureare interrelated and control the coke quality. It is quite understandable that the higherthe oven temperature upon charging, the more rapid is the initial rate of heating.Some studies has been done on heating rate that suggested that there is an appreciablereduction in higher size fraction with higher heating rate accompanied due to higherflue temperature [5].

Apart from heating rate, quenching also has an effect on coke quality. Uponquenching, the coke undergoes the same physico-mechanical changes as any solid.It has been established that depending on the rate of cooling, the stress in pieces ofvarious sizes and shapes acts in different ways. An increase in stress leads to the for-mation of cracks and microfissures due to decreases in coke strength. The hot redcoke is pushed out from the oven; its appearance is characterized by a network of fis-sures extending throughout the coke mass, with a large central crack running throughthe height of the oven. During the subsequent quenching, handling, and screeningoperations, breakage tends to occur along these cracks. The leading method of cool-ing coke is wet quenching. In stepwise quenching, coke is quenched with water insteps. In high temperature, where the structure is denser and more strongly stressed,at the coke pushing temperature (850�C–1000�C), the quenching rate must be as mini-mal as possible. Within the range from 650�C to 850�Cwhen the structure is still quitestressed and the temperature gradient between the surface of the coke and center israther high, the quenching rate can be increased slightly. In the temperature rangefrom 200�C–650�C, the rate of quenching may be increased to such an extent as toprevent the generation of stress exceeding the ultimate strength of the coke [6].

Studies have been made by Jackman et al. [7] on the effect of adding small per-centages of anthracite fines and coke breeze to coal blends to determine their effecton coke size and strength. They observed that the addition of anthracite coal to thebasic blend caused a definite increase in coke size and addition of coke breeze causeda greater increase in the percentage of large size coke than resulted from addition ofanthracite. This coke is less resistant to abrasion than that made from the anthraciteblends. The addition of 10% anthracite causes an increase in coke size equivalent tothat produced by lengthening the coking time from 18 to 30 hours. The coke wasfound to be more abradable when large percentages of anthracite coal were used.

With this background the present research work aims to investigate the method-ology to improve the mean size of coke under the stamp-charge condition. In thisstudy, the effect of some additives on coke size along with influence of the cokingand postcoking conditions has been described.

Experimental

Characterization of Coal

Four different types of coal were used for the experiments: namely, medium indigen-ous coal, prime indigenous coal, semi-soft, and imported hard coking coal. Theproperties of these coals are summarized in Table 1.

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Additives

In this study, we have used different types of additives, namely, pyroxenite, lime, andphenolic resin. Pyroxenite is primarily a group of rock-forming silicate minerals ofvariable composition, among which calcium, magnesium, and iron-rich varieties pre-dominate. Pyroxenite is used as a source of MgO in sinter making. Typical compo-sition of pyroxenite is presented in Table 2. Phenolic resin binder is produced bycondensation of phenol and aldehyde and thermosetting by nature. Chemical andphysical properties of the resin are shown in Table 3.

Carbonization Test

A number of carbonization tests were conducted in the 7-kg Carbolite test oven, understamp-charging conditions using a standard procedure established at R&D, Tata Steel.The coals used for making the coal blends were crushed to a fineness of 90% below3.2mm. Water was added to the coal blend to obtain the desired value of moisture inthe blend. The coal cake was made inside a cardboard box, keeping the bulk densityat 1150kg=m3. The final coal cake thus made was charged into the Carbolite test oven.Before charging the coal cake into the oven, it was ensured that the empty oven tempera-ture was 900� 5�C. After 5 hours carbonization (carbonization time was decided as perthe oven design and charge), the hot coke was pushed out and quenched with water. Theseries of carbonization tests were carried out following the above-mentioned procedureto study the effect of different additives on coke size and with different operating con-ditions. Coke samples were characterized by size analysis, coke strength after reaction(CSR), coke reactivity index (CRI), and petrography.

Characterization of Coke

Size Analysis of the Coke SampleAfter quenching, the coke was left for drying. Dry coke was then stabilized by rotat-ing (100 revolutions) in 5 kg micum drum. The stabilized coke was then subjected toscreen analysis and the weighted average was calculated from screen analysis data.

Table 2. Properties of pyroxenite

Cr2O3 TiO2 Al2O3 MnO MgO SiO2 CaO Fe(T)

% 0.890 0.057 1.580 0.110 24.850 48.030 8.310 4.820

Table 1. Proximate analysis (% db) of coal sample

Sample detail Ash VM IM

Indigenous medium coking coal 15.72 23.56 2.34Indigenous prime coking coal 17.16 18.43 2.88Semi-soft coal 7.97 18.40 2.88Imported coal 9.57 20.40 1.90

VM – volatile matter; IM – inherent moisture.

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Tests for CSR=CRICoke strength after reaction (CSR) and a coke reactivity test (CRI) have been donefollowing the Nippon Steel Corporation (NSC) method. In which 200 g coke of19–21mm size is heated in a reaction tube (78mm diameter� 210mm length) at1100�C for two hours during which CO2 is passed a 5 l=min. The percentage lossin weight of coke during the above reaction is reported as the CRI. This reacted cokeis further tested by rotating in a I drum (127mm diameter� 725mm length) for 30minutes at a speed of 20 rpm. The coke is then screened on a 10mm sieve and thepercent of þ10mm fraction is reported as the CSR.

Petrography of CokeFor microscopic studies, a 5 kg coke sample was crushed to below 3mm size and, byusing a coning and quartering method, 100 g sample was prepared as per the ASTMstandard D 5061-07 for microscopic analysis. The microscopic studies were done byLeica DMS4000 microscope along with QWIN software.

Results and Discussion

Table 4 shows the different properties of the blend used. The percentage of pyroxen-ite was varied between 0.1% to 0.3% from Blend 2 to Blend 4. Blends 5 and 6 contain0.2% lime and resin, respectively. This quantity arrives based on a trial-and-errorbasis. All tests have been repeated thrice in order to get a sample for size analysisand CSR=CRI tests.

Influence of Additives

Figure 1 presents the impact of the addition of additives on coke mean size. It wasfound that 0.1% pyroxenite has no effect on coke mean size, 0.2% pyroxeniteincreased coke mean size from 33.7 to 35.3, and by adding 0.3% pyroxenite, cokemean size to 39mm. The addition of 0.3% lime resulted in an increase in size from33.7 to 34.1mm. The addition of 0.2% resin showed a slightly less effect on cokemean size; size increased to 34.1mm. With the addition of pyroxenite and lime,ash content of the coal blend slightly increases. So in this case, one can get thepositive effect of ash. With the addition of resin, mean size increases to some extent.Resin helps in forming cross-linked structures between different components inthe coal matrix resulting in improvement in coke mean size. The microstructure ofcoke (Figure 2) reveals that with addition of pyroxenite (Figure 2b) and lime(Figure 2c) the number of pores increases, which again helps to get the bigger sizeand high CRI.

Table 3. Properties of phenolic resin

Fixed carbon 36%pH NeutralViscosity 250 cp-s @25�CSolid Content 66.2%Setting time 5min @150�C

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Influence of Operating Parameter

The carbonization of the stamped coal blend cake was carried out at two differentcenter mass temperatures (CMT) viz. 900�C and 850�C. Figure 3 shows the effectof center mass temperature on the size distribution. It was found that with alow-center-mass temperature the mean size of coke increased. This may be due to

Figure 1. Mean size of different blends. (Color figure available online.)

Table 4. Blend details and properties

Blend Blend details (%)Ash%, db

VM%, db CSN

MaxFluidity(ddpm)

1 Base BlendMedium coking coal-45, Prime cokingcoal-9, Semi-soft-29, Imported-17

10.84 21.15 6.5 80

2 Medium coking coal-45, Prime cokingcoal-9, Semi-soft-28.9, Imported-17,Pyroxenite-0.1

10.9 22.48 6 80

3 Medium coking coal-45, Prime cokingcoal-9, Semi-soft-28.8, Imported-17,Pyroxenite-0.2

10.93 22.52 6 78

4 Medium coking coal-45, Prime cokingcoal-9, Semi-soft-28.7, Imported-17,Pyroxenite-0.3

11.01 22.61 5.5 73

5 Medium coking coal-45, Prime cokingcoal-9, Semi-soft-28.7, Imported-17,Lime-0.3

11.34 22.40 6.5 21

6 Medium coking coal-45, Prime cokingcoal-9, Semi-soft-28.8, Imported-17,Resin-0.2

10.74 22.52 6.5 65

VM – Volatile matter; IM – Inherent moisture; CSN – crucible swelling number; ddpm –dial division per minute.

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Figure 2. Coke microstructure: (a): base blend; (b) with pyroxenite; (c) with lime. (Color figureavailable online.)

Figure 3. Effect of CMT on mean size of coke. (Color figure available online.)

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a reduction of thermal shock for which less fissures may be produced. From themicrostructure (Figure 4), it can be found that the coke produced at low-center-masstemperature has a higher amount of anisotropy. As anisotropic carbon phases areless prone to CO2 attack, so a higher amount of anisotropic phases produces high-strength coke.

In order to find out the effect of quenching on coke size, experiments have beendesigned with a stepwise quenching schedule. First, one is complete wet quenching. Inthe second and third steps, there was a combination of wet quenching and dry (air)quenching. Table 5 shows the details of the schedule. Results presented in Figure 5indicate that compared to total wet quenching, stepwise quenching produces biggersizes of coke. In total wet quenching, the coke is subjected to a higher thermal shockcompared to step quenching and, hence, more number of cracks and microfissures areformed in coke pieces leading to smaller sizes. Also in comparison to total wetquenching, step-quenched coke has a higher strength. Figure 6 indicates qualitativelythat there are fewer fissures and isotropic phases in the coke produced by step quench-ing compared to total wet quenching.

Trial Under Commercial Heating Conditions

Based on encouraging results obtained with pyroxenite, box trial was done in atop-charge oven. Trial was done in an oven of top-charge battery in Tata Steel.

Figure 4. Coke microstructure: (a) base blend; (b) with low CMT. (Color figure availableonline.)

Table 5. Different quenching schedule

Quenching method Steps

Total wet quenching 45 s aircooling

45 s watercooling

Step wet quenching (I) 45 s aircooling

15 s watercooling

15 s aircooling

15 s watercooling

Step wet quenching (II) 45 s aircooling

15 s watercooling

30 s aircooling

15 s watercooling

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For charging the coal cake, a cubical box of mild steel (MS) having dimension236mm was fabricated and bulk density (BD) was maintained at 1150 kg=m3 bymanual stamping technique. The coking time was 21 hours and the coking tempera-ture was 1250�C. Results (Figure 7) obtained here also indicate the improvement ofmean size with pyroxenite under commercial heating conditions.

Figure 6. Coke Microstructure: (a) Base blend; (b) Step quenching. (Color figure availableonline.)

Figure 5. Effect of quenching condition on mean size of coke. (Color figure availableonline.)

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Conclusions

Coke size is an important factor for blast furnace operation. Some methodology hasbeen investigated in order to improve the coke mean size. It was found that theaddition of pyroxenite shows a positive effect on coke size. The optimum percentageof pyroxenite was determined from the experiments. Higher amounts of pyroxeniteare not desirable as it tends to deteriorate the coke strength. Lime and resin are alsofound to improve the size to some extent. Operational conditions like quenchingsequence and carbonization at low CMT has an immediate effect on coke mean size.Carbonization at low CMT though showed positive results. On the other hand, aquenching process can be explored further to optimize between different quenchingsequences to obtain the required arithmetic mean size of coke.

References

1. Diez, M. A., R. Alvarez, and C. Barriocanal. 2002. Coal for metallurgical coke production:Prediction of coke quality and future requirements for coke making. International Journalof Coal Geology 50: 389–412.

2. Bertling, H. 1999. Coal and coke for blast furnace. ISIJ (Iron and Steel Institution ofJapan) International 39: 617–624.

3. Banerji, K. C., T. Venugopal, and A. K. Mazumdar. 1976. COMA (Coke Oven ManagersAssociation) 301–308.

4. Prashad, H. N., R. S. Karmakar, M. Tiwary, B. K. Singh, and A. S. Dhillon. 1996.Possibilities of eliminating coke cutting in case of stamp charged coke. Tata Search 52–57.

5. Marshall, C. E., D. K. Tompkins, D. F. Branagan, and J. L. Sanderson. Note on chargingtemperature and coke quality representative study results of american, australian andjapanese coals. Department of Geology and Geophysics, University of NSW.

6. Sharma, R., P. S. Dash, S. H. Krishnan, and D. Kumar. 2004. The effect of soaking timeon properties of blast furnace coke. Tata Search 40–43.

7. Jackman, H. W., P. W. Henline, and F. H. Reed. 1956. Factors affecting coke size. IllinoisState Geological Survey, Circular 213: 1–16.

Figure 7. Size analysis results of plant trial. (Color figure available online.)

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