FR2721534A1 - Method and device for optimizing the catalytic activity of endothermic units such as the reforming of gasolines. - Google Patents

Abstract

A device for one or more combined units including at least one highly endothermic catalytic unit in which a major part of the heat energy is generated in the radiation area of at least one furnace (F10) and where extra heat is added by recovering heat from the fumes at thermal levels dependent on the user level, in recovery exchangers. Such compact facilities are achieved by dispensing with many furnaces and reactors and placing the catalysts in exchanger tubes (ER10), and the activity of the catalysts is optimised by maintaining them at a temperature as close as possible to the most desirable temperature for the related endothermic reactions.

Description

METHOD AND DEVICE FOR OPTIMIZING CATALYTIC ACTIVITY
ENDOTHERMIC UNITS SUCH AS ESSENCE REFORMING.

 The present invention relates to a method and a device making it possible to maintain the temperature of the various endothermic catalytic reactions at the optimum operating operating value of the catalyst throughout the duration of the reactions, while minimizing the number of devices. In the field of petroleum refining, the gasoline reforming units based on a platinum catalyst give a good example of such highly endothermic reactions requiring a high temperature, 400 OC to 600 OC, for example, to obtain a good functioning of the catalyst. .

We currently know various processes carried out industrially, making it possible to carry out these endothermic reactions. One of their general characteristics is that they have several reactors in series and an oven before each reactor. The endothermic reactions in each reactor lower the temperature of the products leaving it and the oven makes it possible to raise the temperature of the products again to the desired value before entering the next reactor. These methods have several significant drawbacks:
-In each reactor the temperature is not homogeneous due to endothermic reactions. The optimum temperature for the catalyst is therefore only reached in a small part of the reactor and the catalyst cannot be used to the best advantage. In a simplified manner it can be said that the part of catalyst at lower temperature will be less effective and will give less severe reactions, while the part of catalyst brought to a temperature above the desired optimum value will undergo larger than average coke deposits and will have to be regenerated more frequently.

 -The multiplication of equipment (reactors and ovens) in the reaction circuit is costly in investment and increases the pressure losses to be overcome in this circuit in particular by the recycling gas compressor which is by far the largest consumer of mechanical energy .

 -On simple conventional units, the regeneration of the catalyst requires a general shutdown of the installations in order to regenerate the catalyst of all the reactors at once.

This causes a fairly long stoppage of production.

On the contrary, on very modern units, the catalyst can be regenerated continuously, but at the cost of a very sophisticated and expensive device which extracts catalyst continuously and returns it to the reactors after regeneration in an external annex installation. Another drawback is the gradual loss of part of the catalyst by attrition during the pneumatic transport of the regeneration circuit.
The device according to the invention overcomes these drawbacks. Indeed, it solves the problem of the operating temperature of the catalyst and makes it possible to choose for the whole of the catalyst the temperature giving the kinetics most favorable to the desired reactions.

The invention also makes it possible to reduce the power of the recycling compressor for the catalytic reforming units of gasolines insofar as several pieces of equipment (5 to 7 reactors and ovens), located in series on the recycling circuit, are replaced by a single one, the recovery exchanger, consisting of parallel tubes containing the catalyst. The invention also provides the advantage of sophisticated units provided with continuous regeneration of the catalyst, that is to say of not stopping production during regeneration, and without having the drawback of the progressive deterioration of the catalyst. By attrition. This being obtained by regenerating the catalyst in place, as on the old simple units, semi-continuously, by operating successively on fractions of the set of tubes containing the catalyst, which can be isolated from the reaction circuit during the regeneration.

 Figure 1 is a simplified process diagram of the reaction section of a catalytic reforming of conventional gasolines.

FIG. 2 is the process diagram of the reaction section of the same catalytic reforming according to the invention
FIG. 3 is a block diagram of a multifunction oven covering several units and showing the successive levels of heat recovery from the flue gases.

 Figure 4 is the block diagram of an isolable element of the recovery exchanger.

 Figure 5 is a sectional diagram of an elementary tube of the recovery exchanger.

 Figure 6 is a sectional diagram of a variant of an elementary tube of the recovery exchanger.

The invention relates to endothermic reactions in general but in order to facilitate understanding throughout the rest of the description relates to the particular case of the well-known process of catalytic reforming of gasolines, which is therefore not limiting.

Figure 1 is a simplified process diagram of the reaction section of a conventional catalytic gasoline reforming. Figure 1 shows a simplified reaction section of 3 ovens and 3 reactors in series to preheat the products intended for reforming reactions and then ensure the 'thermal addition to compensate for the endothermicity of the reactions. Most generally the reaction sections comprise 4 ovens and 4 reactors.

In a simplified way, the liquid feed (1), a naphtha type petroleum cut, receives the gaseous hydrogen recycle cut (2), recovers heat from the effluent of the last reactor (R3) in the exchanger (El) , is brought to the desired reaction temperature in the furnace (F1) and passes over the catalyst of the first reactor (R1). The reactions take place in the gas phase. The endothermic reactions lower the temperature of the products leaving the reactor (R1) too much for the reactions to be able to continue under acceptable conditions in the second reactor (R2), so the effluent from (R1) must be brought to temperature again desired by the second oven (F2). Likewise for the following reactors and ovens up to the exit of the last reactor, here (R3). The effluent from the last reactor is partially condensed in the recovery exchanger (El) then condensed again in the condenser (Al) before reach the separator flask (B1), the liquid phase (4) of which is directed to the distillation section to give the finished product of the reforming unit, the reformate.

The gas phase of the separator flask (B1) is taken up by the recycling compressor (K1) to ensure the desired hydrogen partial pressure in the reaction section.

The excess hydrogen produced (3) is directed to other units. The simplified diagram very clearly shows that the compression ratio of the recycling compressor and therefore its power is directly linked to the complexity and the number of devices in the reaction circuit.

FIG. 2 is the process diagram representing the reaction section according to the invention. As in the conventional process, the reaction effluent is partially condensed in a recovery exchanger (E10) then further condensed in a condenser (A10) before reaching a separator flask (B10). The gas phase of the separator tank (B10) is taken up by a recycling compressor (K10) to ensure the partial hydrogen pressure. In accordance with the present invention, all of the reactors (R1), (R2), (R3) and the ovens (F2), (F3) are replaced by the single equipment (ER10). This equipment is a heat recovery exchanger. It recovers heat from the fumes leaving the radiation zone of the oven (F10) for preheating products intended for endothermic reactions. This exchanger can advantageously be constituted as the convection zone of an oven and include an enclosure channeling the passage of fumes around the tubes in which the products participating in endothermic reactions circulate. According to a characteristic of the invention, the catalyst or catalysts used will be installed in a fixed bed inside the tubes of the exchanger. Thus it contains the catalysts of the reactors (R1), (R2) and (R3), and it provides the thermal support compensating for the endothermic effect of the reactions. According to another characteristic of the invention, this equipment (ER10) may advantageously consist of isolable elements installed in parallel on the reaction circuit and each containing a fraction of the catalyst. The elements being in parallel on the reaction circuit, each element will be the seat of all types of reactions. According to another characteristic of the invention, the elements being in parallel, it will be possible to isolate them from the reaction circuit, element by element , to regenerate the catalyst without stopping the production of the unit. More generally, each element may be heated, by a liquid or gaseous heat fluid, by electric heating or any other means suitable for the process.

FIG. 3 is a block diagram of a multifunction oven covering several units and showing the successive levels of heat recovery from the flue gases. This is a special case of a device making it possible to produce in the radiation zone of a single conventional oven (F10) the greater part of the thermal energy necessary for one or more associated units. The heat transfer fluid consists of the combustion gases from (F10). Energy is supplied at the highest level in the radiation zone of (F10) where the gases are at 800 OC and above, for example up to the flame temperature of the burners. In this radiation zone will be preheated for example the charge of the reforming unit (1) to the desired temperature for endothermic reactions. In this same zone can also be preheated the charge of another associated unit (11) as the pretreatment intended to desulfurize the charge of the reforming.

The fumes leaving the radiation zone of (F10) provide thermal energy at the average level, that is here, for example, between 400 and 1000 OC. According to a characteristic of the invention, it is this energy at a medium level which, in particular, compensates for the energy consumption of the endothermic reactions of the catalytic reforming, in the recovery exchanger (ER10), located in the convection zone of the oven (F10), or completely independent of the radiation area, and receiving the hot gases by flues and ducts, said exchanger (ER10) being divided into several elements, A, B, C, D, ..., isolable, smoke side by simple conventional registers and process fluid side, by sealed isolation valves.

According to a characteristic of the invention, the fumes leaving the recovery at a medium level are directed to the recovery at low temperature, ie for example between 300 and 600 ° C., and at this thermal level it will be possible for example to reboil the columns of distillation of the associated units, here, reforming (4) and pretreatment (12), this recovery being carried out in parallel exchangers equipped with tubes advantageously of the type with increased surface area by fins or the like, and which can be located entirely outside the oven (F10), and receive the hot gases through flues and ducts.

A final recovery can also be made on the fumes leaving the recovery at low temperature, for example by preheating the combustion air of the oven (F10). This ultimate recovery is not shown here because it concerns more the know-how of the furnace manufacturer than the catalytic process. The flexibility of use of this device for distributing thermal energies as a function of their level as well as the regulation of the distribution to users is obtained by the use of simple registers on the smoke circuits. These registers are operated automatically by operators or servo-motors, pneumatic, electric or other conventionally used to operate the control valves, and controlled by the usual regulation system of the unit. The distribution of energy among the users in parallel a given level is therefore done by opening more or less the registers of these users, and if the overall energy balance of this level is surplus, a bypass, also equipped with a register under automatic control, allows the smoke in excess of bypass this energy level and go directly to the lower level. The general optimization of this thermal energy utilization device assumes that the radiation area of the oven (F10) is not oversized, but exceptionally, and to complete the flexibility of the whole, it can be admitted that in the event of a deficit in the average or low energy levels, a part, excess ire, combustion gases from (F10) is extracted from the radiation zone, by a by-pass controlled by a register as in the following levels, without having participated in the heat exchange of this zone, and completes the flow of fumes leaving the radiation area. Being exceptional, this bypass is not shown.

The recovery exchanger (ER10) is made up of several elements, such as (ER1OA), (ER1OB).

Figure 4 is the block diagram of an isolable element (ER1OA) of the recovery exchanger (ER10). The element can comprise one or more elementary tubes and that (ER1OA) represented in example comprises the 3 elementary tubes
ERlOAl, ER1OA2, ER1OA3.

Figure 5 is a sectional diagram of an elementary tube of the recovery exchanger. This elementary tube will advantageously be made from standard tube usually used in the petroleum industry. At one of its ends, an opening with a flange and counter-flange of the same diameter as the tube will be preferred, allowing an easy and rapid disassembly and giving direct access to the catalyst contained in the tube. According to a characteristic of the invention, the catalyst can advantageously be packaged in the form of cylindrical cartridges with an outside diameter slightly smaller than the inside diameter of the elementary tube of the exchanger, and the two ends of each catalyst cartridge comprising a metal grid or any other device retaining the catalyst trapped in the cartridge , but leaving free passage to the gas flow of the process participating in the reactions. The solid catalyst is generally in the form of small spheres or small cylinders and it may be advantageous to put, at one or both ends of the cartridge, a layer of solid particles having a larger particle size than the catalyst, such as alumina or other beads. The first advantage of this conditioning of the catalyst is to allow rapid and clean handling, without heavy external means. The second advantage is to be able to leave a free space of selected length between two catalyst cartridges if this is judged favorable for the reactions or the heat exchange. The third advantage is to be able to operate this exchanger element in a vertical or horizontal position and with the gas flow rising or falling since the catalyst is held in place by its cartridge.

The elementary tube may be a simple tube that is smooth on the outside, but it is also possible to improve the heat exchange by increasing the exchange surface by using tubes with an extended surface, by fins or other similar means, as in air cooler tubes, with fins. Without going into the complexity of endothermic reactions and to stay on the example of gasoline reforming, we can say that part of the reactions is extremely fast, like the dehydrogenation of naphthenes into aromatics and will therefore occur at the very beginning of the passage reactive products on the catalyst and therefore require a significant additional heat on a small amount of the catalyst encountered first by the reactive products, if one wants to maintain the temperature of the catalyst at its optimal value. Then reactions occur which can be just as endothermic, but whose kinetics are slower, such as for example the dehydrocyclization of paraffins and in this case the thermal addition per unit volume of catalyst necessary to maintain the temperature of the catalyst at its optimum value is less. The catalyst concerned is located downstream from the previous one, in the direction of flow of the reactive products. Finally, the last part of the catalyst encountered before leaving the tube is the site of the slowest or non-endothermic reactions, and requires little thermal back-up per unit volume of catalyst. From this it appears that the desirable thermal back-up to the tube containing the catalyst is not homogeneous throughout the tube. It is desirable to achieve a greater thermal flux on the side of the tube corresponding to the entry of the reactive products, an average flow for the middle part of the tube and a weak or zero flux for the part of the tube corresponding to the exit of the products. Since the temperature of the hot fluid in the exchanger (ER10) varies little and the surface of the bare tube containing the catalyst is imposed when its diameter has been fixed, according to a characteristic of the invention, it will be possible to act on the developed exchange surface ("finned tubes") of the tube by choosing high and tight fins for the part close to the product inlet, medium fins for the middle part and then few fins or bare tube for the part near the product outlet. The tube can also protrude from the exchanger and the part of catalyst no longer requiring additional heat is in the part external to the exchanger.

Figure 6 is a sectional diagram of a variant of an elementary tube of the recovery exchanger. According to a characteristic of the invention, the part where the kinetics of endothermic reactions is the highest, that is to say the part of the tube where the desired thermal back-up is the most intense, will be voluntarily increased so as to spread the heat exchange over a longer length of the tube.

For this, use may be made of shorter catalyst cartridges separated by spaces without catalyst, whether or not filled with material inert to the reactions.

Long catalyst cartridges may also be used, but with the catalyst diluted with an inert material with regard to the rapid exothermic reactions considered, or with catalyst layers separated by spaces filled or not with a lining which can improve the exchanges. but not participating in the reactions.

Claims (10)

CLAIMS.  1) Process for optimizing the heat recovery and the activity of the endothermic reaction catalysts operating at high temperature, as on the catalytic reforming units of gasolines, and characterized in that the heat input necessary to maintain the catalyst at the optimum temperature reaction is carried out continuously by direct heat exchange on the elementary tubes containing the catalyst in a fixed bed.  2) Method according to claim 1 and characterized in that the regeneration of the catalyst can be done without having to stop the unit, thanks to the possibility of isolating the elements containing the catalyst to be regenerated, as well as the thermal back-up to these same elements, said elements then being connected to a special circuit intended for regeneration.  3) Method according to claim 1 concerning associated units whose thermal input is obtained by the combustion of a fuel giving very hot gases and characterized in that the greatest possible part of the thermal input for all associated units concerned is obtained in a single device making it possible to optimize the use of hot gases, in the sense that the hottest gases are used to raise the temperature of the reactive products to the reaction temperature, then these same gases brought to mean temperature are used to maintain the catalysts at the optimum reaction temperature, and finally these gases at a lower temperature after the exchange at medium temperature, serve as thermal back-up at the lowest levels of the installation, part of said hot gases , possibly in excess at one of the thermal levels, goes through a bypass circuit parallel to the users of said level, and under control e,  4) Method according to claim 1 concerning units of the type of catalytic reforming of gasolines and characterized in that maintaining the temperature of the catalyst at its optimum level of reaction makes it possible to carry out all of the types of reactions in a single elementary tube containing the catalyst, knowing that the catalytic unit will comprise in parallel as many elementary tubes containing the catalyst as necessary to ensure the capacity and take account of the regeneration, and that each elementary tube may contain a single catalyst or more of different types.  5) Device for optimizing energy consumption and improving the activity of endothermic reaction catalysts operating at high temperature, as on the catalytic reforming units of gasolines, and characterized in that the heat input necessary to maintain the catalyst at the optimum reaction temperature is achieved continuously by heat recovery with direct exchange between the hot fluid constituted by the flue gases leaving the radiation zone of an oven (F10) and the wall to be heated constituted by the envelope of the tubes elements containing the catalyst.  6) Device according to claim 5 and characterized in that all of the elements containing the catalyst and receiving the hot gases leaving the radiation zone of the oven can constitute the conventional convection zone of this same oven and be located above the radiation area, or be completely independent of the radiation area and receive the hot gases through flues and ducts.  7) Device according to claim 5 and characterized in that the hot gases necessary for maintaining the temperature of the catalyst will be obtained at the satisfactory temperature for the proper functioning of the recovery exchanger (ER10) by the radiation zone of the furnace (F10 ) used to raise the temperature of the reactive products of the different units before they reach the catalysts.  8) Device according to claim 5 and characterized in that the hot gases used to maintain the temperature of the elements containing the catalyst are collected in enclosures containing bundles of tubes, possibly with fins improving the heat exchange, so that their residual heat is still recovered, for example for reboiling the distillation columns or preheating combustion air from the oven, said heat recovery being able to be independent of the oven and receiving the hot gases by flues and ducts.  9) Device according to claim 5 and characterized in that the heat exchange between the hot gases and the catalyst installed and kept in place inside an elementary tube in the form of cartridges can be improved and modulated by the use fins non-homogeneously along the tube, larger or more numerous fins being positioned at the places where it is sought to locally increase the thermal back-up, for example by choosing tall and tight fins for the part close to the inlet of the products, medium fins for the middle part then few fins or bare tube for the part close to the outlet of the products, said tube possibly also protruding from the exchanger and the catalyst part no longer requiring additional heat be in the external part to the exchanger.  10) Device according to claim 5 and characterized in that the intensity of endothermic reactions, can locally be attenuated by locally diluting the catalyst in its elementary tube, or by spacing layers of catalyst by layers of inert material as regards reactions but promoting heat exchange, part of said inert material can be positioned at the ends of the catalyst cartridge and be of different particle size than that of the catalyst.