Condensate storage tank material suggestions

[TimboGMO]

Looking for condensate storage tank material suggestions. (carbon steel, lined carbon steel, duplex stainless, fiberglass, etc.) We are looking to purchase (2) several thousand gallon tanks to act as storage/surge tanks for condensate coming back from many buildings connected to our steam distribution system.

We currently have (2) storage tanks from the early 50's that have served us well, that were originally used as lime softening water tanks, I am not sure when they were switched over. These current tanks are fabricated out of carbon steel.

I would be very hesitant to use 304 or 316 SS due to the possibility of SCC, even though our chloride levels are normally low (6.4), there is a possiblilty they could spike if we had problems with water heaters in buildings on our steam distribution system if the water heaters had tube failures and sent raw water into our condensate return stream. A duplex stainless steel could be a possibility.

Below are our condensate conditions:

Chlorides: 6.4 mg/L
Conductivity: 2.8 uS (can be up to 70 temporarily if we have a large water heater failure on steam distribution system)
pH: 7.5-8.5
Temperature: 150-180 degF
hardness: 3-4

Thank you, -Tim

 

[StoneCold]

TIMBOGMO
Let me preface this with the statement "I am no expert on this but"

I would make the tanks out of the same material as the rest of the steam system, probably carbon steel. However my first thought was that you have a huge storage volume. Maybe you have a very large system but just based on a few things I have seen I would guess that you need to talk to a steam expert and reduce your condensate drums down to 500 to 1000 gallons total or less. Maybe there is a rule of thumb for condensate holdup vs #/hr of steam generated but I don't know it.

Let's see what others have to say.

Regards
StoneCold

 

[Keith53]

There is a thumb rule.........If your system utilizes a condensate/make-up blend tank, you should size the tank to hold 20 minutes capacity at 100% fire.....An equal surge volume is also recommended....So let's say you evaporate 30,000 lbs water an hour at 100% fire, then you want a tank that will hold 60,000 lbs when full to overflow with the make-up controls set to keep tank 1/2 full.

 

[Keith53]

Correction to above post, I neglected to factor in the 20 minute/hour ratio of 1/3rd:

If you evaporate 30,000 lbs per hour, then you need a tank that will hold 20,000 lb when full to overflow.

 

[TimboGMO]

We have a separate reverse osmosis make-up system with (2) 28,000 gallon fiberglass storage tanks that feed to the DA's third in line behind the turbine condensate and steam distribution condensate. So, I would assume they would just mainly be sized for possible surging (which I won't know until we get some meters on the lines to the existing tanks).

 

[kenmac777]

We have several large condensate storage tanks here at our combined-cycle power plant.

They are all steel construction, lined internally with an epoxy coating. Carboline has several good products.

Your condensate looks pretty innocuous. Stainless is overkill, and fantastically expensive to boot.

Fibreglass might get pricey once you get into larger sizes.

 

[keens]

I agree with kenmac777. We specialize in API Storage Tanks, and we typically design condensate tanks with A36 w/ internal lining. The lining is usually epoxy coating.

 

[vesselguy]

Agree with kenmac777 and keens 100%. I just researched this same application recently for applicable material and internal coating for all of our tanks in the water treatment section of our project. Use carbon steel with Novolac Epoxy thin coating such as from Carboline or Devoe 253.

 

[TimboGMO]

Thanks guys, I will definetly look into epoxy coating. We are currently leaning towards a rubber lined steel tank. The rubber is rated to 250 degF and the tank is atmospheric, so overheating should not be an issue. Specifically the material applied is called a "Semi-Hard Natural Rubber with Natural Rubber Tie Gum - FDA Approved"