|Title of Invention||
A PROCESS FOR PRODUCTION OF HIGHLY METALLIZED DRI (DRY REDUCED IRON) WITHOUT REMOVAL OF ZN FROM ZN- BEARING IRON ORES AND OTHER LOW BOILING POINT ELEMENTS
|Abstract||A process for producing good quality of DRI from iron ores containing higher contents of low boiling point elements like Na, K, Zn etc comprises flowing Co + H2 + N2 reducing gas from the bottom of the reactor equipment to upward direction wherein the downward moving bed of iron ore takes part in reaction in counter current of reduction gas flow and maximum degree of metallization takes place at a temperature between 750° - 800° C inside the reactor characterized in that said maximum degree of metallization of reduced iron ore is achieved without imparting reduction or vaporization of low boiling elements.|
-2-FIELD OF INVENTION
The present invention relates to a process for production of Dry Reduced Iron (DRI) from Iron ore in a gas based, moving bed counter current reactor or furnace. More particularly the present invention relates to a process for production of highly metallized DRI (Dry Reduced Iron)without removal of low boiling point elements like Na, K, Zn from Iron ores.
BACKGROUND OF THE INVENTION
Generally, the processing of iron ores containing the low boiling point elements like Na, K, Zn etc pose the operation problem like recirculation in the reactor of furnace, vaporization, deposition over descending raw materials and refractory lining of the reactor of furnace.
Deposition of such element over refractory linings and subsequent its damage reduces the campaign life of the reactor or furnace. The deposition over refractory lining further leads to formation of scaffolds which during operation may fall suddenly into the raw material and disturb the thermal-state and hence increased energy consumption.
Deposition over descending raw materials lead to increase in content and hence deterioration of the properties of the raw materials. This in turn leads to various operational instabilities like poor permeability of descending solid bed to the ascending reducing gases, in turn reduces productivity and increases the fuel consumption.
Removal of such elements into the exhaust gas and subsequent carryover and its continuous accumulation in gas pipeline due to gas-recirculation further restricts its use as secondary fuel.
-3-Thus the present invention relates to a new process which eliminates all the above mentioned operation problems imparted in the existing process and produce the good quality DRI from the said ores.
OBJECT OF THE INVENTION
It is therefore an object of the invention to develop a process for production of
highly metallized DRI (Dry Reduced Iron) without removal of from zn bearing
iron ores and other low boiling point elements which eliminates the
disadvantages of the existing conventional state of-the arts.
Another objects of the present invention is to develop a process for production of highly metallized DRI (Dry Reduced Iron) without removal of Zn from Zn bearing iron ores and other low boiling point elements which enhances a higher degree of metallization.
A further object of the present invention is to develop a process for production of
highly metallized DRI (Dry Reduced Iron) without removal of Zn from Zn bearing
iron ores and other low boiling point elements which restricts the removal of low
boiling point elements like Na, K, Zn etc.
SUMMARY OF THE INVENTION
The present invention relates to develop a new dry reduced iron process for processing Zn bearing iron ores ensuring that the Zn remaining in the DRI without going into vapour phase so that the problem associated with Zn vaporization can be overcome. The iron ore (ROM) is first of all beneficiated and then prepare pallets like, conventional process of production. Thereafter a new process develop for
iron-ore reducing at lower than 850° C temperature which prevents Zinc-oxide reduction and its vaporization.
The thermodynamics investigation conducted for gas-based reduction process with objective of restricting the Zn-reduction and achieving higher degree of reduction of iron-oxides. The reduction experiments were conducted for different combinations of C0+N2+ H2 gas mixture at five different temperature levels in the range of 700°-900°C. Zinc bearing magnetic iron ore of known properties was converted into roasted pallets using standard peptization technique and subsequently reduced with the mentioned reducing gas-mixtures. With increasing the reduction temperature, the degree of metallisation increases for all the reducing gas-mixtures CO + N2 and CO+H2. Here N2 is used as a gas carrier. The incorporation of H2 into the reducing gas mixture improves the degree of metallisation but lower the temperature of Zn-reduction from the fired pellets. Thus proper selection of reducing gas mixture and temperature of processing can allow production of DRI without removal of Zn from such iron-ores.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURES
Fig 1 - shows a flow diagram of the existing process.
Fig 2 - shows a flow diagram of the new process as per invention.
Fig 3 - shows a thermal profile representation of pellet roasting.
Fig 4 - shows a photograph of fired pellets
Fig 5 - shows a graphical representation of degree of metallisation.
Fig 6 - shows a graphical representation of energy equilibrium with temperature
Fig 7 - shows a graphical representation of carbon deposition with temperature
Fig 8 - shows a graphical representation of extent of Zinc removal from the reduced
pellets with increasing temperature and for different CO + N2 gas mixture.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to development of a new process of Dry reduction of iron ore containing higher percentage of low temperature boiling metals. According to conventional process phrase the iron ore from runs of mines is first of all mixed with quarters coning method. The mixed ore is then manually magnetically sorted to decrease the gangue content and increase the Fe content of the ore. Finally the sorted ore was screened to get it size distribution as shown in Table 1.
The iron ore is taken in respective fractions as mentioned in Table -1 and ground to under 200 mesh size. The ground ore is well mixed in turbo mixture. Thus mixed ground iron ore is quarter coned and four representative samples is taken from each cone for chemical analysis of these iron ore samples are shown in Table - 2. The ore's FeO and Zinc contents are relatively higher.
2nd stage is the preparation of pellets under conventional route wherein ground ore of below 200 mesh is mixed with 2% binder, bentonite, and again mixed in turbo mixer. The 6.5% moisture is added to thus mixed iron ore and bentonite to make green -mix. The green-pellets is prepared manually from the green -mix. The green pellets then dried in an oven over night.
3rd stage is pellet firing/ roasting the dried pellets are subjected to roasting in a specified thermal cycle, (Fig - 3). The sample is heated upto 1250° C at 3° C/min and held for 2 hours and finally furnace cooled till room temperature is reached.
The photograph of the fired-pellets is shown in fig - 4. The chemical analysis of the fired pellets as shown in table 3. The chemical analysis of fired pellets showing that magnetite fraction of the ore is completely oxidized to Fe203 and hence expecting the improved reducibility of the fired pellets which can be confirmed in subsequent section on gas based reduction of fired pellets.
Gas based reduction as per new process of the invention. The fired pellets are finally reduced in a reduction equipment to simulate a counter current gas based DRI process. The reduction experiments are conducted for 100 gm of sample (fired pellets) and Co + N2 + H2 gas mixtures in the temperature range 700 - 900° C at 50° C internal.
The experimental parameters are represented in Table 4 & Table 5 Table 4: Experimental details of the reduction experiments
Note :- Degree of Metallisation is defined as the ratio of Fe (Metallisation) and Fe (Total) is percentage basis
The degree of metallisation of reduced pellets with the reduction temperature for different combinations of Co + H2 + N2 reduction gas mixture is shown in fig - 5. The degree of metallisation increases with increasing reduction temperature for all the reducting gas mixture i.e Co+ N2 (total flow rate 4.00 LPM in the 95.05 volumetric ratio), H2+N2 (total flow rate 1.05 LPM in the 95.05 volumetric ratio %) and Co + H2 (total flow 3.00 LPM in the 67:33 volumetric ratio %)
The reduction with pure H2 has found better metallisation compared to other two mentioned reducing gas mixtures. The increase in reduction temperature decreases the extent of Fe2 03 reduction with reducing gas CO and increases with reducing gas H2 due to corresponding increase in CO/CO2 ratio and decrease in H2/ H20 ratio. As mentioned in figure 6. The wuestite Fei-x-0 reduction decreases with CO and increases with H2. Further, the reduction of Fe203 with H2 gas has relatively faster kinetics than CO gas, which can be observed the trends between Co + N2 gas mixture versus H2 + N2 gas mixture. Thus addition of H2 gas with CO gas always helps in increasing the degree of the metallisation with increase in the reduction temperature.
The reduction with CO + N2 is observed deposition of the carbon which increases with the decrease in the reduction (fig - 8)
Further reduction with H2 + N2 gas mixture (total flow rate 1.05 LPM in the 95.05 volumetric ratio %) is showing insignificant increase in metallisation with reduction temperature rise.
EXTENT OF ZINC REMOVAL AND ITS REDUCTION TEMPERATURE FROM FIRED PELLETS
The actual Zinc content of the reduced pellets with increasing reduction temperature for different combination of Co + H2 + N2 reducing gas mixtures is shown in fig - 8.
The highest temperature at which the Zinc reduction starts (insignificant removal of Zn from the fired pellets in reduction -stage, hereafter it is being referred as Zn reduction temperature) is varying for different Co + N2 + H2 reducing gas -mixtures.
The Zn reduction temperature was found in the range of 800° C - 750° C, for the above mentioned gas-mixtures. Further it can be observed that the incorporation of H2 gas in the reducting gas-mixture lowers the Zn reduction temperature.
The two prime objectives of the invention are the achieving highest degree of metallisation with insignificant removal of the Zn from the fired-pellets. Based on the result observed, the following conclusions are being drawn.
1. The low boiling point element Zn in the fired pellets can be held below the temperature range 750° C - 800° C depending on the exact composition of the reducing gas mixture of Co + H 2 + N 2
2. The degree of metallisation of fired pellets can be increased through incorporating of the H2 gas in the reducing gas mixture.
3. The extent of Zn removal and its reduction temperature are found to be dependent on the composition of reducing gas mixture Co + H2 + N2. Incorporation of H2 gas into the reducing gas-mixture decreases the Zn education temperature. Further, increase in reduction temperature increases both the chances and extent of Zn removal from the reduced pellets.
The two prime objective of the present invention can be achieved through proper selection of both the reducing gas composition and the upper temperature of the reduction process.
1, A process for production of highly metallized DRI (Dry Reduced Iron) without removal of Zn from Zn-bearing iron ores and other low boiling point elements, comprises:
- Mixing the iron ores with binder and moisture to make green mix obtaining the
ores in either lump form and pellet form
- Firing of the said pellets to get the dry strength to be suitable for storing and
transporting over distances and heights
-charging the said pellets into the reactor or furnaces
- flowing Co + H2 + N2 reducing gas from the bottom of the reactor to upward
direction wherein the iron ore moving in downward direction take part in
chemical reaction with the counter current of the reduction gas flow
characterized in that maximum degree of metallization of reduced iron ore is
achieved at a temperature between 750° - 800° C inside the reactor without
imparting reduction or vaporization of low boiling elements.
2. The process as claimed in claim 1 wherein the reduced gas CO + H2 is mixed
in the ratio of 2:1 (V/V) and N2 is used as gas carrier.
3. The process as claimed in claim 1 wherein the maximum degree of
metallization is achieved in the range of 72% to 77%.
A PROCESS FOR PRODUCTION OF HIGHLY METALLIZED DRI (DRY REDUCED IRON) WITHOUT REMOVAL OF Zn FROM Zn BEARING IRON ORES AND OTHER LOW BOILING POINT ELEMENTS
A process for producing good quality of DRI from iron ores containing higher contents of low boiling point elements like Na, K, Zn etc comprises flowing Co + H2 + N2 reducing gas from the bottom of the reactor equipment to upward direction wherein the downward moving bed of iron ore takes part in reaction in counter current of reduction gas flow and maximum degree of metallization takes place at a temperature between 750° - 800° C inside the reactor characterized in that said maximum degree of metallization of reduced iron ore is achieved without imparting reduction or vaporization of low boiling elements.
|Indian Patent Application Number||885/KOL/2009|
|PG Journal Number||09/2014|
|Date of Filing||19-Jun-2009|
|Name of Patentee||TATA STEEL LIMITED|
|Applicant Address||RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR 831001|
|PCT International Classification Number||C21B13/00|
|PCT International Application Number||N/A|
|PCT International Filing date|