Plant Operation

Thermal Edge
 Table of Contents

cemexbangladesh.com
 Terminology

• Clinker: Comes out of factories

• Clinker + gypsum → Cement, the powder
that you buy in the store

• Cement + Water → Cement Paste

• Cement paste + sand → Mortar
• Cement paste + sand + gravel → Concrete

• There’s also a lot of admixtures

 Cement making process

• Production of a fine “rawmix”

• Thermal processing of rawmix up to
1450C in a kiln
• Grinding the resulting clinker

Poison.org
 Raw materials for cement

• Fairly flexible
• Beware contamination!
• Clays are good, as they need little grinding

iti.northwestern.edu/cement/monograph/Monograph3_2.html
Homogenizing and Blending

6
 Pre-homogenizing Hall

Heidelberg Cement
 Raw Mix Production

Cement Plants and Kilns in Britain and Ireland

 Raw mix production

• The grinding and blending of raw

materials
• ‘Wet process’
▪ Grinding is easy
▪ Blending is easy
▪ Energy intensive
• ‘Dry process’
▪ Everything is hard
▪ Less energy intensive
wcfields.com → If you don’t get the joke on this slide you gotta learn about your culture come on
 Grinding, historically

10

• Coarse grind: Roller mill

▪ Heavy, spinning wheels
• Coarse grind: Hammer mill
▪ Exactly what it sounds like
• Fine grind: plate mill
• All usually powered by
windmills/watermills
• Don’t work for cement!
Stoneforest.com
Eastwoodstone.com
Mangeolassoc.co.uk
 Wet process grinding – Washmill

11
1890
1950 →

Date Diameter ft Speed rpm Power kW Dry t/hour

1840 10 19-28 6-9 2-3
1890 14 16-24 17-25 6-10
1920 20 13-20 50-75 65-95

Cementkilns.co.uk 1950 35 10 260 100

 Wet Process Grinding

12

Cement Plants and Kilns in Britain and Ireland

 The water problem I: Pre 1870

13
• Rawmix contains ~80% What the hell

water
• 4-5 months in ‘Slurry
backs’
▪ Coarse particles settle
out
▪ At ‘butter’ consistency,
put on metal drying
racks, sent to kiln
• Excellent particle size
distribution
Laughingsquid.com
 The water problem II: Post 1870,
Goreham Process
14

• Patented 1858, but used in France ~1750

• Uses a washmill, ~45% water
• Mixed until “creamy” or “thick” then run
through grinding plates
▪ Coarse particles don’t settle
▪ Much more energy required in washmill,
grinding
▪ Loss of homogeneity
▪ Loss of good particle size distribution

I AM SORRY THERE’S SO MUCH TEXT ON HERE BUT IT WILL BE WORTH IT TRUST ME

 There is so much more
interesting history here!
But it’s time to move along.
These are “festoon chain” heat
exchangers

https://www.cementkilns.co.uk/long_wet_kilns.html
 Raw mix preparation

16

gluedideas.com
 Modern mills

17

• Crude steel becomes available ~1870

• Early: plate/roller mills, made with steel
• Contact between plates or rollers no
longer a problem
• Earliest design: Griffin Mill
▪ Basically unchanged today

D&D Beyond
 Griffin Mill

18

hotstonecrusher.com – ahahahahahahha!
“Cement and Concrete,” Louis Carlton Sabin, McGraw Publishing, 1923
 “Tube mill”

19
• Much longer, fine grinding
• Size determined by feed rate
• “…absence of provision in the machine
itself for the return of uncrushed material
(oversize).”

Cementkilns.co.uk
911metallurgist.com  it’s not what you think
 Early ball mill – “Kominor Mill”

20

• Short length, coarse grinding

• Interior plates improve “cascading action”
• Product size controlled by screens
between plates

“Portland Cement,” Arthur Charles Davis, 1904

 Krupp Ball Mill, cir. 1923

21

“Cement and Concrete,” Louis Carlton Sabin, McGraw Publishing, 1923

 Modern tube? ball? mill

22

Understandingcement.com
Sandwasher.com
Crusher unit impacts

23
 Homogenization of rawmix

24

• Wet process: Just stir!

• Dry process:
▪ Clouds of “fluidized” cement powder
▪ Only discovered ~1950
• Along with cheap fuel, a main reason that wet
process lasted so long
• At the end of raw mix production:
▪ 85% of materials smaller than 90 m

The American Reader → I WILL NEVER NOT MAKE THIS JOKE

Pre Kiln Treatments

GrabCAD
 Pre-heaters

26

• Early kilns had no pre-heaters

• 1950s – 1960s: Grate/Spray preheaters

▪ Use exhaust gas from kiln
• 1970s – Cyclone preheaters
▪ Use exhaust gas from kiln
• Late 1970s – Precalciners
▪ Uses fresh fuel burned in a preheater
 Grate preheaters

27
• Semi-dry: Rawmix sprayed with water → nodules
• Semi-wet: Rawmix cakes are broken up
▪ Can clog due to brittle nodules
▪ Exhaust can recondense

Cementkilns.co.uk
 Spray Preheating

28

At the centre is the hot

gas duct rising from the
kiln hearth, at the outlet
of which the spray
wheel is located.

Slurry is fed into the

conical section, and
the wheel at the base
expels it centrifugally.
Above are the gearbox
and the motor.

Peter Ellis via cementkilns.co.uk/long_wet_kilns.html

 Cyclone preheater I

29
• Efficiency of kiln
depends on rate
of heating rawmix

• Separation of
particles
improves rate of
particle heating

cementkilns.co.uk
wikipedia.org
 Five-stage pre-heater system

30

ietd.iipnetwork.org
decarboni.se
31
 Kilns and Clinker Production

O’Donnell Consulting Engineers

 The purpose of the kiln

• Partially melt the 33

rawmix to create clinker

• Particles must mix
while melting to ensure
homogeneity

Cement Equipment
 Lime kilns

34

• Earliest OPC made in lime kilns ~1830

• ~30 “tonnes” per week

Geocaching.com
Google Maps (Obviously)
 Kutztown Festival
GOAT COUNTY FAIR
35

blog.daum.net
 Rotary Kiln

36
• Perfected in PA in 1890s
• ~20 “tonnes” per day
• Slope of a few degrees, rotates ~1 rpm
• After 10 years, 10x more productive
• Today: 100,000 tons/day

Understandingcement.com
How to build a cement kiln

37
 Rotary kilns have gotten bigger

38

80m long; 6m diameter; sloped 3-4%; rotates at 1-2 rpm

Rotarykiln.net  Ahahahahaha, no seriously, this is a site!
 Rotary kilns

• Hot gases enter bottom, exit smokestack

39

▪ After going through pre-heater system

• A variety of fuels can be used
▪ Traditional: Coal, fuel oil
▪ Alternatives: Garbage
▪ Ashes = Trouble
▪ More later….

E & E News
 In the kiln

40

• The raw mix can take 60-90 minutes to

move through kiln
• Necessary to ensure homogenization

British Lime Association

 In the kiln II

• < 450 oC: Dehydration zone 41

▪ Relatively short in modern kilns

▪ Up to half the length of wet process kilns
• 450 – 900 oC: Calcination zone
▪ Rawmix turned into oxides, exhausts
▪ Can be accomplished with pre-heaters
• 900 – 1300 oC: Reaction zone
▪ Solid state reactions (no melting)
▪ Fe, Al act as fluxing agents, encourage rxns
• 1300 – 1400 oC: Clinkering zone
▪ Fe, Al phases become liquid
▪ Allows the formation of calcium silicates
• Cooling zone
▪ Quickly cooled (to 1100 oC) clinker is more reactive
▪ Prevents C3S decomposition (next week!)
▪ Water is sprayed on hot clinker
Reddit (ugh)
 Clinker from the kiln

42

Dylan Moore via cementkilns.co.uk

Alibaba.com
 Cement Kiln Exhaust: The Gnarly Stuff

43
• Gases condense, enrich flue gas
• Refractory metals
▪ High boiling points
▪ Pass through kiln
▪ Chromium, beryllium, barium, nickel
• Volatile metals
▪ Low boiling point
▪ Enter exhaust gases
▪ Mercury, selenium, thallium, etc.
• Particulate emissions standards:
▪ 1950: 3,000 mg/m3
▪ Today: ~30 mg/m3
Washington Poison Center
 Electrostatic Precipitator

44

tapc.com.au
Neundorfer.com
gobizkorea.com
 Final step: Grinding

45

• Cement is blended with other batches

• Gypsum, etc. is added
• Final size is important for reaction
▪ 1 m: 1 day
▪ 10 m: 1 month
• Too many small particles: Flash set
• “Average diameter” often reported
▪ PSD, shape, surface area, etc. more
important
Envato Elements
 ASTM C204 - Standard Test Methods for Fineness
of Hydraulic Cement by Air-Permeability Apparatus

46

• Pressurized air passing through

powder depends on surface area
• A chamber is filled with cement,
and the time required for air to
pass is measured
• The Blaine fineness of OPC
usually ranges from 300 – 500
m2/kg
▪ The units come from an empirical
relationship
testmark.net
 Back to the Kiln

Thyssenkrupp Industries India

 Back to the Kiln

GAME CHANGER????
Total energy consumption

49
 Fuel consumption

50

International Finance Corporation

 Cement industry gets slept on

Alternatives in cement manufacture, Technical and Environmental Review, Cembureau

 Waste Heat Recovery

52

• Heat used to boil water for turbine

• Holcim experimented with WHR in 1982
and 1994
• Holcim’s commercial units: 2006
▪ 271 MW capacity – only 53 MW outside
China
• Lafarge, Heidelberg, Cemex also
installing systems
 Waste Heat Recovery II

53

Cement Lime Gypsum

aircleanenergy.com
 Waste Heat Recovery Worldwide

54

• Reduces overhead ~15 %

• Electricity is ~25 % of production costs

International Finance Corporation

 Why so little in the US?

55

US Department of Energy Industrial Technologies Program

 Waste Heat Variables

56

International Finance Corporation

 California Portland Cement Company’s
Colton Cement Plant
57
• Founded 1891, 750,000 tons of cement/year
• Runs 24/7
• 14 MW load, peak loads of 20 MW
• After a power outage:
▪ Kilns take 8-12 hours to heat up
▪ Cooling/heating can damage equipment
• In 1985, a cogeneration plant was built
▪ Not activated until 2002

1910 – Wikimedia Commons

 Cogeneration case study: CPCC

58
• Cogeneration plant
▪ A fluidized bed coal-fired boiler
▪ Lower emissions than the city’s plant
▪ 20 MW of power
• Two waste heat recovery units
▪ 5-6 MW apiece

Cogeneration and Competitive Power Journal, 17:2, 63-65

 Thank you
Questions?

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