Calculation for DA vent orifice

[liquiddecay]

I have a Deaerator (DA) that is emitting tremendous amounts of steam and hence losing money. I have heard and understand an old adage of a "8-12 inch steam stream that is soft and fluffy and not blowing" should suffice for regulating the discharge through the vent.

However, I know the calculation for the orifice size has to do with the makeup requirements for the system, the tank capacity and possibly something else.

I am curious to see if someone could point me in the right direction for sizing a DA vent orifice.

Thanks in advance.

 

[TF317]

We recently installed two new deaerators. This is straight from the Sterling Install, Operation & Maint. Manual. To determine the correct amount of opening required, the vent valve should be opened approximately one or two turns and the effect on the temp. noted. If no appreciable effect on the temp is noted after a period of one hour, oxygen tests should then be made to determine the effectiveness of venting; satisfactory reduction of oxygen is obtained when tested by a recognized sampling and testing procedure. Normally, the plume of steam would indicate sufficient venting if it appears firm and rises approximately 18" to 3' above the termination of the pipe. If after reducing the vent valve openings a drop in operating temp. is observed, or a difference between outlet temp of the water in comparison with the saturated temp. of the steam is observed, then the venting is not adequate and the vent valve or orifice must be opened further.

The optimum size of the orifice can best be found by drilling a small hole (1/8" to 1/4") and checking dissolved oxygen in the effuent. Also, observe the water temp to see that it is at saturation temp of the steam within the heater. If the oxygen reading is high or the temp is low,increase the hole size in the orifice and recheck. Repeat until the oxygen is below the guarantee level and the temp rises to steam saturation temp. Bottom line is trial and error. Hope this helps. Later.

 

[liquiddecay]

TF, thanks for your reply.

Allbeit I am not trying to refute a manufacturer's procedure to operate their own equipment, I must point to a reference that indicates there is come calculation that can be used to determine size of vent/orifice:

http://www.nrel.gov/docs/fy06osti/39320.pdf

Look at the last sentence of the first paragraph under "How they work."

Anyone else have any ideas?

 

[sailoday28]

Depending on the DA operating pressure, choked flow may exist across the orifice. The flow rate will be a function of the flowing mixture. Therefore a reasonable estimate of the percentage of entrained gases included with the steam must be known. If the operating pressure is low enough, Daltons law of partial pressures can be used to obtain an equivalent gas mixture.

Finally, any restriction of the flow, will require a new heat balance. Note the restriction can increase the amount of dissolved oxygen in the outflow of water.

Regards