By NIRMALYA DEB
Steel Authority of India Limited’s (SAIL’s) Rourkela Steel Plant (RSP) has always held an enviable position within this PSU family in terms of technical efficiency and the technological breakthroughs achieved over the years. In fact, the plant has quite recently set a few records. It set a national record by clocking 48 blows in a single day in a single converter of the steel melting shop (SMS)-II on July 2, 2020.
RSP has come up with many new grades of steel recently and planning for other new grades is on in full swing. “We have produced new ASM grade, SAIL hard disk and plates of various specifications. We supply different grades of rails to the Indian Railways under various government schemes. Even during this pandemic period we supplied 6,000 tonnes of special grade plates to Europe conforming to this region’s standards,” informed a senior RSP official.
“New grades are first manufactured and then tested. Special grades are first sent to customers and commercial production starts once we receive necessary approval. Therefore, the process is quite lengthy. Market sentiments are subdued at the moment due to the pandemic. So, production of new grades that were planned to be developed this year is inevitably getting delayed,” he added.
The new hot strip mill that successfully conducted a trial run on January 31, 2020 was expected to commence commercial production this year. However, experts from Mitsubishi who supplied the entire technical know-how for the mill left for their respective countries after the outbreak of the pandemic.
“We are keeping it on maintenance mode for the time being and the experts are providing tips online,” said the technical expert from RSP. The best in its class strip mill is unique not only in India but even in Asia and the world, he quipped.
Expected to start commercial production in May 2020, the mill is to supply hot rolled coils as input materials to the downstream cold rolling mill, silicon steel mill, pipe plants and also to the dividing line. It will also cater to the requirements of external customers.
The facilities at the 1.44 MnT per annum mill include two walking beam type reheating furnace (225 tonnes per hour), an automated coil box, quick roll change system in roughing stand-1 and finishing mills and coil marking, sampling and conveying systems.
Steel360 takes a close look at the different technical innovations carried out by RSP over the last few years right from raw materials processing to downstream applications.
RSP has adopted several measures to raise cost efficiency and attain superior standards in terms of environmental performance. It was the first integrated steel plant in the public sector set up with German collaboration with an installed capacity of 1 million tonnes (MnT). Subsequently, its capacity was enhanced to 2 MnT of hot metal, 1.9 MnT of crude steel and 1.67 MnT of saleable steel.
After implementing a mammoth modernisation and expansion programme, RSP augmented capacity to the level of 4.5 MnT per year of hot metal from the previous level of 2 MnT. The crude steel-making capacity has increased from the level of 1.9 MnT to 4.2 MnT and production of saleable steel has increased to 3.99 MnT per annum.
RSP was the first plant in India to incorporate the Linz-Donawitz (LD) technology of steel-making. It is also the first steel plant in SAIL, and till now the only one, where 100% of slabs are produced through the cost-effective and quality-centric continuous casting (CC) route instead of the old ingot process. However, close to 90% of SAIL’s production today happens through the CC route.
Moreover, it is the only plant that produces silicon steels for the power sector and high-quality API grade pipes for the oil and gas sector. Its wide and sophisticated product range includes various flat, tubular and coated items.
Apart from increasing the volume, the other benefits envisaged under the modernisation and expansion programme (MEP) are increased economies of scale, expanding customer base, quality upgradation, reduced cost of production and better market compatibility, not to mention improved adherence to environmental norms.
Blast Furnace Modernisation
The core of the modernisation programme were two blast furnaces (BFs) that were designed and rebuilt under a technological collaboration with Danieli Corus.
“BF 1 was built and commissioned in May 2018. The previous working volume was 995 cubic meters (m3) and current working volume is 1,491 m3,” a senior RSP official told Steel360.
“The hot metal production capacity previously was 1,200 tonnes per day. The present capacity stands at 2,900/tonnes per day,” he informed.
One of the biggest BFs of the country, the new blast furnace 5 with a useful volume of 4,060 m3 is designed for a production capacity of 2.8 MnT per annum with an average daily hot metal production of 7,924 tonnes per day. It, too, was designed and developed by Danieli Corus and was commissioned in 2013.
The furnace operates at a high intensification level and for a campaign life of 20 years. Equipped with modern features such as pulverised coal injection system, cast house fume extraction system, cast house slag granulation system, top gas recovery turbines of 14 MW capacity, heat recovery system, plate/stave coolers and conveyor belt charging system, this BF has Level II automation.
“The ancillary plant equipment of BF 1 that were revamped and rebuilt by Danieli Corus are a) the furnace proper with the bell less top charging equipment, b) the flat cast house with twin tap hole, c) ramp for easy access to cast house, d) the new gas cleaning unit (GCP), and d) the new coal direct injection (CDI) unit,” said the RSP official.
These new features and modifications apart, there has been overall “optimisation and operating parameters of the furnace,” he informed, adding that “furnace availability has increased by optimising the maintenance activities.”
Likewise, among the many new auxiliaries of BF 5 are the twin flat cast house with four tap holes, three turbo blowers along with all the auxiliaries that provide cold blast to the stoves of BF 5.
The unit comprising three boiler arrangements, two steam turbo generators and one back pressure turbo generator generates power as well as cold blast to feed the furnace and the stoves.
The 10 torpedo ladles with features like higher capacity and lesser scope of hot metal temperature loss are being used for transferring hot metal from the new furnace to the melt shop or the pig casting machine. These torpedoes are being used for the first time in SAIL. The torpedo ladle repair shop handles jobs like refractory lining, ladle inspection, ladle heating and cooling.
The main feature of the modernisation of the steel melt shop is the new third basic oxygen furnace (BOF) converter. The new top blown third converter of SMS-II) of capacity 1.584 MnT of liquid steel per year is designed with the provision for adoption of combined oxygen blowing from top and inert gas stirring (with argon and nitrogen) from the bottom.
The new Ruhrstahl Heraeus-Oxygen Blowing (RHOB) is also a first time feature of RSP that helps in producing higher strength and high quality special grade steel.
Raw Materials Handling
Post-expansion, the new raw material requirement of RSP has to go up to about 12 MnT per annum from the previous requirement of 5 MnT. The ore bedding and blending plant (OBBP) has a base mix preparation system with on-ground bedding, blending and conveying facilities.
The facilities in OBBP include major installations like wagon unloading (tipplers and track hoppers), iron ore crushing and screening system, raw material storage yard, rod mills and roll crushers for flux and coke crushing, proportioning bins and elaborate conveying systems.
RSP has five old and one new coke oven batteries (COBs) that produce coke as the input for the furnaces. The coke ovens are equipped with wagon tipplers, automatic handling and conveying facilities, coal blending provisions, coke wharfage crushing together with screening and conveying systems.
The new battery 6 is top charged, compound twin flue, under jet and with regenerative heating for provisions for partial recirculation of waste gases. The 7-metre tall battery of 67 ovens has been installed to produce run of oven coke (dry) of 0.768 MnT per year. The computerised heating control system has been installed for the process management system to improve reduction in environmental emission, improve coke quality and productivity.
“The principle of coke dry quenching is based on cooling of hot coke with inert gas circulating in close loop between the chamber of hot coke and the waste heat boiler. Apart from ensuring environment-friendly operation, it is also designed to enhance coke quality,” said the senior official.
The new coal handling plant can hold 15 days stock of coking coal for the new coke oven battery 6 at the rate of 3,500 tonnes per day and CDI coal of 10 days stock at the rate of 1,500 tonnes per day. There are 24 silos for stocking of coking coal and for CDI coal there are six silos, each with a capacity of 2,500 tonnes.
The new coal chemical department (CCD) has been installed to process coke oven gas generated from the new battery 6. This cleans the raw coke oven gas by removing tar, ammonia, hydrogen, sulphur, sulphide and naphthalene. The coke oven gas is cooled finally to 3,000 degree C at the outlet of the final gas cooler. There are naphthalene washer and benzole scrubber to have clean coke oven gas for use in the plant.
The RSP official informed: “The CDI rate per tonne of hot metal for BF 1 is 100 kg per tonne of hot metal (THM) on an operating basis while on a design basis it is 150 kg/THM. The CDI rate in January 2020 was 98 kg/THM. In February too the rate was 98 kg/THM.”
“The objective is to optimise CDI to achieve 0.8 to 0.9 replacement ratio of pulverised coal injection (PCI) coal,” said the official, underlying ongoing efforts to cut down dependence on coking coal.
The new sintering unit 3 has an effective suction area of 360 m³ and an annual production capacity of 3.70 MnT of gross sinter with sinter productivity of 1.3 tonnes per m² per hour. The output stack emission is less than 50 mg/Nm³, which makes the unit an environment-friendly one. The unit is provided with Eirich type mixer and noduliser instead of the conventional mixing and balling drum while a circular cooler has been installed for sinter cooling.
The 4.3 metre wide new plate mill has a capacity to produce one of the widest plates in the country, set up to cater to the customised plate market. The mill can produce a wide range of plates with close tolerances to meet stringent international standards and heavy and wide plates for the rising ship-building and boiler sectors.
While the cold rolling mill produces about 678,000 tonnes of cold rolled sheets per annum, RSP’s silicon steel unit produces steel for the electrical industry through various operations carried out in sophisticated, continuous/semi-continuous processing lines and a reduction mill. Advanced process control and product testing facilities ensure product quality.
A highly sophisticated spiral welded (SW) pipe plant is equipped with submerged arc welding process and produces large diameter pipes. Hydrostatic pressure testing, ultrasonic testing and eddy current testing are some of the features which ensure quality control.
The electric resistance weld (ERW) pipe plant caters to smaller diameter pipe consumers. This plant has been recently upgraded to enable it to produce API grade pipes for meeting the rising demand from the country’s oil and gas sector.