tromp curve dynamic seperator.pdf

Modernisation of Mill Separators Presented by Dr Joe Khor

Contents

1. Introduction 2. Characterisation of separator performance

3. Replacement of 1st generation separators in a German cement plant (Case Study 1) 4. Modification of a 3rd generation separator in a Malaysian cement plant (Case Study 2) 5. Investment consideration

6. Conclusion / Discussion Cemtech Asia 2014 - Kuala Lumpur

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1. Introduction Separators in grinding o Cement manufacture is energy intensive: consuming typically > 3,000 MJ of fuel/t-clinker and > 90 kWh of electricity/t-cement; o Approximately two-third of the electricity consumed is used for the grinding of raw materials, fuels and cement; o Grinding is inherently an inefficient process -especially when mills are operating in open circuit- but closed circuit mills may also not be as efficient as they should be when equipped with separators of the older design.

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1. Introduction Grinding without separator: open circuit mill

o The PSD of the product is wider & for cement, the higher coarse fraction can results in lower strength.

PSD - Open circuit % retained

o In open circuit, material leaving the mill must comply to the finished product fineness, entailing over-grinding & wasted energy, at times also overheating & coating of the mill, which can adversely affect the mill performance;

Coarse

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Fine JK/17.06.2014

1. Introduction

Grinding with separator – closed circuit mill

o The PSD of the product is narrower & for cement, the strength generally higher.

PSD - Closed circuit % retained

o In closed circuit, the finished product is separated externally & the material leaving the mill can be ground coarser: the mill residence time is lower, overgrinding reduced, throughput higher & specific energy consumption lower;

Conventional Separator

Coarse

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High Efficiency Separator

Fine JK/17.06.2014

1. Introduction Principle of dynamic air separation Separator Feed

FRf

FRc

FD

Separator Fines Separator Rejects

FC (FG)

o Air separator relies on the balance of opposing drag (FD) & centrifugal (FC) forces imparted by the air stream on the particles as they spiral down the casing by gravity (FG), to cause the particles to be either moved into the rotating cage & discharged as fines, or continued to spiral down & discharged as rejects for return to the mill

 Separation is imperfect due to uneven air/material distribution, turbulence, particle shape, obstruction of the descending particles, agglomeration, etc Cemtech Asia 2014 - Kuala Lumpur

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2. Separator performance Characterisation of separator performance o Efficiency -or selectivity- of a separator is a function of the particle size & is generally characterised by the percentage of a given particle size in the feed discharged in the rejects; o Plotting the size selectivity [T(x)] against the particle size [x] produces a “Tromp Curve”, which is used to define the separator performance in terms of :     

Bypass, Cut size, Sharpness of cut or separation, Imperfection, Agglomeration / mechanical state, of the separator. Cemtech Asia 2014 - Kuala Lumpur

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2. Separator performance Tromp Curve o Tromp curve of perfect separation -such as by sievingis characterized by a step function from 0 to 100 %, or perfect sharpness of separation o Tromp curve of air separator is imperfect and shows the particle size selectivity [T(x)] with a rightward slope indicating the sharpness of separation & a minimum value called BYPASS Cemtech Asia 2014 - Kuala Lumpur

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2. Separator performance Construction of a Tromp curve The 1st step is to calculate the average recovery of the separator fines & reject, vf & vg : vf 

 Q ( x)   Q ( x) 100%  Q ( x)   Q ( x)

Where: Vf Vg Qa(x) Qf(x) Qg(x)

a

g

f

g

vg 

Q Q

f f

( x)  Qa ( x)

( x )   Qg ( x )

100%

= fraction of fines as a function of particle size [wt-%] = fraction of reject as a function of particle size [wt-%] = fractional amount of feed passing size x [wt-%] = fractional amount of fines passing size x [wt-%] = fractional amount of reject passing size x [wt-%] Cemtech Asia 2014 - Kuala Lumpur

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2. Separator performance Calculating the size selectivity of separator Particle size selectivity [T(x)] is calculated for each particle size analysis from the laboratory as follows: T ( x)  v g 

Qg ( x) Qa ( x)

Where:: ΔQa(x) = amount of feed passing size x [wt-%]; ΔQg(x) = amount of rejects passing size x [wt-%]; Vg = separator rejects as a function of particle size;

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2. Separator performance Calculating the circulating load The circulating load [u] of a separator is calculated from the particles size analysis as follows: u

Where: Vf Qa(x) Qf(x) Qg(x)

1  vf

 Q ( x)   Q ( x)  Q ( x)   Q ( x) f

g

a

g

= separator fines as a function of particle size; = fractional amount of separator feed of size x [wt-%]; = fractional amount of separator fines of size x [wt-%]; = fractional amount of separator reject of size x [wt-%];

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2. Separator performance Bypass o Bypass is the most important value: the lower the bypass, the higher the efficiency o A high bypass is an indication of over-grinding & energy wasting o Bypass of the latest generation high efficiency separator should be < 10% Cemtech Asia 2014 - Kuala Lumpur

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2. Separator performance Cut size o Cut size is defined as that particle size (x50) of which half the particles are collected as fines & half in the rejects o If the sharpness of separation is poor, >50% of the finest particle sizes may end up in the rejects so that no definite cut size exists. o Cut size of the latest generation high efficiency separator should be < 15 µm Cemtech Asia 2014 - Kuala Lumpur

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2. Separator performance Imperfection

o The imperfection is given by: I

( x75  x25 ) 2  x50

o Imperfection of the latest generation high efficiency separators should be < 0.35

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2. Separator performance Sharpness of separation o Sharpness of separation is defined by Eder as follows: x25 x x75

o Sharpness of the latest generation high efficiency separator should be > 0.50

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2. Separator performance Comparison of separator performance Generation

1st

2nd

3rd

Latest CPB

Bypass [%]

30 - 60

10 - 35

8 - 20

2 - 10

> 20

15 - 20

< 15

< 15

> 0.50

0.35 - 0.50

< 0.4

< 0.35

-

< 0.5

> 0.45

> 0.5

3,800

4,500

≈ 5,500

≈ 6,000

Min. Cut size [µm] Imperfection [-] Sharpness of cut Max Blaine [cm²/g]

 The latest CPB G4 separator is develped based on extensive CFD modelling & pilot plant trial;  It has an extremely low by-pass of 2 - 10% depending on the product fineness, and can improve mill output / energy consumption by as much as 20 – 25%. Cemtech Asia 2014 - Kuala Lumpur

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3. Case Study 1 Replacement of G1 separators in Phoenix Cement*, Beckum, Germany (2010)

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3. Case Study 1 Project outline  Objectives / Constraints • Improve cement early strength • Produce high strength cement (> 5,000 cm2/g) • Reduce production cost • Adaption of restricted plant space • Minimal production interruption from changing-over  Existing plant data (CM 1) • Ball mill Ø 3.8 m x 12 m L equipped with Horizontal Impact Crusher & 2 x 1st generation Heyd separators (installed 1969) • Cement type : CEM I 32.5 R & 42.5 R, CEM II/A-LL 32.5 R • Fineness : 3,800 - 4,200 cm2/g (according to Blaine)

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3. Case Study 1 CPB study & findings

 Plant inspection, including axial & circuit sampling to determine the existing mill & separator performance;  Zeisel test to verify the clinker grindability;  Confirmed low performance of Heyd separator due to: - low bypass / separation efficiency, - low sharpness of separation, - insufficient range of fineness setting.

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3. Case Study 1 CPB recommendations  Replace the two1st generation Heyd separators with a single QDK 29-NZ high efficiency separator with the following specifications:

• • • • •

Rated air flow Operating temperature Installed motor rating Max. feed rate Max. fine product

: 143,350 Am3/h : 120 °C : 200 kW : 258 tph : 115 tph

 Adapt the ball charge to the new operating conditions & higher product fineness required for the new type of cement to be produced. Cemtech Asia 2014 - Kuala Lumpur

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3. Case Study 1 Project implementation - adaptation to restricted plant layout / space & minimise stoppage time 2 existing Heyd separators

1 new QDK separator 2 new Cyclones

Existing Ball Mill

Erection & commissioning (6 weeks) Cemtech Asia 2014 - Kuala Lumpur

Swith-over (3d) JK/17.06.2014

3. Case Study 1

Production rate & fineness of CEM II/A-LL 32.5R after the modernisation

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3. Case Study 1 Production rate of CEM II/A-LL 32.5 R of equivalent strengths from the Heyd and QDK29-N separator

Sample

Separator

Blaine fineness [cm²/g]

+63 µm residue [%]

2-day early strength [N/mm²]

28-day final strength [N/mm²]

Production Rate [%]

CEM II/A-LL 32,5R

Heyd

4,100

6.5 – 8

24

48

100

CEM II/A-LL 32,5R

QDK29-NZ

4,144

15%

Original CPB

Competitor

o Competitor-modified (2013): Bypass > 34%

o CPB latest (2014): Bypass < 3%

Latest CPB

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4. Case Study 2 Summary of the improvement results* Results

Units

Before

Cement type

After

Difference

HRF

Blaine fineness

cm2/g

3,892

3,674

-218

+45 µm residue

%

2.81

2.40

-0.41

Output

t/h

113

122

9

Power consumption

kWh/t

47.7

45.6

-2.1

Cement quality – 7 D

N/mm2

40.0

40.0

0.0

Cement quality – 28 D

N/mm2

51.1

51.9

0.8

 For HQC, output increased by 10 t/h & power reduced by 4 kWh/t  ROI estimated to be < 4 months, without considering higher sales * Mill has not been fully optimised by CPB; data provided by Holcim Malaysia Cemtech Asia 2014 - Kuala Lumpur

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5. Investment consideration ROI of a separator modification project in Germany* CEM II/A-LL 32.5 R

Basis: 7,200 h/yr running

Total investment

210,000 €

Electricity saving

(38.8 – 34.1) kWh/t x 127 t/h x 7,200 h/yr = 4,297,680 kWh/yr

Electricity cost saving at av. cost of € 0.08/kWh

0.08 €/kWh x 4,297,680 kWh/yr = 343,814 €/yr

Return on investment

7.3 month (on electricity saving)

Production increase

(127 – 111) t/h x 7,200 h = 115,200 t/yr

Extra sales at 10 €/t profit

115,200 t/yr x 10 €/t = 1,152,000 €/yr

Total benefits

1,495,814 €/yr (on electricity & sales)

Return on investment

1.7 months (electricity + extra sales)

* Based on data of Heidelberger Cement Schelklingen Works Cemtech Asia 2014 - Kuala Lumpur

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6. Conclusion

1. Separators play an important role in mill performance: affecting the output, power consumption & cement quality; 2. Poor performance of separators are often overlooked, due to either their locations –out of sight, out of mind- or failure to audit & benchmark the performance; 3. The latest CPB separators are highly efficient -capable of achieving bypass of < 5% for most cement types & improve mill performance by as much as 25%, as well as ability to produce higher Blaine / quality cement; 4. Higher grinding efficiency & cement quality means higher margin & market shares -ROI is typically < 6 months- as well as a lower carbon foot-print for the environment. Cemtech Asia 2014 - Kuala Lumpur

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6. Discussion

Thank you for your attention, any questions or comments?

For more info, please visit www.christianpfeiffer.net Cemtech Asia 2014 - Kuala Lumpur

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