Tata Steel installs record size iron ore drying and grinding plant

FLSmidth is supplying an iron ore drying & grinding plant for a 6m tonnes per year (tpy) pellet plant being constructed for Centennial Steels. This is a subsidiary of Tata Steel Limited which is expanding its plant at Jamshedpur Works in India.

The pellet plant features state-of-the-art technology and pollution control to ensure minimum impact of increased production on the environment. When the project is completed, Jamshedpur Plant will become the single largest unit and one of the most modern plants in the world.

Sixth largest steel producer in the world
Tata Steel Limited is the world’s sixth largest steel producer and India’s second largest. It is increasing crude steel production from 6.8m tpy to 9.7m tpy with maximum utilisation of existing plants and utilities.

To achieve its objective, Tata Steel is setting up a 6m tpy pellet plant in the shortest possible period of 52 months and within the existing works boundary.

The pellet plant is an extension of Tata Steel’s traditional strategy of being an integrated steel producer. This strategy helps it keep costs down and ride out the vicissitudes of the cycle in the steel industry.

FLSmidth’s largest installation ever
This is FLSmidth’s largest installation ever of an iron ore dry grinding system. The scope of the contract involves two streams of 3m tpy of iron ore being fed to two rotary dryers, two ball mills, two separators and four baghouses along with associated conveyors, airslides and bucket elevators. The plant will be on stream for production by the end of 2010.

The challenge
A project of this size involves complete analysis of the process (iron ore, coal/coke and limestone mixed in the right proportion before being fed to the drying and grinding system). The process ranges from drying and grinding, classification and product collection to venting and dust control.

Since the mill shell is designed as a single piece construction of 6 m diameter, the lathe machine at the machine shop had to be modified to accommodate such a high diameter. The castings for the mill head and trunnions weighed up to 20 tonnes.

The girth gear for the mills was specially designed to achieve the hardness of 320 BHN. The lubrication system for such high pressure and high flow application is the first of its kind installed in India.

The two mill shells measure 6 metres in diameter (height of a two storey building) and 12 metres in length, weighing around 1,500 tonnes each. They are installed 6 metres above ground level on a foundation weighing about 4,500 tonnes and will rotate at a speed of 13 rpm.

Since this is the first time such a heavy mill is being installed in India, field service and logis-
tics personnel are gearing up to be prepared for the challenging installation requirements.

The system and process
The drying process comprises a 5.0 metre diameter x 35.0 m long dryer and includes a 40 MKcal/h hot gas generator. The co-current rotary dryer dries the material and reduces the moisture level to 1%. The hot gas generator uses blast furnace as the main fuel and coke oven gas as start-up fuel.

The dried ore is conveyed to a closed circuit grinding system which involves a ball mill and a dynamic classifier. The 6.0 metre diameter x 10.0 metre long ball mill is driven by a 2 x 5 MW motor arrangement.

The ground ore is classified in a high effi­ciency ROKSH 90 separator (new generation high efficiency dynamic separator) producing an end product of 50 to 55 micron particles. The material fineness is maintained by vary- ing the rotor speed of the ROKSH Separator. The product from the separator is collected in an FLSmidth jet pulse baghouse and conveyed to the ground silo by means of airslides and bucket elevators.

The rejects are returned to the mill for re­- grinding. This option provides the flexibility of varying the particle size collected to achieve the required Blaine size for the pellet making process.

Reducing environmental impact
The exhaust gases contain dust which essentially consists of iron ore fines from the discharge end of the dryer. The dust is collected in the baghouse and conveyed to the ROKSH Separator by the dense phase pneumatic conveying system.

The clean exhaust gases are vented to the atmosphere through the stack. The baghouses are designed to meet an emission guarantee of 10 mg/Nm3.

Contact Bhaskar Ramamurthy.