INTERIM FINAL TECHNICAL REPORT
November 1, 1999,
through October 31, 2000
Project
Title:
RAPID-SETTING CEMENT MANUFACTURE USING FGD
SLUDGE
ICCI
Project Number:
99-1/2.1C-1
Principal
Investigator:
Sankar Bhattacharja, Construction Technology Laboratories (CTL),
Inc.
Other Investigators: F. M. Miller, F. J. Tang, CTL, Inc.
Project
Manager:
Ronald H. Carty, ICCI
Approximately 22 million metric tons of
flue gas desulfurization (FGD) sludge is produced in the U.S., only 7.5%
of which is used for beneficial
purposes. Sludge that has been
converted to sulfate through forced oxidation has been utilized to make wallboard
and portland cement. The presence
of high levels of sulfate and sulfite, along with other constituents, limits
the appeal of these residues for other direct utilization
scenarios. However, FGD residues,
can be utilized in manufacturing a rapid-setting cement based on calcium
sulfoaluminate. This cement type requires raw ingredients high in sulfur
content; FGD residues can provide all the sulfur
necessary. Presently, commercial
rapid-setting cements are made with relatively pure materials and have a
reasonable market demand. This
cement is widely used as rapid-setting and shrinkage-compensating cement,
including highway pavement, and the demand is rapidly increasing as certain
durability-related concerns are being addressed.
Two FGD sludges, one predominantly sulfate
and the other sulfite, were investigated in the 1998-1999 project
period. The performance of Type
I portland cement made with the sulfate sludge clearly indicates that sulfate
sludge is a good source of gypsum in the manufacture of portland
cement.
Sulfite sludge, not suitable for making
portland cement, was used to produce rapid-setting cement in a pilot-scale
rotary kiln system utilizing 13% sulfite sludge, based on dry
weight. The clinkering temperature was approximately 200°C
lower than that required to manufacture portland cement clinker. Also,
substantial energy can be saved in the grinding process due to the softer
rapid-setting clinker. A one-to-one
comparison with a commercial rapid-setting cement clearly indicates that
sulfite-derived rapid-setting cement has superior flow properties and comparable
compressive strength development.
The objective of the present project is
to transfer the technology from the pilot-scale production, performed last
year, to a commercial cement manufacturing
plant. Due to high demand of
cement in the expanding construction industry, the agreement with the cement
plant did not materialize and difficulties were encountered in striving to
accomplish this year’s
objective. However,
a verbal agreement with a cement plant for test burn has been reached, and
an arrangement for drying the wet FGD sludge is currently being
concluded.
Pages
1-9 contain proprietary
information.
EXECUTIVE SUMMARY
The ultimate goal of this project is to utilize the FGD sludge, predominantly a hydrate of calcium sulfite and produced in power plants that burn Illinois coal, to manufacture rapid-setting cement. Annually, approximately 22 million metric tons of flue gas desulfurization (FGD) sludge is produced in the U.S., of which only 7.5% is used for beneficial purposes. (FGD sludge that has been converted to calcium sulfate through forced oxidation finds some use in making wallboard or portland cement as synthetic gypsum, provided it is relatively pure). As a result, the majority of the FGD residues are not very appealing for other direct utilization purposes. The problems of disposal of this sludge are expected to escalate further in the future unless viable utilization technologies are developed and implemented. Illinois produces about 1 million tons of FGD sludge per year. Because of the relatively high sulfur content of Illinois coal, utilization of sludge for commercial purposes is important to encourage continued use of Illinois coal by power plants.
A rapid-setting
cement, also known as calcium sulfoaluminate cement, is substantially different
from ordinary portland cement (OPC) in its setting behavior and strength
development profile. As the raw materials requirements and the phase composition
of these cements are different from those required for making OPC, they fall
under the category of special cements.
This cement requires raw ingredients high in sulfur, while OPC normally
has a maximum of 3.5% sulfate as
SO3. Also, production
of these cements can be carried out at processing temperatures that are
approximately 200°C lower than those necessary for
OPC. Because of lower firing
temperature, the pyroprocessed product is softer and substantial energy can
be saved in the grinding process.
Commercially, this cement is made from relatively pure raw ingredients
and, as a specialty cement, has a significant market
demand. Currently, rapid-setting
cement is not produced in Illinois.
These cements are used in many high volume
applications such as bridge decks, airport runways, patching roadways, sidewalks,
etc. where rapid strength development is
necessary. In addition, they
may be modified for use in shrinkage compensation concrete by mixing with
portland cement and for controlled low-strength materials (CLSM) used for
diggable back-filling of utility
trenches. A 1996 survey indicates
that 81,000 metric tons of rapid-setting cement was produced in the U.S.
In recent years, the use of
rapid-setting cements has increased substantially, as more and more technical
data are generated in regards to their performance and
durability.
The goal is to exploit the compositional
make-up of these residues (which makes them otherwise unattractive) to produce
rapid-setting cement. Of the
following two steps necessary to accomplish the objective of this project,
Step I was accomplished in the 1998-1999 project period.
Step I: Composition formulation, process development, characterization of products, and optimization of composition to meet the primary requirements for commercial rapid-setting cements.
Step
II: Upon successful completion of Step I, "scale-up"
from pilot-scale investigation to demonstration phase where rapid-setting
cement will be produced in a commercial cement manufacturing plant located
in Illinois.
In the 1998-1999 project period two FGD sludges were investigated; one was
predominantly a hydrate of calcium sulfate and the other was a hydrate of
calcium sulfite. Realizing that
sulfate sludge is a good candidate for manufacturing of portland cement,
portland cement clinker was interground with sulfate sludge and the performance
of the resultant cement was compared to that of a cement produced with natural
gypsum. The performance of Type
I portland cement produced with sulfate sludge was equal to or superior to
that of cements made with standard
gypsum. This result clearly
indicates that sulfate sludge is a suitable source of gypsum
used in the manufacture of portland
cement.
Manufacture of rapid-setting cement utilizing
sulfite sludge, not suitable to make portland cement, however, was the major
focus of last year’s project.
Upon successful preparation of several rapid-setting cements in the
laboratory-scale with sulfite sludge, the parameters necessary for the
pilot-scale production were established.
Based upon the information developed in this bench-scale study, rapid
setting cement was produced in a pilot-scale rotary kiln utilizing 13% sulfite
sludge, based upon dry mass of the total raw
ingredients. The clinkering
temperature was about 200°C lower than that typically required to produce
portland cement clinker. The
results of a one-on-one comparison with commercial rapid-setting cement indicated
that for comparable flow, the strength development and time of setting of
these two cements were comparable.
Based upon the
accomplishments made in the pilot-scale program, the present phase requiring
plant-scale demonstration was initiated.
The objective was to accomplish this goal within the framework of
seven tasks that include procurement of raw ingredients to composition
formulation to plant-scale production and characterization of the products
made.
However, significant
difficulties have been encountered in the availability of a cement plant
to conduct the work proposed in the present
phase. Because of high demand for cement in the construction
industry, the agreement initially received in regards to the availability
of a cement plant did not materialize.
Since then, several options have been considered and a number of cement
plants have been actively pursued to become the site for technology
demonstration. Significant progress
has been made in such discussion with a cement plant and an agreement has
been reached on the use of this plant to produce rapid-setting
cement. Since the FGD sludge
is wet and requires drying before shipment and mixing with other raw ingredients,
several drying options have been
considered. Presently, a drying
arrangement near the power plant is being actively pursued, and it is expected
to be finalized in the month of November.
The remainder of this report contains proprietary
information and is not available for distribution except to the sponsor(s)
of this
project.