WO2009100937A2

WO2009100937A2 - Material suitable as co2 absorbent and for use as a bedding material in fluidized beds, and the production thereof

Info

Publication number: WO2009100937A2
Application number: PCT/EP2009/001043
Authority: WO
Inventors: Tonja MARQUARD-MÖLLENSTEDT; Peter Sichler; Michael Specht; Ulrich ZUBERBÜHLER
Original assignee: Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg
Priority date: 2008-02-13
Filing date: 2009-02-13
Publication date: 2009-08-20
Also published as: WO2009100937A3; DE102008010349A1; EP2303429A2

Abstract

The invention relates to a material suitable for CO2 absorption and/or for use as bedding material in fluidized beds, to a method for the production of such a material, to a method for producing a gas low in CO2 utilizing such a material, and to further uses of the material, particularly in the area of gas purification. The material substantially comprises at least one metal oxide and/or at least one carbonate, and is substantially free of any particles having a particle size of <100 μm.

Description

description

As CCb absorbent and for use as bed material in fluidized beds suitable material and its preparation

The invention relates to a material which is particularly suitable for CO ₂ absorption and / or for use as a bed material in fluidized beds, a method for producing such a material, a method for producing a CO ₂ -lower gas with such a material and other uses of the material, in particular in the field of gas purification.

Natural, carbonate-containing minerals such as lime or dolomite are suitable as starting material for absorbents, which can be used in industrial processes, for example for desulfurization or as catalysts, but especially for the separation of CO ₂ , for example from flue gases or from synthesis gases.

To obtain these absorbents, the carbonate-containing minerals are generally subjected to a thermal treatment in which the carbonate is converted under CO ₂ release into an oxide, for example CaO. The oxides produced can reversibly take up and release CO ₂ , for example in the case of CaO according to the following equation:

CaO + CO ₂ <r-> CaCO ₃

In desulfurization processes, for example, the oxides can bind sulfur oxide as occurring in flue gases.

The separation of CO ₂ from gases or their desulfurization is often carried out under fluidizing conditions in fluidized bed reactors, in which ensures a particularly intensive contact between the absorbent and the gas to be treated. In a fluidized bed, a bed of solid particles, in this case the absorbent, is caused to flow by an upward flow of a fluid, for example a CO ₂ -containing gas.

The ability of the oxidic absorbents to absorb CO ₂ or SO ₂ is of course limited. In the case of CO ₂ , however, the absorbents can be regenerated in a simple manner. The regeneration is generally carried out by thermal treatment of the "spent" absorbent, in which the bound CO ₂ is liberated again according to the above equation The thermal treatment for regeneration can also take place in a fluidized-bed reactor.

In large-scale processes, the absorbent is frequently allowed to circulate continuously in one cycle, the CO ₂ absorption taking place in a first fluidized-bed reactor, and the CO ₂ desorption in a second fluidized bed, ie the regeneration of the absorbent. Such a circuit is known for example from DE 199 46 381.

Both in CO ₂ absorption and in the subsequent regeneration of the absorbent, the absorbent particles in fluidized-bed reactors are subject to high thermal and in particular also mechanical stresses, the latter resulting in particular from constant collisions with other particles and with the inner walls of the reactors. At the same time, the chemical composition of the absorbent particles changes as a result of CO 2 uptake or release, which further impairs their structural integrity.

The described stresses are the cause of the deactivation of the absorbent and particulate abrasion occurring in particular in fluidized bed reactors. Less firmly bound particle components dissolve and it continuously creates an extremely ""

fine abrasion, which is discharged through the guided through the fluidized bed gas flow from this. This can result in various problems affecting the operation of fluidized bed reactor plants. On the one hand, considerable amounts of waste sorbents are lost in this way, which must be replaced accordingly (i.d.R continuous). On the other hand, the abrasion via the gas stream can reach downstream plant components such as heat exchangers, catalysts or scrubbers and form deposits there. The function of the downstream system components may be significantly affected by the resulting deposits. As a result, they must be serviced frequently.

In order to counteract this, a gas cyclone for separating solids with a return line can be installed in fluidized-bed reactors to recycle the particles discharged with the gas stream. The gas cyclone at least partially separates the fine attrition from the gas stream which is then e.g. can be returned to the bottom zone of the fluidized bed. As a result, the continuous loss of absorbent in the fluidized bed and the associated discharge of abrasion in downstream equipment parts is limited, but not completely prevented. In addition, too fine abrasion is not detected at all by a gas cyclone. By using a gas cyclone, therefore, the negative consequences of the occurrence of abrasion are only weakened. Accordingly, there is still room for improvement, in particular with regard to the stability of the bed material used.

In particular, the object of the present invention is to find a way of optimizing the operation of a fluidized bed reactor plant with regard to the described problems. Suitable technical measures are to be provided by which the operation can be kept as trouble-free as possible and in particular also low in maintenance. These measures should in particular _

be used in combination with a gas cyclone for the separation of abrasion.

This object is achieved in particular by the material according to claim 1, the method for producing such a material according to claim 15 and the method for producing a CC> ₂ low-gas with such a material according to claim 24. Further solutions are described in the Bescheibung disclosed. In the dependent claims 2 to 14 and 16 to 23 particularly advantageous embodiments of the inventive material and the manufacturing method according to the invention are given. Preferred embodiments of the inventive method for producing a CCVarmen gas can be found in the dependent claims 25 to 29. Further preferred uses of the material according to the invention are defined in claims 30 to 32. The wording of all claims is hereby incorporated by reference into the content of this specification.

The material according to the present invention is preferably present as bulk material. It can be used in particular as CO ₂ absorber and / or as bed material in fluidized beds, in particular as a reactive bed material, and also referred to as such. It consists essentially of at least one metal oxide and / or at least one carbonate. The at least one metal oxide and the at least one carbonate are preferably convertible into each other under CC uptake and release. The material is characterized in preferred embodiments in particular by the fact that it is substantially free of particles having a particle size <100 .mu.m, in particular <200 .mu.m.

As already mentioned, fine, volatile particles, the so-called abrasion, can be discharged from a fluidized bed by means of a gas flow. Depending on the speed of the gas flow, particles with a size of up to several hundred micrometers can be discharged. In powdered absorbents based on conventional Be obtained by a thermal treatment of carbonate minerals manner, the particles have a broad particle size distribution, including a proportion of such fine, volatile particles. Already at the first use of the absorbent, this portion is discharged from the gas stream and at least partially dragged into downstream equipment parts.

On the other hand, the material according to the invention is preferably substantially free of particles having particle sizes <100 μm, preferably <200 μm (also referred to below as undersize), which usually make up a large part of the abrasion which is carried out at normal gas velocities. Accordingly, when using a material according to the invention as an absorbent, the amount of abrasion occurring is markedly lower than with conventional absorbents. The proportion of particularly fine abrasion, which can no longer be detected by gas cyclones, is at least greatly reduced at this stage of the process.

In preferred embodiments, the material according to the invention is in particular also with regard to the accumulation of abrasion due to thermal, mechanical and chemical stress in the case of multiple use, ie when used as an absorbent in a cycle with a periodic sequence of CO ₂ absorption and regeneration of the absorbent, optimized.

Namely, the material according to the invention preferably has mechanically particularly stable particles which can withstand the described loads better, so that correspondingly less abrasion results in the CO ₂ absorption and the regeneration.

The material according to the invention is produced in particular from carbonate-containing materials, in particular by thermal and / or mechanical treatment of at least one carbonate. The mechanical The stability of the absorbent particles is attributable in particular to a mechanical and / or thermal treatment step which can be carried out within the scope of the method according to the invention for producing a material for CO ₂ absorption.

Particularly suitable as a starting material is micritic lime. In the present case, lime should be understood to mean lime which consists at least for the most part of a micrit matrix, in particular a matrix of interconnected carbonate grains with particle sizes <100 μm, preferably <10 μm, in particular <5 μm, particularly preferably <4 microns. Accordingly, the material according to the invention is composed in preferred embodiments of individual, interconnected grains with the dimensions given.

The process for producing a material according to the invention, from which the mentioned stable particles emerge, will be discussed in more detail below.

The material according to the invention may consist of only the at least one metal oxide and only of the at least one carbonate. Preferably, however, it consists essentially of particles which have a core of at least one carbonate and a shell surrounding the core (or shell) of at least one metal oxide.

In a further, particularly preferred embodiment, it consists essentially of particles which have a core of at least one metal oxide and a shell (or shell) surrounding the core of at least one carbonate. In this embodiment, the material according to the invention is largely resistant (passivated) against the influence of atmospheric moisture and accordingly has improved storage and transportability. So the carbonate layer can _ _

also serve the purpose of preventing hydroxide formation in the deeper (underlying) metal oxide. The preparation of the particles provided with a carbonate layer is also discussed in more detail below.

In particular, the particles with the core of at least one carbonate and the shell surrounding the core (or shell) may also be passivated from at least one metal oxide. In this preferred embodiment, the core of the carbonate is surrounded by two shells, namely an inner sheath of the at least one metal oxide and an outer sheath of carbonate.

It is preferred that the sheath (or shell) substantially completely surrounds the core.

The weight ratio of metal oxide to carbonate in the material is preferably between 100: 1 and 1: 100, preferably between 100: 1 and 1: 1, in particular about 10: 1 (oxide to carbonate).

In preferred embodiments, a material according to the invention consists essentially of particles which in particular have an average particle size in the range between 0.3 mm and 3 mm, particularly preferably between 0.5 mm and 1.5 mm. Preferably, it consists essentially of porous particles.

The at least one metal oxide is preferably at least one metal oxide of the type M _x O _y , where M denotes a metal, for example Mg, Ca, Sr, Ba, La, Mn or Y and x and y in the usual way suitable integers describe.

The at least one metal oxide is particularly preferably at least one alkaline earth oxide, in particular CaO or a mixture of CaO and MgO. In preferred embodiments, the at least one metal oxide may comprise a portion of iron oxide and / or silicon dioxide. Possibly. it can also contain alumina.

The proportion of iron oxide in preferred embodiments is less than 10% by weight (residue on ignition, based on the total mass of the material according to the invention).

The proportion of silicon dioxide in preferred embodiments is less than 5% by weight (incineration residue, based on the total mass of the material according to the invention). In particular, this value should not be too high in order not to promote the formation of calcium silicates in operation. In principle, due to the presence of iron oxide, silicon dioxide and / or aluminum oxide, cement clinker phases [eg 3 CaO • SiO ₂ , 2 CaO • SiO ₂ , 2 CaO • (Al ₂ O ₃ , Fe ₂ O ₃ ), etc. ], which can lead to deposits in various plant components (such as heat exchangers).

The proportion of iron oxide, silicon dioxide and aluminum oxide in the material according to the invention is preferably less than 10% by weight, in particular less than 5% by weight (residue on ignition, based on the total mass of the material according to the invention).

The at least one carbonate is preferably at least one carbonate of the type M _x (CO ₃ ) _y , where M denotes a metal such as, for example, Mg ₁ Ca ₁ Sr, Ba, La, Mn or Y and x and y in the customary manner designate suitable integers.

The at least one carbonate is particularly preferably at least one alkaline earth carbonate, in particular CaCO ₃ or a mixture of CaCO ₃ and MgCO ₃ . In preferred embodiments, the at least one carbonate may comprise at least one metal oxocarbonate, in particular at least one metal oxocarbonate of the type M _x Oy (CO ₃ ) ₂ , where M denotes a metal, eg Mg, Ca ₁ Sr, Ba, La ₁ Mn or Y and x , y and z denote suitable integers in the usual way.

MgO is contained in the inventive material in preferred embodiments in a proportion of <3 wt .-% (incineration residue, based on the total mass of the material according to the invention).

Likewise provided by the present invention is a process for the preparation of a material as described above. In accordance with the process according to the invention, carbonate particles are subjected to a heat treatment in which a thermal desorption reaction takes place under CO ₂ release. In preferred embodiments, the method is characterized in that after or during the heat treatment essentially all particles with particle sizes <100 μm, in particular <200 μm, are separated off.

By the latter step can be achieved that abrasion is not already introduced with the starting material in a fluidized bed reactor, as already stated above. The volatiles that can be discharged with the gas stream are thus limited to the abrasion that occurs during operation.

The heat treatment is carried out in favor of a large pore surface in the interior of the particles particularly preferably over the shortest possible time at the highest possible temperatures, preferably at a temperature in the range between 1000 ⁰ C and 1500 ⁰ C, in particular between 1100 ⁰ C and 1300 ⁰ C.

In preferred embodiments, the temperature during the heat treatment is selected so that the particles during the heat treatment of a - -

subject to a sintering process. The material according to the invention is therefore in preferred embodiments a material which has been subjected to a sintering process.

Preferably, in the preparation according to the invention, an initial material (preferably a natural carbonate, such as lime and / or dolomite, see below) is used which has a lime standard of> 400, in particular> 2000.

The lime standard is a measure of the proportion of oxidic impurities. It indicates the total CaO content of the raw material in relation to the CaO content, which can be bound to SiO ₂ , Al ₂ O ₃ and Fe ₂ O ₃ by formation of cement clinker phases:

CaO - 100

KSt = (2.8 • SiO ₂ ) + (1.18 • Al ₂ O ₃ ) + (0.65 • Fe ₂ O ₃ )

(Details of CaO, SiO ₂ , Al ₂ O ₃ and Fe ₂ O ₃ , in each case in% by weight)

This is directly related to the values given above for the proportion of iron oxide, silicon dioxide and aluminum oxide in the material according to the invention.

Such a starting material in preferred embodiments has a high sinterability (i.e., the density of the particle increases significantly in the sintering process).

Sintering usually refers to the process of "compacting a powder or porous body by a temperature treatment below the melting point of the material", which process can be observed macroscopically as a decrease in length, volume and porosity or density increase. The sinterability increases with increasing lime standard. In preferred embodiments, the material according to the invention has a bulk density> 900 kg / m ³ , in particular> 1200 kg / m ³ . Such a material could be obtained in particular from an initial matehal having a lime standard> 400, in particular> 2000, in the context of the process according to the invention. In other words, preferably starting from the mentioned starting material having a lime standard> 400, in particular> 2000 is sintered such that the resulting material according to the invention has a bulk density> 900 kg / m ³ , in particular> 1200 kg / m ³ .

In a preferred embodiment of the method according to the invention, the heat treatment is carried out until the thermal desorption reaction is complete and the carbonate particles are essentially completely converted into oxide particles.

In another preferred embodiment, the heat treatment is stopped before the thermal desorption reaction is complete and the carbonate particles are substantially completely converted to oxide particles. This results in the material described above with a core of carbonate and a surrounding oxidic layer.

The heat treatment can be carried out, for example, under conditions such as occur in a fluidized-bed reactor. In this case, particles, as already mentioned above, are exposed to mechanical stresses, including, in particular, collisions with other particles and with reactor internals, in fluidized-bed reactors, in particular with the inner walls of the reactors. During their transformation, the carbonate particles to be converted at least partially into oxide particles are therefore subject to the same loads which are also exposed to a "finished" bed material during operation of a fluidized-bed reactor. -

As in operation, of course, this also dissolves, for example. unstable particulate constituents or grain breakage occurs, but the broken off portions are then not removed as abrasion from a gas stream, but can be separated essentially completely according to the mentioned preferred embodiments of the method according to the invention, in particular if they have a particle size of 100 μm, in particular of 200 microns, below.

Alternatively, it is of course also possible to subject the carbonate particles in a stationary state to a heat treatment and then subject them to mechanical stress, for example strong shaking, and thus to detach the unstable constituents.

Particularly preferably, the heat treatment can be carried out in a rotary kiln.

From these preferred embodiments of the method according to the invention thus results in particular by sintering thermally stabilized, mechanically pretreated material with particles that have already been freed before their first use of unstable components, which thus can not be incurred in later operation as abrasion. Preferably, the material according to the invention has an abrasion resistance which is comparable to that of quartz sand.

To quantify the abrasion resistance, a grinding test according to Hardgrove, for example, can be carried out. The material according to the invention preferably has an HGI value (Hardgrove Index, determined according to the American ASTM Standard D 409) <60, in particular <50. This applies in particular if it has the above-mentioned preferred values for the bulk density. - -

The material produced according to the described preferred embodiments (thermal treatment or sintering and possibly additional mechanical treatment, ie separation of the particles with a particle size <100 μm, in particular <200 μm) of the method according to the invention differs in summary in two respects from Conventional Absorbenzien: Firstly, it is freed of very fine particles and on the other hand, it has particularly stable particles. From the first use of the material according to the invention as a CO ₂ -Absorbens falls to significantly less wear than conventional absorbents, which has a positive effect on the operating stability, reliability and economy (including less bed material consumption, lower number of required maintenance of a fluidized bed reactor per unit time). The small amounts of accumulating abrasion are largely problem-free by means of conventional particle separation, for example by means of a gas cyclone, separable.

If the heat treatment is carried out under fluidizing conditions in a fluidized-bed reactor, the particles with particle sizes <100 μm, in particular <200 μm, can be separated using a gas cyclone. The separation can thus be carried out continuously during the heat treatment, so that a separate separation step can be omitted.

Of course, it is also possible to separate the particles in other ways, for example by sifting or sieving. This is for example in question when the heat treatment was performed on static material.

The carbonate particles used are particularly preferably particles of natural carbonates, in particular of lime and / or dolomite. They therefore consist essentially of CaCO ₃ or a mixture of CaCO ₃ and MgCO ₃ . _ _

In particularly preferred embodiments of the method according to the invention, the heat-treated particles are subjected to CC> ₂ treatment in a gas atmosphere (recarbonation) so that a layer of carbonate, for example CaCO ₃ , can be formed at least on the particle surface. Preferably, the chemical composition of the particles below the surface (ie in particular the oxidic structure of the particle core) is thereby essentially retained. The recarbonation is preferably carried out before the separation of the particles having particle sizes <100 .mu.m, in particular <200 .mu.m.

Such treatment may result in the already mentioned passivated particles having on their surface a layer of at least one carbonate.

In order to actually restrict the formation of the layer to the particle surface, in particular the parameters temperature, pressure, duration of the treatment and / or composition of the gas atmosphere are carefully selected during the CO ₂ treatment. In detail, the setting of the mentioned parameters depends on many factors, including, but not limited to, the average particle size of the particles to be treated and their other nature.

The mean particle size of the particles to be treated ranges, in some preferred embodiments, between 0.7 mm and 1.5 mm.

The CO ₂ treatment is preferably carried out at temperatures in the range between 600 ⁰ C and 800 ⁰ C, in particular between 650 ⁰ C and 750 ⁰ C. • * "

In the gas atmosphere, a CO ₂ partial pressure between 100 and 700 mbar is preferably set in the CO ₂ treatment.

In addition, it is preferred if, during the CO ₂ treatment, the gas atmosphere has a vapor fraction. The H ₂ O partial pressure is preferably set to values between 100 mbar and 500 mbar, preferably between 100 mbar and 300 mbar. Surprisingly, it has been found that steam positively influences both the properties of the resulting recarbonated material and the rate of recarbonation.

Under all these preferred conditions, ie an average particle size in the range between 0.7 mm and 1, 5 mm, a CO ₂ partial pressure between 100 and 700 mbar, an H ₂ O partial pressure between 100 and 300 mbar and the use of particles from CaCO ₃ or from a mixture of CaCO ₃ and MgCO ₃ as starting material, the duration of a CO ₂ treatment is generally between 1 and 10 hours.

The CO ₂ treatment can be carried out both before and after the separation of the undersize. Preferably, however, the CO ₂ treatment is carried out directly after the heat treatment (CO ₂ desorption), wherein the particles are cooled to a corresponding temperature (preferably <800 ⁰ C) and brought into contact with a CO ₂ vapor mixture. This avoids that intermediate products such as CaO, quicklime / Branntdolomit form unwanted by-products (iw hydroxide) and thereby become unusable. A final fractionation (eg sieving) is recommended for the cooled product (recarbonate) to obtain the desired particle size fraction.

In the context of a process according to the invention with recarbonation, a finely porous recarbonate can be prepared from a coarse-pore oxide again, the structure of which approaches the original structure of the starting material. This fine porosity is with greater inner Surface, which explains the higher activity. In addition, a fine-pored microstructure is mechanically more stable, since many small "bridges" react more elastically to mechanical stresses than a few large "connecting bridges" (which rather act as predetermined breaking points).

The inventive material has excellent characteristics with regard to the parameters CO ₂ uptake rate, and CO ₂ - absorption capacity, in particular if it consists essentially of the above-described particles comprising a core of at least one carbonate, and a cladding surrounding the core of at least one metal oxide or consists of the particles already described with a core of at least one metal oxide and a shell surrounding the core of at least one carbonate.

Preferably, the material has a CO ₂ absorption capacity of> 0.05 g _C θ 2 / goχid-

Furthermore, it may be preferred for the material to have a CO _{2 take} -up rate of> 0.01 gCO 2 / (goid · min) (at a CO ₂ partial pressure of from 0.01 to 0.3 bar in the raw gas, based on Normal pressure, and an absorption temperature between 600 ⁰ C and 700 ⁰ C).

The present invention also includes a method of producing a low-CO ₂ gas. In this method, in a first process step, CO _{2 is separated} from a raw gas (for example, a flue gas or product gas) by means of a material as described above. In a second process step, the material is then regenerated under CO ₂ release. Of course, the first and the second process step can also be repeated periodically, it being then preferred for the material to circulate continuously in a circuit as already mentioned at the outset. When using the material according to the invention as CO ₂ absorber in such a process, both the first use of the CC ₂ absorbent according to the invention and, if appropriate, in the later periodic operation generally produce less abrasion than with conventional absorbents. The reasons for this have already been explained in detail. The above corresponding statements, in particular with regard to the material according to the invention, are hereby incorporated by reference.

To permanently maintain the mechanical stability and thus the abrasion behavior of the CO ₂ absorbent used in particular also contributes to a suitable process control.

In preferred embodiments of the method, in particular a material is used which consists essentially of particles which have at least one core of at least one metal oxide (as is the case, for example, with quicklime). It is preferred that in this embodiment for the first process step, process parameters are selected under which the chemical composition of the core is substantially retained. In concrete terms, this means that the process parameters in the first process step (CO ₂ absorption) are selected such that only the outer layer of the particles is converted into carbonate by taking up CO ₂ . The core itself participates only limitedly in the reaction happening. During the regeneration in the second process step, the conversion is then reversed again under CO ₂ release and the original state is restored.

In further preferred embodiments of the method, in particular, a material is used which consists essentially of particles which have at least one core of at least one carbonate (as is the case, for example, with limestones which are still untreated). In this embodiment, it is preferable that process parameters are selected for the second process step, among which the _ _

chemical composition of the core is substantially retained. Specifically, this means that the process parameters are selected in the second process step so that essentially only the layer surrounding the core is converted into an oxide with CO ₂ release. Here, too, the nucleus itself participates in the reaction process at best only to a limited extent. In the CO ₂ recording in the first process step, the conversion is then reversed again and the original state at least approximately restored.

The process control according to the two described preferred embodiments ensures that the mechanical stability and thus the abrasion behavior of the particles of the CO ₂ absorbent used remains largely the same even after many absorption and regeneration cycles. Presumably, this is due to the fact that in both cases the core participates only limitedly in the reaction process and therefore retains its properties, in particular its mechanical stability.

The transition from carbonate to oxide and vice versa is usually accompanied by a change in the crystalline structure of the absorbent particle. Associated with this may be tensions that weaken the structural integrity of the entire particle. If the core does not participate in the reaction process, the tensions occurring in a particle are presumably much lower, so that the particle as a whole retains its stability.

Preferably, the choice of process parameters includes in particular a coordinated adjustment of process temperature, CO ₂ - partial pressure and / or process duration. In the present case, the duration of the process is to be understood as meaning, in particular, the residence time of the CO ₂ absorbent in the respective process step. In addition, the process parameters in the first process step are selected in particular as a function of the average particle size of the absorbent particles and / or the nature of the raw gas, in particular its CO ₂ content.

The crude gas used is preferably a hydrogen-containing synthesis gas, in particular a synthesis gas obtained from biomass. Furthermore, smoke and process gases can be used as raw gas.

The CCV content in the raw gas usually fluctuates between 10 and 30% by volume and can be reduced to less than 10% by volume (dry gas composition).

In the first process step is seen as a process temperature under atmospheric conditions, preferably a temperature between 600 ⁰ C and 750 ⁰ C is selected. The process time is usually in the WS in the range of a few minutes.

In the second process step (regeneration) is preferably selected as the process temperature un- ter atmospheric conditions at a temperature between 800 ⁰ C and 950 ⁰ C. The process duration is usually in the range of a few seconds to less minutes.

Preferably, both process steps are performed without applying an external pressure.

The first and / or the second process step are particularly preferably carried out in a fluidized-bed reactor in which the CO ₂ -absorbing material correspondingly exists as a fluidized bed. In principle, however, the process according to the invention can also be carried out in other reactors known to the person skilled in the art. The material according to the invention described above can be used not only for the "downstream" removal of CO ₂ from a synthesis gas, but also directly in a gasification process step, for example in the presence of a carbonaceous feedstock in the production of synthesis gas from biomass Material can not only absorb CO ₂ , but also is able to adsorb on its surface so-called tars (cyclic and polycyclic aromatics) In a further process step, these tars can be used for heat generation by combustion for the thermal desorption reaction, as For example, it is already known from DE 10 2004 045 772. In this case, the material according to the invention generally has a catalytic activity with respect to tar degradation which, compared with quartz sand, is less than 0.5 times the tar concentration in the gasification of biogenic input materials under otherwise identical reaction conditions. In other words, the catalytic activity is more than twice that of silica sand.

In this context, it has been found that the described material according to the invention is outstandingly suitable as an oxide catalyst, in particular for the catalytic tar reforming. Accordingly, the use of the described inventive material as oxide catalyst, in particular for the catalytic tar reforming, the subject of the present invention.

Particularly suitable for this is iron oxide-containing material according to the invention.

In addition, the described material according to the invention is also suitable for the separation of sulfur compounds and other impurities contained in gases. The corresponding use is also included in the present invention. Further features of the invention will become apparent from the following description of preferred embodiments in conjunction with the subclaims. In this case, the individual features can be implemented individually or in combination with one another in one embodiment of the invention. The described preferred embodiments are merely illustrative and for a better understanding of the invention and are in no way limiting.

Examples

Production of the material according to the invention in a combined rotary kiln process

The preparation takes place in two stages in preferred embodiments: In a first rotary tubular reactor, carbonate is fired at temperatures above 900 ^° C., CO _{2 being} released. In a second rotary reactor, the intermediate product (oxide) at 650 ⁰ C to 750 ⁰ C again takes CO ₂ (Recarbonatisierung). The separation of particles with a particle size <100 microns can be done continuously or after completion of treatment.

The starting material (e.g., limestone) is preferably added continuously to the first rotary tube reactor. When selecting the particle size of the starting material, depending on the intensity of the heat treatment during the firing process, shrinkage of the particles as a result of sintering must be taken into account (approx. 10% under the conditions recommended below). The product falls continuously into a collecting container.

The CO ₂ release is faster, the higher the temperature. Advantageously, temperatures above 1000 ⁰ C ₁ in particular _ _

above 1200 ⁰ C, which are produced conveniently by direct firing of a gas burner. Then the residence time of the material in the rotary tube should be about 30 minutes. In this step, the material sinters, increasing its strength but also changing the particle size (the grain shrinks). By sintering, the material may lose chemical reactivity, ie, for example, the back reaction to the carbonate (recarbonation) or the hydroxide formation generally proceed more slowly, the more the material has been sintered. This sintering process is intensified by long residence times and / or high temperatures (in the lime industry, a distinction is made between soft, medium and hard fires during the sintering process).

The Recarbonatisierung is procedurally much more difficult to implement than the burning process, since the CO ₂ uptake proceeds only in a narrow temperature window. Ideally, the material passes through an isothermal rotary tube reactor within about 1 h, through which flue gases pass. Good gas-solid contact is a prerequisite for favorable reaction conditions. The temperature window of Recarbonatisierung is bounded below by the reaction rate: At temperatures below 600 ⁰ C, the Cθ is ₂ uptake even at a CO ₂ partial pressure of 1 bar very slow and thus not technically relevant. If the temperature is too high, the thermodynamic equilibrium of the CaO-CaCO ₃ -CO ₂ system is reached, ie the recarbonation reaction is very slow or does not run off any more - in the worst case even calcination conditions are even reached again.

The possible / favorable temperature window for the recarbonation depends on the CO ₂ partial pressure. The temperature can be increased if the CO ₂ partial pressure in the gas phase is greater, ie if, for example, flue gas is enriched with CO ₂ . Higher temperatures and partial pressures increase the reaction rate of CO ₂ uptake. In addition, water vapor has a catalytic effect on the rec- bonatisierungsgeschwindigkeit and improves the overall material properties. As an advantageous gas atmosphere at about 700 ⁰ C, a CC> ₂ partial pressure of 0.3 bar and a water vapor partial pressure of 0.1-0.3 bar is recommended.

Temperatures below 450 ⁰ C to 500 ⁰ C must be avoided in any case, if the gas atmosphere contains water vapor. Otherwise calcium oxide (Ca (OH) 2) would form from calcium oxide (which is still present in the grain even in the case of a recarbonate), resulting in a material which is very unstable mechanically. Therefore, the cooling of the product is preferably carried out in a dry gas atmosphere with a low CO ₂ content (eg 5 mol.%) In order to avoid calcination and hydroxide formation.

Process variant: recarbonatization in a fluidized bed (instead of a rotary tube)

Since a long residence time under isothermal conditions is particularly favorable in the case of recarbonation, a fluidized bed is suitable for this purpose. The intermediate (oxide) thus occurs e.g. from the calcination rotary kiln and is fed directly into a fluidized bed. Recarbonated particles sink downwards due to their greater specific gravity and can be discharged here.

In general, an increase in the total pressure is favorable, in particular for the reaction kinetics of the recarbonation, since higher CO ₂ partial pressures allow greater temperatures and thus a faster CO ₂ uptake is possible.

Claims

- Patent claims

1. Material, in particular for CCvabsorption and / or for use as bed material in fluidized beds, consisting essentially of at least one metal oxide and / or at least one carbonate, characterized in that the material substantially free of particles having a particle size <100 .mu.m, preferably <200 μm, is.

2. Material according to claim 1, obtainable from carbonate-containing materials, in particular produced or producible by thermal treatment of at least one carbonate.

3. Material according to claim 1 or claim 2, characterized in that it consists essentially of particles which have a core of at least one carbonate and a surrounding core surrounding shell of at least one metal oxide.

4. Material according to one of claims 1 or 2, characterized in that it consists essentially of particles which have a core of at least one metal oxide and a surrounding core of the shell of at least one carbonate.

5. Material according to one of claims 3 or 4, characterized in that the sheath enclosing the core substantially completely.

6. Material according to one of the preceding claims, characterized in that it comprises the at least one alkaline earth oxide and the at least one carbonate in a weight ratio of oxide to carbonate between 1: 100 and 100: 1, preferably between 100: 1 and 1: 1, in particular of about 10: 1, autweis.

7. Material according to one of the preceding claims, characterized in that it consists essentially of particles having an average particle size in the range between 0.3 mm and 3 mm, in particular between 0.5 and 1, 5 mm.

8. Material according to one of the preceding claims, characterized in that it consists essentially of porous particles.

9. Material according to one of the preceding claims, characterized in that it is the at least one metal oxide at least one metal oxide of the type M _x O _y , where M is a metal such as Mg, Ca, Sr, Ba, La, Mn or Y and x and y denote suitable integers in the usual way.

10. Material according to one of the preceding claims, characterized in that it is the at least one metal oxide is essentially at least one alkaline earth metal oxide, in particular CaO or a mixture of CaO and MgO, is.

11. Material according to one of the preceding claims, characterized in that the at least one metal oxide comprises a proportion of iron oxide and / or silicon dioxide.

12. Material according to one of the preceding claims, characterized in that it is the at least one carbonate at least one carbonate of the type M _x (Cθ ₃ ) _y , where M is a metal such as Mg, Ca, Sr, Ba, La , Mn or Y and x and y denote suitable integers in the usual way. - Zo -

13. Material according to one of the preceding claims, characterized in that the at least one carbonate is at least one alkaline earth carbonate, in particular CaCO ₃ or a mixture of CaCO ₃ and MgCO ₃ .

14. Material according to one of the preceding claims, characterized in that the at least one carbonate comprises at least one metal oxocarbonate of the type M _x O _y (CO ₃ ) _z , where M is a metal such as Mg, Ca, Sr, Ba, La, Mn or Y and x, y and z denote appropriate integers in the usual way.

15. A method for producing a material according to any one of the preceding claims, characterized by a heat treatment of carbonate particles, in which a thermal desorption reaction takes place under CO ₂ release, and a separation of particles having particle sizes <100 .mu.m, in particular <200 microns, after and / or during the heat treatment.

16. The method according to claim 15, characterized in that the heat treatment at a temperature in the range between 1000 ⁰ C and 1500 ⁰ C, in particular between 1100 ⁰ C and 1300 0C, takes place.

17. The method according to claim 15 or claim 16, characterized in that the heat treatment is carried out until the thermal desorption reaction is completed and the carbonat natpartikel are substantially completely converted into oxide particles.

18. The method according to claim 15 or claim 16, characterized in that the heat treatment is stopped before the thermal desorption reaction is terminated, so that & the carbonate particles are converted into particles having a core of carbonate and an oxide layer surrounding the core.

19. The method according to any one of claims 15 to 18, characterized in that particles of natural carbonates, in particular of lime and / or dolomite, are used as the carbonate particles.

20. The method according to any one of claims 15 to 19, characterized in that the heat-treated particles are subjected to a surface treatment in a CO ₂ -containing gas atmosphere in which forms a thin layer of carbonate on the surface of the particles.

21. The method according to claim 20, characterized in that the CO ₂ treatment at temperatures in the range between 600 ⁰ C and 800 ⁰ C, in particular between 650 ⁰ C and 750 ⁰ C, takes place.

22. The method according to any one of claims 20 or 21, characterized in that in the CO ₂ treatment in the gas atmosphere, a CO ₂ partial pressure between 100 mbar and 700 mbar is set.

23. The method according to any one of claims 20 to 22, characterized in that in the CO ₂ treatment in the gas atmosphere, a H ₂ O partial pressure between 100 mbar and 500 mbar, preferably between 100 mbar and 300 mbar, is set.

24. A method for producing a low-CO ₂ gas, wherein in a first process step CO ₂ from a raw gas by means of a CO ₂ -absorbing material, in particular according to one of - -LO -

Claims 1 to 14, is separated and regenerated in a second process step, the material under CO ₂ release.

25. The method according to claim 24, characterized in that for the first and / or the second process step process parameters are selected, under which the chemical composition of the core of the particles of the material used is substantially retained.

26. The method according to claim 25, characterized in that the process parameters depending on the average particle size of the particles and / or the nature of the raw gas, in particular its CO ₂ content, are selected.

27. The method according to any one of claims 24 to 26, characterized in that a hydrogen-containing synthesis gas, in particular a synthesis gas obtained from biomass, is used as the raw gas.

28. The method according to any one of claims 24 to 27, characterized in that the CO ₂ content in the raw gas is between 10 and 30 vol .-%.

29. The method according to any one of claims 24 to 28, characterized in that the first and / or the second process step is carried out in a fluidized bed reactor.

30. Use of a material according to any one of claims 1 to 14 as a bed material for fluidized bed processes. _

31. Use of a material according to one of claims 1 to 14 in a gasification process step, in particular in the production of synthesis gas from biomass.

32. Use of a material according to one of claims 1 to 14 as oxide catalyst, in particular for the catalytic tar reforming.

33. Use of a material according to any one of claims 1 to 14 for the separation of sulfur compounds and other impurities commonly contained in crude gases.