1. Producing gold out of dust
Sintering
Producing gold out of dust
R D Sharma
AGM
SPIII

2. CONTENT CONCEPT OF SINTERING. RECENT TRENDS IN SINTERING.
A CASE STUDY WHERE BETTER SINTER PRODUCED EXCELLENT RESULT IN BF.

3. Agglomeration Processes
1. Briquetting, 2. Sintering & Pelletizing
1. Briquetting:
The simplest and earliest process for agglomerating fine-grained raw materials is briquetting.
Fine-grained iron ores are pressed into briquettes with the addition of some water or another binder under high mechanical pressure.
These briquettes may undergo direct further treatment or thermal processing before their use.
Their metallurgical behaviour in melting or reduction furnaces is very good
Iron ore briquetting could not make headway since the processing costs are relatively high
Production capacity of briquetting units is limited
It is still utilized to agglomerate small quantities of dust or other circulating materials.
This process has acquired growing importance for briquetting of fine- grained sponge iron.

4. Agglomeration Processes
Sintering: The presently most important agglomeration process is down- draught sintering.
It differs from pelletizing by various characteristics:
coarser-grained ore particles up to a dia. of 8 mm
Coke breeze --- main energy source
Heating up of the granulated mix to slightly above the softening
The final product consists of a spongy sinter cake which is brought to the necessary grain size of mm.

5. SINTERING TECHNOLOGY
An enormous amount of fines (40-50 %) is generated during minining and ore dressing operations. Since the fines cannot be charged directly into the BF, it is necessary to agglomerate them into lumps which is predominately by sintering and pelletizing process. Agglomeration [2] by sintering is achieved by the application of heat which results in the conversion of ore fines into large hard porous lumps is caused by:
An incipient fusion of ore particles at the contact surface which binds them together.
Formation of diffusion bonds through recrystallization and crystal growth of hematite and magnetite which keep the particles together without melting.
Iron ore sintering [3] has stood at the heart of the ferrous metallurgical processes for over half a century. Besides iron ores, it can also be applied for sintering of manganese ore fines. Sintering is a process in which iron ore fines, coke breeze, limestone fines, dolomite/ dunite fines, iron and flux bearing fine waste products of the steel plant are converted into coarse agglomerates on a permeable grate by fusion

6. HISTORY OF SINTERING AT A GLANCE
Year
Raw Materials
Method A.
1887
Sulphide Iron Ore
2 – 3 T of Iron Ore/Batch
Roasting lasted to Hr B.
1905
Iron Ore with Coke or Coal
Full scale agglomeration of mixture in tank C.
1906
Iron Ore with Flue Dust
Vacuum was applied in sintering pot D.
Iron Ore with Coke and Flue Dust
Conveyer type endless sintering machine.

7. Year 1911 First successful operation of Dwight and Lloyed
Sinter machine
Area : 8.3 M²
Strand : mm wide & 7700 mm long

8. Types of sinter[6] Non fluxed sinter– no flux added in sinter
Self flux sinter– extra flux added in BF to cater to coke ash
Super fluxed sinter – no flux added in BF

9. IMPORTANCE OF SINTERING
1) FLEXIBILITY OF CHEMISTRY
2) NO NEED OF ADDING LIME STONE AND DOLOMITE STONE IN BLAST FURNACE
3) DECREASE IN COKE RATE IN BF WITH SUPER FLUXED SINTER – coke rate in BF decreases due to
following reasons[6] :-
a) Elimination of moisture, hydrated water and other volatile material on sinter strand with cheap fuel.
b) Calcination of limestone inside the BF is very expensive of carbon. Approximately kg C/100 kg of CO2 which is equivalent to 230 kg of CaCO3 i.e. limestone, are saved by transferring the calcinations work to the sinter strand.
c) Better reducibility and enhanced indirect reduction (6-7 kgC saved for every one percent increase in indirect reduction).
d) Use of higher blast temperatures because the thermal load is smaller and the slag is pre made. The primary slag melts at higher temp and does so within a vertically narrow softening zone.
e) Avoidance of CO2 generated from limestone in the stack which adversely affects indirect reduction.

10. 4) Narrow softening range 5) Better reducibility 6) Use of sinter increases productivity[7]
performance at Stanton plant
BF PROD. PER DAY (TONS)

11. SP3 MACHINE 1 COMPLEX
SINTER M/C
SINTER

12. Demand of Sinter Blast Furnace Mines Sinter Plant Ore Sinter Ore Fines27

13. Sinter Sinter Machine Ignite Suction Sinter Iron Ore Fines Lime Stone
Coke
Sinter Machine
10500 C
Ignite
Suction
Sinter 28

14. Process Flow of SP-III RAW MATERIAL Mixing cum Nodulising Drum Sinter
(Iron Ore Fines, Coke, Flue Dust, Mill Scale, Lime, Return Fines)
Mixing cum Nodulising Drum
ADDITIVE WATER
Loading chute
Sinter Machine
Sinter
Return
Fines
-5 mm
Crusher
Sinter Cooler No
Screens
Size>5mm
Yes
Final Sinter for Blast Furnace 30

15. PARAMETERS DETERMINING SINTER QUALITY
Fe in sinter : More than 55 %
Feo : 8.0 ± 0.5 as per demand of BF
RI (REDUCIBILITY INDEX) : 65 % Min.
RDI (REDUCIBILITY DEGRADATION INDEX) : 25 % Max.
Granulometry
Mean size of skip sinter : 20 mm (Min.)
+40 mm in skip sinter : 5 % Max.
-5 mm in skip sinter : 5 % Max.

16. PARAMETERS DETERMINING SINTER QUALITY
Mgo :3.0 +/- .5%
Cao-SiO2 : 5.25 ± 1% as per demand of BF
DTI
(DRUM TEST INDEX) :80 % Min.
STI : 95 % Min.
(SHATTER INDEX)

17. Sintering process stages
RDCIS intervention for beneficiation and agglomeration of iron ore fines at BSP
Nov , 2017, BMDC, BSP, Bhilai

18. Pressure drop during sintering
RDCIS intervention for beneficiation and agglomeration of iron ore fines at BSP
Nov , 2017, BMDC, BSP, Bhilai

19. Sinter plants in BSP
SP2 HAS 4 MACHINES OUT OF WHICH 3 M/C HAS SUCTION AREA OF 75 M2 AND ONE HAS SUCTION AREA OF 80 M2.
SP3 HAS 2 MACHINES
M/C-1 HAS SUCTION AREA OF 320 M2.
M/C -2 HAS BEEN COMMISSIONED IN NOVEMBER 2014 HAVING SUCTION AREA OF 360 M2

20. RECENT TRENDS IN SINTERING

21. NEW TECHNOLOGIES
These are the major technology that has been adopted/ patented across worldwide in iron ore sintering process.
Raw material preparation
1. Bedding and blending process
Use of High intensity mixer (Mixing efficiency) in Sinter Plant
3. Addition of lime to sinter mix (>50kg/t)

22. NEW TECHNOLOGIES Sintering process 4. Curtain Flame Ignition System
5. Traveling grate sintering process with EOS technology
6. Exhaust gas treatment through low – temperature plasma
7. Use of halide solution for improvement in high temperature property.
8. Low moisture sintering Operation

23. Raw material blending
Formation of full length bed as per norm of layer formation started from December-15 at ISP resulted in blending efficiency improvement. Variation of available lime in product sinter minimised

24. Blending improvement
Base mix preparation
Before
After

25. Use of High intensity mixer in Sinter Plant
Installed at RSP and BSP

26. Use of High intensity mixer in Sinter Plant
Eirich mixers are fed with fine ore, and then mix the dust thoroughly with the required additives.
Once homogenized, the material is moved into a second Eirich mixer where added moisture helps with granulation.
This process can produce exact results since moisture content can be precisely measured – as the material is well homogenized inside the mixer.
High mixture homogeneity and perfect moisture distribution can be obtained for optimum reaction conditions.
Good agglomeration leads to less dust production, good gas permeability, and reduced coke consumption

27. High intensity mixer and granulating

28. High intensity mixer and granulating

29. Tools of High intensity mixer and granulating

30. High intensity mixer and granulating

31. Material inside High intensity mixer

32. High intensity mixer benefits

33. Addition of lime in sinter mix
Lime strongest process intensifier and binder
Improves permeability in combustion zone
High surface tension of melt
Low viscosity of melt
Short solidification time
Mechanism of lime reaction:
Lime comes in contact with water, process of hydration starts and releases joule/Kg of Cao
Sinter mix temperature increases by 20 deg.C
Strength of granules increases due to quick coagulation of particles

34. Addition of lime in sinter mix
Advantages of lime >50Kg/t
Replaces maximum part of the raw flux charged in the sinter mix which reduces solid fuel rate (reduced calcinations) & the crushing and screening load of harder limestone &dolomite.
Pre heats the sinter mix
Lime acts as binder during pelletisation and helps in process of granulation
Increases the strength of pellets
Prevents formation of zone of over moistening during actual sintering process
Increases the porosity of bed, there by allowing to increase the gas flow through bed
Promotes formation of calcium ferrite
Activates the process of fuel burning in sintering process

35. Curtain Flame Ignition System

36. Curtain Flame Ignition System

37. Curtain Flame Ignition System
To improve the ignition of top layer of sinter mix and to reduce the specific gas consumption curtain flame ignition technology was introduced
The concept involves mounting the small capacity burners on the roof across the sinter bed.
The design concept involves changing the mode of heat transfer to the top layer of sinter bed for ignition by convection where the flame directly impinges on the charge-mix.

38. Curtain Flame Ignition System
Multi-slit burners produce wide, large and stable flame, which eliminates “no flame” areas and supplies minimum heat input for ignition, therefore saving energy. Reduction in total heat input of the order of 30% approximately has been achieved at commercial scale .
After the encouraging laboratory tests, the innovative curtain flame technology has been successfully implemented in sinter machines of SAIL plants

39. Traveling Grate Sintering Process With Emissions Optimized Sintering
(EOS) Technology

40. Traveling grate sintering process with EOS Technology
The Emissions Optimized Sintering (EOS) is a process developed in the 1990s where the entire sinter strand is housed and waste gases from the entire strand are re-circulated back to the entire surface of the strand.
Conventional sintering uses ambient air to transport heat within the sinter bed, requiring a high air flow rate.
EOS® developed by OutoTech, GmBH, Germany uses recycling technology to reduce off-gas volumes by 40 to 50 %, resulting in smaller secondary gas treatment systems.

41. Traveling grate sintering process with EOS Technology
Conventional sintering process
Sintering process with EOS technology

42. Exhaust Gas Treatment Through Low – Temperature Plasma

43. Exhaust gas treatment through low – temperature plasma
Active radicals of low-temperature plasma remove SOX and NOX and radicals.
Reduction in SOX, (>70%), NOX (>95%) and Dioxins (< 0.2 ng-TEQ/Nm3) has been achieved at commercial scale.
This is low cost with high pollutants removal efficiency process. Space requirement is less than other processes.

44. Exhaust gas treatment through low – temperature plasma

45. Use of Halide Solution for Improvement in High Temperature Property

46. Use of halide solution for improvement in high temperature property
The degradation of the iron bearing materials occurs because of reduction and related stresses introduced in the matrix due to phase changes.
It is a great significant to reduce the RDI (Reduction Degradation Index) of sinter by maintaining the reducibility of sinter unchanged, which is the property that will improve the permeability of blast furnace burden column.
Chloride solution can be used for improvement in RDI of sinter, which was immersed with different types and concentrations of solutions

47. Concentration of CaCl2 (%)
Result: Laboratory experiment on spraying of different concentrations of CaCl2 solution on product sinter
Exp. No.
Chemical analysis
RDI RI
FeT, %
FeO, %
SiO2, %
Al2O3 %
CaO %
MgO %
Concentration of CaCl2 (%)
Before CaCl2 spray
After CaCl2 spray
BeforeCaCl2
After Ca Cl2
1 (BSL)
54.47
8.62
5.2
3.24
10.2
3.7
1.0
27.0
14.6
61.5
2 (BSL)
0.5
15.3
3 (ISP)
51.26
7.48
6.0
4.4
13.5
2.7
24.2
12.0
4 (ISP)
50.4
8.6
22.0
61.7
62.2
5 (DSP)
58.7
7.5
4.3
2.6
7.6
2.0
37.6
14.0 6
57.3
9.9
4.8
8.5
0.1
19.8
11.6
55.2
54.5 7
0.2 8
(700 C)
8.4 9
(900 C)

48. Result: Laboratory experiment on spraying of different concentrations of CaCl2 solution on product sinter

49. Low Moisture Sintering Operation
An optimum moisture is required in sintering process.
Moisture has two functions
1) Improvement in balling,
2) Heat transfer in sintering process.
Low moisture helps in reducing coke rate.
Water is passed through a magnetic conditioner which reduces the surface tension from 72 to 65 dynes /sq.cm
Flow ability increases and mixes uniformly through out the sinter mix and helps in increase in ballability of sinter mix.

50. Mechanism Of Permeability Improvement by Addition Of Magnetic Water In The Granulation Drum
Reduction of surface tension water
Improves Degree Of Granulation due to dispersion
Reduction in Moisture Content of Sinter charge mix
Suppression of Re-condensation Process
Improvement in Sinter bed Permeability
Addition of Magnetic water in the Drum in place of normal water
Improvement in balling index
Reduction in specific coke breeze consumption

51. SCHEMATIC DIAGRAM OF MAGNETIC WATER CONDITIONER LOCATION
PMD (mixing drum)
Water line
Shuttle Conveyer
Sinter mix Conveyer
Intermediate bunker
Segregation Plate
Drum Feeder
Pallet

52. Waste heat recovery system at Bhilai
From Circular Sinter Cooler at Sinter Plant-3, to generate hot water for feeding to mixing and nodulising drum (MND) of SP-3
SP-3
From Straight Line Sinter Cooler of machine #4 at Sinter Plant-2, to generate hot water for feeding to secondary mixing drums of all the four machines of SP-2 (heat recovery ≈ 1.5 Gcal/h)
SP-2

53. WHRS scheme at SP#3, BSP Existing Planned
Heat recovery from Sinter Cooler
Unclean Air
Clean Air
to Atmosphere
Existing C
Heat recovery
2 Gcal/h
Planned
Rotation

54. WHRS scheme at SP#3, BSP MIXER PROCESS WATER PLATE HEAT DIVERTER VALVE
EXCHANGER
Hot air
5KL top up tank
SOOT BLOWER
EXPANSION
TANK 10 KL
Soft water unit
TO CHIMNEY
ID FAN
SINTER DUST

55. WHRS system at SP#3, BSP
S P-III, BSP is provided a deep bed circular cooler to cool hot sinter uo tp 100deg. C.
The cooler has a mean diameter of 35m, 3.5m width and height 1.6m. Retention time of sinter in cooler is one hour.
Air is forced by two cooler fans of capacity 13000m3/min each, flow vertically through hot sinter layer
Heat from first two troughs are being used for pre, and post heating of charge and also air for ignition of sinter mix.
Heat from remaining troughs are discharged to the atmosphere and the hot air temperature is 325 0c.

56. WHRS system at SP#3, BSP Proposed WHRS is in closed loop
Soft water is circulated in closed loop through shell and tube Heat Exchanger
In the secondary Plate Heat Exchanger, Process water will be heated from ambient to desired level (90 C)
Insulation of all the hot air ducts and hot water pipes
Requirement of Soft water is bare minimum
Higher water temp. is maintained in closed loop

57. WHRS system details Parameter SP-3 Hot air volume, ‘000 Nm3/h 50 to 60
Hot air Temperature, oC
Water quantity to be heated, t/h 30
Hot water temperature, oC
90 ±5

58. WHRS expected benefits
Recovery of heat to the tune of 1.5 to 2 Gcal/h.
Improvement in productivity by 2 to 5%
Reduction in coke rate by 2 kg/t.
Improvement in Tumbler Index by 1%.
Expected Reduction in CO2 emissions by 5,000 ton/year at SP-3
Reduction in CO2 emission at SP-2: 4,000 ton/year

59. CASE STUDY
IMPROVEMENT IN RAW MATERIAL AND SINTER QUALITY LEADING TO IMPROVEMENT IN HM QUALITY AND PRODUCTIVITY

60. BF PRODUCTIVITY WAS LOW DURING MONTH OF APRIL AND MAY’17

61. SLAG INCREASED TO AS HIGH AS 480 KG/THM DURING THE MONTH OF APRIL AND MAY’17

62. Fe in sinter decreased to 48.7%

63. SiO2 in Sinter was quite high
During april and may’17

64. AL2O3 IN SINTER MONTHWISE

65. PROBLEMS IN BF LOW PRODUCTIVITY OF BLAST FURNACES
HIGH SLAG RATE (AS HIGH AS 478 KG /THM)
LOW % Fe IN SINTER (AS LOW AS 48%)
LOW % OF OXYGEN ENRICHMENT
HIGH INCIDENCES OF TUYER OF BURNING
LOWER BLOWING PRESSURE
POOR QUALITY OF TAP HOLE CLAY
LOW % OF SINTER IN BURDEN

66. REASONS FOR LOW FE IN SINTER
LOW FE IN ORE FINES
HIGH SILICA IN FLUX MATERIAL
HIGH MGO IN SINTER
HIGH AVAILABLE LIME (CAO-SIO2) NORMS
LOW % BURNT LI ME IN SINTER

67. Sio2 in ore fines went up to 7.8%

68. Fe in ore fines was as low as 59.06%

69. STRATEGIES ADOPTED
MAKING OF SEPARATE BED FOR RICH QUALITY DALLI MINES IRON ORE FINES AT OHP TO INCREASE Fe CONTENT
IRON ORE FINES STACKING WITH ATLEAST LAYERS AT OHP TO ENSURE UNIFORMITY IN CHEMISTRY
LOWERING OF SINTER BASICITY TO IMPROVE FE CONTENT AND QUALITY OF SINTER
LOWERING OF PERCENT MGO IN SINTER TO IMPROVE QUALITY OF SINTER
INCREASE PERCENT OF SINTER IN BURDEN TO IMPROVE COHESIVE ZONE PRESSURE DROP
USE OF LOW SILICA FLUX TO REDUCE SLAG COMPONENT IN SINTER

70. Available lime in sinter

71. MGO IN SINTER LOWERED TO IMPROVE STRENGTH AND FE

72. Fe in ore fines increased to 62% from 59%

73. DROP IN SILICA IN FLUX DUE TO BETTER QUALITY OF DOLOMITE AND LIME STONE

74. SINTER BURDEN WAS LOW AND INCREAESED JUNE ONWARDS

75. RESULTS OBTAINED AS A RESULT OF STREAMLINE OPERATIONS

76. BF PRODUCTIVITY WENT UP TO 1.76 FROM 1.38

77. SLAG RATE DECREASED TO 380 KG /THM

78. Coke rate also came down

79. INFERENCES
BETTER QUALITY OF ORE FINES AND SINTER HELPED BF TO PERFORM BETTER.
SMOOTH WORKIN OF BF
LESSER CASE OF TUYERS BURNING
BETTER SINTER PLANT OPERATION DUE TO LESS ALUMINA AND SILICA IN SINTER
BETTER QUALITY OF SINTER LED TO INCREASED % OF SINTER IN BURDEN.

80. ANY QUESTIONS

81. Generating value out of the waste