The temperature on the interface between this layer and the structural wall should be 300F (150C), which is the heat deflection temperature (HDT) of standard novolac EVERs. The temperature on the outer wall normally will decline to about 175F (80C). The figure illustrates this point.
Because the temperature of the FRP is now lower than the HDT or "HDT minus safety margin" of the standard novolac EVERs, the structural wall now can be made using standard techniques.
A suitable resin, a suitable design and good analysis method are the prerequisites for the cost-effective design and manufacture of FRP composites for high-temperature applications, suitable for use at a temperature as high as 420F (220C) in contact with flue gases. The new resin is a novolac EVER with corrosion resistance properties similar to standard novolac EVERs. However, its increased acid resistance allows it to contain the corrosive environments found in the gas inlet sections of scrubbers.
Experience has shown that the use of FRP in applications at temperatures as high as 420F (220C) pushes FRP to the limits of its capabilities. The design and manufacture of such vessels should not be undertaken lightly, and careful consideration must be given to laminate design and quality.
The design of the entire laminate system ," including the use of heat-conductive additives in the liner section, an insulating air gap, and the standard resin structural component ," need to be considered. For a successful application, the resin manufacture, the FRP fabricator, the engineering contractor and the end-user should be involved as early as possible in the project.
New EVER in use
The following case studies highlight some examples of FRP made with the new novolac EVERs and in use in high-temperature applications.** The continued study of equipment in service has proved invaluable to the authors in determining how the vessels performed and allowed further refinements to be developed and adapted to the systems ," increasing their reliability and longevity.
The quench section for a waste incinerator project in Alkmaar, The Netherlands, has a design temperature of 446F. It operates normally between 392F and 428F. The part is 2 meters (m) in diameter and 3 m long and includes many spray and instrumentation nozzles. Three lines of a similar design operate in parallel.
The original piece was installed in 1995. Because of the spray nozzles' positioning, an abnormal degree of thermal shock was induced during service. By mid-1995, some delamination was encountered.
The protective shields were redesigned, incorporating the use of carbon/graphite and an insulating air gap. The thickness of the shields also was reviewed before the replacement program began. The first new shield was installed in 1995, and was reported to be in excellent condition during last inspection in mid-1998. The other equipment operating in parallel units also has been adopted to the new design.
At a power plant in Simmering, Austria, the chimney liner had an operating temperature of 194F, but could be exposed to a temperature as high as 356F during bypass operation and as high as 392F for as long as three hours. The flue gas included water vapors, sulfur dioxide, nitrogen oxides, hydrochloric acid, hydrofluoric acid, etc.
The liner was 4.8 m in diameter by 164 m in height. An FRP liner replaced a double brick liner (about 300-mm thick) with an acid-resistant inner structure. The new composite liner is electrically heated during startup of the power plant to prevent rapid cool-down of the flue gas and condensation of the gas.
* *The FRP was made with DERAKANE 470HT novalac EVERs (Trademark of The Dow Chemical Co.).
*By the authors.
Mason is a senior development specialist at The Dow Chemical Co.'s research facilities in Freeport, Texas. He provides technical support for the DERAKANE EVERs and can be reached at firstname.lastname@example.org. van Buren is a senior development specialist for Dow Deutschland's research facilities in Rheinmanster, Germany, and provides technical support for the DERAKANE EVERs. Contact him at email@example.com.