1. Processing Coal Ash into Products: A Pre-Combustion Perspective
Dr. Jack Groppo
Professor, Department of Mining Engineering
Program Manager, Center for Applied Energy Research
University of Kentucky
Lexington, KY
24th Coal Ash Processing Conference
October 25-27th
Sopot - Poland

2. Basic Principles of Cement Kilns
Wet-process kiln
Precalciner cement kiln

3. Components of Portland Cement
Compound
a.k.a.
Composition
Shorthand
Tricalcium Silicate
alite
3CaOSiO2 ~(Ca3SiO5)
C3S
Dicalcium Silicate
belite
2CaOSiO2 ~(Ca2SiO4)
C2S
Tricalcium Aluminate -
3CaOAl2O3 ~(Ca3Al2O6)
C3A
Tetracalcium Aluminoferrite
ferrite phase
4CaO Al2O5Fe2O3 ~Ca2 (AlX,Fe (1-X))O5 X>0 and <0.7
C4AF
Plus 20-30% glass

4. from combustion of the kiln fuel
The manufacture of cement clinker
Raw Mix is fed into the kiln and gradually heated by contact with the hot gases
from combustion of the kiln fuel
gas
oil
liquid waste materials
solid waste materials
petroleum coke
Successive chemical reactions take place as the temperature of the raw mix rises
70 to 110°C - Free water is evaporated.
400 to 600°C - clay-like minerals are decomposed into their constituent oxides
principally SiO2 and Al2O3.
dolomite (CaMg(CO3)2) decomposes to CaCO3, MgO and CO2.
650 to 900°C - CaCO3 reacts with SiO2 to form belite (Ca2SiO4).
900 to 1050°C - the remaining CaCO3 decomposes to CaO and CO2.
1300 to 1450°C - partial (20–30%) melting takes place, and
belite reacts with CaO to form alite (Ca3O.SiO4)

5. Alite (Ca3O.SiO4) is the characteristic constituent of Portland cement.
Typically, a peak temperature of 1400–1450 °C is required to complete the reaction.
The partial melting causes the material to aggregate into lumps or nodules (clinker).
Typical clinker nodules

6. Basics Principles of Precalciner Cement Kiln
A: Decarbonation of mix
400 to 600°C
B: Intermediates form oC
CaCO3 reacts with SiO2 to form belite (Ca2SiO4)
Remaining CaCO3 decomposes to CaO and CO2
C: Burning Zone oC
belite reacts with CaO to form alite (Ca3O.SiO4)
Partial melting forms clinker

7. Chemical Composition of Raw Materials Used for Preparing Kiln Feed Mix
Chemical Composition of Kiln Feed Mix
Component
Limestone
Marl
Iron Ore
Clay
CKD
SiO2
8.43
27.98
8.56
53.75
9.55
Al2O3
2.74
10.87
6.79
14.4
2.58
Fe2O3
0.94
3.08
68.69
4.99
2.37
CaO
47.62
30.12
5.97
8.71
53.27
MgO
0.97
1.95
0.481
1.8
1.1
SO3
0.7
0.901
0.31
0.301
K2O
0.39
0.2
0.151
1.99
1.08
Na2O
0.04
0.33
0.177
0.62
0.087
LOI
38.54
24.98 5
13.37 29
Other
0.42
0.09
3.28
0.06
0.66
Total
100
Component
Kiln Feed
Case 1
Case 2
Case 3
SiO2
11.601
11.61
11.616
Al2O3
2.522
2.517
2.52
Fe2O3
2.053
20.56
2.052
CaO
44.241
44.267
44.268
MgO
1.422
1.413
1.405
SO3
0.217
0.222
0.219
K2O
0.784
0.708
Na2O
0.042
0.088
0.043
LOI
37.279
37.269
37.281
Total
CaCO3 Content
79.00
79.048
79.05

8. Chemical Compositions of Kiln Feed Mix and Clinker Formed
Component
Kiln Feed Mix
Clinker Formed
SiO2
14.43
Al2O3
3.9
5.8784
Fe2O3
2.27
3.4506
CaO
42.61
MgO
1.09
1.6566
SO3
0.1
0.1527
K2O
0.9
1.3742
Na2O
0.09
0.1374
LOI
34.61
---
Total
100.0
CaCO3 Content
76.09

9. Fly Ash as Kiln Feed Flyash.com Component Pozzolan Type
Portland Cement
Class F
Class C
Class N
SiO2
54.9
39.9
58.2
22.6
Al2O3
25.8
16.7
18.4
4.3
Fe2O3
6.9
5.8
9.3
2.4
CaO
8.7
24.3
3.3
64.4
MgO
1.8
4.6
3.9
2.1
SO3
0.6
1.1
2.3
K2O
0.4
0.8
Na2O
0.2
0.3
Component
Limestone
Iron Ore
Clay
Kiln Feed Mix
SiO2
8.43
8.56
53.75
14.43
Al2O3
2.74
6.79
14.4
3.9
Fe2O3
0.94
68.69
4.99
2.27
CaO
47.62
5.97
8.71
42.61
MgO
0.97
0.481
1.8
1.09
SO3
0.901
0.31
0.1
K2O
0.39
0.151
1.99
0.9
Na2O
0.04
0.177
0.62
0.09
Flyash.com

10. Fly Ash as a Pozzolan
“A pozzolan is a siliceous or siliceous and aluminous material that
in itself possesses little or no cementitious value
but will, in divided form,
and in the presence of water
combine with lime to form cementitious compounds”.
ASTM C a
Origin: Red or purple volcanic tuff from neighborhood
of Pozzoli or Pozzouli on Bay of Naples used by Romans
in manufacture of mortar.

11. Hydration of Portland Cement
2[3CaOSiO2] + 7H2O  3CaO2SiO24H2O + 3Ca(OH)2
Alite
Water
Cementitious CASH Gels
Slaked Lime

12. What does a Pozzolan Do?
Reacts with Ca(OH)2 to form more CASH Gels which:
contributes to gel formation and long term strength
replacing cement and reducing cost
eliminates carbonation reactions
Ca2+ + CO32- = CaCO3
reduces sulfation reactions
Ca2+ + SO42- +2H2O= CaSO4  2H2O
shrinks pores
improving chlorination resistance of concrete and protects rebar
suppresses alkali-silica reactions

13. Pozzolanic Materials Pozzolanas Natural Volcanic Ash
Diatomacious Earth
Cherts and Opaline Shales
Artificial
Silica Fume
Rice Hull Ash
Low Ca Fly Ash
Calcined Kaolin
Pozzolanic and
Cementitious
Artificial
Blast Furnace Slag (glassy)
High Ca Fly Ash

14. Pulverized Coal Combustion

15. PCC Stages of Heating www.babcock.com Superheater Reheater Economizer
Superheater and reheater outlet: temperatures: (538 to 566oC).
Combustion temperatures:
bituminous coal: °C
lower rank coals: °C
Particle residence time in the boiler
typically 2-5 seconds

16. Lime Cycle Limestone CaCO3 carbonation (in mortar) add heat
Quicklime
CaO
Slaked Lime
Ca(OH)2
CaCO3 → CaO + CO2
add heat
add water
carbonation
(in mortar)
CaO + H2O → Ca(OH)2
Ca(OH)2 + CO2 → CaCO3

17. Ash Improvement Technology, Inc.
CleanCem technology produces a cement-like binder
sustainable cement replacement.
US Patent 8,741,054 B2
June 3, 2014
“Production of cement additives from combustion products of hydrocarbon fuels and strength enhancing metal oxides”

18. Relative Weight Percentages
Typical Preferred More Preferred
CaO    
SiO
Al2O
US Patent 8,741,054

19. Table 5. Additives and Beneficial Components for Modifying Composition of Fly Ash.10Ca Si Al
Limestone quarry dust ●
Clay
Kaolin
Recycled crushed glass
Silica Fume
Red mud
Spodumene
Aluminum slag
Lime kiln dust

20. Strength Development Mechanisms
Ordinary Portland Cement (OPC)
hydration of alite to form a calcium-silicate gel phase
Calcium Sulfoaluminate-Belite Cement (CSAB)
hydration of Klein’s compound [Ca4(AlO2)6SO4] to form etteringite
[Ca6Al2(SO4)3(OH)12·26H2O]

21. Circulating Fluidized Bed Combustion
coal + slaked limestone heat + bed ash + fly ash
fuel
steam
anhydrite (CaSO4)
SO2 sorbent

22. calcium-alumina-silica gels similar to those formed in Portland cement
When properly conditioned, CFBC bed ash and fly ash form calcium sulfoaluminate minerals
most importantly
Etteringite Ca6Al2(SO4)3(OH)12·26H2O (calciumulfoaluminate fiber-like crystal)
calcium-alumina-silica gels
similar to those formed in Portland cement
Natural etteringite crystals
Etteringite needles in
fractured cement paste
Jewell, R.G., Rathbone, R.F., Duvallet, T.Y., Robl, T.L and Mahboub, K.C., “ Fabrication and Testing of Low-Energy Calcium Sulfoaluminate-Belite Cements that Utilize Circulating Fluidized Bed Combustion By-Products”, Coal Combustion and Gasification Products Journal, Vol. 7, 18 p., 2015.

23. Calcium Sulfoaluminate-Belite Cement (CSAB)
Fired at 1250oC
Component
CFBC
Spend Bed
Fly Ash
Class F
Class C
Limestone
Bauxite
FGD
Gypsum
SiO2
12.77
25.62
57.44
41.65
7.41
10.61
4.54
Al2O3
5.25
10.34
29.97
22.28
2.76
78.75
1.09
Fe2O3
3.15
9.08
4.94
5.97
0.77
0.06
CaO
48.23
33.74
19.32
81.62
0.28
40.15
MgO
2.47
4.09
0.79
4.43
3.31
0.18
0.37
Na2O
0.05
0.13
0.15
0.04
0.01
K2O
0.36
1.24
2.73
0.61
0.03
Component
CSAB #1
CSAB #2
Clinker
Limestone
39.0
46.0
Bauxite
13.1
15.2
CFBC Spent Bed
27.7
Class F Fly Ash
---
12.9
Class C Fly Ash
6.9
Process Addition
Gypsum
13.3
12.8

24. Tekcrete Fast high performance, fiber-reinforced dry process shotcrete (gunite) product. US Patent 9,284,226
Advantages
• Rapid strength development to 76 Mpa (11K psi) within minutes
• Superior Adhesion – strength for bounding to the most difficult of surfaces
• High build rate – Rapid rate of strength gain allows for high build
• Fiber-reinforced – The large proportion of high modulus fibers permits strain hardening and excellent post peak failure characteristics
• Chloride Permeability – Rated, Very Low for chloride permeability this product is uniquely designed to be used on bridges, roadways, and along coastlines

25. Summary Cement kilns and utility boilers have similar
Operating temperature ranges
Chemistry
Modifying boiler operation is not at all uncommon practice
Emission compliance
Low-NOx burners
Sorbent injection
Ammonia injection for SNCR
CFBC
Maximizing solid waste utilization is sustainable practice
Post combustion processing established
Pre-combustion processing merits consideration
Supplement available ash chemistry with boiler additives
Utilize available heat