Process for controlling oxidation of nitrogen and metals in circulating fluidized solids contacting process

Abstract

A fluidized particulate solids contacting process for reducing regenerator flue gas NOx emissions and / or permitting operating with an increased equilibrium solids vanadium level, which process may be an FCC process or a fluidized particulate solid hydrocarbon treating process, wherein spent FCC catalyst or other spent solid is in a regenerator with an oxygen-containing regeneration gas under catalyst (solid) regeneration conditions which include a combination of at least a regeneration temperature and an oxygen level in the regeneration gas which is effective to burn off the spent solid a majority of carbonaceous deposits thereon, while substantially preventing the formation of NOx, and thereby produce a regenerated solid having a carbon level reduced from that of the spent solid and a flue gas; maintaining the regenerated solid in a fluidized state with a fluidizing media that substantially prevents any further oxidation or regeneration; and returning the fluidized regenerated solid to the reactor (contactor) used in the process.

Description

[0001] This application is a Continuation-In-Part of application Ser. No. 09 / 983,379, filed Oct. 24, 2001.DESCRIPTION OF THE INVENTION[0002] Field of the Invention[0003] This invention relates to an improved circulating fluid particulate solids contacting process for upgrading hydrocarbon feedstocks containing metals, such as vanadium, and / or nitrogen, in which certain regenerator design and operating conditions are employed to (1) reduce the nitrogen oxides (NOx) emissions in regenerator flue gas and / or (2) permit operating with an increased equilibrium solids vanadium level over and above the current state of the art. This invention also relates to an improved fluid catalytic cracking (FCC) process for processing gas oils and residual oils, in which certain FCC unit (FCCU) catalyst regenerator design and operating conditions are employed to reduce the nitrogen oxides (NOx) emissions in the catalyst regenerator flue gas and / or permit operating with an increased equilibrium catalyst...

AI Technical Summary

Benefits of technology

[0022] The above objectives and other advantages of the present invention may be achieved by employing an apparatus for the practice of the FCC, or other fluidized particulate solid process, which incorporates a regenerator design that permits maintaining a reducing atmosphere in the regenerator and / or a regenerator temperature below 1400.degree. F. (760.degree. C.). Reducing atmosphere is defined as one which enables maintaining between 0.07 and 0.4 wt % carbon on solids leaving the dilute phase riser portion of the regenerator. That is, when processing hydrocarbon feedstocks containing vanadium and / or sodium, it has been determined that the catalyst deactivation from vanadium and sodium can be minimized by maintaining a reducing atmosphere in the regenerator. This will retard the formation of vanadic acid and vanadium pentoxide and low melting point sodium compounds, and therefore, as discussed above, the adverse effect of vanadium and sodium on catalyst activity.

[0023] I have also determined that maintaining the regenerator temperature below 1400.degree. F. (704.degree. C.), and still more preferably below 1250.degree. F. (677.degree. C.), that one can also reduce, even in an oxidizing atmosphere, the effect of vanadium and sodium on catalyst activity and agglomeration. While the unit can be designed to operate the regenerator in a reducing atmosphere or at a less than the above regenerator temperature to minimize the catalyst deactivation and tendency to agglomerate, combining both these processing conditions will result in the least catalyst deactivation and substantially eliminate the possibility of agglomeration. Therefore, the preferred apparatus has both a means for controlling both the degree of oxidation of the circulating solids and the circulating solids temperature. In a preferred apparatus, this entails incorporating a dilute phase (<20 lb / ft3 solids density) regenerator and catalyst cooling. While catalyst cooling can be incorporated in the apparatus by use of exchange between circulating catalyst and water to produce steam, it can also be accomplished by using water for solids / catalyst dispersion as discussed in U.S. Pat. Nos. 4,859,315 and 4,985,136, by using water in place of stripping steam, and allowing more or less CO to exit the regenerator in the flue gas.

Problems solved by technology

A major obstacle to the processing of residual oil in catalytic processes, such as the FCC or hydrotreating type processes, has been the concentration of refining "catalyst poisons", such as metals, nitrogen, sulfur, and asphaltenes (coke precursors), which are present in all residual oils and most gas oils, that portion of the crude oil boiling between 650.degree. F.

These "catalyst poisons" accelerate the deactivation of catalyst, reduce catalyst selectivity, increase regenerator flue gas environmental pollutants, and increase the catalyst and operating costs, so that these residual oil processing methods have only been economical, in most cases, by limiting the amount of residual oil in the feed.

Because of the increased capital costs, without any economic benefit, required for treating the FCC regenerator flue gas and the increased operating costs associated with the higher fresh catalyst replacement rates required to control the ECAT metals level when processing increased quantities of residual oil, many refiners elected to install feed hydrotreating as the preferred method of flue gas SOx control.

However, hydrotreating of the FCC feed limited the feed to gas oil, since the introduction of residual oil into the hydrotreater feed would also increase the hydrotreating catalyst costs, and typically, was not economical.

Operators of these units have been reluctant to consider residual oil processing in their FCCU because of the increased capital required to modify the FCCU.

Also, economics (catalyst costs) have limited FCC feedstock to about 30 ppm of metals (Ni+V) in the feed.

The only limit on FCC feed sulfur has to do with the costs associated with making acceptable products and treating the FCC regenerator flue gas.

However, even with these improvements in the FCC process, the amount of residual oil that a refiner has been able to economically convert in the FCC process has been limited by the cost of replacement catalyst required as a result of catalyst deactivation which results from the metals, especially vanadium and sodium, contained in the residual oil feedstock.

With today's feed and product prices, most operators are limited to a FCC catalyst operating costs of less than $1.00 per barrel (0.16 m3) of feed processed in the FCCU.

While the exact mechanism of destruction of zeolite crystals is a subject for debate, the vanadium clearly causes an irreversible loss of zeolite crystallinity and surface area.

However, one of the major problems encountered with these types of hydrocarbon treating processes is that as the level of vanadium increases on the circulating solids there is a tendency of the particles to agglomerate (stick together and quit flowing) as disclosed in Hettinger's European Patent No.

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