Big Savings with Ladle Desulfurization
If you have been following some of the latest posts of Limelight Carbide, you have probably noticed that we are doing extensive research regarding ladle furnace desulfurization ("LF Desulf"). That is because we have noticed that many of our clients are very well familiar with the use of Calcium Carbide (CaC2) for deoxidizing in secondary refining, but not so much when we talk about desulfurization in this specific part of the steelmaking process.
When we ask about desulfurization with Calcium Carbide, the common answer is, "Yes, of course. We use it for Pig Iron/ Hot Metal Desulfurization." And then we ask, "And what about desulfurizing in the Secondary Refining in your LF. Have you ever considered it instead?" For this second question, the most common answer is, "What do you mean?"
Of course all metallurgists know that the resulting deoxidation with CaC2 will cause desulfurization as well, but to actively apply it in this way does not seem so common. The LF Desulf application, however, is very well-developed and understood in other markets. In Brazil, for instance, where our supplier took part in one of the most complete tests of Calcium Carbide applications, the technique of Ladle Furnace Desulfurization with CaC2 is very well-known and used by some of the most important steelmakers in the market.
Based on those experiences with other clients, we wrote a LinkedIn post listing all the application methods of CaC2 in the steelmaking process. (if you missed it, click here for the ppt). We tried to make it simple, direct, and visual with diagrams. (I would love your feedback!)
Continuing the next step of informing and sharing experiences, in this article I will give a quick overview of the benefits and savings achieved by the benchmarks on the topic of Ladle Furnace Desulfurization with Calcium Carbide.
"Based on the initial good and fast results obtained, it was determined that the desulfurization of pig iron (...) would only take place if the sulfur was higher than 0.035%"
In this specific mill, the process included the desulfurization of the pig iron (hot metal - HM) in a Pre-treatment Station (PTS) before the converter. The PTS route was used when the HM sulfur content was above 0.005%, representing a total of 70% of the heats in a year.
What this client understood is that after deoxidizing, an extra addition of CaC2 could still bring benefits by desulfurizing. So they reached out to the CaC2 supplier and referred to another client to adapt and start their own procedure of adding two separate charges of CaC2, one during the ladle tapping stage, and the second addition after the tapping.
CaC2 + 3(FeO)→(CaO) + 2CO ↑ +3[Fe]
CaC2 + 3(MnO)→(CaO) + 2CO ↑ +3[Mn]
FeS + CaC 2 → F e + CaS + 2C
The next step was of course measuring to calculate the savings: ferroalloy consumptions, iron oxides, and desulfurization rates. Quickly the mill begin to see strong results in desulfurization and decided to only use the PTS when HM sulfur contents were above 0.035% (instead of the 0.005%). By doing this, they were loading the converter with the full content of sulfur from the blast furnace and only desulfurizing the steel in the secondary refining stage later at the LF.
This method worked very well for them, as it did for their other unit in Brazil, as well. Comparing both mills' results, it was clear that this Two CaC2 Addition Technique is very impressive in terms of time and material savings. Here is what the technical engineering team published on an article:
"...due to the 98% reduction of the need to desulfurize carbon and alloy steels, there is more availability of equipment to perform dephosphorization of HM for stainless steel;
"The drastic reduction in the need to desulfurize the HM provided enormous advantage to AM Timóteo, both financially and time-wise;
"The foamy slag and homogenization of the ladle surface reduced the percentage of FeO and MnO in the slag, as well as re-oxidation levels;
"There was a reduction (4.7%) in MnS-type inclusions, due to the reduction of total sulfur contents in the steel;
"FeT in the slag reduced 94%, and for MnO, the concentration dropped 93%."
What we can clearly see by these two benchmarks in Brazil is that there is still space to improve the general application of a relatively cheap product and that these opportunities are very well measurable and quickly perceived in terms of financial gains to the mills.
If you are curious to have access to the whole publication, data, and quantified results, please do not hesitate to reach out and we will be happy to help. Our intention is to share knowledge, expertise, and give support so that the US steel industry can become more competitive.
Happy to see you here again!
Daniel