The Trials & Trubulations of Re-Starting a Blast Furnace
RG Steel has been in the process of re-starting their "L" blast furnace at their Sparrows Point flat rolled steel mill. The furnace was brought down under the ownership of Severstal and for the past couple of months RG Steel has been bringing the furnace and its approximately 8,500 tons a day of iron production back to life.
If you are not an integrated mill operations person, then most likely you are much like me and think starting a blast furnace is nothing more than turning on the gas and lighting a burner. Something along the lines of the propane grill in your back yard. Let the thing heat up for a couple of days and then start pumping out hot metal. Nothing to it.
Steel Market Update is fortunate to have John Eckstein, retired metallurgist and manager of quality for Severstal Sparrows Point (now called RG Steel Sparrows Point) as one of our Steel 101 instructors. Steel Market Update wanted to learn more about the process of starting a blast furnace and to learn a little more about the “Beast of the East” which is the nickname of the “L” furnace at Sparrows Point.
SMU: What are the step by step processes from the time the furnace is ready to start (walls are prepared, etc.)?
John Eckstein: As you look at a clean start-up of a cold furnace, all mechanical and electrical operations are checked for operation soundness. Blast Furnace walls are examined for thickness of the refractories and their integrity. All tuyeres* are clear and opened. Also, there can be no water leaks with the tuyeres or any other areas such as the stack plates. (*Note: according to our Steel 101 manual which each attendee receives at the beginning of the class, a Tuyeres are made of copper and are water cooled nozzles that blow super heated blasts of air into the base section of a blast furnace.)
Submarine cars and slag bowls are made ready.
Ore handling facilities are also prepared.
Once ready, the furnace is charged with coal to build heat into the furnace. As the heat builds, the burden which consists of pellets, limestone, sinter (if available), coal and coke is added. The burden is supported by its own strength of the raw materials and the high velocity of the air blasting through the tuyeres. Additionally, most furnaces will now use a combination of natural gas and coal injection as a heat source.
As the heat builds, the burden continues to change to increase the amount of iron units (pellets) until you obtain the first level of operating rates. The furnace will be brought back in steps until it reaches the planned operating rate.
Initial production of pig iron is dumped because of high levels of Silicon and Sulfur.
As the furnace stabilizes and the chemistry is within operating standards, the pig iron will be sent to the BOF for refining into steel.
SMU: How many tuyeres are open in the beginning and what is the process of opening a new tuyere?
John Eckstein: When you start the furnace, you want all of the tuyeres opened. It's only in times when a furnace comes down in an unscheduled pattern will the furnace restart with some tuyeres not operational.
When tuyeres fail during normal operating conditions, the furnace comes down and the wind is reduced in the furnace. It can take 30 to 60 minutes to change a tuyere. When multiple tuyeres fail within a short period of time, these multiple tuyeres will all be changed during this one outage.
SMU: Is it a matter of getting “balance” in the furnace whereby the mixture of coke, iron ore and limestone is correct for making suitable pig iron and how long does it normally take to get this balance?
John Eckstein: Most start ups of a cold furnace can get suitable chemical analysis of the pig iron within a week. That does not mean to say that the furnace is at full production. Just that the chemical analysis of the pig iron is suitable for processing in the BOF.
What is a “slip” in the furnace mean?
A slip is generally due to wedging or bridging the burden in the furnace. A void is created in the burden and the void will increase in size until this wedge or bridge breaks loose. Once that disruption takes place, pig iron can be forced into the tuyeres that will result in the tuyeres becoming clogged. Once the tuyeres are clogged, the furnace has to come down to replace any and all clogged tuyeres.
Slips can be caused by:
1) Solidified slag preventing burden to move
2) Coke containing high levels of fines
3) Too much wind blown based on the burden
SMU: When there is a slip molten metal forces its way into the tuyeres which then need to be replaced (does the furnace have to cool before they can be replaced or just the tuyere need to be cooled and how long does that take?
John Eckstein: The furnace does not have to be cooled to replace a failed tuyere. The wind is reduced in the furnace. To replace a single tuyere can take between 30 to 60 minutes.
SMU: What is a “peel” and how does that differ from a slip?
John Eckstein: A peel in the furnace can be the breakdown of the refractory in the furnace. This can be the result of thermal expansion and contraction of the refractories or processing abnormalities that can physically damage the refractory
SMU: What are common problems a furnace goes through before it is chugging along as it should?
John Eckstein: A blast furnace is a very complex operation that operates at very high temperatures and pressures. There's a list of many potential mechanical and electrical issues that are of concern. Many people can argue of some of the problems that can exit, however here are some areas of concern:
1) Loss of wind
2) Water leaks
3) Chemical analysis of pellets
4) Moisture in the burden
5) Furnace slips
SMU: The “L” furnace needs to produce about 7,000 tons a day minimum in order to work properly?
John Eckstein: The 7,000 ton per day is a good operating rate for L furnace at Sparrows Point. In recent times the furnace has operate between 6,500 - 9,000 tons per day.
The operating rate is driven by the order book requirements. A blast furnace ideally operates best at a steady rate. It will not operate well and can result in premature failure when operating rates are altered significantly either up or down in short time periods.
Steel 101: An Introduction to the Making & Rolling of Steel
The dialogue above gives you a flavor for portions of our Steel 101 workshop. The idea is to get everyone comfortable with the terminology, know what equipment looks like and how it works and what products are produced and how they are sold.
The last day to receive our "early bird" discount for the Steel 101 Chicago program is Monday, June 13th.