Guard bed design

Their physical properties, such as viscosity, density, thermal stability, or surface tension, are important to consider during the design phase of new processes. The demonstration of the thermal and chemical stability of ILs and the recyclability can only be proven through continuous pilot plant runs. On the other hand, the sensitivity to feed impurities that can accumulate in the ionic phase requires feed pretreatments or guard beds for some scheduled applications. 

In fixed-bed hydrocrackers designed to process VGO, residual oils in the feed can reduce catalyst cycle life if they contain even trace amounts of salts, asphaltenes, refractory carbon, trace metals (Fe, Ni, V), or particulate matter. As mentioned in Section 3.4.2, fixed-bed units designed to process residue remove metals and other contaminants with upstream guard beds or onstream catalyst replacement technology. In contrast, ebullated bed hydrocrackers can and do process significant amounts of residual oils. This is because fresh... 

In residue hydroprocessing units, heat release is high, but some licensors avoid using intra-reactor quench because residue feeds often form lumps of coked-bonded catalyst in fixed-bed units. In reactors with complex internals, such lumps are very hard to remove during a catalyst change-out. Therefore, fixed-bed residue units often comprise three or more 1-bed reactors in series with quench in between. In many cases, the first reactor is guard bed filled with one or catalysts designed to remove metals. 

Next, reactors may be designed to accommodate rapid deactivation-regeneration cycles. The best example is catalytic cracking where coke deposition is so fast that decay takes only minutes. Since, in this case, the feed is the precursor to coke, treatment or guard chambers are not practical. The only solution is to use fluidized beds, which provide reaction and regeneration in a continuous cycle. Other cases are slurry and moving bed reactors, w hen deactivation is not so rapid. 

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