Tata Steel, a leading integrated steel mill in India with a capacity of 3.5 million tons per year (3.2 million metric tons), has a total of five vessels in its two steel-making shops. The vessels are equipped with in-house Tar Dolo refractory linings that were not achieving their maximum heats per campaign because fouling in the quencher, secondary venturi and other locations was limiting the availability of the gas cleaning system and the induced draft (ID) fan. Every minute of production lost in the basic oxygen furnace (BOF) shops cost the company approximately US$11,000 per hour. The mill needed to eliminate this midcampaign cleaning of the gas cleaning plant.
The unscheduled shutdowns of the BOF shops were occurring because of severe accumulations of iron and calcium in the quench and scrubbing sections of the gas cleaning system. Because of the ineffective scrubbing, solids were being deposited unevenly on the ID fan, affecting its dynamic balance and causing vibrations. Frequent shutdowns were required for cleaning the fan blades. The problem was most severe in one of the shops in which the ID fan was located close to the mist eliminator.
Another persistent problem involved deposition in the scrubber supply line that reduced pressure and flow. This required low pH cleaning to restore normal flow rates and ultimately led to the replacement of the piping.
The deposits in the scrubber area reduced the throat length and clogged the spray nozzles to such an extent that unscheduled shutdowns were needed for cleaning to maintain an adequate draft throughout the system.
The SUEZ analysis of the deposition pattern indicated that iron was a major constituent in the quench and scrubber areas. On the other hand, calcium was found to be the major contributor to the supply line deposits.
SUEZ recommended that ScaleTrol PDC9323 and PDC9324 deposit control agents be used in place of the existing treatment program. A base line feed of PDC9323 and PDC9324 was made in the supply water header, while an application of PDC9323 was also made at the scrubber inlet line during charge and blow.