The blast-furnace wind from hot-blast stoves is a significant factor of the blast furnace functioning. The technology was analyzed in which the hot wind from hot-blast stoves is not mixed with the cool wind to a constant wind temperature, but is blown directly into the blast furnace. However, it is necessary to compensate for the changes of the theoretical temperature of burning in blast furnace as a consequence of non-stabilized wind temperature, by changing composition of the wind. This can be done by adding different media into the wind with different results from the operational and economical viewpoints. Essentially, the following types of media are used in blast furnaces: steam, oxygen, substitution fuels, nitrogen, and waste gas.Vjetar visoke peći i peći za zagrijavanje značajno utječe na rad visoke peći. Analizirana je tehnologija kod koje se vrući vjetar iz peći za zagrijavanje ne miješa s hladnim vjetrom do postizanja konstantne temperature nego se direktno upuhuje u visoku peć. Međutim, potrebno je promjenama sastava vjetra kompenzirati promjene teorijske temperature izgaranja u visokoj peći uzrokovane nestabiliziranom temperaturom vjetra. Ovo se može obaviti dodavanjem različitih medija u vjetar uz postizanje različitih rezultata s pogonskog i ekonomskog gledišta. U biti, kod visokih peći se koriste sljedeći mediji: vodena para, kisik, zamjenskog goriva, dušika i otpadnih plinova

I. Koštial

J. Terpák

L. Pivka

L\u27. Dorčák

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J. TERPÁK, L’. DOR^ÁK, I. KO[TIAL, L. PIVKAREDUCTION OF COSTS OF IRON PRODUCTION BY CHANGINGPARAMETERS OF THE MIXED BLAST-FURNACE WINDReceived – Prispjelo: 2008-10-14Accepted – Prihva}eno: 2009-07-14Original Scientific Paper – Izvorni znanstveni radINTRODUCTIONThe blast-furnace process consists of a large numberof processes that are physicochemical, thermal and me-chanical interconnected processes. In addition to mainprocesses consisting of iron oxides reduction, pig ironand slag melt creation, also realised are fuel combustion,gas flow, charge and melt flow, dissociation and otherreactions in the solid and liquid phases.Inputs to the blast-furnace process are blast-furnacecharge and combined wind. Blast-furnace charge con-sists of ore charge, coke and slag former. The functionsof coke are putting heat and substances reduction to theblast-furnace, pig iron carbonisation, and creation ofsolid skeleton of the blast-furnace for the gas flow. Thecombined blown wind is the oxygen source for cokecombustion and at the same time hydrogen source as re-duction gas that is created by dissociation of steam. Out-puts from the blast-furnace process are pig iron, slag andblast-furnace gas.Overall the blast-furnace process can be character-ised as a non-stationary process with distributed param-eters. Its basic characteristics are as follows 1- 6:– The blast-furnace is counter current reactor.– The blown wind and off take blast-furnace gas iscontinuous.– The input of charge, pig iron and slag tapping is al-most continuous.– The reduction of iron from charge is nearly ideal,negligible loss of iron is to the slag.– Heat exchange in the blast-furnace is basically fin-ished. It is related to high level of heat utilization.– Relatively low level of utilization of carbon chem-ical energy from coke comes not from process in-completeness, but from its essence.MATHEMATICAL MODELOF THE THEORETICAL TEMPERATUREFrom combustion point of view coke combustion infront of the blast tuyere is important. Coke is heatingfrom 1500 to 1600 °C and next is burning with blast-fur-nace wind that has temperature from 1000 to 1300 °Cand velocity from 120 to 200 m/s. The final product ofincomplete combustion of carbon is mixture of carbonmonoxide, nitrogen and hydrogen.Maximum temperature in oxidation area is where theconcentration of the carbon dioxide is maximal accord-ing to the following reactionMETALURGIJA 49 (2010) 2, 79-82 79The blast-furnace wind from hot-blast stoves is a significant factor of the blast furnace functioning. The tec-hnology was analysed in which the hot wind from hot-blast stoves is not mixed with the cool wind to a con-stant wind temperature, but is blown directly into the blast furnace. However, it is necessary to compensate forthe changes of the theoretical temperature of burning in blast furnace as a consequence of non-stabilized windtemperature, by changing composition of the wind. This can be done by adding different media into the windwith different results from the operational and economical viewpoints. Essentially, the following types of me-dia are used in blast furnaces: steam, oxygen, substitution fuels, nitrogen, and waste gas.Key words: blast-furnace wind, mathematical model, simulationSmanjivanje tro{kova proizvodnje `eljeza promjenama parametara vjetra visoke pe}i. Vjetar viso-ke pe}i i pe}i za zagrijavanje zna~ajno utje~e na rad visoke pe}i. Analizirana je tehnologija kod koje se vru}i vje-tar iz pe}i za zagrijavanje ne mije{a s hladnim vjetrom do postizanja konstantne temperature nego se direktnoupuhuje u visoku pe}. Me|utim, potrebno je promjenama sastava vjetra kompenzirati promjene teorijske tem-perature izgaranja u visokoj pe}i uzrokovane nestabiliziranom temperaturom vjetra. Ovo se mo`e obaviti doda-vanjem razli~itih medija u vjetar uz postizanje razli~itih rezultata s pogonskog i ekonomskog gledi{ta. U biti,kod visokih pe}i se koriste sljede}i mediji: vodena para, kisik, zamjenskog goriva, du{ika i otpadnih plinova.Klju~ne rije~i: vjetar visoke pe}i, matemati~ki model, simulacijaISSN 0543-5846METABK 49(2) 79-82 (2010)UDC – UDK 669.162.2:519.673=111J. Terpák, L’. Dor~ák, I. Ko{tial, L. Pivka BERG - Faculty, TechnicalUniversity of Ko{ice, Ko{ice, SlovakiaC(coke) + O2(g) = CO2(g), (1)while in all another areas the temperature of gas is lowerbecause of incomplete combustion of carbon from coke2 C(coke) + O2(g) = 2 CO(g), (2)or because of reduction of carbon dioxide according toBoudouard's reactionC(coke) + CO2(g) = 2 CO (g). (3)This reaction takes place at the boundary of oxidationzone and transforms all carbon dioxide to carbon mon-oxide 2, 3.The wind humidity and steam interact with carbonfrom coke generating carbon monoxide and hydrogenC(coke) + H2O (g) = CO (g) + H2 (g). (4)Both gases are created by combustion of methanethat is the main part of natural gas 72 CH4(g) + O2(g) = 2 CO (g) + 4 H2 (g). (5)Similar reactions occur at oil injection as substitutefuel.The theoretical temperature of burning is a basic pa-rameter to estimate the state of previous processes. It isbasically about the thermal balance that includes incom-plete combustion of carbon from coke, physical heat ofthe blast-furnace wind, coke and substitute fuels, andconsumption heat for the dissociation of steam, substi-tute fuels, and heat for waste gas heating.The theoretical temperature of the burning is givenby the following equation 1TQ Q Q Q Qc V c V c Vteorc k v dis injH H CO CO N N    2 2 2 2/ K (6)whereQc is the carbon combustion heat from cokeand injected fuel / kJ/kg(coke),Qk is physical heat of coke / kJ/kg(coke),Qv is physical heat of blast-furnace wind /kJ/kg(coke),Qdis is dissociation heat of water vapour and in-jected fuels / kJ/kg(coke),Qinj is physical heat of injected fuels /kJ/kg(coke),V V VH CO N2 2, , is volume of H2, CO and N2 in combustiongas / m3/kg(coke),c c cH CO N2 2, , is specific heat capacity of H2, CO and N2 /kJ/(m3K).A simulation model for the study of impact of heatpart on the theoretical temperature of burning or cokeconsumption was created. A brief algorithm of themodel of theoretical temperature of burning is describedin the following steps:1. Input variables reading.2 Choice of:(a)Calculation Tteor and wind temperature Twindreading.(b)Calculation Twind and Tteor reading.3. Calculation of moist air composition.4. Calculation of steam volume.5. Calculation of blast wind composition.6. Calculation of carbon consumption from injec-tion fuels and oxygen volume for burning thiscarbon.7. Calculation of H2O, CO2, O2, N2 total input vol-ume.8. Calculation of carbon and coke quantity.9. Calculation of heat of incomplete combustion ofcarbon from coke, physical heat of blast-furnacewind, coke and substitute fuels, and consumptionheat for dissociation of steam, substitute fuels.10.Calculation of H2, CO, N2 volume and its specificheat capacity.11.Calculation of Tteor or Twind.SIMULATIONSSimulations are focusing on the possibility to com-pensate for the changes of the theoretical temperature ofburning as a consequence of non-stabilized wind tem-perature, by changing the wind composition. It is a tech-nology in which the hot wind from hot-blast stoves isnot mixed with cool wind to a constant wind tempera-ture, but is blast directly into the blast-furnace. The op-eration of the hot-blast stoves is more economical in thiscase than with the stabilized wind temperature 4.Simulations were realised for 200 000 m3/h blastwind volume, 60 % relative air humidity and 20 °C airtemperature. The following volume of additional mediawas used: steam in the range from 0 to 30 g/m3, 85 % ox-ygen from 0 to 10 000 m3/h, oil injection from 0 to8 000 kg/h, and waste gas from hot-blast stoves (averagecomposition 69,2 %N2, 0 %O2, 25,4 %CO2, 5,4 %H2O)from 0 to 15 000 m3/h.All simulations were realised for constant total windvolume 200 000 m3/h and for constant theoretical tem-perature of burning 2200 °C.MUTUAL COMPARISON OF MEDIAAs a basic unit for mutual comparison we chose 1 Kfor the wind as a value, which we compensate for by dif-ferent means and effects.The mutual comparison was realised according tothis criteria:– The effect on blast-furnace hearth’s operation,coke consumption, contribution of heat by thewind, volume and composition of hearth gases,and the stability of the conditions for blast-furnaceoperation.– Availability of media and operation conditions.– Economical comparison.The effect on the contribution of heat to blast-fur-nace hearth and coke consumptionConsidering the simulation results the most heat con-tributed to the blast-furnace hearth is under the condi-80 METALURGIJA 49 (2010) 2, 79-82J. TERPÁK et al.: REDUCTION OF COSTS OF IRON PRODUCTION BY CHANGING PARAMETERS OF THE MIXED...tion when steam, oxygen, waste gas and oil is added tothe wind, which makes it possible to considerably in-crease the wind temperature, while the oxygen signifi-cantly increases coke consumption.The highest ratio of heat contributed by wind into thehearth occurs when oxygen enrichment of wind is ex-cluded, which makes it possible to further increase thetemperature of the wind at the expense of smaller con-sumption of coke burnt in the area in front of blasttuyere. Here are confirmed the contributions from theenrichment of the wind by nitrogen. It is self-evidentthat the calculated temperatures of the wind 1493 and1683 °C are currently unrealistic and the purpose of theabove comparison is only to evaluate the mutual combi-nations of individual media in the wind.The quantification of influence was realised by themutual comparison of the difference between the basicvariant without additional media and maximal value ofonly one medium. The base for comparison is linear de-pendence between change of medium volume and theextent of change in the observed quantity.The mutual comparison of differences between vari-ants is listed in Table 1. Described in the first row is theimpact of unit change of the amount of medium on thechange of wind temperature. From this follows that with-out oxygen other media increase wind temperature by theconstant theoretical temperature of burning. In the secondrow it is shown as media with wind temperature escalatethe contribution of heat to the blast hearth. The third rowincludes change of coke quantity that is burnt at the frontof tuyere per hour. From this follows that oxygen andsteam increase coke consumption. Waste gas addition de-crease coke consumption very moderately.When recalculating the change of consumption ofthe combustion coke per 1 K of the wind temperature inthe fourth row it is obvious that during the compensationof the change in wind temperature with oxygen or oil aconsiderable „shock“ in coke consumption in thermalprocesses occurs. When using the steam, this impact isless than half (46 % from oxygen) and with compensa-tion by waste gas a decrease of coke consumption forthermal processes occurs, however, only about 13,4 %of the decrease when using oil.From the next rows, where the effect on the volumeand composition of hearth gases is considered, it is obvi-ous that addition of any of the four media brings increasein the creation of hearth gases especially through reduc-tion components such as carbon monoxide and hydro-gen at the expense of nitrogen.For the overall amount of hearth gases the largest in-crease is with oil and the least increase with waste gas.The sum of carbon monoxide and hydrogen at constantamount of hearth gases per time unit has the largest in-crease with oxygen and the least increase with wastes.Availability of mediaand operation conditionsFrom the media suitable for the compensation of thewind temperature should in principle be excluded en-richment of the wind with oxygen a consequence ofwhich is the need for a decrease in wind temperature.For practical use in compensation of increased windtemperature can be considered technological steam andwaste gas. Operational functioning of technologicalsteam is obvious since this medium is commonly used inpractice. As for waste gas, in general, there is a wide va-riety of choice. It is only natural that it will be waste gascreated in the combustion of pure (dustless) gas. In themetallurgy plant there are enough aggregates that pro-duce suitable waste gas. In Japan for example the wastegas from the boiler was used 8.The decisive factor in waste gas utilization is itscomposition, stability of its incidence, storage, andtransport. The technical solution of the question of prac-tical application should be completed, namely the ques-tion of import of waste gas from the source of incidence,adjustment of pressure, analysis of waste gas, measure-ment and regulation in the addition proper.In the case the device for adding waste gas in the suc-tion side of turbine is not designed, technological steamand decreasing the consumption of oxygen can be rec-ommended for practical utilization of compensation ofincreased temperature of wind.Economical comparisonThe evaluation of approximate costs of compensat-ing the increasing temperature of wind by nitrogen,waste gas, oxygen, and steam is given in Figure 1. In thecosts is included the proper cost of media and their im-pact on the consumption of coke in front of blast tuyereswithout considering the costs of the heat brought in byMETALURGIJA 49 (2010) 2, 79-82 81J. TERPÁK et al.: REDUCTION OF COSTS OF IRON PRODUCTION BY CHANGING PARAMETERS OF THE MIXED...Table 1. Influence of compensating substances onblast-furnace operationSubstanceand volumeWastegas/ 103m3/hOxygen/ 103m3/hSteam/ 1g/m3Oil/ 103m3/hTwind / K 14,20 –20,16 8,53 25,90Q 105 / kJ/h 3,33 24,20 23,43 48,88C / t/hC / t/(h⋅K)Twind–0,0714–0,005030,7670,038050,1500,03805–0,972–0,03753V / vol.%V / m3/h0,03700,09130,2580,6310,2040,4990,5731,400VH CO2 / vol.%VH CO2 / m3/h0,1220,1080,8520,7540,1250,1110,3650,323Twind – increase of wind temperature,Q – increase of heat input into BF,C – change of volume of coke,V – increase of hearth gases volumeVH CO2 – increase of H2+CO in hearth gaseswind at the change of its temperature. In view of markedchanges in the prices of media it is necessary to makeoverall economic evaluation only after individual priceshave been approved. The comparison in Figure 1 shouldonly serve for overall evaluation for the choice of media.As for the economic viewpoint of compensation ofincreased wind temperature, the most advantageous isthe compensation by nitrogen (without consideration ofthe costs of N2 – included in the production of O2), thenby waste gas. Oxygen and steam are less advantageous.Oxygen is not suitable for compensation of increasedtemperature of the wind since it increases Tteor (by in-creased burning of coke) and at decreased temperatureof the wind the produced unused oxygen would have tobe cost-inefficiently released into the atmosphere. So inview of technical conditions, steam is exploitable so far.CONCLUSIONFrom economic point of view, the most advanta-geous is the blast wind temperature compensation by ni-trogen, then by waste gas. Oxygen and steam are lesssuitable. Oxygen increases the theoretical temperatureof burning and is therefore suitable for temperature in-crease effect.The results of the model were compared qualita-tively and also quantitatively with real measured data.The presented model is suitable for analysing the com-bustion processes in the reaction zone of the blast- fur-nace, for optimal working regime parameters design andfor monitoring and control of the theoretical tempera-ture of burning. The model was used also for the pulver-ised coal quantity and hot wind temperature optimisa-tion.Acknowledgements - This work was supported by grantVEGA 1/0365/08, 1/0404/08 and 1/4194/07 from theSlovak Agency for Science.REFERENCES1 L. Bro`: Teoretické základy výroby `eleza, SNTL/ALFA,Praha, 1975.2 L. Bro`: Hutníctvi `eleza, SNTL/ALFA, Praha, 1988.3 S. Majer~ák, A. Majer~áková: Hutníctvo `eleza a ocele : I.diel - Výroba surového `eleza a ocele, ES V[T Ko{ice,Ko{ice, 1980.4 J. Terpák: Modelovanie a riadenie technologických proce-sov, habilita~ná práca, FBERG TU Ko{ice, Ko{ice, 2002.5 J. G. Peacey and W.G. Davenport: The Iron Blast FurnaceTheory and Practice, Pergamon Press, Oxford, 1974.6 I. Omori: Blast Furnace Phenomena and Modeling, Else-vier, London, 1987.7 S.L. Jaro{evskij and S.T. Pliskanovskij: Osobennosti tem-peraturnogo re`ima gorna pri rabote domennych pe~ejs vduvaniem prirodnogo gaza i polyugo¾nogo topliva,STA¼, (1987) 5, 7-11.8 A new technology for reducing coke consumption of blastfurnace by means of boiler exhaust gas injection: The EGIprocess, Revue de Metalurgie - CIT Juillet, (1981),616-622.Note: The responsible translator for English language is Ladislav Pivka,Ko{ice, Slovakia82 METALURGIJA 49 (2010) 2, 79-82J. TERPÁK et al.: REDUCTION OF COSTS OF IRON PRODUCTION BY CHANGING PARAMETERS OF THE MIXED...Figure 1. Costs comparison

Smanjvanje troškova proizvodnje željeza promjenama parametara vjetra visoke peći

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