Fluidized Catalytic Cracking - Catalytic fines from slurry oil
Developed in the late 1930’s, Fluid Catalytic Cracking is still the primary conversion process in modern refineries. The Cat Cracker unit is the key to profitability for most refiners; efficient and successful operation determines whether a refiner can be competitive in today’s market or not.
The FCC reactor contains a fluidized bed of catalyst with an equilibrium particle distribution range be-tween 20 and 150 microns. In the reactor, coke forms on the catalyst as a result of condensation reactions and deactivates the catalyst. In order to prevent the formation of coke and to continuously keep providing energy to drive the endothermic cracking reaction, the catalyst is circulated between the reactor and the regenerator to burn off coke. Reaction products leave the reactor in a gaseous state after passing through cyclones that remove the majority of entrained equilibrium sized catalyst particles and smaller catalyst fines. The latter have a great chance of escaping capture in the reactor cy-clones, since the removal efficiency of cyclones re-duces with decreasing particle size. As such, these fines are carried over along with the reactor pro-ducts to the main fractionator of the FCCU and leave the fractionator with its bottom product, also referred to as slurry oil.
By removing these catalyst fines from the slurry oil, product fuel oils can be upgraded, or feedstock can be provided for production of carbon black or other products.
Dahlman designs, fabricates and assembles fully dressed FCC Slurry Oil Filtration packages, based on proven filtration technology with a continuous solids content reduction to < 20 ppm wt.
High quality sintered porous metal filter elements are utilized as filter media and are installed in the filter vessels, in such a way that solids are retained on the inner surface of the elements. Clean filtrate passes through the solids “cake” and filter medium. Once the filter’s delta P has reached its pre-set value after normal filtration mode, the package its cleaning sequence is automatically started. The feed and filtered product connections are both closed and subsequently, the valve connecting a gas accumulator will open towards the FCC Slurry Oil filter vessel. This results in pressurization of the slurry oil contained in the filter vessel. When a quick-opening valve installed below the filter vessel opens, the gas pocket, pressurizing the FCC SO from above, rapidly expands. This results in a reverse flow of the slurry oil, from the outside to the inside of the filter elements. As a consequence, the collected particles/filter cake, dislodges over the entire surface of the filter tubes. The filtered liquid is even forced further back by the expanding gas, transferring the separated solids to the backwash receiver vessel in a matter of seconds.
Dahlman’s gas-assisted backwash technology eliminates channeling and incomplete cleaning. It is considered to be one of the most effective and efficient in-situ cleaning methods. Operating temperature is critical for the reliability of the filtration process; f.i. asphaltene precipitation on the filter media may occur when operating at too low temperatures, resulting in reduced cycle times and undesirable, ex-situ cleaning of the filter
elements. With Dahlman’s filtration technology, the sludge, disposed in the backwash receiver vessel, can be redirected to the riser, while maintaining a continuous flow rate.