Conversion of vacuum condensate system

Warren Worth

Thanks rw,

In this case, the Owner had already removeed the vacuum system, and, in a builing of over 40,000 SF, had installed the smallest Hoffman dual pump condensate receiver. Soon live steam killed the seals, and fresh minicipal water killed the boilers. The old system was wonderful, but, by the time I got there, there was noting left but leaks and failures. I think it was Mark Twain who said

"In the beginning, God create idiots. That was for practice. Then he created school boards." The vacuum removal came during a period of extreme idiocy, and its "soltuion" ruined most of the rest of the condensate system and the boilers. Thanks again for your response.

WCW

Warren Worth

Conversion of a vacuum condensate system

I recently designed a vacuum condensate system conversion to an atmospheric system, with zones of condensate drainage into condensate pumps and a pumped condensate line to a new boiler feedwater unit. The reason we changed from vacuum is that our clinet, self-admittedly, could not commit to a trap maintenance program that would have a chance of keeping steam out of the condensate system. By allowing the system to go atmoshperic at serval points, the presence of steam venting on any given condensate receiver gives at least a clue about where the failed trap might be. The system is large and would be a district steam system if built as a steam system today. The probelm is that the very first segment of the system, where we have the smallest condensate piping and the least amount of pitch, spills on cold start-up. The faility is a school, and they put their plant in warm standby whenever possible. A time clock or a low limit thermostat in the building bring the system out of warm standby into 5 PSIG steam. When this happens, the very first receiver vents a mixture of water and steam.

Our first effort centers around creating a vacuum break in the system, by installing Armstrong #62 vacuum breakers in the drainage end of some "H" pattern traps high in the space. We'll see what this does. Comments?

EBEBRATT-Ed

I would think it likely that a vacuum return system would have smaller piping than an atmospheric return system. Also bringing the system out of night setback it is possible that you have a lot of cold piping in the system that must be warmed up. The increased condensate load coupled with undersized piping is probably causing the spilling along with the fact that a vacuum system will return the condensate to the boiler faster-less hang up in the system.

Maybe a larger condensate tank at this location is needed. If the customer neglects the system it will continue having problems.

Ed

Brad White

I agree with Ed

Vacuum system return piping is fairly tiny by comparison to gravity. Half-inch and 3/4" returns under vacuum can carry a good bit of load, not so with gravity.

Breaking the vacuum is only part of it. The pipe size issue has but one real solution, unfortunately, if you stick with gravity return. But that problem only exists because the vacuum is gone. If the owner would commit to the trap maintenance, you would not be here right now.

If dry returns, the capacity is about half of what it would be if a wet return so that might help. The down-side is, over the years, how much fouling and tuberculation has the piping collected over the years?

When you figure what gravity size would be required and compare it to what is there, what do you see?

Unknown

Your Customer Is Going To Pay For Years To Come.

If you have bad traps it does not matter if it is a vacuum system or not....... If you think you had start-up issues before Ha you ain't seen nothing compared the start-up issue you will have now..... As you already know and have experienced. You also just lost the system efficiency advantage that the vacuum system gave you. How many times have I seen this done? Alot, and the systems never ever ran the same again.

EBEBRATT-Ed

Ok Brad. What is "tuberculation" I'm lookin for my dictionary ........................


Ed

Brad White_184

Hard, encrusted minerals

and other things unmentionable. Root word is same as tuberculosis. I acquired the term from a water treatment contractor treating piping systems, especially condenser water. Fouling as a general term is maybe too general and covers bio-slime and other things. Tuberculation is pretty solid stuff which impedes flow.

You really DO read my posts

[Deleted User]

Sounds like a

recipe for decreased boiler life & way too high fuel bills. We compromised on a couple of jobs, w/ trap servicibility problems, by installing condensate coolers ahead of the vacuum pumps.

Not a perfect solution. But, far better than what you have now. I can almost hear the hammering as steam hits piled up water @ traps trying to dump into overloaded returns on a cold start.

Tom Blackwell_2

Quite frequenty, vacuum systems are installed up front because there is no way some of the loads can drain by gravity. Remember that there is no steam pressure in any of the emitters until the temperature of the piping and radiators rises above steam temperature. Is gravity drainage possible?

Warren Worth

Conversion of a vacuum condensate system

More from the author: several comments have been very appropriate. The condensate receiver for this zone was oversized and the dry return size was evaluated at design time. On paper, there is enough return (at 2-1/2") for the condensate load (8,000 pounds per hour)provided it has some pitch. The return was evaluated at the pitch found in the field, 0 PSI retrun, 5 PSI supply. One problem is that the return becomes obscured as it dies behind obstacels and unexcavated areas or so called "tunnels" that are filled with pipes and have no room for access. The pitch cannot be determined in these areas.

To the author rw, there can be no doubt that a vacuum system would save energy; however, the Owner was presented with the alternatives and made his choice. You might say that there is no excuse for leaving a failed trap in place, and yet, this facility last had trap service in the 1980's. The problem here is that we can't make people service their buildings, especially when their situation is more square footage every year with fewer people, and fewer qualified steam technicians to boot. We gave the Owner the best information we could; they made their choice, and now they have to live with it. We have to make it work.

If anyone has questions about this system, I'll be glad to try and answer them,. So far, everything that has been brought up is on target...but was considered at design time.

Matt_67

Dear Warren

I am not trying to be condescending, but you simply got what you got. (I should say the building owner has got what he has got.)

He now has a system that was (I am sure expertly design in the 1930's to 1950's era I would guess) that now has a lot of unknown design changes from the original intent. Some may be improvements for the better and some may not.

Do I have similar buildings like this? Yes. I have had my share of bear knuckled meetings with building owners, I feel for you. If you have the documentation and they agreed to the compromises well, at that point you nurse it and take their money to maintain it.

As far as for myself I have never removed a vacuum pump. I have a lot of jobs that have it removed and the first problem that will haunt you and never let you go is dealing with condensate corrosion.

The first question that I always ask and the buster meetings is "Exactly how long do you intend to keep the building open? Followed by do you want the buildings heating system in a sell-able condition when you are done.

Plain and simple.

Unknown

It is a vicious cycle

Thanks Warren for the e-mail.

The cycle of steam condensate loss vs. taking on make-up water and it's short and long term effects on a steam system are generally not taken into consideration when you have a high rate of turnover in an administration as what can happen in your case. The lack of qualified people does not help either.

I have made a few studies on the effects on 40 to 60 year old vacuum steam systems that had the same conversions. I've tracked everything from feed water chemistry, chemical treatment, start-ups, summer lay-up, operational controls, control strategies, and then the aftermath of corrosion to the boiler and piping systems. In every case the systems that did receive major intervention suffered major system failures.

What are you to do? Take a lot of pictures and document everything. Then sleep good at night.