Dear Tomislav, 

Phos control in end blow has more to do with lance height control, oxygen flow rate and bottom gas flow rate control. With a particular combination and pattern, Phos window can be guranteed, provided there was no slopping or dry slag in the earlier part of the blow.   Some colants (limited amount) also help to capture phos reversion. 

For the last part of the blow specially, a set of shopfloor trials are needed to decide the optimum strategy based on size of vessel, number of nozzles (and nozzle design), aim tap temperature, desired end carbon,  availability of LD top slag as coolant,  etc etc, with or without sublance. For ultra low phos heats the turndown slag quality has to be sacrificed. 

In this way,I feek that  phos control is very interesting!

OG analysis is  not reliable (in last four minutes approximately,, i.e.  after critical carbon.

Sincerely, 

Brahma

Dear Brahma,

thank you very much on your quickly answer. With your comment about removing of phosphorus, I absolutely agree. I have experiences in BOF steelmaking more than twenty years. Sorry, my question was unclear. I would like to understand the differences between only OG test and OG test with TD (turndown) test in BOF control. 2016 AIST BOF Roundup showed 10 India's BOF shops with OG and TD test. Six of them use OG and TD tests, three use only OG test and one only TD test. I don't understand what is tapping practice in case only OG test in BOF control? For me, this is direct tap without take a sample and measuring of temperature. What is your opinion?

One year ago I asked AIST people about that, but, I wasn't satisfied with his answer.

Sincerely, 

Tomislav

Dear Tomislav, 

Which plant you support and have worked for? Have we ever met?

I am afraid I do not know of any plant  in India doing direct tap in the real sense of the  term. 

Yes in heats which require a reblow, some times they do not take either sample or temperature after reblow and send the heat directly because they almost can guess the temperature and composition.  However, in such a case both temperature and sample are taken once the metal arrives at stirring station or LF.

The  sublance is not used in most plants because it is expensive. In the dynamic control model that we implemented at Visakhapatnam Steel Plant  recently (based on chaos control procedures during mid blow period), the model advises corrective actions during the blow and also the final corrections  approximately 5 minutes before tap. No operator interference is required in"autoblow mode" and all actions take automatically (lance height change, oxygen flow change, ore addition, lime addition etc). But in this case also sample and temperature are  taken at tap. Yes, with this approach in 85% of cases no reblow is required. The idea is do away with sublance altogether because of cost. May be you can consider  implementing such a control system (avoiding the use of sublance) at your plant !!

I am sure you too would  have implemented  some special successful features at your plant: kindly let me know. We would  like to share/implement  knowledge. 

Brahma

it is very happy to see my Prof. Brahma Deo's discussion here...!!! Its very difficult to see such valuable discussion on process metallurgy now a days...

Dear Brahma,

Sorry, again small unclear in our conversation. My English is probably bad. My key question is: "Why there are in AIST BOF Roundup two different testing methods, OG and OG,TD"? According to your explanation, Visakhapatnam Steel Plant use the dynamic control model with OG test, and sample and temperature are  taken at tap (on the turndown vessel). That means, practically there are no different between OG and OG, TD tests in AIST BOF Roundup, or I'm not in right. It is question for AIST people.

Mr. Brahma, I'm very proud to conversation with You. I am metallurgist from Serbia and author of SDM, with turndown test instead using of sub lance or in-blow drop sensors. In attached You can see my CV and a paper about mentioned model. Currently, after retired, I have worked in small private firm in my city, as consultant for oxygen steelmaking.

Sincerely,

Tomislav Bradaric