When you are not running the steam turbine and dumping steam directly into the condenser you need to make sure that the steam conditions match those for steam exiting the turbine. So you use cold water spray to de-superheat the steam.
Too little spray and you will damage the condenser sue to high temp and thermal stresses, too much spray and the high velocity water droplets will cut right through most condenser tubes.

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P.E. Metallurgy, Plymouth Tube

Ed,

I believe that the OP is asking a question about the desuperheaters/attemporators that are part of the HRSG control system.

The spray system you are describing is similar, but is commonly called a "steam conditioning" system or something similar.

As is the custom in these fora, the OP seems to refuse to perform even an elementary search on his topic of interest

Here are my first two search results from GOOGLE when I use "HRSG" and "desuperheater" as search terms:

http://www.powermag.com/designing-hrsg-desuperheat...

http://www.cheresources.com/invision/topic/15486-a...

MJCronin
Sr. Process Engineer

Steam conditioning valve example:

http://www.emerson.com/catalog/en-us/fisher-tbx

MJCronin
Sr. Process Engineer

Thank you for your reply.

So condenser hood spray system is the same design as attemprators?

Regards