Big ole industrial steam boilers

Tim Ritter_2

Anyone here admit to being a big fan of industrial steam boilers? I've got a 24,000 lb/hr steam system that's almost as old as I am that's running a chemical plant. I need to learn more about deaerators, and would like to get some opinions on water treatment configurations for big steam boiler systems. So far the only help I get is from the snakeoil salesmen, and they just want to sell me their systems. Anyone out there have any suggestions of who to talk to or what sources are available (non-partisan).
Thanks - Tim Ritter, Springfield, MO

DanHolohan

Tim!

Great to hear from you. The best guy for this is Tony Conner, who will probably be along directly.

How's things?

Unknown

He sure is!!!

And Scott, at Rhomar, too. That's a boiler treatment company. I wish I knew more.

http://www.rhomarwater.com/

Tony Conner

DAs

Nice intro, Dan & Noel...now I have to live up to the hype You didn't go as far as Timmie M. calling me "superheavyweight", though. As I get closer to 50, that's true in more than one way.

What problems are you seeing, Tim?

The main function of the DA is to mechanically strip the dissolved gases (particularly oxygen) out of the condensate & feed water, before it hits the boiler. You need to take the condensate and make-up water to the boiling point, at whatever the DA operating pressure is. Most industrial DA's will run 5 - 10 PSIG. There are some that are designed run under vacuum. They make the water boil at lower temps by pulling a vacuum on it. I've never worked with one of those, and only ever actually physically seen just one.

See if you can find the manufacturer's literature for the DA. A lot of them (and I do mean a LOT) are not piped up correctly. Check the installation instructions against what's actually there.

Eric

HP Boilers

The VA has a great boiler plant design and schematic. Having done a VA design they know what they want and it works. The Cadillac Plant!

http://www.va.gov/facmgt/standard/

Also there is a great class on boiler chemistry, DA, burners, hardness, ph, RO, DI, water treatment,blowdown,combustion, burners, ect.

Boiler Effeciency Class. Took it about 7 years ago. EXCELLENT.2 day course.

http://www.boilerinstitute.com/

Eric

Boilers

So what is your operating pressure?

And your DA pressure. Do you have an old tray type?

The DA is a pretty simple vessel. More important is your feed water pump suction piping. VERY VERY PICKY and even more easily messed up than DA piping.

Remember that lots of sulfite is a cheap solution to get rid of oxygen.

Tim Ritter_2

Dan!!

Hi Dan! Thanks for the note back. I knew this would be the place to share my woes and get help.

Doing ok here. Not doing much writing these days but hoping to change that. Will have to fill you in on the rest of the details later.

Thanks for the help.
Tim

Tim Ritter_2

Noel -
Thanks for the suggestion. I will check them out.

Tim

Tim Ritter_2

DAs

Tony -
Thanks for the note back. The problems I am seeing in this boiler room are incredibly numerous. Part of the issue is age (25 years), but even more important is the harsh environment and neglect. Prior to me coming here, no one really took an interest in the utilities, they were just taken for granted. Now several years of neglect has finally caught up, and several things are going nuts.

The reason I brought up the DA tank was that it was the first issue I looked at when I first started here. It used to have a pilot-actuated steam regulator on it, but was replaced with a basic 5 psig regulator, and I am not so sure it's appropriate. Sure, it's cheaper than pilot-operated, but may not be doing the job.

I have studied the manufacturer's lit (manuf now out of business as far as I can tell), and we've opened up the beast to see how things look inside. It looks brand new inside, but we're just not getting the heat we should. So I am suspicious of the regulator.

Among other things bugging me about this system is this question: Have you ever heard of anyone putting their softened makeup water directly into a DA tank, rather than the condensate receiver tank? That idea was posed to me recently, but I am not so sure it's a good idea.

Thanks for the help.
Tim

Tim Ritter_2

Boilers

Eric -
Thanks for both your posts. I will check those websites.

Our steam system operates at about 115 psig. The DA is set to operate at 5 psig. It has a set of "spargers", for lack of better terms, to inject the steam into the water.

I am interested to know more about what you mentioned about the feed water pump suction piping. I will look at the VA site to see if that gives more info. I wonder if I have an issue with how that was done. I will do more digging.

Thanks again -
Tim

DanHolohan

I miss you, Tim

Stop by more often.

For those of you who don't know, Tim was one of the stars of Heatway. A very straight-shooter who really cared about what he was doing.

Art Pittaway

Hi Tim.!!! Welcome back.

You might check out Bryan Steam at www.bryanboilers.com, they make small and large industrial DA equipment and may be a good source for background and installation info. The August issue of "PM Engineering" has a 2 page ad for them. Good magazine, articles by that guy Holohan, and it's reasonable.

Tony Conner

DAs

Do a little homework before changing the PRV that supplies steam to the DA. The safety valve on the vessel needs to be able to handle all of the PRV will send it, under worst-case conditions. A whole lotta DAs have seriously undersized safety valves. The only safety valves ahead of the DA, are probably on the boiler. If they lift at 150 PSIG, then that's the upstream pressure you should use. The downstream pressure will likely be 15 PSIG (or whatever the DA is rated for). If these are your conditions, then the pressure drop to size the safety is 150 - 15 = 135 PSIG. The formula I use is:

Cv X delta P X 2.2 = lbs/hr

Some people use 2, instead of 2.2. I like a little bit of a safety factor.

For example, if the PRVs manufacturer listed the Cv of his 2" valve at 35, and you used the pressure drops above, then:

35 X 135 X 2.2 = 10,395 #/hr.

Under normal circumstances, the PRV won't pass anything like the above. Pick the PRV based on the operation conditions: 115 PSIG dropping to 5 PSIG. The pressure drop, along with how many #/hr you need to pass, will let any valve manufacturer (Spirax Sarco, Hoffman, Armstrong, Spence, etc) size a PRV for you.

If the boiler is rated to produce 26,000 #/hr, and assuming there's times when no condensate is coming back, then 26,000 #/hr of water has to be added to the boiler, plus probably something like 10% to allow for blowdown. This is 28,600 #/hr. If the coldest make-up water is, say, 47*F, and the DA is at 227*F, then you have to add 180 BTU to each lb of water that enters the DA.

180 X 28,600 = 5,148,000 BTU/hr

1156 BTU/lb of steam at 5 PSIG means having a PRV that will pass 5,148,000 / 1156 = 4,453 #/hr. This will likely be something like a 1-1/2" PRV.

The Cv on an 1-1/2" valve will be about 20, so the safety would need to pass about: 20 X 135 X 2.2 = 5,940 #/hr.

You should absolutely check my method & math on this stuff, and verify any questions you have with the local inspection authority. There are LOTS of spins on code requirements, from area to area. Very disappointing to find out after a lot of time and money has been spent to be told "You can't do that here."

Most plants I've worked in sent the softened make-up water right to the DA. Just make sure it's going into the right connection. The one plant I worked in where the make-up was sent to the condensate tank suffered very heavy corrosion of the tank, and transfer piping. Some plants use a stainless steel tank to deal with this, but the whole arrangement doesn't normally seem necessary to me. What it WILL do for you, is trim the peak steam loads at the DA. If you've got a plant that has had the load increase over time, and now the peak steam requirements are getting beyond the DA and boilers every so often, then sending the make-up to a condensate tank and pump the mixture to the boiler can get you out of a jam, with minimal cost as compared to adding or replacing the DA, or adding a boiler. If the steam load regularly peaks over the boiler and DA capacity, then it's time to upgrade.

Tim Ritter_2

DAs

Tony -
Wow. Thanks for that last one. I definitely have some homework to do.
You mentioned the issue of demand exceeding the rated capacity of the boiler and DA tank. Everything was sized for 24000 lb/hr, which seemed like alot in 1979. However my latest readings indicate that in some cold periods over the last 2 years, we hit about 17,000. So we were well below the 24,000 mark. But I also realize that these units were sized to deliver 24,000 when they were brand new and hadnt been abused. I think we are darn close to capacity.

I will study and digest what you have sent me. Thanks again for your assistance.

Tim

Tony Conner

The Steam Meter...

...hasn't likely been calibrated in years, and in all likelyhood was probably never that accurate anyway. If it's an orifice plate meter, there should be some info on the tang that sticks out from between the flanges. See if it was initially set for 115 PSIG. If it wasn't, and there's no pressure compensation on the meter (very unusual, if there is) then the meter will have an error. If the operation pressure is lower than the meter was set for, it'll read high, and low if the pressure is higher. Also look to see if it's installed correctly. The tang info should say "Inlet" and "Outlet" so you can tell without actually pulling the flanges apart. (And yes, about 50% of orifice plate are installed...wait for it... BACKWARDS.) Is there a separate fuel meter just for the boiler? If there is, then you can back-out an estimate of how much steam is being produced.

Have you seen inside the boiler? Fireside and water side clean? Is there a thermometer in the breeching so you can see the flue gas temp? On a clean, hard firing boiler, the stack temp will likely run in the higher 500*s, maybe 600*F. On lower loads, something like 400* or 450*. The higher the firing rate, the higher the flue gas temp will go.

Even now, this boiler should have no particular problem making it's rated steam output, and hitting 80% efficiency. (That's real, overall boiler efficiency ("Net BTU out / BTU in, times 100", not just combustion efficiency.) Something that WILL affect output will be the feedwater temp. If the boiler is being fed water that is significantly cooler than what is specified in the manufacturers performance literature, then steam output will be reduced. It'll include factors like inlet combustion air temp, blow down rates, feedwater temp, etc.

Eric

Oversize

Dont forget that your feedwater pump is typically oversized 2-3 times for startup, ect. This is normal. Do you only have 1 boiler? No redundancy?

Tim Ritter_2

Oversize

Eric -
We do have two boilers. One is backup. Thanks for the continued help. The homework continues.

Tim