Waste Heat Recovery for EAF — Innovative Concepts and Industrial Implementation

56 Technical Article

Authors The development of a waste heat recovery plant requires extensive knowledge as well as long A. Fleischanderl experience of the entire plant. Primetals provides waste heat recovery solutions for EAFs, some of technology officer upstream, which are presented in this article. A waste heat recovery plant is introduced, which was installed Primetals Technologies Austria in Italy. Waste heat is used to produce steam for two pickling lines, which are a large distance GmbH, Linz, Austria [email protected] from the EAF. The substitution of the existing gas-fired boilers led to a decisive reduction of operating costs of the steel plant. A heat recovery plant was installed at a steel plant in Sweden, T. Steinparzer where hot water at high pressure is produced and utilized for the local district heating system. head of technology and innovation ECO solutions, Primetals The implementation of waste heat recovery systems for EAFs will be presented in detail, and Technologies Austria GmbH, operational results achieved will be discussed. Linz, Austria [email protected]

P. Trunner n recent years, waste heat recov- decreased and the global steel indus- process engineer waste heat ery in the steel industry has try is dealing with overproduction. recovery, Primetals Technologies I Austria GmbH, Linz, Austria attracted more and more attention. Therefore, steel plant operators are [email protected] Environmental regulations, public forced to reduce production costs funding, as well as required revamps and to optimize their steelmaking of old dedusting systems lead steel processes. plant operators to discuss and to Furthermore, due to growing evaluate possibilities of recovering environmental consciousness and waste heat. tightened emission control by The development of a waste heat authorities, environmental technol- recovery plant requires extensive ogies and energy efficiency have knowledge as well as long experi- become more and more in the focus ence of the entire plant, including of steel plant operators. water-steam cycle as well as the elec- Energy is one of the most impor- tric arc furnace (EAF) process and tant cost factors for integrated iron dedusting system. Innovative waste and steel plants as well as for elec- heat recovery solutions are intro- tric steel mills.1 The vast amount duced and discussed in this article. of electric energy in electric steel Another challenge for waste heat plants forces operators to improve recovery at EAF plants is to identify the overall energy situation, in order a possible utilization for the recov- to reduce the specific costs per ton ered energy. Thus, possible applica- of steel and also to comply with legal tions for a heat consumer inside or requirements in terms of energy outside the steel plant are discussed. efficiency. Industrial implementations of There are various opportuni- waste heat recovery plants are pre- ties along the steelmaking route sented to demonstrate economic for implementing energy efficiency and reliable utilization of EAF waste measures. AIST.ORG

I heat for different applications. Smaller improvements can be implemented in terms of process optimization. The identification of Introduction improvements requires a survey of the existing installations and elabo- In recent decades, global steel pro- ration of the individual improve- duction has increased continuously, ments in terms of feasibility, reliabil- IRON & STEEL TECHNOLOGY

I driven by the big demand of grow- ity, as well as cost-benefit considering markets and economic expan- ations. Such measures can be done

JAN 2018 sion. Nowadays, steel demand has with low or moderate effort. 57

Figure 1

Typical measures to reduce energy consumption.

However, for a more decisive impact on the energy This means the energy consumption per ton of the balance of a steel plant, bigger actions are required. final steel product is mainly caused by the EAF. By recovering waste heat, a large amount of offgas In Fig. 2, the energy balance of a typical scrap- energy can be utilized within the steel plant, leading based furnace is given. It is shown that about 50% of to a significant reduction of energy costs. The largest the required energy input is provided by electricity via amount of waste heat within electric steel mills can be the electrode. The residual energy is mainly related found at electric arc furnaces, where approximately to exothermic chemical reactions in the steel bath. 30% of the total energy input is emitted in the offgas. Additional energy input is provided by gas burners The economic feasibility of an EAF waste heat recov- in the furnace. Depending on the EAF operation ery solution is mainly driven by the type of waste heat and input materials, approximately 30% of the total utilization. Therefore, the waste heat utilization has energy input is dissipated to the offgas. to be a major focus during project development. In the following, economically feasible solutions will be presented even though the price of electric energy is low Figure 2 in current markets. JAN 2018

Waste Heat Recovery Solutions I

IRON & STEEL TECHNOLOGY

Waste Heat Potential of EAF — In most electric steelmaking plants, the EAF is the main metallurgical unit for steelmaking, since it is used for melting and refining of the raw materials. Also, considering I the energy balance of electric steel plants AIST.ORG (mini-mills), the EAF is the biggest energy Energy balance (Sankey diagram) of a scrap-based electric arc furnace consumer along the steelmaking route. (EAF). 58 JAN 2018 I IRON & STEEL TECHNOLOGY I AIST.ORG Eventually the offgas is emitted via the stack at tem stack the via emitted is offgas the Eventually Even if the —Even the if EAF for Systems Recovery Heat Waste Energy flow along offgas system. offgas along flow Energy Technical Article Due to the dynamic operation of the EAF process, as as process, EAF of the operation dynamic the to Due well as idle periods of the furnace, the offgas param offgas the furnace, of the periods idle well as waste heat potential is high enough, there are several enough, several high is are there heat potential waste Fig. in 3. shown are diagram flow process the well as with the energy input and the charged material in in material charged input the and energy the with that the remaining energy is emitted to the environ the to emitted is energy remaining the that ture is further decreased by dilution with air from from air with bydilution decreased further is ture the gap at the entry of the offgas system to ensure a ensure to system offgas of the entry at the gap the recovery. it state is Thus gas CO of downstream terms (e.g., scrap tion acollapsing from of oil combustion composition. Sudden and temperature of flow, terms bulk) within the furnace do not allow gas recovery in in recovery do gas not allow furnace the within bulk) peratures of approximately 100–130°C. This means means This 100–130°C. of approximately peratures challenges for designing a waste heat recovery plant. plant. heat recovery awaste for designing challenges consumers. require Therefore, output. systems ous heat recovery adiscontinu heat thus supply and continuous waste adis in results intensively. This fluctuating are eters ment. The energy balance along the offgas system as as system offgas the along balance ment. energy The other suction sources before entering the filter plant. plant. filter the before entering sources suction other energy is dissipated to the ambient. Offgas tempera ambient. Offgas the to dissipated is energy of the most cooler. part, this In or aforced-draft cooler of evaporation cooler, atype from be can which melting period of the EAF. of the period melting whole the during complete offgas of the combustion in air of excess amount alarge maintain to art of the produc gas CO and processes combustion occurring a buffer to equalize the heat supply for downstream heat supply for the downstream equalize to a buffer a water-cooled duct, followed by a second-stage gas gas followed duct, byasecond-stage a water-cooled Figure 3 In the offgas system, the offgas is cooled down by cooled down is offgas the system, offgas the In not directly does correspond offgas However, EAF 2 ------A deep understanding of the plant layout, space layout, plant space of the A deep understanding ventional water-cooled hot gas line by a heat recovery byaheat recovery line hot gas water-cooled ventional Depending on the plant situation, a tailor-made solu atailor-made situation, plant on the Depending with dilution air or air from other suction points, the the points, suction other from or air air dilution with tion has to be developed. be to has tion temperatures, the boiler is from a type of bundle heat of bundle atype from is boiler the temperatures, boilers of other industries. Also the high dust content dust high the Also of industries. other boilers plant situation is crucial for the design of the plant. plant. of the for design the crucial is situation plant is consequently used for steam or power or for generation steam used consequently is line followed by a second-stage cooler. After mixing cooler. mixing followed After byasecond-stage line recovery boilers. The maximum offgas temperature temperature offgas maximum The boilers. recovery replaced by a waste heat boiler. Due to lower offgas heat boiler. lower to Due byawaste replaced offgas exceeds the usual offgas temperature of comparable of comparable temperature offgas usual the exceeds ered carefully. offgas is cleaned in the filter and discharged via the the via discharged and filter the in cleaned is offgas of setup the to referred is which system, on amodular plant. heat recovery of awaste for design the mental moderate flow velocities, whereas water and/or water whereas velocities, steam flow moderate at boiler the through ducted is offgas Thus gas. of flue for and cooling energy recoverexchanger to waste the gas are more difficult compared to conventional to compared heat more difficult are gas duct. In this case, the offgas cooling is done with pres done is with cooling offgas the case, this In duct. and the specific gas composition have to be consid be composition have to gas specific the and availability, infrastructure and interfaces is funda is interfaces and infrastructure availability, as shown in Fig. 4, consist of a water-cooled hot gas hot gas Fig. of a water-cooled consist in 4, shown as systems, dedusting State-of-the-art system. a dedusting are flowing inside the tubes. the inside flowing are application. suitable other any stack. stack. surized water at elevated temperatures. The hot water hot The water temperatures. at elevated water surized An integral waste heat recovery approach is based based approach is heat recovery waste integral An steel the issues, above-mentioned the from Apart Alternatively, the second-stage cooler can be be cooler can second-stage the Alternatively, Waste heat can be recovered by replacing the con the recovered be byreplacing heatWaste can Furthermore, the offgas parameters from EAF off EAF from parameters offgas the Furthermore, 3 ------59

Figure 4

EAF dedusting system setup.

Depending on the plant situation, as well as on the Figure 5 operator requirements and downstream heat utilization, a proper waste heat recovery concept will be developed. Thus, either the first stage or the second stage will be incorporated in the heat recovery concept. For maximized heat utilization, the first and second stages can be combined. In Fig. 5, the layout of an EAF dedusting system including waste heat recovery system is shown. Offgas coming from the EAF is routed through the heat recovery duct and the second-stage waste heat boiler before entering the filter. It can be seen that the footprint is similar to conventional dedusting systems. Waste heat recovery system for EAF. Efficiency Increase and Benefits — The above-mentioned considerations show that the main benefit of a waste heat recovery system is the reduction of overall energy consumption. Additionally, there are several other benefits that may apply. The main benefits are: • Inner corrosion: Less inner corrosion in the water tubes occur above 200°C because of self- • Reduction of overall energy consumption: With passivation of the tubes. a heat recovery system, the waste heat is uti- • Operational safety: Heat recovery systems are

lized for a certain application. The savings due designed and operated under high pressure. JAN 2018 to heat recovery helps steel plant operators to Therefore, the design of these systems must be

reduce their operational costs. according to pressure vessel design code. This I

IRON & STEEL TECHNOLOGY • CO2 reduction: Following the trend for indus- leads to the benefit that the design is according trial plants to reduce carbon dioxide foot- the high standard of the code and the risk of print, heat recovery systems help to reduce the failures is minimized.4 demand for fossil energy. • Plant layout: The footprint of a waste heat recov- • Dewpoint corrosion: Higher tube wall tem- ery system is similar to conventional dedust- peratures in the cooling duct reduce the risk ing cooling systems. An additional building is I of sulfur corrosion, since the wall temperature required for the equipment of the plant, such AIST.ORG is above the dewpoint of sulfur-oxides in the as pumps, tanks, heat exchangers, etc. offgas. 60 JAN 2018 I IRON & STEEL TECHNOLOGY I AIST.ORG (organic rankine cycle (ORC) or steam turbine) turbine) or steam (ORC) cycle rankine (organic This section discusses the most important applica important most the discusses section This However, a prerequisite is the availability of a steam of asteam However, availability the is aprerequisite In contrast to integrated iron iron integrated to contrast In

Technical Article Utilization of Recovered trical motors. An alternative technology for produc technology alternative An motors. trical to the low steam demand, electric steel plants often often steel plants electric demand, low steam the to tions for waste heat utilization. for waste tions to an external district heating system. Offgas is cooled is Offgas system. heating district external an to hot water can be used either internally or distributed or distributed either internally used be can hot water hot water parameter. Additionally a storage tank is is tank astorage Additionally parameter. hot water ing chilled water is thermal-driven chillers. A widely Awidely chillers. thermal-driven is water chilled ing byelec driven chillers, doneis bycompression-type plants have only a limited a limited have only plants requires an additional investment, which has asignifi has which investment, additional an requires The simplest simplest —The Heating Production/District Water Hot required, in order to provide acontinuous order output. provide in to required, Energy Energy Usually, chilled water pro water chilled —Usually, Production Water Chilled ers are absorption-type heat pumps. absorption-type are ers steel plants: electric within available cally typi are consumers consumer. steam following The ejectors for vacuum oxygen degassing, VOD). Due degassing, oxygen for vacuum ejectors cant influence on the system’s return on investment. system’s on investment. on the return influence cant method of energy recovery is to use waste heat pro to waste use to is recovery of energy method Steam Generation — Generation Steam duction for comfort and process cooling applications applications cooling process for and duction comfort duction. However, the installation of apower block However,duction. installation the duce hot water for heating purposes. The generated generated The duce purposes. for hot heating water demand for steam (e.g., fordemand steam steam ask for a waste heat recovery system with power pro with system heat recovery for a waste ask and economical possibility for waste heat recovery. for waste possibility economical and required on the depending temperatures, at elevated and steel plants, electric steel electric steel plants, and spread and proven technology for such thermal chill for such thermal proven and spread technology • • • • •

(VD/VOD). Air separation plants. separation Air (e.g., consumer steam seawater External plants degassing for vacuum ejectors Steam and/or lines. pickling Galvanizing Public funding: Waste heat Waste funding: Public industries). is improved with such improved with is since authorities, public by funded cases many in recovery technologies are are technologies recovery measures. footprint environmental and efficiency energy desalination, pulp and paper industry, other other industry, paper and pulp desalination, Production of steam is a simple is of steam Production 5

BROAD air conditioning). (source: unit chiller Compact Figure 6 5 ------Thus, the ORC fluid is pre-heated and evaporated by evaporated and pre-heated is ORC the fluid Thus, This section introduces examples for waste heat recov for waste examples introduces section This EAF and the comparable low comparable water/steam the and parameter EAF ORC unit is shown in Fig. in 7. shown ORC is unit Industrial Implementation Implementation Industrial

Considering the fluctuating heat production of an heat of an production fluctuating the Considering where a refrigerant is used instead of water. to Due instead used is where arefrigerant fluid, working the is turbines conventional steam with energy. electric generate to used be heat can waste the external heat source (in this case hot water) and case (in heat this source external the the most economical means of power generation. means economical most the to 450°C. The purpose of the plant was to examine, examine, to was plant of the purpose The 450°C. to the lower boiling point of the refrigerant, low-temper refrigerant, point of the lowerthe boiling Power Generation With ORC Turbine ORC recovered —The With Generation Power located near the waste heat recovery system. A typical Atypical system. heat recovery waste the near located A pilot plant was installed installed was —Apilot plant Plant Pilot Recovery Heat equipment, is located in a separate building, which is is which building, aseparate in equipment, located is expanded in a specially designed turbine. The ORC The turbine. designed aspecially in expanded of such waste heat recovery systems, ORC turbines are are ORC turbines systems, heat recovery of such waste mixture and is operated at fluid temperatures of up temperatures at fluid operated is and mixture amolten salt with exchanger. operated is plant The applications. for different at EAF systems ery fluid is then recooled in the condenser. the recooled then in is fluid amongst others, the following issues: following the others, amongst ature heat sources can be used for power used generation. be can heat sources ature at a steel plant in Germany, using a bundle heat abundle using Germany, at in asteel plant • • • • The entire turbine unit, including its auxiliary auxiliary its including unit, turbine entire The The main difference of an ORC turbine compared compared ORC of an turbine difference main The Influence of high-temperature corrosion (chlo corrosion of high-temperature Influence dust-laden erosion from of particle Influence high at very materials boiler Testing of various heat exchanger. of bundle Design temperatures. rine corrosion). rine offgas. Organic rankine cycle (ORC) turbine unit. turbine (ORC) cycle rankine Organic Figure 7 6 - - - 61 Figure 8

Waste Heat Recovery With District Heating — As part of a revamp of the dedusting system of the EAF at a steel plant in Sweden, an innovative heat recovery system was installed. Thus, recovered waste heat is used to generate hot water for district heating. The water-cooled hot gas line is operated with pressurized water. Heat recovery pilot plant at a steel plant in Germany. The recovered heat is transferred via heat exchangers to a district heating network and is fed to the nearby city. To equalize fluc- Figure 9 tuations of the EAF and to supply constant heat flow to the heating network, a thermocline-type buffer tank is used.

Steam Generation for Pickling Lines — An innovative waste heat recovery system was installed at the EAF of a steel plant in Italy. For Waste heat recovery with district heating. the new 150-ton EAF, the dedusting system was equipped with a waste heat recovery system. The offgas is cooled with pres- Figure 10 surized water at temperatures of approximately 200°C. The hot water is fed to two different pickling lines at distances of 0.9 and 0.3 miles. However, for hot water feed to the consumer, a distance of 2 miles can be realized. A layout of the piping routing through the entire steel plant is given in Fig. 10. In the case of high heat supply of the EAF, water is fed to the storage tank and to the pickling lines (Fig. 11). During EAF idle times, water is circulated, while water from the storage tank is fed to the pickling lines. In case of no Heat supply to two pickling lines. steam consumption at the pick-

ling lines, the water is cooled via JAN 2018 a heat exchanger, in order to pro- Figure 11

vide continuous EAF operation. I

Steam is generated at the pickling IRON & STEEL TECHNOLOGY lines with a Kettle reboiler heat exchanger (Fig. 12). With the newly installed system, the existing gas boilers are substi- tuted. The overall steam produc- I tion is 17 tons/hour, which leads AIST.ORG to annual savings in natural gas of Heat recovery plant with steam generation for pickling lines. 8.2 million m3. 62 JAN 2018 I IRON & STEEL TECHNOLOGY I AIST.ORG However, acustom plant, heat recovery for awaste where steel plants, and iron integrated to contrast In In times of increasing awareness of energy costs, grow costs, of energy awareness of increasing times In Steam generator at pickling line. pickling at generator Steam Technical Article heat of EAF offgas, energy recovery has become more has recovery energy offgas, heat of EAF ized solution has to be developed, in order to provide order developed, provide in be to to solution has ized plants have only a limited demand for steam. Thus, Thus, for demand steam. alimited have only plants process waste heat. Due to the vast amount of waste of waste amount vast the to Due heat. waste process emis tightening and consciousness environmental ing reducing the overall energy consumption or utilizing or utilizing consumption energy overall the reducing Conclusions Conclusions a lot of steam consumers are available, electric steel electric available, are consumers a lot of steam and more in the focus of interest. focus the moreand in several possible waste heat consumers were discussed. were discussed. heat consumers waste possible several system. heat recovery of awaste design role the sive in sion control, steel plant operators are interested in in interested are sion control, operators steel plant Figure 12 Did You Know? The utilization of the recovered energy plays adeci plays recovered of the energy utilization The (patent pending) and unique rolling parameters provide outstanding workshop properties and performance ofthefinalproducts. (patent pending)anduniquerollingparametersprovideoutstanding workshoppropertiesandperformance ues forhardnessandimpactstrength.SSABM43includesanumber ofinnovationsinsteelproduction.Thechemicalcomposition ness andtoughnessvaluesare58 HRCand25J/cm expensive processing. Sweden’s SSABhasbegunsellinganewtypeofsteelthatcanbequenchedinwater, butdoesn’tneedtobeimmediatelytempered, Shearing, blankingandpiercing canbeexecutedwithoutarisk ofmicrocracking,therebyavoidingmoretime-consumingand SSAB IntroducesWater-Quenchable SteelforReliablePerformanceandEasyQuenching M43 canreach3timeshighertoughness thanamediumalloyedchrome-vanadiumorchrome-molybdenum steel.Typical hard- it hasannounced.CalledM43,thenewgradeoffersahighdegree ofhardnessandimpactstrength,thecompanysaid. friendly process.Itsavesenergyandtimeinproductionreduces CO SSAB M43steelcanbequenchedinplainwaterwithoutanimmediate needfortempering,andstillreachexceptionallyhighval- SSAB M43can be quenchedin water insteadofaqueous quenching fluids or oilforacheaper, saferandmoreenvironmentally Heat treatmentresultsinafullymartensitic,fine-grainmicrostructure withanunmatchedhardnesstotoughnessratio.SSAB For evengreatertoughness,low-temperature temperingisenoughtoreach>30J/cm 2 at+20°C. - - - - 1. 4. waste heat to produce steam for the on-site pickling pickling for on-site heat produce the to steam waste tailor-made solution for a waste heat recovery plant. heat recovery solution for awaste tailor-made tial to reduce the overall energy costs and to create create to and costs energy overall reduce to the tial how innovative waste heat recovery solutions led to a led to solutions heat recovery waste how innovative References layout, a holistic plant view is required to develop to a required is view plant layout, aholistic lines can be an attractive method of heat method utilization. attractive an be can lines reduction of energy demand and hence and demand areduction to of energy reduction offgas conditions, as well as the plant situation and and situation plant the well as as conditions, offgas of specific costs per ton steel. per costs of specific 2. due to the characteristics of the EAF and the specific specific the and EAF of the characteristics due the to 5. 3. additional benefits for steel plant operators. However, for operators. steel plant benefits additional Using heat. waste economican solution for utilizing 6. Waste heat recovery from EAF has a large poten alarge has EAF from heatWaste recovery Industrial plants were introduced to demonstrate demonstrate to were introduced plants Industrial

TURBODEN srl,www.turboden.eu. M. Johnson,R. Argyris and T. McGee, “Iron Ores and Coke Supplies F. Zauner, From “NewDevelopmentsinEfficientEnergyRecovery V. Velikorodov, “TheInfluenceofDedustingontheSpecificElectrical T. Steinparzer, forSteelmakingProcesses “OffgasHeatRecovery P. Trunner, andUtilizationofWaste “IntegratedEnergyRecovery Heat 2009, p.30. Germany, 2015. Storage Systems,” Based onThermalEnergyStorage,”dissertation,2014. Electric Arc FurnaceOffgasbyUsingInnovativeThermalEnergy Energy InputoftheArc Furnace(inGerman),”Ph.D.thesis,2009, p. 48. for the German Steel Industry,” for IntegratedPlantsandEAFRoute,” 2 emissions. Conference Proceedings. Conference andExposition,Nashville,Tenn., USA,andpublishedinthe This paperwaspresentedatAISTech 2017—TheIron&SteelTechnology 2 10th EEC Conference Graz, Conference EEC 10th withhardnessstillatalevelof56 HRC. Int. J. Machine Tool Res., Tool Machine J. Int. ESTAD Conference, Conference, ESTAD 2012. Düsseldorf, Düsseldorf, 25–50, F -