Optimized Reactor Centerpipe

This application claims priority to U.S. Provisional Patent Application Ser. No. 63/568,931, filed on Mar. 22, 2024, the entirety of which is incorporated herein by reference.

In a common form, the reforming process can employ the catalyst particles in several reaction zones interconnected in a series flow arrangement. There may be any number of reactors in the reforming reaction zone, but usually the number of reaction zones is 3, 4 or 5. Because reforming reactions occur generally at an elevated temperature and are generally endothermic, each reaction zone usually has associated with it one or more heating zones, which heat the reactants to the desired reaction temperature.

The catalyst particles are typically comprised of one or more Group VIII (IUPAC 8-10) noble metals (e.g., platinum, iridium, rhodium, and palladium) and a halogen combined with a porous carrier, such as a refractory inorganic oxide. U.S. Pat. No. 2,479,110, for example, teaches an alumina-platinum-halogen reforming catalyst. Although the catalyst may contain about 0.05 to about 2.0 wt-% of Group VIII metal, a less expensive catalyst, such as a catalyst containing about 0.05 to about 0.5 wt-% of Group VIII metal may be used. In addition, the catalyst may contain indium and/or a lanthanide series metal such as cerium. The catalyst particles may also contain one or more Group IVA (IUPAC 14) metals (e.g., tin, germanium, and lead), such as described in U.S. Pat. Nos. 4,929,333, 5,128,300, and the references cited therein. The halogen is typically chlorine, and alumina is commonly the carrier. Suitable alumina materials include, but are not limited to, gamma, eta, and theta alumina. One property related to the performance of the catalyst is the surface area of the carrier. Preferably, the carrier has a surface area of about 100 to about 500 m2/g. The activity of catalysts having a surface area of less than about 130 m2/g tend to be more detrimentally affected by catalyst coke than catalysts having a higher surface area. Generally, the particles are usually spheroidal and have a diameter of about 1.6 to about 3.1 mm (about 1/16 to about ⅛ inch), although they may be as large as about 6.35 mm (about ¼ inch) or as small as about 1.06 mm (about 1/24 inch). In a particular reforming reaction zone, however, it is desirable to use catalyst particles which fall in a relatively narrow size range.

Typical feed inlet temperature for the reformers are between 440 and 580° C. (824 and 1076° F.), or between 500 and 580° C. (932 and 1076° F.), or between 540 and 580° C. (1004 and 1076° F.), or at least above 540° C. (932° F.). The reformers may have different operating temperatures, for example, with a first reforming reactor having a temperature between 500 to 540° C. (932 to 1004° F.) and a second, subsequent reforming reactor having a temperature greater than 540° C. (1004° F.). The reformers can be operated at a range of pressures generally from atmospheric pressure of about 0 to about 6,895 kPa (g) (about 0 psi (g) to about 1,000 psi (g)), or about 276 to about 1,379 kPa (g) (about 40 to about 200 psi (g)). The lower operating pressure is especially preferred to achieve higher aromatic yield. The reaction conditions also include a liquid hour space velocity (LHSV) in the range from 0.6 hr−1 to 10hr−1. Preferably, the LHSV is between 0.6 hr−1 and 5 hr−1, with a more preferred value between 1 hr−1 and 5 hr−1, and with a most preferred value between 2 hr−1 and 5 hr−1. The catalyst also has a residence time in the reformers of between 0.5 hours and 36 hours.

There is a desire for a low cost solution to improving process benefits such as

improved aromatic yield, hydrogen yield, higher reformate octane and/or higher unit throughput without increasing the size of the reforming reactor.

The optimized centerpipe of the present invention increases the volume of the catalyst bed in new or existing reactors by optimizing the centerpipe geometry.

For existing reforming units, the centerpipe can be optimized using this approach which allows the catalyst volume to be increased by 3 to 25% without replacing the reactor shell and without the catalyst pinning constraints. The increase in the unit operating margin by higher aromatic yield performance or higher reformate RONC (research octane number, clear) products, higher hydrogen yield or/and higher unit throughput provides an economic justification for revamping the existing stacked reactor centerpipe in a refinery.

A revamped unit with an optimized reactor center pipe could significantly increase the amount of catalyst in the existing reactor.

The optimized centerpipe can be used in conjunction with improved catalysts to further improve aromatic and/or hydrogen yields and/or throughput of the unit.

In particular, the center pipes in reactors 2, 3, and 4 commonly have a generous amount of catalyst pinning margin compared to reactor 1 for a stacked reactor arrangement or side-by-side reactor arrangement. For a radial flow reactor with a moving bed catalyst, the reactant flows from the scallop to the centerpipe, When the flow rate through a given cross section area of the centerpipe is too high, the radial flow would pin the catalyst pill against the centerpipe wall, increasing its friction and this could prevent the catalyst from moving. When the centerpipe diameter decreases, the gas flow rate for a given cross section area of the centerpipe increases. To avoid catalyst pinning, the centerpipe diameter must be large enough to avoid pinning. However, it would become wasteful with lower reactor utilization if the centerpipe diameter is larger than necessary.

The centerpipe comprises a top connection section, a bottom connection section and an intermediate section.

The diameter of the perforated section or screen (the intermediate section) of the reactor centerpipe may be reduced for optimization, while retaining the original centerpipe outlet diameter and the geometry of the existing centerpipe support plate. In another words, the diameter of the profile screen section is smaller than the rest of the centerpipe. By keeping the top and bottom of the centerpipe geometry the same as the original dimensions, it enables the refinery to replace the existing centerpipe with this concept without modifying the rest of the reactor. Therefore, it has little or no impact in turnaround duration, or loss of production compared with replacing it with larger stacked reactor shell having the same configuration as the existing centerpipe.

Typically, the top flange area and the bottom plate of the centerpipe will not be modified. There is a transition from the top flange area to the intermediate section of the centerpipe at an angle of about° to° from vertical. The transition cone can be made of blankoff or slotted plate which can avoid stagnant catalyst and allow gas to pass through. The transition cone enhances catalyst and gas flow distribution. The intermediate section has a smaller diameter than the top flange plate, the bottom plate, or both. The intermediate section has openings or perforations.

In some embodiments, the intermediate section will be reduced only with respect to the top connection, or only with respect to the bottom connection, or with respect to both the top and bottom connections.

The reduction in the diameter of the intermediate section can be done in one or more of the reforming reactors. The reduction could be the same in all reactors, or it could be different in one or more of the reactors.

There are several factors to consider in providing the transition between the intermediate section of the centerpipe and the bottom connection which has a larger diameter. The design should minimize stagnant catalyst buildup and heel catalyst formation (catalyst with coke level greater than 10% due to stagnant nature) and provide good gas flow distribution. It should retain the mechanical integrity of the centerpipe. Finally, it should minimize or eliminate the need for additional field work for implementation or centerpipe installation for a revamped unit.

One possibility for the bottom of the optimized centerpipe involves multiple ceramic ropes that loop around the very bottom of the profile wired screen. The ceramic rope system is made of more than one ceramic ring with different rope diameters. By placing a loop with smaller diameter rope at the top and a loop with bigger diameter rope at the bottom, together they form a 5 to 45 degree slope from vertical at the base of the optimized centerpipe. This angle is sufficient to overcome the angle of repose of catalyst pills such that no stagnant catalyst can be formed there. Alternatively, multiple bottom plates with increasing outer diameter, a conical ring made of slot plate or punch plates, a conical blanket off, or a transition cone could be used. Alternatively, the bottom transition can be made of a truncated cone that provides the slope angle to avoid stagnant catalyst. The truncated cone could be made of non-perforated or perforated plate.

The catalyst bed volume is defined by the annular space between the scallops and centerpipe for a radial flow reactor for a given reactor shell diameter and tangent length.

The diameter of the first reactor centerpipe is commonly sized based on pinning constraint (in some cases, it could be other constraints). The downstream reactors, e.g., reactors 2 to 4, typically have a large margin in pinning constraint. Many of the commercially operating reforming units have the same centerpipe outside diameters for all reactors for a given reactor stack. By doing so, all of them can be removed from the reactor body flange at the top of the stack for service and repair during turnaround.

The reactor pressure drop includes the inlet loss, the scallop riser loss, the axial loss along the scallop, the scallop front face, the catalyst bed (bed depth), the centerpipe screen, the perforated plate (artificial imposed pressure drop), the axial loss along the centerpipe, and the mitered elbow and the outlet loss.

For a reactor with tapered scallops (i.e., a bigger cross section area at the top and a smaller cross section area at the bottom), it would have a higher velocity head compared to the velocity head of the centerpipe. This could lead to higher skewed vapor maldistribution compared with non-tapered scallops. To overcome this, an artificial pressure drop could be imposed on the perforated centerpipe, but this leads to a higher overall reactor pressure drop leading to a higher reactor operating pressure.

To increase the aromatic yield and/or feed rate throughput of an existing reactor, a common revamp design includes adding a new reactor in the existing unit.

With a bigger reactor catalyst bed volume for a given catalyst bed height, the reactor pressure drop tends to be higher. The higher the reactor pressure drop is, the higher the operating reactor pressure is. Higher operating reactor pressure directionally decreases aromatic yields in the given operation condition. This is demonstrated bywhich shows the relationship of aromatic yield increase (due to bigger catalyst volume) with reactor pressure drop increase. The benefit of aromatic yield increase due to a given catalyst volume could be eroded by reactor pressure drop increase (or at higher operating reactor pressure.

It is well known that higher reactor pressure drop tends to reduce vapor mal-distribution in the catalyst bed.

Decreasing the centerpipe diameter increases the catalyst bed depth between the scallop and the centerpipe. Decreasing the centerpipe diameter reduces the area available for perforation or open area of the centerpipe screen. Together, they increase the pressure drop between the scallop and the screen of the centerpipe. To optimize catalyst and reactant contact for yield improvement, this is helpful to correct inherent axial vapor mal-distribution of a reactor bed. By reducing the vapor mal-distribution, a smaller artificial pressure drop can be imposed in the perforated plate of the centerpipe. This results in an overall increase in reactor pressure drop as measured from the reactor inlet flange to the reactor outlet flange.

Decreasing the centerpipe diameter leads to a higher velocity head. In some cases, it would become a better match to the scallop velocity head. With an improved balance in velocity heads, this could allow the design to impose a lower artificial pressure drop in the perforated plate of centerpipe while achieving the same or better vapor-distribution within the catalyst bed. This reduces the overall reactor pressure drop as measured between the reactor inlet flange and the reactor outlet flange.

The net result of the optimized centerpipe in most cases is the same or lower overall reactor pressure (reactor flange-to-flange). In some cases, there might be a slight pressure drop increase with the smaller centerpipe diameter, but with a significant increase in the catalyst volume, while maintaining or improving the mal flow distribution.

and Table 1 illustrate the results of a case study for the process. It is commonly believed that there is an inherent vapor axial mal-distribution along the length of the catalyst bed from top to bottom, and that an artificial pressure drop needs to be imposed in the centerpipe's perforated plates to correct the mal-distribution, resulting in a significant overall increase in reactor pressure drop between the inlet and outlet of the reactor. However, the case study demonstrates that reducing the centerpipe diameter leading to an increased catalyst volume for a given catalyst bed height actually helps to improve vapor mal-flow distribution. Therefore less artificial pressure drop can be imposed in the centerpipe's performated plate. The net result is that the overall reactor pressure drop increase (flange-to-flange) could remain the same or negligible increase when the diameter of the centerpipe is optimized. Catalyst volume increase can significantly improve aromatic yield. Even though higher operating reactor pressure due to increase in reactor pressure drop directionally decrease aromatic yield, the catalytic yield performance prediction kinetic model demonstrates that aromatic yield loss is not sensitive to slight operating pressure increases, as shown in. The sensitivity curve in, generated by the catalytic yield performance prediction kinetic model demonstrates that the aromatics yield increase is sensitive to the catalyst volume increase when the reactor centerpipe diameter is reduced without leading to significant flow mal-distribution. When the selection of the centerpipe diameter is properly optimized, it will significantly increase aromatic yield due to catalyst volume increase with little or no aromatic loss penalty due to increase in reactor pressure. The sensitivity curve inshows that there is a 0.036 wt % aromatic yield gain for every 1% of catalyst volume increase, i.e., 0.36 wt % of aromatic yield improvement for a 10% increase in catalyst volume. The sensitivity curve in

shows that the benefit of aromatic yield due to catalyst volume increase reduces by only 0.04 wt % for every 0.5 psid pressure increase. Table 1 shows that optimized centerpipe improved the vapor mal-distribution of reactor 4 from −4.5% to +0.3%, while the reactor differential pressure increased only by 0.28 psid.

When the openings in the perforated plate of the centerpipe are profiled instead of the commonly used even distribution (e.g., having more openings at the low flow centerpipe region and less openings at the high flow centerpipe region), it could potentially reduce the overall reactor pressure drop further while maintaining or improving mal-flow distribution.

The diameter of the reactor centerpipe is the same for most of the operating units in a stacked reactor for easy design (such as avoid swaging the shell diameter of reactor stack) and allows common spare centerpipe parts replacement. However, it is not necessarily the most optimal catalyst utilization to maximize aromatic yield for a given existing stacked reactor shell.

The case study demonstrates that the aromatic yield improvement from the catalyst volume increase enabled by an optimized centerpipe significantly outweighs the aromatic yield loss due to the small increase in the operation reactor pressure.

It is well known that it is very difficult to react C7 paraffins in the feed to form aromatics. This reaction is promoted by high reactor temperature and long residence time in the catalyst bed. Since the reforming reactions are mostly endothermal reactions especially in reactor 1, and less in reactors 3 and 4, the average catalyst bed temperature is higher in reactors 3 and 4 compared with reactor 1. Increasing the catalyst volume in reactors 3 and 4 by reducing the centerpipe diameter to be smaller than the centerpipe in reactor 1 provides the optimal kinetic conditions in terms of longer residence time and higher operating catalyst bed temperature to promote the C7 paraffin reaction conversion to aromatics and thus higher aromatic yields.

One aspect of the invention involves a method of increasing aromatic yield, or hydrogen yield, or reformate octane, or combinations thereof for a selected set of operating conditions in a reforming process. In one embodiment, the method comprises: providing a feed to a reforming reaction zone comprising at least two reforming reactors. The first reforming reactor comprising a first shell, a first centerpipe positioned in the first shell, and a first catalyst disposed between the first shell and the first centerpipe. The first centerpipe has a first top connection section having a first top diameter, a first bottom connection section having a first bottom diameter, and a first intermediate section having a first intermediate diameter, and first openings sized to permit a flow of feed and to prevent a flow of the first catalyst. The second reforming reactor comprises a second shell, a second centerpipe positioned in the second shell, and a second catalyst disposed between the second shell and the second centerpipe. The second centerpipe has a top connection section having a second top diameter, a bottom connection section having a second bottom diameter, and a second intermediate section comprising second openings sized to permit a flow of feed and to prevent a flow of the second catalyst. The second intermediate section has a second intermediate diameter less than the second top diameter, or the second bottom diameter, or both, of the second centerpipe, wherein the second intermediate diameter of the second intermediate section is less than a first intermediate diameter of the first intermediate section. The diameter of the first shell does not change, the diameter of the second shell does not change, the reactor tangent length of the first shell does not change, and the reactor tangent length of the second shell does not change. The feed is passed through the first and second catalyst in the first and second reactors forming a reaction product, and the reaction product is removed from the reforming reaction zone.

In some embodiments, the second centerpipe replaces a centerpipe in an existing reforming reactor comprising a top connection section, a bottom connection section, and an intermediate section, wherein a diameter of the top connection section, the bottom connection section, and the intermediate section of the existing reforming reactor are the same.

In some embodiments, the first top diameter and first bottom diameter of the first reforming reactor are the same as the second top diameter and the second diameter of the second reforming reactors.

In some embodiments, the ratio of the second intermediate diameter of the second intermediate section to the first intermediate diameter of the first intermediate section is in a range of 0.6 to 0.95.

In some embodiments, the difference between the first intermediate diameter of the first intermediate section of the first reforming reactor and the second intermediate diameter of the second intermediate section of the second reforming reactor is in a range of 1 inch to 30 inches, and wherein the first intermediate diameter of the first intermediate section is larger than the second intermediate diameter of the second intermediate section.

In some embodiments, the first or second centerpipe or both of the reforming reaction zone replace a first or second existing centerpipe or both in an existing reforming reaction zone comprising at least two reforming reactors, the first or second centerpipe or both in the existing reforming reactor comprising a first or second existing top connection section having a first or second existing top diameter, a first or second existing bottom connection section having a first or second existing bottom diameter, and a first or second intermediate section having a first or second existing intermediate diameter, wherein a ratio of the first or second intermediate diameter of the first or second intermediate section of the reforming reaction zone to the first or second existing intermediate diameter of the intermediate section of the first or second existing centerpipe or both in the existing reforming reactor is in a range of 0.6 to 0.95.

In some embodiments, the first top diameter, the first bottom diameter, and the first intermediate diameter of the first reforming reactor are the same. In some embodiments, the first intermediate diameter is different from the first top diameter, or the first bottom diameter, or both.

In some embodiments, the intermediate diameter of the second (or subsequent) reforming reactor is different from the top diameter of the top connection, or the bottom diameter of the bottom connection, or both.

In some embodiments, the first reforming reactor further comprises a first scallop comprising a front face, a back face, and opposing sides, the first scallop positioned between first shell and the first centerpipe wherein the first catalyst is disposed between the front face of the first scallop and the first centerpipe; or wherein the second reforming reactor further comprises a second scallop comprising a front face, a back face, and opposing sides, the second scallop positioned between second shell and the second centerpipe wherein the second catalyst is disposed between the front face of the second scallop and the second centerpipe; or both.

In some embodiments, a layer of the first intermediate section of the first centerpipe has a non-uniform pattern of the first openings, or a layer of the second intermediate section of the second centerpipe has a non-uniform pattern of the second openings, or both.

In some embodiments, the nonuniform pattern of the first openings comprises an area of the first openings near the bottom of the centerpipe less than an area of the first openings near the top of the centerpipe; or the nonuniform pattern of the second openings comprises an area of the second openings near the bottom of the centerpipe less than an area of the second openings near the top of the centerpipe; or both.

In some embodiments, the reforming reaction zone comprises at least one additional reforming reactor comprising at least one additional shell, at least one additional centerpipe positioned in the at least one additional shell, and at least one additional catalyst disposed between the at least one additional shell and the at least one additional centerpipe, the at least one additional centerpipe having a top connection section having an additional top diameter, a bottom connection section having an additional bottom diameter, and an intermediate section having an additional intermediate diameter, the intermediate section of the at least one additional reforming reactor comprising additional openings sized to permit the flow of feed and to prevent the flow of the at least one additional catalyst, the additional intermediate diameter of the intermediate section of the at least one additional reforming reactor being less than the first top diameter, or the first bottom diameter, or both of the intermediate section of the at least one additional reforming reactor, wherein the additional intermediate diameter of the intermediate section of the at least one additional reforming reactor is less than the first top diameter of the first intermediate section, or the second intermediate diameter of the second intermediate section, or both, wherein a diameter of the at least one additional shell does not change, and wherein a reactor tangent length of the at least one additional shell does not change.

illustrate one embodiment of a portion of a reforming reactoraccording to the present invention. The reactor shellis shown with a scallop. The dotted line shows the location of the original centerpipewhich is being replaced (or redesigned in a new reactor). The original catalyst volumeis contained between the scallopand the original centerpipe. The redesigned centerpipeprovides additional catalyst volume. The diameter of the centerpipe at the top (2RT) and/or the diameter of the centerpipe at the bottom (2RB) is greater than the diameter of the intermediate portion (2RI). There is a top transitionand a bottom transitionbetween the original centerpipewhich is being replaced and the redesigned centerpipe

The existing centerpipe supportis replaced with a new centerpipe support. This allows the existing connections at the top and/or the bottom to be maintained.

illustrates the method for optimizing the centerpipe diameter in a reforming reactor zone.

In one embodiment, the aromatic yield can be optimized by determining an optimized centerpipe diameter. The first stepis to reduce the intermediate diameter of the second centerpipe by a selected amount (X%) of the intermediate diameter of the first centerpipe. In the next step, the increased catalyst volume in the second reforming reactor is calculated based on the reduced intermediate diameter of the second centerpipe. In step, the aromatic yield increase is determined based on the increased catalyst volume, the previous operating reactor pressure, and the original reactor inlet temperature using a catalytic yield performance prediction model. In step, using new physical properties of the gas from the catalyst yield performance prediction model from stepand the reduced centerpipe diameter, a revised reactor pressure is calculated. In step, a new aromatic yield increase is determined based on the increased catalyst volume and the revised reactor conditions, such as new pressure and physical properties of the stream using a catalytic yield performance prediction model. In step, the new aromatic yield increase and reactor flow distribution are compared with a previous aromatic yield increase. If the new aromatic yield increase is greater than the previous aromatic yield increase, the process is repeated by returning to stepand selecting a greater catalyst volume increase. If the new aromatic yield increase is less than the previous aromatic yield increase, the previous selected reduced centerpipe and its corresponding catalyst volume increase provides the optimal aromatics yield increase and are selected step.