Fluidized bed coking process

An improved fluidized bed coking process wherein a residuum feedstock is introduced into a first stage comprised of a short vapor contact time reactor containing a horizontal moving bed of fluidized hot particles. Carbonaceous material is deposited onto the hot particles on contact with the hot particles, and a vapor product is produced. The hot particles, containing the carbonaceous deposits, are fed to a second stage fluidized bed coking process.

FIELD OF THE INVENTION 
The present invention relates to an improved fluidized bed coking process 
wherein a residuum feedstock is introduced into a first stage comprised of 
a short vapor contact time reactor containing a horizontal moving bed of 
fluidized hot particles. Carbonaceous material is deposited onto the hot 
particles on contact with the hot particles, and a vapor product is 
produced. The hot particles, containing the carbonaceous deposits, are fed 
to a second stage fluidized bed coking process. 
BACKGROUND OF THE INVENTION 
Although refineries produce many products, the most desirable are the 
transportation fuels gasolines, diesel fuels, and jet fuels, as well as 
light heating oils, all of which are high-volume, high value products. 
While light heating oils are not transportation fuels, their hydrocarbon 
components are interchangeable with diesel and jet fuels, differing 
primarily in their additives. Thus, it is a major objective of petroleum 
refineries to convert as much of the barrel of crude oil into 
transportation fuels as is economically practical. The quality of crude 
oils is expected to slowly worsen with sulfur and metals content and 
densities increasing. Greater densities mean that more of the crude oil 
will boil above about 560.degree. C., and thus will contain higher levels 
of Conradson Carbon and/or metal components. Historically, this 
high-boiling material, or residua, has been used as heavy fuel oil, but 
the demand for these heavy fuel oils has been decreasing because of 
stricter environmental requirements. This places greater emphasis on 
refineries to process the entire barrel of crude to more valuable lower 
boiling products. 
Coking processes are presently the major refinery processes for converting 
heavy feeds, such as residua, to more valuable lower boiling products, but 
are typically too severe for obtaining optimum mounts of gasoline and 
distillate boiling products without producing an undesirable amount of 
coke and light gases. It would be desirable to first distill, or vaporize, 
volatile materials of resids prior to coking to obtain higher yields of 
such desirable transportation fuel products. 
The two types of coking most commonly commercially practiced are delayed 
coking and fluidized bed coking. In delayed coking, the resid is heated in 
a furnace and passed to large drums maintained at temperatures from about 
415.degree. C. to 540.degree. C. During a long residence time in the drum 
at such temperatures, the resid is converted to coke. Liquid products are 
taken off the top for recovery as "coker gasoline", "coker gas oil", and 
gas. Conventional fluidized bed coking process units typically include a 
coking reactor and a burner. A petroleum feedstock is introduced into the 
coking reactor containing a fluidized bed of hot solids, preferably coke, 
and is distributed uniformly over the surfaces of said coke particles 
where it is cracked to vapors and to carbonaceous material which is 
deposited onto the particles. The vapors pass through cyclones which 
remove most of the entrained coke particles. The vapor is then discharged 
into a scrubbing zone where remaining coke particles are removed and the 
products are cooled to condense heavy liquids. The resulting slurry, which 
usually contains from about 1 to about 3 wt. % coke particles, is recycled 
to extinction to the coking zone. 
The coke particles in the coking zone flow downwardly to a stripping zone 
at the base of the coking reactor where a stripping gas, such as steam, is 
used to remove interstitial product vapors from, or between, the coke 
particles, as well as some adsorbed liquids from the coke particles. The 
coke particles then flow down a stand-pipe and into a riser which moves 
them to a burner where sufficient air is injected for burning at least a 
portion of the coke and heating the remainder sufficiently to satisfy the 
heat requirements of the coking zone where the unburned hot coke is 
recycled. Net coke, above that consumed in the burner, is withdrawn as 
product coke. 
While fluidized bed coking has met with a substantial amount of commercial 
success, there still remains a need in the industry for methods that can 
increase the liquid yields, the quality of liquids, or both. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a two stage 
process for converting a heavy hydrocarbonaceous feedstock having a 
Conradson Carbon content of at least about 5 wt. %, to lower boiling 
products; which process comprises: 
(a) partially converting the feedstock to lower boiling products by 
introducing the feedstock into said first stage which is conducted in one 
or more short vapor contact time reactors comprised of a horizontal moving 
bed of fluidized hot particles wherein upon contact of the feedstock with 
the hot particles vapor phase products are produced and carbonaceous 
material is deposited onto the hot particles, which first stage is 
operated: (i) at a temperature from about 450.degree. C. to about 
700.degree. C.; (ii) under conditions such that the solids residence time 
and the vapor residence time are independently controlled, which vapor 
residence time is less than about 2 seconds, and which solids residence is 
from about 5 to about 60 seconds; and 
(b) further converting said partially converted feedstock to lower boiling 
products in a second stage comprised of a fluidized bed coking process 
unit comprised of a coking reactor and a burner, said coking reactor 
containing a coking zone, a scrubbing zone located above the coking zone 
for collecting vapor phase products, and a stripping zone located below 
the coking zone for stripping hydrocarbons from particles passing 
downwardly from the coking zone, which second stage is operated by: 
(i) passing the vapor phase product from said first stage to said scrubbing 
zone of a fluidized bed coking process unit wherein entrained particles 
are removed and conversion products are collected overhead; 
(ii) collecting, from the scrubbing zone, a stream of light products having 
an average boiling point equal to or less than about 510.degree. C.; 
(iii) collecting, from the scrubbing zone, a product stream having average 
boiling point of greater than about 510.degree. C.; 
(iv) passing, from the first stage, the particles having carbonaceous 
material deposited thereon to the coking zone of a fluidized bed coking 
process unit, past the stripping zone where hydrocarbons are stripped with 
a stripping gas; 
(v) passing a portion of said stripped solid particles from the stripping 
zone to said burner containing a combustion zone which is comprised of a 
fluidized bed of solid particles and which is operated at a temperature 
from about 40.degree. to 200.degree. C. greater than that of the coking 
zone to partially combust carbonaceous material on said particles, thereby 
heating said particles to a temperature in excess of the temperature of 
the coking zone; and 
(vi) recycling at least a portion of the heated particles from the 
combustion zone to said short contact time reactor of said first stage. 
In a preferred embodiment of the present invention, an additional heavy 
hydrocarbonaceous feedstream is introduced into said coking zone. 
In still another preferred emboiment of the present invention, a portion of 
the hot particles is passed from the burner to the coking zone of the 
fluid bed coking process unit. 
In another preferred embodiments of the present invention, the feedstock is 
a vacuum resid and the fluidized bed coking process unit contains a coking 
zone, a heating zone, and a gasification zone wherein the solids are 
recycled form the heating zone to the coking zone and solids are recycled 
from the heating zone to the gasification zone, which gasification zone is 
operated at a temperature from about 870.degree. C. to about 1,100.degree. 
C.

DETAILED DESCRIPTION OF THE INVENTION 
Suitable heavy hydrocarbonaceous feedstocks for use in the present 
invention include heavy hydrocarbonaceous oils, heavy and reduced 
petroleum crude oil; petroleum atmospheric distillation bottoms; petroleum 
vacuum distillation bottoms, or residuum; pitch; asphalt; bitumen; other 
heavy hydrocarbon residues; tar sand oil; shale oil; coal; coal slurries; 
liquid products derived from coal liquefaction processes, including coal 
liquefaction bottoms; and mixtures thereof. Such feeds will typically have 
a Conradson carbon content of at least 5 wt. %, generally from about 5 to 
50 wt. %. As to Conradson carbon residue, see ASTM Test D189-165. 
Preferably, the feed is a petroleum vacuum residuum. 
A typical petroleum chargestock suitable for the practice of the present 
invention will have the composition and properties within the ranges set 
forth below. 
______________________________________ 
Conradson Carbon 5 to 40 wt. % 
Sulfur 1.5 to 8 wt. % 
Hydrogen 9 to 11 wt. % 
Nitrogen 0.2 to 2 wt. % 
Carbon 80 to 86 wt. % 
Metals 1 to 2000 wppm 
Boiling Point 340.degree. C.+ to 650.degree. C.+ 
Specific Gravity -10 to 35.degree. API 
______________________________________ 
Reference is now made to the sole FIGURE hereof wherein a heavy 
hydrocarbonaceous feedstock which is relatively high in Conradson Carbon 
and/or metal-components is partially converted to lower boiling products 
in a first stage wherein the feedstock is fed, via line 10, to short vapor 
contact time reactor 1 which contains a horizontal moving bed of fluidized 
hot particles which are received from heater 3 via line 42. It is 
preferred that the particles in the short vapor contact time reactor be 
fluidized with assistance by a mechanical means. The particles are 
fluidized by use of a fluidized gas, such as steam, a mechanical means, 
and by the vapors which result in the vaporization of a fraction of the 
feedstock. It is preferred that the mechanical means be a mechanical 
mixing system characterized as having a relatively high mixing efficiency 
with only minor amounts of axial backmixing. Such a mixing system acts 
like a plug flow system with a flow pattern which ensures that the 
residence time is nearly equal for all particles. The most preferred 
mechanical mixer is the mixer referred to by Lurgi AG of Germany as the 
LR-Mixer or LR-Flash Coker which was originally designed for processing 
for oil shale, coal, and tar sands. The LR-Mixer consists of two 
horizontally oriented rotating screws which aid in fluidizing the 
particles. Although it is preferred that the solid particles be coke 
particles, they may be any other suitable refractory material. 
Non-limiting examples of such other suitable refractory materials include 
those selected from the group consisting of silica, alumina, zirconia, 
magnesia, or mullite, synthetically prepared or naturally occurring 
material such as pumice, clay, kieselguhr, diatomaceous earth, bauxite, 
and the like. The solids will have an average particle size of about 40 to 
1000 microns, preferably from about 500 to 500 microns. 
When the feedstock is contacted with the hot solids, which will preferably 
be at a temperature from about 590.degree. C. to about 760.degree. C., 
more preferably from about 650.degree. C. to 700.degree. C., a major 
portion of the feedstock will be vaporized. The residence time of vapor in 
short contact time thermal zone 1 will be an effective amount of time so 
that substantial secondary cracking does not occur. This amount of time 
will typically be less than about 2 seconds, preferably less than 1 
second, more preferably less than about 0.5 seconds. That portion of the 
feed that does not immediately vaporize on contact with the hot solids 
will form a thin film on the particles where cracking reactions occur. 
This results in the formation of additional vapor products and a minor 
amount of carbonaceous material depositing on the hot particles. The 
residence time of solids in the short vapor contact time reactor will be 
from about 5 to 60 seconds, preferably from about 10 to 30 seconds. One 
novel aspect of the present invention is that the residence time of the 
particles and the residence time of the vapor products in the short vapor 
contact time reactor are independently controlled. Most fluidized bed 
processes are designed so that the solids residence time, and the vapor 
residence time cannot be independently controlled, especially at 
relatively short vapor residence times. It is preferred that the short 
vapor contact time reactor be operated so that the ratio of solids to feed 
be from about 10 to 1, preferably from about 5 to 1. It is to be 
understood that the precise ratio of solids to feed will primarily depend 
on the heat balance requirement of the short contact time reactor. 
Associating the oil to solids ratio with heat balance requirements is 
within the skill of those having ordinary skill in the art, and thus will 
not be elaborated herein any further. A minor amount of the feedstock will 
deposit on the particles the form of combustible carbonaceous material. 
Metal components will also deposit on the particles. Consequently, the 
vaporized portion which exits thermal unit 1 via line 11 will be 
substantially lower in both Conradson Carbon and metals when compared to 
the original feed. Use of this first stage, in combination with second 
stage fluidized coking will result in increased liquid yields and 
decreased gas and coke yields, when compared to fluidized coking alone. 
Both the vaporized product stream and the solids are passed to a second 
stage, the fluidized bed coking stage, via lines 11 and 15 respectively to 
the space 13 between the top of fluidized solids bed 14 in coking reactor 
2 and the scrubber 25. The solids flow downwardly through the reactor 2, 
pass stripping zone 17, to heater 3. The vaporized product stream passes 
through cyclone system 20 where entrained solids are removed and returned 
to the bed of fluidized solids via dipleg 22. A light product stream 
comprised of steam and 510.degree. C. minus fractions are collected 
overhead via line 28. A heavy stream comprised of a 510.degree. C. plus 
fraction is collected via line 26, at least a portion of which can be 
recycled to short vapor contact time reactor 1 via line 27. 
The fluidized bed coking unit can be any conventional fluidized bed coking 
process unit and its specific configuration is not critical to the present 
invention. For illustrative purposes, a fluidized bed coking process unit 
is shown which is comprised of a coking reactor, a heater, and a gasifier. 
In broad terms, the operation of the coking unit proceeds as follows: a 
heavy hydrocarbonaceous chargestock is passed via lines 10a and 27 to 
coking zone 12 of coker reactor 2, which coking zone contains a fluidized 
bed of solid, or so-called "seed" particles, having an upper level 
indicated at 14. A fluidizing gas, e.g. steam, is admitted at the base of 
coker reactor 2, through line 16, into stripping zone 17 of the coking 
reactor in an amount sufficient to obtain a superficial fluidizing 
velocity. Such a velocity is typically in the range of about 0.5 to 5 
ft/sec. A portion of the decomposed feed forms a fresh coke, or 
carbonaceous material, layer on the hot fluidized particles. The solids 
are partially stripped of fresh coke and occluded hydrocarbons in 
stripping zone 13 by use of a stripping gas, preferably steam and passed 
via line 18 to heater 3 which is operated a temperature from about 
40.degree. C. to 200.degree. C., preferably from about 65.degree. C. to 
175.degree. C., and more preferably about 65.degree. C. to 120.degree. C. 
in excess of the actual operating temperature of the coking zone 
The pressure in the coking zone is maintained in the range of about 0 to 
150 psig, preferably in the range of about 5 to 45 psig. Conversion 
products from both the short vapor contact time reactor and the coking 
zone are passed through cyclone system 20 of the coking reactor to remove 
entrained solids which are returned to the coking zone through dipleg 22. 
The vapors leave the cyclone through line 24, and pass into scrubber 25, 
containing a scrubbing zone, at the top of the coking reactor. If desired, 
a stream of heavy materials condensed in the scrubber may be recycled to 
either short vapor contact time reactor 1 or to coking reactor 2 via lines 
26 and 27 respectively. The coker conversion products are removed from the 
scrubber 25 via line 28 for fractionation in a conventional manner. 
In heater 3, stripped coke from the stripping zone 17 of coking reactor 2 
(cold coke) is introduced via line 18 to a fluidized bed of hot coke 
having an upper level indicated at 30. The bed is partially heated by 
passing a fuel gas into the heater via line 32. Supplementary heat is 
supplied to the heater by coke circulating from gasifier 4 through line 
34. The gaseous effluent from the heater, including entrained solids, 
passes through a cyclone system which may be a first cyclone 36 and a 
second cyclone 38 wherein the separation of the larger entrained solids 
occurs. The separated larger solids are returned to the heater bed via the 
respective cyclone diplegs 39. The heated gaseous effluent, which contains 
entrained solids, is removed from heater 3 via line 40. 
As previously mentioned, hot coke is removed from the fluidized bed in 
heater 3 and recycled to the short vapor contact time reactor 1 via line 
42, then to coking reactor 2 to supply heat to both the short vapor 
contact time reactor and the coking reactor. It is understood that a 
portion of hot coke can also be passed directly to the coking zone 12. 
Another portion of coke is removed from heater 3 and passed via line 44 to 
a gasification zone 46 in gasifier 4 in which is also maintained a bed of 
fluidized solids to a level indicated at 48. If desired, a purged stream 
of coke may be removed from heater 3 by line 50. 
The gasification zone is maintained at a temperature ranging from about 
870.degree. C. to 1100.degree. C. at a pressure ranging from about 0 to 
150 psig, preferably at a pressure ranging from about 25 to about 45 psig. 
Steam via line 52, and an oxygen-containing gas, such as air, commercial 
oxygen, or air enriched with oxygen via line 54, are passed via line 56 
into gasifier 4. The reaction of the coke particles in the gasification 
zone with the steam and the oxygen-containing gas produces a hydrogen and 
carbon monoxide-containing fuel gas. The gasified product gas, which may 
contain some entrained solids, is removed overhead from gasifier 4 by line 
32 and introduced into heater 3 to provide a portion of the required heat 
as previously described. 
As previously mentioned, while the invention herein has been illustrated 
with a process unit comprised of a coking reactor, a heater, and a 
gasifier, it could just as well have been illustrated in a fluidized bed 
coking process unit containing only a coking reactor and a burner. Both of 
these types of fluidized bed coking units are very well known to those 
having ordinary skill in the art and thus it is not necessary to describe 
them in detail with respect to their ancillary equipment, such as values, 
compressors, pumps, etc.