WO2016074977A1

WO2016074977A1 - Device for capturing a target gas and method for operating the device

Info

Publication number: WO2016074977A1
Application number: PCT/EP2015/075503
Authority: WO
Inventors: Gerald Sprachmann; Tobias Proell; Gerhard SCHÖNY; Hendrik Dathe; Gerardus Antonius Franciscus Van Mossel
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2014-11-10
Filing date: 2015-11-03
Publication date: 2016-05-19

Abstract

The present invention relates to a device for capturing a target gas from a gas stream. The device comprises two countercurrent multistage fluidized bed reactors (1, 2), and a first solid particles feed (8, 14, 18, 24) and a second solid particles feed (7, 13, 17, 23). The first solid particles feed (8, 14, 18, 24) extends from the bottom of the second reactor to the top of the first reactor to transport solid particles from the second reactor (2) to the first reactor (1). The second solid particles feed (7, 13, 17, 23) extends from the bottom of the first reactor to the top of the second reactor to transport solid particles from the first reactor (1) to the second reactor (2). The first and second reactor comprise sieve plates and/or nozzle plates (35), with downcomers (37) and preferably overflow weirs (36). The downcomers (37) comprise one or more mechanical devices, preferably one or more adjustable mechanical flaps (38) and/or one or more slides (39), for control of the downcomer pressure drop.

Description

DEVICE FOR CAPTURING A TARGET GAS AND METHOD FOR OPERATING THE DEVICE

Field of the invention

The present invention relates to a device for capturing a target gas, such as carbon dioxide, from a gas stream, such as flue gas. The present invention further relates to a method of operating the device.

Background of the Invention

During the last decades there has been a substantial global increase in the amount of carbon dioxide emission to the atmosphere. Emissions of carbon dioxide into the atmosphere are thought to be harmful due to its

"greenhouse gas" property, contributing to global warming. Following the Kyoto agreement, carbon dioxide emission has to be reduced in order to prevent or counteract unwanted changes in climate. Large

anthropogenic sources of carbon dioxide emission are processes that combust fossil fuels, for example coal, natural gas or petroleum products, for electricity generation, transportation and heating purposes, and for production of steel and cement. These processes result in the production of gases comprising carbon dioxide. Thus, removal of at least part of the carbon dioxide prior to emission of these gases into the atmosphere is desirable.

Processes for removal of carbon dioxide from gases are known in the art. Many processes are based on liquid absorption processes, with varying compositions of the absorption liquids. A drawback of these processes is the high energy consumption in the stripper unit to recover the absorbent, leading to a lower overall energy output. EP-A-2463013 describes a process for removing carbon dioxide from a gas stream in an energy-efficient and relatively simple manner by contacting the gas stream with a regenerable solid adsorbent in a circulating fluidized bed system with two reactors, each having a single stage fluidized bed. The disadvantage of this device is that high C02 capture efficiencies (percentage of C02 removed from the gas) require high solid

recirculation rates and/or high flows of stripping gas into the regenerator and thus high amounts of

regeneration energy.

WO 2011/041317 describes a fluidized reactor system for removing impurities from a gas.

WO 2013/155293 describes a fluidized bed method and system for gas component capture.

Thus, there is a need for a more efficient device, and a method for the startup of a device, for the removal of a target gas, such as carbon dioxide, from gases using solid adsorbents.

Summary of the Invention

Accordingly, the present invention relates to a device for capturing a target gas, such as carbon dioxide, from a gas stream, wherein the device comprises :

• a first countercurrent multistage fluidized bed reactor (1) and a second countercurrent multistage fluidized bed reactor (2); each said reactor (1, 2) having at least two beds (40) of solid particles to be fluidized; and

• a first solid particles feed (8, 14, 18, 24) and a second solid particles feed (7, 13, 17, 23);

wherein each said reactor has a solid particles outlet (41, 42) provided in the lower part of the respective reactor (1, 2) and a solid particles inlet (43, 44) provided in the upper part of the respective reactor (1, 2 ) ;

wherein the second feed (7, 13, 17, 23) extends from the solid particles outlet (41) of the first reactor (1) to the solid particles inlet (44) of the second reactor

(2), on the one hand, and the first feed (8, 14, 18, 24) extends from the solid particles outlet (42) of the second reactor (2) to the solid particles inlet (43) of the first reactor (1), on the other hand, to form a loop for circulating the solid particles;

wherein the first reactor (1) has a gas stream inlet (3) for supplying the gas stream to be treated and a treated gas outlet (5) for discharging a treated gas stream depleted from said target gas;

wherein the second reactor (2) has a stripping gas inlet (4) for supplying a stripping gas for stripping target gas from the solid particles within the beds (40) and an enriched stripping gas outlet (6) for discharging stripping gas enriched with said target gas;

wherein the first solid particles feed (8, 14, 18,

24) comprises a first riser (14) for lifting the solid particles with a gas to a level higher than the solid particles inlet (43) of the first reactor (1), a first particles-gas-separator (18) provided at the upper end of the first riser (14) for separating the solid particles from the gas, and a first lower connection (8) connecting the solid particles outlet (42) of the second reactor (2) to the lower end of the first riser (14);

wherein the second solid particles feed (7, 13, 17, 23) comprises a second riser (13) for lifting the solid particles with a gas to a level higher than the solid particles inlet (44) of the second reactor (2), a second particles-gas-separator (17) provided at the upper end of the second riser (13) for separating the solid particles from the gas, and a second lower connection (7)

connecting the solid particles outlet (41) of the first reactor (1) to the lower end of the second riser (12); wherein the first reactor comprises in the range of from 3 up to 30 sieve plates and/or nozzle plates (35), with downcomers (37) and preferably with overflow weirs (36) ;

wherein the downcomers (37) in the first reactor comprise one or more mechanical devices, preferably one or more adjustable mechanical flaps (38) and/or one or more slides (39), for control of the downcomer pressure drop; and

wherein the second reactor comprises in the range of from 3 up to 30 sieve plates and/or nozzle plates (35), with downcomers (37) and preferably with overflow weirs (36) ;

wherein the downcomers (37) in the second reactor comprise one or more mechanical devices, preferably one or more adjustable mechanical flaps (38) and/or one or more slides (39), for control of the downcomer pressure drop .

In accordance with the present invention the efficiency of the device with respect to the amount of C02 (=carbon dioxide) that has been adsorbed on the solid particles has increased, bringing about a substantial improvement in overall C02 capture efficiency. This is due to the improved counter current contact between the carbon dioxide containing gas stream and the solid adsorbent particles, on the one hand, and the improved counter current contact between the stripping gas and the solid particles to be stripped from C02, on the other hand. Suitably, the process leads to a carbon capture efficiency of at least 80%, more preferably 90%, thus the resulting carbon dioxide-depleted gas stream comprises preferably less than 20% of the C02 which was present in the carbon dioxide containing gas stream before

treatment, more preferably this is less than 10% of the C02 which was present in the carbon dioxide containing gas stream before treatment, most preferably this is less than 5% of the C02 which was present in the carbon dioxide containing gas stream before treatment.

The present invention further relates to a method for starting up a process in which a device according to the present invention is operated. The startup method comprises steps of:

• controlling the pressure drop in downcomers (37) in the first reactor by adjusting the one or more mechanical devices, which preferably is/are one or more adjustable mechanical flaps (38) and/or one or more slides (39) , until the downcomers (37) are filled, and

• controlling the pressure drop in downcomers (37) in the second reactor by adjusting the one or more mechanical devices, which preferably is/are one or more adjustable mechanical flaps (38) and/or one or more slides (39), until the downcomers (37) are filled.

Detailed Description of the invention

The present invention relates to a device for capturing a target gas, such as carbon dioxide, from a gas stream, wherein the device comprises:

• a first countercurrent multistage fluidized bed reactor and a second countercurrent multistage fluidized bed reactor; each said reactor having at least two beds of solid particles to be fluidized; and • a first solid particles feed and a second solid particles feed;

wherein each said reactor has a solid particles outlet provided in the lower part of the respective reactor and a solid particles inlet provided in the upper part of the respective reactor;

wherein the second feed extends from the solid particles outlet of the first reactor to the solid particles inlet of the second reactor, on the one hand, and the first feed extends from the solid particles outlet of the second reactor to the solid particles inlet of the first reactor, on the other hand, to form a loop for circulating the solid particles;

wherein the first reactor has a gas stream inlet for supplying the gas stream - which fluidizes the beds of the first reactor and is treated by the beds of the reactor - and a treated gas outlet for discharging a treated gas stream depleted from said target gas;

wherein the second reactor has a stripping gas inlet for supplying a stripping gas - which fluidizes the beds of the second reactor and strips target gas from these beds - and an enriched stripping gas outlet for discharging stripping gas enriched with said target gas;

wherein the first solid particles feed comprises a first riser for lifting the solid particles with a first lift gas to a level higher than the solid particles inlet of the first reactor, a first particles-gas-separator provided at the upper end of the first riser for

separating the solid particles from the first lift gas, and a first lower connection connecting the solid particles outlet of the second reactor to the lower end of the first riser;

wherein the second solid particles feed comprises a second riser for lifting the solid particles with a second lift gas to a level higher than the solid

particles inlet of the second reactor, a second

particles-gas-separator provided at the upper end of the second riser for separating the solid particles from the second lift gas, and a second lower connection connecting the solid particles outlet of the first reactor to the lower end of the second riser.

To improve the contact between the gas stream and the solid particles even more, the adsorption zone comprises from 3 up to 30 fluidized beds (stages), preferably from 4 up to 15 beds (stages) . These beds are created by using sieve plates and/or nozzle plates. These sieve plates and/or nozzle plates comprise downcomers. Further, the sieve plates and/or nozzle plates preferably comprise overflow weirs.

These downcomers in the first reactor comprise one or more mechanical devices, such as adjustable mechanical flaps, for control of the downcomer pressure drop.

To improve the contact between the stripping gas and the target gas-enriched solid particles even more, the desorption zone comprises in the range of from 3 up to 30 fluidized beds (stages) , preferably from 4 up to 15 fluidized beds (stages) . These beds are created by using sieve plates and/or nozzle plates. These sieve plates and/or nozzle plates comprise downcomers. Further, the sieve plates and/or nozzle plates preferably comprise overflow weirs.

These downcomers in the second reactor comprise one or more mechanical devices, such as adjustable mechanical flaps, for control of the downcomer pressure drop.

As already indicated, the present invention relates to a device for removing a target gas from a gas stream. The device is especially suitable for treating any gas comprising carbon dioxide as target gas to be removed.

For example, the gases to be treated may be natural gas, synthesis gas, obtained for instance by (catalytic) partial oxidation and/or by steam methane reforming of hydrocarbons, e.g. methane, natural or associated gas, naphtha, diesel and liquid residual fractions, gases originating from coal gasification, coke oven gases, refinery gases, hydrogen and hydrogen containing gases, and flue gases. Suitably, the gas comprises in the range of from 0.1 to 70% (v/v) of carbon dioxide, preferably from 1 to 45% (v/v) . In the event that the gas is a flue gas, the amount of carbon dioxide will generally be lower, suitably from 0.1 to 20% (v/v) and the gas will usually also comprise oxygen, preferably in the range of from 0.25 to 20% (v/v), more preferably from 0.5 to 15% (v/v) , still more preferably from 1 to 10% (v/v) . As the temperature of the gas stream to be treated will

typically be relatively high, preferably the gas stream is cooled prior to being introduced in the first reactor. Cooling of the gas stream prior to being introduced in the first reactor may be done by means known in the art, for example using a fan, a cooler or a gas-gas exchange.

In the first reactor, the target gas containing gas stream, such as a carbon dioxide containing gas stream, is contacted with solid particles in an adsorption zone. The adsorption zone comprises at least two fluidized beds of said solid particles. The beds - each forming a so called stage - are arranged above each other, so that the solid particles are essentially flowing downwards from bed to bed and the gas stream is essentially flowing upwards. This results in more efficient C02 removal as compared to co-current flowing processes or to single- stage processes where the solids are mixed throughout the stage.

Once the solid particles have reached the bottom of the adsorption zone in the first reactor, it has been enriched with the target gas, such as carbon dioxide, and regeneration of the solid particles is required.

Therefore, at least part of the target gas-enriched solid particles as obtained in the first reactor is transferred to the second riser, which uses a second lift gas to transport the solid particles upwards. To separate the solid particles from the second lift gas, a second particles-gas-separator is required. Suitably, the second particles-gas-separator comprises one or more cyclones, and/or filters and/or inertial separators and/or baffle separators and/or gravity separators for carrying out the separation .

The second lift gas is preferably a gas that is about the same as the target gas or it might even be pure target gas. In case of carbon dioxide being the target gas, the second lift gas might comprise carbon dioxide as main component. Part of the second lift gas or all the second lift gas leaving the second particles-gas- separator might, according to a further embodiment of the invention, be recycled to the second riser using a compressor or fan.

In the second reactor of the invention, at least part of the target gas-enriched solid particles, such as carbon dioxide-enriched solid particles in case C02 is the target gas, is regenerated in a desorption zone to obtain target gas-depleted solid particles and a target gas-enriched stripping gas. The desorption zone comprises at least two fluidized beds of said solid particles . The fluidized beds - each forming a so called stage - are arranged above each other, so that, here again, the solid particles are essentially flowing downwards from bed to bed and stripping gas is essentially flowing upwards. The stripping gas can comprise carbon dioxide and/or any condensable gas such as alcohols and others, more preferably the stripping gas comprises steam, or a mixture of the named examples with or without steam.

Once the solid particles have reached the bottom of the desorption zone, a large part of the target gas, such as C02, has been removed from the particles and these depleted solid particles can be reused again in the first reactor of the invention. To this end, at least part of the target gas-depleted solid particles as obtained in the second reactor is passed to the first riser, where a first lift gas transports the solid particles to the top of the first riser. The first lift gas is preferably a gas that is inert to the target gas adsorption reaction

(which target gas might according to the invention be carbon dioxide) . Examples of such inert gases are air, nitrogen, steam or combinations thereof. According to preferred embodiment of the invention, a part of the target gas-depleted gas stream, that is obtained at the gas outlet of the first reactor of the invention, as first lift gas. Part of the first lift gas or all the first lift gas leaving the first particles-gas-separator can be recycled to the first riser using a compressor or fan.

To separate the particles from the first lift gas, a first particles-gas-separator is required, located at the upper end of the first riser. Suitably, the first particles-gas-separator comprises one or more cyclones and/or filters and/or inertial separators and/or baffle separators and/or gravity separators for carrying out the separation .

Preferably, substantially all of the fluidized carbon dioxide-depleted solid adsorbent as obtained in the second reactor is recycled to the adsorption zone of the first reactor.

In case of carbon dioxide as target gas, the solid particles - also called solid adsorbent - used in the reactors can comprise any solid that interacts with carbon dioxide. Examples are activated carbon, molecular sieves, metal organic frameworks (MOF's), covalent organic frameworks (COF's), zeolitic-imidazolate

frameworks (ZIF's) and others. Preferably the solid adsorbent comprises a carrier material that has been impregnated or grafted with one or more carbon dioxide absorbing or adsorbing compounds. Suitably, the solid adsorbent is a carrier material that has been impregnated or grafted with one or more carbon dioxide absorbing compounds. Preferably, the solid adsorbent comprises a carrier material that is selected from the group

consisting of porous materials, activated carbons, zeolites, metal-organic frameworks, and zeolitic- imidazolate frameworks, more preferably mesoporous materials. Preferably, mesoporous supports are one of silica, alumina, titania, zirconia, magnesium oxide, amorphous silica-aluminas (ASA) , PMA (Polymethyl

methacrylate ) or combinations thereof, more preferably silica. The properties of the carrier material should be such that sufficient carbon dioxide adsorbing or

absorbing material can be impregnated or grafted on it. Preferably the pore volume should be greater than 0.9 ml/g. Another preferred property of the carrier material is good fluidization behaviour, i.e. preferably a spherical shape and a high attrition resistance. The size of the carrier material is more or less equal to that the final solid adsorbent; the particle size required is determined by the gas velocity in the first reactor, second reactor, and the two risers. Typically, an average particle diameter of the solid particles that can be applied is between 200 and 4000 micrometer.

The one or more carbon dioxide absorbing compounds might, according to an embodiment of the invention, comprise one or more amines. Suitable amines to be used include primary, secondary and/or tertiary amines, especially amines. Suitable examples include monoethanol amine (MEA) , diethanolamine (DEA) , triethanolamine (TEA) , diisopropanolamine (DIPA) and methyldiethanolamine (MDEA) or mixtures thereof. A preferred amine is a secondary or tertiary amine, preferably an amine compound derived from ethanol amine, more especially DIPA, DEA, MMEA

(monomethyl-ethanolamine) , MDEA, or DEMEA (diethyl- monoethanolamine ) , preferably DIPA or MDEA. Preferably, use is made of one or more polyethylene amines. Suitable examples include diethyleneamine, triethylenetetraamine, tetraethylenepentamine, tetraacetylethylenediamine, and polyethyleneimine. More preferably, use is made of polyethyleneimine, tet aethylenepentamine,

polyethylenehexamine, or any mixture thereof. Most preferred is to use polyethyleneimine and combinations of polyethylenimine and other active compounds, such as (3- aminopropyl) triethoxysilane (APTES) .

Preferably, the first reactor is operated at a temperature in the range of from 20-100 °C and a pressure in the range of from 0.8-100 bara, preferably in the range of from 0.8-40 bara, and more preferably in the range of from 0.95-20 bara. The volume ratio of the volume of the first reactor taken in by the gas compared to the volume taken in by the solid particles is not critical, but as an example a value in the range of 2-200 can be mentioned. The first reactor produces a gas stream with a reduced target gas content and target gas-enriched solid adsorbent.

In a preferred embodiment of the present invention, at least part of the target gas-enriched solid adsorbent as obtained in the first reactor and re-introduced into the second reactor is preheated before re-introduction. Preferably, substantially all of the target gas-enriched solid adsorbent as obtained in the first reactor and re- introduced into the second reactor is preheated before re-introduction. Such preheating can suitably be carried out by means of a heat exchanger.

Preferably, the second reactor is operated at a temperature in the range of from 60-140 °C and a pressure in the range of from 0.8-100 bara, preferably in the range of from 0.8-40 bara, and more preferably in the range of from 0.95-20 bara. The volume ratio of the volume of the second reactor taken in by the gas compared to the volume taken in by the solid particles is not critical, but as an example a value in the range of 2-200 can be mentioned. The second reactor produces a gas stream with an increased target gas content and target gas-depleted solid adsorbent.

In a preferred embodiment of the present invention, at least part of the target gas-depleted solid adsorbent as obtained in the second reactor and re-introduced into the first reactor, is cooled before re-introduction.

Preferably, substantially all of the target gas-depleted solid adsorbent as obtained in the second reactor and re^¬ introduced into the first reactor is cooled before re- introduction. Such cooling can suitably be carried out by means of a heat exchanger.

In the context of the present invention the phrase

"substantially all" is meant to mean more than 95%, preferably more than 98%, and more preferably more than 99% of the solid adsorbent or gas stream in question.

Preferably, the height-to diameter ratio of the staged first and second reactor to be used in accordance with the present invention are in the range of 0.25-30. This ratio will depend on the cleanup-target and on the plant capacity: height increases with cleanup-target and diameter increases with capacity. The adsorption zones in the first reactor are preferably equipped with internal cooling means to control the temperature in the

adsorption zones and to withdraw the released heat of adsorption. These internal cooling means in the first reactor are preferably arranged inside the fluidized beds and comprise heat exchanger surfaces. The desorption zones in the second reactor are preferably equipped with internal heating means to control the temperature in the desorption zones and to supply the required heat of desorption. These internal heating means in the second reactor are preferably arranged inside the fluidized beds and comprise heat exchanger surfaces .

The first riser used to lift the target-gas-enriched solid particles leaving the first reactor at the bottom, is preferably operated at gas velocities between 1 and 20 m/s with specific solids fluxes of 10-300 kg/(m^^'s).

Preferred embodiments comprise heat exchanger surfaces in the first riser to adjust the temperature of the solid particles to be sent to the second reactor. In especially preferred embodiments these heat exchanger surfaces are located in the bottom of the first riser. In this case the cross section in the bottom of the first riser is by a factor of 2-10 larger than the cross section of the transporting zone of the first riser.

The second riser used to lift the target-gas- depleted solid particles leaving the second reactor at the bottom, is preferably operated at gas velocities between 1 and 20 m/s with specific solids fluxes of 10- 300 kg/(m^2's) . Preferred embodiments comprise heat exchanger surfaces in the second riser to adjust the temperature of the solid particles prior to be sent to the first reactor. In especially preferred embodiments these heat exchanger surfaces are located in the bottom of the second riser. In this case the cross section in the bottom of the second riser is by a factor of 2-10 larger than the cross section of the transporting zone of the second riser.

In preferred embodiments of this invention, heat is withdrawn from the solid particles in the second riser using the described heat exchanger surfaces in the second riser and transferred to the solid particles in the first riser using the described heat exchanger surfaces in the first riser (lean/rich heat exchange) .

In addition to carbon dioxide, other contaminants can also be suitably removed from the gas stream. Such other contaminants can for instance be hydrogen sulphide, COS, sulphur oxide and nitrogen oxide.

According to a further embodiment of the device according to the invention, the first lower connection can be provided with a first gas sealing to prevent said stripping gas - fed to the bottom zone of the second reactor - from passing into the first riser whilst allowing solid particles to pass; and/or the second lower connection can be provided with a second gas sealing to prevent gas stream - i.e. target-gas rich gas fed to the bottom zone of the first reactor - from passing into the second riser whilst allowing solid particles to pass. A gas sealing, provided in the lower connection between one reactor and the riser feeding the solid particles to the other reactor, prevents transport of gas from the internal of the one reactor to the internal of the other reactor. Providing gas sealing in both the lower

connections prevents transport of gas between the internals of the reactors in both directions. As will be clear such transport would have, amongst others, a negative influence on the efficiency of the processes inside the reactors.

Said gas sealing can according to the invention be achieved by means of purge gas. When a purge gas is injected in the so called lower connection in a

sufficient amount and/or with sufficient pressure, the purge gas will flow through the moving (bed of) solid particles and create a pressure drop from the point of injection - viewed with respect to the flow direction of the solids through the lower connection - upstream and downstream. Thus, a kind of buffer is created in the lower connection, which buffer blocks gasses, coming from the bottom zone of the reactor upstream of the point of injection, effectively, whilst allowing the solid particles to pass. Accordingly, the device according to the invention comprises according to a further embodiment a purge gas system; wherein the first and/or second gas sealing each comprise at least one purge inlet for introducing a purge gas into the first respectively second lower connection; and wherein the purge gas system - Il ls arranged to feed the at least one purge inlet of the first respectively second gas sealing with a respective quantity of purge gas which is sufficient to achieve in the first respectively second lower connection a pressure drop of the introduced purge gas, which pressure drop prevents the passing of gas from the second respectively first reactor to the first respectively second riser.

When using at least one purge gas inlet, the first and/or second lower connection can according to a further embodiment of the invention comprise a lower purge inlet and an upper purge inlet provided up stream of the lower purge inlet. This allows for example the use of off gas from the first reactor as purge gas to be introduced in relative - with respect to the total quantity of purge gas - large quantity through the lower purge inlet of the first lower connection and a gas inert with respect to the processes in both reactors to be introduced in relative - to the total quantity of purge gas - small quantity through the upper purge inlet. Alternatively or supplementary, it also allows to use the lower purge inlet to control the flow of solid particles to the riser by varying the amount and/or pressure of the purge gas introduced through the lower purge inlet, whilst the upper purge inlet maintains a reliable gas sealing.

According to a further embodiment of the device according to the invention, the first and/or second lower connection is formed by an L-shaped pipe having a vertical leg, a horizontal leg and a bend connecting the vertical leg to the horizontal leg. The free end of the vertical leg debouches in the bottom zone of the reactor and the free end of the horizontal leg debouches in the riser. The horizontal leg is essentially horizontal and allows transport of solid particles through the connection in a moving or fluidized bed fashion. The vertical leg is essentially vertical, meaning that the transport of solid particles through this vertical leg can be gravity based.

In case of an L-shaped pipe as first and/or second lower connection, the lower purge inlet associated to the L-shaped pipe can according to a further embodiment of the invention be provided at the bend; wherein the upper purge inlet associated to the L-shaped pipe is provided at the vertical leg. In this embodiment, the lower purge inlet might have an injection direction parallel to the horizontal leg. The transport of solid particles through the L-shaped pipe can in this way be controlled by the amount and/or pressure of gas introduced into the lower purge inlet at the bend.

In order to provide a controlled transport of solid particles to the riser, the first and/or second lower connection can, according to a another embodiment of the invention, be provided with a screw feeder arranged inside a pipe part of the first respectively second lower connection. By varying the rotational speed of the screw, a higher or lower flow rate of solid particles to the riser is achieved.

According to another embodiment of the invention, the transport of solid particles through the riser can be controlled by providing the first and/or second lower connection with a control valve provided inside the first respectively second lower connection for controlling the flow of solid particles to the first respectively second riser .

In this respect it is noted that it is conceivable that the first lower connection is provided with a screw feeder whilst the second lower connection is provided with a control valve - or the other way around -. It is also conceivable that one of the lower connections is provided with either a screw feeder or a control valve, whilst in the other lower connection the flow of solid particles is controlled by means of a purge inlet (as discussed above) .

When using a purge gas for gas sealing, the device according to the invention might according to a further embodiment comprise: a control unit; a pressure sensor arranged to measure the gas pressure in or near the solid particles outlet of a reactor; and a further pressure sensor to measure the gas pressure in or near the location where the lower connection associated to the reactor debouches in the associated riser; wherein the control unit is connected to the sensors to receive sensor signals representative for the gas pressure measured by the respective sensors and to the purge gas inlet to send a control signal for controlling the flow of purge gas through the respective purge gas inlet; and wherein the control unit is arranged to generate said control signal in dependency of the sensor signals received, preferably in dependency of the difference in pressure as measured by the sensors, such that the purge gas introduced into the lower connection prevents passing of gas from the reactor through the lower connection to the riser. In case of two lower connections with a purge gas inlet, pressure sensors associated to the other lower connection may be provided as well. These pressure sensors might be connected in similar manner to a further or the same control unit connected to the purge gas inlet of the other lower connection, which is arranged to generate in similar manner a control signal for

controlling the flow of purge gas through the other respective purge gas inlet as well. It is noted that in this case the control signal for the purge gas inlet of one lower connection might depend from the pressures measured by the pressure sensors associated to the other lower connection as well. When using a screw feeder, control valve or other control device for controlling the flow of particles through one or both the lower

connections, a similar configuration of control unit(s) and pressure sensors can be used as in relation to the purge gas. The main difference than will be that the control unit will be connected to the screw feeder, control valve or other control device to send the control to the screw feeder, control valve or other control device .

In case of a control valve, this might according to the invention be a sliding valve. A slide valve is a valve comprising a slide which, in general, is moveable in a direction perpendicular to the flow direction of the solid particles. The slide might however also be moving in a direction slanting with respect to the flow

direction of the solid particles.

According to a further embodiment of the device according to the invention, the gas atmosphere in the first riser is in open communication with the gas atmosphere in the top of the first reactor, and the gas atmosphere in the second riser is in open communication with the gas atmosphere in the top of the second reactor. This means that in this preferred embodiment no gas sealing devices are necessary in the upper connections between the first particles-gas-separator and the first reactor and, accordingly, between the second particles- gas-separator and the second reactor. By selecting appropriate operating pressures for the reactors and risers it is possible to minimize the purge gas flows necessary for the first and second lower connection.

Doing so obviates the necessity for any gas flow barrier preventing gas flow from the first riser to the first reactor and from the second riser to the second reactor and results in the gas seals provided in the lower connections being sufficient to prevent gas exchange between the reactors .

According to a further embodiment of the invention, the target gas is carbon dioxide; and the solid particles are solid particles capable of adsorbing and releasing carbon dioxide. Several examples of such solid particles have already been mentioned above, see the entire paragraphs where the 'carrier material' and 'amines' are discussed.

According to a further aspect, the disclosure also relates to a method for operating a device according to the invention. This method comprises the steps of:

• feeding target gas depleted solid particles, through the solid particles inlet of the first reactor, to the upper bed of the first reactor, and allowing these solid particles to flow downward from bed to bed through the first reactor;

• feeding a gas stream, such as flue gas, through the gas stream inlet into the first reactor, and passing the gas stream in upward direction through the at least two beds of solid particles, whilst these beds are being fluidized by the gas stream, and the solid particles adsorb the target gas, such as carbon dioxide;

· discharging the target gas depleted gas stream through the treated gas outlet;

• discharging target gas enriched solid particles from the first reactor through the solid particles outlet of the first reactor into the second lower connection ;

• transporting the target gas enriched solid

particles from the solid particles outlet of the first reactor, through the second lower connection, to the solids inlet of the second riser (which transporting can, for example, be done by means of gravity, pressure difference and/or a moving device, like a screw

conveyor) ;

· preferably, sealing the gas atmosphere in the bottom of the first reactor from the gas atmosphere at the solid particles inlet of the second riser by means of one or more purge gas inlets;

• lifting the target gas enriched solid particles in the second riser, by means of a second lift gas supplied at the lower end of the second riser, to the second separator at a level higher than the solid particles inlet of the second reactor;

• separating the gas enriched solid particles from the second lift gas in the second separator;

• feeding the separated gas enriched solid particles through the solid particles inlet of the second reactor to the upper bed of the second reactor and allowing these solid particles to flow downward from bed to bed through the second reactor;

• feeding a stripping gas, such as steam, through the stripping gas inlet into the second reactor, and passing the stripping gas in upward direction through the at least two beds of solid particles, whilst these beds are being fluidized by the stripping gas, and the solid particles are being stripped from target gas;

• discharging the target gas enriched stripping gas through the stripping gas outlet; • discharging the target gas depleted solid particles from the second reactor through the solid particles outlet of the second reactor into the first lower connection ;

· transporting the target gas depleted solid

particles from the solid particles outlet of the second reactor, through the first lower connection, to the solids inlet of the first riser (which transporting can, for example, be done by means of gravity, pressure difference and/or a moving device, like a screw

conveyor) ;

• preferably, sealing the gas atmosphere in the bottom of the second reactor from the gas atmosphere at the solid particles inlet of the first riser by means of one or more purge gas inlets;

• lifting the target gas depleted solid particles in the first riser, by means of a first lift gas supplied at the lower end of the first riser, to the first separator at a level higher than the solid particles inlet of the first reactor; and

• separating the gas depleted solid particles from the first lift gas in the first separator.

In the step wherein a gas stream, such as flue gas, is fed through the gas stream inlet into the first reactor, and the gas stream is passed in upward direction through the at least two beds of solid particles, whilst these beds are being fluidized by the gas stream, and the solid particles adsorb the target gas, such as carbon dioxide, target gas enriched solid particles and a target gas depleted gas stream are obtained.

In the step wherein a stripping gas, such as steam, is fed through the stripping gas inlet into the second reactor, and the stripping gas is passed in upward direction through the at least two beds of solid

particles, whilst these beds are being fluidized by the stripping gas, and the solid particles are being stripped from target gas, target gas depleted solid particles and target gas enriched stripping gas are obtained.

According to a further embodiment of the method according to the invention, the method further comprises the step of: providing a first gas sealing in the first lower connection by introducing into the first lower connection a first purge gas in a quantity and/or with a pressure sufficient to achieve in the first lower connection a purge gas pressure drop preventing passage of gas from the second reactor through the first lower connection to the first riser. Preferably, said purge gas pressure drop equals the pressure difference between the solid particles outlet of the second reactor and the entrance of solid particles in the first riser.

According to a further embodiment of the method according to the invention, the method further comprises the step of: providing a second gas sealing in the second lower connection by introducing into the second lower connection a second purge gas in a quantity and/or with a pressure sufficient to achieve in the second lower connection a purge gas pressure drop preventing passage of gas from the first reactor through the second lower connection to the second riser. Preferably, said purge gas pressure drop equals the pressure difference between the solid particles outlet of the first reactor and the entrance of solid particles in the second riser.

According to a further aspect, the invention also relates to a method for starting up a process in which a device according to the invention is operated,

wherein the startup method comprises steps of: • controlling the pressure drop in downcomers (37) in the first reactor by adjusting the one or more mechanical devices, which preferably is/are one or more adjustable mechanical flaps (38) and/or one or more slides (39), until the downcomers (37) are filled, and

• controlling the pressure drop in downcomers (37) in the second reactor by adjusting the one or more mechanical devices, which preferably is/are one or more adjustable mechanical flaps (38) and/or one or more slides (39), until the downcomers (37) are filled;

and wherein the process in which a device according to the invention is operated comprises the steps of :

· feeding target gas depleted solid particles, through the solid particles inlet (41) of the first reactor, to the upper bed of the first reactor, and allowing these solid particles to flow downward from bed to bed through the first reactor (1) ;

· feeding a gas stream, such as flue gas, through the gas stream inlet (3) into the first reactor (1) , and passing the gas stream in upward direction through the at least two beds (40) of solid particles, whilst these beds (40) are being fluidized by the gas stream, and the solid particles adsorb the target gas, such as carbon dioxide ;

• discharging the target gas depleted gas stream through the treated gas outlet (5);

• discharging target gas enriched solid particles from the first reactor through the solid particles outlet (41) of the first reactor (1) into the second feed (7, 13, 17, 23); • lifting the target gas enriched solid particles in the second riser (13) , by means of a gas supplied at the lower end of the second riser (13), to the second separator (18) at a level higher than the solid

particles inlet (44) of the second reactor (2) ;

• separating the gas enriched solid particles from the gas in the second separator (18) ;

• feeding the separated target gas enriched solid particles through the solid particles inlet (44) of the second reactor (2) to the upper bed of the second reactor (2) and allowing these solid particles to flow downward from bed to bed through the second reactor (2);

• feeding a stripping gas, such as steam, through the stripping gas inlet (4) into the second reactor (2), and passing the stripping gas in upward direction through the at least two beds (40) of solid particles, whilst these beds (40) are being fluidized by the stripping gas, and the solid particles are being stripped from target gas;

· discharging the target gas enriched stripping gas through the stripping gas outlet (6) ;

• discharging the target gas depleted solid particles from the second reactor through the solid particles outlet (42) of the second reactor (2) into the first feed (8, 14, 18, 24);

• lifting the target gas depleted solid particles in the first riser (14), by means of a gas supplied at the lower end of the first riser (14), to the first

separator (17) at a level higher than the solid

particles inlet (43) of the first reactor (1); and

• separating the gas depleted solid particles from the gas in the first separator (17) . In a process in which a device according to the invention is operated, preferably the first lower connection (8) is provided with a first gas inlet to prevent said stripping gas from passing into the first riser (14) whilst allowing solid particles to pass;

and/or wherein the second lower connection (7) is provided with a second gas inlet to prevent gas stream from passing into the second riser (13) whilst allowing solid particles to pass.

Preferably, the target gas is carbon dioxide; and wherein the solid particles are solid particles capable of adsorbing and releasing carbon dioxide.

Figures

The present invention will be further elucidated with reference to the drawings, wherein:

Figure 1 shows a schematic diagram of an embodiment of a device according to the invention;

Figure 2 shows, schematically, a detailed view of two stages of the first reactor of the device as shown in figure 1;

Figure 3 shows, schematically, a detailed view of an alternative embodiment for the so called lower connection of the device according to the invention; and

Figure 4 shows, schematically, a detailed view of another alternative embodiment for the so called lower connection of the device according to the invention.

Fig. 1 shows a schematic diagram of an embodiment of the device according to the invention. The main

components of said device are two counter-current multistage fluidized bed reactors 1, 2 and two solid particles feeds 8, 14, 18, 24; 7, 13, 17, 23, which solid particle feeds might also be called solid particle transport lines, in short feeds respectively transport lines. Both the first reactor 1 and the second reactor 2 are divided in two or more stages, fig. 1 showing as an example 6 stages per reactor. The first solid particles feed - comprising a first lower connection 8, a first riser 14, a first particles-gas-separator 18, and a first upper connection 24 - extends from the lower end of the second reactor 2 to the upper end of the first reactor 1 and serves the purpose of transporting solid particles from the lower stage of the second reactor 2 to the upper stage of the first reactor 1. The second solid particles feed - comprising a second lower connection 7, a second riser 13, a second particles-gas-separator 17, and a second upper connection 23 - extends from the lower end of the first reactor 1 to the upper end of the second reactor 2 and serves the purpose of transporting solid particles from the lower stage of the first reactor 1 to the upper stage of the second reactor 2. Solid particles fed to the upper stage of a said respective reactor 1, 2 flow downward, from stage to stage, to the lower stage of the respective reactor 1, 2. The solid particles are thus circulated through a loop formed by the first reactor 1, the second feed 7, 13, 17, 23, the second reactor 2 and the first feed 8, 14, 18, 24 of the device according to the invention.

Solid particles fed to the first reactor 1 by the first feed 8, 14, 18, 24 are introduced into the first reactor 1 through the solid particles inlet 43 of the first reactor 1. Solid particles fed to the second reactor 2 by the second feed 7, 13, 17, 23 are introduced into the second reactor 2 through the solid particles inlet 44 of the second reactor 2. The gas stream to be treated is fed through gas stream inlet 3 into the first reactor. This gas stream flows, inside the first reactor 1, in upward direction to the top of the first reactor 1. This gas stream leaves the first reactor 1 as a treated gas stream through the treated gas outlet 5 at the top of the first reactor 1. A stripping gas is fed through a stripping gas inlet 4 into the second reactor reactor 2. This stripping gas 2 flows, inside the second reactor 2, in upward direction to the top of the second reactor 2. This stripping gas leaves the second reactor 2 as target gas-enriched stripping gas through the stripping gas outlet 6 at the top of the second reactor 2. Both reactors 1 and 2 are thus operated countercurrent .

Further both reactors are operated to provide a fluidized bed 40 of solid particles at each stage. In the first reactor 1 the fluidization of the beds 40 is caused by the gas stream passing through the beds, and in the second reactor 2 the fluidization of the beds 40 is caused by the stripping gas passing through the beds. Whilst passing the gas stream through the beds 40 of the first reactor 1, a target gas to be captured is adsorbed by the solid particles, resulting in a target gas- depleted gas stream. Whilst passing the stripping gas through the beds 40 of the second reactor 2, the

stripping gas strips the target gas to be captured from the solid particles, resulting in a target gas-enriched stripping gas .

The solid particles leave the bottom stage of the first reactor 1 through a solid particles outlet 41 and leave the second reactor 2 through a solid particles outlet 42. A lower connection 7 of the second feed is joined to the solid particles outlet 41 of the first reactor 1, and a lower connection 8 of the first feed is joined to the solid particles outlet 42 of the second reactor 2. The first feed comprises, viewed in flow direction of the solid particles, subsequently the lower connection 8, a first riser 14, a first separator 18 for separating gas and solid particles, and an upper

connection 24 connection the first separator 18 with the solid particles inlet 43 of the first reactor 1. The second feed comprises, viewed in flow direction of the solid particles, subsequently the lower connection 7, a second riser 13, a second separator 17 for separating gas and solid particles, and an upper connection 23

connecting the second separator 17 with the solid particles inlet 44 of the second reactor 2. In order to transport the solid particles upward through the first riser 14, a first lift gas is introduced through a lift gas inlet 16 at the bottom of the first riser 14. In order to transport the solid particles upward through the second riser 13, a second lift gas is introduced through a lift gas inlet 15 at the bottom of the second riser 13. In the first separator 18 - which may be gravity

separator, baffle separator, cyclone or filter-like separator -, the solid particles are separated from the first lift gas. The solid particles separated in the first separator 18 subsequently flow downwards through the upper connection 24 to the solid particles inlet 43 and are delivered to the upper stage of the first reactor

1. First lift gas separated in the first separator 18 is discharged via a gas discharge line 20 comprising a compressor 22 and is joined to the lift gas inlet 16, so that the first lift gas can be reused in the first riser 14 and is in fact recycled. In the second separator 17- which may be gravity separator, baffle separator, cyclone or filter-like separator -, the solid particles are separated from the second lift gas. The solid particles separated in the second separator 17 subsequently flow downwards through the upper connection 23 to the solid particles inlet 44 and are delivered to the upper stage of the second reactor 2. Second lift gas separated in the second separator 17 is discharged via a gas discharge line 19 comprising a compressor 21 and is joined to lift gas inlet 15, so that the second lift gas can be reused in the second riser 13 and is in fact recycled. One or each of the risers 13, 14 may be provided with one or more additional gas inlets 15A, 16A which can be used to introduce lift gas at different height levels into the risers 13, 1 .

The gas atmosphere in the first riser 13 is in open communication with the gas atmosphere in the top stage of second reactor 2 via the second separator 17 and upper connection 23. In the same way, the gas atmosphere in the second riser 14 is in open communication with the gas atmosphere in the top stage of first reactor 1 via the first separator 18 and upper connection 24. With the term ^xopen communication' it is meant that free gas movement through the upper connections 23 and 24 is possible.

In gas capturing, it is essential that the gas phases in each reactor are effectively sealed from each other. This means that essentially only gas species selectively taken up by the solid particles, following e.g. adsorption on the solid particles or chemical reaction with the solid particles, are transported from the gas flow through one reactor to the gas flow through the other reactor. Non-selective leakages between the two main gas flows are not desired.

However, taking into account that the pressure gradient between the top and bottom of the second riser 13 will be lower than the pressure gradient between the top and bottom stage of the first reactor 1, that the pressure gradient between the top and bottom of the first riser 14 will be lower than the pressure gradient between the top and bottom stage of the second reactor 2, that there is an open communication between the top stage of the second reactor 2 and the second separator 17, and that there is an open communication between the top stage of the first reactor 1 and the first separator 18, there will result a pressure gradient between the bottom stage of the first reactor 1 and the lower end of the second riser 13 as well as a pressure gradient between the bottom stage of the second reactor 2 and the lower end of the first riser 14. In order to prevent leakage of gas from inside the respective reactor 1, 2 through the lower connection 7, 8 to the riser 15, 16, the each lower connection is, according to the invention, provided with a gas seal preventing passing of gas from the inside of the reactor through the lower connection to the riser, but allowing passage of solid particles from the reactor through the lower connection to the riser.

According to the invention, each gas seal features one or more purge gas inlets. Referring to figure 1, there is shown, as an example, one lower purge gas inlet 9, 10 for each lower connection 7, 8 and two upper purge gas inlets 11, 12 for each lower connection 7, 8.

Hence, preferably the device of the present

invention further comprises at least one inlet (10, 12; 9, 11) for introducing a gas into the first (8)

respectively second (7) lower connection. More preferably the at least one inlet of the first and/or second lower connection comprises a lower inlet (10, 9) and an upper inlet (12, 11) provided up stream of the lower inlet.

Preferably the first (8) and/or second (7) lower connection is formed by an L-shaped pipe having a vertical leg, a horizontal leg and a bend connecting the vertical leg to the horizontal leg.

More preferably the lower inlet (10, 9) associated to the L-shaped pipe is provided at the bend; wherein the upper inlet (12, 11) associated to the L-shaped pipe is provided at the vertical leg; and wherein the lower inlet (10, 9) preferably has an injection direction parallel to the horizontal leg.

In the embodiment of figure 1, the lower connections

7, 8 are both L-shaped. Each said lower connection is formed by an L-shaped pipe having a vertical leg and a horizontal leg, which legs are connected by a bend. As can be seen in figure 1, the vertical leg has two parts, the upper part of which is slanting. Similarly also the horizontal leg might have two parts slanting with respect to each other. Such a connection is also called a L-valve type connection.

The solid particles flow rates out of each reactor 1, 2 are controlled by influencing the gas flow rates in the lower purge gas inlets 9, 10 of the L-valve-type connections 7, 8.

Heat can be transferred to or removed from each of the reactors using heating surfaces 25, 26 with inlets 27, 28 and outlets 29, 30 for a heat carrier fluid. These heating surfaces may be located at the wall of the reactor or - see fig. 2 - immersed in the fluidized beds 40 of one or more stages. Further, heat may be exchanged with the risers using heating surfaces 31, 32, which, in preferred embodiments, allow for counter-current heat transfer between gas-solid mixture and heat transfer medium on each side using a heat carrier fluid cycle 33 and a circulation pump 34. Fig. 2 shows a detailed view on two stages of a preferred embodiment of the reactors 1, 2. In each stage, the solid particles are kept fluidized and the bulk of the gas stream (first reactor) or stripping gas (second reactor) is forced to pass the solid particles of each stage by the use of internals such as nozzle or sieve plates 35 causing the solid particles to form a fluidized bed 40. An over flow weir 36 allows solid particles to pass into a down-comer section 37 when the height of the fluidized bed rises to above the weir due to solid particles being fed from stage above said bed. The downcomer section 37 may be operated in fluidized or moving-bed regime. In order to allow for proper start-up of such a reactor system, an adjustable flap 38 is used in each downcomer to adjust the pressure drop of the, during system start-up, empty downcomer. During operation of the reactors 1 and 2, the adjustable flaps 38 in each stage can be used to control the gas-solids contact within the downcomer sections 37. Alternatively, the fluidization gas flow rate fluidizing the downcomer section can be controlled using an adjustable mechanical device 39, like a slide, for gradually covering the fluidization nozzles or sieve tray holes in this area.

Further, Fig. 2 shows a preferred embodiment of the heat transfer surface 25 as it might be used in one or more of the stages of the reactors 1,2. This heat transfer surface 25 is immersed in the fluidized bed 40 and has an inlet 27 and an outlet 29 for heat carrier fluid. Such individual heat transfer surfaces 25 can be used in each stage of the reactors to achieve a certain desired temperature distribution.

Preferably the device of the present invention further comprises a control valve (46) . The first (8) and/or second (7) lower connection may be provided with a control valve (46) arranged inside the first (8)

respectively second (7) lower connection for controlling the flow of solid particles to the first (8) respectively second (7) riser. The control valve (46) preferably is a sliding valve .

Fig. 3 shows an alternative embodiment of the second lower connection 7 for transport of solid particles from the first reactor 1 to the second riser 13 using a mechanical valve 46 and a purge gas inlet 11. The mechanical valve 46 comprises a slide which is movable about perpendicular to the lower connection 7. This embodiment can also be applied to first lower connection 8 for transport of solid particles from the second reactor 2 to the first riser 14.

Preferably the device of the present invention further comprises a screw feeder (45) . The first (8) and/or second (7) lower connection may be provided with a screw feeder (45) arranged inside a pipe part of the first (8) respectively second (7) lower connection.

Fig. 4 shows another alternative embodiment of the second lower connection 7 for transport of solid

particles from the first reactor 1 to the second riser 13 using a screw feeder 45 for particle flow control and a purge gas inlet 11 for gas sealing. This embodiment can also be applied to the first lower connection 8 for transport of solid particles from the second reactor 2 to the first riser 14.

As discussed before, two or more purge gas inlets 9, 10, 11, 12 are provided by the present invention in the lower connections 7, 8 in order to avoid gas leakages between the first and second reactor 1, 2. Purge gases, which are acceptable in both main gas flows through the reactors, are preferably introduced through the purge gas inlets 9-12 in a sufficient quantity and/or with a sufficient pressure to achieve a purge gas pressure drop between the purge gas inlet and the location where solid particles are introduced into the riser - i.e. the location of the solid particles inlet of the riser -, which equals the pressure difference between the bottom stage of the reactor and the location where the solid particles are introduced into the riser. In this case the purge gas will flow predominantly towards the riser while only a small part of it, the excess, will be directed against the stream of solid particles towards the bottom stage of the reactor. Thus, gas leakage from the bottom stages of the reactors 1, 2 towards the risers 13, 14 through lower connections 7, 8 is effectively prevented.

Purge gases can be inert gases, steam or recycled off-gas of the system, either in dry or in raw state. In order to reduce the consumption of additional inert gases for purging, a two-stage introduction of purge gas can be done. In such an embodiment, the main pressure gradient is built up by a main purge gas inlet 9, 10, where part of the lift gas of the riser can be used, while an inert gas is only used in a much smaller quantity in the secondary purge gas inlet 11, 12, located upstream of the main purge gas inlet in the sense of solid particles flow direction .

In a preferred application of the invention, flue gas is treated in the first reactor 1 and steam is used to strip off selectively transported species of target gas, such as C02, in the second reactor 2. In order to avoid any undesired dilution of the steam/C02 mixture by non-condensable flue gas constituents such as N2 or 02, and to avoid, at the same time, leakage of the separated gas species into the off-gas leaving the first reactor 1 through the treated gas outlet 5, a combination of purge gases is used. In lower connection 7, where solid particles leave the first reactor 1, the pressure gradient is built up by a main purge gas stream of recycled second lift gas and the smaller, secondary purge gas stream introduced closer to the outlet of the first reactor 1, consists of dry C02 rich gas, preferably recycled from the off gas leaving the second reactor 2 through the stripping gas outlet 6 and subsequently dried. The gas atmosphere in the gas loop of the second riser 13 thus will consist of a C02 rich gas and

communicates via connection 23 with the C02 rich gas atmosphere in the top of the second reactor 2. In lower connection 8, where solid particles leave the second reactor 2, the pressure gradient is built up by a main purge gas stream of recycled off gas leaving the first reactor 1 through the treated gas outlet 5 and the smaller, secondary purge gas stream introduced closer to the outlet of second reactor 2, consists of pure steam.

The gas atmosphere in the gas loop of the second riser 14 thus will consist of a gas which largely resembles the off gas of the first reactor 1 and communicates via upper connection 24 with the C02 rich gas atmosphere in the top of the first reactor 1. Accumulation of steam and problems with steam condensation in the gas loop of first riser 14 are effectively avoided in this way. List of reference numbers

first reactor 16 lift gas inlet of 31 heating surface first riser 14 second riser 13 second reactor 16^a additional gas 32 heating surface inlet first riser 14 gas stream inlet 17 second particles- 33 heat carrier

gas-separator fluid cycle stripping gas 18 first particles- 34 circulation pump inlet gas-separator

treated gas 19 gas discharge 35 sieve plate outlet line of second

particles-gas- separator 17

stripping gas 20 gas discharge 36 overflow weir outlet line of first

particles-gas- separator 18

lower connection 21 compressor 37 downcomer section lower connection 22 compressor 38 adjustable flap

(lower) purge gas 23 upper connection 39 adjustable inlet mechanical device

(lower) purge gas 24 upper connection 40 bed

inlet

(upper) purge gas 25 heating surface 41 solid particles inlet of first reactor outlet of first

1 reactor 1

(upper) purge gas 26 heating surface 42 solid particles inlet of second reactor outlet of second

2 reactor 2 second riser 27 inlet of heating 43 solid particles surface 25 inlet of first reactor 1 first riser 28 inlet of heating 44 solid particles surface 26 inlet of second reactor 2 lift gas inlet of 29 outlet heating 45 screw feeder second riser 13 surface 25

a additional gas 30 outlet heating 46 control valve inlet surface 26

Claims

C L A I M S

1. A device for capturing a target gas, such as carbon dioxide, from a gas stream, wherein the device comprises:

wherein each said reactor has a solid particles outlet (41, 42) provided in the lower part of the respective reactor (1, 2) and a solid particles inlet (43, 44) provided in the upper part of the respective reactor ( 1 , 2 ) ;

wherein the second feed (7, 13, 17, 23) extends from the solid particles outlet (41) of the first reactor (1) to the solid particles inlet (44) of the second reactor (2), on the one hand, and the first feed (8, 14, 18, 24) extends from the solid particles outlet (42) of the second reactor (2) to the solid particles inlet (43) of the first reactor (1), on the other hand, to form a loop for circulating the solid particles;

wherein the first solid particles feed (8, 14, 18, 24) comprises a first riser (14) for lifting the solid particles with a gas to a level higher than the solid particles inlet (43) of the first reactor (1), a first particles-gas-separator (18) provided at the upper end of the first riser (14) for separating the solid particles from the gas, and a first lower connection (8) connecting the solid particles outlet (42) of the second reactor (2) to the lower end of the first riser (14) ;

wherein the second reactor comprises in the range of from 3 up to 30 sieve plates and/or nozzle plates (35), with downcomers (37) and preferably with overflow weirs (36) ; wherein the downcomers (37) in the second reactor comprise one or more mechanical devices, preferably one or more adjustable mechanical flaps (38) and/or one or more slides (39), for control of the downcomer pressure drop .

2. The device according to claim 1, wherein the device further comprises a at least one inlet (10, 12; 9, 11) for introducing a gas into the first (8) respectively second (7) lower connection.

3. The device according to claim 2, wherein the at least one inlet of the first and/or second lower

connection comprises a lower inlet (10, 9) and an upper inlet (12, 11) provided up stream of the lower inlet.

4. The device according to one of the claims 1-3, wherein the first (8) and/or second (7) lower connection is formed by an L-shaped pipe having a vertical leg, a horizontal leg and a bend connecting the vertical leg to the horizontal leg.

5. The device according to claim 4 in combination with claim 3, wherein the lower inlet (10, 9) associated to the L-shaped pipe is provided at the bend; wherein the upper inlet (12, 11) associated to the L-shaped pipe is provided at the vertical leg; and wherein the lower inlet (10, 9) preferably has an injection direction parallel to the horizontal leg.

6. The device according to one of the preceding claims, especially according to claim 3, wherein the first (8) and/or second (7) lower connection is provided with a screw feeder (45) arranged inside a pipe part of the first (8) respectively second (7) lower connection.

7. The device according to one of the preceding claims, wherein the first (8) and/or second (7) lower connection is provided with a control valve (46) arranged inside the first (8) respectively second (7) lower connection for controlling the flow of solid particles to the first (8) respectively second (7) riser.

8. The device according to claim 7, wherein the control valve (46) is a sliding valve.

9. The device according to one of the preceding claims, wherein the gas atmosphere in the first riser (14) is in open communication with the gas atmosphere in the top of the first reactor (1), and

the gas atmosphere in the second riser (13) is in open communication with the gas atmosphere in the top of the second reactor (2) .

10. A method for starting up a process in which a device according to one of claims 1-9 is operated,

wherein the startup method comprises steps of:

· controlling the pressure drop in downcomers (37) in the first reactor by adjusting the one or more mechanical devices, which preferably is/are one or more adjustable mechanical flaps (38) and/or one or more slides (39), until the downcomers (37) are filled, and

and wherein the process in which a device according to one of claims 1-9 is operated comprises the steps of:

• feeding target gas depleted solid particles, through the solid particles inlet (41) of the first reactor, to the upper bed of the first reactor, and allowing these solid particles to flow downward from bed to bed through the first reactor (1) ;

• feeding a gas stream, such as flue gas, through the gas stream inlet (3) into the first reactor (1) , and passing the gas stream in upward direction through the at least two beds (40) of solid particles, whilst these beds (40) are being fluidized by the gas stream, and the solid particles adsorb the target gas, such as carbon dioxide ;

· discharging target gas enriched solid particles from the first reactor through the solid particles outlet (41) of the first reactor (1) into the second feed (7, 13, 17, 23);

• lifting the target gas enriched solid particles in the second riser (13), by means of a gas supplied at the lower end of the second riser (13), to the second separator (18) at a level higher than the solid

particles inlet (44) of the second reactor (2);

• discharging the target gas enriched stripping gas through the stripping gas outlet (6);

separator (17) at a level higher than the solid

particles inlet (43) of the first reactor (1); and

• separating the gas depleted solid particles from the gas in the first separator (17) .

11. The method according to claim 10, wherein in the process in which a device according to one of claims 1-9 is operated, the first lower connection (8) is provided with a first gas inlet to prevent said stripping gas from passing into the first riser (14) whilst allowing solid particles to pass; and/or wherein the second lower connection (7) is provided with a second gas inlet to prevent gas stream from passing into the second riser (13) whilst allowing solid particles to pass.

12. The method according to claim 10 or 11, wherein the target gas is carbon dioxide; and wherein the solid particles are solid particles capable of adsorbing and releasing carbon dioxide.

13. Method according to any one of claims 10-12, further comprising the step of: providing a first gas inlet in the first lower connection ( 8 ) by introducing into the first lower connection ( 8 ) a gas in a quantity and/or with a pressure sufficient to achieve in the first lower connection ( 8 ) a pressure drop preventing passage of gas from the second reactor (2) through the first lower connection ( 8 ) to the first riser (14) .

14. The method according to claim 13, wherein said gas pressure drop equals the pressure difference between the solid particles outlet (42) of the second reactor and the entrance of solid particles in the first riser (14) .

15. The method according to one of claims 10-14, further comprising the step of: providing a second gas inlet in the second lower connection (7) by introducing into the second lower connection (7) a gas in a quantity and/or with a pressure sufficient to achieve in the second lower connection (7) a gas pressure drop preventing passage of gas from the first reactor (1) through the second lower connection (7) to the second riser (13), and wherein optionally said gas pressure drop equals the pressure difference between the solid particles outlet (41) of the first reactor and the entrance of solid particles in the second riser (13) .