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A Safer and Quicker Method for Removing Coked Refractory from Fluid Catalytic Cracker Unit Risers
The Fluid Catalytic Cracking Unit (FCCU) is one of the most important facets of an oil refinery. This paper seeks to explain the advantages of using a new technology that steps beyond the current archaic use of jack hammers to remove coked refractory from the inside of FCCU Risers.
Accordingly, in order to withstand the higher operating temperatures of around 700°C in the FCCU process, the riser and other components are constructed from carbon steel and lined with refractory material. The refractory is usually retained within a hex mesh anchoring system and is generally around 25mm thick. Thicker refractory material, up to 125mm with a grid of formed steel anchors welded to the carbon steel shell may also be used in some parts of the FCCU riser. The catalyst used is circulating at high temperature and velocity and is very corrosive, so the refractory linings must be resistant to corrosion and provide sufficient insulation to protect the carbon steel outer shell.
The coke that is produced during the cracking reactions is deposited on the surface of the catalyst molecules and on the refractory, resulting over time in a coke-impregnation of the lining.
This is particularly problematic in the refractory lining of the riser but also occurs in the linings of other components. As well as building up on the outer surface of the refractory lining the coke impregnates right through to the steel shell which affects flow conditions and severely compromises its insulating performance. This compromised performance results in the refractory linings having to be removed and replaced about once every 4 to 8 years.
Under normal circumstances manually operated jack hammers are used to chip the refractory material away from the steel shell. However, this process requires workers to enter the confined spaces inside the riser and other components of the FCCU.
The work is extremely labour intensive and dangerous and requires a full shut down of the FCCU for a considerable period of time. There is a risk of injuries and health complications for workers operating jack hammers in the confined and toxic environment inside the FCCU riser.
With shutdowns potentially costing a refinery millions of dollars per day, it is imperative to minimise their duration. Jack hammering the refractory lining from the steel shell is a slow and hence costly process. Furthermore, the jack hammering operation usually results in damage to the hex mesh and steel shell from the jack hammer.
The coke-impregnated refractory lining also becomes exceptionally hard (in the order of 150 – 170 mpa), making it extremely difficult to remove. In some instances, the coke-impregnated refractory lining is too hard to remove effectively by jack hammering and consequently, entire sections of the FCCU riser must be cut away and replaced.
This process is prohibitively expensive and also extends the shutdown periods.
Silver Raven’s Solution
Safety has been the principle motivator in the changing approach to improve methods for removing coked refractory from FCCU’s. The revolutionary Silver Raven remotely controlled blasting system has been designed primarily to provide a safer method for removing coke impregnated refractory from inside refinery reactor risers. The system can also be used in numerous similar applications where it is necessary to remove spent refractory linings or hard deposits from vessels or pipes.