Raw Meal Beneficiation  Learning Objectives

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• Knowledge of the three major concepts in raw meal blending/homogenisation
• Knowledge of the basic concepts for kiln dust handling
• Knowledge of kiln feed concepts

Raw Meal Beneficiation Concepts

Silo Concepts

• Air-fluidized systems
• Aerated gravity systems
• Gravity systems

Air Fluidized Silo Systems

Batch type,           two store arrangement

Air Fluidized Silo Systems:      Aeration System

Air Fluidized Silo Systems  :Operation

Performance Diagram of Batch Type Homogenizing Silo

Air-Fluidized Silo Concept:   Valuation

+ Most efficient raw meal homogenizing system

– High energy consumer

– Application limited to about 2000t vessels,
thus sufficient for production lines up to 3000t/d

– High investment for new installations

Air Fluidized Silo Systems:   Over-Flow System

CTS’ Vario-Flow System

Air Fluidized Silo Systems:   Blending Efficiency

Aerated Gravity Systems  inverted cone concept

Design and operation concepts

• Spider on top of silo for meal distribution
• Inverted cone concept – empty cone (IBAU; K-P)       – center chamber (BMH)
• One sector activated a time
• Aeration sequence as to minimize funnel intersection
• Single product discharge

Aerated Gravity Systems:   Inverted Cone Silos

Blending Silos        design + operation criteria

• No. of outlets: > D/2
• Cone/wall distance: < 2 m
• Max. air pad length: < 2.5 m
• Aeration air pad width:                                    200 mm
• Aerated bottom area: > 35 %
• Min. aeration air rate:

> 1 m3/min/m2

• Aeration sequence time:      6 – 12 min
• Aeration sequence

IBAU type blending silo

K-P tangential type blending silo

• No. of outlets: > D/2
• Cone/wall distance: < 2 m
• Max. air pad length: < 2.5 m
• Aeration air pad width: 200 mm
• Aerated bottom area:

> 35 %

• Min. aeration air rate:

> 1 m3/min/m2

• Aeration sequence time:      6 – 12 min
• Aeration sequence as for IBAU type

CPT  type blending silo

• Cone/wall distance: < 2 m
• Max. air pad length: < 2.5 m
• Aeration air pad width: 200  mm
• Aerated bottom area:

35 – 50 %

• Min. aeration air rate:

1 – 2 m3/min/m2

• Aeration sequence time:      6 – 12 min
• Aeration sequence as for IBAU type

Blending Silos    Multiple outlet silo

• No spider required on top of silo for meal distribution
• Flat bottom concept with multiple (7) outlets
• Product discharge at different rates from the outlets   creating controlled   declination of the layers

FLS-CF type blending silo

• Max. air pad length: < 2.5 m
• Aeration air pad width: 200 mm
• Aerated bottom area:

35 – 50 %

• Min. aeration air rate:

1 – 2 m3/min/m2

• Aeration sequence time: !!! strictly follow the operation   manual !!!

Aerated Gravity Systems:    Blending Behavior

Aerated Gravity Systems:   Validation

+Applicable for wide capacity ranges (5’000 – 20’000t)

+Low energy consumer

-Limited beneficiation potential 5:1

-Decreasing beneficiation potential with increasing raw meal uniformity ex raw mill

-Insufficient reduction of
– long term fluctuations
– peak and step type disturbances

Homogenizing versus Blending

Gravity Systems: The Multi-Pack System

7+1-Pack-Silo:   Operation Mode

• Separate chamber for kiln dust handling
• Subsequent filling of silo cells
• Simultaneous reclaim from all cells

Raw Meal Preparation

Raw Meal Preparation  Performance Indicators

• Residual moisture raw meal:target value:    £ 0.5 [%]

• Uniform fineness (CoV: R 90 µm): target value:  £ 5    [%]

• Uniformity of kiln feed (standard deviation  sLSF) target  value:  £ 1.2 [ – ]
• Silo blending efficiency

Raw Meal Preparation Uniformity Goals

• Characteristics for product uniformity and   goals for excellence

Raw Meal Preparation Benchmarks

Raw Mix Preparation Uniformity Goals

Reasons for Insufficient Raw Meal Uniformity

• Bad condition of silo (e.g. water ingress)
• Malfunction of the silo system
• Non-uniform raw meal distribution
• Inadequate aeration sequence
• Inadequate filling degree
• Insufficient aeration time (batch type silo)
• Inadequate raw mix preparation
• Inadequate kiln dust handling
• Inadequate feed rate control to kiln

Impacts on Kiln Feed Uniformity

• Operation of the homogenizing/blending silo
• The method of dust handling
• The equipment available for kiln feed proportioning

Continuous Blending Silos:           Problems

Aeration Air Problems with Distribution

Improve air distribution by the installation of solenoid valves  replacing mechanically delicate air distributors

Continuous Blending Silos   Measures

• Operate the silos at high filling levels (> 75 %)
• Activate single sectors at a time rather than two opposite sectors
• Select optimum sector activation sequence preventing intersection of funnels at material surface

Continuous Blending Silos:   Problems 

Continuous blending silos can hardly deal with long term compositional fluctuations

Continuous blending silos can hardly deal with peak/step type compositional fluctuations

Addition of kiln dust into a blending silo may be a reason for such peak type fluctuation !!!

Effect of Inadequate Raw Mix Preparation on Raw Meal Uniformity

Effect of Inadequate Raw Mix Preparation on Raw Meal Uniformity

Kiln Dust Handling

Kiln dust Handling  Testing the Separation Factor

Testing the separation factor as a measure to judge a raw meal’s tendency to segregation

• sampling of raw meal ex raw mill
• chemical analysis of total sample: main elements LSF
• split sample into sub-samples: < 32 mm fraction  32 – 90 mm fraction    > 90 mm fraction
• chemical analysis of sub-samples: main elements LSF
• calculate separation factor (SF): LSF<32mm/LSFtot

Þ  range of not critical raw meals:  0.8 < SF < 1.2

Kiln Dust Handling  Problem 3: Concepts

compound operation mode

• Kiln dust/raw meal mix fed into blending silo

direct operation mode

• Kiln dust added into blending silo
• Kiln dust addition into kiln feed bin, by-passing the blending silo
• Diluted kiln dust added into blending silo
• Kiln dust addition to kiln feed bin out of separate kiln dust bin
• Kiln dust discharge to separate kiln dust bin and continuous proportioning to cement

Kiln Dust Handling By-Pass to Meal Silo

Evaluation:

+  standard arrangement simple, inexpensive

–  compositional step type variations when starting/stopping the raw mill

–  compositional variations may become excessive with out-of-range meal qualities             (0.8 < SF < 1.2)

Applications: many

Kiln Dust Handling Dilution of Kiln Dust

Evaluation:

+  simple arrangement

–  gradually changing composition of the raw meal stock on hold in the silo when stopping the raw mill

–  additional silo outlet

–  compositional variations may become excessive with out-of-range meal qualities                 (0.8 < SF < 1.2)

Applications: SCL, Chekka

Kiln Dust Handling  Separate Kiln Dust Bin

Evaluation:

+  narrow range for compositional kiln feed variations

–  expensive solution

Applications: Holnam, Holly Hill project

Kiln Dust Handling Proportioning to Cement

Evaluation:

+  valve for kiln dust enriched with     Cl and/or S

(Separate) Kiln Dust Bin          Design Concept

Kiln dust bin

• sizing: acc. spec. requirements
• installation: on load cells
• product activation:  by aeration or mechanical

Rate control

• feeder: – Rotor Scale – Coriolis type flow meter

Transport

• feed point: to raw meal at inlet of kiln feed bin

Kiln Feed Proportioning

Kiln Feed Proportioning   Demands

• consistent raw meal reclaim from feed bin
• permanent gravimetric rate control
• high feed rate accuracy for a wide control range

-short term:  better than ± 1.0 % ref to 10 s measurements

-long term:  better than ± 0.5 % referring to set point

• sensitivity to set point adjustments: better than ± 0.5 %
• consistent raw meal transport to the kiln
• high operation reliability
• fully enclosed design
• low maintenance requirements

Kiln Feed Proportioning: Bin Design and Operation

• Sizing: for at least 15 min of kiln operation
• Installation: on load cells
• Operation: at constant level   (70 – 80 % filling)
• Feed rate control out of blending silo:  by flow control   gate

Kiln Feed Bin  Design and Operation

• Sizing: for at least 15 min of kiln operation
• Installation: on load cells
• Operation: at constant level   (70 – 80 % filling)
• Feed rate control by flow control out of blending silo:  gate

Feeder Selection

Feeder Survey (1)

Feeder Survey (2)

Feeder Selection        Conclusion

First choice

• Pfister
  Rotor Scale
• Schenck
  Coriolis type flow meter
• Polysius
  POLDOS SR system

Second choice

• impact flow meter
• weigh feeder
• air-lift systems
• loss-in weight systems

Applications

Rotor Scales

• Holcim (US), Devil’s Slide
  SRW1.18 175 t/h
• Cementos Progresso
  FRW 2.2 270 t/h
• Holcim (Costa Rica), Cartago
  FRW 2.14 74 t/h
• Holcim (Maroc), Oujda
  FRW 3.14 200 t/h
• Holdercim, Pedro Leopoldo
  FRW 3.20 400 t/h

Coriolis Type Flow Meter

• China Cement Hongkong 1999
  (Green Island Cement)
  MULTICOR S300 2 x 210 t/h
  (installed above preheater)

POLDOS SR

• Apasco, Orizaba 160 t/h
• Holcim (Liban), Chekka 440 t/h
• Holcim (US), Holy Hill project 495 t/h
• SLC, Greenport project 495 t/h

System Arrangement 

at Ground Level

standard solution

+  no automatic sample transport

+  access for sampler maintenance

+  meal recirculation via second silo outlet

+  kiln dust dilution possible via second silo outlet

+/-  silo not elevated but additional structure

–  additional bucket elevator

–  high kiln feed bucket elevator

–  long reaction time for set point adjustments

below elevated Silo

standard solution

+  no additional bucket elevator

+  easy meal recirculation via second silo outlet

+  no automatic sample transport

+  access for sampler maintenance

+  kiln dust dilution possible via second silo outlet

+/-  no additional structure but elevated silo

–  high kiln feed bucket elevator

–  long reaction time for feed rate adjustments

on roof of Meal Silo

Application:  Apasco, RA2 project

+  reduced reaction time on feed rate adjustments

+  no additional structure

+   no additional bucket elevator

+  reduced height of kiln feed bucket elevators (two stages)

+  easy meal recirculation

+  kiln dust dilution possible via second silo outlet

–  automatic sample transport

–  access for sampler maintenance

 at Top of Preheater

Application:  Apasco, AP mod

++  short reaction time on feed rate adjustments

+  easy meal recirculation via second silo outlet

+  kiln dust dilution possible via second silo outlet

+/-  no additional structure but additional space requirement and loads for preheater structure

–  automatic sample transport

–  access for sampler maintenance

The Raw Meal Preparation Sequence

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