During present pandemic crisis, due to sluggish demand, many Steel majors have either banked or blown-out their Blast Furnaces. Let us all discuss following points wrt practices being followed at different Steel Plants:
1. Preferring Blanking or Blowing-out, if the tenure of stoppage/shutdown is uncertain ??
2. Blow-in Burden philosophy has not seen any major change over the years. At our Steel Plant, Blow-in Burden is designed incorporating all sorts of additives like LD Slag, Quartzite and Mn Ore which complicates the burden and it has always been observed that actual Slag chemistry & HM Si differs drastically from that expected with designed burden. On many occasions, the revival process gets hampered due to abnormal liquid formation causing fluidity/drainage issues and leading to tuyere burning etc.
In my view, a review of Blow-in Burden architecture is required wrt following points:
(i) Use of special sinter with modified chemistry (if possible), so as to do away with use of heat consuming slag formers like LD Slag & Quartzite during initial phases of revival when the furnace is the most heat deficient. (Modified chemistry wrt sinter B2 or Available lime and also adjusting sinter proportion in burden to achieve desired tapped slag. In any case, a burden without slag formers or minimum amount of slag formers is anytime beneficial for a reviving BF as its heat demand will always be very less as compared to a complicated burden being practised presently.)
(ii) Use of maximum HBT (Maximum means the highest HBT that Stoves can provide, beyond its normal capacity, with very low blast volume requirements during initial phase of revival, considering limitation of Hot Blast System, if any) from day one so as to avoid charging excessive coke through top and then worrying about how to slag coke ash out.
(iii) Start of PCI early on during revival
BF Experts may please opine on the above and share their practices.
From the time of the beginning of the Russian aggression in the Donbas, and then during the crisis of the Ukrainian metallurgical industry until the pandemic Covid19, our company (Iron & Steel Institute, Dnipro, Ukraine) has experience in blowing a BF after long stops. So, BF's were stopped for up to 150 days or more without the release of freezing iron (BF#3 and #5 of Yenakiieve Iron & Steel Works; BF#9 and #12 of Dneprovsky Iron & Steel Integrated Works).
The regulating rules for blowing of BF's after long stopping have been developed. In accordance with the regulations, it is necessary to perform the following technological operations: keeping of the reduced (in comparison with the conventional one) ore load on the volume of the charge; use of low-melting materials with low basicity in the burden of the first volume (fluorspar) and the first working batches (including possibility of supplying of lowmelting materials through air tuyeres); use of sector blowing from the iron tap side with a small number of air tuyeres; ensuring of a stable heating along the height “tap — air tuyere” before blowing start (by installing of pipes into the cast iron tap to supply natural gas and air for its combustion); observance of low intensity of increase of gas blowing parameters and opening of air tuyeres in one sector; maintenance of a reduced ore load (in comparison with the accepted one) of ore load of the first working burden with reduced iron content in the charge.
Upon reaching 35–40% of the open tuyeres in the presence of normal heating of the BF and the charge disappears, close part of the working tuyeres not above the working iron tap and open the tuyeres in pairs uniformly over the entire circumference of the BF to 50–60% to create blowing “sectors” around the circumference of the BF. The further opening of air tuyeres should be done taking into account maintaining the uniformity of sectors around the circumference of the BF. This event allows you to smooth out the regional unevenness and warm up the central zone of the charge column without increasing the intensity of coke burning.
It is advisable to blow-out the BF for a long stops with the subsequent partial scraping of materials through the embrasures of the air tuyeres.
What are the guidelines for heat supply to the BF during revival ? Is it necessary to provide heat to the BF only through top charged coke rather than using higher than normal HBT ?? Moreover, can PCI be used for providing heat directly at tuyere level, after some 25 % of tuyeres get opened ?
What is the burden distribution guideline for charging initial lean burdens during revival of the BF ?
Can i request all BF Experts to share their practices for early revival of a disturbed BF like in case of a chilled /cold hearth or starting after an extended shutdown with frozen salamander ?? What specific practice was adopted to ensure smooth revival ?
The efficiency of increasing the temperature of the blast, the beginning of the supply of PCI is determined, first of all, by preparing the BF for start-up, the features of blowing and the number of days of shutdown, and, secondly, by heating the melting products of the first release (slag to cast iron ratio, Si in cast iron). PCI can be started both on the third or fifth day from the start of blowing, and a month after the start of blowing. The main task of a successful blowing is to ensure a developed central gas distribution. Early supply of PCI can provoke an excessively developed periphery temperature. An increase in ore load is also advisable after satisfactory smelting products in the first releases. Everything is individual and requires careful analysis.
Dear Colleagues:
Generally I agree with most general concepts provided by Mr. Semenov.
Below are my opinion and answers on questions based on huge 40+ years experience
1. Preferring Banking vs. Blowing-out: if less than 15 days - Banking is better. If stop planning for above 30 days - Blowing down preferable, + top salamander tap - recommended, cool BF, clean the hearth make some necessary repair and prepare to traditional Blow-In
2. Use of special sinter with modified chemistry ( lover B) is great idea, but only few plants can really do this. NLMK in Lipetsk has this practice
3. Use of maximum HBT = It is Ok, for first couple hours, but put in consideration optimal RAFT and inject O2 if needed due to HBT is below700 C.
4. Start of PCI early on during revival = Better to start with Nat Gas early after coke lit on all open tuyeres. PCI possible to use, but after at least 60% tuyeres get open
5. For real cases it is always recommended to call several experts to assist in Challenging BF operation prior BF stop, during the stop and during recovery. I can to work as expert from home office and on the site. Detailed info - upon request
Best Regards, Michael ALTER
1. Blow-out ot be preferred is length of outage is unknown. It is extremely helpfiul to cast the salamander, becauses the you can revive the furnace with all tuyeres open.
2. Connection tuyeres taphole to be secured with an oxyfuel lance, using oxygen and a coolant gas. The coolant gas is normally natural gas or propane, but nitrogen is an option as well.
3. The charge to consist after the coke blank with a charge of 100-200 t scrap/DRI to provide good connection tuyeres-taphole. This eliminates the use of special sinter, which would be anuisance anyway.
4. Use of maximum HBT: agree. Russian technology requires focus on T Flame, but the focus of my restarts are: bringing as much heat as possible.
5. Use of PCI. PCI is not to be used for heat/energy input, but for normalization of HM Si. As soon as the top is hot (topgas temp > 100 C) and the connection tuyeres-taphole is firmly established (HMT > 1380-1400 C) and at least 75% of the tuyeres are open, then you can charge a burden designed for PCI (coke rate 400-450 kg/tHM). During a blow-in the furnace is normally overfuelled. The additional fuel can be used by putting in a PCI burden, but not putting the PCI on the furnace until the HM Si is < 1.5%. We have experience with putting the PCI burden within 24 hrs after blow-in, PCI on fce 36-40 hrs after blow-in and all Silicons< 1% on 3rd or 4 th day after blow in.
6. Slag design: B2 ~0.9, Al2O3 < 18%.
7. Separation HM and slag. Separation depends on fce size, but genrally with 8-9 tuyeres operating per taphole you can separate and plate the hot metal.
Thank you, Maarten for additions!
About Slag composition: At NLMK, Russia out target is to get Al2O3 below 14% and in the USA - even below 13%. In Russian plants in Siberia they accommodated with Al2O3 below 17%
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