Patent Application
20100206456
The present invention relates generally to abrasion resistant blocks or bricks that may be installed in structures used to carry corrosive materials and the like, such as power plant combustion emission systems or similar plant processes. More specifically, the present invention includes a system and method for producing and installing into such systems abrasion resistant blocks or bricks that are formed from a composite material comprising vinyl ester resin, fly ash and coal slag. These composite blocks are manufactured and installed within ductwork and exhaust flues of emissions structures, forming the inner walls of the structure that are in direct contact with the corrosive materials passing through the system. The composite blocks are installed either to repair existing ductwork that has become corroded over a period of time, or in the initial manufacture of such systems in order to improve abrasion and chemical resistance of the ductwork, thus significantly extending the life and functional duration of the system.
Often, the ductwork that carries gaseous emissions from the power generator of a power plant through the environmental scrubbing process and out into the atmosphere becomes corroded and eroded through years of exposure to such gaseous emissions. For example, in Flue Gas Desulfurization (FGD) systems, the ductwork is exposed to high temperatures, high acid concentrations (including H2SO4), entrained and suspended particulates, and wet/dry interfaces of the condensing acids from suspension in the gaseous flue gas stream. Typically, the power plant emissions system includes a scrubber/absorber to remove sulfur dioxide, or SO2 and other oxides of Sulphur and Nitrogen as well as chlorides. These gases are generally exposed to an aqueous neutralization stream in the scrubber, causing a reaction with the sulfur dioxide, which can produce calcium sulfite, calcium sulfate and sulfuric acid and other detrimental exposures. The SO2, SO3, and H2SO4 can cause significant corrosion of the emission system structure, including the ductwork.
When the emissions systems of power plants, or other similar structures, become corroded, eroded or otherwise degraded from years of exposure to such conditions, it becomes necessary to repair and maintain these systems. Replacing such systems can be prohibitively expensive, so other means for extending the life of the emissions systems and ductwork have been developed. One way that has been utilized commercially to extend the life of these systems is by providing a liner within the ductwork and system. These liners are typically applied to the inside of the ducts, tanks, pipes, and other structures used to carry the gaseous emissions, and the liners may be comprised of resinous liners such as polyester, vinyl ester, epoxies, and/or urethane as well as borosilicate blocks and potassium silicate gunnites. These liners are used to protect the emissions structures primarily against chemical corrosion which can be exacerbated by temperature gradients across the walls of the ductwork that cause condensation of acids in the ductwork.
One disadvantage to using resinous liners for these applications is that they do not typically provide the necessary insulation against temperature gradients and associated acid condensation, which can lead to the increased likelihood of corrosion, cracks and general degradation of the emission transmission structure.
The borosilicate blocks are used to form walls and protective structures that are built up against the inner walls of the emissions structure. These borosilicate blocks offer increased insulative properties and thus a reduction in condensation of acids, but do not provide significant abrasion resistance, thereby reducing their effective lifespan within the system. Alternatively, the silicate gunnite materials may applied directly to the inner walls of the emissions structure in areas where the abrasion is expected to be significant but fail to yield a life expectancy similar to that of the borosilicate blocks that are not exposed to abrasion and thus required repair and replacement or contribute to the premature failure of the system.
Within the emissions structures are areas that experience increased turbulence, which are usually caused by the shape of the structure itself. In these “target zones”, the gas flow is redirected in a different direction (such as a turn in the ductwork), and the corrosive gases directly impact the walls of the structure. Thus, the target zones show increased evidence of erosion due to the abrasion created by the more direct impact angles of the corrosive and abrasive gas flow. Increased abrasion resistance is required in the target zones, in order to increase the functional life of the emissions systems in these areas.
Thus, it would be desirable to provide a material that could be formed into blocks and applied within emissions structures, in order to increase abrasion resistance and adequate insulation, particularly in the target zones. It would also be desirable to provide a method for installing such abrasion resistant materials within such structures.
Therefore, it is an object of the present invention to provide an abrasion resistant material for installation against the interior surfaces of power plant emissions structures, in order to form an inner sleeve that increases resistance to chemical corrosion, abrasion and erosion, and provides significant insulation to such structures.
Additionally, it is an object of the present invention to provide a composite material that may be formed into blocks, wherein the composite includes vinyl ester resin, fly ash and coal slag.
Further, it is an object of the present invention to provide a composite material that may be installed directly and adhered to other lining materials installed in such a way as to form an additional, abrasion resistant layer to form a composite insulative and abrasion resistant protective system.
In a preferred embodiment, the abrasion resistant material is formed from vinyl ester resin (about 10% to about 40% by weight), coal slag (about 30% to about 70% by weight), and fly ash (about 5% to about 30% by weight). In order to prepare the material, the vinyl ester resin is mixed together with the fly ash, coal slag and a curing catalyst. Additional aggregates may be included, including powdered ceramics or vermiculite (preferably up to about 10% by weight) for additional abrasion resistance, weight reduction and increased insulative properties, when necessary.
The mixture is then cast into molds that provide a texturized mounting surface on one side, so that an adhesive layer may be applied thereto, which helps to form a strong bond during installation. The composite material is then cured at 150 F for several hours. After curing, the composite material is removed from the mold and cut into blocks of desired size and shape, using commercially available saws and blades. These blocks may then be applied to the inner surfaces of an emissions structure (or to the inner walls of any structure that requires such abrasive resistant and insulative properties) by using commercially available corrosion inhibiting adhesives, grouts and mortars.
In one embodiment, the blocks may be formed as a single-layer with the homogenous mixture as set forth above. In another embodiment, the blocks may be formed as a dual-layer composite, wherein an outer layer is the vinyl ester resin/fly ash/coal slag mixture as set forth above, and an inner layer is formed from other commercially available materials, such as borosilicate block, brick, or any other suitable material. In use, the dual-layer composite blocks are oriented and installed within the structure so that the inner layer is adhered to the existing structure, and the outer layer is exposed to the corrosive gas flow.
In order to install the composite blocks into an emissions structure, the blocks are adhered to the inner faces of existing walls, ceilings and/or floors of the structure. The blocks are preferably staggered, similarly to the arrangement of a standard brick wall, for increased structural integrity. Essentially, the blocks are used to form an inner sleeve within the existing emissions structure, where the inner sleeve comprises walls formed from the composite blocks. Commercially available corrosion inhibiting adhesives, grouts and mortars may be used for such installation.
In an alternate embodiment, the composite material may be applied or installed in-situ to form a laminate over the existing inner surfaces (including surfaces made from concrete, steel, brick, block, or any existing inner surface) of the emissions structure. In this case, the material is applied via trowel or a similar instrument while the material is in an uncured state. Then, the composite material is allowed to cure after installation. This arrangement allows more flexibility with respect to the desired thickness of the laminate, and still provides the enhanced physical characteristics inherent in the materials, including insulative and abrasion resistant properties. Further, the material may be applied to a pre-existing liner or inner sleeve consisting of, for instance, borosilicate blocks, in order to enhance the abrasion resistant qualities of the emission structure.
These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:
A first embodiment of the abrasive resistant composite block system is shown in
In order to prepare the composite material, the vinyl ester resin is mixed together with the fly ash, coal slag and a curing catalyst. Examples of preferred catalysts include diaroyl peroxide, tertiary alkyl hydroperoxides, and alkyl peresters of percarboxylic acids, although other known catalysts may be used. Additional aggregates may be included, including powdered ceramics or vermiculite (preferably up to about 10% by weight) for increased abrasion resistance, weight reduction and increased insulative properties, when necessary. One advantage to these particular materials is that fly ash and coal slag are waste by-products of coal powered electrical plants, which makes them inexpensive to obtain, and allows some of the waste to be recycled into productive material. Additionally, the coal slag is well suited as a component for abrasion the resistant materials described herein, because it is itself resistant to abrasion due to the high strength and angular geometry of its granules.
The mixture is then cast into molds that provide a texturized mounting surface on one side, so that an adhesive layer may be applied thereto, which helps to form a strong bond during installation. The composite material is then cured at 150 F for several hours. After curing, the composite material is removed from the mold and cut into blocks 16 of desired size and shape, using commercially available saws and blades. These blocks 16 may then be applied to the inner surfaces of an emissions structure (or to the inner walls of any structure that requires such abrasive resistant and insulative properties) by using commercially available corrosion inhibiting adhesives, grouts and mortars.
In one embodiment, the blocks 16 may be formed as a single-layer with the homogenous mixture as set forth above. In another embodiment, the blocks 16 may be formed as a dual-layer composite, wherein an outer layer (top layer) 20 is the vinyl ester resin/fly ash/coal slag mixture as set forth above, and an inner layer (bottom layer) 22 is formed from other commercially available materials, such as borosilicate block, brick, or any other suitable material. In use, the dual-layer composite blocks are oriented and installed within the structure so that the inner layer is adhered to the existing structure, and the outer layer is exposed to the corrosive gas flow.
To install the composite blocks 16 into an emissions structure 2, it may be desirable to clean the inner surfaces of the emissions structure 2 by performing abrasive blasting, such as sand blasting those surfaces. The blocks 16 are adhered to the inner faces of existing walls, ceilings and/or floors of the structure as shown in
Optionally, a ceramic epoxy paste may be used as an adhesive agent for installing the blocks to the inner surfaces of the emissions structure, and may also be used in place of mortar between the blocks. Additionally, the blocks may then be overcoated with the ceramic epoxy paste layer.
In an alternate embodiment, the composite material may be applied or installed in-situ to form a laminate over the existing inner surfaces (including surfaces made from concrete, steel, brick, block, or any existing inner surface) of the emissions structure 2. In this case, the material is applied via trowel or a similar instrument while the material is in an uncured state. Then, the composite material is allowed to cure after installation. This arrangement allows more flexibility with respect to the desired thickness of the laminate, and still provides the enhanced physical characteristics inherent in the materials, including insulative and abrasion resistant properties. Further, the material may be applied to a pre-existing liner or inner sleeve consisting of, for instance, borosilicate blocks, in order to enhance the abrasion resistant qualities of the emission structure.
Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein. All features disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
