We are evaluating a proposal to recover most of the small amount of steam that vents with the non condensible gases from a deaerator. The feed is about 50% preheated city water and 50% recovered condensate. The deaerator runs at about 5 psig and there does not seem to be much steam coming out of the vent. The proposed recovery device contacts some of the feed water with the vent gases to recover the steam. The economics assume that 1% of feedwater is currently lost as steam. How could we accurately calculate this current steam loss. We have seen models that assume 0.5% for this loss. If this is our case it would half the proposed savings.

How is your vent rate controlled?  Typically, either a valve is just cracked open or an orifice is used.  If it's an orifice, it's fairly simple to calculate.

If you have a valve(Safety Valves), you might want to look at putting a cap on the outlet with a small hole and open the valve fully.  Keep increasing the orifice till you have the flow of steam you want and then go back and calculate the steam vent rate based on the orifice size.

I'm not sure if the flow rate of the steam would be enough to justify it.  Plus, since the deareator is removing dissolved gases, your exchanger will also need to vent these off the steam side to prevent gas blanketting which will further reduce the amount of heat recovered.

If the device is already patented, why should the manufacturer worry? Why the secrecy? I agree with TDK2 - something doesn't add up here.

Is this "patented device" significantly cheaper than a small stainless steel heat exchanger? I KNOW that will recover the heat of the vent steam, especially with cold make-up water on the other side. No "propietary device/technology" fooling around, either.

Talk to the DA manufacturer about what kind of orifice size they recommend with your model of DA, and operating conditions. If you can't get any worthwhile information, I'd try just installing an isolation valve ahead of the gate valve, and try an 1/8", and see what you get. A little trail & error should tell you what you need to know. You'll need to monitor things like operating load, and sulphite (I'm assuming you're using sulphite as an oxygen scavenger) consumption and residuals.

With a delta-P of 5 PSI (DA operating pressure to atmosphere), an 1/8" orifice will pass 7.5 lbs/hr, according to Spirax Sarco's "Hook-Ups". A 1/2" orifice will only pass 119 lbs per hour. I don't think your project will have to cost very much before the payback drifts away. I think you'll get a lot more bang for your buck just repairing/replacing a couple of failed steam traps in the plant

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