API 660 Data Sheet: Heat Transfer rate Required Vs. Service

[Meck91]

Reference API 660 data Sheet:
Is heat transfer rate REQUIED is or can be same as heat transfer rate (SERVICE)?
Just want to confirm that Heat Transfer rate (Required) is what process usually specifies for the intended service of exchanger, and is basically the requirement from Process. In response exchanger manufacturer provide information on Heat Transfer Rate (Service), means that the exchanger they will manufacturer will transfer this much heat. If manufacturer is quoting off-the-shelf type of exchanger then the heat transfer rate required can be different than the heat transfer rate service.
However, if the supplier is providing a custom built exchanger than heat transfer rate (Service) must be at least equal to or slightly higher than the heat transfer rate (Required0).
Please comment on my interpretation of these two valves.

Thanks in advance.

Meck91.

 

[speco]

Meck91,

Since nobody else has responded to your question, I'll try it.

Normally, on a TEMA type data sheet, you will see three heat transfer coefficients (also called rate). They are the clean rate, the dirty rate, and the service rate.

The clean rate is the calculated rate with the fouling factors removed, based on the exchanger configuration and fluid flows and properties.

The dirty rate is the rate including the fouling factors, therefore always lower than the clean rate.

The service rate is based on the actual process heat load and calculated (corrected) LMTD, based on the actual effective surface. That is Us = Q/(lmtd X surface)

The service rate should be the lowest of the three, and never higher than the dirty rate.

I am not sure what you mean by the "required rate".



Regards,

Speco (

http://www.stoneprocess.com)