Iron Ore Pelletization Technology

Transcription

1 Iron Ore Pelletization Technology & Need Sanjay Wadhwa M.P. Bhardwaj D.D. Kapur Korus Engineering Solutions Pvt. Ltd. 1

2 Need for Pelletization In our country as a whole, about 65% of iron ore production is in the shape of fines as against 35% of lumps due to the fragile nature of our Iron ores. The ratio of fines to lumps at the time of mining itself has been increasing on an average of 1% every year. Another 10-15% fine is generated at the time of converting it into sized ore, handling at mines, railway sidings and ports. 2

3 Need for Pelletization Due to selective mining, naturally found iron ore deposits are depleting, hence there is a dire need to use it with wisdom and conserve the same to the best possible extent. As per the projections* made in 2010, the reserves of high grade lumpy ore will last for about ten years. (* - Adapted from C-tempo) 3

4 Need for Pelletization To meet the increased demand of the Steel industry, even the Low Grade Iron Ores need to be utilized for which they have to be concentrated by removing the gangue material by grinding to the liberation size. These Concentrated fines have essentially to be pelletized. Subsequently, the Ministry of Mines has decided to lower the cut off level of Fe in hematite ore from 55% to 45%. This category of ore will be separately stored in the mines and will require crushing and grinding prior to beneficiation. 4

5 Need for Pelletization Pellets form one of the best options of agglomeration of fines, due to their excellent physical and metallurgical properties. Moreover, due to their high strength and suitability for storage, pellets can be easily transported over long distances, with repeated transshipments if necessary. 5

6 Indian Scenario At present, the total installed capacity of pellet plants in India is about 14% of world pellet capacity. India is placed at 7th position. USA maintains the leading position followed by Brazil & China. The existing capacity of pellet production in India is about 67 million tonnes*. (* - adapted from C-tempo) 6

7 Indian Scenario Pellet Producing States * (* - Adapted From C-tempo) 7

8 Pellet Producing Capacities (Present and Anticipated till 2015) * Country/ Company District State Adhunik Metaliks Jamshedpur Jharkhand Arya Iron and steel Barbil Orissa Akshita Industries Ardent steel (subsidiary of GPIL, Hira Group) Keojhar Orissa Bhusan power and steel Jharsguda Orissa BMM Ispat Hospet Karnataka Brahmani River Pellets Ltd. Stemcor) Jajpur Orissa Cosmos sponge and iron Chhattisgarh Essar Paradip Orissa Visakhapatnam Andra Pradesh Essel Mining Euro bond industries Jabalpur Madhya Pradesh Godawari Power and Ispat Ltd. (Hira group) Raipur Chhattisgarh Ispat Industries Visakhapatnam Andra Pradesh (* - Adapted From C-tempo)

9 Pellet Producing Capacities (Present and Anticipated till 2015) * Country/ Company District State JSPL Barbil Orissa JSW Steel Bellary Karnataka KIOCL Karnataka Mandovi Goa Goa Monnet Ispat Raigarh Chhattisgarh MSP Steel Jharsguda Orissa Raigarh Chhattisgarh MSPL Koppal Karnataka NMDC Dantewada Chhattisgarh Bellary Karnataka Sarda Energy Raipur Chhattisgarh SAIL Gua Jharkhand Shri Bajrang power & Ispat Raipur Chhattisgarh Sunil Ispat and Energy Tata Steel Jamshedpur Jharkhand Xindia steels Phase II Karnataka Unspecified India Total India (* - Adapted From C-tempo)

10 Agglomeration Agglomeration is done either by Sintering or Pelletizing. The fundamental difference between Sintering and Pelletization is that while the coarser spectrum of fines of the order of mm are gainfully utilized in sintering process, the micro fines or the so called ultra fines of the order of micron, which otherwise is unsuitable for production of sinter, are utilized in Pelletization 10

11 Pelletization Process Pelletization is a process of agglomeration where micro fines, either in the form of beneficiated concentrate or without beneficiation, are rolled into green balls (9-16mm) before subjecting them to high temperature for heat hardening. 11

12 Pelletization Process Green Ball Formation Drying of Green Balls Preheating Induration Cooling 12

13 Green Ball Formation Green Ball formation is the first step of pelletization The ball formation is achieved by rolling of solids and liquid mix in balling units. The green ball formation is similar to snow-ball growth by layering. 13

14 Green Ball Formation - Stages Water Particle Liquid Bridge Addition of particles due to Rolling Voids Compaction due to Rolling Surface tension of the water film keeps the particles together 14

15 Green Ball Formation - Stages Dry solids when come in contact with water, the ore surface is wetted and particles contact each other. Due to surface tension of water film, liquid bridge is formed. As a result of movement of particles in the balling unit more and more particles combine with the help of water droplets and form agglomerates. 15

16 Green Ball Formation - Stages The interiors of the agglomerates, have lot of voids which go on compacting by further addition of water. The agglomerates grow as more and more materials stick in layers. In the final stage particles are fully coated with water film and held together with surface tension force of water droplets. The balls are compacted because of rolling actions of balling machine. 16

17 Green Ball Formation - Stages Development of Different Layers in a Pelletizing Disc. Movement of Feed in Various Stages. 17

18 Properties of Green Ball Strength of pellets depend upon properties of green balls during the subsequent stages of pelletization process The two most important properties of green balls are crushing strength and drop resistance. Higher crushing strength prevents green pellets from breaking and higher drop resistance provide transportability. These two properties are achieved from good quality concentrates, use of binder and optimum use of water in green ball formation 18

19 Factors Effecting Green Ball Strength Grain size Size distribution Specific surface area (cm 2 /g) Wetability and Adsorption capacity of water The above properties depend upon the fineness of ore (less than 0.045mm or 325 mesh) 19

20 Compressive strength of green pellets in N/pellet Influence of particle size : I) Hematite-green pellets II) Ore mixture-green pellets III) Ore mixture-fired pellets Particle size <0.045mm in % Specific surface in cm²/g Influence of particle size and specific surface area on compressive strength of green and indurated hematite pellets III II I Compressive strength of fired pellets in N/pellet 20 Adapted from: Pelletizing of Iron Ore By Kurt Meyer

21 C o m p ressiv e s tre n g th in N /p e lle t II I I Compressive strength II Tumble resistance Particle size <0.04mm in % Influence of particle size on compressive strength and tumble resistance of indurated pellets T u m b le resista n c e <0.6 m m in % Adapted from : Pelletizing of Iron Ore By Kurt Meyer 21

22 specific surface of ore III I 1100cm²/g II 2850cm²/g III 3270cm²/g II A 3 I III B 30 II 20 I H2O in % Combind effect of moisture content and specific surface area on green pellet properties 22 Compressive strength of green pellets in N/pellet Drop numbers X 46cm Adapted from : Pelletizing of Iron Ore By Kurt Meyer

23 I) Pellet forming efficiency II) Moisture in green pellets I Pellet forming efficiency in kg/m²h %H2O in green pellets Adapted from : Pelletizing of Iron Ore By Kurt Meyer II %H2O in magnetite concentrate Influence of original moisture content in concentrate on pelletizing disc - efficiency

24 Use of Binder There are two types of binders:- Organic (no more used in iron ore pelletization) Inorganic Inorganic binders are bentonite, Ca(OH) 2, Lime etc. Bentonite is more commonly used in pelletization of iron ore. It contains 60-70% SiO 2 and 15-20% Al 2 O 3. It combines with water and form a gel 5 to 6 times of its weight. Its volume increases 10 times. It envelopes ore grains together with water and provide bonding. The bentonite is used in very small quantity ( %). The binder provide strength to green ball because of its binding properties. 24

25 50 I green pellets II dry pellets II Compressive strength in N/pellet II I Bentonite in % Hematite Magnetite Influence of bentonite on green and dry pellet compressive strength I Adapted from : Pelletizing of Iron Ore By Kurt Meyer 25

26 Drying of Pellets The following drying processes are adopted. Up Draft Down Draft Combine up & down Draft The combined process gives faster drying. 26

27 Drying of Pellets Drying of pellets is done in the temperature range of C. In the drying process water slowly evaporates and water bond of green pellets is replaced by solid bond. Drying process depends upon speed of hot gases and duration of heating. Normally, drying process takes about min. 27

28 Drying of Pellets Drying of green pellets start when hot air or combustion gases flow over green balls. Gas temperature, dew point, quantity of gas flow and gas velocity play an important role in drying of pellets. The process starts with evaporation of moisture from the surface of pellets. After this evaporation, water from the interior of the pellets is emitted by capillary forces to the surface and evaporates. As long as this process continue, the drying velocity remains constant. If the drying velocity on the surface of pellet is higher than the water emission from the interior of the pellet, the drying process travels downward. The capillary action dries down and water vapour not able to travel to the surface, thus drying velocity slows down. 28

29 Drying of Pellets There are three different drying velocity ranges:- Range I Water evaporates at constant velocity i.e. evaporation of surface water. Surface water dries faster than the water emitted from the interior of pellets. In this case drying velocity slows down. If the pellet contains moisture other than surface and capillary water, the drying procedure continues under other conditions. In this case temperature of the drying gas is of importance for dissociation of water compounds. Range II Range III 29

30 Surface moisture Capilary moisture Hygroscopic moisture I II III Drying Phases of moist material Drying stages of moist material 30 D rying velocity in kg/m ².h Adapted from : Pelletizing of Iron Ore By Kurt Meyer

31 Preheating of Pellets In the grate kiln process preheating zone is C. During preheating process several reactions take place such as decomposition of carbonates, sulphates, hydrates etc. In this process oxidation of magnetite takes place to hematite 2Fe 3 O 4 +½O 2 = 3Fe 2 O 3 Fresh crystals of hematite provide very strong bonds to pellets. The pellet strength goes up from 200N at 400 C to 1100N at 1100 C. There is no change of strength if pellets prepared form hematite concentrates because no re-crystallisation takes place of hematite at preheating temp. 31

32 Induration of Pellets After drying, pellet passes to preheating and induration or firing zone. The temperature of firing zone is C. The change in crystalline structure at high temperature in firing zone either by crystal transformation and growth upon oxidation of magnetite to hematite or by crystal growth when only hematite is used, provide strong bonding action to the ore particles which in turn provide sufficient compressive strength to the pellet. 32

33 Bonding by Change of Structure Re-crystallisation of hematite takes place at 1300 C to 1350 C. The basic changes in firing cycles are :- Re-arrangement of molecules due to which particles draw closure. Further rise of temperature, mobility of ions in the latice increases which leads to rearrangement of molecules, vacancies are occupied and inclusions are eliminated. 33

34 Bonding by Change of Structure Basic changes in firing cycles Cont. Dislocations intensify which help adjacent crystals to diffuse. Crystal bridges are formed between individual grains. These bridges lead to a consolidation of conglomerate. On further energy supply, bridge formation changes to bridge bonding and re-crystallisation intensify. After the final stage pores between the grains get smaller and rounding of grains takes place. 34

35 Bonding by Change of Structure Basic changes in firing cycles Cont. After this stage and on further heating, fusion and melting will start, which must be avoided. After induration cycle, pellets get sufficient compressive strength (>2500 N) which is required for transportation and storage. Hematite pellets consume more energy and give less output as compared to magnetite pellets. Total heating cycle of hematite pellets is longer than magnetite pellets or mixed concentrates pellets. Total thermal cycle of hematite is 39 min. as compared to 33 min. of magnetite pellet. 35

36 Adapted from : Pelletizing of Iron Ore By Kurt Meyer 36

37 Cooling of Pellets Pellets comes out from indurating furnace at temp C, are cooled by blowing air in the cooler. The air is preheated during cooling which is used in drying and preheating of green pellets. The process gives optimum energy utilization. Pellets are cooled below 100 C and send to storage bunker. Indurated pellets can be transported to any distance and can be stored for any length of time without deterioration. 37

38 Quality of Pellets Cold Compressive strength : >2500 N/ Pellet Tumble Index +6.33mm : >95% Abrasion Index -0.5mm : <5% Pellet Size (9-16mm) : >89-90% Fines (-1mm) : <1% High porosity, reducibility and metallization degree Chemical composition depends upon the quality of concentrates used. 38

39 Pelletization Process Routes There are two major processes dominating the world Pelletization scenario Traveling Grate Process Grate Kiln Process 39

40 Process Routes Comparison Item Traveling Grate Grate Kiln Heat hardening cycle Drying, preheating, induration and cooling are done on a single grate. Drying and preheating on a grate, Induration in rotary kiln and cooling in annular cooler. Grate bars Grate bars subjected to high temp; side & bed layers necessary. No side or bed layers necessary. Bed depth is nearly half. Pellet movement Pellets remain stationary throughout the process. Pellets tumble continuously in rotary kiln. Burners Large number of burners along the length of induration furnace. Single burner is used for the kiln. Fans Several fans operating in series with multiple fan controls Less number of fans with single fan control Largest m/c 768m2 (CVRD) and 744m2 (Samroo) with capacity 7 MTPA and 6 MTPA each LKAB-3, GIIC-Bahrain and Tildon-2 with capacity of 4 Mt/yr each Installed capacity About 193 Mt. About 113 Mt. Process flexibility Due to same speed through the Drying, Induration & Cooling zones, any changein one section effects the residence time in another Independent speed control of the Grate, Kiln and Cooler are available. 40

41 Our Experience 4.5 mtpa Iron Ore pellet Plant at Barbil for JSPL Straight Grate Technology 1.2 mtpa Iron Ore Pellet Plant at Bhilwara for Jindal SAW. Grate Kiln Technology. 41

42 Our Experience PELLET PLANT JSPL Barbil Orissa. Capacity Million Tonnes Per Annum 42

43 Detail Engineering Plant Facilities Stacker-cum-Re-claimer for storing & Reclaiming the Ore Wagon Tippler to receive Coal & Lime stone through rail road` Additive Storage for Coal & Lime Raw Material Storage Bins Rotary Dryers 2 Nos. Iron Ore Grinding Ball Mills 2 Nos. Bentonite Grinding Mill -1 No. 43

44 Detail Engineering Plant Facilities- Cont. Storage Bins for Ground Ore, Bentonite and Lime stone Mixing & Blending Paddle Mixers 2 Nos. Storage Bins for Mixed & Blended material 6 Nos. Pelletizing Discs 6 Nos. Indurating Furnace -1 Nos. Screening Station Pellet Storage & Wagon Loading Facility Interconnecting Conveying Network 44

45 Detail Engineering Water System Raw water Reservoir with Pumping & Filtration system Make-up Water Cooling Water Recirculation system Process Water system Compressed Air System Plant Air Atomizing Air Instrument Air Fuel supply system Furnace Oil Unloading, Storage & Pumping system Coal Gas supply system LPG storage & supply system 45

46 Detail Engineering 220/ 33 kv Switch Yard (MRSS) 33 kv/6.6kv main Substation 6.6kV Local Substation Transformers Power Distribution, Motor Control Centers & Distribution Boards Drives & Automation HT,LT control Cables & Accessories Plant Earthing Plant Shop Lighting Plant Communication Power Factor Improvement Equipment AC, DC Motors Electrical Installation 46

47 Construction Work Volume Concreting (excluding Raw Material Storage & Rail Siding) Steel Structure (including Indurating Fce.) Plant & Equipment Technological Structure Refractory m t t 3200 t 2000 t 47

48 Quality of pellets Constituents Value (%) Fe (t) SiO Al 2 O CaO 1.20 MgO 0.18 Others 0.45 Basicity (CaO/SiO 2 )

49 Mechanical Properties of Finished Pellets Size 9 to 16 mm 93% + 16 mm 5% max - 5 mm 3% max Porosity 24 to 28% Cold Crushing Strength (CCS) 250 kg/p (min) ASTM Tumbler Index (+6.35 mm) 94% max Abrasion Index (-0.6 mm) 4% max JIS Swelling Index 18% max JIS Reducibility 70% min Compression Strength after Reduction 30Kg / p 49

50 Services Required (per Tonne of Pellet) Fuel ( Producer Gas / Furnace Oil) k Cal Make Up Water 0.26 m 3 Compressed Air 8.0 Nm 3 Grinding Media 0.25 Kg Refractory 0.15.Kg Electric Power 77 kwh ( for Pellet Plant Including Raw Material Storage) Electrical Power (for Coal Fuel Gasification) 19 kwh 50

51 Our Experience PELLET PLANT Jindal SAW, Bhilwara (Rajasthan). Capacity 1.2 Million Tonnes Per Annum 51

52 Our Experience Main Equipments / Units Iron Ore Concentrate Storage Shed Proportionating Building Iron Ore Concentrate Bins 2 x 370 m3 (1100 t each) Sized Iron Ore Bin 1 x 35 m3 (100 t) Ground Bentonite Bins 2x 40 m3 (35 t each) Dust Bins 2x 35 m3 (100 t each) Pelletizing Disc Building Pelletizing Discs 6 x 6 mø 30 tph ; 40 to 50 Indurating Building Travelling Grate Rotary Kiln Circular Cooler 4 x 42 m; Bed Area 168 m2 5 m Ø x 35m 69m2 52

53 Construction Work Volume Concreting m 3 Steel Structure 572 t 53

54 Process Flow & Site Pictures 4.5 mtpa Pellet Plant Process Flow Site Pictures 1.2 mtpa Pellet Plant Process Flow Site Pictures 54

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