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FAQ's - Steel

Our customer service department answers many questions regarding our lime products for all the industries we serve. The questions range from lime applications and use to storage, shipping and handling. As a resource to our customers and website viewers, the listing below represents the most frequently asked questions.

 

Can I store the lime outside?

No, quicklime products are very hydroscopic and can react with the moisture in the air. Quicklime products should be stored in silos or at a minimum under roof.

What is the shelf life of lime products in a storage tank?

Quicklime products should be stored in silos or at a minimum under roof. Shelf life depends on the amount of exposure to air and the elements. Products stored in moisture proof silos can last several months or more if air infiltration can be kept to a minimum.

 

What is the difference between high calcium quicklime, dolomite quicklime and magnesian quicklime for the steel maker?

The chemistry of these limes are related to the natural stone from which they are processed. High calcium quicklime has approximately 97% CaO with MgO less than 3%. High Calcium lime is utilized in the furnace for slag production and in the secondary steelmaking process to promote desulfurization, inclusion entrapment, and insulation against air and to prevent temperature losses. Dolomitic quicklime contains natural combinations of CaO and MgO, with CaO content as low as 60% with a corresponding MgO content of up to 40%. This is used primarily for meeting the MgO requirements of the EAF slag to prevent refractory wear and promote good foaming properties to protect the sidewalls of the furnace.A specific Magnesian quicklime called SteelCal is available from Carmeuse. This product provides natural combinations of Calcium and Magnesium Oxides, ranging from of 5% to 12% of MgO. This product is utilized in the furnace to promote early dissolution of MgO with additional dolomitic lime added later to meet the increasing need of MgO in the slag.

 

Does the reactivity test for lime indicate how it will react in producing a slag in the electric arc furnace?

No. The reactivity test uses water to determine a rate of temperature rise within a given time period. This is useful for chemical applications and soil applications. However, inthe high temperature chemistry reactions seen in the EAF there is very little correlation to the lime quality as related to the reactivity test. Important factors for lime are the sulfur content, silicon content, LOI and lime sizing. What makes lime go into solution quickly is the fluxing agents that react with lime in this environment. FeO is the primary fluxing agent with silicon and aluminum acting to help also flux lime.

 

What is typical lime consumption for the electric furnace practice?

Lime consumption depends on the material input and quality of the material which contains acidic compounds such as silicon and aluminum. To maintain the properB3 ratios of 1.5 to 1.9 depends on the steel quality being produced and the balance of fluxes with the material quality that is added to the furnace. Lime consumption can therefore range from 50 lbs per ton of steel to 110 lbs per ton of steel.

 

Why is adding more lime to the BOF a problem when trying to reduce Phosphorous?

Basicity is an important factor in reduction of phosphorous in the BOF. However, the increasing amount of lime usage will increase the basicity to a point that without any fluxing agents present the slag will become crusty and will not mix with the steel to promote phosphorous removal in the steel. Silicon content of the metal provides thefluxing of the lime since FeO is extremely low in BOF slags as compared to EAF slags.Alternate materials could be used to lower the basicity ratio so that a creamy slag canreact during mixing for phosphorous removal.

 

How does lime melt in the furnace when temperatures reach about 3000° F and lime melts at 4,658° F ?

Key requirements involved are the generation of iron oxide (FeO) as the primary fluxing agent, MgO content which along with temperature and slag basicity influences a reduction in the melting temperature of the lime.

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