IL111411A

IL111411A - Device and process for carrying out endothermal chemical reactions

Info

Publication number: IL111411A
Application number: IL11141194A
Authority: IL
Original assignee: Deutsche Forsch Luft Raumfahrt
Priority date: 1993-10-26
Filing date: 1994-10-26
Publication date: 1998-09-24
Also published as: DE4336503C2; AU672137B2; DE4336503A1; IL111411A0; AU7590294A

Description

DEVICE AND PROCESS FOR CARRYING OUT ENDOTHERKAL CHEMICAL REACTIONS The invention relates to a device for carrying out endothermal chemical reactions with the participation of particles, comprising a reaction vessel, in which the particles are heatable by electromagnetic radiation.

Within the scope of research projects, the gasification of, for example, oil shale with the aid of electromagnetic radiation was tested on a laboratory scale as carbonaceous material in stationary fluidized beds, whereby the fluidized bed apparatuses were irradiated from outside.

The problem with these known solutions is to be seen in the fact that they are not very efficient on an industrial scale.

The object underlying the invention is therefore to provide a device of the generic type, in which an optimized adaptation of the absorbed radiant power to an essentially complete gasification of the carbonaceous material is possible.

This object is accomplished in accordance with the invention, in a device of the type described at the outset, in that the reaction vessel has a heating zone, in which absorber particles or absorber particles and particles are heatable by direct absorption of the radiation, and that the reaction vessel has a holding or resting zone, in which the absorber particles give off heat to the particles to maintain the chemical reaction.

The inventive solution is therefore to be seen in the fact that, on the one hand, the radiation is absorbed in a suitable manner and, on the other hand, the heat is then made available to the particles for such a time that these are capable of as optimum a chemical reaction as possible.

The advantage of the inventive solution is to be seen, in particular, in the fact that, on the one hand, absorber particles or absorber particles and particles are heated in the heating zone and the heat stored in the absorber particles is then made available for a sufficiently long time to make a sufficiently large amount of heat available for the endothermal reaction process with the particles and thereby to achieve an essentially complete reaction with the particles.

The heating zone can be of different designs. It would, for example, be possible to convey the absorber particles in the heating zone over a horizontal path.

It is, however, particularly advantageous for the heating zone to have a dropping or fall path for the absorber particles or the absorber particles and the particles, which is penetrated by the radiation. The advantage of a heating zone designed in this manner is to be seen in the fact that the particles fly freely due to the fall path and, therefore, there is no necessity to keep the particles, which heat up to a considerable extent in the heating zone, in heat contact with a complicated conveyor means resistant to boiling temperature and thereby lose heat.

In principle, it would be conceivable in the case, in which absorber particles and particles pass through the heating zone, to guide these such that they pass through the heating zone separately, i.e., for example, also in the form of separate fall paths.

It is, however, particularly advantageous for the particles and the absorber particles to pass through the heating zone mixed with one another and, therefore, prior to both the absorber particles and the particles being heated they are already mixed together. This means that following the heating zone the reaction with the particles in the resting zone can continue in a simple manner without further measures due to the uniform mixing with the absorber particles.

A mixing of the absorber particles and the particles is preferably achieved by the absorber particles and the particles being mixable in a mixing zone arranged upstream of the heating zone. The mixing zone is preferably formed by a mixer which merges the two free-falling streams of particles into one another.

In principle, the inventive solution could operate such that the absorber particles and the particles or residues thereof leave the reaction vessel together following the resting zone.

It is, however, particularly expedient for the absorber particles to be conveyed in the reaction vessel in a circuit through the heating zone and the resting zone since this dispenses with the necessity of supplying large amounts of absorber particles through suitable locks, for example, to the reaction vessel and removing them from it.

For this purpose, it is preferable for the absorber particles to be adapted to be brought to the heating zone in a return means from a discharge means following the resting zone.

This recirculation can be designed in the most varied of manners. For example, this return means can operate mechanically. It is, however, even more advantageous for the return means to operate with a carrier gas because the problems of moved parts at high temperatures are thereby avoided.

In addition, in the case of a return means operating with carrier gas, the recirculation of the absorber particles leads to a separator which separates the carrier gas from the absorber particles .

The separator is preferably arranged to follow the return means and generates a freely falling absorber particle layer.

In order to achieve, in addition, a preliminary heating of the absorber particles in the return means, it is preferable for the return means to likewise be heatable by the radiation.

In a particularly advantageous embodiment, the return means has a radiation-absorbing surface.

Theoretically, the radiation-absorbing surface could be arranged such that it is acted upon by radiation separately while at another location in the reaction vessel the absorber particles are acted upon likewise by radiation on their own or as a mixture with the particles.

It is, however, particularly advantageous for the absorber particles or the absorber particles with the particles to form an absorber curtain in front of the radiation-absorbing surface of the return means.

This absorber curtain is preferably selected to be so thin that the radiation not impinging on absorber particles or particles impinges on the radiation-absorbing surface of the return means, and via this heats up the absorber particles returned in the return means so that no radiation energy is lost.

In the simplest case, the return means is designed such that it has a return channel, the front side of which facing the radiation forms the radiation-absorbing surface at least in the heating region.

With respect to the design of the resting zone, no details have been specified in conjunction with the previous comments on individual embodiments. In an advantageous embodiment, for example, the resting zone is formed in the reaction vessel by a holding or resting tank, whereby this resting tank is preferably designed such that it catches the absorber curtain, formed by the absorber particles or the absorber particles and the particles, moving through the heating zone.

This resting tank is preferably designed such that in it the absorber particles and the particles form a bed, in which the absorber particles and the particles are in direct, preferably bodily heat contact with one another.

Alternatively thereto, it is, however, also conceivable to provide the resting zone as an additional fall or conveyor path for absorber particles and particles, in which these are moved along.

Since new absorber particles and particles are constantly being fed to the resting zone, it is necessary to transport these away from the resting zone again.

For this purpose, a discharge means is preferably provided for the absorber particles and the residues of the particles remaining after the gasification.

In the case of a resting tank, the discharge means is designed in the simplest case such that it forms a channel leading out of the tank, preferably a channel following the direction of gravity.

In order to be able, in addition, to feed absorber particles to the return means again following the resting zone, a particle separator is preferably provided downstream of the resting zone and this particle separator draws off at least some of the residues of the particles following the chemical reaction.

The particles can, themselves, carry a substance which is subjected to an endothermal chemical reaction. It is, however, also conceivable for the particles themselves to represent a catalyst which serves to catalyze chemical reactions when heated by the electromagnetic radiation.

The inventive solution is particularly suitable when the chemical reaction is a reaction of gasification, during which a product gas results.

Carbonaceous materials, the carbon of which is gasified, are preferably considered as materials for the particles.

In a particularly advantageous embodiment of the inventive solution, the absorber particles are ash particles, for example, of gasified particles so that no exact separation between the residues of the particles and the absorber particles is to be carried out but rather the ash collecting in the resting zone is removed after this zone to the same extent as new ash results in the resting zone while the remainder of the ash particles is guided to the heating zone via the return means as absorber particles. These particles are heated up in the heating zone due to the radiation and, thereafter, transfer their heat to the particles in the resting zone in order to maintain, for example, the gasification process of the particles.

In the inventive solution, the carrier gas for the absorber particles could, for example, be an inert gas. This would, however, have the disadvantage that the inert gas has, in turn, to be constantly separated from the product gas resulting during the gasification of the particles.

For this reason, it is particularly advantageous for product gas to be used as carrier gas so that no complicated separation between the carrier gas and the product gas is required in the reaction vessel but rather a common discharge of product gas can be provided, from which carrier gas is, in turn, obtained.

With respect to the heating zone, it has so far merely been specified that the absorber particles or absorber particles and particles are heated up by electromagnetic radiation in this zone.

It is, however, particularly advantageous for the heating zone to be designed such that the absorber particles or absorber particles and particles passing therethrough directly absorb the solar radiation reflected from mirror systems to the reaction vessel. In this case, energy can be obtained in a particularly simple manner from solar radiation, namely by this being reflected directly from a mirror system or a large mirror field onto the reaction vessel and into the heating zone. The mirror system is preferably designed such that it focuses the solar radiation onto the heating zone, whereby the size of the heating zone is dependent on the focusing.

In order to protect the heating zone from undesired outer influences and also, in particular, to enable the product gas to be collected in a simple manner, it is preferable for the radiation to enter the reaction vessel through a window so that the interior of the reaction vessel is closed by the window.

To prevent the window becoming soiled by absorber particles or particles which cake on the window due to the high temperatures, the window is preferably provided with a cleaning means which prevents the deposit of absorber particles or particles on an inner side of the window. In this respect, the provision of the fall path in the heating zone also proves to be particularly advantageous since the amount of cleaning gas required can be kept much less, in contrast to absorber particles and particles transported in a stream of carrier gas, since the turbulences are less.

The cleaning means is preferably designed such that it generates a stream of cleaning gas which cleans the window free on its inner side facing the absorber particles or particles.

An inert gas can, for example, be used as cleaning gas. In order to avoid a complicated separation of cleaning gas and product gas in this case, as well, it is advantageous for the product gas to be used as cleaning gas of the cleaning means so that this can also, in turn, be removed via the product gas discharge means already provided for the reaction vessel.

In addition, the invention relates to a process for carrying out endothermal chemical reactions with the participation of particles, in which the particles are heated in a reaction vessel by electromagnetic radiation in order to cause the chemical reaction to take place. The object specified at the outset is accomplished in accordance with the invention, in a process of the type specified above, in that the electromagnetic radiation impinges in a heating zone, in which absorber particles or absorber particles and particles are heated directly by the radiation, and that a resting zone is provided after the heating zone, the heated absorber particles giving off heat to the particles in this resting zone to maintain the chemical reaction.

Additional, advantageous embodiments of the inventive process are already mentioned in conjunction with the advantageous embodiments of the inventive device.

Oil shale, lignite, pit coal, biomass or similar substances are preferably used as materials for the material particles.

The temperatures in the heating zone are preferably at more than 800°C, even better at more than 1000°C depending on the type of chemical reaction, in particular gasification.

Additional features and advantages of the invention are the subject matter of the following description as well as the drawings of one embodiment.

In the drawings: Figure 1 is a schematic illustration of an inventive gasification means; gure 2 is a longitudinal section through the reaction vessel, and Figure 3 is a cross section through the reaction vessel along line 3-3 in Figure 2.

An embodiment of an inventive gasification means, designated as a whole as 10, comprises a solar collector system 12 which reflects solar radiation in the direction of a reaction vessel designated as a whole as 14.

This reaction vessel 14, illustrated as a whole in Figure 2, comprises a thermally insulated housing 16 with a radiation window 18 which is arranged therein and through which radiation 20 focused by the solar collector system 12 enters an interior of the reaction vessel 14.

The radiation 20 thereby impinges on an absorber curtain 24 consisting of absorber particles and material particles of the material to be gasified, this curtain falling downwards via a fall path 22 due to the action of gravity. The absorber curtain 24 is heated by the focused radiation while passing through a heating zone 26.

Following the heating zone 26, the heated particles of the absorber curtain 24 pass into a resting zone 28 which is formed by a resting tank 30. In this resting tank 30, the absorber particles and the material particles of the material to be gasified are collected and are in heat contact with one another so that the absorber particles have the possibility of passing on heat to the material particles. This means that the endothermal gasification reaction already started in the heating zone 26 can be maintained in the material particles until the material particles are gasified essentially completely, essentially by absorbing heat from the absorber particles.

The mixture of absorber particles and essentially gasified material particles passes out of the resting tank 30 preferably designed as a thermally insulated receptacle, through a standpipe 31 which serves to compensate the pressure ratios, to a particle separator designated as a whole as 32, in which the absorber particles are for the greater part conveyed into a return means 36 by a gas supply 34 and the lesser part to an ash discharge means 38.

The return means 36 comprises a return channel 37, in which carrier gas is supplied in addition via a carrier gas supply 40 and this carrier gas conveys the absorber particles in the return channel 37 from the particle separator 32 to a separator 42. In this respect, the return channel 37 preferably proceeds from the particle separator 32 along a rear side 44 of the housing 16 located opposite the radiation window 18 as far as the separator 42 arranged above the heating zone 26. In the separator 42, the carrier gas and the absorber particles are separated and these absorber particles form an absorber particle layer 48 which falls downwards along a front side of the return channel 37 facing the radiation window 18 and falls into a mixer 50. In this mixer, material particles are added to the absorber particle layer via a supply means 52 and mixed therewith so that the absorber curtain 24 already mentioned exits from the mixer 50 and likewise drops along the front side 46 of the return channel 37 via the fall path 22 through the heating zone 26.

The front side 46 of the return channel 37 is designed in the region of the heating zone 26 as radiation-absorbing surface 54 which, for its part, absorbs the radiation 20 not completely absorbed by the absorber curtain 24, contributes to a heating of the return channel 37 in this region and thereby already brings about a preliminary heating of the absorber particles conveyed in the return channel 37 so that these arrive in the separator 42 already preheated.

Due to the heating up of the absorber particles and material particles forming the absorber curtain 24, the gasification reaction already commences in the material particles in the heating zone 26 and a product gas results. The gasification reaction continues after leaving the heating zone 26 and is maintained in the resting zone 28 by heat transmission from the absorber particles to the material particles so that the material particles are essentially gasified in the resting zone 28. The product gas thereby occurring preferably exits from an opening 56 of the resting tank 30 catching the absorber curtain 24 and flows via the interior of the reaction vessel 14 to a product gas discharge means 62 arranged in the base portion 60 of the housing 16. The product gas is supplied from the product gas discharge means 62 to a particle separator 64, preferably a cyclone, which separates remaining ash particles out of the product gas and then supplies the product gas to an intermediate storage means 66 for the product gas, whereby cooling preferably takes place in addition in a cooler 68 provided between the particle separator 64 and the intermediate storage means 66 for the product gas. Already prior to leaving the reaction vessel 14, the product gas is cooled in a heat exchanger 70 which is arranged in the base portion 60, whereby the heat exchanger 70 has a heat exchanger element 72, which is penetrated by the carrier gas flowing to the carrier gas supply 40. This heat exchanger element already removes heat from the out-flowing product gas and the discharged ash and heats the carrier gas flowing to the carrier gas supply 40 accordingly.

Product gas from the intermediate storage means 66 for the product gas is likewise preferably used as carrier gas and this is supplied via a condenser 74 to the heat exchanger element 72. Similarly, a condenser 76 is provided which likewise condenses product gas from the intermediate storage means 66 for product gas and supplies this to the gas supply 34 of the particle separator 32, whereby this stream of gas can also be heated via a heat exchanger.

Moreover, the inventive gasification device is preferably- operated such that ash particles remaining . during the gasification of the material particles are used as absorber particles so that absorber particles are automatically formed from the material particles after the gasification reaction. In this respect, the amount of ash to be removed via the ash discharge means 38 is such that the quantity of absorber particles in the reaction vessel remains approximately the same.

As illustrated in Figure 3, the radiation window 18 is provided, in addition, with a cleaning means 80 for keeping the radiation window 18 clear, in particular on its side facing the absorber curtain 24. This cleaning means causes a film 82 of cleaning gas to flow over an inner side of the radiation window 18 facing the absorber curtain 24, whereby this film of cleaning gas prevents absorber particles or material particles adhering to the inner side 84 of the radiation window 18. This film 82 of cleaning gas is supplied via a cleaning gas supply 86 which is likewise supplied from the condenser 76 or from an additional condenser so that product gas is also used as cleaning gas. In this case, as well, heating is possible via a heat exchanger.

The entire reaction vessel 14 is, therefore, penetrated in its interior merely by product gas which, on the one hand, results therein and, on the other hand, is supplied thereto in order to convey a defined quantity of absorber particles in the circuit and, on the other hand, to separate in the particle separator 32 the amount of ash resulting in accordance with the material particles supplied and at the same time to operate the cleaning means 80 for the radiation window 18, as well.

As illustrated in Figure 3, the return channel 37 preferably extends as a flat channel designed like the segment of an arc over the rear side 44 of the housing 16 and engages with its radiation-absorbing surface 54 around the curved or flat inner side 84 of the radiation window 18. This means that it is possible to homogenize the temperature of the radiation window 18 via its distance since each point of the radiation window 18 "sees" a large proportion of the radiation-absorbing surface 54 and, therefore, receives the thermal return radiation from almost the entire region of the radiation-absorbing surface 54 and the radiation curtain 24 so that a local and disadvantageous overheating of the radiation window 18 is avoided.

In addition, the absorber curtain 24 is advantageously designed such that a predetermined fraction of the radiation 20 always impinges on the radiation-absorbing surface 54, is absorbed thereby and therefore leads to a defined heating of the absorber particles conveyed by the carrier gas through the return channel 37.

Due to the curvature of the radiation-absorbing surface 54 it is also ensured that the radiant flux density of the radiation 20 is essentially homogeneous over the entire radiation-absorbing surface 54.

In order to be able to start up the inventive gasification device without having product gas already available, an inert gas storage means 90 is preferably provided in addition and inert gas can be supplied to the carrier gas supply 40 from this storage means via the condenser 74 to circulate the absorber particles. This inert gas can also be used to clean the system.

Claims

1. 11411/2 P A T E N T C L A I M S Device for carrying out endothermal . chemical reactions with material parotides , comprising a reaction vessel, said material particles being heatable therein by electromagnetic radiation, characterized in that the reaction vessel (14) has a heating zone (26), that absorber particles or absorber particles and said material particles are heatable in said heating zone by direct absorption of the radiation and that the reaction vessel ( 14 ) has a resting zone ( 28 ) , said absorber particles giving off heat to said material particles in said resting zone in order to maintain the chemical reaction.

2. Device as defined in claim "1, "characterized"' in- that' the heating zone (26) has a fall, path (22) for the absorber particles or the absorber particles and the material particles, the radiation (20) penetrating said path.

3. Device as defined in claim 1 or 2, characterized in that the material particles and the absorber particles pass through the heating zone (26) mixed with one absorber.

4. Device as defined in any of the preceding claims, characterized in. that the absorber particles and the material particles are mixable in a mixing zone ( 50 ) arranged upstream of the heating zone (26). 111411/2 - 17 -

5. Device as defined in any of the preceding claims, characterized in that the absorber particles are conveyed in the reaction vessel (14) in a circuit through the heating zone (26) and the resting zone (28).

6. Device as defined in claim 5, characterized in that the absorber particles are adapted to be brought to the heating zone (26) in a. return means (36) from a discharge means following the resting zone (28).

7. Device as defined in claim 6, characterized in that the return means (36) operates with carrier gas.

8. Device as defined in claim 6 or 7, characterized in that the return means (36) leads to a separator (42) separating the carrier gas from the absorber particles.

9. Device as defined in claim 8, characterized in that the separator (42) generates a freely falling absorber particle layer (48).

10. Device as defined in any of claims 6 to 9, characterized in that the return means (36) is heatable by the radiation ( 20 ) .

11. Device as defined in claim 10, characterized in that the return means (36) has a radiation-absorbing surface (54).

12. Device as defined in claim 11, characterized in that the absorber particles or the absorber particles with the material particles form an absorber curtain (24) in 111411/2 - 18 - front of the radiation-absorbing surface (54) of the return means (36).

13. Device as defined in claim 12, characterized in that the absorber curtain (24) allows part of the radiation (20) entering the heating zone (26) to impinge on the radiation-absorbing surface (54).

14. Device as defined in any of the preceding claims, characterized in that the resting zone ( 28 ) in the reaction vessel (14) is formed by a resting tank (30).

15. Device as defined in claim 14, characterized in that the resting tank (30) is designed such that in it the absorber particles and the material particles form a bed, the absorber particles and the material particles being in direct heat contact with one another in said bed.

16. Device as defined in claims 6 to 15, characterized in that a particle separator (32) is provided downstream of the resting zone (28), said separator drawing off at least some of the residues of the chemically reacted material particles.

17. Device as defined in any of the preceding claims, characterized in that the absorber particles are ash particles of gasified material particles.

18. Device as defined in any of claims 7 to 17, characterized in that the carrier gas is a product gas 111411/2 - 19 - resulting during the gasification of the material particles .

19. Device according to any of the preceding claims, characterized in that the heating zone (26) is designed such that the absorber particles or absorber particles and material particles passing through said heating zone directly absorb the solar radiation (20) reflected from mirror systems ( 12 ) to the reaction vessel ( 14 ) .

20. Device as defined in any of the preceding claims, characterized in that the radiation (20) enters the reaction vessel (14) through a window (18).

21. Device as defined in claim 20, characterized in that the window (18) is provided with a cleaning means (80) preventing the deposit of absorber particles or material particles on an inner side (84) of the window (18).

22. Device as defined in claim 21, characterized in that the cleaning means ( 80 ) is designed such that it generates a stream of cleaning gas (82) cleaning the window (18) free on its inner side (84) facing the absorber particles or material particles.

23. Device as defined in claim 21 or 22, characterized in that the cleaning gas of the cleaning means ( 80 ) is product gas. Process for carrying out endothermal chemical reactions with material particles, wherein said material particles - 20 - are heated in a reaction vessel by electromagnetic radiation to cause the chemical reaction to take place, characterized in that the electromagnetic radiation impinges in a heating zone, absorber particles or absorber particles and material particles being heated directly by the radiation in said heating zone, and that a resting zone is provided after the heating zone, the heated absorber particles giving off heat to the material particles in 'said resting zone to maintain the chemical reaction.