DIRECT REDUCED IRON
Direct Reduced Iron is basically a kind of Iron oxide. Also it is known as Sponge iron. Direct Reduced Iron is richer than Pig Iron. It contains 90-94% of iron. The manufacture of Direct Reduced Iron as follows. The Iron ore is crushed & freed from foreign particles except the Iron Oxide, compressed at normal ambient temperature into Iron Oxide pellets. These pellets are passed down through a furnace with counter current flow, known as Reducing Gas. The pellets are heated below melting point of Iron, the reaction between Iron ore pellets & hot gas removes the oxygen from the Iron ore leaving metallic Iron pellets with sponge like structure (Cold moulded type). The Sponge iron can react with oxygen, return to it’s previous state as Iron oxide, but this is extremely slow in dry conditions. Special treatment known as Passivation can reduce it’s reaction with oxygen, whereby the briquettes are coated with sodium silicate or ageing in which the briquettes are allowed to form an iron oxide coating. India is the world’s largest producer of Direct Reduced Iron. Direct Reduced Iron can be split into two distinct sub-groups, they are Cold moulded pellets & Hot moulded briquettes. Hot moulded Direct Reduced Iron briquettes are a more refined product, formed by the further processing of cold moulded pellets.
Self heating hazard & burning
Direct reduced Iron can react with oxygen very fast, if sea water (NaCl) introduced. Normally when Direct Reduced Iron is transported onboard Ships, there are high chances for this during bad weather. The reaction of Direct Reduced Iron & oxygen is exothermic, since it produces heat. The sponge structure of Direct Reduced Iron is a plus point for this reaction. Direct Reduced Iron is a pyrophoric substance, so it can spontaneously ignite in air. The temperature can rise up to about 150 degree Celsius, known as Auto oxidation temperature. When heated Direct Reduced Iron reacts with water it can give out Hydrogen gas, which is known as Catalytic dissociation of the water. Direct Reduced Iron burning can be noticed as, the glowing red color. If hydrogen is present it glows in blue haze color.
Precautions while transporting in ships
Inerting the atmosphere will be a good solution, for this Nitrogen must be used. If Carbon dioxide used, it can be broken to Carbon monoxide which can serve as toxic & flammable gas. Hydrogen should be less than 1% by volume & oxygen should be maintained at 5%.
Precautions should be taken while carrying Direct Reduced Iron & it should be properly sealed to avoid coming into contact with sea water.
The passivation should be proved by competent authority in writing.
In case of fire Nitrogen should be used, If fuel oil tanks are below burning Cargo hold, dry ice or Carbon dioxide should be injected through sounding pipes. Never use Carbon dioxide or water to fight a fire of Direct Reduced Iron.