EP0117200A1 - Arrangement for the thermal transformation of a gaseous mixture containing hydrogen and hydrocarbons - Google Patents

Abstract

An installation for chemical conversion of a gas mixture containing hydrogen and hydrocarbons comprises a series of reactors in which the gas mixture undergoes endothermic reactions at temperatures within the range of 350 DEG C. to 900 DEG C. A furnace is placed upstream of each reactor for reheating the gas mixture prior to introduction into the reactor. The furnaces are equipped with electric heating resistors which are intended to be placed in direct contact with the gas mixture as it is introduced into each furnace.

Description

The present invention relates to an installation for the chemical transformation of a gas mixture containing in particular hydrocarbons and hydrogen.

This installation comprises reactors in which the above-mentioned mixture reacts according to globally endothermic reactions at temperatures between approximately 350 and 900 ° C., under high pressure and in the presence of a catalyst. This installation also comprises an oven arranged upstream of each reactor to heat the gas mixture before its introduction into the reactor.

• . le reforma^ge du naphta en présence d'un catalyseur à base de platine pour l'obtention des essences;
• . la désulfura--ion des hydrocarbures à l'hydrogène.

The invention mainly applies to the following installations:

• . the reformed ^g e naphtha in the presence of a platinum catalyst to obtain the species;
• . desulfurization - ion of hydrogen hydrocarbons.

In known installations, the furnaces for reheating the gaseous mixture of hydrocarbons and hydrogen are conventional furnaces supplied with liquid or gaseous fuel of fossil origin. These ovens include bundles of tubes of reduced section heated by combustion of fuel of fossil origin, in which the above-mentioned gas mixture is passed.

These reheating ovens have many drawbacks.

First of all, the passage of the gaseous mixture to be heated through the bundles of tubes leads to very large pressure drops, which requires the use of very high power compressors thereby consuming a lot of energy.

On the other hand, temperature regulation in such ovens is delicate and requires special attention from the operators of the installations.

In the case of a catalytic reforming installation, care must be taken in particular that the skin temperature of the tubes of these furnaces does not exceed 650 ° C. to avoid any risk of rupture of these tubes, which would have catastrophic consequences.

Furthermore, taking into account the shape of the flame, significant variations in skin temperature are observed along the tubes and in the same section, and which can be variable depending on the position of the tube considered.

In addition, the aforementioned flame ovens are bulky mainly depending on the fact that a single ply of tubes surrounds the flame.

On the other hand, the thermal efficiency of these ovens hardly exceeds 80% even in the case where the heat evacuated in the fumes from the combustion of fossil fuel is recovered by heat exchange.

In addition, the use of a fuel of fossil origin for the operation of these ovens leads to an additional consumption of an expensive energy product which it is advisable today to save, in particular in the Western countries, to limit the use in applications where this energy source is strictly essential.

The object of the present invention is to create an installation which overcomes all the aforementioned drawbacks.

The installation targeted by the invention for the chemical transformation of a gaseous mixture containing in particular hydrogen and hydrocarbons comprises a succession of reactors to react the above-mentioned mixture according to globally endothermic reactions at temperatures of between 400 and 900 ° C. approximately, under high pressure and in the presence of a catalyst. An oven is arranged upstream of each reactor to heat the gas mixture before its introduction into said reactor.

According to the invention, this installation is characterized in that the ovens are constituted by an enclosure comprising an inlet and an outlet of the gas mixture and containing one or more electrical resistance (s) for heating intended to be placed (s) in direct contact with the gas mixture introduced into this enclosure.

These electric ovens in which the electrical resistance is directly in contact with the gas mixture have a significantly lower pressure drop than that of conventional ovens.

Electric resistance heating furnaces thus replace furnaces supplied with fossil fuel, such as light or heavy fuel oil.

Consequently, it is possible either to reduce the power of the compressors used to recycle the gaseous effluents, or to reduce the overall energy consumption of the installation by adding to it one or more charge / effluent heat exchangers.

Furthermore, these electric ovens make it possible to regulate the heating temperature of the gas mixture in a much more precise and easier manner than in the case of conventional ovens, so that any risk of overheating liable to cause accidents is avoided and insufficient heating capable of reducing the yield of the reactions.

In addition, the thermal efficiency of these ovens is significantly higher than that of conventional ovens.

Furthermore, the fact that electricity is used as an energy source for these ovens avoids any additional consumption of fossil fuel, the cost of which is increasingly higher than that of electricity produced in hydroelectric and nuclear power plants.

According to a particular version of the invention, the installation comprises, in parallel with each furnace supplied with fossil fuel, an electric furnace constituted by an enclosure comprising an inlet and an outlet for the gaseous mixture and one or more electrical heating resistors intended to be placed in direct contact with the gas mixture introduced into this enclosure, and means for passing the gas mixture at will either through the furnaces supplied with fuel of fossil origin, or by the electric resistance furnaces.

Thus, such an installation could operate for example during the winter months in the conventional manner, using conventional ovens supplied with fuel of fossil origin and outside this period, using electric ovens, periods in which consumption overall electricity is less strong and where the cost of the latter can be more reduced.

Other features and advantages of the invention will appear in the description below.

• . la figure 1 est un schéma d'ensemble d'une installation de reformage catalytique du naphta;
• . les figures 2 et 3 sont des vues partielles de l'installation, montrant en particulier l'emplacement des vannes.

In the appended drawings given by way of nonlimiting examples:

• . FIG. 1 is an overall diagram of an installation for catalytic reforming of naphtha;
• . Figures 2 and 3 are partial views of the installation, showing in particular the location of the valves.

FIG. 1 schematically represents an installation for the catalytic reforming of naphtha obtained by distillation of crude oil, intended to produce gasolines with a high octane number.

This installation includes 4 reactors R ₁ , R ₂ , R ₃ , R ₄ in which the reforming reactions are carried out between a gaseous mixture of hydrocarbons enriched in hydrogen at temperatures around 500 ° C, pressures between 15 and 30 bars and in the presence of a platinum-based catalyst. These reactions are generally endothermic.

To this end, upstream of each reactor R ₁ , R ₂ , R ₃ , R ₄ is placed an oven F ₁ , F ₂ , F ₃ , F ₄ which makes it possible to preheat the mixture of hydrocarbons and hydrogen to the optimum temperature before this mixture enters the following reactor R ₁ , R ₂ , R ₃ , R ₄ .

The mixture 1 of hydrogen-enriched hydrocarbons is introduced into the first furnace F ₁ by means of a pump 2. The effluent 3 from the last reactor R ₄ passes through heat exchangers 4 disposed upstream of the first furnace F ₁ and arranged to carry out a heat exchange between this effluent 3 and the gas mixture 1 which is introduced into the first furnace F ₁ . This heat exchange makes it possible to preheat the initial gas mixture 1 before it enters the furnace F ₁ .

The effluent 3 after this heat exchange is cooled in an air cooler 5 then in a water cooler 6, before entering a separator flask 7 in which the gas to be recycled is separated from the reformate. This reformate is recovered at 8. Part of the gas to be recycled 9 coming from the separator 7 is compressed by means of a compressor 10 which re-injects it downstream of the pump 2 to mix it with the starting naphtha.

According to the invention, the installation includes in parallel with each furnace F ₁ , F ₂ , F ₃ , F ₄ supplied with fossil fuel, an furnace F ₅ , F ₆ , F ₇ , F ₈ constituted by an enclosure 11, 12, 13, 14 comprising an inlet 15a , 16a, 17a, 18a and an output 15b, 16b, 17b, 18b and which contains electrical heating resistors 19, 20, 21, 22.

These heating resistors 19 to 22 are placed in direct contact with the gas mixture introduced into each of the electric ovens F ₅ , F ₆ , F ₇ , F ₈ .

These electric ovens F ₅ , F ₆ , F ₇ , F ₈ are constructed in such a way that the mixture of hydrogen and hydrocarbons passes through these ovens with a low pressure drop. These electric ovens may conform to that described in French patent application No. 83 02763 of 21.2.1983, in the names of the applicants and which is entitled "Electric heating device by direct Joule effect to heat a gas mixture".

Furthermore, the installation according to the invention comprises means for passing the gas mixture at will either through conventional ovens F ₁ , F ₂ , F ₃ , F ₄ supplied with fossil fuel, or through the ovens with electrical resistances F ₅ , F ₆ , F ₇ , F ₈ . These means are constituted (see FIGS. 2 and 3) by valves V _I , V ₂ ... V ₄ , V ₅ placed at the inlet and at the outlet of conventional ovens F ₁ , ... F ₄ and of the valves V ₆ , V ₇ ... Vg, V ₁₀ placed on the branches 23 ... 27 which extend between the conventional ovens F _I ... F ₄ and the electric ovens F ₅ ... F ₈ .

It can also be seen in FIGS. 1 and 2 that one or more additional heat exchangers 28 are placed on the branch 23 comprised between the outlet 4a of the first exchangers 4 and the inlet 15a of the first electric furnace F ₅ . These exchangers 28 are arranged to carry out an additional heat exchange between the gas mixture introduced into the first electric furnace F ₅ and the gaseous effluent 3 coming from the last reactor R ₄ . Valves V ₁₁ , V ₁₂ placed upstream and downstream of the exchangers 28 on a circuit 29 connected with that of the effluent 3 and a valve V ₁₃ placed on a bypass circuit 30 directly connected to the first exchangers 4, allow either to passing the effluent 3 through the exchangers 28 during the commissioning of the electric ovens F ₅ , ... F ₈ , either directly and only in the first exchanger 4 during the commissioning of the conventional ovens F ₁ ,. .. F ₄ .

The pressure drop caused by the exchanger (s) 28 is less than the reduction in pressure drop achieved during the commissioning of the electric ovens F ₅ , ... F ₈ .

The operating characteristics of an installation as shown in FIG. 1 are given below, treating 1600 tonnes per day of naphtha.

When examining the table above, it can be seen that the pressure drops are much lower in electric ovens F ₅ to F ₈ than in conventional ovens F ₁ to F ₄ . This gain is around 3 bars in total.

Because of this reduction in pressure drops, it would be possible to reduce the power of the compressor 10.

When the compressor 10 is kept, which is the case of the example shown in FIG. 1 and of the aforementioned table, the reduction in pressure losses provides the installation with a credit for pressure losses, which makes it possible to insert into the installation, one or more additional exchangers 28 which will allow the initial mixture 1 to be carried by the heat exchange with the effluent 3 coming from the last reactor R ₄ at a temperature of 460 ° C. or more before it enters the first oven F ₅ , instead of 427.5 ° when using conventional ovens.

Since in both cases the gas mixture must be brought to approximately 525 ° C before entering the various reactors, it is possible, thanks to the additional exchangers 28, to reduce the power, that is to say the energy consumption of the first electric oven Fs.

It can be seen that in the case of operation of the installation with electric ovens F ₅ , F ₆ , F ₇ , Fε, a gain of 4.5 MW is achieved, compared with conventional ovens, at the level of the first oven F ₅ .

Many other advantages are provided by the use of electric ovens F _s to F ₈ .

The fact of being able to operate the installation in dual energy, that is to say either with conventional ovens or with electric ovens, allows in the event of failure of conventional ovens to make the installation immediately operational, without shutting down the entire installation.

It is advantageous to operate the installation with electric ovens, during periods when overall energy consumption is reduced and when relatively inexpensive hydroelectric or nuclear power can be available.

Furthermore, when the installation operates with electric ovens F to F _B , it is possible to adjust with very great precision, the heating temperature of the gas mixture which is introduced into the various reactors.

Thus, one can avoid temperature fluctuations around the set point, and better use the catalyst at the inlet of the reaction mixture, and maintain its effectiveness for a longer period.

Of course, the invention could include only electric ovens in total replacement of conventional ovens.

In this case, the installation could be specifically adapted to total operation with electric ovens.

Thus, thanks to the gain in pressure drops achieved by the use of electric ovens, it is possible either to significantly reduce the power of the compressor 10 for recycling hydrogen, or to increase the number of heat exchangers such as 4, 28 which reduce the total power of electric ovens, so that in all cases a significant energy gain is achieved.

Of course, the invention could relate only to a partial replacement of conventional ovens for one or more electric ovens.

Alternatively, we could multiply the number of furnaces and reactors by correspondingly decreasing their respective sizes, to tend towards a quasi-isothermal temperature profile within the catalyst. This would allow better use of the catalyst, therefore a reduction in the overall volume of catalyst and thus a saving in the supply of catalyst, the cost of which is particularly high since it is based on noble and rare metals.

Furthermore, in cases where the pressure drop credit provided by the operation of the installation with electric ovens is not used to improve the charge-effluent heat exchange, i.e. to reduce energy consumption overall, this pressure drop credit allows more efficient operation of the installation, in particular better use of the catalyst, by adapting the operating conditions of the unit. Thus, for example, the lowering of the average pressure in the installation makes it possible to obtain a higher yield of gasolines.

Of course, the invention is not limited to the example which we have just described which relates to the catalytic reforming of naphtha to produce gasolines.

Thus, the invention is applicable in all cases where high power heating of a mixture of hydrocarbons and hydrogen is carried out under high pressure, upstream of one or more reactors in which the globally endothermic reactions take place. , at temperatures between 350 and 900 ° C approximately.

Thus, the invention can also be applied in particular to installations for the treatment of desulfurization of hydrogen hydrocarbons.

In all these installations the replacement conventional ovens supplied with fossil fuel by electric furnaces with low pressure drop allows energy savings of up to 45% to be obtained, which is quite surprising.

Claims (7)

1. Installation for the chemical transformation of a gaseous mixture (1) containing in particular hydrogen and hydrocarbons, this installation comprising a succession of reactors (R ₁ , ... R ₄ ) for reacting the above-mentioned mixture according to globally endothermic reactions, at temperatures between 350 and 900 ° C approximately, under high pressure and in the presence of a catalyst, as well as an oven (Fs ... F ₈ ) disposed upstream of each reactor (Ri .. R4) for heating the gas mixture before its introduction into said reactor, characterized in that the ovens (F ₅ ... F ₈ ) consist of an enclosure (11 ... 14) comprising an inlet (15a ... 18a) and an outlet (15b ... 18b) of the gas mixture and one or more electrical heating resistors (19 ... 22) intended to be placed in direct contact with the gas mixture introduced into this enclosure, these ovens (F ₅ ... F ₈ ) with a pressure drop significantly lower than that of conventional ovens s supplied with fossil fuel. 2. Installation for the chemical transformation of a gaseous mixture (1) containing in particular hydrogen and hydrocarbons, this installation comprising a succession of reactors (R ₁ ... R ₄ ) for reacting the above-mentioned mixture according to reactions overall endothermic at temperatures between 350 and 900 ° C approximately, under high pressure and in the presence of a catalyst, as well as an oven (F ₁ ... F ₄ ) supplied with fossil fuel placed upstream of each reactor (R ₁ ... R ₄ ), for heating the gas mixture before its introduction into the reactor, this installation being characterized in that it comprises, in parallel with each furnace (F ₁ ... F ₄ ) supplied with fossil fuel, an oven (F ₅ ... F ₈ ) consisting of an enclosure comprising an inlet (15a ... 18a) and an outlet (15b ... 18b) of the gas mixture and one or more electrical heating resistors (19 ... 22 ) intended to be placed in direct contact with the gas mixture introduced into this enclosure and means (V ₁ , V ₂ , ... V ₆ , V ₇ , 23 ... V ₉ , V ₁₀ , 27) for passing the gas mixture as required either by the furnaces (F ₁ ... F ₄ ) supplied with fuel of fossil origin, or by the furnaces (F ₅ ... F ₈ ) with electrical resistance, these furnaces having a loss of load significantly lower than that of conventional ovens (F ₁ ... F ₄ ) supplied with fossil fuel. 3. Installation according to claim 2, applied to the catalytic reforming of naphtha, comprising ovens (F _I ... F ₄ ) supplied with fuel of fossil origin disposed respectively upstream of reactors (R ₁ ... R ₄ ) , heat exchangers (4) arranged upstream of the first oven (F ₁ ) and arranged to carry out a heat exchange between the gas mixture (1) introduced into this first oven (F ₁ ) and the gaseous effluent (3) from the last reactor (R ₄ ), characterized in that one or more heat exchangers (28) are placed on the bypass (23) between the outlet (4a) of the first exchangers (4) and the inlet (15a) of the first electric oven (F ₅ ) and arranged to carry out an additional heat exchange between the gas mixture (1) introduced into this first electric oven (F ₅ ) and the gaseous effluent (3) coming from the last reactor (R ₄ ). 4. Installation according to claim 3, characterized in that it comprises means (V ₁₁ , 29, V ₁₂ , V ₁₃ , 30) for passing the gaseous effluent (3) from the last of the reactors (R ₄ ) or in the additional heat exchangers (28) when all or part of the electric ovens (F ₅ ... F ₈ ) are put in service, either directly and only in the first exchanger (4) when all the ovens (F ₁ ... F ₄ ) supplied with fossil fuel is in service. 5. Installation according to any one of claims 1 to 4, characterized in that the pressure drop caused by electric ovens (F ₅ ... F ₈ ) is 5 to 15 times lower than that of furnaces supplied with fuel of fossil origin. 6. Installation according to any one of claims 2 to 5, characterized in that the pressure drop caused by the additional exchanger (s) (28) can reach a value equivalent to the gain in pressure drop achieved during the setting in service of some or all of the electric ovens (F ₅ ... F ₈ ). 7. Installation according to any one of claims 3 to 6, characterized in that the power of the first electric oven (Fs) is more than 20% lower than that communicated to the process fluid in the case of the first oven (F _I ) supplied with fossil fuel.

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