Protecting Blowdown Tank from freezing 1

[curtis2004]

Hi Everyone,
I have potential issue of blowdown tank freezing. It is installed just outside of boiler house since I did not have space inside.
Right now, blowdown is controlled by separte controller which will open valve every 45 minutes for minimum of 1 minute. In the same time conductivity probe will sense blowdown conductivity and if conductivity is high it will keep open blowdown valve open until conductivity falls below certain level. So hot condensate is cycled every 45 minuts and there is small amount of cold water flow pouring inside blowdown tank.
Everything works fine so far. Blowdown temperature out of the tank is around 100 F. The tank itself is cold. However, my customer raised concerns that during winter time temperature will fall far below freezing point and blowdown tank may freeze. I checked and found out that January temperatures may fall as low as -18 C for that region.
Did anyone experienced similar issue? Is there any issue at all? What can be done?
Thank you,

Curtis

 

[MisterDonut]

Install a small throttled bypass line that is open at all times. Conductivity controller will compensate by reducing the blowdown duration.

 

[curtis2004]

I have 100 psi steam boiler. What should be by-pass line size? 1/4" or 3/8" will be enough? Do you have any particular valve (type or manufacturer) for this type of service? This valve will experience 100 psi hot condensate on inlet side and ~5 psi on discharge side (95 psi PD through it) and will have steam flashing on discharge side.
Thank you for advice,
Curtis

 

[MisterDonut]

Curtis,
You want a valve designed for continuous boiler blowdown service. Velan, Yarway, Everlasting and Gestra are just a few of the manufacturers I can think of. Valve product data should have sizing guidelines based on differential pressure. If you size the valve to handle about half of your total expected blowdown at 66% open, this leaves some room to adjust while letting a steady hot flow of blowdown into the tank to tryto keep it from freezing. I dont think you will find one smaller than 1/2".

 

[curtis2004]

Thank you, Mister Donut.