UDC 669.162.267.4 : 662.611.2 5 : 669.162.259 : 661.51.091
Blast Furnace Operation with 25 to 60% Oxygen-blast to Make Top Gas Composition Suited for Ammonia Synthesis*
By Takashi OKAMOTO,** YoshilloslIke TADA,** alld Takll SUGIURA **
Synopsis in the syntheti c process, a bout 2250 N m3 of effective 0 The tOj) gas of a pig iron blast furnace, which was ol)erated with 55 0 gas mixture of CO + H 2, is genera ll y regarded as re Oxygen- 45° 0 Nitrogen blast, had been directly used for ammonia. syn quired per ton of a mmoni a. thesis. G as from an electric iron smelting furnacc with a The o/)eration of test furnaces and an industrial furnace was velY suc high content of CO had been supplied from our com cessful even with such high oxygen blast; the results of the operation are pa ny to the neighbouring T oa Gosei C hemical Ind ustry reported in th is paper. Co . since 1953. 6,7) In 1 954, an increased producti on B ased on the results on the test furnaces, the cleaned tol) gas 07' heavy oil of ammonia was scheduled , but ra tiona li zing by con together with the blast was blown through the tuyeres to lower the com bustion teml)erature at the tuyeres and to increase the volume of the ascending version of the raw gas was a probl em in the chemi cal bosh gas. industry. Various kinds of methods producing the T he industrial o/)uation had been successfully continued for three J'ears raw ga were investigated and compa red . Among 0 and ten months at max. 55 0 oxygen in the blast and produced about them , one utili zing electric iron smelting furnacc gas 90 000 t offoU/dry pig iron and 134 X 10' N m " 0/ effective gas (CO I is a n extremely ra ti ona l a nd technicall y ful ly co m
H 2 ) equivalent to about 60 000 t of ammonia. pleted method, requiring no additiona l fu el, elcctri c power a nd equipment for producing the gas. But, 1. Introduction the gas evolved per ton of pig iron was a compara ti vely In Ya hagi Iron Co., Ltd., both of foundry pig iron sma ll qua ntity. Thus, to increase the gas producti on, a nd raw gas for ammoni a synthesis had been produccd a great increase in el ectric power a nd iron sources a re by a blast furnacc with hi gh oxygen blas t from 1958 required . to 1962. Aftcr vari ous calcula ti ons on ma terial a nd Under these circumsta nces, a n operation of the thermal bala nces, and tcchnical a nd cconomical con blast furnace with 55 % oxygen-blast was pla nned . sidera ti ons, a midget tcs t furnace was opera ted a nd Oxygen gas was byproduced in electrolys is of water then, a n industrializing tcs t furnace. Finall y, a n in and sep a ration of air a t the syntheti c a mmoni a pl a nL. dustrial furnace, having da il y capacity of gas equiva By this operation, more gas is evolved perton of pig lent to 40 t of ammonia a nd 40 to 50 t of pig iron, iron than by the electric iron smelting process, becausc had been opera ted continuously for about four years. of the m ore coke used as heat so urce. :Nloreover, if a H owever, because of th e general tendency of cha nge furnace can be opera ted with 1.65 t of coke ra ti o, raw in ra w gas so urce from solid fuel to Ouid one, th e gas equivalent to I t of a mmonia a nd 1.2 t of pig iron synthe ti c chemi cal industry based on so lid fu el mct can be prod uced from 2 t of coke on calcul a ti on. cconomical difficulties, even in case of simulta neous Subtracting 1. 5 t of coke per ton of a mmonia usuall y producti on of pig iron. ConsequenLly the opera ti on required in such conventional gas p roducers as a semi had to bc stopped.1- 5). wa ter ga furnace or Winkler furnace fr om 2 t of coke, Thc process consists essentiall y of high oxygen blast the rest, namely 500 kg of coke, can be used for prod uc a nd circul a tion of recovered own top gas or injecti on ti on of a bout 1. 2 t of foundary pig iron . The meth od, of heavy o il for controlling the combustion tempera ture conside ring cos ts for equipments, seemed very a ttrac a t the tuye res. ti ve, compa red with gas producers with solid fu el or According to the foll owing Eq . (1) for syntheti c other p rocesses using heavy oil or crude oil which were rcacti on of a mmoni a, 1 973 m3 of hydrogen is theore on the way of devclopment a t th a t time. ti call y rcq u i rcd pcr ton of the prod uc L. In order to utili ze the top gas alone for ammonia synthesis, extremely high content of oxygen in th e N2 +3H 2 = 2NH3 ...... ( 1) blas t is necessary. Nam ely, for a mmonia synthes is, CO + H 20 = H 2 + C02 •. . ..•.•.•...••••• (2) nitrogen content in the raw gas is des ira ble to be a bout
If CO is rcacted wi th exccss o f steam in the presence one-third by volume of CO + H 2 according to Eqs. of a catalys t a t 450 0 to 500 a C, it can be easil y con (1) a nd (2). Now, onl y the reacti on expressed by Eq.
verted to hydrogen accord ing to Eq. (2) a nd CO 2 (3) in the below is ass umed to takc place a t the tuye re thus produced can be removed by wa tcr-washing a fter level. comprcssion. Therefore, CO can be consid ered to bc chemicall y equivalent to hydrogen . C + 1/202 + 1/3N2 = C + 1/ 1202 + 1/3N2 +5/ 120 2 '-----....---- Practi call y, taking into account losses in conversion, (a ir)
washing, purge of condensed impure gases or leakage = CO + I /3N2 ...... (3)
* Origina ll y published in Tetsu-to-Hagane, 58 ( 1972), 637, in .Ja pa nese. Eng li sh version received A ugust 6, 1973. ** Ya hagi Iron Co., L td., howa-cho, Minato-ku, Nagoya 455.
[ 122 ) Report Transactions ISIJ, Vol. 14, 1973 ( 1 23 J
Then, if the blast consist of 1/2 g mol of oxygen Technical problems and contradictions of a nticipa a nd 1/3 g mol of nitrogen for I g atom of carbon in tions on the operation with the high oxygen blast as coke, in other words, the oxgen content in the blast stated above should be clarified experimentall y. is 60%, or about equal volumes of a ir and oxygen a rc mixed for the blast, according to Eq. (3), the ratio III. The Progress of Experimental Research by volume of CO to ni trogen in the furnace gas is just Two stages of experimenta l research were conducted 3 : I a nd suitable for ammonia synthesis. [n reality, as follows. CO a nd hydrogen may be formed or consumed by 1. Preliminary Test by a lvJidget T est Furna ce miscell aneous other reactions such as gas reduction, carbon so lution a nd water gas reaction in the furnace. A very small furnace was constructed ; its hearth H owever, the blast should be at least enriched w ith area was a sixteenth of the following industrializing oxygen to about 55 %. test furnace and its form in the horizonta l section was The idca of producing simultaneously pig iron and initia ll y circular and subsequently rectangular. Sin raw gas [or chemical synthesis by such blast containing tered ore was used as iron source and vari ous kinds of very much oxygen had been proposed previously by refractory brick were lined to compare one with R . Durrer and others and experimental data in Ger a nother. m a ny a nd in the Soviet U nion were reported. 8 - 101 1. The Structure of the Test Furnace H owever, it seems that there had never been any Dimension of the hearth 200 \', 160 x 195 report on their development or industria li zation. (mm) A process by a slagging gas producer was tested a t Shaft height above LUyeres 735 710-480 Agochi Plant of K orean Synthetic Petroleum Co., Ltd. (mm) Inner volu me of the furnace 1 0 .023 0 .022-0 . 010 during the second world war,ll,l2 by K obe Steel above tuycres (m ') 3 14 Ltd.1 , 1 a nd by Sumitomo Chemical Co. , L td. after N umber of LU yeres 6 4 the war. H owever, the main object wa to obtain Production of' pig iron (kg/hI') 4-7 4 - 7 the gas but production of pig iron was only the second one. 2. Condition of the Test No report on the indust ri a li zati on of iron ma king \ 'olume of lOtal oxygen blown 10-1 5 by m eans of such 55° ° oxygen blast might be largely (rna/ hI') owing to many technical d ifTicu lties besides economical T e mperature of the blast atmospheric tcmp. reasons or th e local conditions. Oxygen content in the blast 30-55 (vol%) II. Technical Problems on the 55% Oxygen Blast Size of coke (m m) 5-15 Size of sintered orc (mm) 3-5 La rge thermal and chemical differences compa red with the a ir blast are a nticipated in th e operation :--.iote: volume of total oxygen blown means thc lOta l of with the 55 ~o oxygen blast. oxygen from thc air and enriched-oxygen. From the thermal point of view, temperature in the combusti on zone at the tuyeres increases even at 3. Results of the Test the same bl ast tempe rature a nd the temperature gra ( I) Chemical composition of pig Iron produced dient in the shaft becomes steep owing to fast heat Constituent C Si S exchange with charged raw materia ls by decreased quantity of the bosh gas as the hea t carrier. Owing 0 o' 2.30-4.081.32-10.500.016-0 . 103 to the latter phenomenon, a so-call ed low sha ft fur (2) Chemical composition of furnace gas evolved nace can be u cd in the case of oxygen-blast opera tion, which has a n ad vantage of possibility to make Constituent CO H, CO, use of soft coke o r ores but, on the other hand, dis vol% 39.3-67.3 0.2-3.5 3.4-1 0.0 advantage of decrease in the degree of indirect reduc tion or unstable operations. C H. 0 , N, CO + H ,/N, From the chemical point of view, the evolved bosh 0-0.2 0. 1-0.2 24.8-54. 6 0 .74-2.74 gas, being poor in nitrogen a nd rich in CO , is ex pected to accelerate indirect reduction on the contrary. 4. SUlTllTlary of the Operational Results In the practical operation, if the same quantity of Though the furnace wa very small and each of oxygen per unit time is to be blown by the blast into total 18 test runs was con tinued only for 1 to 6.5 hrs, the furnace of the same diameter, decreased volume a qualitative tendency was grasped by the tests with of the gas passing through the furnace leads to 30 to 55% oxygen in the blast. d ecrease in quantity of dust evolved and , on the ( I ) Furnace Conditions a nd Composition of Pig Iron other hand, in crease in quantity of oxygen blown When oxygen content in the blast increased over by the same quantity of the blast can raise the ra te 40%, the composition of pig iron produced was often o f furnace operation. unstable a nd high in sulfur owing to frequent hanging, Besides, in crease in content of oxygen in the blast in particular in the upper portion of the furnace, slip would inAuenee the extension of oxidizing zo ne to the and " R ohga ng» (cold working). The travelling furnace cen ter from the tuyeres a nd a lso the tem time of the charge through the furnace ranged 15 to perature distribution in the hearth. 45 min on calculation.
Report [ 124 ) Transactions ISIJ, Vol. 14, 1974
(2) Composition of Furnace Top Gas blast" . Gas with a lmost expected composition was evolved 4. SUInttlary of the Operation Data according to the oxygen content in the blast, and its It was clarified by this experiment that iron making oxygen content was so small in quantity as to be by the high oxygen blast was technicall y practicable. negligible, even when the furnace condition was fairly (I ) The Oxygen Content in the Blast a nd Furnace unstable. The degree of indirect reduction was es Conditions timated to be 20 to 40% from the composition of the Though the furnace was able to be operated at top gas. the oxygen content in the blast as much as 55 % , (3) Coke Ratio hanging occurred so frequently that furnace conditions Coke ratio could not be reduced to less than 3 t were unstable a nd troublesome for continuation of per ton of pig iron owing to the small size of the the operation. furnace and intermittent operation. (4) R efractories Table 1. Condition of test operation Carbonaceous brick was most suitable for the hearth. Above the tuyeres, high-alumina brick Blast showed the best corrosion resistance a nd carbonaceous Tuyere dia. 16-25 mm brick was effective because of less adhes ion of charge Velocity at tuyeres 60-130 Nm/sec or slag. Total volume of oxygen in blast 120-170m'/hr In short, mooth descend ing of the charge through Oxygen content in blast the furnace by preventing it from hangin g was re Blast temperature garded as a n essential condition for the success in the Top gas blown 0-100 m' /hr operation with the high oxygen blast and lowering of Burden temperature at the tuyeres by blowing-in of top gas, Size of sinter 3- 10 mm, 1.5-3 mm Size of coke 10-20 mm steam or CO2 was concluded to be necessary to obtain stability of furnace conditions a nd pig iron composi tions. Table 2. Examples of test operation data
2. Experiment Jar Industrialization Test A B C Experimental operation was conducted for 92 days. Period (days) 5.5 5.3 4.7 The industrializing test furnace was lined mainly with l3last chamotte bricks with inner diameter of the hearth Oxygen content in 39.0 57.0 54.5 enriched blast (% ) 800 mm, total inner vo lume about I m 3, expected dail y capacity 2.5 t of pig iron and 7 750 m 3 of effective gas. Air (m' /hr) 3 10 143 158 Oxygen (m 3/hr) 92 120 11 7 1. The EquipInent for the Blast The blast was cold. Oxygen (99.7 % oxygen) was Top gas blown (ms/hr) 0 0 90 drawn from the main pipe of the above-mentioned Oxygen content in total 39.0 57.0 41. 1 blast (% ) chemical plant and mixed with air from a blower by Temperature (0C) 14. 3 23 .4 23 . 3 hand-operated adjustment of Row rate of oxygen a nd Charge (kg/ t pig iron) air to obtain required oxygen content in the com Sinter 1528 1565 1530 posite blast. After passed through water layer of a 2100 1952 2452 humidity conditioning tower (to adjust its tempera Coke 346 421 484 ture and humidity) and then through a mist separator, Limestone the blast was blown into the furnace through four Dolomite 127 116 149 tuyeres inclined downward at 12°. Mn ore 51 47 55 In the latter period of the test, a part of the cleaned Pig iron top gas was circulatedly blown into the furnace through Production (kg/day) 2428 2373 2287 the tuyeres together with the oxygen-enriched blast. Analysis (% ) C 2.71 2.97 3.01 Si 7.36 5.26 6.34 2. Conditions of the Test Operation S 0.041 0.076 0.045 See Table I. Top gas 3. Results of the Operation Production (m 3/t pig iron) 5356 4059 5281 Table 2 shows three typical examples of the result Analysis (vol% ) CO 54. 1 66.5 65.2 of the test operation. In the table, at the test A, 1-1 , 3.0 4.9 5.0 the oxygen conten t in the original blast was about N2 37.8 22.2 24 .5 40% a nd at the tests Band C about 55 % , but that CO2 4.8 6.1 5.0 in the total blast at C was about 40% because of O 0.1 0 . 1 0.1 mixing with the circulated top gas. Hereinafter, to 2 CR, 0.2 0.2 0 .2 avoid a confusion with the original oxygen-enriched 1.51 2.87 blast (for short, enriched blast), "total blast" will % CO+%H2/% N2 3.22 1 Slag be used to mean the urn of the original enriched Volume (kg/t pig iron) 705 77 1 866 blast and the top gas blown through the tuyeres 1. 51 and its oxygen content is called that in the " total % CaO+%MgO/% Si02 1.40 1.32
Report Transactions ISIJ, Vol. 14, 1974 ( 1 25 )
Combustion tem pera ture at the tuyeres was locall y ing top gas circ ula tedly. very high even with the cold blast a nd slag forming
constituents contained in the cha rge su ch as Si02 IV. Operations of the Industrial Furnace were vap orized probably as SiO to ascend through the furnace. They conden sed a t the upper portion 1. The Progress in Operation Technique a nd filled intersp aces of grains of th e cha rge a nd T he initi a l scale of produc tion of the pla n t was preven ted the gas from passing through . This top gas equivalent to 40 t of amm onia a nd 40 t o f pig phenom enon was observed throughout both tes ts by iron per d ay. From the results of the funda m ental the midget furnace a nd this furnace. One example researches, following consider ations were included in of chem ical a nalysis of white fume evolved from the the des igning of the equipm en ts.
midget furnace is as fo llows : C; 7. 38, Si02 ; 32.24, (I) T op gas w as circulatedly blown throug h the CaO ; 17.72% . tuyeres togeth er with the original oxygen-enriched The cha rge arrived rapidly at the high temperature blast to dilute th e oxygen conten t in the blast for a void zone right a bove the tuyeres from the low temperature ing extrem ely hig h tempera ture at the tuyeres a nd zone o f the furnace top. Thus, the d egree of indirect m odera ting the tem perature gradien t in the furnace. reduction was as low as 30 to 40% , resu lting in un (2) In orde r to stabilize furnace conditions a nd the stable furnace conditions, in spite of h igh con tent of composition a nd volume of th e evolved top gas by C O in the bosh gas. Trial blowing of a pa rt of d ecrease in fluc tua tion of the b last condition , each of cleaned top gas circula tedly through the tuyeres to the blast components, i.e. a ir, oxygen a nd th e cir dilute the oxygen con tent in the total blast to a bout culated top gas was set consta n t in tempera ture a nd 40% could improve furnace conditions rem a rkably. humidity by saturating it wi th water vapor a t 20°C . On the sam c principle, increase in water vapor con The oxygen con ten t a nd volum e of the enrich ed b last ten t in the blas t by ra ising the temperature of water a nd ratio o f the volume of the circulated gas to the in the humidity conditioning tower from 20°C to 33° enriched blast w e re a ll a u tom atically controlled . to 35°C was effective for sta ble o pera tions without (3 ) Closer con trol of gra in size of raw m aterials. h a nging. (4) A con tinuous system w as adop ted to c ha rge (2) T op Gas raw materia ls to the furna ce from a hopper at the The composition of top gas was expected from the furnace top, being capable of a djusting the c ha rging m a teria l bala nce a nd extrem ely low in content of ra te a nd keeping stock line a lways at a prede te rmined
gases sue h as oxygen , C H 4 , H 2 S, a nd S02' M ore level. This was very necessa ry b ecause the furnace stable furnaee conditions a nd less fluctuations in the conditions were far more se nsitive against ch a nge in gas composition could be expected b y a pplica tion of the stock line, compa red wi th the convention a l blast a utom atic control system for the blast equipment. furnace. (3) Coke R a ti o (5) As to refractori es, ca rbon blocks were used I t seem ed that opera tions with coke ra tio 2 t per for the inner layer from the h earth to the sha ft a nd ton of pig iron were som ewha t difficult. But, its c ha m otte bricks for the outer layer of the furnace d ecrease w as expected by better therma l effi ciency in lin ing . a la rge furnace a nd by prevention of hanging by blow- The profile of the furnace w as cha nged three times
Furnace NO. 1 NO . 2 NO.3 2000 1 21001 0 0 '" 5;
0... 0 M
0 U") :;;: '".... 1 3426 5; 317 11 0
0 0 CD ;:!:
0 ;::0
Fig. I. CD Tuyere ® S lag notch ® Tap hole Profi les o f the high oxygen b last D Chamotte brick ~ Car bon block D Carbon s tamp furnace
R eport [ 126 ) Transactions lSI], Vol. 14, 1974
as shown in Fig. I . No.1 furnacc wo rked during the when blast was cold a nd at 26 to 30% when blas t first campa ign, Nos. 2 a nd 3 furnaces during the was ho t (600°C:) by blowing the top gas circul atedly. second and the third campa igns, respectively. Because CO2 in the blown-in top gas consumes coke At the initia l stage of industria li zation of this and h eat, the blowing o f top gas was displaced process, gas producer process with liquid fuels such by heavy oil injection a tomized with compressed a ir as heavy oil or cl'ude oil was not yc t in general use. in the latter half of the third campaign. This was Therefore, prod ucti on cost of the gas by the iron the first case of industrial oil inject ion into th e blast making process was more inexp ensive than that by furnace in J a pan. conventiona l Winkler or semi-wa ter gas furnaces and the present proce s was more profitable even with 2. The EquijJment
hig h coke ratio. The blast was cold and the furnace 1. Profiles of the Furnace was of a profile of a low sha ft one having 2 580 mm of The combustion ra te of coke (the a m ount of coke the hearth diameter and 4 100 mm of effective height burnt pe r unit timc a nd unit area of the hearth) on above the tuyeres. No. I furnace was 0.41 t(m2hr, those of Nos. 2 and 3 From the experience of the test furnaces, som e being 0.87 and 0.68, resp ectively. The height of the troubles were expected to occur at least a t the initial furnace was decided on the ass umption tha t the oxygen stage of the operation but, in practi ce, the operati on conte nt in the total b last was 40% , but in practice could be sta rted very smoothly and continued for the furnace condition was still unstable at this oxygen about onc year with satisfactory res ul ts (the first content a nd stable one could be con tinued at 30 to campaign). In this period, 35 to 40 t per d ay of 36% . On th is account, the volume of gas ascending foundry pig iron with 2 to 3 % of sili con and raw gas through the furn ace in creased and the temperature of equivalent to 900 to 950 kg o f a mmonia per ton o f top gas was over 400°C. When production in crease pig iron wcre simultaneously produced with blast of of pig iron was decided , th e height was increased abou t 55% oxygen and 1.4 to 1.6 t of coke ra tio. without remodeli ng the frame in the case of Nos. 2 After thc first campaign, to m eet the increased d e and 3 furnaces. ma nd of pig iron, the furnace body was remodeled to No.1 furnace did no t have bos h . Jt was based on increase in the height and inne r volume of the furnace. the experience of hanging in the test furnaces a nd In the second campa ign, self-flux ing sin te red ore was examples of low shaft furnaces in Liege,!b) Gerlafin used with decrease in coke ash (from 13.5- 14 to 11 - genl6) a nd Tros tbcrg.li) As the practical operation 11. 5%). The production of pig iron increased to on No. 1 furnace showed that hanging was prevented about 90 t per d ay a nd coke ratio decreased to about by blowing the top gas, it was concluded the presence 1. I fr om 1. 3 t. of bosh was rather favorable to prevent unstable fur J n the meantime, th c so urce of raw gas was gradua ll y nace conditions owing to other reasons, in particula r cha nging from solid fuels such as coal or coke to Auid cold working. Accordingly, bosh a nd bell y of Nos. ones such as na tura l gas, coke oven gas, heavy o il or 2 a nd 3 furnaces were fo rmed by furnace refr actories. Cl"ude o il in the field of ammonia production industry, T a bl e 3 shows dimension and other d a ta in com a nd a lso in the chemical pla nt, to which thc top gas pa rison with those of other low shaft furnaces. of the furnace had bee n supplied . This cha nge was 2. Refractories of the Furnace Body res ul ting in lowering remarkably the production cost Cabonaceous refracto ry was selected for the lining of CO and hydrogen. Consequently, our pl a nt was of the furnace body to prevent hanging, because it forced to decrease in coke ratio as low as possible. was effective from the experience in the test furnaces H owever, it was still necessary a nd economical for the on account of less adhesion of raw m ateri a ls or ha lf furnace to be operated with the 26 to 35 % oxygcn melted m atters. The inner lining of Nos. I and 2 blast to mainta in the productio n of pig iron without furnaces was carbon blocks from the hearth to the remodeling the furnace profile. On the other ha nd, the shaft, the thickness of which was 500 mm at the bot small content of nitrogen in the crude o il furnace gas tom, 400 mm at the hearth in No. I furnace and needed mixing w ith a fair am ount of the top gas for 490 mm in No.2, respectively, 200 mm at the upper ammonia synthesis, even when operated with such end of the shaft. The outsid e of thc carbon blocks low oxygen blast. A hot stove of steel p ipe type was was lined with chamotte bricks, the thickness of which additionally provided a nd hot blast operation with was 720 mm a t the bottom a nd 230 mm in the side. rela tively low oxygen content was tar ted (the third Because of a small furnace, the re fr actories of the campa ign). furnace body initia ll y were not forccdly cooled to The oxygen content in the enriched bl as t, d epend diminish heat loss. From the latter ha lf of the second ing on the amount of the gas from the electric iron campa ign, water was sprayed at the sha ft for cooling. smelting furnace a nd the operation of the gas pro In the practical operation, as the hanging scracely ducers in the chemical pl a nt, was 55% on an average, happen ed and the carbon blocks were considerably ra nging from 50 to 60% in the first and second cam worn out, particularly a t the shaft, p a rtly because of pa igns a nd 26 to 35 % in the third campa ign. In the a bscnce of cooling boxes, the sha ft of No.3 fur each case, stable furnace conditions and contro lled nace was lined onl y with chamotte bricks to enl a rge sili con content in pig iron were achieved by keeping the inner volume. The centra l portion of th e bottom the oxygen con tent in the total blast at 30 to 36% in Nos. 2 a nd 3 furnaces was carbon-sta mped instead
Report Transactions lSIJ, Vol. 14, 1974 ( 127 )
T a bl e 3. Compa ri son of low sha ft furn aces
Ya hagi Iron Co., Ltd. industria l furnace Oberha u- Ge rl a fin- Li ege l S) sen9) gen l 6 ) Campaign No. I No. 2 No. 3
O va l H earth dia. (mm) D 2580 2400 2 744 2400 1500 1200 X 3 000 Throat dia. (mm) 1800 2000 2 100 2200 1 500 Working height (mm) h 4100 5 530 5 650 5620 5700 2 700 /tID 1.59 2.31 2 . 06 2 . 88 2.37 1.80 Working inner volume (m ' ) 16.5 27.5 39. 6 20 .8 33 .0 4.8 Tota l oxygen blown pe r unit a rea of hearth 259 520 406 490 485 226 (m '/m 2 hr) C oke b urn t per uni t a rea of heanh (kg/ m 2 hr) 414 867 680 808 700 Coal 546 Pi g iron producti on pe r unit of tota l inncr I. 5 1 2.57 2 . 69 2.07 . 12 1. 20 volume (tim' d ay) Velocity of top gas a t the throa t (Nm/scc) 0 . 67 0 .94 1.00 0 .78 0 . 20 T e mp. of tOP gas (OC ) 276 290 430 619 Oxygen content in enriched blast (%) 50 .2 55.7 33 . I 26 .4 30 .5 40 O xygen content in IO tal blast (%) 33 . 2 35 .1 28 .0 T e mp. of cnriched blast (0C) 6 1 65 570 773 641 Atm. te mp.
= Pipe line or belt conveyor -0-0 Control line, indi cator, recorder , integrating met er or regul ator
00000000 00000000 00000000 00000000 12
21
21 Fig. 2. Opera tion control syste m o f the high oxygen blast lurnacc
I: a ll' 12 : ore a nd coke bins 2 : oxygen 13: indicato r o f revolution of c ha rgc r 3 : cleaned top gas 14: stock-I ine recordcr 4: temp. conditioning wa te r 15: gas cooling tower 5 : cooli ng watcr 16 : The isen wash er 6: gas washing wa te r 17 : mist sepa rato r 7: humidity conditioning tower 18: booste r 8: blower 19 : gas ho ld e r
9: O 2 a nalyse r 20 : bl owe r 10: furnace bod y 2 1 : to the chemical pla nt II : d ust catcher
Report [ 128 J Transactions lSIJ, Vol. 14, 1974 of carbon block lining. above-mentioned . 3. The Equipment for the Blast Air a nd oxygen were mixed after passed through At the chemical plant, the user of the gas, ammonia the respective fl ow rate control valve and then sucked was then syntheti call y made from the mixed raw gas, by a blower. which comprized the oxygen-enriched blast furnace Air, oxygen and the circulated gas were respectively gas about half as much as the tota l amount, semi sprayed with well water at about 20°C to obtain con water gas and a li ttle amount of electric iron smelting stant temperature a nd humidity. Figure 2 shows the furnace gas. Namely, it was forced to supply the operation control system of the furnace before the hot appointed amount of the blast furnace gas a t the ap stove was provided. 4. The Tuyere pointed value of (CO + H 2 )/N 2 about 3, depending upon the amount of ammonia production, the semi As the tuye re o f the test furnaces was of simple water gas and the electric furnace gas supply. structure and backfired frequently from the inside of In operation with the combined blast, consisting of the furnace, it was d esigned for the industrial fur air, oxygen and the circulated gas, flu ctua tion in the nace as shown in Fig. 3 (a) and (b), having a narrow amount of total oxygen blown, oxygen content in en blowing opening for the circul ated gas to be blown with riched blast or the mixing ratio of the circul a ted gas sufficien t velocity in relation to that of flame propaga caused troubles not only in supply of the gas but also tion. in the operation itself. C hanges in the combustion The number of tuyeres was eight. The inner dia temperature at the tuyeres and in the locati on of m eter of tuyeres was 60 mm in Nos. I a nd 2 furnaces melting zone in the furnace resulted in hanging or and 67 mm in No.3 with 80 to 100 Nm/sec of blast unstable furnace condition. Fo r insta nce, as d escribed velocity a t the outlet of the tuyeres. In the third later, the difference in oxygen content in the blast by campaign, in stead of the circulated gas, less than I % gives the effect corres ponding to that of about 1 l per min of heavy oil per tuyere was injected at 2 6S oC in the blast temperature for the theoretical com 40° to SO°C, 4 to S kg/cm , with atomizing air at 2.S bustion temperature at the tuyeres. Accordingly, a to 3.S kg/cm 2 through a nozzle of 2 mm in diameter. special control device for the blast was adopted as
(a) Furnace No.1, 2 Top 0 2 enriched gas blast
Top gas (b) Furnace No.3 0 2 enriched blast / I . II / L _,~~ ,-
L ~r---~
1--
Fig. 3. Tuyere of the industrial furnace --1-1--1
Report TransKtions ISIJ, Vol. 14, 1974 r 129 )
5. The Hot Stove steel pipe type hot stove was equipped. The steel In the th ird campaign, the furnace was operated p ipes were 40 mm in inner diameter and 3 mm in with the hot blast, and the preheated enriched blast thickness, made of SUS 41, SUS 27, and STP 38 at was mixed with the cold ciruculated gas. Because the high, medium, and low temperature parts, respec the oxygen content in the enriched blast was about tively. 35%, blast temperature was limited to 600°C and a
Table 4. Examples of industrial operation data
Campaign No. I No.2 o. 3 No.3 Cold blast Cold blast Hot blast H ot blast, oil injection
Period, data obtained (hr) 96 96 48 727 Blast Oxygen content in enriched blast (%) 50 . 2 55. 1 33.5 26.0 Air (m'/hr) 1 700 2410 6150 6460 Oxygen (99.2-99.7% 0,) (m'/hr) 1000 1860 1 120 440 Total oxygen (m'/hr) 1354 2352 2403 1 795 Top gas blown (m '/hr) 1380 2440 1300 0 Oxygen content in total blast (%) 33.2 35. 1 28.0 26.0 Temp. of enriched blast (0C) 61 65 570 620 Temp. to top gas blown (0C) 64 68 83 Analysis of raw materials (%) Sinter T. Fe 54.39 56.91 54.23 57.49 56.65 61.73 CaO 7.20 9.61 10.43 7.77 8.19 1.48 SiO, 10.99 7.44 7.62 8.03 7.45 8.24 Moisture 0.75 0.76 0.75 1.55 0.76 0 75 Coke V. M . 1.24 1. 59 1,51 I. 12 F. C 84 ,66 87,12 87 ,44 87 .76 Ash 14,10 11,29 11.05 11.12 Moisture 4,16 4,29 4,05 4.04 Charge (kg/t pig iron) Self-Auxing sinter 1 709 1 627 639 1017 1509 135 Coke I 336 1 033 872 660 Limestone 293 0 0 0 Mn ore 39 13 9 12 Heavy oil 0 0 0 80 Pig iron Production (t/day) 36,8 87, I 106,5 96,4 Analysis (%) C 3,79 4.06 4,04 3 ,98 Si 2,72 2,44 2.47 2,27 Mn 0.48 0,55 0.50 0,49 S 0.04 0.02 0,02 0,03 Top gas Production (m'/t pig iron) 2952 2 144 2407 2405 Analysis (vol %) CO 59,6 59,5 40,4 32.4 H , 1.7 3.3 2.0 2.8 CO, 10 ,3 13,4 13.7 11. 9
N 2 28, 1 23,6 43.8 52 ,8 CH. 0.3 0,2 0. 1 0,1
% CO+%H,/%N2 2.18 2,66 0,97 0.67 Temperature (OC) 276 290 430 360 Slag Volume (kg/t pig iron) 709 374 363 325 Analysis (%) CaO 41,03 42.81 40.72 44,69 SiO, 34.41 34,85 33.91 34,89 % CaO/%SiO, 1.19 1,23 I. 20 1.28
Definition: Air } = Enriched blast} Oxygen = Total blast Top gas blown Total oxygen blown = Oxygen in the industrial oxygen gas+oxygen In the air
Report ( 130 ) Transactions ISIJ, Vol. 14, 1974
3. The Result of the Operation u The industrial furnace was operated for about three ci. years a nd ten months from the first to the third cam E ~ 2500 paign, namely from April 1958 to April 1962 and 3 0" about 90 X 10 t of pig iron was produced with about Vi X 6 3 .D" 134 10 Nm of effective gas equivalent to a bout E 0 60 X 103 t of ammonia. Several examples of the V. Consideration I , I ! ! ! ! SOO ! ! ! ! 900 ! 600 700 1000 1. The Relation Between Oxygen Content in the Total -Temp. of air blas t eel Blast and the Theoretical Combustion T emperature Fig. 4. Relalion belween blast temp., oxygen contenl in en The stable operation of the high oxygen blast fur riched blasl, and lheoretical combustion temp nace was uccessful , when the top gas (d isplaced by heavy oil in the third campaign) was circulatedly blown with the enriched blast through the tuyeres. t- 2500 The practical operational experience showed clearly that 30 to 36% of oxygen conten t in the total blast is most favorable for stabilizing the furnace condition .~" "' ..0" in the case of cold blast and 26 to 30% in the case of E o the preheated enriched blast at about 600°C. Be <.> 2000 cause the stable operation would mainly depend on the relation between oxygen content in the total blast ~ ~ Ojl ratio := C i; ~:k~i la~~j:~;e~urnt and the combustion temperature at the tuyers, the ~ in {,"o nt of tuyeres theorctical combustion temperature was calculated with the following ass umptions. -,--!;;--,--,--,--,---:':::--.J...,.",=-.l-.l-f;:1 --'---"----"-----'--:!. ( I ) The following equation is used to simplify 11500~L-..J--i';;:-20 ....' 60 calculation of th e mean specific heat for CO, oxygen ! SOO! ! 900 and nitrogen, and also for CO2 and hydrogen in the Temp. of air blast ('C) circulated gas which are little in quantity. Fig. 5. Relalion between blast temp., oxygen content in 0.302 + 0.000022 I (kcal/m3 t C, t is temperature or enriched blasl, o il ratio, and theoretical combusti on gas in °C.) temp (2) The sensible heat of carbon in coke preheated by the ascending gas during descending to the com in coke. The quantity of carbon consumed by CO2 bustion zone in the furnace is assumed to be 0.4 X in the circulated gas after Eq. (4) is added separately, 0.75 tg kcal/kgC after R amm's equation,I91 where, 0.4: mean specific heat of carbon (kcal/ Vb X (0,302 + 0,000022tb)x tb+ 2 445- 1 709C02 kgt C) +0,4x 0.75 X (l + C02 X 12 ,0 1/22.4) X tg to: theoretical combustion temperature = Vgx (0.302+0.000022tg)xtg ...... (5) (0C) where, Vb: volume of the total blast (m3) 0.75 tg: preheated temperature of carbon. Vg: volume of produced bosh gas (m3) (3) Assuming that the blast is in a dry state, heat tb: temperature of the blast COC) absorption by the decomposition of water vapor is not tg: theoretical combustion temperature considered. (0C) (4) Carbon dioxide in the circulatcd gas is con 3 CO2 : volume of CO2 in the total blast (m ) verted to CO by carbon in coke after Eq. '(4). 2 445: heat of combustion of ear bon in coke to CO (kcal/kgC) CO2 + C = 2CO ...... (4) 1 709: heat of reaction of carbon in coke wi th 3 (5) The composition of heavy oil C; 86, H ; 12 % CO2 (kcal/m C02 ), 1. Case of Circulatedly Blowing the Top Gas Calculation according to Eq. (5) gives the relation Assuming that carbon in coke burns to CO by between the temperature of the blast, oxygen content oxygen in the blast at the tuyeres and neglecting heat in the total blast and the theoretical combustion tem loss and as h and volatile matter in coke, the foll owing perature as shown in Fig. 4. The curve A in the Eq. (5) can be obtained according to the above figure shows the relation between the blast temprea mentioned assumptions for one kilogram of carbon ture and theoretical combustion temperature in the Report Transactions ISIJ, Vol. 14, 1974 [ 131 J Table 5. Comparison of gas reduction a nd solution loss carbon ,n the indutrial operation (kg/t pig iron) Oxygen reduced Gas reduction of OFe (% ) Solution D OL ll er s loss carbon Campaign Reduced by Total Reduced by Reduced __ CO J-f CO by 2 a t abrove C I H 2 C (~~~I ) , (b) I (c) (a) ( ~ ) (:) tuyeres Non-Auxing sin ter charge 73 238 I_50 361 31 66 14 80 61 55 No. 1 I -- I I -- I I Self-Auxing sinter charge 9 1 232 32 355 35 65 9 74 47 68 ------No.2 82 23 372 32 72 6 78 46 62 " -- 26_7 I I o. 3 83 263 25 37 1 32 71 7 78 21 62 " I --- 0"'0 : 0 reduced from iron oxide OF. reduced by CO and H 2 X 100 Gas reduction of O~-e (%): 0 0th e!'s : 0 reduced from oxides other than iron oxide OFe 100.------,------. case of air blast, while the B group curves, between • No n·f1uxing sinter charge oxygen content in the total blast and the theoreti cal ° Self·f1u xin g si nt er charge Number : 02 content in en riched blast (%) combustion temperature in the case of oxygen-en 80 (number ) : , total blast (%) Hot riched cold blast (O°C), each of which corresponds to blast 55 ( 3~ ) 033 (28 ) 0, 2, 4, and 6% of CO2 in the tota l bl ast, respectively. c o 0· 54 (33 ) The C group curves show the rela ti ons in the case of U 60 50 (33 ) ::> oxygen-enriched hot blast preheated at 600°C, each ~ Industrial '".... Midget T est furnace of which corresponds to 0 a nd 2% of CO2 in the furnace furnace ~. 40 total blast, res pectively. .... 55 (41 ) If the usual blast temperature of th e conventional 1'--I 1 .. 1 I 55 (41 ) blast furnace is assumed to be between 600° a nd 1 1 I OOO °C, the theoretical combusti on tempera ture ranges 20 L _-I from 2 090° to 2 410°C from the figure. The optimum range o r oxygen content in the total blast of the in dustria l furnace was 30 to 36% in the cold blast opera °0~----~----~2-----J3------4L-----J5 tion (the first and second campaigns), and 26 to 30% - Travelling time ( hr ) in the hot blast operation at a bout 600°C (the third Fig. 6. R elation between travelling time and indirect reduc campaign), respectively. Because CO 2 in the total tion blast was about 4% in the former case, and 2% in the latter case, the range of the theoreti cal combus The equation is for one kilogra m of th e total carbon tion temperature in the industria l furnace is 2 060° to in coke plus in heavy oil, and it is ass umed that heat 2 420°C and 2 330°C to 2 570°C from the figure. In of combustion or carbon in heavy oil to CO is the same the la tter case, the temperature would be a little lower as that of coke . than this range in reali ty, because the circulated gas The curve A in the figure is the same as in Fig. 4; was not preheated. the B group curves show the rela tions between oil 2. Case of Injecting Heavy O il ratio, oxygen content in the blast and the theoretical By neglecting the effects of water, ash, oxygen, combustion temperature in the case of the oxygen nitrogen, and ulfur contained in heavy oi l and their enriched blast preheated a t 600°C. Because the sensible heat and calculating according to the follow oxygen content in the total blast was 26 to 27 % and oil ing Eq. (6), the relation between the temperature of ratio a bout 0.1 % in the industrial furnace, the range the blast, oxygen content in the blast, the ratio of of the theoretical combustion temperature is 2 240° injected heavy oil and the theoreti cal combustion tem to 2 290°C, which lies in the middle of that of the perature is obtained as shown in Fig. 5. conventional blast furnace. In the above considerati ons, the assumed range of VbX (0.302 +0.000022tb ) X tb+ 2 445- 440 the u ual blast temperature of the conventional blast X r/0.86 + 0.4 x 0.75 X (I - r) X tg furnace, 600° to I OOO°C, that is the base of the con = Vgx(0.302 + 0.000022tg) x tg ...... (6) sidera tions, is rela tive and approximate and water vapor contained in the blast is neglected to make where, r: oil ratio, the ratio of carbon in heavy calculations simple. Nevertheless, it is conjectured oil to the total carbon in coke a nd heavy that the high oxygen blast furnace can be operated oil burnt with oxygen in the blast at the stably in the same range of the theoretical combustion tuyeres temperature, 2000° to 2 500°C , as the conventional 440: heat of decomposition of heavy oil blast furnace. (kcal/kg of heavy oil ) Report ( 132 J Transactions ISIJ, Vol. 14, 1974 2. Degree of Gas Reduction blast operation are reported on the test furnaces a nd Effects of the circulated top gas on reaction kineti cs the industri al rurnace utilizing top gas for ammonia in the furnace a re complicated . Carbon dioxide in synthesis. Our experience and technique of the the circulated gas can not pass through the layer of combined blast in the blast rurnace operation would incandescent coke at the tuyeres without any chemical be very rare in the world history o f iron making. reaction. It would react with coke according to Eq. Acknowledgements (4) to form CO which will be mixed with CO formed W e express our sincere gratitude to Profe ssor-Dr. by reaction between coke and oxygen or steam in T einosuke Vagi, Professor Emeritus or K yushu Uni the blast. (Solution loss like reaction at the tuyeres) versity, for his kindest g uidance throughout planning, T able 5 shows the degree of gas reduction (the re experiment, and industrializing. duction by CO and hydrogen ) a nd solution loss carbon per ton of pig iron on the basis of the res ults of the REFERENCES industrial operation. It is assumed that a ll CO 2 I ) J apan Society for the Promotion of Science No. 54 Com . in the circulated gas is conver ted to CO a t the tuyeres. for Ironmaking: No. 5 1 M eeting R eport, No. 596-1 ( 1960), 1- 8. 3. The Relation between the D egree of Indirect Reduction 2) J apan Society of the Prom otion of Science No. 54 Com. and the Travelling Time of the Charge in the Furnace fo r lronmaking : No. 54 Meeting R eport, No. 656 ( 196 1). While the oxygen-enriched blast operation has such 3) T. Sugiura : Thesis for D egree, ( 1962), unpublished. a feature tha t the height of the furnace shaft can be 4) T. Okamoto: Thesis for D egree, ( 1962), unpublished. low, d ecrease in the degree of indirect reduction is 5) Y. Tada and S. K ashima: Tetsll-to-Hagane, 54 ( 1968), 994. foreseen from the decrease in the effective volume for 6) Y. Tada: Tetsu-lo-Hagane, 39 ( 1953), 866. 7) T. Okamoto a nd Y. Tada: Preprint of the 4th Interna ti ona l the progress of indirect reduction. However, on the Congress on Electro-heat, held in Stresa in Ita ly, ( 1959). other hand, increase in the degr ee of indirect reduction 8) H . K o ppcnberg a nd 'vV. Wenzel: Die Sauerstoffmetallur would be expected from increase in the partial pres gie del' Schachtofenprozesse, ( 1953), 128, V erlag Stahleiscn. sure of CO in the bosh gas. 9) H . Schumacher: Stahl ll . Eisen, 73 ( 1953), 257, W. W en On the basis of operations on the test furnaces a nd zel. the industrial one, the relation b etween the travelling 10) R . Durrer : V erhLitten von Eisenerzen tra nslated by K . Asai time of the charge and the d egree of indirect reduc and K . K a na mori , ( 1955), 153, M aruze n. tion is shown in Fig. 6. In the figure, range of the II ) E. Muna kata: Bunri, ( 195 1), 147, Maruzen. degree of indirect reducti on in the midget furnace is 12) T. Yasumoto : Yokoro Seirenho, ( 1954), 170, Sangyotosho. roughly estimated from the composition of the top 13) M . lkoma: Kob e Steel Engineering Rej)orls, 1 ( 195 1), 19. gas. The travelling time of the charge has a great 14) H . S ug isawa, M. M atsuura, and H . Suemitsu : Kobe Steel Engineering RejJorls, 2 ( 1952), 15, 2 ( 1952),6 1. effect on the degree of indirect reduction, while the 15) Iron and Sleel, 26 ( 1953), 5. composition of the bosh gas has little influence in the 16) H . Erne: Stahlll. Eisen, 74 ( 1954), 1644. range of 33 to 55% oxygen in the blast. 17) H . H e librLigge: Stahill. Eisen, 69 ( 1949),256. 18) P . Coheur: J. Metals, 7 ( 1955),872. VI. Conclusion 19 ) A . N. R amm: Sovremcnnye Problemy M etallurgii , ( 1958), In the present report, the results of the high oxygen No. 35. Report