Can I manually control condensate return into boiler feed tank?

LoafofBreadhead_123

Sorry folks. I posted this a few weeks ago but lost in outer space.
Situation: Three Fulton upright boilers fed by a feed tank that has condensate coming into it with makeup water. There used to be a control module but it was only rated to 90 degrees operating temperature and burned up within the first week as it was installed in the boiler room which is always over a hundred degrees. So the control, which controlled when the boilers fired, and thus controlled steam output and further, condensate amounts, no longer controls anything. Boilers thus fire randomly which means condensate, in this case, comes back in volume more than make up (whose valve is temperature controlled and is set at the optimal 180 to 190 degree range) water can overcome temperature wise. So, the condensate comes back hot and in a volume that the cold water makeup cannot overcome. In order to maintain 180-190 degrees in feed tank, the make up water is on constantly and water from tank is constantly overflowing.
You may ask why we don't replace the controller? The one installed is obsolete and it would cost a lot to install a new system (thousands). So my idea is to install a simple manual control to the condensate return so I can control the volume coming into the tank and thus the temperature in the tank. The condensate comes into the tank from above and has a gate valve just before the tank. My idea is to put an overflow above the gate valve and use the gate valve to control the amount of condensate coming in. Excess would go out overflow so as not to back up condensate. Does this sound reasonable?

Jamie Hall

I think I at least need more information on this system. Such as... clearly, if you have constant makeup, this is an open system -- consumptive use? If so, where does the condensate come from, and more or less what fraction of the steam supply returns as condensate?

How is the makeup water heated? Is there a possibility that the condensate could also be temperature controlled in some manner? If it's too hot, for instance, mixed with some cooler makeup water (a simple temperature control valve might do?). Or too cold, run though a similar preheater to the one used for the makeup water?

I hope that whatever pumps are used to return water to the boilers are controlled by the boiler water level? If not, what controls them?

What controls the amount of makeup water? Level in the condensate tank?

The problem with manual control is that somebody has to do it; this is subject to error -- and in any event is a constant labour expense. In any case, don't use a gate valve to control flow. Just don't. Gate valves are meant to be and designed to be only fully open or fully closed. A ball valve can be used or, in some instances, a globe valve.

EBEBRATT-Ed

What @Jamie Hall said.

We need more information, it sounds like your dumping a lot of water. Why? You cant dump hot water down a drain hotter than 120 degrees.

You say the MU water is temperature controlled. That doesn't sound like MU water that sounds like a condensate cooler

pedmec

i agree with ebratt. the only time i have seen tempered steam condensate is on high or elevated pressure system draining to a flash tank. and flash tanks are used to prevent the steam condensate that is being used in elevated or high pressure systems to help prevent condensate from flashing back in steam after the steam traps when the return is back at atmospheric pressure in the receiving tank. after its in the flash tank then it goes to the condensate boiler feed tank. you don't want steam blowing out of the tank vent or worse flashing in the pumps inpellar.

also i'm not familiar with fultons full line of boilers. i've only seen them in a high pressure systems used for dry cleaners, steam presses, etc. are you operating a high pressure system?

LoafofBreadhead_123

It's a low pressure system. As posited in post, there is make up cold water in the feed tank to offset and cool condensate coming in. The condensate amount coming back would be hard to measure. It is condensate from boiler steam production after use and all comes back to the feed tank by gravity. There is a cooler for blowdown steam from boilers that cools the water before it goes into the drain. This would be where condensate overflow would go. This is not an old system (10 yrs. old). It has a chemical feed which was neglected by vendors and is the reason for all of this. I have the system back up and running, have replaced plumbing and valves damaged by lack of chemicals and soft water and have everything up and running (feed water tank at 185, chemicals and soft water back online and feed valves and condensate coming in to tank). I simply have too much water in tank and it's overflowing. If I can control condensate and lower temperature coming in, than make up cold water will not have to run constantly to cool condensate. It seems like a logical fix to simply lower condensate volume coming in so that temp can be within range of temp controlled make up water. 0-220 degrees.

Question: Is there no instance of condensate being controlled as it comes into feed tank? And why can't one do so.? It would not be hard to manipulate manually in this instance because it's low pressure and a simple system. Agree about ball valve. One is being used to control condensate from one line that was originally installed with system which led me to believe that one can be used in main line return. What is the worst that can happen if a ball valve controls condensate input and excess condensate goes to water cooler and then to drain? I don't see a safety concern as it's less heat coming in and not more. There is no flashing.

Jamie Hall

I'm still puzzled. It seems as though you are describing a more or less closed low pressure system? In which case, there should never be excess condensate. In fact, the condensate returned cannot exceed the amount of water boiled. Perhaps more to the point, that condensate should never be hot enough to flash, although it might be warmer that 185 F. But would that be a problem? Why?

I would point out that the less makeup water you have, the less chemicals you will need. It would be much better to use a heat exchanger to cool the condensate, if for some reason that is necessary, with cold water -- which might then be useful as hot water somewhere else -- rather than waste condensate and thus have to add cold water.

I must be missing something here. What? It might help to know what the steam is being used for...

LoafofBreadhead_123

LoafofBreadhead_123

LoafofBreadhead_123

dopey27177

Just for fo.
Is more than one boiler firing at the same time?
If so more return water will return to the combination feed and condensate tank.
Also how is the water level controller hooked up for feed water insertion.

Jake

retiredguy

The answer to your first question is NO; that is not the way to fix your problem. That cold water that enters the condensate tank is not supposed to be cooling the returning hot condensate. It is only there to make sure that the condensate tank does not run out of water when the steam system does not return all it's condensate. In a good, tight, steam system, that cold water line should rarely feed water to that tank. You have problems out in the system which need to be addressed and repaired. The returning hot condensate should never be run to a drain to keep the tank from overflowing. You need to return 100% of that condensate to the tank and only supply the system with untreated cold water as is necessary. That untreated fresh water, that should be treated and maybe even be deaerated, is going to ruin those boilers. I am guessing that the steam traps are in need of repair or replacement as are other devices in that system. You can not correct a worn out system, where the owner does not want to do the required maintenance by doing "BAD" things like dumping the condensate. I have seen systems all over Pennsylvania that operate this way only to find out that the boilers only last a few years and that the operating costs are excessive. It is time to call in the experts and have them fix this system before it is too late. Do the owners a favor and get the help that they need. my 2 cents.

Pumpguy

We still don't have the whole story on how your system works.

What is the industry and application this system is applied to?

We really need the answers to @Jamie Hall's questions to advise further.

LoafofBreadhead_123

So: Since the controller that fires the boilers does not work, yes, all the boilers can fire at once and this is why there is more condensate than necessary. So to retiredguy: The system, besides the controller, is in good shape. It is a fairly small system the feeds two autoclaves and a washing machine. The system can run on one boiler which would create a lot less condensate coming back. I am fully aware of the cost benefits of using treated condensate i.e. "dead water" created between 180 and 190 degrees and we have a chemical feed working appropriately. Everything is in order except that we don't have a controller controlling the sequence of the boilers so they run simultaneously creating too much steam condensation. Also, condensated, much like blow down steam, goes to cooler pictured so it goes to drain under 120 degrees. All the traps in the system have been checked and work fine. The condensate comes back at about 200 degrees and in an amount that overflows tank. The problem to me is very basic. Since the controller does not work, the boilers create too much condensate coming back which provides too much heat to the feed tank which is then regulated by aqua stat set at 180 degrees which then trigger cold water. So cold water continues to run all the time to cool down tank to 180. So, if a new controller were installed, this would solve the problem but the cost is a problem for us and we wont get funding anytime soon.
Summary: All current systems are in working order except controller. Three boilers can run at same time causing too much condensate. I don't need this much condensate to heat water to 180. A controller would fix the problem. So the question is: Can a solution, short of installing a new controller, be found? Do I need to install a controller to control return condensate or can I do it another way? I guess I'm having a hard time understanding the problem with dumping too much condensate, cooling it appropriately before it goes down the drain and supplying feed tank with appropriate amount so that I don't need to cool it continually with cold water. Too much treated condensate seems like a better problem to have than not enough.

Pumpguy

Maybe I'm wrong here, or maybe confused myself, but I think there's a confusion in the sequence of events.

Your boilers make steam, not condensate. The condensate you get back is a result of the steam giving up its heat and condensing back into water.

It seems to me if you can control the condensing rate of your process, that will result in less returning condensate.

LoafofBreadhead_123

dopey. You nailed it. See above comment. Yes, three boilers can fire at same time creating more condensation then when controller was operating. The feed tank water level is controlled by two valves. One of the valves is controlled by an aqua stat set at the desirable 180 degrees with set point at 5 degrees. The other water valve is controlled by a float switch which never is low enough to operate since the aqua stat switch is always on to overcome too much condensate. I don't understand the problem with using a ball valve to control condensate input for and having excess condensate cooled and sent to drain so it doesn't back up into system. It's basically being dumped out the overflow now anyway. So let me ask the question to you all this way:

What would happen if I install a ball valve on the incoming condensate line with an overflow going to water cooler (keep in mind that condensate is being cooled in feed tank now and being dumped to drain) so that correct amount of condensate comes into feed tank which will provide the need for far less cold water make up and provide the correct amount in feed tank to provide boilers? Right now, condensate is being dumped anyway. What difference would it make to dump excess BEFORE it enters tank, than AFTER, like now? Keep in mind that the only equipment problem is dead control module which was junk (failed first week in and company now out of business). All other equipment (traps, boilers controls etc.) is in good working order and is well maintained. I'd rather have a manual system we can maintain than electronics that continually fail. So, once again, what is wrong with manually controlling incoming condensate? Is there a safety issue? Condensate is being dumped right now anyway.

jhewings

Any condensate that you dump will ultimately be replaced with make up water. With steam boilers it is considered advisable to use as little make up water as possible. You say you are dumping condensate anyway so what's the difference? Your boilers will likely fail from corrosion caused my excessive make up water. Fixing the controller will likely cost far less than 1, 2,or3 new boilers.

Jamie Hall

Ah... at some risk of sounding like a complete idiot (not uncommon), if one boiler can handle the load, why on earth are you allowing all three to fire? Could you, perhaps, bypass the automatic controller, which doesn't work, with manual control?

There must be a reason... and I hope it's not that you can't spare the time to do it (perhaps as much as 5 minutes per shift).

dopey27177

I do not know how much condensate is dumped each day. Think of this!
Domestic water water costs money plus the additional fee for sewage, typically sewage costs are 133% of cost of water.

Stop using water to cool condensate, let the combination feed water and condensate tank be filled by the float only. Run you system on one boiler and do boiler sequencing manually.

Dopey

Jamie Hall

This whole operation defies logic.

Let me look at it another way.

You have three boilers (apparently you only need one at a time, but let's overlook that for the moment).

Three boilers firing will produce a certain amount of steam from a certain volume of water. That steam will pass into the pipes and out to the consuming devices. Once there it will condense.

The volume of condensate will be equal to the volume of water boiler, less any lost to leaks. You cannot possibly gain volume going from water to steam to water. No way.

Now as the boilers make steam, they need feedwater. That feedwater comes from the condensate receiver tank. The condensate receiver tank receives the condensate from the system. The volume of condensate is roughly equal to the volume of water boiled.

So pump it back into the boilers and you're good to go.

There is no conceivable reason to dump condensate and add fresh water. None.

There is no conceivable reason to have to cool hot condensate so you can dump it. None.

Maybe it's the way it has always been done, but it's flat out wrong, expensive, and harmful.

retiredguy

Whether you fire 1, 2, or 3 boilers to satisfied the load you should not get too much condensate back to the condensate tank unless that tank is undersized for the system or there is a problem within the system itself. The system only sends back to the tank the amount of condensate based on the amount of steam used by the load (connected equipment). The amount of steam being produced does not dictate the amount of condensate being returned to the condensate tank. There has to be something else wrong with your system to provide an excess of returned condensate or water that is overfilling the tank. I would check the whole system to see if there is water being added or introduced somewhere in the system that would cause the condensate tank to overflow. Has anything been changed in the system recently or is everything the same as it was when it was first engineered and installed. I have never seen an aquastat installed to sense the temperature of the returning condensate and use that temperature to add cold water to cool the returning condensate to 180F or below. It makes no sense. If the correct pumps are installed they can handle condensate well above 180 degrees F. I would look for something else that is infiltrating that condensate return water.

109A_5

If I have to guess, I'd say you are using the Domestic Cold Water 'pressure' to get water back into the boiler(s) since there may be a pump that is not working due to the absence of the controller. And you need the 'pressure' to get the water through the condensate system and past the non-functioning pump.

Water exits the boiler(s) as steam and (assuming no leaks) an 'equal' amount of water returns, no need for make up water. The amount of boilers makes no difference, 1 or 100 running. If you have 100 Boilers running there will be more steam and thus more condensate, as long as the pipe size can handle the volume of return condensate water, no problem. Cooling the condensate to have it go back to the boilers is a serious waste of energy. Unless it is needed to prevent pump cavitation. To me cooling of condensate to go down the drain is done (and only needed) with district steam since it is a one way open system. You don't have district steam since your boiler(s) are on site.

I don't fault you for wanting the ability to run the system manually. There maybe benefits to that ability. You need to determine where the condensate return restriction is.

Also, in my opinion, if you can live and exist in that environment so can an electronic controller, in fact an electronic controller can probably function in an excessively hot environment much longer than a human. You need a good Electronics Technician and get that controller working correctly, your life will simply be easier when things work correctly. The energy and water savings may pay for the cost of the controller's repair.

109A_5

LoafofBreadhead_123 said:

There used to be a control module but it was only rated to 90 degrees operating temperature and burned up within the first week as it was installed in the boiler room which is always over a hundred degrees.

More thoughts; 90 degrees Fahrenheit ??? Consumer Electronics is better than that !!! This controller should be commercial or industrial grade. Even the TECO SG2, $150 is rated for 55 Degrees Celsius. Are you sure the 90 was not non-condensating Relative Humidity ?

And even if some Engineer devised such a blunder put the controller in a better environment, it probably only needs wires to move it to a better location. Spend your time on something better than babysitting boiler condensate.

109A_5

LoafofBreadhead_123 said:

Do these pumps work ? If so what controls them ? Do they feed the boilers ? Is the water level in the range of the sight glass ? If not why not ?

109A_5

More thoughts; If the intent was to cool the condensate why wouldn't they just run the condensate through a heat exchanger, so no reason (or need) to manage excess water. I think the intent here is to warm the makeup water so cold water can't get to the (potentially HOT) boiler(s). If the system piping and radiation is larger than the water in the boiler(s) can safely support you need a reserve of water so the water level in the boiler(s) does not get dangerously low. The condensate tank acts as an accumulator so you DON'T have to add makeup water, unless the system looses steam or water elsewhere, which in this case it sounds like it should not. The only condensate management should be to control the pumps to maintain the correct boiler water level. In other words you don't have too much condensate, you have too much makeup water !!!

Additionally, I'm guessing since the controller is inoperable the functional path of 'the boiler(s) needs water' and the condensate pump(s) turning on to accomplish that task is now broken.