I am looking to recover condensate from a heat exchanger back to the boiler. Condensate will gravity drain from the exchanger to a condensate tank and then it will be pumped back to the boiler.

I am confused as to whether or not I need a steam trap on the condensate line from the HX to the condensate tank. Is it recommended to recover the "flash steam" and send that back to the HX? Otherwise the steam is going to flash and vent to atmosphere when the condensate enters the tank. Can anyone advise.

You need to do a heat balance(Balance Valves) around the Hx.  You haven't given any information from which to give an informed tip, but it is quickly appearant that flash steam can't climb back uphill to the operating pressure to get back into the Hx unless of course, all this happens at atmospheric pressure???? or you intend to thermocompress it back up to the Hx operating pressure.

Unless you have a user that can take the steam at the operating pressure of the flash/condensate tank, you are going to lose the flash steam.

Or unless unless your Hx is putting out such subcooled condensate that there will be no flash steam from the condensate tank.You do not need a steam trap if you have a pressurized condensate receiver with a pump to return the condensate to the boiler. There are prepackaged systems available to do what you ask.

You need a steam trap in the condensate line out of the heat exchanger to maintain the chest pressure and hence the higher condenstaion pressure of the steam. The Steam trap should then discharge to a flash drum - this flashes low pressure steam off to be used elsewhere and has a second trap off the base to an atmospheric condensate tank which should have a vent condenser to capture vented steam and return condensate to the condensate tank to be pumped back to the boiler.

Alternatively, if there is no use for the LP steam, then the heat exchanger trap should discharge directly to the atmospheric condensate tank.

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