High Carbon Ferrochrome / Charge Chrome are produced in Submerged Electric Arc Furnace. We have 2 furnaces in-line with a name plate capacity of 45 MVA & 33 MVA with a combined annual capacity of producing 142 KTPA of High Carbon Ferro Chrome. The furnace is stationary and is semi-closed on top.
The process adopted is high temperature smelting process, in which chrome ore is reduced with the help of the reductant like coke. The gangue material in the ore is removed by suitable fluxing material. The raw materials like chrome ore, coke and fluxes are selected to obtain desired grade in the output as per the requirement of the customer. All the incoming raw materials are analyzed for quality before feeding into the furnace.
The charge mix containing chrome, coke and flux is taken into the furnace with the help of computerized batching system. The necessary heat required for a process is provided by electric energy to the charge through the electrodes. At the tip of the electrode electric arcing takes place and generates high heat energy to smelt chrome ore into HC Fe Cr/ Charge Chrome with coke (carbon) as reducing agent. In the process of smelting, gangue content in chrome ore forms the slag whose composition and fluidity are maintained by flux addition. Both hot metal and slag are tapped at regular intervals depending upon the power consumption. The slag is granulated. The metal is handled through decantation process and skimming process before cast in the metal casting beds prepared with slag dust and plastic clay. The metal after cooling is handled manually into different size fractions as per the requirement of the customer. This is a continuous process in which charge mix is taken regularly and slag & metal taped at regular intervals. Stage-wise inspection is carried out to get the quality product.
High Carbon Ferrochrome: – Specifications
- Chromium (Cr) – 60% Min
- Silicon (Si) – 4% Max
- Carbon (C) – 6-8%
- Phosphorous (P) – 0.02% Max
- Sulphur (S) – 0.05% Max
- Iron (Fe) – 40% Max
Applications of High Carbon Ferrochrome
- It is used mainly as Chromium supplement in Steel making.
Raw Materials
Chrome Ore:
- Supplement of Chromium in the form of its oxide, Cr2O3. Available in Fines, Friable and Lump forms
Reductant
- Source of Carbon to reduce the chromium oxide
- Suitable materials are metallurgical coke, anthracite coal etc.
Flux
- Used to control the composition of the slag, ensures to join the gangue contents in the chromite
- Viz., Quartz – source of SiO2
- Bauxite – source of Al2O3
- Magnesite – source of MgO
- Limestone – source of CaO
Agglomeration – Briquetting Process
Chrome ore is in friable, and fines form hence it cannot be used directly into the smelting furnace for reasons of safety and bad performance. Friable fines and chrome ore concentrates are therefore briquetted and used along with hard lump / friable lump for the production.
To make the briquette sufficiently hard, the chrome ore fines are dried for removal of moisture. The dried fine is mixed thoroughly with certain quantity (~2%) of hydrated lime powder and molasses (~5-6%) in the mixer muller and fed to the briquetting press. Briquetting segments are used in press. The screened briquettes are cured for about 7 days in the storage yard after which they’re blended with other raw materials & then fed into the furnace through day bins.
There are four dryers installed with 3 X 20 MT per hour and the other with 1 X 10 MT per hour drying capacity. There are two briquetting presses available each with 20 MT per hour briquetting capacity.
Metal Recovery Plant (MRP)
The slag skulls and slag metal mixture generated in the handling yard is fed into the ground hopper of Metal Recovery Plant. It is discharged on the belt conveyor by a feeder and is conveyed to screen (6 & 20(mm) aperture). After screening the +20(mm) fraction is fed to crusher for further breaking below 20(mm) size and is again screened and the process of recirculation after screening is continued along with new fed slag and mixture. The –20(mm) fraction is jigged to get the 0-4(mm) hatch metal and 4-10(mm) and +10(mm) as jigged metal. Middling after processing slag at MRP will be recycled in the furnace as remelt. The slag handling capacity of the Metal recovery plant is 30 MT per hour with 20% of metallics in it.