A new technology is being introduced to North America that will allow refiners to unload spent catalyst from hydroprocessing units under air rather than nitrogen, thus eliminating many of the hazards and expenses related to inert entry.
The technology, called CATnap catalyst passivation process, was developed by Kashima Engineering Co., Japan, in the early 1980s. It has been used increasingly in the Far East since that time (Table 1).
Today over half the spent hydrotreating catalyst in Japan is unloaded by this technology.
Through an exclusive licensing arrangement, CRI International Inc. and its affiliate, Catalyst Technology Inc. (Cat Tech), are now offering the technology outside the Far East. Their first commercial unloading in the U.S.--a hydrocracker at a West Coast refinery--was successfully completed in February of this year.
The technology passivates pyrophoric or self-heating catalysts by the application of a proprietary mixture of chemicals. The mixture contains organic compounds which deposit a film on the catalyst particles and any surfaces with which they come in contact. This film retards oxygen penetration, thereby suppressing oxidative reactions.
The test results in Fig. 1 demonstrate this passivating effect. The solid line shows the heat release of a spent, untreated CoMo catalyst as it is gradually heated in air to 400 C. The catalyst starts heating up at about 120 C. when the metal sulfides react to form metal oxides.
A second reaction representing carbon burn commences at around 300 C. The same catalyst passivated by the CATnap process (dotted line) is shown to be stable to greater than 300 C. under the same test conditions.
PROCEDURE
The passivation process utilizes the injection and absorption of a chemical inhibitor. This procedure may be a departure from the refiner's normal unit shutdown and unloading procedure in that the unit is partially cooled under oil.
The details of the shutdown procedure are customized for each application, depending on past practices, process flow scheme, unit configuration, catalyst type, etc. However, the generalized procedure is outlined in Fig. 2.
Initially, the feed rate is reduced by about two thirds while the reactor starts cooling down. When the unit is below reaction temperatures, a carrier oil of prescribed viscosity and boiling range is introduced to displace the normal process feed.
Once the feed oil is flushed out, the carrier oil is put on total recycle, and the chemical inhibitor is injected and circulated for prescribed amount of time.
The unit is then cooled to a target temperature (typically 280-300 F. or 140-150 C.).
Oil flow is discontinued, and the reactor is further cooled under flowing gas (hydrogen, nitrogen, or some other suitable gas).
At this point, the unit may require evacuation or purging with nitrogen to reach permissible entry limits for H2S, SO2, lower explosion limit (LEL), CO, and Ni(CO)4. The working area is then purged with air and the catalyst is unloaded by conventional techniques.
The advantages of the process fall into four categories: safety, time savings, cost reduction, and intangibles. These are outlined in Table 2.
The most important feature of the technology is that it eliminates the life-threatening nature of working in a nitrogen atmosphere. Nitrogen is especially dangerous in that it only takes a single lung-full to render a person unconscious.
Although with this technology reactor entry technicians (RETs) are working in breathable air, they are outfitted with full life-support equipment. Safety is further enhanced by the handling of passivated catalyst and the minimization of hazardous dust normally present when catalysts are dumped by conventional dry procedures (Fig. 3).
Commercial experience has shown that the process can save significant time.
The elimination of hot H2 strip and cooling down with liquid can reduce shutdown time. Also, the equipment and procedures used with the technology can reduce the actual unloading time. These improvements can save a refinery as much as 1-2 days in turnaround time.
In particular, this technology allows the use of an improved vacuum system which removes the catalyst much faster and with less abrasion. The dust-free nature of the process eliminates the need for bag filters and other dust-control equipment.
Probably the most significant value to the refiner is having his unit back on stream more quickly, thus minimizing lost production.
Intangible benefits are difficult to quantify but are nevertheless important.
For example, not having to deal with a life-threatening environment improves morale and can increase productivity and quality of work.
Another important feature of the technology is that the catalyst is fully regenerable by thin-bed, moving-belt technology, with dedicated inert stripping of hydrocarbons.
A variety of hydrotreating and hydrocracking catalysts have been tested and have qualified for regeneration through laboratory studies and commercial runs.
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