Steam condensate metering issues

[SAK9]

I am looking at the existing condensate metering system at a site where there is a wide gap between steam flow rate and condensate flow rate(condensate being about 40% lower).The condesate is pumped back to the feed tank by means of pump trap units which produces a pulsating flow.The flow rate varies from 2000kg/hour to 15000 kg/hr depending on steam demand.What will be an ideal type of flow meter(totalizing type) for this application?Will a single meter be ok or two in parallel /

Thanks in advance

 

[quark]

Do you have flow meter on the steam line as well? What is the accuracy of the meter and if there is no meter how you are checking steam flow rate vis-a-vis condensate flow rate? Is your condensate header pressureized or are there any chances of flashing? Are there any equipment where you are not recovering condensate from?

Positive displacement meters work well in condensate line well. I don't see any reason as to why single meter will not work.

 

[SAK9]

Thanks for your response Quark.There is an orifice type meter on the steam line.Condensate is being pumped into a tank discharging into top of the tank and is at around 70C.Client reckons the recovery should be around 85%.Only loss is through traps and minor leaks

 

[quark]

Is your orifice meter density compensated?

 

[SAK9]

Density compensation is there.So steam flow measurement appears accurate

 

[steamdog]

I have had problems with the condensate meter due to two phase flow. If there is flashing of the hot condensate then you will have this problem, too. Also, if you have vented receivers on the condensate pumps, you will loose some condensate volume in flash. So, you should use a flow meter with no pressure drop associated with it.

If you have those steam driven 'pump/traps' they have available a cycle counter, since each cycle is a fixed volume of fluid, you could use this to calculate flow.

 

[quark]

Steamdog has a good suggestion. The meters will show erratic readings in case of two phase flow. PD meters, in particular, doesn't bother about what is flowing inside. They can be very inaccurate (as they are counters rather) and give you reading as long as something rotates them.

In any case, 40% seems to be quite huge. Your turndown ratio is about 7.5 and my experience with orifice flow meters with such turndown ratios is bad. A couple of things here for you to check.

Since, your condensate temperature is 70C, there must be some flashing. If your steam pressure is 10 barg, you have approximately 21% flashing.

Check the rate of flashing corresponding to your steam pressure.

If it is superheated steam then you require both temperature as well as pressure readings for density compensation.

Check at what flow rate the difference is significant. If the difference is higher at peak flow rate and lower at lower flow rates then the DP transmitter may not suit your application. You may have to go for two transmitters instead.

Steamdog's suggestion of counting pumping trap is good. If you don't have this provision then try to do condensate receiver fill test(isolating fresh water feed).

Good luck,