Steel 360 visited the Tata Sponge iron plant nestled in the hilly and picturesque terrain of Joda in Odisha’s Keonjhar district – home to one of the country’s best and most abundant iron ore reserves. The 360-acre facility has three functional rotary kilns churning out around 1400 tonne of sponge iron per day
According to data furnished by the World Steel Association, the secondary steelmaking sector in India accounts for close to 50% of crude steel production on an annual basis and, therefore, DRI production in the country has gathered pace over the years. India is the world’s largest DRI producer, primarily via the coal-based route. The country produced a whopping 22.34 mnt of DRI in 2017, almost two-thirds of which was produced in rotary kilns that employ coal as the reductant and fuel.
It deserves mention that sponge iron as a feed is preferred by EAF manufacturers as it is an iron source relatively uniform in composition, and virtually free from tramp elements. It is used increasingly in EAFs and IFs to dilute the contaminants present in the scrap that is charged in these processes. It has an associated energy value in the form of combined carbon, which has a tendency to increase furnace efficiency.
Among the major sponge iron manufacturers in India, Tata Sponge has carved a niche for itself. The Tata Sponge plant nestled in the hilly and picturesque terrain of Joda in Odisha’s Keonjhar district – home to one of the country’s best and most abundant iron ore reserves – has three functional rotary kilns churning out around 1400 tonne of sponge iron per day.
The Company commenced its journey as IPITATA Sponge Iron Limited in 1982. It was a joint venture between Tata Steel Limited and the Industrial Promotion & Investment Corporation of Orissa Limited (IPICOL) for the production of sponge iron, based on the TISCO Direct Reduction (TDR) technology. Later, in 1991, Tata Steel acquired IPICOL’s entire stake and Tata Sponge became an associate company of Tata Steel, wherein the parent company holds 54.5% of shares.
The finished product is a single-grade, end-use product consumed in steel manufacturing. The chemical properties of the sponge iron manufactured at Tata Sponge are of the highest standards, with total Fe content of 90%-92%, phosphorous 0.05% (max) and sulphur 0.03% (max). Overall uniformity in size is a major advantage, with the lumps being + 3mm and the sponge iron fines being 0-3 mm. The sponge iron with high metallic iron content along with consistent chemical and physical characteristics provides secondary steelmakers the much-needed flexibility in preparing their furnace charge to produce finer quality steels.
The manufacturing facility has an adjoining fly ash brick plant and railway siding of its own that helps ferry prime quality iron ore from Khanbandh in eastern Joda and transport the finished product to specific destinations. Sponge iron manufacturing is highly sensitive to raw material characteristics that would help obtain the rated capacity and the desired product quality. Hence, it is essential to examine the chemical and physical characteristics of raw materials, both individually and in combination. The basic raw materials for the production of sponge iron are iron ore, non-coking coal and dolomite.
During sponge iron manufacturing, iron ore is reduced in solid state. Unlike the conventional steel melting processes, the gangue content of iron ore cannot be separated as slag. Hence, it becomes essential to select an ore with high iron content and low gangue content, to optimize yield during steelmaking. In order to ensure a better kiln campaign life and output, the iron ore is made to undergo a series of other tests viz. shatter, tumbler and abrasion indices, reducibility, etc. By virtue of its location in the northern part of Orissa, Tata Sponge enjoys proximity to good iron ore reserves.
Engineers at the Tata Sponge factory informed Steel 360 during our recent tour of the plant that the preferred ore ranges between 5 and 18 mm in size with an eye on its reducibility and the predominant feed is 10-10.5 mm. The kilns are horizontally inclined huge cylinders, two with diameters of 72 mm that churn out 410-420 tonne each of sponge per day, and the other which is 80 mm in diameter produces 514 tonne per day, as per current production statistics.
The overall nameplate capacity is 390,000 tonne per annum; however, the company received a clearance from the Union Ministry of Environment, Forests and Climate Change in 2017 for enhancement of DRI production by 35,000 tonne per annum to 425,000 mtpa in the existing facility. The rotary kilns are supplied by the Tata Growth Shop in Jamshedpur.
Further value is added to the process in the form of power generation, with the company exporting the surplus power (by-product) from the two existing power plants to the parent company through Waste Heat Recovery Boilers (WHRB), enabling the company to help reduce carbon emissions, earn carbon credits and effectively participate in the global movement against climate change. The two power plants have a cumulative capacity of 26 MW. Hot gases pass through the WHRBs at 950? and, as a result, hydrocarbon evaporation occurs. Water is injected through a bundle of pipes and steam is generated at a temperature of 170?.
Conforming to stringent environmental norms, energy through waste heat recovery has emerged as one of the best alternatives today. The Ministry of Environment & Forests has made it compulsory for DRI plants to generate captive power by using kiln waste heat in order to emphasize on power generation in a non-conventional way. Tata Sponge’s first power plant using waste heat was commissioned in 2001. Later, it added another power plant in 2006 to increase its overall power producing capacity to 26 MW.
Explaining the ideal raw material characteristics and the proportion in which they are fed into the kilns, engineers at Tata Sponge said for every 1000 units of iron, 950 units of carbon (coal) is fed, of which 30% are fines. The imperatives, which determine the quality of coal, are chemical properties such as fixed carbon, ash content and volatile matter as well as physical properties – reactivity and ash fusion temperature, which is < 1300?. The maximum permissible sulphur content is 0.6%.
The company acquires quality coal from the collieries of Central Coalfields, South Eastern Coalfields and Mahanadi Coalfields. Besides, to maintain the desired quality and improve kiln campaign life, the company also imports coal from South Africa and purchases washed coal.
Engineers at the process control room of the plant explained to Steel 360 that the temperature inside the kilns is 850?-1100? in which Fe2O3 reacts with CO to form FeO (sponge iron) and CO2, which after a process of cleansing is subsequently released into the atmosphere. There are eight blowers in all that supply air into the kilns to facilitate burning and the coal is subsequently converted into CO and CO2. Around 50% of the coal gets consumed at the feed end side and likewise at the discharge end side the remaining gets consumed. The coal is 6000-7000 kcal/kg and for the production of 1 tonne of DRI, 80 kwh/tonne is required.
The kilns rotating along their fixed orbits is a sight to behold as the process is incessant. After a period of 250 days there follows an interlude of 20 days of shut down, after which operations resume. From the kilns the DRI is passed through the magnetic separator and lumps and fines are processed. The non-magnetic residue comprising coal, dolomite and char are separated. Experts are of the view that in terms of steel manufacturing lumps below 20 mm are ideal in terms of reducibility while the fines generated which are below 0-3 mm are directly sold in the market.
The kiln refractory material is high in alumina which ensures proper insulation inside the kiln by trapping the heat inside. It also provides binding strength to the refractory kiln.
The manufacturing facility is enveloped in greenery and even a quick tour around it is enough to convince the visitor of the high ecological, hygienic and safety standards followed by a company which has become a byword for quality and sustainability in India and across the world.