Originally Posted By: userfriendly
Is the steam condensed and recycled, or is it lost in a single use? It seems that if new water is "hard" recycling would make sense.
Condensed and re-used.
700MW takes about half a tonne per second of steam at 16MPa and 538C...need to keep it all in the cycle.
The Condenser is maintained at 6-8kPa absolute (so quite a heavy vacuum), so the condensing takes place at around 35-40C, with the heat moved to the Circulating water (and then onto the towers)...that system runs at around 15,000L/sec, and is where these chemicals would be used, as the evaporation in the towers concentrates the salts in the water.
The water on the clean side (to the boiler) is put through a demineralisation plant before use, and on the return after being condensed goes through another online "polishing plant", which is another demineralising plant to get rid of anything that might have been picked up in the cycle.
Dosed with Ammonia (for pH), and Hydrazine/Carbohydrazide (oxygen scavenging), it gets pumped back to the boiler.