Economizer Question

[JonRiley56]

All,

How is it that water pumped through an economizer into a boiler doesnt just flash to steam in the coil itself, or is it not a problem if it does? With all the cautoinary statements on not adding cold water to a dry hot boiler, it seems like I would be doing the same in an economizer unless I recirc through it at which point I am back to a very warm hotwell and potential pumping issues.

As I ponder putting an exhaust preheater on the boiler side of my pumps it occurs to me that it may well become the weak link in trying to run my hydros, either in the unit itself, or the connections, and perhaps I should be thinking conventional economizer. I am troubled by the possibility of essentially making a small monotube boiler above my watertube and having the flashed steam cause major turbulence going into my steam drum, or having it overcome my check valves on the water inlet side if it builds significant pressure at the flash.

thoughts ?

jon

[DetroiTug]

Hi Jon,

An economizer will boil dry and the incoming cold water will flash to steam - so much so that a relief valve must be attached to the coil to handle the surge in pressure. Overview: There should be an isolation valve at the boiler for the feedwater inlet, then a good check valve, then the economizer if used, then a manual valve, then it's a good idea to have a second check valve right before the economizer.

I just learned the best method (in my case)for mounting the relief valve on the economizer is mount it up high (on the side of the stack etc). Then attach it with copper tube, this copper tube (about 4 feet in my case), acts as a cushion and keeps the relief valve from popping off every time water comes in.

It's also not a bad idea to have a bypass network on the economizer so it can be isolated and bypassed if a leak develops. The relief valve definitely needs to monitor this potentially isolated section of piping.

How the surge will effect the level? I'm guessing it will be negligible.

-Ron

[barts]

If you have a relief valve after your pumps and no valve or check valve between them and the economizer, that relief will protect the economizer in case someone closes the boiler feed valve or the economizer overheats. The bypass can be a piece of replacement tubing that is ready to be fitted; I've not needed one in 22 years of steaming with copper economizers, but I generally don't fire heavily unless I've gotten the engine turning already (and thus water is flowing in the economizer). Note that the relief can and should be set at a pressure that's higher than the boiler safety so long as that's within the safe operating regime of the pumps, valves, economizer, etc. This allows you to easily feed the boiler even when operating near the maximum safety pressure w/o drips/weeps from the pump relief valve.

On Otter I built the cold water plumbing to handle the full hydrotest pressure of the boiler; that way I can use the hand feed pump to perform the spring hydro .

- Bart