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Re: overheating and overpressure

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Posted by Larry on July 02, 2002 at 08:08:27:

In Reply to: overheating and overpressure posted by Russ on June 29, 2002 at 22:03:31:

: I work at a plant that has hog fired hot water boilers that heat kilns to dry wood. The kilns are controlled by a computer, and occasionally crash. When the computer has a problem the valves leading to the kilns close and the water stops circulating resulting in extreme temperature and pressure in the boilers. Even if the fuel feed system stops, there is still enough fuel in the boilers to continue to create lots of heat.
: The safety valves do there job, but it still shakes the building enough to break hot water unions and valves.

: My question is: Should we just change out the valves so that they fail open, or is there more to it than that?

I would have the design engineer review the total system before just "changing-out" the valves.
Do a "process hazard review" or "what if analysis" of the total system. What happens to the "system" during a power outage?
Install a second computer running in parallel with the primary computer.
Develop a procedure to dump or smother the heat source.
When the safety valve reduces the pressure, with the heat source remaining constant and no circulation, the hot water within the system begins to flash into steam bubbles which rapidly collapse causing water hammer and most likely also causes cavitation at your circulating pumps.
Install an automatic recirculating valve (Yarway) and piping assembly between this "fail closed" valve and the boiler makeup water source.
Your current operation has high potential for serious injury to personnel.
Have a safe shift.

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