RFCS project OSCANEAF

On-line slag composition analysis for electric arc furnaces

Summary

Elec­tric steel­ma­king has fast gai­ned ground in deve­lo­ped count­ries due to redu­ced CO₂ emis­si­ons com­pared to blast fur­nace steel­ma­king and bet­ter pro­duc­tion fle­xi­bi­li­ty. Due to increased scrap usa­ge, the qua­li­ty of the scrap is get­ting worse and worse. This is reflec­ted in the increase of non-metal­lic mate­ri­al in the scrap. Fluc­tua­tions in EAF scrap char­ge com­po­si­ti­on cau­ses signi­fi­cant fluc­tua­tions in the EAF slag com­po­si­ti­on, sin­ce the non-metal­lic mate­ri­al in the scrap accu­mu­la­tes in the slag.
Fluc­tua­ti­on of slag com­po­si­ti­on cau­ses many chal­lenges in EAF steel­ma­king. In stain­less steel­ma­king one of the most important goals in EAF is to keep the chro­mi­um con­tent of the slag low, sin­ce it cau­ses cos­ts due to increased alloy­ing addi­ti­ons and pro­blems in recy­cling of slag. In car­bon steel­ma­king it is important to ensu­re foa­ming slag con­di­ti­ons, which increa­ses ener­gy effi­ci­en­cy of the EAF. Due to the slag com­po­si­ti­on fluc­tua­tions the slag foa­ming is some­ti­mes hin­de­red when the slag com­po­si­ti­on drifts to the com­po­si­ti­on area with low foamability.
The­re are curr­ent­ly very few methods available for ana­ly­sing slag com­po­si­ti­on in EAF. One of the most popu­lar methods to gain infor­ma­ti­on of slag com­po­si­ti­on is taking slag samples and ana­ly­sing them in labo­ra­to­ry. Curr­ent­ly, the­re is no method available to ana­ly­se slag com­po­si­ti­on in indus­tri­al EAFs on-line.
The objec­ti­ve of the pro­ject is the deve­lo­p­ment of a con­ti­nuous mea­su­re­ment sys­tem for EAF slag com­po­nent ana­ly­sis based on opti­cal emis­si­on spec­tro­sco­py. The aim for stain­less steel gra­des is the ana­ly­sis of Cr₂O₃ and MnO con­tent, while for car­bon steel gra­des the aim is to ana­ly­se CaO, SiO₂, Al₂O₃ and MgO con­tent of the slag. The pro­po­sed tech­no­lo­gy will fol­low the­se criteria:

• remo­te and con­ti­nuous mea­su­re­ment sys­tem for slag com­po­nent analysis,
• low main­ten­an­ce sys­tem design,
• opti­mi­zed ope­ra­ting prac­ti­ces based on con­ti­nuous slag com­po­si­ti­on data incre­asing resour­ce and ener­gy efficiency.

This pro­ject aims to deve­lop a tech­no­lo­gy, which enables the online ana­ly­sis of elec­tric arc fur­nace and lad­le fur­nace slag com­po­si­ti­on in EAF steel­ma­king. Curr­ent­ly the­re is no method available to ana­ly­se slag com­po­si­ti­on online in indus­tri­al elec­tric arc fur­naces in Euro­pean or world­wi­de level. Bet­ter under­stan­ding of slag com­po­si­ti­on allows bet­ter con­trol of the Cr₂O₃ con­tent in stain­less steel­ma­king, which redu­ces alloy­ing and addi­ti­on mate­ri­al cos­ts. In car­bon steel­ma­king the infor­ma­ti­on of online slag com­po­si­ti­on makes it pos­si­ble to opti­mi­se the slag com­po­si­ti­on in order to redu­ce metal los­ses, slag amount and refrac­to­ry wear. Addi­tio­nal infor­ma­ti­on on scrap mel­ting and slag for­ma­ti­on enables the bet­ter timing of car­bon injec­tion and increa­ses ener­gy efficiency.

Results achieved so far

In the first half of the pro­ject the acti­vi­ties were focu­sed on the labo­ra­to­ry and pilot sca­le test­ing. The aim of the­se work packa­ges was to pro­vi­de fun­da­men­tal under­stan­ding of arc emis­si­on spec­tra, defi­ne the opti­mal mea­su­re­ment sys­tem for indus­tri­al sca­le mea­su­re­ments and pro­vi­de gui­de­lines for cor­rect mea­su­re­ment posi­ti­on and mea­su­re­ment prac­ti­ce for indus­tri­al sca­le. A preli­mi­na­ry result of the inves­ti­ga­ti­ons in labo­ra­to­ry and pilot sca­le is that the main slag con­sti­tu­ents CaO, SiO₂, Al₂O₃, MgO and Cr₂O₃ can be mea­su­red with the new sys­tem with an avera­ge abso­lu­te accu­ra­cy bet­ween 0.1 and 1.9 wt-%. The accu­ra­cy esti­ma­te is preli­mi­na­ry and sub­ject to chan­ge. The hard­ware and soft­ware deve­lo­p­ment first lead to the ear­ly pro­to­ty­pe used in labo­ra­to­ry and pilot sca­le and for a very first instal­la­ti­on at a lad­le fur­nace. This ear­ly pro­to­ty­pe was desi­gned to be loca­ted so that it would not be sub­jec­ted to extre­me tem­pe­ra­tures and slag spray. The fol­lo­wing design and deve­lo­p­ment work on the advan­ced pro­to­ty­pe was con­duc­ted with the aim of using the pro­to­ty­pe to per­form the first indus­tri­al test­ing at an EAF. The advan­ced pro­to­ty­pe and espe­ci­al­ly the mea­su­re­ment head was rede­si­gned to with­stand extre­me tem­pe­ra­tures and slag spray, among­st other things by inte­gra­ting an acti­ve slag rem­oval system.

The indus­tri­al test­ing at the lad­le fur­nace star­ted with a first instal­la­ti­on of the ear­ly pro­to­ty­pe at an LF. Mea­su­re­ment data was recor­ded for a peri­od of six weeks, but unfort­u­na­te­ly the qua­li­ty of the mea­su­red spec­tra was not opti­mal. Only one of the three spec­tro­me­ters mea­su­red good qua­li­ty data. Indus­tri­al test­ing at the EAF for stain­less steel gra­des has been pre­pared by plan­ning of the EAF fur­nace roof adjus­t­ments nee­ded at the par­ti­ci­pa­ting steel plants for the instal­la­ti­on of the mea­su­re­ment sys­tem. Instal­la­ti­on of the modi­fied roof/roof ele­ments is delay­ed. The work on Indus­tri­al test­ing at the EAF for car­bon steel gra­des is plan­ned to start after the end of the first half of the pro­ject as scheduled.

Publications

Pau­na, H.; Will­ms, T.; Aula, M.; Ech­ter­hof, T.; Fabri­ti­us, T.: Pro­s­pects of Plas­ma Ana­ly­sis for Elec­tric Arc Fur­naces, 7th Inter­na­tio­nal Con­gress on Sci­ence and Tech­no­lo­gy of Steel­ma­king – ICS 2018, 13.–15. June 2018, Venice, Italy

Will­ms, T.; Ech­ter­hof, T.; Pfei­fer, H.; Aula, M.; Fabri­ti­us, T.; Anders­son, N.; Til­li­an­der, A.; Jöns­son, P.; Joki­nen, M.; Puuk­ko, E.; Prasch­ko, S.; Klung, J.-S.: On-line slag com­po­si­ti­on ana­ly­sis for elec­tric arc fur­naces — Sta­te of the Art (SoA), Pro­ject report, 29.09.2016

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This pro­ject recei­ves fun­ding from the Rese­arch Fund for Coal and Steel under grant agree­ment No 709923.