Thermal shocking a FCC power recovery expander

[0707]

Small amount of water present in wet steam is extremely difficult to vaporize at FCC expander inlet 48-inch flue gas line. When expander vibration limits goes up one has to do thermal shocking the expander rotor to spall catalyst particles.

48-inch Flue gas line temperature is around 700ºC and the cooling rate for the thermal shock is 150ºC/h. When flue gas pipe temperature reaches 400ºC is injected superheated steam of 24-bar g misted with boiler feed water to spall catalyst particles of rotor expander blades to bring machine vibrations to limited acceptable levels.

This steam cyclic quenching procedure is prone to SS TP304H flue gas line structure; leading to corrosion, weld cracking and thermal fatigue of 48-inch flue gas line downstream steam quenching injection point.

What are others practice on this matter? The spalling of catalyst fines from expander rotor blades is done the same way as we do?

A discussion from the forum on this post will be appreciated.

Regards
Luis Marques

 

[westcoastr]

i know of one refinery that injected walnut hulls to knock off the fines from the blades.. it didn't completely solve the problem but bought them some time. the expander failed later as it does about once a year, much to the delight of competing refineries in the area.