FEED PREPARATION OF FCC SLURRY OIL RETENTATE FOR DOWNSTREAM PROCESSING

Abstract

A method for preparation of FCC slurry oil retentate for downstream processing while simultaneously cleaning catalyst fine retentate from filter elements or separation media of a filter assembly of an FCC slurry oil filtration system includes front-washing the filter or separation media with a low boiling point solvent, and then backwashing the filter elements with the same solvent. The front wash and backwash is conducted at a temperature of below 350 F. and at a pressure of about 25-75 psig.

Claims

1. A method for preparing catalyst fines retentate from filter or separation elements of a filter assembly of a slurry oil filtration system for downstream processing while simultaneously removing accumulated retentate from the filter or separation elements; the method comprising: front washing the filter or separation elements of the filter assembly by passing a low boiling point solvent (LBPS) from an upstream side of said filter assembly through said filter or separation elements to a downstream side of said filter assembly, the LBPS having a boiling point at atmospheric pressure of less than 300 F.; and then, back washing the filter elements with the same LBPS to dislodge retentate from the filter or separation elements; said backwashing step forming a backwash mixture comprised of the LBPS and dislodged retentate.

2. The method of claim 1 wherein the LBPS is petroleum ether, methylene chloride, chloroform, or dimethyl formaldehyde.

3. The method of claim 1 including a step of draining slurry oil from one or both of the downstream side of the filter assembly prior to carrying out the front washing step.

4. The method of claim 3 including a stop of draining slurry oil from the upstream side of the filter assembly prior to carrying out the front washing step.

5. The method of claim 1 including a step of cooling the filter assembly to below 350 F. prior to said front washing step.

6. The method of claim 1 including a step, prior to said front washing step, of introducing pressurized filtered slurry oil into the upstream side of said filter assembly to force unfiltered slurry oil from the upstream side of the filter assembly, through the filter or separation elements, and to the downstream side of said filter assembly.

7. The method of claim 6 wherein said filtered slurry oil is introduced into said filter assembly at a pressure of about 25 psi to about 75 psi.

8. The method of claim 6 wherein said filtered slurry oil is introduced into said filter assembly at a pressure of about 50 psi to about 75 psi.

9. The method of claim 6 wherein said filtered slurry oil is at a temperature of between about 250 F. and about 350 F.

10. The method of claim 9 including a step of cooling the filter assembly to below 350 F. prior to said front washing step; said cooling step comprising said step of introducing pressurized filtered slurry oil into the upstream side of said filter assembly.

11. The method of claim 6 comprising a step of draining the downstream side of the filter assembly, and optionally draining the upstream side of the filter assembly, after said step of introducing pressurized filtered slurry oil is completed and prior to carrying out the front washing step.

12. The method of claim 1 wherein, after said step of front washing said filter element is completed, said filter elements will be substantially submerged in said LBPS; said step of back washing said filter elements comprising forcing the LBPS in the downstream side of the filter assembly through the filter or separation elements to the upstream side of the filter assembly.

13. The method of claim 12 wherein the backwash mixture is delivered to a solid-liquid separator where the LBPS is separated from the retentate.

14. The method of claim 12, wherein said backwashing step comprises pressurizing said filter assembly prior to forcing the LBPS through the filter elements.

15. The method of claim 14 wherein said filter assembly is pressurized to about 25 to about 75 psi.

16. The method of claim 14 wherein said filter assembly is pressurized using an inert gas.

17. The method of claim 1 wherein the backwash mixture is sent to a solid-liquid separator to separate the LBPS of the backwash mixture from the retentate and to dry to retentate to allow for the reclaiming of the FCC Catalyst component of the retentate.

18. A method for removing catalyst fines retentate from filter or separation elements of a filter assembly of a slurry oil filtration system; the method comprising: draining a downstream side of the filter assembly; cooling the filter assembly to below 350 F.; after the cooling step, front washing the filter or separation elements of the filter assembly by passing a low boiling point solvent (LBPS) from an upstream side of said filter assembly through said filter elements to the downstream side of said filter assembly, the LBPS having a boiling point at atmospheric pressure of less than 300 F.; then, back washing the filter or separation elements by forcing the same LBPS from the downstream side of the filter assembly, through the filter elements, to the upstream side of the filter assembly; said step of backwashing including pressurizing the filter assembly.

19. The method of claim 18 including, prior to said draining step, a step of introducing pressurized filtered slurry oil into the upstream side of said filter assembly to force unfiltered slurry oil from the upstream side of said filter assembly, through the filter elements, and to the downstream side of said filter assembly.

20. The method of claim 19 wherein said filtered slurry oil is at a temperature of between about 250 F. and about 350 F.; said cooling step comprising said step of introducing the pressurized filtered slurry oil into the filter assembly.

Description

DESCRIPTION OF THE FIGURES

[0039] FIG. 1 is a schematic of a FCC slurry oil filtering system; and

[0040] FIG. 2 is a schematic representation of a front wash filtration or separation assembly of the filtering system for use with the disclosed method.

DETAILED DESCRIPTION

[0041] The following detailed description illustrates the claimed invention by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the claimed invention, and describes several embodiments, adaptations, variations, alternatives and uses of the claimed invention, including what I presently believe is the best mode of carrying out the claimed invention. Additionally, it is to be understood that the claimed invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. The claimed invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

[0042] It will be appreciated that, in a typical FCC system, the slurry oil run downstream from a fluid catalytic cracking unit will be directed to a filtering stage where contaminants are filtered from the slurry oil stream. The filtration of the slurry oil stream is conducted as a continuous process. As can be appreciated, over time, the filter will become clogged with retentate, and will need to be cleaned. Thus, a typical filtering stage comprises a plurality of filter assemblies 10 and appropriate valving and valving controls which allow a filter assembly to be taken off line when its filter element is clogged and which directs that contaminated slurry oil stream to a filter assembly which is not currently clogged, and is available for filtering. In a typical slurry oil filtration system, the flow of slurry oil to the clogged filter assembly will be throttled down, and an awaiting, clean filter assembly, to which the flow of slurry oil will be redirected, is throttled up, thereby providing a fluent transition of the slurry oil stream from the clogged filter assembly to the clean filter assembly.

[0043] A typical filter assembly 10 (shown in more detail in FIG. 2) includes a housing 12 having a tubesheet 14 with a plurality of filter elements 16 extending upwardly from the tubesheet. For example, a filter assembly that is 36 in diameter can have up to 120 filter elements. The tube sheet 14 and filter elements 16 divide the interior of the housing 12 into an upstream side (the volume below the tube sheet and within the filter elements) and a downstream side (the volume above the tube sheet outside of the filter elements). As seen in FIG. 2, the housing 12 has a cylindrical portion 12a above the tube sheet and an inverted conical portion or heel 12b below the tube sheet. A neck 12c depends from the bottom of the housing heel 12b.

[0044] During normal filter operation, contaminated FCC slurry oil stream enters the filter assembly 10 via an inlet line 18 on the upstream side of the housing (i.e., below the tube sheet). The contaminated slurry oil is forced upwardly through the filter elements 16, and filtered (clean) slurry oil exits the filter assembly on the downstream side of the housing through an outlet line 20 near the top of the housing 12. Contaminants are trapped by the filter elements 16 as the filtrand/retentate. The filtrand/retentate is generally catalyst particles, but can include some asphaltenes. During normal operation, the filtered slurry oil can be collected in a slurry oil storage tank (not shown) or directed back to the slurry oil run down stream en route to the slurry oil product storage tank. As filtrand cakes on the surface of the filter elements, a pressure drop occurs on the downstream side of the tube sheet, and the pressure differential between the upstream and downstream sides of the tube sheet increases. The pressure differential is monitored, for example by a pressure differential gauge 22 which is in communication with both the upstream and downstream sides of the housing. Any desired means could be used to monitor the pressure differential between the two sides of the housing. For example, pressure sensors in each side of the housing to send output to a receiver (such as a PLC computer) which then compares the output of the two sensors. When the pressure difference (AP) between the upstream and downstream sides of the filter assembly reaches about 60 PSI, it is time to take the filter assembly off line and clean the filter elements. At this point, about 0.25 (about 6 mm) of catalyst fines will have been deposited on the filter elements, and the efficiency of the filter assembly has been reduced enough that it is time to initiate a wash cycle, to remove the filtrand from the filter elements.

[0045] Initially, the filter assembly 10 is shut (throttled) down, so that the flow of slurry oil to the filter assembly will ultimately cease. This is accomplished by a measured closing of a valve 18V in the slurry oil feed pipe. As noted above, while the filter assembly 10 is being throttled down, a cleaned filter assembly is being throttled up for use. As the valve 18V is being closed, a corresponding valve in the inlet line of the clean filter is being opened, so that slurry oil will be redirected to this clean filter assembly to filter the slurry oil of catalyst and, if present, asphaltenes.

[0046] Subsequently, clean slurry oil from a liquid-liquid separator 30 is introduced into the upstream side of the filter assembly. Preferably, recycled clean (filtered) slurry oil is introduced into the upstream side of the filter assembly through a line 34 which, for example, can join the inlet line 18 downstream of the valve 18V. A valve 34V in line 34 is opened to permit the flow of the recycled (filtered and separated) slurry oil into the inlet line 18. The clean (filtered) slurry oil is introduced at a pressure of about 25 psi to about 75 psi, and preferably about 50 psi. The high pressure of the recycled slurry oil will, in effect, push the contaminated slurry oil (from the FCCU) that is in the heel 12b (downstream side) of the filter assembly up through the filter elements 16. Sufficient clean slurry oil is pumped into the upstream side of the filter assembly such that the upstream side of the filter assembly contains substantially only clean recycled slurry oil. Substantially all of the contaminated slurry oil will be pushed though the filter elements 16 to the downstream side of the filter assembly.

[0047] Once the contaminated slurry oil from the upstream side of the filter assembly has been pushed through to the downstream side of the filter assembly, the downstream side of the filter assembly is drained. This is accomplished by opening a valve 24V in a drain line 24. The drain line 24 is proximate (and above) the tube sheet 14, so that the slurry oil in the downstream side of the filter assembly will be drained under the force of gravity. A pump can be used to aid in draining of the slurry oil from the downstream side of the filter assembly. Draining of the housing can also be facilitated by pumping an inert gas, such as nitrogen, into the filter assembly through a gas feed line. This gas, which is used for draining, can be pumped into the filter assembly either on the upstream side through a gas line 26 or downstream side through a gas line 32. The gas lines 26 and 32 include valves 26V and 32V, respectively, and the appropriate valve is opened to allow the gas to enter the filter assembly. The gas will displace the slurry oil in the downstream side of the filter assembly to force the slurry oil out through the slurry oil drain line 24. If the gas is introduced from the upstream side of the filter assembly, it can push some of the residual slurry oil in the filter assembly through the filter assembly to be drained through the drain line 24.

[0048] Once the contaminated slurry oil in the upstream side of the filter assembly has been pushed through to the downstream side of the filter assembly, the upstream side of the filter assembly will be filled substantially with the clean, filter slurry oil. If desired, the upstream side of the filter assembly can be drained of the clean filtered slurry oil through a line 25 and valve 25V. Inert gas can be used to facilitate draining the upstream side of the filter assembly in the same manner as in the step of draining the downstream side of the filter assembly. The cleaned slurry oil drained from the upstream side of the filter assembly will be directed to the liquid-liquid separator 30.

[0049] As is known, the contaminated slurry oil which enters the filter assembly from the FCC unit is quite hot, on the order of 450 F. to 550 F. (about 230 C. to about 290 C.). As discussed below, the washing method uses a low boiling point solvent (LBPS). Such solvents have boiling points, at atmospheric pressure, in the range of up to at least 175 F., and even up to about 300 F., which is well below the temperature of the slurry oil, and hence well below the temperature in the filter assembly 10 during normal filtration operation. For example, the low boiling point solvent can be dimethylformaldehyde, petroleum ether, chloroform, or methylene chloride (which have a boiling points, at atmospheric pressure, of about 136 F., about 108-144 F., about 142 F., and about 103 F., respectively). Thus, it is necessary to cool the filter assembly 10 to prevent flashing of the LBPS. The recycled slurry oil is at a temperature of between about 250 F. and about 350 F., and preferably about 300 F. The introduction of the recycled slurry oil will cool the filter assembly 10 down from the 450 F. to 550 F. of slurry oil coming from the FCC unit to approximately 300 F. The use of the recycled slurry oil thus accomplishes two purposespushing the contaminated slurry oil from the upstream side of the filter assembly through the filter elements to the downstream side of the filter assembly and simultaneously cooling the filter assembly. Other means can be used to cool the filter assembly. For example, cooling coils that surround (or pass through) the filter housing can be used to cool the filter assembly. Any other means can be used to cool the filter assembly. This cooling step reduces the temperature of the filter assembly and, in particular the filter elements, to reduce the temperature in the filter assembly to a point that will prevent flashing of the LBPS upon introduction of the LBPS.

[0050] Once the filter assembly has been cooled, a valve 28V in a solvent inlet pipe 28 is opened to allow solvent to flow into and through the filter assembly to start a front wash of the filter elements. The solvent is introduced into the filter assembly at a pressure of about 100 psig to about 250 psig, and preferably about 150 psig to about 175 psig. At these temperature and pressure conditions, the solvent will not flash, and thus will remain in a liquid state. The solvent enters the upstream side of the filter assembly at a ratio of solvent:cake retentate of about 1:1-100:1. The range can be, for example about 1:1-50:1 or about 1:1-25:1 or about 1:1-10:1. As further alternatives, the ratio can be about 5:1-50:1 or about 5:1-25:1 or about 8:1-50:1 or about 8:1-15:1 or about 8:1-10:1 or about 3:1-10:1 or about 4:1-9:1 or about 5:1-8:1 or about 6:1-7:1.

[0051] During the front wash, the solvent flows through the filter elements from the upstream side of the tube sheet to the downstream side of the tube sheet and fills the filter housing 12 to a level in which the filter elements 16 are substantially covered. As the LBPS flows through the filter, the LBPS infuses into the pores of the catalyst filtrand to at least partially liberate hydrocarbons contained within the catalyst pores. At a temperature of around 300 F. and pressure of about 50 psig, it is expected that in excess of 90% (and potentially more than 94%) of the hydrocarbons contained within the catalyst pores will be liberated. The solvent also washes hydrocarbons from the outer surface of the catalyst. The solvent within the downstream side of the housing will thus have hydrocarbons entrained in the solvent. This solvent/hydrocarbon stream will exit the filter assembly through the exit pipe 20 to be delivered to a liquid-liquid separator 30 over a line 34 where the solvent will be separated from the hydrocarbon. The front wash continues until a solvent:filter cake ratio (on a volume:volume basis) of about 4:1 to about 8:1 is achieved. For a 50,000 BPD cat cracker (which produces about 2500 BPD slurry oil run down) this front wash step can take about 40 minutes when solvent is introduced into the filter assembly at about 20 gal/min (at the above noted pressure of about 50 psig). At the end of the front wash, the solvent is not drained from the housing assembly, and thus fills the housing assembly to at least the height of outlet pipe 20. As such, filter elements 16 are substantially submerged in solvent. Importantly, there is a gap between the top of the LBPS in the filter housing and the top of the filter housing. A period of additional time of front washing with cooled solvent may be required to facilitate the next step in the process (the backwashing step) to reduce the system temperature to a level suitable for backwashing

[0052] During the front wash, the resolution of the components of the front-washing, i.e. residual FCC slurry oil and solvent, are sent to the liquid-liquid separator 30, as noted above, where the LBPS is condensed and recovered. The recovered solvent can, for example, be recycled to be used as the front wash solvent. The liquid-liquid separator 30 can, for example, be similar to the separator disclosed in my above noted Pat. No. 9605214, which is incorporated herein by reference. Alternatively, the separator 30 can be any type of commercially available separator. The FCC Slurry Oil and/or mobilization hydrocarbon, in the case of SOCFB processing, is recovered from the liquid-liquid separator as a finished refinery product and stored for transport and sale.

[0053] After the front wash is completed, the valve 20V in the exit pipe 20 is closed. The valves 24V, 26V, and 28V are also closed. The valve 18V in the inlet line 18 remains closed. In addition, a valve 12V in (or below) the neck 12c is closed as well. Thus, the interior of the filter assembly is essentially isolated. Once the valves are closed, a valve 32V in a gas inlet pipe 32 is opened to introduce an inert gas, such as nitrogen, into the downstream side of the filter assembly. As illustratively shown, the gas inlet pipe 32 is located near the top of the housing 12. Preferably, the gas inlet opens into a gap above the LBPS in the housing 12. As such, the gas inlet line 32 preferably is above the outlet line 20. Gas is pumped into the housing until the pressure within the housing reaches about 50 psig to about 75 psig, and preferably, about 60 psig. At that point, the valve 12V in the neck 12c is opened (preferably quickly), and the gas and solvent flow through the filter elements, from the downstream side to the upstream side to dislodge catalyst retentate from the filter elements 16. This will force the catalyst down into the conical heel portion 12b of the housing, and then into the neck 12c. This backwash step essentially blows the solvent and catalyst particles out of the filter assembly through the neck 12c. The resolution of the components of the backwash mixture (i.e. the FCC catalyst retentate, solvent, and any residual FCC slurry oil blown out of the filter assembly when the valve 12V is opened) are sent to a solid-liquid separator 40 of any type to separate the solvent from the catalyst particles. For example, the solvent can be separated from the catalyst using a dryer, such as disclosed in my above-noted U.S. Pat. No. 9,605,214, to a vacuum dryer, such as a Ross Vertical Cone dryer, or to a heated dryer, such as a heated hollow flight dryer.

[0054] When a sufficient amount of solvent is used during the frontwash of the filter assembly, the resulting catalyst, dried of solvent, will be amenable to transport by typical FCC catalyst pneumatic transport systems. For example, additional solvent will not be necessary if the solvent:catalyst ratio is about 1:1 to about 8:1, preferably about 2:1 to about 8:1, and more preferably about 4:1, by volume.

[0055] Although not disclosed, one of ordinary skill in the art will recognize that the disclosed system will also include necessary pumping equipment to move the various solutions through the system.

[0056] While the specific embodiments have been described, numerous modifications come to mind without significantly departing from the spirit of the invention and the scope of protection should only be limited by the scope of the accompanying claims.