|We are having 350TPD Sponge Iron Plant in Sipcot Industrial Growth Centre Perundurai, Erode (DT), Tamil Nadu. We procure Iron Ore from Bellary (DT) Karnataka, Coal from South African and Dolomite form Dindugal (T.N). We supply Our Sponge Iron Products to various Induction Furnace, Foundry Division and also for Blast Furnace.
Sponge Iron Rotary Kiln Process
In this process, a Refractory lined Rotary Kiln is used for reduction of iron ore in solid state. The Kiln is mounted with a slope of 2.5 % downwards from the feed end to discharge end.
Sized and weighed Iron Ore is continuously fed into the kiln along with a proportionately dozed coal, which has the dual role of fuel as well as reductant. Small quantities of limestone/ Dolomite are added to prevent sulphur pick up by Iron at elevated temperature from the coal.
A number of Air Tubes are provided along the length of Kiln. The desired temperature profile is maintained by controlling the volume of combustion air through these tubes and a Central Burner axially in the free space over charge.
There is a Coal Injection System at the discharge end of the Rotary Kiln through which finer Coal (-4 mm and + 4 to -8mm) is injected pneumatically to prevent Carbon starvation and to keep the required temperature profile throughout the Kiln.
The Rotary Kiln is broadly divided into two zones, namely, the Preheating zone and Reduction zone. The preheating zone extends over 15 to 20 % of the length of the kiln. In this zone, the moisture in the charge is driven off, and the volatile matter in the coal, liberating over a temperature range of 300 to 800 degree C, is burnt with the combustion air supplied through the air tubes in the free space above the charge. Heat from the combustion raises the temperature of lining and the bed surface. As the Kiln rotates, the lining transfers the heat to the charge.
Charge material, preheated to about 900 to 950 degree C enters the reduction zone. Temperature of the order of 1000 to 1050 deg C is maintained in the reduction zone, which is the appropriate temperature profile to facilitate solid-state reduction of iron oxide to metallic iron.
The reduced product is discharged into a Rotary Cooler along with coal char, Ash, calcined limestone and other non metallic impurities, where they are cooled to below 100 Deg C indirectly by spraying water on the outer surface of Rotary Cooler. The product is screened and magnetically separated into magnetic (Sponge Iron) and non magnetic (Coal char, Ash and other impurities) The Product (Sponge Iron) and Waste Product are taken into respective Storage Bins.
The Waste Flue Gasses are sent through either one of the following Heat Recovery Equipments for recovering the Heat and cooling the Gasses:
Waste Heat Recovery Systems
The option available for the commercial exploitation and reduction of specific fuel consumption and cost of production is the waste Heat recovery and power generating system.
Waste Heat carried away by the flue gases is being recovered by the Waste Heat recovery Boilers and gainfully used for Steam and hence power generation.
Further analysis and studies in the above work has helped to develop Energy Efficient Direct Reduction Process for the manufacture of Sponge Iron. This system envisages recovery of the sensible heat and utilize partly for Pre-heating the Iron Ore and the balance to generate steam and power.
Recovery of Heat to Pre-Heat the Iron ore and generate steam makes the Direct Reduction Process more energy efficient and more commercially viable and attractive proposition.
Waste Heat Recovery Power plant Process
Production of Sponge Iron in DR Kiln generates huge quantities of Flue gas carrying considerable sensible heat. Generally, the Waste Gases are burned in two stages in a Chamber known as After Combustion Chamber (ABC) by injecting excess Air to neutralize the poisonous and harmful un-burnt Carbon Monoxide. The burning of the residual CO releases additional heat energy in to the Waste Gases calling for two stages cooling with high pressure atomized water spray. Further, the Hot Gases have to be cooled from 900 to 200 Deg Centigrade, so that the Electro Static Precipitator withstand the temperature. When we install a Waste Heat Recovery Boiler, two benefits could be achieved. Here, the Cooling is achieved by a high Pressure water Sprays. Sulphur Di-Oxide is a constituent of the Waste Gases and while cooling becomes a highly corrosive Wet SO2 which corrodes the steel Components like Gas Ducts, Fan Casing, and Impellers etc. All these Equipments would call for high Capital and Revenue (Maintenance) cost.
In the case of a Waste Heat Recovery Boiler, the Hot Gases exchange the heat energy to the Boiler Feed Water to gainfully convert in to Steam which intern could be used for Power generation. A Waste Heat Recovery Power Plant would be an ideally suited proposition to effectively make use of the sensible heat of DR kiln off gases generated during the process of Sponge Iron manufacture.. The quantities and heat content of DR kiln off gas is enough to produce about 8.0 MW power. Thus the Waste Heat Recovery Power Plant would not only make the plant less dependent on external source of electric power but would also result in Energy conservation and Environment Protection. The details of facilities envisaged are given in the following paragraphs.
Fuel: The fuels available for power generation are:
Off Gases from DR kiln after “After Burning Chamber (ABC)
The waste Heat Boiler will be installed behind the ABC of DR kiln in bypass configuration. The flue gases after ABC will be taken to unfired furnace chamber and them flow over banks of super heater, convective evaporator and economizer before being discharged to atmosphere through ESP, ID Fan and chimney of DR Kiln. In case of outage of Waste Heat Boiler, Flue gases will pass through GCT- ESP ID Fan and Chimney. The flue gases will pass over various heat transfer surfaces to ESP and then finally discharges in to chimney by ID Fans. The boiler will have its own ESP, ID fans and Chimney.
The heat extracted and cooled waste Gases get cleaned in the Electro Static Precipitator. The dust collection efficiency would be of the highest order and the emission level would be within the norms stipulated by the State and Central Pollution Control Boards.