Blowdown Separator

Weil

I recently installed 3 steam boilers for a retirement home in Chicago. The engineer is asking for a blowdown separator. I have only seen these on high pressure steam boilers. Since when skimming a boiler it is to be performed while warm not hot. Thoughts are appreciated.

EdTheHeaterMan

What pressure are you operating?
What is the boiler size?
Blow Down is different than Skimming.
Is Blow-down performed daily , weekly?
ALSO... we like pictures!!!

ChrisJ

EdTheHeaterMan said:

What pressure are you operating?
What is the boiler size?
Blow Down is different than Skimming.
Is Blow-down performed daily , weekly?
ALSO... we like pictures!!!

Not to hijack the thread but what is the difference between surface blow down and skimming? I've seen both terms in multiple places.

JUGHNE

The engineer seems late to the game. Did he include this in the original plans/drawings/specs?
He should be able to explain the how and why of it all.

Yes, we would like pictures.

Jamie Hall

Blowdown is totally different from skimming, not just different. Which is it you really want here?

I might add -- blowdowns are really only called for if the use is consumptive -- that is, the steam is not condensed and recycled. They are used -- if they are used routinely -- to control total dissolved solids, which otherwise build up and can cause foaming and carryover issues.

Weil

Installed 3 Weil McLain 788's with Beckett modulating burners 2,050,000 BTU's each. Vacuum system reaching 2.5 PSI. And I am only talking skimming. 100% condensate return. Skimming is performed weekly.

Jamie Hall

If you're only talking skimming, then you have relatively low flow -- and no pressure. A simple oil/water separator should do the trick. Whether it will make the engineer happy is another question altogether...

Weil

i should add that skimming was performed initially multiple times after installation. Now the LWCO's are blown down weekly. And they have chemical treatment and weekly testing.

JUGHNE

Very impressive, great looking job!
Looks to be very serviceable for the future.
Skim ports with valves piped right to drain.
I don't know what more one could ask for.

This must be a large retirement home.
3 zones or common manifold?

EBEBRATT-Ed

@Weil

Is he asking for a blow down separator or is he thinking of a flash tank which would cool the condensate befor going to the sewer

Weil

Thank you. Common inverted header. I am a steam guy. I am just looking for confirmation for this engineer that it is not needed. I really appreciate your responses.

Weil

It is a 120 year old hotel converted to a retirement home.

Jamie Hall

If your man is really looking for a blowdown separator -- presumably to discharge only relatively clean water (no particulates, no oil) to the sewer, can't you pipe the blowdowns to a decent size grease trap? Say 15 minutes retention time and you should be pretty darn clean. I'd consider it overkill (there isn't going to be much except maybe some rust in there -- very little oil), but... sometimes the customer wins.

nicholas bonham-carter

What sort of chemicals are they putting in?
Is there a problem with the water supply?
Are the boilers staged?—NBC

retiredguy

In my area, either term could be used, flash tank or blow down separator and they both accomplish the same thing, cooling the hot water/steam below some given temperature before it enters a sewer system. If this device has a cold water line with a temperature sensing device then you may be in an area where it is against a "code" to allow water in excess of a given temperature to enter a sewer system. The skimming that you referenced is probably what we called "surface blow". I rarely saw surface blow down on any system or boiler that small, however I think it is a good addition on and steam boiler. When I was still working there were very few engineers that did what I thought of as exceptional work. Most were engineers in name only.

By the way, that is a good looking installation.


And as @Jamie Hall wrote;
Blowdown is totally different from skimming, not just different. Which is it you really want here?

I might add -- blowdowns are really only called for if the use is consumptive -- that is, the steam is not condensed and recycled. They are used -- if they are used routinely -- to control total dissolved solids, which otherwise build up and can cause foaming and carryover issues.

ethicalpaul

Possibly dumb question here: why is the skimming weekly? Is there some oil getting introduced into the system?

ChrisJ

ethicalpaul said:

Possibly dumb question here: why is the skimming weekly? Is there some oil getting introduced into the system?

Commercial stuff is a different animal.
As @retiredguy said, could be other stuff from makeup water.

PMJ

A blowdown separator was part of the original design of the low pressure 200HP steam boiler I had installed. As I recall the Engineering firm designing the system said it was a code requirement. Its purpose is to cool down the water from the blowdown and protect the sewer system. Blowdown water comes from the bottom of the boiler where the sediment collects.

SlamDunk

Our blow down separator is used to send flash steam thru the roof vent (to prevent separator from pressurizing) and cool the water enough to not melt PVC sewer pipe or sewer pipe seals. And just as I typed this, I see that @PMJ said the same thing

Weil

Thanks guys. He is only concerned with temperature above 180 degrees Fahrenheit entering the drain. I misspoke. We are not skimming weekly. We are just blowing down the LWCO's weekly.

JUGHNE

Does this go to a sump pit or directly to the drain?

JUGHNE

I service a boiler a little smaller than one of these.
The blowdown and all draining goes into a large sump pit.
It probably holds 30 gallons before the pump starts and probably has half that sitting in the bottom half. Blow down water would mix with existing cooler water and the pump runs very seldom.

Another possible solution which I hate to say is a 5 gallon metal bucket at each blow off point. Would really detract from the fine piping though. Then could be blown down into the buckets and then emptied as they cooled, maybe the next day.

The blow down of each LWCO is just to flush the bowl and assure the burner stops?

EBEBRATT-Ed

Around here the sewer temperature limit I have herd of is 120-125

dopey27177

With temperatures as low as 120 you will need more than a 5 gallon bucket or 30 gallons of water in a sump pit.

Remember the bottom blow down is also used to empty the boiler of water in the event of overfill.

For the job to be safe (proper tmp control) a flash tank installed properly, a pit or container large enough to hold at least 100 gal. of water and a cold water supply to add enough cold water to cool the hot boiler water to the required temp the pump discharges the blow down water.

By the way that is a magnificent boiler room install.

Jake

Mike_Sheppard

My local code is no higher than 140 degrees into drains. Plenty of low pressure steam boilers around here have flash tanks with a thermostat and cooling water.

Joe_Dunham

NYC buildings with con-ed steam (district steam) have dilution tanks. The waste condensate is pumped into the tank and ultimately the sewer. There's a thermostatic valve that mixes cold water into the tank to bring it below (130 or 140, I forget) The top of the tank on the side has a tapping connected to drain, and the bottom has a valve to drain sediment once in awhile. Theres also steam separators . Some big NYCHA boiler rooms have these. Its just a big tank with a baffle in it to catch carry over and dry up the steam before it goes to the buildings

Dave in QCA

Like one of these. We had one to which our pair of 338 HP Kewanee boilers were connected to.
https://www.plumbingoverstock.com/products/steamist-68007-commercial-blowdown-tank?variant=4108531990633&gclid=CjwKCAjw_LL2BRAkEiwAv2Y3SUKfutmNRiejgqFqxXB1X5hQ4nBGBJTWFSFYsv9dojxN89hNGN-OOxoCrwsQAvD_BwE