One of the present authors, in a paper to the Iron

and Steel Institute in 1954 entitled "The Future of Steel Melting", re-introduced the idea of continuous counterflow steel melting.



In this paper it was stated that a  suitable  counterflow

furnace, in which the heat of the waste gases from a melt-ing chamber is used to preheat  the  charge  in a counter current system, could attain  thermal efficiencies of the order of 70%, compared with the maximum  possible  effic-iency of 50% for the existing open hearth furnace

Eyre, J W

English

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PAPER NO. 1 2STEEL MELTING IN A PILOT PLANT SHAFT FURNACE(*)J.W. Eyre,United Steel Cos. Ltd.,of Great Britain,C.Hulse and M.W. Thring,Sheffield University, U.K.One of the present authors, in a paper to the Ironand Steel Institute in 1954 entitled "The Future of Steel Melting",re-introduced the idea of continuous counterflow steel melting.In this paper it was stated that a suitable counterflowfurnace, in which the heat of the waste gases from a melting chamberis used to preheat the charge in a countercu_•rent system, could attainthermal efficiencies of the order of 70%, compared with the maximumpossible efficiency of 50% for the existing open,hearth furnace.In such a counterflow unit the temperature of theheating gases would be progressively reduced and a much lower finalwaste gas temperature would be attainable than is possible-in theopen hearth.Further possible advantages of a counterflow system arethat refractory wear due to the alternate heating and cooling whichtakes place in the batch process, should be reduced, heat losses-fromlarge charging doors would be eliminated, and finally, the fume inthe waste gases might be reduced, as this would be collected to someextent in the charge as the gas passes through.There are a number of possible ways in which counterflowmelting units may be applied to improve steelmaking techniques, Someof them are as follows:-as) a complete steelmaking unit in which arefining bath or baths would follow in thepreheating zone and in which refining could becarried out batchwise or, preferably, continuously.O Paper for presentation at the Symposium on Pilot Plants inMetallurgical Research and Development - 15th to 18th February,1.960, Jamshedpur.Not to be reproduced in any media. (C) National MetallurgicalLaboratory, Jamshedpur.: 3 :Doc: P.9.tis a result partly of this model work, and partlyon the basis of experience gained with the experimental unitas the investigation proceeded, a large number of possible shapeswere suggested from time to time.tl number of factors combined to limit the experimentationactually carried out. These were as follows:-(a) Owing to the fact that the furnace was somewhat largerthan had originally been planned, there was a factor of spacelimitation, and it was not possible to include all desirable featuresin a number of shapes tried. In some cases the final design of aparticular shape was a compromise between the desired features andlimitations imposed by the lack of space. Moreover the increased sizeof the unit rendered it more difficult and costly to dismantle andrebuild in between trials.(b) The fuel available, towns gas of calorific value 450B,Th.Uts per cubic foot, was limited to a supply of 3,000 cu.ft. perhour.(c) In order to obtain adequate flame temperature in themelting chamber, it was necessary to make use of preheated combustionair. This was provided by a separately gas fired air preheater. kgain,owing to the increased size of the experimental unit, the airpbeheater available was incapable of oroviding the total com-bustion air necessary at a temperature much in excess of 40CP C. Inlater trials this difficulty was overcome by using a small proportionof pure oxygen mixed with the combustion air for the sole purpose ofsimulating a condition of higher air preheat.3. THE EXPER.2-1ENThL FURN-CERefractories:For reasons of economy, the original furnace was builtthroughout of first quality firebrick, and this was quickly erodeddue to iron oxide attack.In subsequent trials, both high grade'silica bricks andall basic construction up to the base of the shaft, were tried.The latter was more satisfactory.Firing of the furnace:Special premixing type of burners were developed for thecombustion of the townts gas which was used for firing the furnace,and their operation was quite satisfactory, but with the air preheatattained (4000C maximum) a really short, intense flame was neverachieved during the earlier trials.Doc: P.94To simulate a higher degree of air preheat, a slightoxygen enrichment of the combustion air was tried during thelast 4 trials and improved results wore immediately obtained.The waste gases were extracted from the top of theshaft through a bricklined ducting, by means of an induced draughtfan.Operation of the FurnaceThe furnace was always brought up to working temperatureprior to the commencement of charging, since it was felt COCA.the metal was charged to a hot, thoroughly soaked furnace, therisk of severe oxidation in the shaft, and the bridging of the metalwhich would result from this, would be greatly minimised.Small lots of pig and scrap, sized 4" to 0 wore weighedout in buckets, each lot weighing about a half or one hundredweight.The weighed pig and scrap mixture appropriate to the particular runwas charged to the double boll arrangement at the top of the preheatingshaft. The charging rate was adjusted to maintain the stockline atthe required level. The stockline height was determined by insertinga rod through four holes arranged around the top of the shaft andnoting the depth to which the rod could be inserted. xs the metal atthe base of the shaft was melted, the bath gradually filled upwas generally necessary to tap it at roughly hourly intervals.Thl procedure on tapping was to chip away as much aspossible of the plug filling the tap hole by means of a crowbar,and then to finish the operation of opening up with an oxygen lance.The metal was teemed into a pan standing on a bogey running on railsin casting pit in front of the furnace. ,rrafter tap}oing, the taphole- was made up.with a mixture ofanthracite and dolomite. Steel hooks were inserted in the moltenmetal in the pan to facilitate lifting. rafter a suitable period forcooling, the full pan was lifted off the bogey and replaced by anempty one, the ingots then being weighed and transported for storageon a separate bogey.Experimental data collcte.Details of materials charged and tapped , together withtemperature measurements , fuel and air rates , waste gas analysesand furnac e pressures ware recorded.lei nn I , 111 1 _ ^I^I RIIp^NHi ^ry ,Doc: P.9RESULT: OF FURN-CE TRL^LSRunning conditionsIt was found pos°'ible to split the 21 trials herediscussed into 64 periods on basis of the running conditionsencountered and the type,, of charg melted. Running conditionswere defined as "running well", "running fairly well" , "runningpoorly" or "running very poorly", dopendinL* upon the ease with whichthe charged material fluw(,d down the shaft and into the forehear h.The first two categories wore considered satisfactory.The factors which affected the running conditions wereconsidered to be a s follows :-a)b)The height of the stock column.The nature of the charge ( i.e. percentage scrapin the mixture).c) Th,, furnace shape.d) The hearth temperature.e) The thermal input to the furnace and combustionconditions.The latter two itoms-vere -not completely independent.The running cond!-ti.onq_;ihta;.-ned with five of the shapes tried,and for various charge compositions ' re shown in Table 1.The following pointsi. Of th_ 64 periods included in the table, 44of then: gave satisfactory running conditions.Of the,, 10 periods in which 100% pig iron was_,:d, s'_tisfa:actory running; conditions werechar,-obtain.-;d in seven periods. It should perhapsbe pointed out in this connection that most ofthe runs w(:;r,: started do 100% pig iron, andalmost no trouble was experienced. The twoperiods of vary poor running obtained for 100%pig iron in the case of shape 'C' were due to thefact th--t lima was being charged with the pig tothe shaft and-this causad. immediate bloeka.ge.10 - ^ H IHT 1 1lal ^H • C') IH HNHcdn IJ0OdJOOd Hl I t I ► H^^C)0TTeM'3TTaMN^iIHHI HH I IC'.)^;H r-I t, )NQ 100d•AN I1C.?CUH9)R.U),^OOdTTaM'@TTM{HH1IICONGII1IIIIICY)copCc^.ciiU)I °,z° od • AJoodTTaM' ITTaM HNHCJHH0T oJzood•AJoodrnHH HHHoU)T a 'TTaM CoH CCCo^° H c^) U)HJOOd°A H N C7amUroodTTal^l' 3TTa1:JOOd•AH )H ^HCr) NLUHHCocnTTaM_^.TTaMN^'`) HHHCoacdaciip4 P.cii cdF-i0FaU 0f^0 U0(n0 LU 0 LU 0N+N O NIIciianr4hArI rI H 00 •a.0 In 0cC00 N LU CI 0 0HH7 Doc. P.9The single run with relatively poor runningconditions may be ascribed to lack of temperaturein the forehearth. Generally, there was nodifficulty at all in maintaining a flow of 100% pigand one would conclude that a full scale furnace,for a continuous counterf low melting, of pig ironwould present no difficulty in full scale operation.ii. There were 40 periods during which a mixture of50% pig iron and 50% scrap was charged, and 27of these produced satisfactory running conditions.iii. The furnace ran satisfactorily during all the6 periods in which the charge consisted of between50 and .100% pig iron.iv. There were 8 periods during which the furnacecharge contained more thp.n 50% scrap, and for 4 ofthese the running conditions were satisfactory.v Within the very narrow range of stock heightsemployed (70 to 80 inches generally), this didnot appear to affect running conditions (by stockheight is meant the actual height of the column ofmetal in the shaft measured alone the centre line).Vi .^-s the percentage of the scrap in the char ge increased,,the running conditions became worse.vii :.s the percentage of scrap in the charge was raisedto 50%, the hearth temperature required for moodrunnin,_ conditions increased.Thermal efficiencyapparent thermal efficiencies throughout the trials werein the region of 40%, although on several short periods with 100%pig iron efficiencies of 60% to 70% were achieved.,knalvsis of the oroductIt became apparent that the furnace was capable ofproducing a high carbon melt (`-neater than 1) with a pig ironcontent of 50% or more of the charge. Considerable dephosphorisationwas carried out by adding controlled quantities of lime to the bath.Doc: P.98Metallic YieldMetallic yields were determined on occasions by cleaningthe ingots of slag at the end of a trial and roweighing.The figures obtained applied to trials as a whole,including periods of poor running and emptying when the oxidationrate was more severe. They ranged from 89 to 92%, suggesting thatduring good running conditions, eminently satisfactory metallicyields were obtained.RyfractoriocThe furnace construction was eventually such that therefractories performed satisfactorily, and trials of 100 hours ormore duration wer carried out without severe refractory wear. Itwam-found relatively easy to fettle the banks of the melting chamberwhen this became necessary.CONCLUSIONS1. It was shown to be extremely easy to melt chargesof 100% pig! iron in a shaft furnace with very little oxidation ofthe charge and no serious bridging.2. It was also shown to be possible to melt pig iron andscrap mixtures in a counterflow shaft furnace, although indicationswere that als th. porcentege of scrap in the charge increased, so didthe problems of bridging and oxidation.3. During the trials only one basic shape of furnace was •tried, so that it was not found possible to prodict the best designfor a counterflow unit.4. The thermal efficiencies obtained in the experimentalunit were most encouraging and suggest that efficiencies in a productionunit of the order pr-;dieted by Thring ( that is 70%, Ref. 1) should beattainable.5. It was shown that melts of varying carbon contentcould be attained dopcndin,- on the type of char,- to the furnace,and the furnace conditions pr,-,v-ailing. Dephosphorisation was alsocarried out. Insufficient attention was devoted to the factorscontrolling the analysis of the melt to enable these to beelucidated fully.6. The refractory difficulties existing in the experimentalfurnace wor overcome to lar.,e extent, but the indications were thatin a production unit of a shape similar to that used in the trials, itwould be necessary to overcome the problem of refractory wear in there,ion of the throat.. Or"9'"11I II IiNINM.WIR^N 11 `i L. ^ ! Ir 117 P I TTR TP.fl ll 117 TIT I. If R h n111PN' rrr M1r.to" fl '.","'IT'^^'-^^

Steel Melting in a Pilot Plant Shaft Furnace

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Steel Melting in a Pilot Plant Shaft Furnace

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