4 replies to this topic

[sidewinder]

I've been struggling to determine the set pressure for cascading TRVs. Below is the scenario:

I've got an atmospheric diesel tank with HHL of 21.3 meters. The density of the diesel is 852 kg/m3. I have TRVs at inlet and outlet of the tank which protect the piping from over-pressure due to thermal expansion when blocked in. Tank inlet operating pressure is 920 kPag with design pressure of 1600 kPag, and tank outlet operating pressure is 180 kPag with design pressure of 400 kPag. The spring setting (differential set pressure) at the TRVs closest to the tank is 100kPa (i.e. at inlet/outlet of tank).

I have attached a simple hand sketch to illustrate the setup. 

 

Thanks and regards,

Chris

Edited by sidewinder, 05 August 2016 - 02:21 AM.

[mirandomka]

I have seen the cascaded TRVs in the tank farm design before too.

 

Set pressure, or really is the spring set pressure = design pressure - superimposed backpressure which is the the next TRV set pressure; at the same time > than normal operating pressure

 

If your tank last TRV is set 100 kPa(g) but your operating P is 180 kPa(g) (static) it means your TRV maybe adujusted for 180 kPa(g), thus, will not open until it's really 280 kPa(g).

 

Thus, the one TRV before it should be set to 1600-280 kPa(g) = 1320 kPa(g) and since it's above 920 kPa(g), the design should work.

 

Btw, this assumes cascaded conventional TRVs with adjusted spring set pressure.

 

If you use BB, then, you have to show the really opening pressure not the adjusted set pressure. The first one (furthest from the tank) will be set at 1600 kPa(g). The second one can be set at 30%~50% of 1600 kPa(g), so maximum 800 kPa(g), however, you may have a problem during normal operation if the second one's location is not that close to the tank...

 

The above applies to the inlet side. But you can apply the same logic.

[fallah]

I've been struggling to determine the set pressure for cascading TRVs. Below is the scenario:

I've got an atmospheric diesel tank with HHL of 21.3 meters. The density of the diesel is 852 kg/m3. I have TRVs at inlet and outlet of the tank which protect the piping from over-pressure due to thermal expansion when blocked in. Tank inlet operating pressure is 920 kPag with design pressure of 1600 kPag, and tank outlet operating pressure is 180 kPag with design pressure of 400 kPag. The spring setting (differential set pressure) at the TRVs closest to the tank is 100kPa (i.e. at inlet/outlet of tank).

I have attached a simple hand sketch to illustrate the setup. 

 

Thanks and regards,

Chris

 

Nothing attached....

[sidewinder]

 Sketch.pdf   126.47KB   184 downloads

[sidewinder]

Oops! find attached sketch