Developments In Direct Reduced Iron
Developments In Direct Reduced Iron ( DRI )
Direct reduced Fe ( DRI ) is produced through the solid province decrease of Fe oxides derived from Fe ore or electric discharge furnace ( EAF ) mulcts for the usage as a virgin Fe beginning in the EAF or basic O furnace ( BOF ) processes. Virgin Fe beginnings are needed in the EAF procedure to thin the remainders ( Cu, Ni, Cr, Mo, or Va ) nowadays from old steel doing operations in the bit steel used as the primary natural stuff used in the EAF. DRI is produced in many different procedures utilizing several different fuels and different provender stocks. The DRI processes use several reaction vass including shaft furnaces, rotary fireplace furnaces, fluidized bed reactors, traveling bed reactors, and rotary kilns. The fuels used in the procedures are chiefly coal or natural gas, these fuels are used to make a reduction ambiance and elevated temperature to make a more favourable reaction. The quality of the DRI is measured by the sum of metallic Fe ( Fe or Fe3C ) is present in the merchandise. This figure is called metallization and is reported in a per centum of the entire mass of the merchandise. The merchandises of the DRI procedures are either pelletized into DRI or briquetted into hot briquetted Fe ( HBI ) .
The decrease of the Fe ore or EAF mulcts takes topographic point in several reactions that cut down the Fe oxides to metallic Fe ( eq. 1 and 2 ) . The reduction gases are produced by burning natural gas or a C beginning so adding the heated burning merchandises to the reaction vass.
Fe2O3 + 3H2 ( g ) > 2Fe + 3H2O ( combining weight. 1 )
Fe2O3 + 3CO ( g ) > 2Fe + 3CO2 ( combining weight. 2 )
Hydrogen and C monoxide are formed from burning natural gas, while merely C monoxide is formed when coal or coke is combusted. The difference between the procedures is how the provender stock is exposed to the burning gases.
The most common type of reaction vas is the shaft furnace where the provender stock is fed into the top of the furnace so dropped through the vas to be exposed to the reduction gasses so extracted from the underside of the furnace. The conceiver of utilizing the shaft furnace for DRI production is the Midrex corporation and is known as the Midrex Process. The Midrex procedure uses a Reformed natural gas as the decrease gas and requires the usage of pelletized Fe ore as a provender stock. The natural gas is combusted in a reforming vas so fed into the shaft furnace where it is assorted with extra natural gas and O to make some more chemical energy for the procedure ( figure 1 ) . The fluke gas is so fed through a station burning chamber and the energy extracted from station burning is used to preheat the provender gas. This gas is so fed to a bag house where it is scrubbed before being reintroduced to the ambiance.
This procedure creates chiefly DRI pellets due to the provender stock being pelletized Fe ore and at that place non being a demand to alter the geometry through briquetting. A mistake of the Midrex procedure is its dependance on pelletized ore. The procedure requires the provender stock to incorporate no more than 3 % mulcts. The DRI pellets produced have a high metallization of 95 % on norm, doing it the highest quality DRI. The usage of the station burning allows the Midrex procedure to derive the bulk of the available energy and is what has made it favourable for the bulk of world-wide DRI production
A faster production method and 1 that has more flexibleness than the shaft furnace is the rotary fireplace furnace or the Fastmet procedure. The rotary fireplace furnace is a uninterrupted operation that feeds stuff into a revolving furnace that passes the stuff through the reduction atmosphere so removes the stuff near when it completes the full rotary motion ( figure 2 ) . Unlike the Midrex procedure the Fastmet procedure uses mulcts as a feedstock. This allows for the recycling of EAF mulcts and mill dust that would be otherwise disposed of as a risky stuff. The Fastmet procedure uses a C cut downing agent and O burners. The C can be from legion beginnings such as coal, C bearing wastes, and coke. The procedure is seldom run utilizing coke due to the high cost of the coke and the procedure being capable of running on lower quality C mixes. The procedure requires a pelletizing or a briquetting operation due to the provender stock being mulcts. The full procedure requires between six and twelve proceedingss to finish. The rotary fireplace furnaces produce a direct reduced Fe with a metallization runing from 85-92 % depending on the quality of the provender stock.
Fluidized bed reactors are a batch reactor that introduces the stuff into the reactor so the reduction gasses are fed into the underside of the vas with adequate force per unit area to drift the provender stuff. This natation of the provender stuff allows for all of the surface country of the stuff to be exposed to the reduction gasses. There are several signifiers of fluidized bed reactors being used in the market today. The difference between the reacting vass is the figure of responding vass and the type of fuel used to making the reduction gases. The first type of fluid bed reactor is the Finmet procedure using Fe ore mulcts or EAF dust as a provender stuff and natural gas as a cut downing fuel. This procedure uses up to a four phase reactor with the progressive phases utilizing a higher gas speed and a lower reaction clip to derive between 91 % and 93 % metallization ( figure 3 ) . The Finmet procedure requires a briquetting operation because the provender stock is mulcts but because of necessitating a high pureness natural gas fuel it produces a really low residuary HBI.
The following two procedures, Circofer and Circored, both feature a two phase fluidized bed reactor with the first phase being a short keeping clip vas with a high gas speed and the 2nd phase a long keeping clip with a low gas speed ( figure 4 ) . The difference between the two is that the Circofer procedure uses metallurgical coal for a fuel while the Circored procedure uses natural gas. Both of these reach an mean 92 % metallization and provender pellets.
Hsysla steel developed a traveling bed reactor to make DRI ( figure 5 ) . The Hyl procedure provenders lump Fe into the procedure and a high H content reformed natural gas. The high H is created by reforming with a nickle-based accelerator. The Hyl procedure uses an elevated temperature and force per unit area to increase the processing clip for the reactions. The high H and the elevated temperature and force per unit area create a high quality DRI with 93 % mean metallization.
The concluding reactor vas is the Allis Chalmers controlled Atmosphere Reactor ( ACCAR ) . The ACCAR uses a counter flow rotary kiln. The rotary kiln procedure uses a low quality but extremely reactive coal to make cut downing gasses ( figure 6 ) . The rotary kiln produces a DRI with a 92 % metallization. The responding vas does non use any of the station burning in the procedure but station burning vass have been added to the procedure to make adequate energy to power the full installation and add some back to the grid.
With DRI being produced in many different treating methods there are some cardinal characteristics that set some appart from the others. The rotary kiln, shaft furnace, and the traveling bed reactor vass produce the highest metallization. The rotary fireplace furnace has the fastest procedure clip. The most popular on the market right now is the Midrex shaft furnace with about 60 % of the market portion of DRI production ( table 1 ) . DRI is a stuff that EAF operations have come to depend on and will go on to increase usage due to the high cost of hog Fe and the continued recycling of bit steel.
Table 1 ) Comparative sum-up of procedures as of 2008