FlexLadleHeat: Flexible use of hydrogen and ammonia in ladle furnaces in the steel industry to reduce CO₂ emissions

Lad­les are used in the elec­tric steel rou­te to trans­port mol­ten steel bet­ween the elec­tric arc fur­nace, the secon­da­ry metall­ur­gy and the cas­ting plant. The lad­les, con­sis­ting of a cru­ci­b­le-shaped steel struc­tu­re, are lined with refrac­to­ry mate­ri­als for ther­mal insu­la­ti­on. The refrac­to­ry is sub­ject to con­ti­nuous ther­mal stress during ope­ra­ti­on and is worn away and worn out in the pro­cess. For this reason, the refrac­to­ry is regu­lar­ly reli­ned. After reli­ning, the refrac­to­ry mate­ri­al must be dried and pre­hea­ted befo­re being used with mol­ten steel. This dry­ing and pre­hea­ting pro­cess takes place in the lad­le manage­ment system.

Trans­port ladle

In the lad­le manage­ment sys­tem, hori­zon­tal lad­le fires are used for pre­hea­ting. Ver­ti­cal lad­le fires, in which the trans­port lad­les stand upright, are used to dry the new­ly lined refrac­to­ry. In the hori­zon­tal lad­le fires, the lad­le is pre­hea­ted, and smal­ler jobs are car­ri­ed out hori­zon­tal­ly. During pre­hea­ting, the lad­le is clo­sed with a lid in which the gas bur­ner is inte­gra­ted. The bur­ners ope­ra­te in the power ran­ge from 1 to 5 MW and are usual­ly ope­ra­ted with natu­ral gas-air mix­tures. Oxy­fuel sys­tems with oxy­gen as an oxi­diser are used to achie­ve hig­her effi­ci­en­ci­es and lower exhaust gas los­ses. The trans­port lad­les are pre­hea­ted to over 1000 °C. Pre­hea­ting the lad­le redu­ces the heat los­ses of the melt in the lad­le, lowers the neces­sa­ry over­hea­ting in the elec­tric arc fur­nace and thus redu­ces the tap-to-tap time. Lad­le pre­hea­ting is an indis­pensable part of steel pro­duc­tion and the switch to hea­ting with hydro­gen-based fuels is the­r­e­fo­re an important step towards CO₂-neu­tral steel production.

Lad­le fire in open environment

In the Flex­L­ad­le­Heat joint pro­ject, the Depart­ment for Indus­tri­al Fur­naces and Heat Engi­nee­ring (IOB) is deve­lo­ping an inno­va­ti­ve lad­le firing sys­tem for the fle­xi­ble use of hydro­gen and ammo­nia to pre­heat trans­port lad­les in an elec­tric steel­work tog­e­ther with the Chair of Cera­mics at the Insti­tu­te of Mine­ral Engi­nee­ring (GHI), Badi­sche Stahl­wer­ke GmbH (BSW) and Badi­sche Stahl-Engi­nee­ring GmbH (BSE).
The pro­ject offers the poten­ti­al to dra­sti­cal­ly redu­ce the CO₂ emis­si­ons of Badi­sche Stahlwerke’s lad­le fur­nace sys­tem through the fle­xi­ble use of hydro­gen-based fuels. Hydro­gen and ammo­nia are to be used in fle­xi­ble pro­por­ti­ons bet­ween 0 and 100 vol.-%, depen­ding on avai­la­bi­li­ty. This includes the deve­lo­p­ment of a new bur­ner and safe­ty tech­no­lo­gy, as well as con­trol and regu­la­ti­on tech­no­lo­gy. By imple­men­ting a digi­tal pro­cess model for lad­le pre­hea­ting, addi­tio­nal pri­ma­ry ener­gy savings of up to 10 % are to be achie­ved in addi­ti­on to the savings from oxy­fuel operation.

The IOB’s task in this pro­ject is to deve­lop digi­tal pro­cess models based on nume­ri­cal flow simu­la­ti­ons (CFD) and to car­ry out expe­ri­men­tal inves­ti­ga­ti­ons of the lad­le fur­nace sys­tem to vali­da­te the pro­cess models that have been deve­lo­ped. Nume­ri­cal simu­la­ti­ons are a pro­ven tool in the design and opti­mi­sa­ti­on of ther­mopro­ces­sing sys­tems and enable para­me­ter stu­dies to be car­ri­ed out in a time and cost-effi­ci­ent man­ner. As such, they can also be used to opti­mi­se lad­le fur­nace sys­tems and as a basis for the sub­se­quent crea­ti­on of a redu­ced fur­nace model that con­tri­bu­tes to the effi­ci­ent ope­ra­ti­on of the lad­le fur­nace. The scope of sui­ta­ble simu­la­ti­on models ran­ges from model­ling actu­al flu­id flow to models for tur­bu­lence, heat trans­fer by con­vec­tion, ther­mal radia­ti­on and che­mi­cal (com­bus­ti­on) reactions.