Energy consideration in cement grinding considerationChristian... · Energy consideration in cement...

Energy consideration in cement grinding

© Christian Pfeiffer Maschinenfabrik GmbH2

Introduction

Reasons for energy considerationsIntroduction

o Rising consumption

depleting energy

resources

o Depleting resources

escalating energy prices

o Consumption generates

increasing green house

gases

o Energy costs are a

major expense in

cement production



Statistics

Energy consumption in cement production



Statistics

Energy consumption in cement production

o ~ 2 % of the global primary energy, or 5 % of global industrial

energy, is consumed in cement production, of which:

85 - 90 % is thermal energy & 10 - 15 % electricity;

o ~ 25 % of cement cost is due to energy costs, of which:

o ~ 50 % is for electricity, mainly for grinding.



Consumption

Consumption of energy in cement plantDry process



Consumption

Consumption of energy in cement plantDry process

o Modern plant able to achieve 3,000 kJ/kg clinker & 90 kWh/t

cement

o Electricity required for crushing, raw materials / coal milling &

finished grinding represents ~ 25% of overall primary consumed

in cement production

o 65% of the electricity consumed is used in the grinding

operations



Consumption

Power consumption in cement plant

~ 65 % of

electricity in

cement plants

is consumed in

the grinding

processes



Consumption

Typical power requirement of finished ball mill

Example:

Total consumption 3333 kW,

104 t/h product

=>

Total Power Consumption

= 32,0 kWh/t

Mill Power Consumption

= 27,5 kWh/t (85,8 %)



Performance

Grinding inherently inefficient ...Performance



Performance

Grinding inherently inefficient ...

o Only < 2 - 5% of energy input is theoretically required to fracture

particles; the bulk of the input energy ends up largely as heat &

typically generates ~ 25 kcal of heat per kg cement ground

o Mill temperature could rise to 140 ˚C and causes gypsum to

dehydrate & produces “false set” in cement, as well as “media

coating” which impairs grinding efficiency

o typically, ~ 0.8 m³ of cooling air is required to remove the heat



Performance

Example: material grindability & correlation with ball millEvaluation of performance with help of Zeisel test

Guiding values for the grindability of an OPC cement 95/5 are

o 27-32 kWh/t at 3000 cm²/g acc. Blaine





Performance

Detrimental effects of feed moistureon energy consumption

o Typically, every 1%

increase in moisture

content above 0.5%

increases energy

consumption by >10%,

especially at higher

product fineness

o At limiting moisture, eg. above ~ 5% in limestone,

a ball mill may not be

operable!

TPH kWh/t



Performance

Influence of media filling ratio on specific power

consumption



Performance

Influence of equipment / process design

o Process / equipment configuration (mill L/D & speed, closed v

open circuit, pregrinder & type, mechanical v pneumatic

transport, ducting arrangement, dampers, etc)

o Equipment design including the separator, mill internals such as

liners (lifter/classifying), diaphragm (flow control), media, etc

o Degree of automation such as fuzzy logic / total feed / sonic

control, auto sampling, etc)



Performance

Optimising mill internals


Well designed /

upgrade of mill

internals may

improve mill

output, product

quality & specific

power

consumption by

10 - 20 %.


The new CPB separator generation:

OptiTromp

First results with the new QDK technology

High efficiency separator QDK


New QDK separator: design basis

Result of CFD analysis: improvement of air flow pattern




Changes in air guide vanes and rotating cage

New design

Guide vanes Number increased, directed

tangentially to rotating cage

Cage rods Number increased,

free cage surface area appr. 90 %,

backwards curved cage rods

New design

Former design

Air guide vanes

(louvres)

Separation zone

Rotating cage



Separating zone

Form

er

Actu

el




Changes in design of spiral casing

Approximation of an ideal spiral

design

Leading to an almost ideal

distribution of separation air into

the separation zone



0

10

20

30

40

50

60

70

80

90

100

0 1 10 100 1000

T(x

) [%

]

Particle Size x [µm]

Trompcurve T(x)

CEM I 32,5R

CEM I 42,5R

CEM II/A-LL 32,5R

CEM I

32,5 R

CEM I

42,5 R

CEM II/A-

LL 32,5 R

Bypass

[%]

3,9 6,9 5,7

Om

[cm²/g]

rejects

670 720 620

Om

[cm²/g]

cement

3510 4260 4140

Om

[cm²/g]

feed

2080 1970 2230

Separator efficiency



Functioning of mill shell liners

1st compartment 2nd compartment

Shell liners

CPB Shell liners


Lifting height

-decreasing-

Lifting height

-maintained-

Conventional liner

Activator liner

1st compartment liners: activator liners

Shell liners


1st compartment

activator liners

Shell liners


2nd compartment classifying liners

Shell liners


CPB mill diaphragms

Cement mill diaphragm

• Intermediate Diaphragm (ID)

• Discharge Diaphragm (DD)

• Functions & requirements

Retain media in 1st / 2nd

compartments for different grinding

actions

Regulate material flow & particle

size to maximize grinding efficiency

Mill ventilation not obstructed (low

ΔP)

Low maintenance (constant slot

opening, no breakage or loosening

of plates )

Structure stability & long useful life


CPB Monobloc® Diaphragm Structure


A strong, rigidly welded steel frame afixed to mill shell via “Tie Plates“

to avoid direct rotational stress transmission from mill shell & ensures

an exceptionally long useful life & maintenance-free operation


Flexible plates division


Provides further cost reduction opportunity

Easy conversion from 3 to 4 plates division


Maximum free diaphragm area


= Lower Δp & maximum mill ventillation / optimum air velocity

v = 1.8 m/s v = 1.8 m/s

Calculated air velocity above ball charge

p = 2.4 mbar


Material flow control


Allows optimization of material levels in 1st & 2nd compartments &

ensures maximum grinding efficiency


Air-material separation


Negates particles “throw” & maximizes effective grinding length

• Older design

• 旧的设计

• Current design

• 现在的设计


Performance

Operations & maintenance considerations

Efficient grinding can only be achieved by maximizing the feed

throughput, rapid removal of the desired fines to avoid over-

grinding, transferring of optimum impact / shearing forces from the

grinding media to the materials being ground & minimize

generation of wasteful heat, wear, vibration & noise.



Performance

Relationship between power consumption &

product fineness

For every 100 cm²/g

increase in fineness

increases power

consumption by 1-2 kWh/t

for closed circuit mill & 2-3

kWh/t for open circuit mill.


20

25

30

35

40

45

50

55

60

2500 3000 3500 4000 4500 5000

Open circuit kWh/t Closed circuit kWh/t


Performance

Good practices in operations & maintenance

Maintain maximum, continuous feed without over-fill of material

which cushions & absorbs the impact energy in 1st chamber or lifts

media & causes reverse or even de-classification of media in the 2nd

Chamber

Avoid meal starvation -eg at feed inlet, in front & behind

intermediate diaphragm- & wasteful metal to metal contact between

the grinding elements causing wear & tear, generate heat & noise

Conduct regular mill sampling/analysis to maximise feed & periodic

technical audit to ensure optimum process conditions

Maintain optimum milling temperature (ventilation/water spray) &

use grinding aid (if cost effective) to minimise media coating &

particles re-agglomeration

Adhere to a well design planned maintenance programme



Performance

Use of additives & grinding aids

o Use appropriate grinding

aid such as air entrainer

or strength enhancer

o Provide water injection to

maintain optimum milling

temperature; water also

acts as a grinding aid

o Reduce clinker factor &

use filler such as

limestone and/or

extenders such as slag,

fly-ash or other pozzolan



Performance

Energy Improvement Potentials in Grinding

o Pre-grinding (e.g. roll press) => 10 - 30 %

o Separator upgrade => 5 - 25 %

o New mill internals (liners / diaphragm) => 5 - 20 %

o Mill operations & maintenance => 5 - 10 %

o Using grinding aids => 3 - 10 %

o Using fillers / Extenders => 10 - 50 %*

* Based on total energy consideration



Performance

Case example 1: Results of mill internal upgrade



Performance

Case example 2: Results of conversion

to high performnace QDK



Performance

Case example 3: Operational results of QDK

conversion & mill internals upgrade



Performance

Case example 4: Results of the russian plant upgrade

Before upgrade After upgrade

Cement type CEM400 D0 CEM400 D0 CEM400 D0

Product fineness [Blaine] 2.800 cm²/g 2.800 cm²/g 3.160 cm²/g

Average

production rate

76,0 t/h 103,0 t/h

(- 35,5 %)

88,0 t/h

(- 15,8 %)

Specific energy

consumption of

mill drive (at counter)

36,0 kWh/t 26,6 kWh/t

(- 26,0 %)

31,1 kWh/t

(- 15,7 %)

Cement strength after 28

days

44,2 MPa 44,2 MPa 44,2 MPa

Significant reduction in specific power consumption of the mill was

achieved despite relatively coarse products.



Conclusions

Conclusions

o Energy consideration in cement grinding makes sense: it

decreases production cost, increases output & reduces green

house gas emission;

o Proven technology available for both new & existing plant /

equipment upgrade to generate attractive ROI;

o Energy consideration should be regarded a basic responsibility

of cement producers to help conserve the fast depleting fossil

fuels & minimize impact of GHG on the environment to ensure a

sustainable development of the cement industry.


© Christian Pfeiffer Maschinenfabrik GmbH42 Energy consideration in cement grinding

Any questions?Feel free to ask!

Thank you for your

kind attention.

Date post:	06-Feb-2018
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