WO1996000764A1

WO1996000764A1 - Device for optimising the catalytic activity of endothermic units such as petrol reforming units

Info

Publication number: WO1996000764A1
Application number: PCT/FR1995/000830
Authority: WO
Inventors: Jean Dufourneaud
Original assignee: Jean Dufourneaud
Priority date: 1994-06-28
Filing date: 1995-06-22
Publication date: 1996-01-11
Also published as: FR2721534A1; AU2798695A

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

DEVICE FOR OPTIMIZING THE CATALYTY ACTIVITY OF ENDOTHERMIC UNITS SUCH AS ESSENCE REFORMING.

The present invention relates to 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 on a platinum-based catalyst give a good example of such highly endothermic reactions requiring a high temperature, 400 ° C. to 600 ° C., for example, in order to obtain good operation. 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 processes have several significant drawbacks: - In each reactor, the temperature is not homogeneous due to the 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 way we can say that the part of catalyst at lower temperature will be less effective and will give reactions of less severity, while the part of catalyst brought to temperature higher than the desired optimal value will undergo deposits of coke larger than the average 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 production stoppage.

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 most favorable kinetics for the desired reactions. The invention also makes it possible to reduce the power of the recycling compressor for the catalytic reforming units of gasolines because several pieces of equipment (5 to 7 reactors and ovens), located in series on the recycling circuit, are replaced by a single one, the reactor- recovery heat exchanger, consisting of parallel tubes containing the catalyst. The regeneration of the catalysts is conventional and known to those skilled in the art.

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 in the old simple units, in an i-continuous manner, operating successively on fractions of the set of tubes containing the catalyst, which can be isolated from the reaction circuit during the regeneration.

FIG. 1 is a simplified process diagram of the reaction section of a conventional catalytic reforming of gasolines. FIG. 2 is the process diagram of the reaction section of the same catalytic reforming according to the invention

Figure 3 is a block diagram of a multi-function oven spanning multiple units and showing successive levels of heat recovery on the fairies.

Figure 4 is the block diagram of an isolable element of the recovery reactor-exchanger. Figure 5 is a sectional diagram of an elementary tube of the recovery reactor-exchanger.

Figure 6 is a sectional diagram of a variant of an elementary tube of the recovery reactor-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 process of catalytic reforming of gasolines, which is therefore not limiting. The process of catalytic reforming of gasolines is known to one skilled in the art.

Figure 1 is a simplified process diagram of the reaction section of a conventional gasoline catalytic reforming. Figure 1 shows a simplified reaction section with 3 ovens and 3 reactors in series to preheat the products intended for reforming reactions and then ensure 1 * thermal back-up 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 (FI) and passes over the catalyst of the first reactor (RI). The reactions take place in the gas phase. The endothermic reactions lower the temperature of the products leaving the reactor (RI) too much for the reactions to be able to continue under acceptable conditions in the second reactor (R2), so the effluent from (RI) 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 exchanger (El) then condensed again in the condenser (Al) before reaching the separator flask (Bl), 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 partial hydrogen 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 an exchanger (E10) then further condensed in a condenser (A10) before reaching a separator flask (B10). The gas phase of the separator flask (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 (RI), (R2), (R3) and the ovens (F2), (F3) are replaced by a single piece of equipment (ERIO), a heat-recovery reactor-exchanger. It recovers heat from the fumes leaving the radiation zone of at least one furnace (FIO). The reactor-exchanger is conventional and known to those skilled in the art.

The refining furnace with radiation zone is conventional and known to those skilled in the art.

The recovering reactor-exchanger can advantageously constitute 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 (s) used will be installed in a fixed bed inside the tubes of the reactor-exchanger. Thus it contains the catalysts of the reactors (RI), (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 (ERIO) 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 (FIO) the greater part of the thermal energy necessary for one or more associated units. The heat transfer fluid consists of the fumes from (FIO). Energy is supplied at the highest level in the radiation zone of (FIO) where the gases are at 800 ° C 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 the same zone, the load of another associated unit (11) may also be preheated, such as the pretreatment intended to desulfurize the load 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 ° C. 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 reforming catalytic, in the recovery reactor-exchanger (ERIO), located in the convection zone of the furnace (FIO), or even completely independent of the radiation zone, and receiving the hot gases by flues and ducts, said reactor-exchanger ( ERIO) being divided into several elements, ER10A, 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 according to their level as well as the regulation of the distribution to the users is obtained by the use of simple registers on the circuits of fumes. These registers are operated automatically by .operators or servomotors, 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 between users in parallel with 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 excess smoke to 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 (FIO) is not oversized, but exceptionally, and to complete the flexibility of the assembly, it can be admitted that in the event of a deficit in the medium or low energy levels, a portion, in excess, of the combustion gases of (FIO) 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 zone. Being exceptional, this bypass is not shown. The recovery reactor-exchanger (ERIO) consists of several elements, (ER10A), (ER10B).

Figure 4 is the block diagram of an isolable element (ER10A) of the recovery reactor-exchanger (ERIO). The element can comprise one or more elementary tubes and that (ER10A) represented in example comprises the 3 tubes ER10A1, ER10A2, ER10A3.

Figure 5 is a sectional diagram of an elementary tube of the recovery reactor-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 quick and easy disassembly and giving direct access to the catalyst contained in the tube. According to a characteristic of the invention, the catalyst may 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 reactor-exchanger, and the two ends of each catalyst cartridge comprising a metallic grid or any another device retaining the catalyst trapped in the cartridge, but allowing free passage to the gaseous 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 element of the reactor-exchanger 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 can be a simple tube which 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 heat boost 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 occur reactions 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 back-up per unit volume of catalyst necessary to maintain the temperature of the catalyst at its optimal 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 the exit of the tube is the seat of the slowest reactions or not endothermic, and requires little additional heat per unit volume of catalyst. From this it appears that the desirable thermal addition 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 inlet of the reactive products, an average flux for the middle part of the tube and a weak or zero flux for the part of the tube corresponding to the outlet of the products. Given that the temperature of the hot fluid in the reactor-exchanger (ERIO) varies little and that the surface of the bare tube containing the catalyst is imposed when its diameter has been fixed, according to a characteristic of the invention, will be able 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 then few fins or bare tube for the part near the product outlet. The tube can also protrude from the reactor-exchanger and the part of the catalyst no longer requiring additional heat is outside.

Figure 6 is a sectional diagram of a variant of an elementary tube of the recovery reactor-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 we can use cartridges of shorter catalyst and separated by spaces without catalyst, whether or not lined 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

CLAIMS.

1) 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 thermal 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 at least one furnace (FIO) and the wall to be heated constituted by the envelope elementary tubes containing the catalyst forming the recovery exchanger (ERIO).

2) Device according to claim 1 and characterized in that all of the elements containing the catalyst and receiving the hot fumes leaving the radiation zone of the furnace can constitute the conventional convection zone of this same furnace and be located above the radiation area, or be completely independent of the radiation area and receive the hot smoke by flues and ducts.

3) Device according to claim 1 and characterized in that the hot fumes used to maintain the temperature of the elements containing the catalyst are collected in enclosures containing bundles of tubes, possibly with fins improving 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 completely independent of the oven and to receive the hot fumes by flues and ducts.

4) Device according to claim 1 and characterized in that 1 'heat exchange between the hot fumes and the catalyst installed and maintained in place inside 1 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.

5) Device according to claim 1 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 retaining or promoting heat exchange.

6) Device 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 towards these same elements, said elements then being connected to a special circuit for regeneration.