1 91 CHAPTER 7 COMMISSIONING OF 65 MT ENERGY OPTIMIZING FURNACE AT SISCOL 7.1 INTRODUCTION SISCOL commissioned the world s largest 65 MT capacity EOF on 18 th October 2007 with the successful tapping in the very first attempt (Figure 7.1). On the very first day of commissioning, two heats were taken with a short gap which shows the preparedness prior to commissioning. Safe operation was ensured and the quality of steel manufactured was as per the specifications. Figure 7.1 EOF (65 MT) under tapping 7.2 BASIS FOR 65 MT EOF INSTALLATION Prior to commissioning of 65 MT EOF at SISCOL, the successfully operating EOF in the world were of 35 to 40 MT capacity as shown in
2 92 Table 7.1 at CS Pains in Brazil, and at Hospet Steels and SISCOL in India. Three numbers large size EOFs were installed at Aliperti- Brazil, Trieste- Italy and at TISCO- India but not successful on commercial scale, and therefore their operations stopped. Weber et al (1989) have explained the reasons for 60MT EOF at CS Aliperti Brazil not performing successfully on commercial scale, which has been elaborated in section 2.5 of page 21 & 22. The reasons for 80MT EOF at Tata Steel have been elaborated in section 2.6 page 22 & 23 and also by Chatterjee et al (2005) in section 2.7 page 23 to 31. Pfeifer et al (1998) have elaborated upon the operating results for 60MT EOF at AFS, Italy as mentioned in section 2.1 page 35. As a part of the expansion program at SISCOL, between various options available for LD converter, EAF and EOF, it was decided to install a 65 MT EOF based on capital cost and operating cost. In one steel melt shop where two production lines are operating, it is better to have both the furnaces of equal size and therefore, the second furnace should have been 45 MT capacity since it was already a proven equipment at three places, as specified above. Moreover, same size ladles in both the production lines in SMS would be very convenient since it allows tremendous flexibility. In the case of two numbers 45 MT EOF, the average heats per day per EOF was working out to 32 casts per day, to produce one million ton per year. With one EOF of 45 MT capacity and one EOF of 65 MT capacity, the average number of heats per day works out to 27/28 to produce one million ton per annum. In view of high percentage of special steel production, the second alternative was perceived to be more beneficial. Hence, SISCOL decided to take a challenging task to install a 65 MT EOF and to make it commercially successful. After going through the literature, and learning from the reasons for failure of the large size EOFs put up in the past, it was decided to go through the design parameters for the new 65 MT EOF very carefully such that during hot commissioning and regular operation, it performs satisfactorily. The
3 93 equipment specifications for 65MT EOF were submitted by the Engineering Consultants based on their design parameters. However, in the past, the higher capacity EOF at ALIPERTI - Brazil, TISCO - Jamshedpur and AFS - Italy, did not perform satisfactorily on commercial scale and all these plants were closed down. Hence, the specifications submitted by the Engineering Consultants were examined by the author in more detail based on the experience of operating the 45MT EOF successfully. Learning from the literature survey and taking corrective measures played a very important role in successful commissioning of 65MT EOF at SISCOL. The final equipment specifications of 65MT EOF is enclosed in Appendix II. 7.3 OPERATING RESULTS Table 7.1 Main features of 65 MT EOF 1 Technology MINITEC Brazil 2 Capacity per annum 0.6 million MT 3 Steel grades Carbon and Low alloy special steels 4 Shell diameter 6500 mm 5 Hot Metal Input per Heat 60 MT (81%) 6 Scrap Input per Heat 14 MT (19%) 7 Oxygen blowing Top & side combined blowing 8 Blowing time 30 minutes 9 Tap to Tap time 45 minutes 10 Number of heats per day 32 heats 11 Total Refractory consumption 8 Kg / MT 12 GCP system Wet Type 13 Exhaust Gas volume at Peak of blow NM 3 /hr 14 Clean-ness of Exhaust gas <50 mg/nm 3 15 Spare bottom with shell Faster Bottom Changing 16 Bottom Tilting Slag flushing & slag free tapping 17 E.B.T type Steel launder Slag free tapping.
4 94 The main features of 65 MT EOF at SISCOL is shown in Table 7.1. In the very first campaign of 65 MT EOF refractory life of 603 heats was achieved, in which 37,344 MT billets were produced. During this campaign the steel qualities manufactured were carbon construction steel, carbon and low alloy steels for forging and automotive applications, free cutting steels, cold heading quality steels and drawing quality carbon steels. The key operating parameters during the first campaign are shown in Table 7.2. Table 7.2 First campaign key operating data of the 65 MT EOF S.No. Key Operating Parameter Parameter achieved 1 Hot metal in Charge 80.11% 2 Solid scrap charge 19.89% 3 Average heat size MT (billets) 4 Charge to liquid Metal 90.1% 5 Charge to billet yield 87.1% 6 Blowing time 38 minutes 7 Oxygen consumption 66 M 3 /MT 8 Average power consumption 65 KWh/MT 9 Average lime consumption 58 Kg/MT 10 Refractory consumption 6.5 Kg/MT 11 Gunning material consumption 4.16 Kg/MT The operation and consumption norms were not the very best in the first campaign as expected. Action plan has been drawn up to improve upon the operational parameters to the desired levels in the subsequent campaigns. The operating parameters of the 65 MT EOF in the recent campaign is listed
5 95 in Table 7.3 which shows that there is an improvement in the EOF working as compared to the first campaign. Table 7.3 Key operating parameters of 65 MT EOF Parameter Oct-07 Nov-07 Dec-07 Jan-08 Feb-08 Mar-08 Number of Heats Percentage Hot Metal in charge Percentage Scrap in charge Total Liquid steel produced at EOF Total Billets produced at CCM Billet Yield % Avg. heats per working day Avg. Billets produced per heat Blow Time 0:46 0:41 0:38 0:39 0:36 0:35 Power Consumption Kw/MT Lime Consumptiom Oxygen Consumption Brick consumption Kg/MT Gunning Consumption Kg/ MT The various qualities of steel produced through the 65 MT EOF route during the last six months are carbon constructional steels, low alloy steels, free cutting steels, cold heading quality steels, ball bearing steels, etc.
6 96 It is important to mention that the steel produced from the first campaign was meeting the quality specifications. From the very first campaign of the new EOF (65 MT), full attention was given for achieving safe operation. There are differences in the operating parameters between 45 MT EOF and 65 MT EOF. The operating parameters of the 45 MT EOF are better than the 65 MT EOF. The main areas where the improvements need to be made in the 65 MT EOF are: Blowing time, Refractory life, and avoiding water leakage in the roof upper piece, sliding skirt and scrap pre heater lower piece. Necessary actions are being taken to achieve the above improvements. Effort has been made to improve the lime quality with respect to size and chemical composition to achieve shorter blowing periods. The author is also considering injection of lime fines into the EOF for quick dissolution and formation of slag for better de-phosphorization. The 65 MT EOF scores over the 45 MT EOF with regard to thermal balance, while in the 45 MT EOF proper thermal balance is achieved with 80% hot metal and 20% scrap for auto-thermic process. However, in the 65 MT EOF, similar situation is achieved with 75% hot metal and 25% scrap. This is possibly due to the benefit of large capacity in the 65 MT EOF due to which the thermal heat losses per ton capacity is lower. It has also been observed that due to higher heat size the temperature drops during tapping as well as continuous casting are also lower than in the case of 45 MT EOF. In the 65 MT EOF, continuous feeding of sponge iron was carried out to control the temperature of the steel bath during first half of the campaign whenever high temperature was achieved. Later it was established that the temperature in 65 MT EOF could be achieved with iron ore addition
7 97 which was far cheaper than the sponge iron. Now we have implemented the process of temperature control using only iron ore. The sponge iron is used in the EOF only when scrap is in short supply and sponge iron prices are more favourable vis-a-vis scrap or pig iron 7.4 CAPITAL INVESTMENT IN 65 MT EOF The capital expenditure for the installation of new 65 MT EOF including upstream and downstream facilities for iron and steel making including back up equipments for 600,000 MT per annum capacity, has been much below the industries norms, at Rs. 13,000/- per ton per annum of capacity creation. This proves the point that by adopting EOF route for capacity increase, SISCOL has achieved low capital cost as perceived at the time of deciding the project. The entire project was commissioned in 18 months from the stage of ground breaking. Photographs of the key equipments of the 65 MT EOF are enclosed in appendix III. The experience of 65 MT EOF commissioning at SISCOL by the author has proved beyond all doubts that if the design parameters are selected carefully and the equipment is manufactured as per those design parameters, the 65 MT EOF is a suitable equipment for mass production of steel on commercial scale. The quality of the product, safety of operation, productivity and cost of production is as per the target norms. There is still further scope for significant improvement which would be achieved in the due course.