BE1022706B1 - Respectively exothermic and endothermic reactor of physi- or chemisorption between a gas and a granular solid - Google Patents

Abstract

The present invention relates to a reactor for physi- or chemisorption between a gas loaded with adsorbate in vapor form and a granular solid, comprising a reaction vessel (14) intended to contain a bed of grains stirred by controlled vibrations and through from which passes a gas flow, provided with: - vibratory means (3) to give the grains both vertical agitation and centrifugal movement allowing them to circulate from the center of at least one of said sieves (1) towards the periphery thereof and - means (2, 20) allowing, thanks to the aforementioned vibratory movements and / or the upward flow of gas, to raise the grains arriving at the periphery of said sieve (1) to a level higher than the level of said sieve (1 ) from where they fall by gravity to the center of said sieve (1).

Description

RESPOTENTLY EXOTHERMIC AND ENDOTHERMIC REACTOR OF PHYSI- OR CHEMISORPTION BETWEEN GAS AND SOLID

GRANULAR

OBJECT OF THE INVENTION [0001] The present invention relates to the field of thermochemical energy storage in the long term, in particular in the case of solar thermal applications.

BACKGROUND AND STATE OF THE ART [0002] Today, the storage of an energy produced essentially seasonally, such as solar energy, is of great interest and this is particularly the case for the use of the heat of reaction absorbed and restored in simple low temperature chemical reactions such as the hydration / dehydration of inorganic salts such as silica gel or zeolites.

Thus, in the case of a gas, air for example, containing an adsorbate such as water vapor, surrounding a volume of grains of a granular solid, it is known that this adsorbate will be transferred by differential pressure to the reaction surface of the grains where the adsorbate is adsorbed on this reaction surface, either by physical reaction (no modification of the adsorbate and the surface) or by chemical reaction (new chemical bonds between adsorbate and surface).

In the context of solar thermal applications, during periods of high sunlight efficiency, that is to say, mainly in summer, the solar energy produced excessively in relation to the heating or hot water requirements. is used for endothermic dehydration regeneration of the energy storage material by blowing hot dry air through the material. In contrast, during periods of low sunlight efficiency (mainly in winter), contacting the storage material with moist air releases heat stored in the material by exothermic hydration. The heat released by this adsorption is transferred by conduction, convection and / or radiation to the gas which has supplied the water vapor and which also serves as heat transfer.

Generally, the thermochemical storage using solid-gas reactions is carried out in a reactor that brings together the solid and the gas. The solid, if granular, is traversed by the gas, for example air carrying a moisture content associated with the presence of water vapor. The reaction is carried out by transfer of the water vapor molecules to the reaction surface of the solid, mainly inside porous grains with a high specific surface area, in the sense of an adsorption of water vapor which gives off heat. (exothermic reaction) to the surrounding air or in the sense of desorption when bringing heat with air (endothermic reaction).

The yield of the abovementioned energy transfer (adsorbed or released) depends on: the conduction of the granular material; - the exchange of heat between the grains and the air surrounding them; - the efficiency of the heat exchanger which stores energy (summer), or restores energy (winter); transfer of water vapor molecules to the adsorption sites; the intrinsic kinetics of the adsorption phenomenon.

The implementation of this process has been carried out in particular in the manner described in the three recent references below.

In Benoît Michel et al., Experimental investigation of an innovative thermochemical process operating with a hydrate and moist air for thermal storage of solar energy: global performance, Applied Energy 129 (2014) 177-186, a new system is presented. Open thermochemical intended for high density and long term seasonal storage. It implements a reactive salt (hydrated) / water pair and works with moist air. Specific hydration powers ranging from 0.75 to 2 W / kg were achieved for a salt bed energy density of 388 kWh / m3. Two important parameters for the control of the storage system were identified and investigated: the equilibrium drop (or the difference between the moist air inlet conditions and the thermodynamic equilibrium of the reaction) and the mass flow rate of the humid air. These two parameters have an important influence on the kinetics of reaction and consequently on the thermal power of the reactor.

[0009] In H. Kerskes et al., Developmentofa Thermo-Chemical Energy Storage for Solar Thermal Applications, ISES, Solar World Congress, August 28th-September 2nd, 2011, recent developments in the field of thermal energy storage at low temperature and in particular the main components of a solar heating system with seasonal energy storage. The reaction chamber consists of a shallow parallelepiped container, fed in its upper part by a hydrated mass flux (heating mode) or dry (regeneration mode) and coming out of its lower part respectively in dry form and hydrated. The flow of vertical material is driven by gravity through the reactor (cross flow reactor). The flow of air, respectively wet and dry, crosses the reactor laterally. In exothermic mode, the heat released in the air passing through the chamber is recovered in an air / water heat exchanger. A difficulty encountered in this type of reactor where the granular solid is mobile, is the potential existence of "dead zones", due to the fact that the material circulates in the reactor with different speeds. At the extreme, the material no longer circulates in these places and becomes inactive, which reduces the efficiency of the reactor both in regeneration mode and in heating mode. One solution proposed is to install guides in the reactor which make it possible to obtain a more homogeneous flow of the material.

In the patent application FR 2 976 192 A, entitled "solid reactor / heat transfer gas and reagent comprising a helical conduit in which the solid and the gas circulate against the current", a specific embodiment is also described to obtain a solid-gas exchange. In this document, the exchange between the gas and the solid is not done by passage of air through a static solid bed but in cross-over between the descending solid and the ascending gas in the helical conduit. In this case too, the granular material is not stationary in the reactor.

OBJECTS OF THE INVENTION [0011] The present invention aims to provide a physic or chemisorption reactor of granular material, which is compact and in which the exchange of energy between the grains and the air flow is optimized or improved. compared to the state of the art.

The invention also aims to improve the transport of water vapor to the entire reaction surface of the grains.

In particular, the invention aims to increase the thermal power of the reactor in both heating mode and regeneration mode.

Main Features of the Invention [0014] The present invention relates to a physical or chemisorption reactor between a vapor adsorbate-loaded gas and a granular solid comprising a reaction vessel for containing a stirred grain bed. by controlled vibration and through which a gas flow passes, comprising: - a gas circulation system producing a gas stream loaded with adsorbate in the form of vapor passing through the reactor from bottom to top; - an inlet tank in the upper position for feeding grain flow; a plurality of circular planar screens arranged in a stepped manner to receive a flow of grains entering and / or descending by gravity; an outlet reservoir in the lower position for harvesting an outgoing grain flow; means for controlling and adapting the temperature and the adsorbate content of the grains; - Means for the gravity conveyance of grains from one stage to another and / or to the outlet tank, characterized in that the reactor further comprises: - vibratory means for imparting to the grains both a stirring vertical and a centrifugal movement to circulate them from the center of at least one of said sieve to the periphery thereof and - means allowing, thanks to the aforementioned vibratory movements and / or the upward flow of gas, to raise the grains arrived at the periphery of said sieve at a level higher than said sieve where they fall by gravity in the center of said sieve.

According to preferred embodiments, the reactor of the invention further comprises at least one of the following characteristics, or an appropriate combination thereof: the means allowing, thanks to the aforementioned vibratory movements and the upward flow gas, to raise the grains arrived at the periphery of said sieve to a higher level where they fall by gravity in the center of said sieve respectively comprise a helical ramp located at the periphery of said sieve, followed by a downward ramp to the middle of said sieve; said vibratory means comprise motorized vibrating elements with low energy consumption; the vibrating elements are unbalance motors or electromagnetic vibrators; - The reactor vessel is secured to a fixed frame by elastic elements; the elastic elements are of the silent-block or spring type; the reactor comprises means for supplying the inlet tank in an upper position from a storage silo and means for feeding the storage tank from the outlet tank in the lower position, in such a way that the circuit traveled by the grains is a closed circuit; the gas circulation system is an air circulation system and / or the adsorbate is water vapor; - the air circulation system is closed, open or semi-open; the adsorbate vapor is injected into the gas circulation system with the gas itself; the adsorbate vapor is injected into the gas circulation system by spraying; the reactor comprises internal means of uniform distribution of the gas flow through the sieves; the step sieves are arranged in series and / or in parallel over the height of the reactor; the granular solid used comprises a porous matrix optionally impregnated with salt; the porous matrix may be a zeolite, a bentonite, a silica gel or a MOF (metal organic framework) and the salt is a chloride or a sulphate. However, the invention is not limited to the aforementioned porous matrices or to the aforementioned salts.

The invention also relates to a thermochemical solid / gas reaction method implemented by means of a reactor according to any one of the preceding claims, characterized by the following steps: - the reaction vessel is fed with granular material to from the inlet reservoir in the upper position so that the granular material is deposited on at least one circular screen; the reaction vessel is subjected to an ascending gas flow; the temperature and the adsorbate content of the grains are controlled; the reaction vessel is subjected to vibrations which give the grains both a vertical stirring and a centrifugal movement towards the periphery of the sieve, so that, once arrived at said periphery, the grains are conveyed upwards to a level higher at the level of said sieve and are then brought back down the center of the sieve and so on, cyclically; when said temperature and said adsorbate content reach a set value, said grains are evacuated by gravity to one or more lower sieves and / or to the outlet tank in the lower position.

BRIEF DESCRIPTION OF THE FIGURES [0017] FIG. 1 represents an exemplary embodiment of the reactor according to the present invention.

Figure 2 shows the reactor of Figure 1 with its ancillary equipment.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION [0019] According to the present invention, the concern for the efficiency of mass (water vapor) and energy transfers is at the heart of the design of the reactor system. . It is a matter of applying the principle of the fluidized bed, to promote as much as possible the transport of water vapor to the reaction surface by placing the grains of a suitable granular material in "suspension" in the air. It is also to promote with the invention the transfer of energy of these grains to the air by ensuring that the entire outer surface of each grain is in contact with the air. The flow of air must therefore be turbulent around each grain.

In order to optimize the exchanges of mass and energy, the reactor, as shown in FIG. 1, has a bed of grains which are agitated by vibrations and through which passes a directed air flow of bottom up. The grain bed is deposited on a circular sieve 1 and its stirring movement is controlled in such a way that, while imparting vertical stirring, a centrifugal movement is also made to circulate the grains from the center of the sieve to the periphery of the sieve. this one.

The flow of grain arrived at the periphery is then taken up by a helical ramp 2 which raises a certain height in the reactor and then returns to the center of the sieve via a straight down ramp 20. Thus the bed of grains undergoes agitation and a mixture strongly favoring the exchange of energy and mass (water vapor). This device can equip several sieves 1.6 or all sieves.

In addition, this type of movement advantageously allows to evacuate the grain flow outside the sieve area once it has reached its degree of humidification or optimal dehumidification, thanks to a control of the humidity of the reaction air. This evacuation is either directed by gravity to a lower screen 6 or to the outlet tank 9. The evacuation is effected for example by the opening of a valve in the periphery of the cylinder surrounding the screen. The grains having a centrifugal movement out through this valve to a vertical or oblique conduit which directs them to a lower screen 6 or to the outlet tank 9 (not shown).

Still according to the invention, the reactor comprises vibrating elements 3, preferably low energy consumption, for example unbalance motors or electromagnetic vibrators, which provide the desired vibration of the assembly attached to a static frame 5 by elastic elements 4, for example of the type with silent-blocks or with springs. This vibration gives each grain displacement components in two directions, respectively a vertical direction and a tangential direction. Still according to the invention, this vibration is adjustable in intensity, frequency and direction in order to optimally control the movement of the grains.

The advantage of having a centrifugal circular agitation with recirculation ramp back is multiple: - this allows to mix the bed and offer the best conditions for diffusion of steam to the internal reaction surface grains; this makes it possible to increase the energy transfer between the grains and the air; this reduces the pressure losses of the air through this bed which is fluidized by the agitation and not only by the air flow; this prevents the agglomeration or the segregation of grains as well as the creation of preferential passages for the flow of air; - This allows to evacuate the grain flow outside the sieve area when it reaches its degree of humidification or optimal dehumidification.

According to the invention, the choice of the characteristics of the sieve 1, 6 is achieved in order to have a high rate of air passage and a low pressure drop and a mesh size which is smaller than the size. minimum grain of the bed. The choice of the technical characteristics of the sieve is also guided by a good compatibility with degradation phenomena such as corrosion.

The concept of the reactor of the invention provides for the use of one or more sieves 1, 6 placed in several stages with a gravity circulation of the grain outlet of a stage to the lower stage (not shown). right here).

This multi-stage design allows more complete treatment of exo- or endothermic reactions.

As shown in Figure 2, the reactor is fed grain flow by gravity 8 at its upper stage. Outside the reactor, there are advantageously two solid grain storage tanks, a first tank 7 in the upper position for the grain feed and a second tank 9 in the lower position for harvesting the outgoing grain flow.

An air flow 12 passes through the sieves 1, 6 from bottom to top, they may be arranged in series or in parallel.

A ventilation circuit supplies the reactor with air with temperature and humidity characteristics adapted to the specific thermochemical reaction that takes place inside the reactor. The reactor advantageously comprises internal components that distribute the airflow uniformly through the screens (not shown).

The reactor thus defined can be placed in an open, semi-open or closed air circulation system. Indeed, the air flow through the reactor is part of a circuit. This circuit can be closed, that is to say that it is the same air that passes permanently in the circuit. This circuit comprises elements other than the reactor according to the invention, such as heat exchangers, humidifiers or fans. This circuit can also be open in the direction that is allowed atmospheric air and it can combine the open system and the closed system alternately (semi-open system).

The upper storage tank 7 may in particular be connected to a granular solid feed device 10, known per se to those skilled in the art, for example by Archimedes screws capable of transporting granular material, the granular solid from a storage silo 13, while the lower storage tank 9 may be connected to a feed device 11, also known per se to the person skilled in the art, so as to replenish the storage tank 13 The moisture required for the operation of the reactor can be injected with the gas itself or by spraying and extracted by systems known to those skilled in the art.

Sample Data for the Reactor [0034] In an exemplary embodiment, the size of the grains is of the order of 0.35 mm and their conductivity is of the order of 1 W / m.K. The external surface of the grains is of the order of 16000 m2 / m3 of grains.

For example, the sieve opening is 40% and that of the pores of 0.05 mm.

If we assume a forced convection exchange coefficient of 25 W / m2.K, we can evaluate the heat exchange at 400 kW / K.m3 grains. Assuming a DeltaT = 3K, between the grain surface and the air, the power could reach 1.2 MW / m3 of grain.

List of reference symbols 1. sieve with recirculation ramp 2. helical ramp 3. vibrator 4. elastic element 5. static chassis 6. additional sieve 7. upper grain tank 8. gravity feed 9. lower tank 10. cooling device upper feed 11. lower feeding device 12. air flow 13. storage tank 14. container 20. descending ramp

Claims (16)

A physics or chemisorption reactor between a vapor adsorbate-loaded gas and a granular solid, comprising a reaction vessel (14) for containing a grain bed agitated by controlled vibrations and through which a flow of gas, comprising: - a gas circulation system producing a gas stream (12) loaded with adsorbate in the form of vapor passing through the reactor from bottom to top; - an inlet tank in the upper position (7) for feeding grain flow; a plurality of circular planar screens (1, 6) staggered to receive a flow of grains entering and / or descending by gravity; an outlet reservoir in the lower position (9) for harvesting an outgoing grain flow; means for controlling and adapting the temperature and the adsorbate content of the grains; means for the gravity feed of the grains from one stage to another (1, 6) and / or to the outlet tank (9), characterized in that the reactor further comprises: vibratory means ( 3) to give the grains both a vertical agitation and a centrifugal movement to circulate them from the center of at least one of said sieves (1) to the periphery thereof and - means (2, 20) allowing by virtue of the aforementioned vibratory movements and / or the upward flow of gas, to raise the grains arriving at the periphery of said sieve (1) to a level higher than the level of said sieve (1) from which they fall by gravity in the center of said sieve ( 1). 2. Reactor according to claim 1, characterized in that the means (2, 20) allowing, thanks to the above vibratory movements and / or the upward flow of gas, to raise the grains arrived at the periphery of said sieve (1) to a level upper where they fall by gravity in the center of said screen (1) respectively comprise a helical ramp (2) located at the periphery of said screen (1), followed by a downward ramp (20) to the middle of said screen (1). 3. Reactor according to claim 1, characterized in that said vibratory means (3) comprise motorized vibratory elements with low energy consumption. 4. Reactor according to claim 3, characterized in that the vibrating elements (3) are unbalance motors or electromagnetic vibrators. 5. Reactor according to claim 1, characterized in that the vessel (14) of the reactor is secured to a fixed frame (5) by elastic elements (4). 6. Reactor according to claim 5, characterized in that the elastic elements (4) are of the type silent-blocks or springs. 7. Reactor according to claim 1, characterized in that it comprises feed means (10) of the inlet reservoir in the upper position (7) from a storage silo (13) and feed means (11) of the storage tank (13) from the outlet tank in the lower position (9), so that the circuit traversed by the grains is a closed circuit. 8. Reactor according to claim 1, characterized in that the gas circulation system (12) is an air circulation system and / or in that the adsorbate is water vapor. 9. Reactor according to claim 8, characterized in that the air circulation system (12) is closed, open or semi-open. 10. Reactor according to claim 1, characterized in that the adsorbate vapor is injected into the gas circulation system (12) with the gas itself. 11. Reactor according to claim 1, characterized in that the adsorbate vapor is injected into the gas circulation system (12) by spraying. 12. Reactor according to claim 1, characterized in that it comprises internal means of uniform distribution of the gas flow through the sieves (1, 6). 13. Reactor according to claim 1, characterized in that the stepped sieves (1, 6) are arranged in series and / or in parallel over the height of the reactor. 14. Reactor according to claim 1, characterized in that the granular solid used comprises a porous matrix optionally impregnated with salt. 15. Reactor according to claim 14, characterized in that the porous matrix is a zeolite, a bentonite, a silica gel or an MOF and the salt is a chloride or a sulphate. 16. A solid / gas thermochemical reaction method implemented by means of a reactor according to any one of the preceding claims, characterized by the following steps: - the reaction vessel (14) is fed with granular material from the storage tank; entering the upper position (7) so that the granular material is deposited on at least one circular screen (1); the reaction vessel (14) is subjected to an ascending gas flow (12); the temperature and the adsorbate content of the grains are controlled; the reaction vessel (14) is subjected to vibrations which give the grains both a vertical stirring and a centrifugal movement towards the periphery of the screen, so that, once reached the periphery, the grains are conveyed upwards to a level higher than the level of said sieve (1) and are then brought back down to the center of the sieve (1) and so on, cyclically; when said temperature and said adsorbate content reach a set value, said grains are evacuated by gravity to one or more lower screens (6) and / or to the outlet tank in the lower position (9).