Patented Flexible Multipoint Thermocouple Assembly
INHERENT DESIGN CHARACTERISTICS OF THE PATENTED FLEX-O™ASSEMBLY
Long, non-flexible multipoints present problems in shipping storage, storage and installation. They must be shipped on large trucks, stored in large spaces and must be installed using a crane with a boom at least twice the height of the vessel.
The FLEX-O™, on the other hand, may be coiled due to its spiral construction and installed with ease due to the bimetal strips at each point. The FLEX-O™ is shipped coiled in crates 7' x 7' x 2', simplifying shipping, handling and storage. More importantly, two men may conveniently uncoil and insert a FLEX-O™ into either top, side or bottom entry vessels without the use of heavy equipment.
The bimetal strip design allows removal and replacement of the thermocouples during operation. The strip produces a pressure of 5 p.s.i. between thermocouple tip and thermowell wall at process temperatures. This pressure is adequate for accurate temperature measurement without impeding removal during vessel operation should this become necessary.
The FLEX-O™, a multipoint thermocouple assembly, mounts individual thermocouples on a bimetallic strip. The bimetallic strip is composed of two dissimilar metals with different coefficients of expansion. The strip remains flat at ambient temperature, but bends outward as the process temperature rises. The thermocouples are thus forces against the well wall when the reactor is operational, but they retract during shutdown.
The FLEX-O™has substantially faster response time than other pipewell multipoint designs due to the low mass at the sensor tip.
TEST THERMOCOUPLE - 1/8" O.D., 304 SS SHEATHED
RESPONSE - 63.2% OF STEP CHANGE FROM 32º F TO 212º F
NOTE A THERMOCOUPLE BOTTOMED IN TUBING WELL
NOTE B GAYESCO FLEX-O™ DESIGN WITH THERMOCOUPLE FORCED
AGAINST INNER WALL OF WELL BY BIMETALLIC MEMBER
NOTE C THERMOCOUPLE BOTTOMED IN GUIDE TUBE, END OF WHICH IS
WELDED TO HEAT CONDUCTING STUB THRU & WELDED INTO
WALL OF PIPE WELL
Warpage Problems Minimized
Pipewell warpage is unfortunately a common occurrence by reactors. High process temperatures and shifts in the catalyst bed are the usual causes of well warpage. Occasionally, design requirements even necessitate the installation of a curved pipewell. The performance of the FLEX-O™ in these situations is unparalleled. the small diameter, spiral arrangement; bimetallic strips and flexibility all contribute to easy installation in all but the most severely damaged wells. This saves the expense and trouble of well replacement and reactor shutdown by making usable wells out of those that would otherwise have to be replaced. (The adjoining picture is the actual FLEX-O™ removed from the warped pipewell)
A special patented secondary containment system can be designed into each FLEX-O™ assembly. this prevents contact of the process with the atmosphere in the event of thermowell failure, protecting both the process and operators.
THE PURGE TUBE FLEX-O™ DESIGN
GAYESCO was recently granted its ninth patent for further innovations in temperature measurement system design. This latest design, called the Purge Tube Flex-O™ (patent # 5,152,608) incorporates a purge system into GAYESCO's patented FLEX-O™ Multipoint Thermocouple design. The result is a unique product offering superior reliability, utility and safety. With the invention of the FLEX-O™, GAYESCO substantially improved the science of reactor temperature measurement. The FLEX-O™ allows temperature measurement at various levels throughout the reactor with the use of multiple sensing points; and it does so while offering a flexibility feature that makes installation easier. Additionally , that flexibility ensures that the sensing tip remains in continuous contact with the inside diameter of the pipewell, even in the event of pipewell warpage. These characteristics, as well as FLEX-O's™ replaceability, speed of response, bimetallic actuation and point density, have made this design a standard used throughout the industry.
With the incorporation of a purge system within the FLEX-O™, four design factors are packaged into a single assembly:
Multipoint multilevel temperature sensing
Purging of well contaminants
Internal pipewell pressure relief
The Multipoint design usually encapsulates the thermocouples in a protective pipewell, inserted directly into the vessel. In the interest of safety, the thermocouples are pressure sealed as they exit the protective well, to contain any pressure leakage due to primary well failure.
One disadvantage of using such a secondary sealed or partially sealed well, however, is that accumulations of corrosive elements may, in time, form at certain locations within the well. These usually reach highest concentration levels in areas where the temperature gradient is the highest (such as in the primary nozzle area in the reactor). If this situation occurs, the result could be the deterioration of the thermocouple sheaths or thermal elements, or a premature failure of the pipewell.
An additional safety concern involves the migration of gas, especially hydrogen, from the reactor into the pipewell, resulting in the internal pipewell pressure build up. Because the pipewell is a sealed system which remains at pressure even when the reactor is down for maintenance, a risk of accident is high if personnel in the area are not aware of this phenomenon.
The placement of the purge tube directly within the FLEX-O's™ protective well minimizes these problems. The additional employment of check valves in the system enhances the advantages of the secondary seal system.
The incorporation of the purge system directly into the FLEX-O™ posed a two fold design challenge; it had to be such that it would not add limitations to the flexibility of the system; and it could not decrease the number of thermocouples that could be supplied in the bundle. In short, the system's designers wanted all the advantages of the internal purge system without having to sacrifice the flexibility, accuracy, or response characteristics of the Flex-O™ temperature measurement system.
To accomplish this, the center support member used as the "flexible backbone" of the FLEX-O™ system was replaced with a single, heavy wall center support tube. This tube not only effectively provided a conduit for the introduction of a purge gas into the wall, but it succeeded in doing so without inhibiting the desired flexibility characteristics. It was also important in designing the Purge Tube Flex-O™ that the purge gas be introduced near the bottom of the well, so that the purging effect would be allowed to flow from the bottom of the closed system up the length of the well, and then exit through a purge outlet outside the vessel. The spent purge gas could then be vented to atmosphere or a suitable disposal area.