TICAL CONFIGURATION

Portland Cement Association Sustainable Manufacturing Fact Sheet

July 2005
IZONTAL CONFIGURATION

POWER PLANT BYPRODUCTS

Resource efficiency means using fewer virgin raw materials. Increasingly, cement

plants are turning to industrial byproducts and materials that otherwise would be

discarded as sources for the basic elements needed for cement making.

After completing detailed analyses on their chemical characteristics to determine

the effect on process chemistry and facility emissions, many cement plants can

utilize byproducts from the electric power industry as a raw material in the

manufacture of the clinker—the intermediate product in the process—or as an

ingredient in the final cement product. more

 Portland Cement Association Sustainable Manufacturing Fact Sheet

POWER PLANT BYPRODUCTS

continued

Three general classes of byproducts from electric power plants can be used in the manufac-
ture of portland cement: fly ash, bottom ash / boiler slag, and flue gas desulfurization
THE CEMENT-MAKING PROCESS
(FGD) materials.
Portland cement manufacturing Fly ash and bottom ash/ boiler slag contain large amounts of silica and alumina as well as
is a four-step process: calcium and iron [TFHRC 2002]. All of these components are needed in the cement
1. Raw materials, including limestone manufacturing process. FGD materials can replace the natural gypsum that must be added to
and small amounts of sand and clay, the final product to control the setting of concrete [EPRI 1999]. Currently, over 55% of U.S.
come from a quarry usually located portland cement plants use one or more of these byproducts to produce clinker or cement.
near the cement manufacturing Fly Ash
plant. Limestone is typically about
Fly ash is the fine, powder-like material collected by the particulate matter control devices at
80% of the raw mix and is the
coal-burning power plants. Depending on chemical and physical attributes, some fly ash can
primary source of calcium.The
be blended into the final cement product or used at the ready-mixed concrete plant. In the
remaining raw materials provide appropriate proportions in concrete, fly ash decreases permeability and increases long-term
the silica and the necessary small strength [ACAA undated].
amounts of alumina and iron.
The American Coal Ash Association (ACAA) reported that 70 million short tons of fly ash
2. The materials are carefully analyzed, was produced in 2003, with over 12 million short tons used in concrete, concrete products,
precisely combined and blended, and grout. Over 3 million short tons of fly ash was used in kiln feed for the manufacture of
and then ground for further process- clinker or cement [ACAA 2004].
ing. This is called kiln feed.
In 2005, 39 portland cement plants were using fly ash as a raw material in the manufacture
3. The ground materials are heated in of clinker, and 3 plants were blending fly ash into one or more cement products. (Figure 1
an industrial furnace, called a kiln,
shows the locations of the plants utilizing fly ash.)
that reaches gas temperatures of
1,870°C (3,400°F). The heat caus- FIGURE 1
es the kiln feed to turn into a new Map of U.S. Portland Cement Plants Currently Utilizing Fly Ash
substance called clinker. The kiln
ME
WA
flame is fueled by powdered coal,
MT ND VT
powdered petroleum coke, natural NH
OR MN MA
NY
gas, oil, and/or recycled materials ID
WI
MI
CT
SD
burned for energy recovery. WY
PA
NJ

IA
NE OH MD DE

4. Red-hot clinker is cooled and NV IL

IN
WV
UT VA
CO
ground with a small amount of CA KS
MO KY

gypsum and typically other mineral NC

TN

components. The end result is a AZ

OK
SC
NM AR

fine, gray-colored powder called MS

GA
AL

portland cement.
TX LA

At each stage, process data are FL

continuously monitored to produce a
high-quality product, improve energy Portland cement plants using fly ash as a raw material in the manufacture of clinker (39)
efficiency, and minimize emissions. Portland cement plants blending fly ash into one or more cement products (3)

Bottom Ash and Boiler Slag

CEMENT OR CONCRETE?
These materials are collected in the bottom of coal furnaces at electric power plants. Bottom
The terms cement and concrete are ash is a dark gray or black, sand-like material that collects in the bottom of dry-bottom boilers.
often misused. Cement is an ingredi- Boiler slag is retained as a molten material in wet-bottom boilers and is discharged into quench-
ent of concrete. It is the fine gray ing water where it crystallizes and fractures into black glassy pellets [TFHRC 2002].
powder that, when mixed with water,
sand, and gravel or crushed stone, Nearly 20 million tons of bottom ash and boiler slag was produced in the United States in
forms the rock-like mass known as 2003. Over 500,000 tons of it was used in kiln feed for the manufacture of clinker and over
concrete. Cement acts as the binding 310,000 tons used in concrete, concrete products, and grout [ACAA 2004].
agent or glue.
In 2005, 21 portland cement plants were using bottom ash / boiler slag as a raw material
in the manufacture of clinker (as shown in Figure 2).
 FIGURE 2

Map of U.S. Portland Cement Plants Currently Utilizing Bottom Ash / Boiler Slag

ME
WA

MT ND VT
NH
OR MN MA
NY
WI CT
ID MI
SD
WY NJ
PA
IA
NE OH MD DE
NV IN
IL
WV

CA
UT CO
VA
USE OF POWER PLANT BYPRODUCTS
KS KY
MO
NC
TN
The Buzzi Unicem plant in
AZ
NM
OK
AR
SC Chattanooga, TN, uses all three
GA byproducts from coal-fired power
MS AL
plants: fly ash, bottom ash, and
TX LA
synthetic gypsum. The fly ash and
bottom ash are part of the kiln feed
FL
and become part of the clinker, while
the gypsum is used in the finish mills
Portland cement plants using bottom ash / boiler slag as a raw material in the manufacture of clinker (21) in the production of portland cement.

USE OF SYNTHETIC GYPSUM

The synthetic gypsum produced by

Flue Gas Desulfurization Materials
coal-fired power plants is often a
At some coal-fired power plants, sulfur dioxide emissions are controlled by flue gas moist material. At the CEMEX plant in
desulfurization (FGD) systems in which lime or limestone reacts with the gaseous sulfur to Knoxville, TN, it is mixed with cement
form calcium sulfate or calcium sulfite. This material is referred to as synthetic gypsum. kiln dust—a byproduct from the pro-
When properly processed, the calcium sulfate can be used at portland cement plants to duction of clinker—to improve material
replace the natural gypsum that must be added to the final product to control the setting handling. The result is a powder that
of concrete [EPRI 1999]. can be added to the clinker in the
finish grinding mill to produce portland
In 2003, over 420,000 tons of synthetic gypsum from FGD systems was used at portland cement. This allows the beneficial
cement plants out of the nearly 12 million tons produced by the electric power industry use of two byproducts: one from the
[ACAA 2004]. In 2005, 20 portland cement plants were using FGD materials in the cements electric power industry and the second
(as shown in figure 3). more from the cement manufacturing
process.

FIGURE 3

Map of U.S. Portland Cement Plants Currently Utilizing Flue Gas Desulfurization Materials

ME
WA

MT ND VT
NH
OR MN MA
NY
WI CT
ID MI
SD
WY NJ
PA
IA
NE OH MD DE
NV IN
IL
WV
UT VA
CO
CA KS
MO KY

NC
TN
OK
SC
AZ
NM AR FOR ADDITIONAL INFORMATION
MS
GA PLEASE CONTACT:
AL

TX LA Portland Cement Association

1130 Connecticut Avenue, Suite 1250
FL
Washington, DC 20036-3925
Voice: 202.408.9494
Portland cement plants using FGD materials blending fly ash in one or more cement products (20)
Fax: 202.408.0877
E-mail: sustainablemanufacturing@cement.org
 Portland Cement Association Sustainable Manufacturing Fact Sheet

POWER PLANT BYPRODUCTS

References

2003 Coal Combustion Product (CCP) Production and Use Survey, American Coal Ash Association, Aurora, CO,
USA, October 1, 2004.

Coal Ash Fact Sheet, American Coal Ash Association, Aurora, CO, USA, Undated.

Environmental Focus: Flue Gas Desulfurization Byproducts, BR-114239, Electric Power Research Institute, Palo
Alto, CA, USA, 1999.

User Guidelines for Waste and Byproduct Materials in Pavement Construction, FHWA-RD-97-148
(www.tfhrc.gov/hnr20/recycle/waste/index.htm), Turner Fairbank Highway Research Center, Federal Highway
Administration, United States Department of Transportation, McLean, VA, USA, May 2002.

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Portland Cement Association is a trade association representing cement companies in the United States and
Canada. PCA’s U.S. membership consists of 46 companies operating 102 plants in 36 states. PCA members
account for more than 97% of cement-making capacity in the United States and 100% in Canada.

Portland Cement Association

5420 Old Orchard Road 1130 Connecticut Avenue, Suite 1250
Skokie, Illinois 60077-1083 Washington, DC 20036-3925
847.966.6200 Fax 847.966.9781 202.408.9494 Fax 202.408.0877

www.cement.org

© 2005 Portland Cement Association. All rights reserved. IS331