processes

Article Improvement of Energy Efficiency and Productivity in an through the Modification of Side-Wall Injector Systems

Yonmo Sung 1,* , Sangyoun Lee 2, Kyungmoon Han 2, Jaduck Koo 3, Seongjae Lee 3, Doyoung Jang 4, Changyong Oh 5 and Byunghwa Jang 5

1 Department of Energy and Mechanical Engineering, Gyeongsang National University, Tongyeonghaean-ro 2, Tongyeong-si, Gyeongsangnam-do 53064, Korea 2 EAF Production Team, Hyundai Steel Company, Incheon 22525, Korea; [email protected] (S.L.); [email protected] (K.H.) 3 D/Bar Steel Making Department, Hyundai Steel Company, Incheon 22525, Korea; [email protected] (J.K.); [email protected] (S.L.) 4 Mechanical Engineering Team, Hyundai Steel Company, Incheon 22525, Korea; [email protected] 5 Environment and Energy Engineering Team, Hyundai Steel Company, Chungcheongnam-do 31719, Korea; [email protected] (C.O.); [email protected] (B.J.) * Correspondence: [email protected]

 Received: 28 August 2020; Accepted: 22 September 2020; Published: 23 September 2020 

Abstract: The energy cost of producing steel in an (EAF) has a sizable influence on the of and electricity. Therefore, it is important to use these energies efficiently via a tailored oxy-fuel combustion burner and lance. In this study, an important modification of the side-wall injector system in the EAF at Hyundai Steel Incheon works was implemented to reduce electrical energy consumption and improve productivity. A protruding water-cooled jacket, including a newly designed burner, was developed to reduce the distance between the jet nozzle and the molten steel. In addition, the jet angles for the burner and lance were separately set for each and refining mode. The modifications led to a reduction in electrical energy consumption of 5 kWh/t and an increase in productivity of approximately 3.1 t/h. Consequently, total energy cost savings of 0.3 USD/t and a corresponding annual cost savings of approximately 224,000 USD/year were achieved.

Keywords: electric arc furnace; oxy-fuel burner; oxygen lancing; natural gas; energy savings;

1. Introduction In the recycled steel processing industry, the electric arc furnace (EAF) is an energy-intensive facility. Electric energy, with a moderate addition of chemical energy, provides sufficient heat to melt recyclable charged in the EAF [1]. For the production of 1 t of steel at 1600 ◦C from steel scrap at 25 ◦C, a typical EAF process, approximately 60% of the energy input comprises electric energy and chemical energy provides the remaining 40% [2]. Similar values have been reported for the energy required to melt steel scraps in EAFs [3,4]. Efforts are needed to improve the efficiency of electricity use in the EAF sector owing to the recent rise in electricity rates and the implementation of the greenhouse gas emission trading system [5]. Therefore, to improve the efficiency of heat used in the EAF, it is important to utilize a heat source other than electric power. To save energy in EAFs, it is important to optimize the utilization of chemical energy; energy can potentially be saved by reducing electrical energy use while increasing the chemical energy input [6,7]. Chemical energy, supplied by a side-wall injector system, is an auxiliary form of energy and is delivered by the oxidation of fossil

Processes 2020, 8, 1202; doi:10.3390/pr8101202 www.mdpi.com/journal/processes Processes 2020, 8, 1202 2 of 10 fuels; exothermic reactions of chemical elements, such as , , , and ; and by post-combustion of carbon monoxide [8,9]. Hence, this study focuses on modifying the side-injector system, with an oxygen lance and an oxy-fuel burner to enhance energy efficiency in EAFs. The prices of natural gas (NG) and electricity, or their ratio, have a large on the production costs of steel in the EAF [10]. Table1 lists the energy prices of industrial NG and electricity in di fferent countries (the prices are converted to cent/kWh content to simplify the energy comparison [11,12]). The maximum and minimum prices for NG are 1.05 cent/kWh in and 7.27 cent/kWh in Switzerland, respectively. For electricity prices, the values are 6.81 cent/kWh in the USA and 17.12 cent/kWh in Italy, respectively. Replacing electricity by NG in an oxy-fuel burner, is more effective at a high ratio of electricity to NG prices. The maximum and minimum values for the ratio of NG and electricity are 7.86 in Canada and 1.39 in Sweden.

Table 1. Comparison of energy prices of industrial NG and electricity with different countries in 2018 [11,12].

Country NG (Cent/kWh) Electricity (Cent/kWh) Electricity/NG (-) Canada 1.05 8.24 7.86 USA 1.36 6.81 5 Germany 3.03 14.28 4.72 United 2.99 13.66 4.57 Kingdom Italy 3.88 17.12 4.57 Belgium 3.10 13.41 4.32 Spain 2.96 12.52 4.23 Slovakia 3.38 13.87 4.10 Portugal 3.29 13.28 4.04 Turkey 1.97 6.98 3.55 Japan 4.52 15.79 3.49 Poland 2.96 9.39 3.17 Ireland 4.10 12.63 3.08 Netherlands 2.97 9.13 3.07 Hungary 3.09 9.26 3.00 Czech Republic 3.17 9.47 2.99 Austria 3.69 10.83 2.93 Greece 3.55 10.26 2.89 France 4.28 11.42 2.67 Luxembourg 3.25 8.20 2.52 Korea 4.24 9.85 2.32 Denmark 4.11 9.13 2.22 Switzerland 7.27 11.99 1.66 5.27 7.70 1.46 Sweden 4.93 6.85 1.39 Mean values 3.53 10.88 3.43 Max. values 7.22 17.12 7.86 Min. values 1.05 6.81 1.39

In South Korea, as of 2018, both energy prices are below the mean values shown in Table1. However, the ratio of both prices is higher than the mean value. During the last 15 years, the of NG has continuously increased in South Korea but the price of electricity has decreased since 2014, as shown in Figure1[ 11,12]. From 2006 to 2014, the average price ratio of NG and electricity was 1.67. Therefore, either oxy-fuel burner operations in EAFs have been minimized in South Korea or the system was not in use between 2006 to 2014, in particular at the Hyundai Steel Company. The price ratio of NG and electricity increased from 2014. For these reasons, the or development of oxy-fuel burners in South Korea has increased in the recent years; hence, research was initiated into the system modification presented herein. Processes 2020, 8, x FOR PEER REVIEW 3 of 10

Processesfuel burners2020, 8 ,in 1202 South Korea has increased in the recent years; hence, research was initiated into3 of the 10 system modification presented herein.

Figure 1. Variation of the prices of industrial NG and electricity and their ratios from 2004 to 2018 in South Korea [[11,12].11,12].

In EAFEAF operations,operations, severalseveral oxy-fueloxy-fuel burners,burners, includingincluding oxygen lances, have beenbeen integratedintegrated toto reduce electricalelectrical energyenergy consumptionconsumption byby substitutingsubstituting electricityelectricity withwith fuels.fuels. The oxygen lance andand oxy-fuel burner can be usedused forfor pre-heating,pre-heating, cutting,cutting, and removing cold spots to ensureensure uniformuniform temperaturetemperature distribution distribution inside inside the the furnace furnace and and promot promotee the circulation the circulation of molten of molten steel in steelthe refining in the refiningprocess, process,thereby therebyreducing reducing the tap-to-tap the tap-to-tap time time(TTT) (TTT) by byapproximately approximately 6%, 6%, improving improving power consumption and productivity [[5].5]. When optimizing the oxy-fuel burnerburner/lance,/lance, the electricelectric powerpower 3 savings cancan bebe expected expected to to be be 20–40 20–40 kWh kWh/t/t (t: (t: tons tons of steel),of steel), by injectingby injecting NG, NG, which which is 0.3 is Nm 0.3 Nm/kWh3/kWh [13]. 3 Typical[13]. Typical savings, savings, ranging ranging from 2.5–4.4 from kWh2.5–4.4/Nm kWh/Nmoxygen3 injection,oxygen injection, can be achieved, can be withachieved, electricity with savingselectricity of savings 0.14 GJ/ tof [14 0.14,15 ].GJ/t [14,15]. Oxygen jet jet and and oxy-fuel oxy-fuel flame flame configurations configurations modifica modificationstions have been have researched been researched to reduce to electrical reduce electricalenergy consumption energy consumption in EAFs [16–19]. in EAFs Megahed [16–19 ].et Megahedal. [16] conducted et al. [16 an] conducted upgradation an by upgradation using oxygen by usinginjections oxygen with injections jet location, with length, jet location, and flowrate length, at andEzz flowrateFlat Steel. at The Ezz modifications Flat Steel. The led modifications to a reduction led in toelectrical a reduction power in consumption electrical power by 64 consumptionkWh and an increase by 64 kWh in furnace and an productivity increase in of furnace 30%. Thomson productivity et al. of[17] 30%. investigated Thomson the et effect al. [17 of] the investigated oxy-fuel burner the e ffratiecto ofon the energy oxy-fuel efficiency burner in Co-Steel ratio on Lasco’s energy EAF. efficiency They inconcluded Co-Steel that Lasco’s the EAF.decrease They in concludedspecific electrical that the energy decrease consumption in specific electrical(4%) and energyTTT (4.5%) consumption could be (4%)realized and by TTT optimizing (4.5%) couldthe oxygen-to-fuel be realized ratio by optimizing in the oxy-fuel the combustion oxygen-to-fuel burner. ratio Memoli in the et oxy-fuel al. [18] combustionachieved electrical burner. energy Memoli savings et of al. approximately [18] achieved 27% electrical through energy multi-point savings supersonic of approximately oxygen injection 27% throughwithin a multi-pointreal-scale EAF supersonic with a nominal oxygen capacity injection of within 105 tons. a real-scale Cantacuzene EAF et with al. [19] a nominal investigated capacity the ofdistribution 105 tons. ofCantacuzene lancing oxygen et al. among [19] investigated multiple locations the distribution to improve of the lancing effectiveness oxygen of among oxygen multiple usage in locationsan EAF. Through to improve this thetailored effectiveness use of oxygen, of oxygen the el usageectrical in energy an EAF. consumption Through this was tailored reduced use from of oxygen, 427 to the400 electricalkWh/t and energy the power-on consumption time was (POT) reduced was also from re 427duced to 400from kWh 41/ tto and 37 themin. power-on Kirschen time et al. (POT) [20] wasdemonstrated also reduced that from the assessment 41 to 37 min. of multiple Kirschen EAF et al. energy [20] demonstrated balances did not that reveal the assessment a significant of influence multiple EAFof NG energy consumption balances on did the nottotal reveal energy a significantinput in an influenceEAF but did of NGdemonstrate consumption an associated on the total decrease energy in inputthe electrical in an EAF energy but requirement. did demonstrate an associated decrease in the electrical energy requirement. The above-mentionedabove-mentioned studies studies showed showed that that the the reduction reduction in electrical in electrical energy energy consumption consumption of EAFs of primarilyEAFs primarily depends depends on the on oxygen the oxygen usage ofusage the burner of the andburner lancer, and inlancer, terms in of terms the installation of the installation location, flamelocation, type, flame injection type, angle, injection and angle, ratio of and NG-oxygen. ratio of NG-oxygen. In particular, In theparticular, injection the angle injection of the jetsangle requires of the optimization according to the time step (period), such as the heating/melting of scraps and refining of

Processes 2020, 8, x FOR PEER REVIEW 4 of 10 Processes 2020, 8, 1202 4 of 10 jets requires optimization according to the time step (period), such as the heating/melting of scraps andmolten refining steel. of Therefore, molten steel. the jet Therefore, angles from the thejet an oxy-fuelgles from burner the oxy-fuel and oxygen burner lance and have oxygen to be lance separately have tomaintained be separately at their maintained corresponding at their roles corresponding during each roles period. during A jet each with period. an impinging A jet with point an tooimpinging close to point too close to the refractory walls can cause excessive consumption of the refractory, while a jet the refractory walls can cause excessive consumption of the refractory, while a jet that is less inclined that is less inclined with respect to the horizontal plane can produce splashing of hot steel [15]. If the with respect to the horizontal plane can produce splashing of hot steel [15]. If the distance from the jet distance from the jet nozzle to the molten steel is too large, the fuel and oxygen usage efficiency in nozzle to the molten steel is too large, the fuel and oxygen usage efficiency in the side-wall injectors the side-wall injectors will be reduced. This study primarily focuses on these specific aspects, which will be reduced. This study primarily focuses on these specific aspects, which include modifications to include modifications to the side-wall injector system, with different burner and lance jet angles, but the side-wall injector system, with different burner and lance jet angles, but also closely modifies the also closely modifies the distance from the jet nozzle to the molten steel. A protruding water-cooled distance from the jet nozzle to the molten steel. A protruding water-cooled copper jacket, including a copper jacket, including a tailored oxy-fuel burner, was developed. The energy savings and tailored oxy-fuel burner, was developed. The energy savings and productivity performance before and productivity performance before and after modification were evaluated for a real-scale EAF. after modification were evaluated for a real-scale EAF.

2. Materials Materials and Methods

2.1. Modification Modification Concept of Side-Wa Side-Wallll Injector System For Improving EnergyEnergy EEfficiencyfficiency andand ProductivityProductivity inin the EAF Figure 22 showsshows the modification modification concept concept of of the the side-wall side-wall injector injector system system in the in thepresent present study. study. The Theconventional conventional injector injector (Badische (Badische Stalhl-Engineering, Stalhl-Engineering, Kehl, Germany), Kehl, Germany), before beforemodification, modification, was a hybrid was a system,hybrid system,which operates which operates the oxy-fuel the oxy-fuel combustion combustion and oxygen and oxygen lance. lance.The new The newmodified modified system system was wasdesigned designed to operate to operate the burner the burner and lance and lanceseparately, separately, using usingthe existing the existing three li threenes for lines the for supplied the supplied gases. Forgases. the Forconventional the conventional system installed system in installed the EAF in wall, the shown EAF wall, in Figure shown 2a, in a problem Figure2a, arises; a problem the efficiency arises; ofthe heat efficiency transfer of becomes heat transfer low since becomes the distance low since between the distance the injector between and themolten injector steel and is large molten during steel the is scraplarge duringheating, the meting, scrap heating,and refining meting, periods. and refining In addition, periods. the Ininjection addition, angles the injectionfor both anglesthe oxygen for both jet and the oxy-fueloxygen jet burner and oxy-fuel flame were burner fixed flame at 40° were to the fixed hori atzontal. 40◦ to theThis horizontal. may cause This the mayoccurrence cause theof non-melted occurrence scrapof non-melted and the reduction scrap and in the reaction reduction efficiency in reaction between efficiency the molten between steel the and molten layer. steel Therefore, and slag layer. it is Therefore,necessary to it enhance is necessary the efficiency to enhance of heat the efficiencytransfer by of introducing heat transfer a designed by introducing injector a system designed to close injector the distancesystem to between close the the distance injector between nozzle theand injector molten nozzle steel. Figure and molten 2b shows steel. the Figure design2b shows of the thenew design injector of systemthe new to injector differentiate system the to injectio differentiaten angle the by injection separating angle the by lance separating (40°) and the burner lance (40(25°)◦) androles. burner Separated (25◦) nozzlesroles. Separated were installed nozzles at werethe protruding installed at water-cooled the protruding jacket water-cooled to enable jacketthe injection to enable of the injectionoxy-fuel offlame the andoxy-fuel oxygen flame jet with and oxygendifferent jet angles, with different as as angles, closer asjetwell distances. as closer The jet oxy-fuel distances. burner The has oxy-fuel two lines burner for supplyinghas two lines oxygen for supplying and NG and oxygen the lance and NGhas anda single the lanceoxygen has supply a single line. oxygen This new supply jet allowed line. This a newshorter jet distanceallowed ato shorter the molten distance steel, to theas compared molten steel, to asthe compared conventional to the jet, conventional allowing an jet, increase allowing in anthe increase chemical in energythe chemical usage energyand production usage and efficiencies production in efficienciesEAFs. in EAFs.

(a) (b)

Figure 2. ModificationModification schemes schemes of of the the side-wall side-wall injector injector system: system: (a (a) )conventional conventional system; system; (b (b) )new new system. system.

Processes 2020, 8, 1202 5 of 10 Processes 2020, 8, x FOR PEER REVIEW 5 of 10

2.2. Flame Test of the Oxy-Fuel BurnerBurner andand ThermalThermal//MechanicalMechanical AnalysisAnalysis of of Protruding Protruding Water-Cooled Water-Cooled Copper CopperJacket for Jacket the Side-Wallfor the Side-Wall Injector Injector System System To minimize the the system system modification modification costs, costs, the the existing existing oxygen oxygen and and NG NGsupply supply lines lines for the for oxy- the fueloxy-fuel burner burner and andoxygen oxygen lance lance have have been been used used wi withoutthout additional additional lines. lines. The The new new modified modified oxy-fuel oxy-fuel burner, as shown shown in in Figure Figure 2,2, has only only one one suppl supplyy line line for for oxygen oxygen in in the the nozzle. nozzle. This This damages damages the oxy-fuelthe oxy-fuel flame flame formation formation and andhence hence degrades degrades the pe therformance performance of the of oxy-fuel the oxy-fuel burner. burner. Therefore, Therefore, the designthe design of the of theburner burner nozzle nozzle was was optimized. optimized. The The nu numbermber of of nozzle nozzle holes holes was was modified modified from from 6 6 to 12 to enhance the mixing performance of NG and oxygen. The effect effect of the nozzle configurationconfiguration of the oxy-fuel burnerburner on on the the flame flame performance performance was was tested. test Ined. this In flamethis flame test, the test, burner the burner nozzle wasnozzle selected was selectedby comparing by comparing conventional conventional oxy-fuel oxy-fuel burner and burner new and modified new modified burner flames. burner flames. EAFs operate at high thermal and mechanicalmechanical loads. The protruding water-cooled jacket must have sufficient sufficient strength to withstand collisions with falling heavy scraps. The scrap is charged during the EAF process and the cooling performance of the jacketjacket at high temperatures must be maintained efficiently.efficiently. Figure3 3 shows shows thethe flameflame photosphotos obtainedobtained withwith andand withoutwithout damagedamage toto thethe coolingcooling jacketjacket surface. InIn FigureFigure3a, 3a, flames flames generated generated at the at oxy-fuel the oxy-fuel burner burner nozzle nozzle and cracked and surfacecracked by surface a damaged by a damagedcooling jacket cooling are jacket shown are and shown this damageand this isdamage attributed is attributed to the weight to the of weight the scraps of the and scraps material and materialsoftening softening at the EAF at operatingthe EAF operating temperature. temperat Evenure. though Even the though amount the ofamount NG and of oxygenNG and supplied oxygen suppliedto the burner to the was burner the same was inthe both same cases, in both the oxy-fuel cases, the combustion oxy-fuel combustion flame in Figure flame3a isin smaller Figure than3a is smallerthat in Figure than that3b. in The Figure heat of3b. oxy-fuel The heat combustion of oxy-fuel willcombustion be distributed will be bydistributed generating by junk generating flames junk and flamesthus there and is thus an inetherefficient is an chemicalinefficient to chemical thermal energyto thermal conversion. energy conversion. The junk flames The junk caused flames by caused system bydamage system are damage not favorable are not for favorable the EAF refiningfor the EAF process refining as compared process toas the compared undamaged to the oxy-fuel undamaged flame, oxy-fuelas shown flame, in Figure as shown3b. in Figure 3b.

(a) (b)

Figure 3. Oxy-fuelOxy-fuel combustion combustion flames flames of ofthe the burner burner installed installed at protruding at protruding water-cooled water-cooled box: box: (a) (flamesa) flames generated generated at atoxy-fuel oxy-fuel burner burner nozzle nozzle and and cracked cracked surface surface with with system system damage; damage; ( (bb)) observed flameflame without system damage.

In this context, context, computational computational fluid fluid dynamics simulations were carried out using the the commercial commercial simulation programprogram ANSYS ANSYS to to better better understand understand the the temperature temperature and and stress stress distribution distribution on the on jacket. the Thejacket. eff Theects effects of the ribof the height rib height and thickness and thickness of the of protruding the protruding water-cooled water-co boxoled onbox the on thermal the thermal and andmechanical mechanical characteristics characteristics were were evaluated. evaluated. This canThis help can designhelp design the protruding the protruding water-cooled water-cooled jacket withjacket high with durability high durability and without and without any damage any damage due to due scraps to scraps charged charged in the EAF.in the EAF.

2.3. Evaluation of EAF Performance Before and After System Modification The melting experiments were tested in a real-scale EAF at Hyundai Steel Incheon works, with a nominal capacity of 120 t per charge and a three- current supply from a 95 MVA transformer.

Processes 2020, 8, 1202 6 of 10

2.3. Evaluation of EAF Performance Before and After System Modification ProcessesThe 2020 melting, 8, x FOR experiments PEER REVIEW were tested in a real-scale EAF at Hyundai Steel Incheon works, with6 of 10 a nominal capacity of 120 t per charge and a three-phase current supply from a 95 MVA transformer. The furnacefurnace hashas a a diameter diameter of approximatelyof approximately 6 m 6 and m isand equipped is equipped with three with side-wall three side-wall box-type box-type systems, systems,including including an oxygen an lance,oxygen oxy-fuel lance, oxy-fuel burner, andburner, carbon and injector. carbon injector. Performance Performance parameters, parameters, such as 3 3 suchelectric as powerelectric (kWh power/t), (kWh/t), oxygen consumptionoxygen consumption (Nm3/t), NG(Nm consumption/t), NG consumption (Nm3/t), carbon(Nm /t), injection carbon injection(kg/t), POT (kg/t), (min), POT TTT (min), (min), TTT product (min), rate product (t/h), and rate cost (t/h), savings and (USD cost/ yr),saving haves been(USD/yr), evaluated have bybeen the evaluatedconventional by the injector conventional system (before) injector and system the new(before) injector and systemthe new (after). injector system (after).

3.3. Results Results and and Discussion Discussion

3.1.3.1. Flame Flame Characteristics Characteristics of of the the Developed Developed Oxy-Fuel Oxy-Fuel Burner Burner FigureFigure 44 showsshows thethe oxy-fueloxy-fuel burnerburner flameflame tests.tests. AA photographphotograph ofof thethe experimentalexperimental testtest rigrig withwith burnerburner and and fluid fluid supply lines lines for for fuel fuel and and oxygen is is shown in in Figure 44a.a. TheThe nozzlenozzle andand flameflame configurationsconfigurations ofof the the conventional conventional and and newly newly designed designed jets are jets shown are shown in Figure in4 b.Figure Case A14b. represents Case A1 representsthe conventional the conventional burner with burner three supplywith three lines su beforepply modification.lines before modification. Cases A2 and Cases A3 represent A2 and theA3 representinitial and the final initial burner and models final withburner two models supply with lines, two respectively. supply lines, Even respectively. though the size Even and though area of the the sizenozzle and hole area changed of the nozzle according hole to changed the variation according in cases to the A1–A3, variation the entire in cases area A1–A3, remained the the entire same area for remainedeach case, the in termssame offor the each fuel case, and in oxygen terms of nozzles. the fuel The and initial oxygen model nozzles. (case The A2) initial can be model conceptualized (case A2) canmost be easily conceptualized as only the auxiliarymost easily oxygen as only is removedthe auxiliary from oxygen the existing is removed burner (casefrom A1).the existing The purpose burner of (casethe initial A1). The model purpose is to identify of the initial the characteristics model is to identify of a single the oxygencharacteristics nozzle andof a single set the oxygen burner nozzle design anddirection. set the The burner flame design in case direction. A1 showed The a flame strong in elliptical case A1 configuration showed a strong in the elliptical center and configuration it can be seen in thethat center NG does and not it can diff usebe seen into that the surroundingsNG does not duediffuse to the into presence the surroundings of the auxiliary due to oxygen. the presence However, of theit can auxiliary be seen oxygen. that the However, flame in case it can A2 be (as seen shown that inthe the flame dotted in case box) A2 is strongly(as shown formed in the atdotted the center, box) iswith strongly a blue formed flame, owingat the center, to the bulkwith oxygena blue flam supplied.e, owing Moreover, to the bulk the oxygen flame forms supplied. with Moreover, a yellow band the flamedue to forms the combustion with a yellow reaction band of thedue surrounding to the combustion air with reaction NG. Therefore, of the thesurrounding initial model airis with expected NG. Therefore,to show a lowthe initial combustion model e isffi expectedciency as to a largeshow amount a low combustion of NG does efficiency not participate as a large in combustion amount of NG and doesdiffuses not into participate the surroundings; in combustion thus, and the mixingdiffuses of in NGto andthe surroundings; oxygen is an important thus, the nozzlemixing design of NG factor and oxygenfor suitable is an oxy-fuel important combustion. nozzle design factor for suitable oxy-fuel combustion.

(a) (b)

FigureFigure 4. 4. Oxy-fuelOxy-fuel burner burner flame flame tests: tests: ( (aa)) photo photo of of flame flame test test rig; rig; ( (bb)) flame flame photos photos with with different different types types ofof burner burner nozzle configuration. configuration.

ToTo improve the mixing of NG and and oxygen oxygen for for ox oxy-fuely-fuel combustion, combustion, the the final final model model was was designed designed with a 12-hole nozzle for fuel and oxygen supply. In addition, the holes for supplying both NG and oxygenoxygen were locatedlocated at at the the edge edge of of the the nozzle nozzle to increaseto increase the widththe width of the of flame. the flame. In Figure In Figure3b, the 3b, flames the flames in case A3 seem to be the most stable and active combustion reaction among cases A1–A3. The flame width—in particular just behind the nozzle—increased in comparison with that in other cases due to the increasing nozzle diameter of the fuel and oxygen. Considering the scrap melting operational characteristics of the oxy-fuel burner in EAFs at high temperatures, the burner must incorporate a water-cooling jacket. In addition, it must be designed to separate the NG and oxygen

Processes 2020, 8, 1202 7 of 10 in case A3 seem to be the most stable and active combustion reaction among cases A1–A3. The flame width—in particular just behind the nozzle—increased in comparison with that in other cases due to the increasing nozzle diameter of the fuel and oxygen. Considering the scrap melting operational characteristics of the oxy-fuel burner in EAFs at high temperatures, the burner must incorporate a water-cooling jacket. In addition, it must be designed to separate the NG and oxygen nozzle parts for maintenance. Therefore, the final burner model was designed to facilitate cooling, water circulation, and repair.

3.2. Thermal and Mechanical Characteristics of the Developed Protruding Water-Cooled Copper Jacket Figure5 shows the analysis of the jacket with di fferent rib heights and thicknesses. For the simulation conditions, a static load of 15 t of charging scraps and cooling water inside the water-cooling jacket, with a temperature of 30 ◦C, were set at an external temperature of 1000 ◦C, as shown in Figure5a. Case B1 represents the initial model, with a rib height and thickness of 30 and 20 mm, respectively. Cases B2 and B3 represent at comparable model, with a 40 mm height and 20 mm thickness, and the final model, with a 30 mm height and 30 mm thickness. As shown in Figure5b,c, a higher protruding jacket rib height, corresponds to reduced cooling performance. However, the equivalent (von Mises) stress was reduced and the temperature was relatively low when the thickness of the rib was high, i.e., lower height and thicker rib of the protruding jacket result in a better load stress and cooling capacity. The final model, case B3, exhibited the superior thermal and mechanical characteristics among the three cases. The maximum stress and temperature were approximately 383 MPa and 92 ◦C, respectively.

3.3. Improvement of EAF Performance Before and After System Modification The EAF performance was evaluated using a newly designed side-wall injector system consisting of an oxy-fuel burner, oxygen lance, and carbon injector, mounted on the developed protruding water-cooled jacket, as shown in Figure6. The jets have two di fferent operational modes: the oxy-fuel burner and oxygen lance mode, both of which cause chemical exothermic reactions. The oxy-fuel burner operates during periods of scrap charging and melting. The oxygen lance follows the burner mode in the order of operation during the refining periods. In the present EAF performance test, 304 charges were performed for 17 days before system modification and 155 chargers were performed for 9 days after system modification. The operating results before and after the installation of the new system are summarized in Table2. To evaluate the economic advantages, Figure7 shows the di fferences between pre- and post-modification in terms of key values, such as production rate, TTT, POT, and consumption of electric energy, oxygen, NG, and carbon. The benefits are a 0.8 min reduction in POT and 5 kWh/t in power savings. The oxygen jet efficiency increases because of the relatively short distance between the jet nozzle and molten steel by the protruding side-wall injection and its ability to use the optimal injection angle of the oxy-fuel burner flame to efficiently melt scraps after modifying the system. However, the consumption of oxygen and NG increased by 2.5 Nm3/t and 0.2 Nm3/t, respectively. Half of the oxygen consumption was used to prevent clogging of the nozzle due to scattering from the molten steel when injecting the burner and oxygen while approaching the molten steel. Consequently, the total conversion cost was reduced by 0.298 USD/t and productivity increased by 3.1 t/h. Processes 2020, 8, x FOR PEER REVIEW 7 of 10 nozzle parts for maintenance. Therefore, the final burner model was designed to facilitate cooling, water circulation, and repair.

3.2. Thermal and Mechanical Characteristics of the Developed Protruding Water-Cooled Copper Jacket Figure 5 shows the analysis of the jacket with different rib heights and thicknesses. For the simulation conditions, a static load of 15 t of charging scraps and cooling water inside the water- cooling jacket, with a temperature of 30 °C, were set at an external temperature of 1000 °C, as shown in Figure 5a. Case B1 represents the initial model, with a rib height and thickness of 30 and 20 mm, respectively. Cases B2 and B3 represent at comparable model, with a 40 mm height and 20 mm thickness, and the final model, with a 30 mm height and 30 mm thickness. As shown in Figure 5b,c, a higher protruding jacket rib height, corresponds to reduced cooling performance. However, the equivalent (von Mises) stress was reduced and the temperature was relatively low when the thickness of the rib was high, i.e., lower height and thicker rib of the protruding jacket result in a better load stress and cooling capacity. The final model, case B3, exhibited the superior thermal and mechanical characteristicsProcesses 2020, 8, 1202 among the three cases. The maximum stress and temperature were approximately8 of383 10 MPa and 92 °C, respectively.

(a)

(b)

Processes 2020, 8, x FOR PEER REVIEW 8 of 10

3.3. Improvement of EAF Performance Before and After System Modification The EAF performance was evaluated using a newly designed side-wall injector system consisting of an oxy-fuel burner, oxygen lance, and carbon injector, mounted on the developed protruding water-cooled jacket, as shown in Figure 6. The jets have two different operational modes: the oxy-fuel burner and oxygen lance mode, both of which cause chemical exothermic reactions. The oxy-fuel burner operates during periods of scrap(c charging) and melting. The oxygen lance follows the burnerFigureFigure mode 5. 5. AnalysisAnalysis in the orderof of protruding protruding of operation water-cooled water-cooled during box boxthe for forrefining th thee side-wall side-wall periods. injector injector In the system system present with with EAF different diff erentperformance rib rib test,heightheight 304 charges and and thickness: thickness: were ( (aperformeda)) analysis analysis condition condition for 17 daysand and case; case;before ( (bb)) distribution distributionsystem modification of of equivalent equivalent and (von (von 155 Mises) Mises) chargers stress; stress; were performed((cc)) temperature temperature for 9 days distribution. distribution. after system modification.

FigureFigure 6.6. DevelopedDeveloped protruding protruding water-cooled water-cooled jacket jacket instal installedled at the atEAF the wall EAF with wall different with operating different operatingmodes. modes.

The operating results before and after the installation of the new system are summarized in Table 2. To evaluate the economic advantages, Figure 7 shows the differences between pre- and post-modification in terms of key values, such as production rate, TTT, POT, and consumption of electric energy, oxygen, NG, and carbon. The benefits are a 0.8 min reduction in POT and 5 kWh/t in power savings. The oxygen jet efficiency increases because of the relatively short distance between the jet nozzle and molten steel by the protruding side-wall injection and its ability to use the optimal injection angle of the oxy-fuel burner flame to efficiently melt scraps after modifying the system. However, the consumption of oxygen and NG increased by 2.5 Nm3/t and 0.2 Nm3/t, respectively. Half of the oxygen consumption was used to prevent clogging of the nozzle due to scattering from the molten steel when injecting the burner and oxygen while approaching the molten steel. Consequently, the total conversion cost was reduced by 0.298 USD/t and productivity increased by 3.1 t/h.

Table 2. Overview of EAF performance before and after system modifications.

Item Before After Difference Cost [USD/t] Production [t] 37,945 19,437 Charge number during the test (time, day) 304 (17) 155 (9) Electrical consumption [kWh/t] 396.2 391.2 -5 -0.41 Oxygen consumption [Nm3/t] 18.8 21.3 +2.5 +0.2 Natural gas consumption [Nm3/t] 0.2 0.4 +0.2 +0.072 Carbon consumption [kg/t] 11.4 10.3 -1.1 -0.16 Power-on time [min] 49.2 48.4 -0.8 Tap-to-tap time [min] 62.4 61.1 -1.3 Productivity [t/h] 120 123.1 +3.1 Total energy cost savings [USD/t] 0.298 Annual production [t/yr] 774,908 Annual cost savings [USD/yr] 224,329

Processes 2020, 8, 1202 9 of 10

Table 2. Overview of EAF performance before and after system modifications.

Item Before After Difference Cost [USD/t] Production [t] 37,945 19,437 Charge number during the test (time, day) 304 (17) 155 (9) Electrical consumption [kWh/t] 396.2 391.2 -5 -0.41 Oxygen consumption [Nm3/t] 18.8 21.3 +2.5 +0.2 Natural gas consumption [Nm3/t] 0.2 0.4 +0.2 +0.072 Carbon consumption [kg/t] 11.4 10.3 -1.1 -0.16 Power-on time [min] 49.2 48.4 -0.8 Tap-to-tap time [min] 62.4 61.1 -1.3 Productivity [t/h] 120 123.1 +3.1 Total energy cost savings [USD/t] 0.298 Annual production [t/yr] 774,908 Processes 2020, 8,Annual x FOR PEER cost REVIEW savings [USD/yr] 224,329 9 of 10

Figure 7. Differences in electricity, oxygen, natural gas, carbon, power-on-time, tap-to-tap time, and Figure 7. Differences in electricity, oxygen, natural gas, carbon, power-on-time, tap-to-tap time, and productivity before and after system modification. productivity before and after system modification. 4. Conclusions 4. Conclusions In order to save electrical power in EAF operations, a side-wall injector system featuring an oxy-fuelIn order burner to andsave oxygen electrical lance power has beenin EAF developed. operations, The a side-wall protruding injector water-cooled system copperfeaturing jacket an oxy- was designed,fuel burner based and onoxygen thermal lance and has mechanical been developed. analysis, The to closeprotruding the distance water-c betweenooled copper the jet nozzlejacket was and moltendesigned, steel, based but on also thermal to separate and themechanical burner and analysis lance, separatelyto close the with distance different between jet angles. the jet Any nozzle damage and suchmolten as surfacesteel, but cracks also by to charging separate scraps the burner was not an observedd lance in separately the developed with cooling different jacket. jet angles. The oxy-fuel Any burnerdamage nozzle such as was surface designed cracks through by charging various scraps flame testswas fornot di observedfferent nozzle in the geometries. developed Thecooling developed jacket. burnerThe oxy-fuel was operatedburner nozzle properly was designed without degrading through va therious flame flame performance tests for different in comparison nozzle geometries. with the conventionalThe developed one. burner was operated properly without degrading the flame performance in comparisonFor the with overall the conventional performance one. of energy efficiency and productivity before and after system modification,For the overall the electrical performance energy consumptionof energy efficien wascy reduced and productivity by 5 kWh/t andbefore the and productivity after system was increasedmodification, by 3.1the t /electricalh. Thus, theenergy total consumption energy cost savings was reduced calculated by 5 bykWh/t the consumptionand the productivity of electricity, was oxygen,increased NG, by 3.1 and t/h. carbon Thus, achieved the total byenergy 0.298 cost USD savi/t. Thengs annualcalculated cost by savings the consumption of the EAF of in electricity, this study wereoxygen, approximately NG, and carbon 224,329 achieved USD/yr. by 0.298 USD/t. The annual cost savings of the EAF in this study were approximately 224,329 USD/yr. Author Contributions: Conceptualization, J.K.; methodology, C.O.; validation, D.J.; investigation, B.J.; dataAuthor curation, Contributions: S.L. (Seongjae Conceptualization, Lee); writing—original J.K.; methodology, draft preparation, C.O.; validation, Y.S.; writing—review D.J.; investigation, and B.J.; editing, data Y.S.;curation, supervision, S.L. (Seongjae K.H.; project Lee); writing—original administration, S.L. draft (Sangyoun preparation, Lee). Y.S.; All authorswriting—review have read and agreedediting, to Y.S.; the published version of the manuscript. supervision, K.H.; project administration, S.L. (Sangyoun Lee). All authors have read and agreed to the Funding: This work was supported by the development fund foundation, Gyeongsang National University, 2019; published version of the manuscript. and this study was partly supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) andFunding: the Ministry This work of Trade, was supported Industry & by Energy the development (MOTIE) of the fund Republic foundation, of Korea Gy (Granteongsang No. National 20172010106310). University, Conflicts2019; and ofthis Interest: study wasThe partly authors supported declare noby conflictthe Korea of Institute interest. of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) of the Republic of Korea (Grant No. 20172010106310).

Conflicts of Interest: The authors declare no conflicts of interest.

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