steam inlet flow control compare to condesnate flow control

[uu78hswang]

Dear Sir

I have two control scheme need your help.
Fig.2 (condensate flow control), there is a temperature controller(TIC) directrly regulates Valve B, and an increase in steam could open the valve wide even if only a little condnsate were held back in the exchanger.
My following question is
Q1. It is said that a condensate receiver, with is pressure balanced against that of the supply steam and with a level controller regulating Valve B would prevent steam from blowing through the exchanger and condensate receiver. I don't quite understand this.
Q2. why is the respnse of the temperature controller in this arrangement can be very slugglish cause of the slowness of changing the condensate level in the exchanger?
Q3. in Fig2, exchanger with a shell of 17 1/4 in I.D. and
124 1-in-dia. tubes. the maximum rate of steam condensation in it would be about 3280lb/h. Valve A would have to be large enough to pass this flow with a head of h, which might provide a differential of 1 pis. A valve having a flow coefficient Cv of 7.4, how coud get it pass 3700 lb/h of steam?

Thank you so much for your kindly help.

Best regards,

steven

 

[TBP]

In figure #1, add a steam trap on the condensate out of the heat exchanger. This is nothing more than an automatic valve that opens when it senses air or water, and closes when it senses steam.

Figure #2 merely substitutes the steam trap with a control valve. This will in effect give you a variable orifice steam trap and will work just fine. In this arrangement, there is only an isolation valve on the steam inlet to the heat exchanger.

Look at Spirax Sarco's website for a lot of really good information on steam & condensate systems. I've used their thin, soft-cover book "Hook-Ups" for years. Try to get a copy - lots of great information.

Also, I believe that you show the temp sensor on the inlet process flow. It needs to be on the outlet.

 

[davefitz]

I am not sure of the exact answer to your question, but can add:
a) In fig 1, where the process outlet temp is controlled by modulating the pressure of the steam in the shell side , The process fluid OUTLET temp proably should be coupled to the valve controller, while you show the INLERT as connected. Raising the shellside pressure raises the saturation temperature of the steam, . If the condnesate return drain valve ( not shown) would also allow a variable liquid level setpoint within the HX, then one could also vary the amount of surface area that is exposed to condensing heat transfer and thus offer a second means of controller process outlet temperature, but might introduce or secondary issues ( such as tube to tube temperature unbalances).
b) in fig 2, you again show the temperature controller linked to the inlet process fluid temp, and not the outlet - I think these should be reversed. The condenater return drain valve off the invert of the shell does not seem to add any functional advantage.