3 replies to this topic

[AMPIR]

Hi dears;

I shall design a hot oil system. My system includes a heater with vertical radiat section and horizontal convection section.

Do you know how shall elevation of hot oil expansion vessel be selected?

Is it required that Hot oil expansion tank located in highest point of system (convection setion) or it can be possible to consider elevation of the radiant section?

[Zauberberg]

I cannot see what is the area of your concern here, and no additional details are available.
The system is hydraulically driven - in the sense that you have to ensure maximum hot oil flow through the heating/cooling circuit regardless of the expansion vessel elevation. This is equal to proving minimum required NPSH for hot oil pump and choosing an adequate pump with sufficient differential head for selected design/height of expansion vessel. Any extra energy will be dissipated as soon as hot oil enters the vessel.

Best regards,

[AMPIR]

I cannot see what is the area of your concern here, and no additional details are available.
The system is hydraulically driven - in the sense that you have to ensure maximum hot oil flow through the heating/cooling circuit regardless of the expansion vessel elevation. This is equal to proving minimum required NPSH for hot oil pump and choosing an adequate pump with sufficient differential head for selected design/height of expansion vessel. Any extra energy will be dissipated as soon as hot oil enters the vessel.

Best regards,

Zauberberg;

As per Shell standard:



" The expansion vessel shall be connected to the system return line on the pump suction side. The vessel should be elevated so that the normal operating level of the HTF in the vessel is higher than the highest possible HTF level in the system. (This will facilitate proper venting and provide sufficient NPSH for the pump.)
[*]If this requirement is difficult to meet, a lower elevation may be selected but additional design measures are required to prevent vapour being locked in the higher parts of the circuit; to evacuate such a vapour lock if it occurs; to cater for HTF draining into the expansion vessel during a shut down to avoid HTF overflow into the flare system; and to ensure that the HTF system pressure remains positive at the highest point to avoid boiling"




As I mentioned before in this basis elevation of Hot oil expansion tank in my system shall be 18.5 m (elevation of the convection section of hot oil heater ) so I try to reduce it. Unfortunately there is no more detail in Shell standard and so I do not have any basis to reduce this elevation.

[Zauberberg]

Laleh,

Can you upload the sketch of your system?
To be honest, I do not see any practical impact or engineering logic for placing expansion vessel at such high elevation. This would mean, for example, that you will require ANY vessel which has a vapor space to be located at the maximum height in the plant, in order to prevent "vapor locking" or increased back-pressure on the liquid side that is pumped into the vessel. This is even harder to happen in heavy, non-volatile hot oil service. Or, simply, why don't you place hot oil return line somewhere close to the expansion vessel bottom and keep it submerged in all cases? This will prevent any "vapor" backflow.

Also, control system design is of high importance in such applications (that's why the sketch would be of much assistance). For example, having a control valve as close as possible to the hot oil return (expansion vessel) would minimize any impacts on liquid flow since upstream of control valve is 100% liquid.

And, in my opinion, most of Shell standards are a bunch of crap, I've seen them and they are looking nice only from the outside. Inside each book is the principle "say as much and - at the same time - as little as you can and sell your product as expensive as you can".

Best regards,