FINAL TECHNICAL
REPORT
November 1, 1999, through October
31, 2000
Project Title: AGRO-FGD SCRUBBER
SLUDGE WALLBOARD
COMPOSITES
ICCI
Project
Number:
99-1/2.1C-2
Principal
Investigator:
Vivak M. Malhotra, Southern Illinois University
at
Project Manager: Dr. Ronald H. Carty, ICCI
ABSTRACT
In pursuit of our goal of developing technology for the formation of Agro-wallboard materials from sulfate-rich flue gas desulfurization (FGD) scrubber sludge, we undertook, during the first year the following measurements: (a) extraction of microfibrils from natural products, (b) systematic characterization of microfibrils with the help of differential scanning calorimetry (DSC), novel in-situ high-temperature diffuse reflectance-Fourier transform infrared (ISHT-DR-FTIR), and dynamic mechanical analyzer (DMA) techniques, and (c) fabrication and formulation of wallboard materials and the evaluation of their mechanical properties. The Agro-wallboard composites were formed in 4 inch by 4 inch by 0.2 inch and 6 inch by 6 inch by 0.2 inch sizes. Our materials were composed of more than 85 weight percent (wt %) or more of City Water, Light and Power (CWLP) plant's sulfate-rich scrubber sludge. Our results suggested that microfibrils had hydrogen-bonded water which facilitated bonding with sludge crystallites. Moreover, this water during combustion reaction would act as a fire retardant. The mechanical strength test data, both on commercially bought samples and our Agro-wallboard materials, suggested that: (a) most of the strength for a conventional wallboard came from the support paper and (b) our Agro-wallboards, without any paper support, were much stronger than the conventional wallboard with paper support. Our results also suggested that water-to-scrubber sludge ratio, formation temperature, formation pressure, type and concentration of microfibrils were critical parameters, which governed the ultimate mechanical properties of the Agro-Wallboard materials. In addition, our results suggested that our wallboard composites could be directly painted using conventional painting approaches.
Pages 1 to 23 contain proprietary
information
EXECUTIVE
SUMMARY
Objectives: The main objectives of this project are:
(a) to develop protocols and engineering procedures for the development and fabrication of value-added Agro-wallboard products from sulfate-rich CWLP (City Water Light & Power, Springfield, Illinois) scrubber sludge, natural fibers, and pore initiator additive. The success of the protocols will be judged by the consistent wallboard produced.
(b) to enhance the mechanical strength and water-resistance of Agro-wallboard material via surface pore impregnation technique. Our wallboard materials will be composed of 95 wt % or higher sulfate-rich scrubber sludge.
Introduction: About 22 million tons of flue gas desulfurization (FGD) scrubber sludge are currently produced in the U.S. every year. Most of it is disposed in the landfills near power plants. In Illinois, Indiana, and Western Kentucky 6 million tons of wet scrubber sludge are currently produced. About 7,000 MW of additional capacity is expected to be wet scrubbed in the near future in response to the Clean Air Act Amendments of 1990; and this will further increase the amount of wet scrubber sludge produced annually. Currently only about five percent (5%) of wet scrubber sludge is utilized nationally. Most of the FGD scrubber sludge, which had found some use in Portland cement or agriculture or plaster is sulfate-rich sludge. The wallboard industry is reluctant to use FGD by-product gypsum because of the impurities, both organic and inorganic, and variations in the product from batch to batch. However, for sulfite-rich scrubber sludge the utilization is much bleaker even though some use as structural fill and as aggregates has been proposed. Therefore, there is a strong need to develop additional utilization strategies for wet FGD scrubber sludge.
In 1998, the U.S. gypsum demand reached 27.8 billion square feet according to the Gypsum Association. Presently, the U.S. produces about 17 million tons per year of the current demand of 28 million tons per year. The rest is imported. An important strategy for the wet scrubber sludge utilization will be, therefore, to develop wallboard type materials from it. Unfortunately, the requirements for wallboard manufacturing from scrubber sludge are very stringent. It will be difficult, if not impossible, to consistently produce sulfate-rich scrubber sludge of high quality from FGD residues, which meets the conventional wallboard manufactures' needs. The physical and chemical properties of FGD residue are strongly influenced by the variability in the organic and inorganic content of the coal. Moreover, the crystal size of the gypsum is of a critical importance in conventional wallboard manufacturing and will be difficult to duplicate as is currently done from natural gypsum because of impurities in coal-derived sludge. Therefore, it is clear from the above discussion that additional technologies are required which will convert Illinois scrubber sludge into marketable products, which are economical.
Experiments:
To develop wallboard
materials from sulfate-rich scrubber sludge and for these materials to tolerate
variations in the composition of the scrubber sludge, we conducted fundamental,
as well as, applied studies. We
developed procedures to extract microfibrils from natural products, which
are especially abundant in Southern
Illinois. These microfibrils
were evaluated and characterized by undertaking differential scanning calorimetry
(DSC) and dynamic mechanical analyzer (DMA) measurements at
30°C
< T <
500°C. Moreover, we probed the structural
properties of microfibrils by undertaking novel in-situ high-temperature
diffuse reflectance-Fourier transform infrared (ISHT-DR-FTIR) in the temperature
range of
30°C to
500°C.
Using the characterization data obtained from DSC, DMA, and ISHT-DR-FTIR
measurements, we devised strategies of forming composites from CWLP scrubber
sludge. The composites were
assembled in 4" x 4" x 0.2" and 6" x 6" x 0.2"
sizes. The 4" x 4" x 0.2"
Agro-wallboard composites, formed from scrubber sludge and microfibrils,
are shown in Fig. 1. In pursuit
of forming these materials, a number of variables were
evaluated. The effects of these
variables on the mechanical performance was gauged by conducting DMA tests
in creep mode, by compressive strength tests, and by flexural strength
measurements in a three-point bending
mode.
Figure
1. Picture of the Agro-wallboard
composites formed from sulfate-rich FGD scrubber sludge containing natural
microfibrils. Note, unlike commercial wallboard materials, our
Agro-wallboard materials do not require paper
support. The sample size is
4” x 4”
x
0.2”.
Results and Conclusions: From DSC, DMA, and ISHT-DR-FTIR measurements at 30°C < T < 500°C on microfibrils, we concluded the following:
(1) Water was hydrogen bonded to the -CH2OH and - OH groups of the microfibrils. The hydrogen-bonded water desorbed at T > 110°C. Consequently, this water would retard combustibility of our Agro-wallboard materials.
(2) The highest temperature to which microfibrils were exposed should be
limited to
300°C
because beyond that temperature the microfibrils became fragile due to
decomposition
reactions.
(3) It seemed that microfibrils were thermally stable in the temperature
range in which typical wallboard perform, hence, could be used in our
Agro-wallboard
materials.
Figure 2. Picture of the Agro-wallboard composites of size 8” x 6” x 0.2” formed from sulfate-rich FGD scrubber sludge containing natural microfibrils. The top sample was surface treated for moisture resistance
Figure 3. This figure depicts the mechanical strength of our Agro-wallboard materials and a commercial wallboard. Unlike commercial wallboard, our Agro-wallboard materials do not contain any paper support.
(4) The ISHT-DR-FTIR measurements revealed that there are four distinct structure ranges of microfibrils, i.e., Phase I: 30°C - 200°C, Phase II: 200°C - 360°C, Phase III: 360°C - 420°C, and Phase IV: T > 420°C.
(5) The mechanical strength test data suggested that: (a) most of the strength for a conventional wallboard came from the support paper and (b) our Agro-Wallboards, without any paper support, were much stronger than the conventional wallboard with paper support (see Figs. 3 and 4). Therefore, it appeared to us that we should develop products without paper support. This would reduce the cost of fabricating wallboard materials.
(6) In an effort to develop Agro-Wallboard materials without any paper, we evaluated a number of variables, namely, water-to-scrubber sludge ratio, formation temperature, types of fibers, concentration of fibers, and type and concentration of binders.
(7) It appeared that water-to-scrubber sludge ratio had a profound effect on the density and the flexural strength of the wallboard formed. In fact, a linear relation was observed between the water-to-sludge ratio and flexural strength.
(8) The formation temperature also drastically affected the strength of the material.
(9) Molding pressure played an important role in determining the flexural and compressive strength of the wallboard. The higher the molding pressure the higher was the compressive and flexural strength of the wallboard.
(10) Besides microfibrils, we evaluated other natural products or by-products for incorporation in our Agro-wallboard materials. Our microscopic results on formed composites suggested that not all natural products or microfibrils were suitable for wallboard. In fact, two types of microfibrils gave much superior results.
Figure 4. This figure reproduces the observed modulus of our Agro-wallboard materials and a commercial wallboard. Unlike commercial wallboard, our Agro-wallboard materials do not contain any paper support.
The remainder of this report contains proprietary information and is not available for distribution except to the sponsor of this project.