5 replies to this topic

[Rajarshi1]

Hi,

 

I am working on flowsheet of a hydrotreater unit that has 2 cases - Start of Run (SOR) and End of Run (EOR).

I am confused regarding which UA value for the heat exchanger among the two cases should be governing? Is it always the higher UA value, or is there some additional considerations also?

 

Any input will be highly appreciated.

 

Thanks and regards,

Rajarshi

[latexman]

I suggest you focus on the A value.  The larger A will be needed to successfully run both conditions.

[Shankar12]

I suggest you to concentrate on EOR value because at the End of Run heat transfer resistance increases, so you should take the margin while doing calculation.

 

Regards- 

Shankar

[Amit J]

I suggest you have to evaluate multiple scenarios from SOR to EOR but EOR scenario with conservative UA is likely to be governing considering impact of fouling, scaling.

 

Consider appropriate margin because there could be multiple variables over the lifespan of facility viz. change in composition, change in utility operating parameters, min-max flow rates,  etc.

 

Regards,

A

[Saml]

I am making several assumptions here:

- Your are an engineer specifying the exchanger.

- You already have the PFD for the cases to be considered for design.

- Other cases (different feedstocks, climate, turndown) may be required to be checked for operability, but not for design.

(ie: you have a cooler that is designed for 35°C ambient temperature at full capacity. You may check that the plant won't shutdown if ambient temperature breaks a record of 42°C at the location, but you are not required to design for that condition)

 

You should specify for the design case that requires the larger unit (plus the specified margin if any), and verify that it can be controlled on the other cases.

[Rajarshi1]

Hi all,

 

Thank you very much for your inputs.

 

Regards,

Rajarshi