WO2016169865A1

WO2016169865A1 - Method for thermochemical conversion of a carbon-containing feedstock, performed continuously in a reactor at least partially using the energy from solar radiation

Info

Publication number: WO2016169865A1
Application number: PCT/EP2016/058455
Authority: WO
Inventors: Nathalie Dupassieux; Sylvain RODAT
Original assignee: Commissariat A L'energie Atomique Et Aux Energies Alternatives
Priority date: 2015-04-22
Filing date: 2016-04-15
Publication date: 2016-10-27
Also published as: FR3035394B1; FR3035394A1

Abstract

The present invention relates to a method for thermochemical conversion of a carbon-containing feedstock into reaction products, including the following steps: a/ when the amount of solar energy received via an opening of a reactor is greater than a first predetermined value, performing an endothermic reaction for converting the carbon-containing feedstock within the reaction area(s) of the reactor, the amount of heat required by the endothermic reaction being supplied at least in part by the amount of solar energy entering the reaction area(s); b/ when the amount of solar energy received via the opening is lower than the first predetermined value, performing at least one reaction to convert the carbon-containing feedstock within the reaction area(s), steps a/ and b/ being carried out continuously.

Description

METHOD OF THERMOCHEMICAL CONVERSION OF A CONTINUOUS CARBON CHARGE INTO A REACTOR USING AT LEAST PART THE ENERGY OF SOLAR RADIATION.

Technical area

The present invention relates to a novel process for the thermochemical conversion of a carbonaceous feedstock into conversion products, implemented continuously in a so-called "solar" reactor, that is to say using at least partly the energy of the radiation solar.

The present invention also relates to concentrating solar power plants for the implementation of this new process.

The main application of the invention is the conversion of a carbonaceous feedstock, in particular a hydrocarbon or a biomass, into a synthesis gas containing predominantly hydrogen (H2) and carbon monoxide (CO), in particular to produce liquid fuels (Diesel Fischer-Tropsch "FT", Dimethyl ether "DME", Methanol) or gaseous (synthetic natural gas, "SNG" or "Synthetic Natural Gas" in English) or other synthetic chemicals, such as methanol for example or unsaturated and / or aromatic hydrocarbons such as products from the steam cracking of light petroleum fractions.

The term "carbonaceous feedstock" refers to any combustible material consisting of carbon-containing compounds.

It can therefore be biomass, ie any inhomogeneous material of vegetable origin containing carbon, such as lignocellulosic biomass, forest or agricultural residues (straw), which can be almost dry or soaked with water as household waste.

It can also be a hydrocarbon, especially a fuel of fossil origin, such as coal.

It may also be industrial combustible waste containing carbon, such as plastics or tires.

It can also be a combination of biomass and fossil fuel. State of the art

The so-called "solar" reactors are chemical reactors adapted to convert at least partly the energy of the concentrated solar radiation into heat in order to implement endothermic reactions such as reforming, gasification, decarbonation, cracking, etc.

From the prior art, many designs of solar reactors adapted to several chemical reactions or in a preferred manner for a type of reaction are known. We can cite here the publication [1], which makes a general review of the designs of all known solar reactors, or the publication [2] which focuses on solar reactors particularly adapted to reforming or publication [3] which details those for gasification.

The inventors of the present invention have found that research on solar reactors has clearly focused on the optimization of their architecture. And, that little or none of the known reactors can answer a problem of primary importance in chemical engineering, namely the possibility of implementing a continuous reaction.

Thus, all the solar reactor solutions proposed to date only allow the implementation of reactions in a limited way during the day, namely during the sunning phases. However, a discontinuous operation of reactors is not very compatible with conventional industrial processes (chemistry, refining ...) that require stabilized operating conditions.

For the relatively low temperature reactions, typically between 400 and 500 ° C, most designers consider associating with the reactors heat storage systems, such as those used in solar power generation plants.

For the reactions at the highest temperatures, typically between 500 and 1500 ° C, in particular above 700 ° C, the heat storage systems are unsuitable because the thermal losses are high or very high and the storage materials are not necessarily available because of the important thermal cycling to which they are subjected, the conductivity, the possible durability ... Among the attempts at improvement, one can quote the publication [4] which proposes the hybridization of a solar reactor by positioning an external burner in order to introduce external heat resulting from the combustion, instead of the heat from the solar radiation, at the opening of the cavity, which cavity is the reaction zone. In fact, the external combustion heat is introduced exactly where the concentrated solar radiation penetrates, which can not make it possible to envisage an operation on an industrial scale, ie continuously stable, of the decarbonation reaction aimed at . Indeed, the change of type of heat brought to the reaction, ie solar heat to heat by combustion and vice versa, necessarily introduces a discontinuity in the reaction.

The study summarized in the publication [5] for its part envisages the supply of external heat by means of a heat transfer fluid, that is to say the realization of an allothermal reactor. The disadvantage of this type of reactor is that, by definition, the energy input is not direct since an intermediate heat transfer fluid is used. However, using an intermediate heat transfer fluid previously heated by solar energy, necessarily involves the implementation of an additional heat exchanger with the associated heat losses. In addition, it is difficult to find a heat transfer fluid for applications in which the temperatures encountered are high or very high, especially above 1000 ° C.

The authors of the publication [6] have proposed a solar reactor equipped with a diaphragm to adjust the opening size of the reactor to the available solar power without providing a solution to ensure the continuity of reaction for the period without sunshine.

Thus, the inventors have found that there are few solutions to ensure continuity in solar reactors. However, all the dynamic models show that the temperature rise time of a reactor is long and constraining, which is incompatible with industrial use.

The use of solar energy in addition to a contribution of fossil fuel or biomass has already been studied for the gasification reaction: see publication [7]. But in this study, the combustion and gasification reactors are decoupled, which is detrimental to the material and energy efficiency of the overall process. There is therefore a general need to improve the thermochemical conversion processes implemented in a solar reactor, in particular in order to make possible continuous stable operation for use on an industrial scale and to increase the material and energy.

Presentation of the invention

The invention aims at solving at least part of this need and relates to a process for the thermochemical conversion of a carbonaceous feedstock into reaction products, implemented in a reactor whose enclosure comprises at least one reaction zone, at least an opening through which solar radiation is able to enter the reaction zone (s), the method comprising the following steps:

a / when the quantity of solar energy received by the opening is greater than a first predetermined value implementing an endothermic conversion of the carbonaceous charge within the reaction zone (s) the amount of heat required by the endothermic reaction being provided at least in part by the amount of solar energy entering the reaction zone (s);

b / when the quantity of solar energy received by the opening is less than the first determined value, implementation of at least one conversion reaction of the carbonaceous charge within the reaction zone (s) (s), the same reactor, the amount of heat required is provided by another source of energy than the amount of solar energy received

the steps a / and b / being carried out continuously.

Step b / according to the invention is implemented within the (the) zone (s) reaction (s) of the same reactor, with a supplement with an external heat input.

Advantageously, the process according to the invention concerns reforming-type reactions and in particular autothermal reforming of methane, which up to now has not been carried out continuously with the addition of solar energy.

Thus, according to the invention, the heat input into the same reactor can be done either by solar energy, preferably concentrated, or by another energy source, or a combination of both.

The fact of being able to bring the solar energy directly within the reaction zone makes it possible to avoid losses related to one or more multiple exchangers required for an intermediate heat transfer fluid as in the publication [5]. The method according to the invention is advantageously autothermal, since it is possible to have a yield both of energy and of material of the increased carbon charge.

According to an advantageous embodiment, the reactor comprises a shutter of thermal insulating material, movable between a closed position in which it completely closes the opening and a plurality of open positions in each of which it leaves at least partially cleared the opening,

the step a / is carried out with an opening of the shutter in one of the plurality of the open positions, and

step b / is carried out with closure of the shutter.

Preferably, the solar radiation is concentrated before entering the opening of the reactor.

According to an advantageous embodiment, the method comprises:

during step a /, the simultaneous implementation of an exothermic reaction and an endothermic reaction within the reaction zone (s), the quantity of heat required by the reaction endothermic being provided in part by the amount of solar energy entering the (the) zone (s) reaction (s) and partly by the heat released by the exothermic reaction;

during step b, the simultaneous implementation of the same exothermic and endothermic reactions as in step a /, the quantity of heat required by the endothermic reaction being provided completely by the heat released by the exothermic reaction; .

According to another advantageous embodiment, the method comprises:

during step a /, the only implementation of an endothermic reaction within the reaction zone (s), the quantity of heat required by the endothermic reaction being provided completely by the quantity solar energy entering the reaction zone (s);

during step b /, the simultaneous implementation of the same endothermic reaction as that of step a / and of an exothermic reaction within the reaction zone (s), the amount of heat required by the endothermic reaction being provided completely by the heat generated by the exothermic reaction. The endothermic reaction may be advantageously steam reforming or dry reforming and the exothermic reaction may be partial oxidation or catalytic partial oxidation.

The process according to the invention may constitute a method of autothermal conversion of a hydrocarbon to synthesis gas.

According to yet another advantageous embodiment, the method comprises:

during step a /, the only implementation of an endothermic reaction within the reaction zone (s), the quantity of heat required by the endothermic reaction being provided in part by the amount of solar energy entering the reaction zone (s) and in part by the heat generated by combustion in the enclosure;

during step b /, the only implementation of the same endothermic reaction as in step a /, the quantity of heat required by the endothermic reaction being provided completely by the heat released by combustion in the pregnant.

According to yet another advantageous embodiment, the method comprises:

The combustion in the enclosure may be a combustion of a part of a reaction product, such as synthesis gas, or a combustion of the carbonaceous feedstock.

The endothermic reaction may advantageously be a gasification reaction of a biomass, especially a lignocellulosic biomass, or a cracking reaction or steam reforming of carbonaceous feedstock.

According to one variant, the displacement of the shutter and the flow rate of the reagents within the zone (s) are controlled according to sunshine data.

The endothermic reaction and, where appropriate the exothermic reaction, is carried out at high temperatures, typically above 500 ° C., in particular between 500 ° C. and 1500 ° C. It is specified that in the context of the invention, all the concentration or high concentration systems with mirrors or lenses used to concentrate the solar rays on a reduced surface, are suitable. It also specifies that the notions of concentration and high concentration are related to the concentration factor usually called "suns" (or "suns" in English), and indicates how much the incident energy of the sun is multiplied. Thus, usually, we define:

the low concentration: from 2 to 100 "suns";

the average concentration: from 100 to 300 "suns";

the high concentration: beyond 300 "suns".

The invention also relates to a concentrating solar power plant, tower type, for implementing the method described above, comprising:

- a tower,

a field of mirrors, called heliostats, each adapted to concentrate the sun's rays towards a fireplace located on the tower,

a reactor whose enclosure comprises at least one reaction zone, at least one opening through which solar radiation is likely to enter the reaction zone (s), and a shutter made of thermal insulating material, movable between a closed position in which it completely closes the opening and a plurality of open positions in each of which it leaves at least partially open the opening,

central in which the (the) aperture (s) of the reactor is (are) arranged (s) at the focus of heliostats.

According to a first embodiment variant:

- the tower is arranged in the center of the mirror field,

the reactor is cylindrical, the opening of the reactor being carried out over the entire periphery of the enclosure, the reaction zones being constituted by tubes provided with a catalyst for the steam reforming or dry reforming reaction, the shutter being constituted by an annular shutter adapted to slide around the opening,

- The reactor further comprises at least one burner adapted for carrying out a partial oxidation reaction within the tubes.

According to a second variant embodiment:

the tower is arranged on one side of the mirror field, the opening of the reactor is carried out on a part of the periphery of the enclosure, the reaction zones being constituted by tubes provided at the same time with a catalyst for the steam reforming or dry reforming reaction, and for a catalyst for the reaction partial catalytic oxidation.

Finally, the invention relates to a concentrating solar power plant, tower type, for implementing the method described above, comprising:

- a tower equipped with one or more mirrors, said mirror (s) of reflection,

a field of mirrors, called heliostats, each adapted to focus the sun's rays towards a focal point in which the mirror (s) of reflection are (are) arranged,

a reactor whose enclosure comprises at least one reaction zone, at least one opening through which solar radiation is likely to enter the reaction zone (s), and a shutter made of thermal insulating material, movable between a closed position in which it completely closes the opening and a plurality of open positions in each of which it leaves at least partially cleared the opening, the reactor further comprising at least one burner adapted for implementation a combustion around the tubes,

central in which the reactor is arranged on the ground with its (their) aperture (s) arranged (s) at the focus of (the) mirror (s) reflection.

The solar power plant may advantageously comprise one or more photovoltaic cells (PV), where appropriate with their concentration or high concentration system, on the outer face of the shutter of the reactor.

detailed description

Other advantages and features of the invention will emerge more clearly from a reading of the detailed description of the invention, given by way of illustration and without limitation with reference to the following figures among which:

FIG. 1 shows, in the form of curves, the evolution of the molar flow rates of the various reagents and reaction products in an autothermal methane reforming process according to the invention, in which 100% of the energy required for the reaction can be brought by solar energy;

FIG. 2 shows, in the form of curves, the evolution of the molar flow rates of the various reagents and reaction products in an autothermal reforming process. methane according to the invention, wherein only 10% of the energy required for the reaction can be provided by solar energy. FIG. 3 is a schematic view of a first example of a concentrated solar power station comprising a solar reactor, intended to implement an authothermic methane reforming process according to the invention,

FIG. 4 is a diagrammatic view of a second example of a concentrated solar power station comprising a solar reactor, intended to implement an authentic methane reforming process according to the invention,

FIG. 5 is a schematic view of a third example of a concentrated solar power station comprising a solar reactor, intended to implement a steam reforming process according to the invention.

It is specified that in each of Figures 3 to 5, the solar reactor 2 according to the invention is enlarged for the sake of clarity.

The inventors of the present invention have considered the methane reforming reaction for the production of synthesis gas.

The steam reforming of methane is an endothermic reaction that produces synthesis gas and takes place at about 800 ° C and at a pressure of between 20-40 bar. It is written as follows:

CH ₄ + H ₂ O-> CO + 3H ₂ (1)

with an enthalpy associated ΔΗ ° (25 ° C) equal to 206 kJ / mol.

Partial oxidation is a slightly exothermic reaction that also produces syngas and is written as follows:

CH ₄ + 1/20 ₂ -> CO + 2H ₂ (2),

with an enthalpy associated ΔΗ ° (25 ° C) = - 44 kJ / mol.

The simultaneous implementation of these two reactions is known as such and it allows the so-called autothermal reforming in which the heat generated by the partial oxidation reaction can be used for the steam reforming reaction.

The inventors have thought that it is possible to implement this reaction in a solar concentrating reactor, that is to say using as heat required by the steam reforming reaction, a concentrated amount of solar energy.

In other words, as long as the solar concentration device associated with the solar reactor delivers a sufficient quantity of energy, the endothermic reaction of steam reforming can be carried out entirely or partly thanks to the contribution of solar energy. As sunshine decreases, the decrease in the solar energy supply afferent is then offset by the simultaneous implementation of the exothermic partial oxidation reaction.

To achieve this compensation, it is then necessary to increase the flow of oxygen in the reaction zone of the reactor to promote the partial oxidation reaction.

Advantageously, to automate this compensation, it is possible to consider monitoring the concentrations of the reaction products, with measuring means, such as on-line gas analyzers, at the outlet of the reactor. Alternatively, it can also be done knowing the solar energy incident on the reactor from a weather model that can determine depending on the time and sunshine received the share of energy that must be provided with the partial oxidation reaction. One can still consider a control-command by temperature measurement within the reactor.

To modulate at will the amount of solar energy that is to be used in the process, the inventors have thought to use a reactor with one or more openings through which (which) solar radiation is likely to enter the (the) zone (s) reaction (s), and a shutter of thermal insulating material, movable between a closed position in which it completely closes the opening and a plurality of open positions in each of which it leaves unobstructed at least partially opening,

Thus, the autothermal methane reforming process according to the invention comprises the following steps:

a / when the amount of solar energy received by the aperture is greater than a first predetermined value, opening the shutter in one of the plurality of open positions, and performing an endothermic conversion reaction; the carbon load within the reaction zone (s), the quantity of heat required by the endothermic reaction being provided at least in part by the amount of solar energy entering the zone (s) ) reactionary (s);

b / when the quantity of solar energy received by the opening is less than the first determined value, closure of the shutter and implementation of at least one conversion reaction of the carbonaceous charge within the (of the ) reaction zone (s) of same reactor, the quantity of heat required being provided by another source of energy than the quantity of solar energy received,

the steps a / and b / being carried out continuously.

Thus, the present invention makes it possible to use a single reactor for methane reforming, in a continuous manner with an almost constant maintenance of the temperature and therefore of the stable operating conditions.

Therefore, the method according to the invention makes it possible to ensure a controlled quality of the reaction products with continuous operation since even in the absence of solar energy, it is possible to implement a heat input by an exothermic reaction at within the reaction zone or an external heat input by combustion.

Compared to a method with a solar reactor according to the state of the art that can be used only during the day, and still under certain imperative conditions of sunshine, the profitability of the process according to the invention is much better.

Finally, the process according to the invention makes it possible to increase the material yield, since the concentrated solar energy is preferred over the heat evolved by the partial oxidation reaction for the steam reforming reaction.

In other words, the solar energy provided makes it possible to burn less methane in the partial oxidation reaction, and thus to use more methane as a reagent in the steam reforming reaction. Solar energy input can be used to save heat input by methane oxidation or to increase synthesis gas production.

To validate the process according to the invention, the inventors have carried out simplified calculations, made on material balances from equations (1) and (2) with the associated enthalpies.

These calculations show that it is still possible to maintain the autothermal reforming reaction by adjusting the flow rates of the various reagents (CH ₄ , H ₂ 0, 0 ₂ ) and this as a function of the solar energy input concentrated in the zone. reaction.

The curves shown in FIGS. 1 and 2 make it possible to illustrate the operation of a solar reactor respectively with a total solar hybridization or limited to 10%

Thus, the curves of FIGS. 1 and 2 show the molar flow rates of reagents and products involved as a function of the selectivity between reactions (1) and (2). This selectivity is influenced by the molar ratio between oxygen (0 ₂ ) and methane (CH 4) in the reaction charge, which is varied according to the amount of solar energy brought in, in order to ensure that Generally energy-equilibrated process, ie autothermal reforming, in which the amount of solar energy supplied must compensate for the energy requirement for the steam reforming reaction. In other words, depending on the flow rates of oxygen and methane injected into the reaction zone (s) of the reactor, one or the other of the reactions (1) and (2) will be favored, because the concentrations of these reagents will influence the thermodynamic equilibrium and the kinetics of the reactions.

Figure 1 shows that this choice of control induces a decrease in the production of H ₂ and CO when there is a solar energy input. Indeed, the introduction of reagent to carry out the partial oxidation reaction is decreased or stopped. Below a certain predetermined value, the partial oxidation reaction conducted for the supply of heat to the steam reforming reaction also contributes to the production of synthesis gas.

It is further observed that when there is solar energy input, a significant reduction in methane consumption is obtained, due to the fact that the contribution of carbon energy by partial oxidation of the methane is compensated by the contribution of solar energy. .

One could also look for the operating conditions allowing a constant production of H ₂ or CO, but the balance between these two productions is very difficult to reach, considering that the stoichiometries of the reactions (1) and (2) are not not equivalent. Indeed, it is found that when only solar energy is supplied, the ratio of production between H ₂ and CO is approximately equal to 3 times, which corresponds to the stoichiometry of the reaction (1), while is about 2 during the phase without solar energy input during which the exothermic reaction (2) is preponderant. These large variations in the gases produced can be difficult to manage in some downstream processes, but can be very well valued in others, particularly in SOFC fuel cells or via the use of a buffer storage.

In order to be able to ensure production and quality stability of the synthesis gas, it is possible to reduce the solar energy input to a value of 10% for example, as shown in FIG. In this Figure 2, we see that the decrease in proportion to the share of solar energy provided, which is therefore at most 10% against 100% in Figure 1, allows to have relatively constant molar rates of gas produced. It is thus possible to envisage a reduced solar energy input, here equal to 10%>, which makes it possible not to destabilize the downstream processes, among which may be mentioned a purification, a Fisher-Tropsch process ....

In addition to the advantage of being able to maintain a more stable composition of the product gases, another advantage of limiting the contribution of solar energy to a certain percentage in the overall conversion process is to avoid having to completely stop the operation of the ( burner (s) dedicated to the implementation of the partial oxidation reaction or total combustion.

On the other hand, in the illustrated example of the autothermal methane reforming shown in FIGS. 1 and 2, the production of the gases varies as a function of the quantity of solar energy supplied, since the partial oxidation exothermic reaction consumes methane.

To implement the thermochemical conversion according to the invention for applications at high temperatures, typically between 500 and 1500 ° C., generally greater than 800 ° C., the inventors have thought of different variants of reactor construction and arrangement. in a concentrated solar power station. Concentration is required given the high temperatures above to be achieved.

Various exemplary embodiments for the autothermal reforming of methane or steam reforming of methane are described in relation to FIGS. 3 to 5.

Figure 3 shows a device with a solar power station 1 which concentrates the energy on the tubes of a solar reactor.

More specifically, the central 1 comprises a tower 10 and a field of mirrors, called heliostats 11 each adapted to focus the sun's rays to a focus on the tower 10. The tower 10 is arranged in the center of the mirror field 11.

The plant 1 further comprises a cylindrical reactor 2 arranged on the top of the tower.

The chamber 20 of the reactor comprises tubes 22 parallel to each other which constitute the reaction zones of the reactor. The tubes 22 are provided with a catalyst for the steam reforming or dry reforming reaction, On the entire periphery of the enclosure 20 is made an opening 21 through which solar radiation is likely to enter the tubes 22.

A sliding shutter 23, forming a guillotine flap, of annular thermal insulation material is mounted movably around the opening 21 between a closed position in which it completely closes the opening and a plurality of opening positions in each from which he leaves it released at least partially.

Finally, the reactor 2 comprises at least one burner 24, shown schematically, which is adapted for carrying out a partial oxidation reaction within the tubes. As shown schematically, the burner 24 is on the top of the chamber 20 of the reactor 2. Other positions are possible. The chosen position is determined beforehand by modeling the configurations and thermal powers of the reactions envisaged.

The arrangement of the reactor 2 is such that the opening 21 is at the focus of the heliostats 11. Thus, with this arrangement, the cylindrical geometry of the reactor 2, the arrangement of the tower 10 in the center of the solar field 360 °, it It is possible to irradiate the tubes 22 at 360 °.

The flap 23 may thermally insulate the tubes 22, partially or completely in the absence of sunshine, which allows to drastically reduce the radiative losses, that is to say the losses associated with the radiation reemitted by the tubes and walls of the reactor, and therefore to increase the energy efficiency of the process. These radiative thermal losses in play can be potentially important because they are proportional to the surface of the opening left by the flap 23. To know the positioning of the shutter 23 to achieve optimally, we can consider performing a control-command of its displacement by taking into account the internal temperature of the reactor.

Advantageously, it is conceivable to carry out control-control of the shutter 23 as well as the burner 24, and flow rates of reactive products from a predefined model and / or short-term weather forecasts in order to achieve the overall process. autothermal reforming under stabilized conditions, while minimizing radiative losses. In particular, it is preferable to consider positioning the flap 23 in its closed position as soon as the radiative losses become greater than the quantity of solar energy supplied. The solar power station shown in FIG. 4 is a variant of that represented in FIG.

Here, the tower 10 is arranged on one side of the mirror field 11.

The reactor 2 does not comprise a burner.

Indeed, the tubes 22 are here provided with both catalyst of the steam reforming reaction, and catalyst of the catalytic partial oxidation reaction. The chosen oxidation and steam reforming catalysts and the regulation of the reactive gas flows as a function of the solar energy provided make it possible to ensure the good kinetics of the reactions (1) and (2) of the desired autothermal reforming. It is conceivable that a given tube 22 has a part dedicated to catalytic combustion or partial catalytic combustion which is upstream with respect to the direction of circulation of the reactive gases and a part dedicated to the steam reforming reaction which is downstream.

The opening 21 of the reactor is here carried out on only a part of the periphery of the enclosure 20.

In this illustrated example in order to obtain more important solar concentration factors than by the one only generated by the mirrors 11, it is advantageous to envisage an additional solar concentration device on the walls of the reactor enclosure around the opening 2 Thus, it is advantageous to envisage a device of frustoconical shape around the opening. By increasing the concentration factor, the radiative losses associated with the reactions can be reduced: for example, doubling the concentration makes it possible to pass the same solar energy through an opening area halved, ie 50% less radiative losses.

The base of this additional concentration device is open and defines the opening 21. Thus, the flap 23 can close more or less this opening 21.

The flap 23 may be a diaphragm type device, as illustrated. It is also possible to envisage a guillotine-type shutter 23 as in the example illustrated in FIG. 3. Whatever the shape of the shutter 23 retained, it must be able to completely close the opening 21 during the phases where the sun is not enough.

Another configuration of solar power station 1 "intended to implement a non-autothermal steamforming process is shown in FIG.

Such a configuration is known by the British name "beam down". It allows to obtain the concentrated radiation on the ground via a reflection secondary to the top of the tower 10 which is provided with a reflection mirror 12. This configuration according to Figure 5 has the intrinsic advantage of allowing easier installation because at ground level.

Here, the reactor 2 is thus arranged on the ground with the opening 21 arranged at the focus of the reflection mirror 12.

The opening 21 of the reactor 2 is always provided with a flap 23 whose displacement makes it possible to thermally isolate the enclosure 20 from the outside, in order to minimize the radiative losses, typically at the end of the day or during periods of low sun.

The reactor 2 comprises in its enclosure 20 a plurality of burners 24 each adapted for the implementation of a combustion around the tubes 22 internally coated catalyst only the steam reforming reaction. These burners 24 therefore have the function of achieving the total combustion of methane to compensate for the variability of the solar energy input. As shown, the burners 24 are arranged all around the enclosure 20. It can also be envisaged to arrange them at the top and / or bottom of the enclosure 20. A positioning at high point has the advantage of allowing to keep a flow solar energy penetrating through the opening 21 and a combustion flow in the same direction, which can promote the thermal stability as well as the reaction stability of the process. For the circulation of flue gases from combustion, it is possible to envisage a countercurrent or co-current circulation of the circulation of the reactive gases and of the synthesis gas.

The vaporeforming reaction can thus be implemented inside the tubes 22, the heat input being carried out in part or entirely by the solar energy concentrated by the mirrors 12 and partly or entirely by the combustion made by the burners 24.

Whatever the configuration of the solar power station 1, 1 "envisioned, with the hybrid solar reactor 2, there is obtained a process for converting methane into synthesis gas which can be operated continuously in a stable manner.

Other improvements and variations may be provided without departing from the scope of the invention.

Thus, although described with reference to an autothermal reforming process (FIGS. 3 and 4) or to a steam reforming process (FIG. 5), concentrated solar power plants can be used for autothermal dry reforming process or not. Dry reforming can be envisaged as well with biogas (rich in CO2) as on acid gases currently can also be exploited because of their high CO2 content.

Other methods of conversion at high temperatures, such as gasification or cracking of hydrocarbons and, more generally, any process in which part of the feedstock or reaction products are consumed for heat in the reaction zone or for external heat input by burner.

Furthermore, although not shown, one can advantageously provide the flap 23 of the reactor with one or more photovoltaic cells (PV), if necessary with their concentration system or high concentration. Thus, we can recover the share of concentrated solar energy that is not used in the form of heat in the conversion process in the reactor: this part of solar energy is thus transformed into electricity by the (the ) cell (s) PV.

In the solar reactors 2 shown in FIGS. 4 and 5, instead of having a single opening 21, one can envisage having several of them, especially if the thermal power required by the process used is greater.

It is possible to envisage a combination between the three solutions represented respectively in FIGS. 3, 4 and 5.

REFERENCES CITED

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[3]: M. Puig-Arnavat, E.A. Tora, J.C. Bruno, A. Coronas, "State of the art on reactors design for solar gasification of carbonaceous feedstock", Solar Energy, 97, 2013, 67-84.

[4]: A. Meier, E. Bonaldi, G. M. Cella, W. Lipinski and D. Wuillemin, "Solar chemical reactor technology for industrial production of lime solar energy", 80 (10), 2006, 1355-1362.

[5]: R. Xu, T. F. Wiesner, "Dynamic model of a solar thermochemical water-splitting reactor with integrated energy storage and storage", International Journal of Hydrogen Energy, 37, 2012, 2210-2223.

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Claims

Process for the thermochemical conversion of a carbonaceous feedstock into reaction products, carried out in a reactor whose enclosure comprises at least one reaction zone, at least one opening through which solar radiation is likely to enter the reactor the reaction zone (s),

the method comprising the following steps:

a / when the quantity of solar energy received by the opening is greater than a first predetermined value, implementing an endothermic conversion of the carbonaceous charge within the reaction zone (s) (s) ), the amount of heat required by the endothermic reaction being provided at least in part by the amount of solar energy entering the reaction zone (s);

b / when the quantity of solar energy received by the opening is less than the first determined value, implementation of at least one conversion reaction of the carbonaceous charge within the reaction zone (s) (s) the same reactor, the amount of heat required is provided by another source of energy than the amount of solar energy received

the steps a / and b / being carried out continuously, the reactor comprising a shutter (23) of thermal insulating material, movable between a closed position in which it completely closes the opening and a plurality of opening positions in each of which it leaves at least partially open the opening,

the step a / being carried out with an opening of the shutter in one of the plurality of the open positions, and

step b / being carried out with closure of the shutter.

2. Thermochemical conversion process according to claim 1, wherein the solar radiation is concentrated before entering the opening of the reactor.

3. autothermal thermochemical conversion method according to one of claims 1 or 2, comprising:

during step a /, the simultaneous implementation of an exothermic reaction and an endothermic reaction within the reaction zone (s), the quantity of heat required by the reaction endothermic being provided in part by the amount of solar energy entering the (the) zone (s) reaction (s) and partly by the heat released by the exothermic reaction; during step b, the simultaneous implementation of the same exothermic and endothermic reactions as in step a /, the quantity of heat required by the endothermic reaction being provided completely by the heat released by the exothermic reaction; .

4. autothermal thermochemical conversion method according to one of claims 1 or 2, comprising:

during step b /, the simultaneous implementation of the same endothermic reaction as that of step a / and of an exothermic reaction within the reaction zone (s), the amount of heat required by the endothermic reaction being provided completely by the heat generated by the exothermic reaction.

5. autothermal thermochemical conversion process according to one of claims 3 or 4, the endothermic reaction being steam reforming or dry reforming and, the exothermic reaction being partial oxidation or catalytic partial oxidation.

6. Method according to one of claims 3 to 5 constituting a method of autothermal conversion of a hydrocarbon to synthesis gas.

7. Thermochemical conversion process according to one of claims 1 to 3, comprising:

8. Thermochemical conversion process according to one of claims 1 or 2, comprising: during step a /, the only implementation of an endothermic reaction within the reaction zone (s), the quantity of heat required by the endothermic reaction being provided completely by the quantity solar energy entering the reaction zone (s);

9. Thermochemical conversion process according to claim 8, the combustion in the chamber being a combustion of a portion of a reaction product, such as synthesis gas, or a combustion of the carbonaceous feedstock.

10. Thermochemical conversion process according to one of claims 8 or

9, the endothermic reaction being a gasification reaction of a biomass, in particular a lignocellulosic biomass, or a cracking or steam reforming reaction.

11. Thermochemical conversion process according to one of claims 1 to

10, according to which the control of the displacement of the shutter and the flow rate of the reagents within the zone (s) as a function of sunlight data.

12. Thermochemical conversion process according to one of the preceding claims, wherein the endothermic reaction and, where appropriate the exothermic reaction, is carried out at high temperatures, typically greater than 500 ° C, especially between 500 ° C and 1500 ° C.

13. A method of generating electricity, comprising the steps of:

- Establishment of one or more photovoltaic cells (PV), where appropriate with their concentration or high concentration system on the outer face of the shutter of the reactor implementing the method according to any one of claims 1 at 123,

recovery of the electricity converted by the PV cell or cells when the shutter is either in one of its partial opening positions or in its closed position.

14. Concentrating solar plant (1, 1 "), tower type, for implementing the method according to any one of claims 2 to 13, comprising:

- a tower (10), a field of mirrors (11), called heliostats, each adapted to concentrate the rays of the sun towards a focus located on the tower,

a reactor (2) whose enclosure (20) comprises at least one reaction zone (22), at least one opening (21) through which solar radiation is capable of entering the reaction zone (s); (s), and a shutter (23) of thermal insulating material, movable between a closed position in which it completely closes the opening and a plurality of open positions in each of which it leaves at least partially open the opening,

15. Solar power station (1) according to claim 14, wherein

the tower (10) is arranged in the center of the mirror field (11),

- The reactor (2) is cylindrical, the opening (21) of the reactor being formed over the entire periphery of the enclosure (20), the reaction zones being constituted by tubes (22) provided with a catalyst for the steam reforming reaction. or dry reforming, the shutter being constituted by a shutter (23) of annular shape adapted to slide around the opening,

- The reactor further comprises at least one burner (24) adapted for carrying out a partial oxidation reaction within the tubes.

16. Solar power plant (1 ') according to claim 14, wherein

the tower (10) is arranged on one side of the mirror field (11),

- The opening (21) of the reactor is carried out on a part of the periphery of the enclosure (20), the reaction zones being constituted by tubes (22) provided with both catalyst of the steam reforming or reforming reaction. dry, and catalyst of the catalytic partial oxidation reaction.

17. A tower-type concentrating solar power station (1 ") for carrying out the method according to any one of claims 1 to 12, comprising:

a tower (10) equipped with one or more mirrors (12), called mirror (s) of reflection,

a field of mirrors (11), called heliostats, each adapted to focus the sun's rays towards a focal point in which the mirror (s) of reflection are (are) arranged, a reactor (2) whose enclosure (20) comprises at least one reaction zone (22), at least one opening (21) through which solar radiation is capable of entering the reaction zone (s); (s), and a shutter (23) of thermal insulating material, movable between a closed position in which it completely closes the opening and a plurality of open positions in each of which it leaves at least partially open the opening, the reactor further comprising at least one burner (24) adapted for the implementation of a combustion around the tubes, central in which the reactor is arranged on the ground with its (their) opening (s) arranged (s) at home mirror (s) of reflection.

18. Solar power station according to one of claims 14 to 17, comprising one or more photovoltaic cells (PV), where appropriate with their concentration or high concentration system, on the outer face of the shutter of the reactor.