3 replies to this topic

[rajprocess]

Dear Forum members,

 

we have a electric heater for super heating C4 stream (routine) for regenerating driers in C4 isomerization unit (UOP). we need to carry out a special procedure for stripping out sulfur (temporary poison) from butamer reactors with hydrogen as regenerant with same heater. Heater has trip&permissive on high element temperature and low flow through the heater. The low flow trip @7mtpd for normal operation, where as the maximum flow for the sulfur stripping procedure is 3mtpd. To have this operation we need to freeze this reading from engineering station. 

what is the importance of low flow trip?

is it for protecting element from over heating?

if so , is high temperature trip is not suffiecient ?

kindly help me in this regard and please share any information related to this topic and suggest any books for better understanding of the process electric heaters...

 

thanks and regards,

Edited by rajprocess, 02 November 2014 - 09:06 PM.

[samayaraj]

Hi Raj,

 

Low flow trip to electric heaters is generally given to safe guard the filaments failure due to high temperature. In other cases, low flow trip is given for decomposition of process fluid after certain temperature. In my exp, I faced a failure of electric heater used to heat nitrogen gas. By mistake, operator forgot to close bypass valve for the heater and more nitrogen flow was passed through the bypass line instead of heater and finally filaments got burnt!

 

Its better to give give the trip command to heater from low flow which is more safer than the surface temperature of heater. Since, the temperature rise may happen quickly which will affect the filament and the equipment too...

 

Another incident related to heater failure. Electric heater used to heat liq sodium. Here too, the bypass valve of heater was in open condition. But there was no "low flow trip" and after some minutes, filament got burnt. This is due to location of flow meter on the downstream of heater isolation valve. If the flow meter is fixed at the inlet /immediate outlet of the heater, "Low Flow Trip" would have actuated and trip the heater...

 

 

#Samayaraj 

[rajprocess]

Thanks for you explanation!

 

You mentioned heater elements got burnt in two cases, Is high temperature trip not existing or it is bypassed?

[samayaraj]

In the above two cases i said, first doesn't have high temp trip (Filament Surface temp). After the incident, it was incorporated.

 

The second case it has surface temp indicator only not the trip. In all the above cases, trip command was from low flow only. Later, surface temperature was taken as trip.

 

In general, it better to give trip signal from low flow provided the flow meter is fixed at the inlet/ immediate outlet of heater. We can give from surface temperature too, but we cannot expect what is the temperature in the filament core. This may be higher than surface temperature of heater.

 

 

#Samayaraj

Edited by samayaraj, 04 November 2014 - 08:31 AM.