Materials
The mineral processing and mining industry
uses a variety of strong acids to extract minerals from low grade ores. The principal acid used in mineral processing is sulfuric acid, which is very corrosive to most all metals as well as concrete. If steel is used for the storage tanks or process equipment, a protective coating or lining will also have to be applied. Most of these coated or lined tanks require ongoing maintenance to keep the steel protected. A better option in these applications is to
use FRP equipment made with a resin that is resistant to these strong acids. The most common resin used for these applications is a bisphenol A epoxy vinyl ester resin. Many pieces of equipment can be made using epoxy vinyl ester resins. These applications include but are not limited to electrolytic cells, electro-winning cells, electrostatic precipitators, extractors, ducts, fans, scrubbers, stacks, stack liners, cell covers, grating, railings, storage tanks, settling tanks, pipes, pumps, and cooling towers. There are many case histories available to support the successful use of epoxy vinyl ester resins in such applications. A few of these are shown at the end of this paper.
Fig. 2. Chimney with two FRP stack liners in operation in North Carolina.
these acid gases is the wet FGD scrubbing system. Limestone slurry is typically used as the scrubbing medium. This will eliminate about 99 per cent of the sulphur dioxide in the flue gases. The scrubbing environment is highly corrosive to metals but the scrubbers, limestone slurry piping, water piping, duct work, and stack liners can all be made out of properly designed and fabricated FRP. The proper resin needs to be specified to obtain long maintenance- free service. Other areas in the power plant where FRP can be use are mist eliminators, cooling towers, storage tanks, and cable trays. FRP is very cost competitive compared to the high nickel steel alloys that would otherwise have to be used in this corrosive environment. Equipment made from high nickel alloys is at least twice the cost of comparable FRP
equipment. The other option would be to use a coating or an FRP lining on the steel equipment. Although this is a viable alternative, maintenance costs tend to be significantly higher with the coatings and linings. One of the very first uses of FRP was in a chlor-alkai
plant. A chlorinated polyester resin was developed to withstand the corrosive environment of the cell covers and cell headers. Novolac epoxy vinyl esters have also been used in making the cell headers at chlorine plants. Other areas where FRP components can be used successfully are piping, storage tanks, grating and hand rails. The use of FRP has also expanded into many other chemical process plants. Some areas ideal for FRP are where mineral acids are present or where chlorides are present. Chlorides in water such as salt water and brine are very aggressive toward stainless steel. These are ideal applications for FRP because equipment manufactured from corrosion grade isophthalic polyester resin or epoxy vinyl ester resins are almost inert to salt water at temperatures up to 180°F. These resins have been used for FRP in piping and cooling towers especially when sea water is used. Other applications include tanks, reactors, scrubbers, piping, gratings and duct work. A few examples are shown below. Wastewater treatment facilities have many applications
where FRP is currently being employed. Sodium hypochlorite is the material of choice for treating waste water currently. The
Fig. 3. FRP Stack liners.
The bleaching process used in the manufacture of paper is very corrosive. The most common material used for the bleaching paper now is chlorine dioxide. Brominated novolac epoxy vinyl ester resins have been found to provide optimum resistance to chlorine dioxide based on testing at paper mills. The types of equipment in a paper mill that can be made out of properly designed and fabricated FRP are up flow tubes, towers, tanks, washer drums, drum covers, pipe, scrubbers, and hoods. Many case histories are also available to demonstrate the viability of FRP in these applications. The US power industry is in the process of installing flue
gas desulphurisation (FGD) units at all of its coal burning power plants to reduce the amount of acid gases that are emitted from these units. The process that is most effective in eliminating
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Fig. 4. FRP Abrasion resistant limestone slurry piping to power plant scrubber.
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