Steam purge into atm tank

[scorer]

I am looking at the likely build up in pressure inside an atmospheric storage tank when purging steam into the tank for instance to clean out a transfer line. Assuming 6 barg steam is used through a 1 inch line, then from a choked flow calc, I estimate that the max possible flow of steam is about 0.34 kg/s. At atmospheric pressure, this expands to around 1634 m3/hr. What size vent is needed to prevent tre pressure building up over the 0.5 psig mark for atmospheric tanks. Am I correct in thinking that to prevent a build up of pressure, the vent must pass more than the in flow.

 

[IFRs]

YOu must also check for vacuum when the steam cools. Ths can collapse a tank easily.

 

[TD2K]

You do a similar calculation as you did for the chocked flow of steam into the tank.

In the second case, you have a maximum pressure inside the tank of 0.5 psig (or whatever pressure you want to limit the inside pressure to) flowing through a vent to the atmosphere. Ignoring any condensation of steam, you have 0.34 kg/sec flow rate to be vented (yes, the outflow capacity should be definitely as great as the inflow to avoid possible tank damage).

Do you have manway vents on the roof that you plan to open and allow the steam to vent through? Are these open vents (eg. open nozzles) or pressure/vacuum vents pallet type vents?

 

[JoeTank]

scorer,

Although you are correct to be concerned about the correct vent size, your statement about an atmospheric storage tank and allowing an internal pressure build up of 0.5 psig should also cause you great concern. If the tank is an API or AWWA field-erected flat-bottom tank, an internal pressure of 0.5 psig will damage the tank. Such tanks often have a permissible internal pressure that would be measured in only inches of water.

Perhaps you could respond with some info about the tank dimensions and a general description. That would permit me to give a more specific comment regarding proper tank design.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com