28 replies to this topic

[gemhag]

Hi,

sorry for the delay - I updated the sketch at the beginning of the discussion with the position of the temperature transmitter.

I calculated all scenario's and found that the determining scenario is exterior fire combined with normal hot oil flow/heat exchanger duty.

The releif valve that's installed certainly is large enough (API J orifice) - for my worst scenario a H is sufficient,

thank you for your input - next time I'll upload a better sketch at the beginning

regards

[Propacket]

A great discussion indeed. Well explained by Paulhorth and Ankur.

 

gemhag,

Do you mean that hot oil valve failure coupled with external fire leads to a larger orifice that that of hot oil valve failure coupled with water side blocked.

[S.AHMAD]

Gemhag

1. By studying the flow diagram I am very sure that you have a pump and most centrifugal has a check valve, therefore waterside overpressure can be caused by inadvertently closing the outlet valve. When this valve is closed, the waterside results in no flow so overpressure is the results of:

a. Thermal expansion due to block-in discharge

b. Pump's shut-off pressure

2. In most cases, from my experience, 3/4"x 1" TRV is more than enough to cater for thermal expansion, but in your case by looking at the size of the PSV (Std-J), I strongly believe that the PSV is sized based on pump's shut-off pressure. Please check

3. How do you calculate the heat duty of 14 MMKcal/h? If you are using W.Cp.Delta-T, where delta-T is the normal duty delta-T then you are wrong!

4. In any heat exchanger simulation, it must satisfy the 3-basic equation:

The hot an the cold streams heat given by Q = mass x sp. heat x delta -T and the heat exchanger given by Q = U.A.LMTD. When the valve stop, no flow on the water side and hence the U, heat transfer coefficient is lowered since the Reynold's no is zero therefore the heat duty is reduced accordingly. Hence U and LMTD changes accordingly. That is why we normally use the design heat duty for determining the TRV required for thermal expansion which is more than sufficient.

[gemhag]

Thank you Mr. Ahmad, especially for the explanation in point 4,

regards,