SPONGE IRON POWDER BY HYDROGEN REDUCTION.
National Mineral Development Corporation (NMDC) is a Government of India organization undertaking, engaged in mining and processing of various minerals, primarily iron ore. A significant tonnage of this iron ore is available in powder form and due to its distinct bluish tinge is called “blue dust”. It is well known that the finer the ore, the better is the result of beneficiation & hence the produced concentrate of blue dust is practically pure hematite with only around 0.35 % of remnant silica.
After our results of hydrogen reduction of blue dust concentrate at ARCI, India, 1998 became known, NMDC started negotiation with & Gas Institute of National Academy, Ukraine (GI) to implement the technology at their Research Center, Hyderabad, India.
They proposed to develop technology of carbon free iron powder production in semi-industrial scale of 300 TPY output with main criteria specific energy consumption and particular characteristics of the powder.
But reduction of iron ore by hydrogen has drawback due to high cost of the hydrogen and long time of processing in one stage reduction due to diffusion limitation of final stages of the reduction. So, it had been proposed to apply two stages hydrogen reduction process as it had been established after “frozen furnace” experiment.
WHAT HAD BEEN DONE?
By May 2009 all construction and installation works were completed. After testing and commissioning each unit separately, Preliminary Trials were conducted during December 2009. Fig. 2 shows a general view of the main shop.
According to the contract Preliminary Trials were to be at least 15 days of continuous non-stop running and 7 days within them had to achieve full output and quality of the powder. The trials took 20 days of continuous work due to re-circulation being stopped because of 4 power cuts in just one shift. 20 tons of the new grade of sponge iron powder were produced at a rate of 1 t/day (according to the contract) and of a quality which satisfied the contract specification. The main parameter of the project was a specific power consumption in whole technological route, including electrolyser and all axiliary equipment of no more than 12 kWh/kg of powder. The trials achieved 8.9 kWh/kg.
Records of the trials without re-circulation of hydrogen showed a consumption of 7m3 of hydrogen per kg of oxygen in the initial fed-stock. This is theoretically using only 20% of the hydrogen for reduction. With re-circulation the data showed 1.65-1.80m3 of hydrogen per kg of oxygen, a utilization of 70-75% of the initial hydrogen being used for reduction.
The powder grade preliminary named BDP-18 had the following properties:
Oxygen content – 0.2…0.4% (hydrogen loss method by MPIF standard test)
- Carbon content – 0.003…0.005% (ELTRA analysis)
- Apparent density – 1.80…2.00 g/cm3 (by MPIF standard test)
- Flow ability – 45…55 s/50 g (by MPIF standard test)
- Compressibility – up to 6. 8 g/cm3 at 700 MPa load (at Brovary Powder Plant lab test, Ukraine)
- Green strength – up to 90 MPa at 6.5 g/cm3 (at Brovary Powder Plant lab test, Ukraine)
New pilot plant had been built and whole technological route tested.
Theoretical background of hydrogen reduction of iron oxides shows that at least 40% of its chemical energy never could be used.
– Hydrogen recirculation and regeneration system can provide re-using of the ballast exhaust hydrogen.
– On the basis of laboratory scale modeling of the hydrogen reduction of iron oxide with recirculation at Gas Institute of National Science Academy of Ukraine, the patent of Ukraine No 65632 had been claimed and issued.
– In the actual circumstances of the implementation at the National Mineral Development Company Research Center, Hyderabad, India, the patented scheme seemed very rigid and not reliable.
– Simulation of the recirculation system at workshop of “Fluidtherm technology”, Chennai, India allows redesigning the recirculation system to match local condition.
– New technological scheme had been implemented at Pilot Sponge Iron Plant at NMDC, Hyderabad, India.
– The new scheme proved its reliability during 15 days of continuous run of control official acceptance trials.
THE TECHNOLOGY CAN BE REALIZED WITH MODERNIZATION AND MODIFICATION AGAINST AN ORDER.