MXPA97006742A - Process to improve the gasoleo current of the detonation zone in a retard cochizer - Google Patents

Abstract

The present invention relates to a process of coking or delayed pyrolysis, in which the vapors leaving the coking drum are fed to a coking fractionator when the vapors are separated in a vapor stream leaving, intermediate liquid streams and a stream of diesel fuel. the detonation zone containing a substantial amount of particulate solid material, the improvement is characterized in that it comprises: a) subjecting the gas oil stream from the detonation zone to a filtration step to reduce the amount of particulate solid material therein; ) passing the diesel stream from the detonated area filtered from step (a) to a catalytic bed hydroprocessing unit fi

Description

PROCESS TO IMPROVE THE GASOLINE CURRENT OF THE AREA DETONATION IN A DELAYED COOXIZER BACKGROUND OF THE INVENTION 1. Field of the invention This invention relates to delayed coking, and more particularly to a coking or delayed pyrolysis process in which the vapors leaving a coke drum are passed to a coking fractionator when the vapors leaving the coker are separated in a stream of steam, intermediate liquid streams and a stream of diesel from the lower detonation zone. 2. Background of the technique A coking or pyrolysis process of the type mentioned above is described in detail in U.S. Patent No. 4,518,487 to Graf et al. As described in that patent, the performance distribution of the coker product is improved by removing a stream of detonation zone diesel from the bottom of the coker fractionator instead of returning the coke.

REF: 25590 flow to the coke drum for recycling in the coker as is usually done in the above coking processes, all described in detail in the aforementioned U.S. Patent No. 4,518,487. Although the process described in the "487" patent provides significant improvements, it is susceptible to the disadvantage of producing a gasoil stream from the detonation zone that is difficult to improve for further processing. The stream contains significant amounts of finely divided particulate solids as well as a high viscous mesophase material. The mesophase material is essentially liquid coke which is entrained in the vapors that leave the coke drum. In order to improve the value of the diesel stream from the detonation zone, it needs to be hydrotreated. However, the entrained solids and the mesophase material quickly plug and plug the catalyst bed of a hydrotreater when an attempt is made to pass the current through the hydrotreater. Diesel fuel from the detonation zone not subjected to hydrotreatment can be processed in a fluidized bed catalytic cracking unit (FCC unit), but the yield distribution of the non-hydrotreating stream is poor due to its high aromatic content and other factors. Previous attempts to filter the current of diesel fuel from the detonation zone so that it can be hydrotreated have not been successful due to rapid plugging of the filter, difficulties in regenerating the filter medium and other factors.

BRIEF DESCRIPTION OF THE INVENTION According to the present invention, the gasoil stream from the detonation zone is filtered to remove substantially all of the solids which would otherwise plug the catalyst bed in a hydrotreater. The reduced stream of solids is then passed through a fixed catalytic bed hydroprocessor such as a hydrodesulfurizer or a hydrocracking unit to reduce the sulfur content of the stream and modify the molecular structure of the stream components and to improve its value in a subsequent processing unit. The product performance distribution from the fluidized bed catalytic pyrolyzer (FCC unit) is significantly better for diesel fuel from the hydrotreated detonation zone compared to the product performance distribution from a gas oil in the detonation zone not treated.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic flow diagram showing the coking or pyrolysis process of the prior art of the type to which the present invention pertains. Figure 2 is a schematic flow chart showing a coking process incorporating the improvements provided by this invention. Figure 3 is a schematic flow chart depicting a filter of the type used in the present invention.

DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 is a simplified flow chart illustrating the coking or pyrolysis process described in U.S. Patent No. 4,518,487. As shown in Figure 1, the coker feed from line 10 passes through oven 12 and then into one of coke drums 14. The vapors projecting from the drum 14 pass through the pipe 16 to the coker fractionator 18. A recycle liquid such as coker gas oil is sprayed into the detonation zone of the fractionator 18 via pipe 20 to make contact with the incoming vapors to decompose the suspended particulate material and to condense the higher melting temperature components into the vapor stream of the incoming coker. The humid gas leaving gas stream, from the fractionator 18, is removed by means of the pipe 22, and the intermediate liquid fractions are removed by means of the pipes 24 and 26. A diesel fuel from the detonation zone containing suspended solids and a viscous mesophase material is removed from the bottom of the fractionator 18 by means of the pipe 28. In the prior art, this gas stream from the detonation zone (FZGO) is typically added to the feed of an FCC unit. Figure 2 illustrates schematically the improvement of this invention with respect to the prior art process. The common elements in figures 1 and 2 are numbered the same. In Figure 2, the FZGO is fed to the filter 30. From the filter 30, it advances to a hydroprocessing unit 32 and from there to the FCC unit 34. The hydroprocessing unit 32 can be a hydrodesulfurizer or hydropolyzer, but in any case it is a hydrotreating unit that contains a fixed catalyst bed. In the prior art, the FZGO current can not be fed to a fixed bed catalytic hydrotreator due to the fast sealing of the catalyst with the suspended solids and the viscous mesophase material. As a result, the FZGO stream containing a high level of aromatics should be fed unfiltered to an FCC unit in which the distribution of product yield from FZGO is poor due to the high aromatic content. Additionally, the FZGO current often contains sulfur in an amount that presents problems with product specifications. In some cases, the FZGO current must be used in lower value current such as to process fuel. It has been determined that if substantially all of the suspended solids greater than about 25 micrometers in diameter are to be removed from the FZGO stream, the stream can be fed back to a fixed bed catalytic hydrotreater without plugging or plugging the catalysed bed. A filter cut at 25 microns reduces a major portion of the total suspended solids, and the remaining smaller particles pass through the catalyst bed without presenting a serious problem of plugging. Any filter which effectively removes substantially all the particles of micrometers and larger can be used of the process of this invention. You can use filters that eliminate even smaller particles, for example as small as approximately 10 microns, but do not tend to be as cost effective. A particularly effective filter for the process is an engraved metal disc filter of the type sold by PTI Technologies Inc. of Newbury Park, CA. The etched metal disc filter is comprised of one or more filter elements formed into multiple stacked discs and is extremely effective, is easily regenerated and is relatively simple to operate and control. The regeneration stage, which involves backflushing with a high pressure gas charge, with or without a subsequent solvent discharge, it only requires a period from half a minute to four minutes, so that it is feasible to operate only with a filter unit, insofar as the filter feed can be retained in a purge tank or similar during the back-off stage. Alternatively, two or more filter units can be multiple and can be individually re-discharged so that the feed through the filter is continuous. A preferred filter is shown schematically in Figure 3 and includes a filter unit 30, a feed pipe 36, a filter outlet pipe 38, a gas accumulator 40 and a waste tank retro download. In operation, the FZGO of the line 36 is fed to the filter unit 30 and exits via the pipe 38. When the back pressure on the filter 30 reaches a preset level, the power to the unit is stopped, and a quick opening valve (not shown) in the accumulator 40. The pressurized gas from the accumulator 40 flows back through the filter unit 30 and washes the solids accumulated on the surface of the filter to a holding tank 42 or to a unit or waste site for proper process. Preferably, the filter is designed to cycle when the back pressure reaches a pre-set level. It has been found that the back pressure is reduced to almost zero after the back-off cycle, which indicates a substantially complete removal of the accumulated solids. As mentioned above, a back-off solvent subsequent to the pressurized gas regeneration step can be used, if desired.

OPERATION OF THE MOST FAVORED MODALITY The most preferred embodiment of the invention will now be described with reference to Figure 2. The coker feed from the coker oven 12 is fed to one of the coke drums 14, and the vapors of the coker are fed to the lower part of the fractionator 18. A heavy gas oil stream from the pipe 20 is sprayed into the detonation zone of the fractionator 18, where it makes contact with the incoming feed, condenses the heavier components and removes suspended solids by washing. A detonation zone gas oil, containing the condensed coker vapors, solids and viscous mesophase material, is withdrawn from the fractionator 18 by means of the pipe 28. The product streams of the fractionator 18 are recovered by means of the pipes 22, 24 and 26. The diesel fuel from the detonation zone (FZGO) of the pipe 28 is passed to the filter 30 where the larger suspended solids of approximately 25 microns are removed. The filtered FZGO then passes to the catalytic hydrotreating unit 32 (preferably a hydrodesulfurization unit), wherein the FZGO is desulfurized and / or structurally modified to be more susceptible to fluidized bed catalytic pyrolysis. The filtered FZGO does not clog the catalyst bed in the hydrotreater, and the hydrotreated FZGO provides a product with a lower sulfur content and a better product distribution performance from the FCC unit compared to the FZGO that has not been hydrodesulfurized. As indicated above, you can use one or more filter units with periodic or sequential backflushing to maintain performance, and the removed solids may be used or discarded.

EXAMPLE I In this example, 440 barrels per day of the diesel stream from the detonation zone of a commercial coker are fed to an etched metal disc filter designed to remove particles larger than 25 micrometers in size. The filtered stream is passed directly to an FCC unit during the first two weeks of the test, to confirm that the filter does in fact remove substantially all of the particles larger than 25 micrometers. After confirmation of the effectiveness of the filter, the filtered current is then fed to a fixed bed catalytic hydrotreator for several weeks. The filter is designed to automatically back off when the pressure drop across the filter reaches 1.4 kg / cm2 (20 psi). The pressure drop across the filter immediately after the backoff is almost zero, which indicates an effective backoff. During the cycle of filling the coke drum, the filter is backfilled approximately every two hours.

Approximately 50 percent by volume of the particulate material in the diesel fuel in the detonation zone is greater than 25 micrometers. The filtered stream does not contain particulate material greater than 25 micrometers, and the particulate content of the filtered stream is low enough to not cause difficulties when it is found for weeks that the filtered stream is supplied to the hydrotreater. Table 1 below shows the results of the filter operation for several days in which an analysis of the suspended solids was performed.

TABLE 1 The previous example illustrates the effectiveness of an etched metallic disc filter to remove suspended solids from diesel fuel from the detonation zone so that the filtered stream can be processed in a fixed bed catalytic hydrotreator without the catalyst being clogged. it would occur with an unfiltered stream. Although certain embodiments and details have been shown for the purpose of illustrating this invention, it will be apparent to those skilled in the art that various changes and modifications may be made herein without departing from the spirit or scope of the invention. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (8)

1. In a process of coking or delayed pyrolysis, in which the vapors leaving the coking drum are fed to a coking fractionator when the vapors are separated in an outgoing vapor stream, intermediate liquid streams and a stream of diesel from the detonation zone which contains a substantial amount of particulate solid material, the improvement is characterized in that it comprises: (a) subjecting the gas oil stream from the detonation zone to a filtration step to reduce the amount of particulate solid material therein; and (b) passing the gas oil stream from the detonated area filtered from step (a) to a fixed bed catalytic hydroprocessing unit.

2. The delayed coking process according to claim 1, characterized in that the filtration step substantially eliminates all of the solid particulate material having a particle size greater than 25 micrometers.

3. The delayed coking process according to claim 1, characterized in that The catalytic hydroprocessing unit is a hydrocracking or hydropyrolysis unit.

4. The delayed coking process according to claim 1, characterized in that the catalytic hydroprocessing unit is a hydrodesulphurizer.

5. The delayed coking process according to claim 4, characterized in that the diesel fuel from the hydrodesulfurized detonation zone of the hydrodesulfurizer is fed to a FCC unit (fluidized bed catalytic pyrolyzer unit).

6. The delayed coking process according to claim 1, characterized in that the filtering step includes filtering through a filter element consisting of a stack of engraved metal discs.

7. The delayed coking process according to claim 6, characterized in that the filter element is periodically re-discharged.

8. The delayed coking process according to claim 7, characterized in that a plurality of filter elements are used, and the elements are sequentially backflushed, so that at least one filter element is always available in the current to eliminate solids from the detonation zone.