WO2012120173A1 - Method for capturing co2 - Google Patents

Abstract

The present invention relates to a method for the capture of CO₂ in a tube exchanger with amino-alcohol-impregnated alumina supports under combined conditions of TSA, PSA and vapour entrainment and subsequent reconditioning of the sorbent.

Description

 CO CAPTURE PROCEDURE?

The present invention relates to a process for the capture of CO2, in a gas treatment circuit in fixed-bed reactors with alumina supports impregnated with amino alcohols, under conditions of TSA, PSA and steam entrainment combined.

STATE OF THE PREVIOUS TECHNIQUE

Currently, all post-combustion CO2 capture plants use procedures based on chemical absorption with an aqueous solvent of alkanolamine, monoethanolamine (MEA) and diethanolamine (DEA) are the most frequent solvents. However, they have numerous drawbacks for treating gaseous streams, including the large amount of heat required to regenerate the solvent and the operating problems caused by corrosion and chemical degradation, which result in high capital costs and functioning. In total, 75-80% of the capture and sequestration cost of 90% of the CO2 from an electric power production plant is attributable to the capture and compression stage. It is therefore crucial to develop means of capturing CÜ2 at low cost to sequester CO2 emissions on an industrial scale.

It is considered that chemical absorption in regenerable solid sorbents is one of the most promising technologies to capture CO2 from gaseous streams, because it would allow a reduction in energy consumption, the heat capacity and regeneration temperature of the sorbent could be reduced solid.

Recently, it has been described about regenerable sorbents based on substrates for the capture of post-combustion CO2 in gaseous streams from electric power plants fueled with fossil fuels. Several different methods have been used to synthesize solid chemosorbents for CO2 capture [WO2009 / 061470]. I also know describes the use of amines or polyamines grafted on a solid nano-sized support to improve some characteristics of the gaseous sorbents in the solid phase. For example, a procedure for creating CO2 chemosorbents is based on the insertion of amine groups into nanostructured mesoporous silica supports [US 5087597].

An additional hypothesis has also been proposed, called "molecular envelope" (or "molecular basket" in English) in which nanostructured mesoporous silicas are used, where porous nanosilica support material is used, with a large pore volume for the purpose. to obtain a high adsorption capacity while to increase the selectivity and affinity of the adsorbent for CO2, polyamines are introduced into the pores, which have a high affinity for CO2 [US 7795175].

Other materials recently used to trap carbon dioxide are metal-organic reticular materials (MOF). MOFs are nanocrystalline structures composed of organic and inorganic components arranged in a crystalline network structure. These structures are constructed using an ionic metal core or axis, to which organic ligands bind. The lengths of the organic ligands define the volume of the gaps, the diameter of the pores of the crystalline lattice, and the geometry of the gap. The physical adsorption capacity and the selectivity of the MOF depend on these parameters. Organometallic skeletons are more suitable for pressure swing adsorption (PSA) with a loading pressure (15/40 bar, 1500/4000 kPa) and atmospheric pressure desorption. MOFs with uncoordinated amine functionalities inside the pores have also been prepared in an effort to improve yields in the application of the chemosorption process and temperature oscillation adsorption (TSA).

All the aforementioned materials require complex syntheses, and their production on an industrial scale is expensive. Whereas the application for the capture of CO2 in an electric power plant needs large quantities of materials, cheap and simple preparation methodologies would be necessary to prepare solid sorbents.

Regardless of the typology of the materials used, a critical aspect refers to the definition of a suitable procedure for the capture of post-combustion CO ₂ by solid sorbents in an electric power plant. For an efficient recovery of CO ₂ , a large amount of solid sorbent must be used in a process that provides a low pressure drop and easy regeneration of the sorbent, due to a high concentration of CO ₂ and the flow of the gaseous streams of the Electric Energy Plant.

The typology of the C0 ₂ capture procedure with solid sorbent depends on the particle size of the material used. In the case of using sorbents in the form of a powder, a high pressure drop is generated which means that a fluidized bed is needed, in this case, the procedure normally used is a gas washing equipment, of a fluidized bed in circulation, with a part of the sorbent transported by the same gas flow in a separate device where the sorbent is regenerated by heating it and then cooled and recirculated in the absorber.

On the other hand, when a sorbent in the form of granules is used, a lower pressure drop is generated and in this case a fixed bed procedure would be employed. However, in order to carry out the regeneration stage, a mobile bed is usually used for the use of granules, where the sorbent is continuously recirculated between the absorber and the desorber to provide a continuous supply of regenerated material. Both procedural solutions, both fluidized bed and mobile bed, have drawbacks with respect to a fixed bed: the fluidized bed and the mobile bed have a lower capture efficiency than the fixed bed and produce a loss of mass of friction sorbent and / or abrasion. In addition, the outward diffusion from the porosity of the solid CO ₂ released from the sorbent during regeneration may not occur spontaneously only by increasing the temperature and then steam entrainment and / or vacuum depressurization should also be applied. The need for gas entrainment and / or use of vacuum makes it more difficult to work with procedures based on a fluid or moving bed. DESCRIPTION OF THE INVENTION

The present invention provides a method for the capture of C0 ₂ comprising a gas stream treatment circuit, using fixed bed reactors under TSA conditions (temperature oscillation absorption), PSA (pressure oscillation absorption ) and steam entrainment combined.

One aspect of the present invention relates to a CO2 capture process in a gas stream treatment circuit, in at least two fixed-bed reactors (from now on the process of the invention), comprising the steps: a ) CO2 absorption from the gas stream, at a temperature between 20 and 60 ° C (TSA conditions). Fixed bed reactors have a sorbent in which CO2 is to be absorbed. This stage of CO2 absorption is an exothermic chemo-absorption, so the reactors can be cooled to achieve a more efficient CO2 capture and lengthen the absorption time, b) desorption of C0 ₂ at a temperature between 60 and 120 ° C, a pressure of between 0.08 and 0.8 atm and a steam flow rate of between 5 and 25% by volume of the desorbed CO2 (combination of TSA, PSA and gas entrainment conditions). At this stage the regeneration of the sorbent occurs when the saturation capacity of the CO2 is reached, and c) reconditioning of the sorbent at a temperature between 20 and The process of the invention is a discontinuous process based on a gas treatment circuit, however, since the fixed bed reactors are working alternately as an absorption or desorption device, controlling the relationship between the flow rate and the conditions of each stage. of the procedure, the absorption and desorption times can be temporarily coupled so that they are similar, obtaining a continuous CO2 capture process. This optimization of the times reduces the number of reactors necessary for the capture of CO2. In a preferred embodiment in the process of the invention, desorption times can be matched to absorption times thanks to the combination of TSA, PSA and steam entrainment.

The entrainment gas may be any gas known to a person skilled in the art, although water vapor or nitrogen is preferably used.

In another embodiment the process of the invention comprises three fixed bed reactors.

Fixed bed reactors have the advantage that they are more efficient, easier to operate and optimize.

Preferably, the fixed bed of the reactors comprises a pelletilized alumina sorbent impregnated with at least one amino alcohol. More preferably, the amino alcohol is selected from diethanolamine (DEA), monoethanolamine (MEA), diglylamine (DGA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), triethanolamine (TEA) or any combination thereof. More preferably, the amino alcohol is diethanolamine. More preferably, the amino alcohol content is between 30 and 40% by weight with respect to the total sorbent.

By "pelletilized alumina" in the present invention is meant that alumina solid finely divided into powder, which has been transformed into larger particles and of a stable nature at temperature, humidity and mechanical pressure. In a preferred embodiment, the temperature and pressure control of steps (a), (b) and (c) is carried out by heat exchangers containing finned tubes. In a more preferred embodiment the finned tubes are made of aluminum with tubular geometry. (See figures 1 and 2). In a preferred embodiment the heat exchanger used in the process of the invention is characterized in that it comprises:

- a tube (1) for the circulation of the thermal fluid comprising longitudinal radial fins (2) and an internal cavity (4) through which a thermal fluid circulates, - a wall that wraps the free ends of the radial fins, comprising the wall, an internal wall (6), an external wall (5) and an insulating jacket between the two (7) the tube, the fins and the internal wall being configured so that a solid pelletized sorbent (3) is located between them which flows the gas that contains the CO2. More preferably, the heat exchanger further comprises a thermocouple (8) for measuring the process temperature.

In this way the design of the exchanger is such that there is no direct contact between the sorbent and the thermal fluids of the heat exchanger (see Figure 3). This prevents degradation of the sorbent, since it has impregnated amino alcohols. An embodiment of the heat exchanger is illustrated by way of example and without limitation of the invention in Figure 3.

This sorbent impregnated alumina aminoalcohol is achieved that the process of the invention present a high selectivity and capacity for absorption of C0 _2.

The thermal fluid that flows inside the tube provided with fins of the heat exchanger, can heat (or cool) by conduction the sorbent placed in the cavities between said fins, as illustrated in Figures 2 and 3. Also the tube bundle can have a stream of cooling water in the absorption mode, and by condensation steam in desorption mode. Any other thermal fluid known to any person skilled in the art can also be used. In a preferred embodiment the absorption of step (a) is carried out at a temperature between 35 and 45 ° C.

In another preferred embodiment the desorption of step (b) is carried out at a temperature between 80 and 90 ° C.

Preferably the desorption of step (b) is carried out at a pressure of 0.1 atm.

In another preferred embodiment the reconditioning step (c) is carried out at a temperature between 35 to 45 ° C.

In a preferred embodiment, the process of the invention has a CO2 absorption capacity greater than 90%. The process of the present invention can be used to capture carbon dioxide from a coal power plant.

Another aspect of the invention relates to the heat exchanger for carrying out the process of the invention characterized in that it comprises:

- a tube (1) for the circulation of the thermal fluid comprising longitudinal radial fins (2) and an internal cavity (4) through which a thermal fluid circulates,

- a wall that wraps the free ends of the radial fins, comprising the wall, an internal wall (6), an external wall (5) and an insulating jacket between both (7) the tube, the fins and the inner wall being configured so that between them a solid pelletized sorbent (3) is located through which the gas containing the CO2 flows

In a preferred embodiment, the heat exchanger further comprises a thermocouple (8) for measuring the process temperature.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention.

DESCRIPTION OF THE FIGURES

Fig. 1. Shows the view of the cross-section (a) and the external surface (b) of the finned tube contained in the heat exchanger

Fig. 2. Shows the horizontal section of the heat exchanger that contains the finned tube.

Fig. 3. Shows the diagram of the vertical section of the heat exchanger.

Fig. 4. Shows the CO2 absorption curve over time, with a sorbent of 630 g of alumina impregnated with 36% by weight of alumina.

EXAMPLES

The invention will now be illustrated by tests carried out by the inventors, which demonstrates the specificity and effectiveness of the process of the invention for the capture of CO2. In order to carry out laboratory tests that evaluate the effectiveness of the capture procedure of C0 ₂ post-combustion based on sorbents solid, a specifically manufactured prototype that simulates a sub-sector of industrial equipment has been used. The reactor, which reproduces on a laboratory scale a geometry similar to that proposed for the actual application, allows to analyze the mechanism of heat and mass exchange, as well as the absorption / desorption phenomena inside the solid sorbent.

The device was designed similarly to a tubular heat exchanger (1000 mm long, Dl 50 mm, constituted by a jacketed cylindrical vessel inside which is housed a tube equipped with extruded aluminum fins with external fins that if extended radially to the width of the entire length with up to providing a more efficient heat exchange In Figure 1 a and b, the section and the external surface of the finned tube used in the realization of the fixed bed reactor can be observed respectively. Figure 2 shows in detail the horizontal section of the heat exchanger constituted by an aluminum tube (1) longitudinally provided with fins (2) and covered by an internal wall (6) and an external wall (5), between which there is a jacket (7) The thermal fluid flows both through the cavity of the finned tube (4) and through the outer jacket of the heat exchanger (7) The free space between the fins Longitudinal s is filled by pelletized solid sorbent (3) through which the gas containing CO2 flows

Figure 3 describes the vertical cross-section of the exchanger where the same elements described in Figure 2 are present. Figure 3 shows the inlet and outlet of the gas stream and the thermal fluid used as a heat exchange medium. The fluid used as a means of heat exchange is water which flows through the interior of the tube fitted with fins and the outer jacket, thus not directly in contact with the sorbent.

Depending on whether the thermal fluid is heated or cooling the fixed bed, the device will be able to function alternately and sequentially as a C0 ₂ absorber or desorber. The thermal fluid that flows inside the finned tube, heats (or cools) by conduction the sorbent placed in the cavities between the fins and externally delimited by the wall of the internal unit surrounding the finned tube. In addition, to ensure the improvement of heat exchange by conduction with the sorbent, the reactor is also provided with an outer jacket through which the flow of the thermal fluid that leaves the tube provided with fins is transported, so that it is a heat exchanger. hot.

The temperature control of the thermal fluid is carried out by means of a cooled / heated recirculation bath for the control of the external temperature. The temperature of the sorbent bed is measured by thermocouples (8) directly in contact with the sorbent granules and placed in the upper, intermediate and lower part of the reactor as seen in Figure 3.

The fixed bed reactors were loaded with a bed of solid sorbent (spherical alumina granules impregnated with 36% by weight of diethanolamine) and fed with simulated gas streams.

In the experiment of absorption of CO _2, the test conditions were as follows:

- Composition of the gas inlet (v / v): CO ₂ = 10%; 0 ₂ = 3% v / v; H ₂ O = 10% v / v; SO ₂ = 50 ppm; NO = 50 ppm; N ₂ = up to 100%; - Amount of sorbents: 630 g;

- Flow rate: 300 Nl / h;

- Absorption temperature: 40 ° C

The desorption stage was carried out under the following conditions:

- Desorption temperature: 85 ° C - Pressure: 100 mbar (10,000 kPa)

- Drag gas flow (N ₂ ): 0.6 Nl / h; The performance of the procedure has been evaluated by measuring the "net CO2 capture capacity" and the "useful absorption time", defined respectively as the amount of CO2 absorbed per gram of sorbent and the time until the CO2 concentration at the outlet of the reactor it remains less than 1% in volume during an absorption cycle (that is, until the fixed bed reactor allows 90% capture efficiency of C0 ₂ compared to its feed content which is of 10%)

Figure 4 shows the curve corresponding to the concentration of CO2 output recorded during an absorption cycle. Under the conditions tested, a "net capture capacity of C0 ₂ " of 50 mg C0 ₂ / g of sorbent and a "useful absorption time" of more than 30 minutes have been measured. A complete regeneration of the sorbent can be obtained in a time equal to 30 minutes operating at 85 ° C, 10,000 kPa and with 0.6 Nl / h of N2 flow as entrainment gas. In addition, consecutive adsorption-desorption cycles were repeated hundreds of times using the same sorbent without any loss in its absorption capacity.

The experimental results showed that the process of the invention based on the fixed bed reactor heat exchanger is suitable for application to the capture of CO2 because it allows to quickly achieve the temperatures at which the sorbent operates in the absorption stages and regeneration, an effective C0 ₂ capture and a complete regenerability of the sorbent. Additionally, thanks to the same duration of the absorption and regeneration stages, the continuous process can be easily carried out by means of a limited number of reactors operating alternately and therefore as an adsorption or desorption device.

Evaluation of the advantages of the proposed procedure

Based on the results obtained, the energy expenditure of the proposed post-combustion CO2 capture procedure used solid sorbents and the possible energy savings have also been estimated with respect to commercial technology based on the aqueous solution of amines.

To this end, through a computer simulation program of a

A _dtrr as _r ee

plant Producc is _p or _r ion power, we evaluated the impact of CO2 capture post-combustion on the electrical efficiency of the plant and on the net energy produced for a typical electric power plant 660 MWe fed Powdered p coal. In all simulations led to

_'r e _g en.

This was taken as reference _(k P _{) by} 90% CO2 capture from the gas stream. The plant simulations were carried out in reference to the conventional plant (without C0 ₂ capture), and for the following configurations:

- the same electric power production plant associated with a conventional CO2 capture by MEA in aqueous solution;

- the same plant working with a capture system based on the process of the invention with solid aminated sorbent for CO2.

Table 1 below summarizes the main results.

Table 1- Modeling results:

£ =, - _* SO ^φ -— ^

 to O> .— -

Case C5 l § X

 S ° = ¥ a = __¿5

Without capture of - - 657.5 43.0 C0 ₂

Capture of

C0 ₂ with MEA - 120 17 3605 - 48.5 475.6 31, 1 in solution Capture of

C0 ₂ with the

 process

 yes 85 10,000 20 2359 29.2 47.4 532.2 34.8 of the invention

 with sorbent

 solid

As shown in Table 1, the post-combustion CO2 capture procedure proposed by the inventors using solid sorbent saves more energy than one that uses aqueous monoethanolamine solution, which is potentially capable of saving 3.7 percentage points of net efficiency. of the plant.

Claims

one . Procedure for capturing CO ₂ , in at least two fixed-bed reactors, comprising the steps: a) absorption of CO ₂ , from a gaseous stream, at a temperature between 20 and 60 ° C, b) desorption of C0 ₂ at a temperature of between 60 and 120 ° C, a pressure of between 0.08 and 0.8 atm and a steam flow rate of between 5 and 25% by volume with respect to the flow of desorbed C0 ₂ . c) reconditioning of the sorbent at a temperature between 20 and 60 ° C. 2. A method according to claim 1 comprising three fixed bed reactors. 3. A method according to any one of claims 1 or 2, wherein the fixed bed of the reactors comprises a pelletilized alumina sorbent impregnated with at least one amino alcohol. 4. The method according to claim 3, wherein the amino alcohol is selected from diethanolamine, monoethanolamine, diglylamine, diisopropanolamine, methyldiethanolamine, triethanolamine or any combination thereof. 5. Method according to claim 4, wherein the amino alcohol is diethanolamine. 6. Method according to any of claims 3 to 5, wherein the amino alcohol content is between 30 and 40% by weight with respect to the total sorbent. 7. Method according to any of claims 1 to 6, wherein the temperature and pressure control of steps (a), (b) and (c) is carried out by heat exchangers. 8. Method according to claim 7, wherein the heat exchanger is made of aluminum with tubular geometry. 9. Method according to any of claims 1 to 8, wherein the heat exchanger is characterized in that it comprises: - a tube (1) for the circulation of the thermal fluid comprising longitudinal radial fins (2) and an internal cavity (4) through which a thermal fluid circulates, - a wall that wraps the free ends of the radial fins, comprising the wall, an internal wall (6), an external wall (5) and an insulating jacket between both (7) with the tube, the fins and the internal wall being configured. so that a solid sorbent including pelleted (3) through which flows the gas containing C0 ₂ is located. 10. Method according to claim 9, wherein the heat exchanger further comprises a thermocouple (8). eleven . Process according to any one of claims 1 to 10, wherein the absorption of step (a) is carried out at a temperature between 35 and 45 ° C. 12. Method according to any of claims 1 to 1 1, wherein the desorption of step (b) is carried out at a temperature of between 80 and 90 ° C, a pressure of between 0.1 and 0.3 atm and a flow rate of steam entrainment of between 5 and 15% by volume with respect to the flow of desorbed CO2. 13. Method according to any of claims 1 to 12, wherein the reconditioning step (c) is carried out at a temperature between 35 to 45 ° C. 14. Heat exchanger for carrying out the process according to any of the preceding claims characterized in that it comprises: - a tube (1) for the circulation of the thermal fluid comprising longitudinal radial fins (2) and an internal cavity (4) through which a thermal fluid circulates, - a wall that wraps the free ends of the radial fins, comprising the wall, an internal wall (6), an external wall (5) and an insulating jacket between both (7) with the tube, the fins and the internal wall being configured. so that among them is a solid pelletized sorbent (3) through which the gas containing CO2 flows 15. Heat exchanger according to claim 14 further comprising a thermocouple (8).