I am looking to recover condensate from a heat exchanger back to the boiler. In-line pumpsCondensate 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.v

This need to do a heat balance 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????Suber-water pumps 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.Screw pumps
Remember that all a steam trap really is, is an automatic valve. It opens when it sees air or water, and closes when it sense steam. That's it.

Assuming that you'll have a temperature control valve on the steam line ahead of the HX, then you must have a trap. Remember that the 40 PSIG will not always be available, such as at partial load - particularly at low load - you can have VERY low pressures in the HX and at the steam trap inlet as the control valve throttles-in. When the valve closes, you'll pull a vacuum in the HX. A vacuum breaker and having the condensate drain by gravity to a vented receiver is the correct arrangement.

The other way to pipe this, is to use a control valve on the condensate outlet, instead of a trap. In this arrangement, the steam is supplied at line-pressure, through an isolation valve. You'll have 40 PSIG steam pressure in the HX, and available at the condensate control valve inlet at all times. You can size the HX to permit subcooling of the steam, if you wish. But that's an economic decision.Self-priming pumps

In  fact you have to use trap if the Re-boiler steam not totally condensed.  Other wise use flush drum with level control and the vapor will be sent back to the re-boiler top.
But remember that steam should enter the re-boiler near the saturation point by the means of de-supper heater otherwise you will have problem to recover the condensate .

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