FCC plus hydrocracker optimization covers several additional units including the reformers, H2 plants, sulfur plants, and LCO hydrotreaters (neat or mixed with other feeds). If the H2 plant and/or sulfur complex (including amine and sour water strippers) are constraining, then these constraints need to be considered in the optimization.

The FCC bottoms (decant oil or slurry bottoms), along with cycle oils, are often blended into internal and external fuel oils. With the lower sulfur regulation, high sulfur FCC bottoms will be a discounted stream based on sulfur content; and then further, on catalyst content. 

Feedstock atomization typically comes down to the design and reliability of the feed injector. Obtaining good atomization of the feed is important for optimizing the performance of any FCC. Feedstock atomization facilitates the rapid and efficient vaporization of the feed inside the riser, which can then initiate the cracking reactions.

Slurry recycle and slurry separator backwash are two very different processes with varying objectives and negative impacts. Slurry recycle is typically done intentionally for the purpose of increasing coke make to help a unit that is short on heat balance. Such units are usually processing very light, sweet feeds and are unable to meet their processing objectives without additional heat input. Slurry separator backwash is required to remove the collected solids from the slurry filter/separator to ensure their efficient operation. 

Coke ratcheting occurs in hot-wall reactor/riser systems. When the system is at operating temperature, the parent metal expands more than the hex mesh lining does. This expansion creates small voids between the hex mesh biscuits that are large enough for hydrocarbon vapors to enter and come in contact with the parent metal. Coke forms in these voids.

Deposit formation is usually linked to catalyst depositing on the turbine blades. The deposits are mostly a function of catalyst loading of the inlet flue gas. An increase in catalyst loading could be due to several factors, including performance of the third-stage separator, loss in cyclone efficiency, change in catalyst attrition properties, excess fines in fresh catalyst, an increase in fresh catalyst additions, and/or an increase in flue gas rates due to higher air rates.

A number of operating factors influence catalyst losses from the regenerator that can lead to particulate matter (PM) emissions. These factors include: the number of fines present in the freshly added catalyst, the number of fines generated in the unit, the amount of catalyst transport to the cyclones by entrainment, and the cyclone performance.

In addition to the “standard” contaminants of nickel, vanadium, iron, and sodium, there are a variety of other feed contaminants that can impact FCC performance. For example, tight oils (also known as shale oils) can contain high levels of potassium, magnesium and calcium in addition to the iron normally found in them8. While bio-based feedstocks are not yet widely processed in commercial units, they would be expected to contain higher levels of calcium, sodium, magnesium, and potassium than conventional feed sources since these elements all play an important role in biological systems. High levels of phosphorous have been found on synthetic crudes.

Preplanning is an important part of ensuring that the catalyst reformulation and post-audit are successful. Before the catalyst trial begins, it is important to define catalyst objectives and establish a clear evaluation plan on how these objectives will be monitored and evaluated for the trial. Sample and data collection guidelines and establishing a good base case should be done before the trial. It is critical that the samples and processed data needed to monitor the reformulation are routinely collected before and during the trial.

The following tables list the demonstrated technologies to reliably measure main column bottoms (MCB) level. Regardless of the technology used, it is important to have redundant level indication. The Best Practice is to employ two level transmitters with a selector switch for MCB level control. For displacers, guided-wave radar, and dP level transmitters, redundant transmitters should be on independent vessel taps. There are benefits to having two different level technologies employed. For point level measurement, at least two points should be measured for high and low levels.