ES2955373A1 - DUAL FLUIDIZED BED MODULE FOR SOLAR-POWERED BIOMASS AND WASTE GASIFICATION AND ASSOCIATED INSTALLATION AND OPERATION METHOD (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Dual fluidized bed module (2) with input of fluctuating solar energy and installation (1) for obtaining syngas, and associated operating method, where the dual fluidized bed module (2) comprises a gasification unit (3), a combustion unit (5), separate sealing chambers (6, 7), a cyclone (16) and extraction elements for the extraction of solid heat-carrying particles (13) that are heated and stored in an installation that comprises a heating unit. concentrating solar energy (10) and in separate storage tanks (11, 12), where said solid heat-transfer particles (13) are introduced into the gasification unit (3) to produce a syngas through an external solar energy contribution that is fluctuating . (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

DUAL FLUIDIZED BED MODULE FOR SOLAR ENERGY BIOMASS AND WASTE GASIFICATION AND INSTALLATION AND OPERATION METHOD

ASSOCIATED

OBJECT OF THE INVENTION

The present invention refers to a dual fluidized bed module, an installation and an associated operating method, which allow syngas to be produced from biomass and solar energy continuously with high flexibility despite the intermittencies characteristic of solar energy. In particular, the dual fluidized bed module is fed with solid heat-carrying particles previously heated in a receiver that concentrates solar thermal energy, and the different elements of the module are configured to compensate for thermal fluctuations of external solar heat, allowing it to operate in a highly allothermal (where most of the energy needed to maintain the process at the appropriate thermal level comes from solar energy), as well as in an autothermal mode (where the heat required for gasification comes only from the combustion of char), as well as in any intermediate mode of operation.

BACKGROUND OF THE INVENTION

Biomass/waste gasification with steam is widely studied and has reached industrial development through the use of dual fluidized bed gasifiers (DFBG). These devices have two main units: a gasifier in which the volatilization of the biomass and the partial conversion of the carbonaceous residue of the fuel (char) takes place, and a combustor in which the unconverted char is burned with air in the gasifier. (along with additional fuel if necessary). The heat released by combustion is transported to the gasifier through the circulation of a solid heat transfer between the two units. By carrying out the combustion of the char in a separate unit, two gaseous streams are obtained: one of synthesis gas from the gasifier and another of combustion gas from the combustor. When these currents are generated separately, the synthesis gas (syngas) has a calorific value and hydrogen content. relatively high compared to other gasification systems. The gasification unit is considered allothermal, since it receives heat from the combustor, however, the system as a whole (combustor gasifier) is autothermal (considering that no additional fuel is added to the combustor). This is the usual way of operating of the DFBGs that currently exist, such as those developed by the Technical University of Vienna, ECN (Energy Research Center of the Netherlands) and marketed by companies such as Repotec or Dahlman [1], [2],

Although this process is of great interest, from the point of view of maximizing the renewable fraction in energy production processes, what is really interesting is supplying the heat necessary for gasification from an external renewable source such as the sun. In this way, the chemical energy of the syngas produced contains not only the energy of the biomass, but also an additional fraction of solar energy.

Furthermore, by reducing the amount of char that is oxidized in the combustor (more so the greater the fraction of solar energy introduced into the system), the fraction of carbon in the syngas increases (reducing the fraction that comes out in the form of CO ² with the Combustion gases). This makes it possible to increase the amount of carbon captured since, in synthesis applications (for example hydrogen production or liquid biofuels), gas conditioning allows CO ² to be extracted for sequestration (CCS) or use (CCSU). This aspect is a great advantage over conventional (non-solar) gasification carried out at DFBG, where the fraction of the fuel that ends up as CO ² in the combustion gas is much higher and cannot be separated economically as it is very diluted in nitrogen.

Regarding the solar gasifiers that have been proposed to date, they can be classified depending on how the solar energy comes into contact with the reactants into: directly irradiated gasifiers [3]—[7], in which the fuel is exposed directly to the radiation, and indirectly irradiated, in which the radiation hits an intermediate material. Within the indirectly irradiated, three approaches have been proposed: (i) irradiating the external walls of the reactor [8]; (ii) using a two-cavity reactor [9] and (iii) using a heat carrier [10]-[12] (processes such as the one presented in [13] combine approaches (i) and (iii)).

Despite the aforementioned advantages, solar gasifiers have not reached commercial development due to several challenges and difficulties that still entail their design and operation, among them, the need to transfer heat at the appropriate speed and the continuous operation of the gasifier. taking into account the intermittent nature of solar energy.

The first attempt to address the problem of solar intermittency, in order to guarantee a continuous gasification operation, was carried out by Bruckner in 1985 [14]. His proposal was based on decoupling the reactor from the solar receiver by using of two heat transfer fluids: molten slag that was heated in a solar tower receiver and stored (the thermal storage had a capacity of 16 h) and a steam stream that was used as HTF between the storage and the gasifier. The steam also acted as a reagent in the gasification of the coal, although only a small fraction of it was converted (18%) while the rest was recirculated (after heat recovery).

After Bruckner's attempt, two other close concepts have emerged [10], [11], [15], in which the system is simplified by using only solid particles as heat transfer fluid. The concept presented by Guo et al. [10], [11] propose a solar gasification process in DFBG for the production of liquid fuels through Fisher Tropsch. The idea is based on the possibility of circulating the solids leaving the DFBG combustion unit directly to the gasification unit, as in a conventional DFBG, or directing them to a solar receiver in which their thermal load is increased before be circulated back to the gasifier. Two intermediate solids tanks (one for the warm solids coming out of the combustor and another for the hot solids coming from the solar receiver) make it possible to cushion the intermittency of the solar resource in the process. Although the works of Guo et al. They are the first to propose a solar gasifier concept of this type. Their studies focus on the analysis of solar performance in the overall Fischer-Tropsch liquid synthesis process where the char conversion is treated merely as a parameter. constant over time (and independent of the solar resource).

A concept similar to that of Guo et al. has been recently proposed [16], [17]. The procedure combines the technology of dual fluidized beds with the technology of solar tower receivers. Solid particles (type B according to the Geldart classification) act as HTF circulating between the solar receiver and the gasifier. To dampen solar intermittency, two tanks are used: the hot material tank, in which the solids that have been heated in the solar receiver are stored, and the warm material tank, in which the solids extracted from the DFBG are stored. The concept of solar gasification was analyzed based on a gasification model, identifying the range of reasonable operating conditions to carry out the process. In addition, the performance of the concept was studied in a generic way (without yet knowing the geometry, design, or operating procedure of the unit) together with a reference solar field to know the dimensions of the solar field, as well as the size of thermal storage that would allow a reference biomass solar gasification process to operate. On the other hand, in [18] (where a hydrodynamic model of a cold experimental unit of a conventional DFBG is developed and validated) the main problems (related to hydrodynamics) that arise when trying to implement the concept of solar gasification in a conventional DFBG are identified. DFBG.

To date, no work has explained how to carry out the design and actual operation of a reactor that allows the idea generally outlined in [16], [17] and [18] to be implemented in practice. That is, , there is no technical solution that allows the hybridization of biomass gasification with solar energy through the use of solid particles such as HTF, allowing the continuous operation of the unit, regardless of the external heat input (solar resource).

[1] J. Karl and T. Proll, ''Steam gasification of biomass in dual fluidized bed gasifiers: A review,” Renewable and Sustainable Energy Reviews. 2018, doi: 10.1016/j.rser.2018.09.010.

[2] J. Corella, JM Toledo, and G. Molina, “A review on dual fluidized-bed biomass gasifiers,” Ind. Eng. Chem.

Res., vol. 46, no. 21, pp. 6831-6839, 2007, doi: 10.1021/ie0705507.

[3] RW Taylor, R. Berjoan, and JP Coutures, “Solar gasification of carbonaceous materials,” Sol. Energy, vol. 30, no. 6, pp. 513-525, 1983, doi: 10.1016/0038-092X(83)90063-4.

[4] JP Murray and EA Fletcher, “Reaction of steam with cellulose in a fluidized bed using concentrated sunlight,” Energy, vol. 19, no. 10, pp. 1083-1098, 1994, doi: 10.1016/0360-5442(94)90097-3.

[5] GJ Nathan, BB Dally, ZT Alwahabi, PJ Van Eyk, M. Jafarian, and PJ Ashman, “Research challenges in combustion and gasification arising from emerging technologies employing directly irradiated concentrating solar thermal radiation,” Proc. Fuel Inst., vol. 36, no. 2, pp. 2055-2074, 2017, doi: 10.1016/j.proci.2016.07.044.

[6] T. Kodama, “High-temperature solar chemistry for converting solar heat to Chemical fuels,” Prog. Energy Combust. Sci., vol. 29, no. 6, pp. 567-597, 2003, doi: 10.1016/S0360-1285(03)00059-5.

[7] K. ZENG et al., “Concentrated solar gasification biomass system for synthesis gas preparation and metal smelting,” CN109355108A, 2019.

[8] G. Flamant et al., “Dense suspension of solid particles as a new heat transfer fluid for concentrated solar thermal plants: On-sun proof of concept,” Chem. Eng. Sci., vol. 102, pp. 567-576, 2013, doi: 10.1016/j.ces.2013.08.051.

[9] ED Gordillo and A. Belghit, “A bubbling fluidized bed solar reactor model of biomass char high temperature steam-only gasification,” Fuel Process. Technol., vol. 92, no. 3, pp. 314-321, 2011, doi: 10.1016/j.fuproc.2010.09.021.

[10] P. Guo, PJ Van Eyk, WL Saw, PJ Ashman, GJ Nathan, and EB Stechel, “Performance assessment of Fischer-Tropsch liquid fuels production by solar hybridized dual fluidized bed gasification of lignite,” Energy and Fuels, vol . 29, no. 4, pp. 2738-2751, 2015, doi: 10.1021/acs.energyfuels.5b00007.

[11] P. Guo, WL Saw, PJ Van Eyk, EB Stechel, PJ Ashman, and GJ Nathan, “System Optimization for Fischer-Tropsch Liquid Fuels Production via Solar Hybridized Dual Fluidized Bed Gasification of Solid Fuels,” Energy and Fuels, vol. 31, no. 2, pp. 2033-2043, 2017, doi: 10.1021/acs.energyfuels.6b01755.

[12] P. LYU, X. SONG, Y. BAI, J. WANG, W. SU, and G. YU, “System and a method for co-producing oil and gas by graduating conversion of biomass heated by solar energy, ” CN113444536A.

[13] F. PENG, L. YONGJUN, Z. YUCHUN, and W. BING, “System for Producing High-Quality Gas,” US 2021/0115345 Al, 2021.

[14] A. P. Bruckner, “Continuous duty solar coal gasification system using molten slag and direct-contact heat exchange,” Sol. Energy, vol. 34, no. 3, pp. 239-247, 1985, doi: 10.1016/0038-092X(85)90061-1.

[15] A. Nzihou, G. Flamant, and B. Stanmore, “Synthetic fuels from biomass using concentrated solar energy - A review,” Energy, vol. 42, no. 1, pp. 121-131, 2012, doi: 10.1016/j.energy.2012.03.077.

[16] M. Suárez-Almeida, A. Gómez-Barea, A. F. Ghoniem, and C. Pfeifer, “Solar gasification of biomass in a dual fluidized bed,” Chem. Eng. J., vol. 406, 2021, doi: 10.1016/j.cej.2020.126665.

[17] A. Gómez-Barea, M. Suárez-Almeida, and A. Ghoniem, “Analysis of fluidized bed gasification of biomass assisted by solar-heated particles,” Biomass Convers. Biorefinery, vol. 11, no. 1, pp. 143-158, 2021, doi: 10.1007/s13399-020-00865-0.

[18] M. Suárez-Almeida, A. Gómez-Barea, C. Pfeifer, and B. Leckner, “Fluid dynamic analysis of dual fluidized bed gasifier for solar applications,” Powder Technol., vol. 390, pp. 482-495, 2021, doi: 10.1016/j.powtec.2021.05.032.

DESCRIPTION OF THE INVENTION

The present invention aims to solve some of the problems mentioned in the state of the art. More particularly, in a first aspect of the present invention a dual fluidized bed module for the gasification of hybridized biomass with energy input from a solar source. The proposed dual fluidized bed module presents flexibility to different thermal loads, which allows it to work continuously even under strong intermittencies in the contribution of external energy, in this case, solar energy.

The dual fluidized bed module comprises a gasification unit that operates as a bubbling fluidized bed and is fed by biomass, steam and solid heat transfer particles that are previously heated in a concentrating solar energy unit or in the combustion unit, generating thus an output syngas and a carbonaceous residue known as char.

Likewise, the module comprises a combustion unit provided with a combustion riser tube, said combustion unit operates as a circulating fluidized bed and is configured to burn, through combustion with air/enriched air, the char generated in the gasification unit.

Both units described are linked to each other by separate sealing chambers (known in the art as “loop seais” due to its name in English).

The first sealing chamber or lower sealing chamber connects the gasification unit with the combustion unit, sealing both units in a gas-tight manner, preventing the passage of gases between both units.

Likewise, said first sealing chamber is fed with steam (or air, depending on the process) to circulate a stream of solids comprising the char from the gasification unit to the combustion unit through a lower supply chamber and a chamber lower recycle.

The second sealing chamber or upper sealing chamber connects the combustion unit with the gasification unit, which is fed with steam, allows the circulation of solid material from the combustion unit to the gasification unit and prevents gases from passing through. from one unit to another (gas sealing). This transfer of solids allows the combustion energy to be recovered to be used in gasification and finally incorporated into the syngas.

A cyclone operatively connected to the combustion unit and the second sealing chamber separates the combustion gases from the solid materials coming from the bed of the combustion unit.

The greater the fraction of solar energy introduced into the system, the less residual char needs to be burned in the combustion unit. Furthermore, this allows increasing the fraction of carbon in the syngas (reducing that which comes out in the form of CO ² with the combustion gases). This allows increasing the amount of carbon captured since, in synthesis applications, gas conditioning allows CO ² to be extracted for sequestration (CCS) or use (CCSU). This aspect is a great advantage over conventional (non-solar) gasification carried out at DFBG, where the fraction of the fuel that ends up as CO ² in the combustion gas is much higher and cannot be separated economically as it is very diluted in nitrogen.

As mentioned, the dual fluidized module aims to produce syngas under any external heat load (in the form of solid heat transfer particles previously heated with solar energy), it has been found that to make this possible:

(i) the gasification unit must be designed with sufficient width to allow the residence time required by the char to be achieved to achieve the maximum required conversion (when the external heat input to the system is maximum) at the given operating conditions. , under a maximum pressure loss of the fluidized bed that is reasonable and, at the same time, allows operation in autothermal conditions (minimum char conversion) giving rise to a minimum pressure loss of the fluidized bed such that its operation is possible.

(ii) the design of the supply chamber (SC) of the lower loop signal with a length and cross section such that it allows compensation (modifying the relative gas-solid velocity in the SC, ie, from changes in the solids circulation of the system and/or changes in the gas feed of the lower signal loop) the variation of pressure loss that takes place in the system due to the reduction/increase of the unit inventory gasification result of the reduction/increase of the external heat input to the system (ie, Maximum pressure loss in the gasifier Minimum pressure loss in the gasifier)

The lower sealing chamber and its configuration is essential, it regulates the hydrodynamics of the system allowing it to operate both in completely autothermal mode (without external heat input from the solar field) and at intermediate and high solar energy loads.

The lower supply chamber has a geometric configuration that makes it possible to compensate for variations in pressure losses as a result of fluctuations in the external heat input, and the gasification unit is wide enough to achieve char conversions of up to 80% in operating times. residence of between 1 to 30 minutes.

The gasification unit must be sized to present maximum pressure losses of 300 mbar and minimum pressure losses of 10 mbar. Likewise, the configuration of the lower supply chamber must be such that it allows these pressure fluctuations of the gasification unit to be compensated.

In a first mode of operation, the lower seal chamber is configured to be fed with a solids flow comprising unconverted char and an internal stream of bed material.

In said first mode of operation, said solids stream is variable and the temperature of the combustion unit is not allowed to fluctuate.

In a second mode of operation, the lower sealing chamber is configured to be fed with a flow of solids that also includes the heat transfer particles of the external stream, where said flow of solids is constant, varying the temperature of the unit. combustion.

Preferably, for either of the two modes of operation, the lower supply chamber (6) has a height (h) between 0.7 to 2 m.

For the first mode of operation, the lower supply chamber has a cross section that is between 0.03 and 3% of the cross section of the gasification unit.

For the second mode of operation, preferably the lower supply chamber has a cross section that is between 0.07% and 7% of the cross section of the gasification unit (3).

With any of the configurations described above, in an extreme case without contribution of solar fraction, the module can operate in autothermal mode (without contribution of external heat). Under a significant amount of available solar energy it operates in a highly allothermic mode, and at any other intermediate point it is capable of operating by varying the amount of char burned in the combustor.

The module may also be provided with first extraction elements, connected to or forming part of the gasification unit, which are configured to extract the solid heat-transfer particles from the external stream.

Likewise, as an alternative, it may have second extraction elements, connected to or forming part of the combustion unit, which are configured to extract the solid heat-carrying particles from the external stream.

The above-mentioned operational advantages, as well as other operational advantages, will become evident below when detailing the method of operation and the installation subject to the present invention.

In a second aspect of the present invention, an installation is described comprising the dual fluidized bed module according to any of the above-mentioned embodiments and the concentrating solar energy unit.

More particularly, the installation further comprises:

- a first storage tank that receives a joint flow of solid heat-transfer particles once they have been heated in the concentrating solar energy unit,

- a second storage tank that receives solid heat-transfer particles at the outlet of the gasification unit or at the outlet of the combustion unit,

where the solar concentration unit comprises a plurality of heliostats that concentrate the radiation in a receiver of a solar tower where the solid heat-transfer particles from the second storage tank are heated.

In a third aspect of the present invention, a method of operation of the module described above is described, which comprises the following steps:

- introducing biomass, steam, the solid heat transfer particles from the first storage tank and/or an internal stream of heat transfer material from the combustion unit, into the gasification unit,

- convert, in the gasification unit, said biomass into an output syngas and into a residual char generated after the volatilization of said biomass, in a residence time of the char in said gasification unit that comprises from 1 to 30 minutes giving leads to char conversions of between 15-80% depending on the thermal load of the heat transfer particles,

- introducing a gas, which may be vapor or air, into the lower sealing chamber and transporting a stream of solids comprising the internal stream of solid heat transfer particles and unconverted char, from the gasification unit to the combustion unit through of the lower sealing chamber, maintaining the temperature of the combustion unit constant, - adjust the flow rate of said stream of solids depending on the thermal load of the heat transfer particles of the external stream to meet the energy demand of the combustion unit. gasification,

- combust the unconverted char in the combustion unit with a minimum oxygen excess over the stoichiometric of 5%,

- introducing steam into the second sealing chamber by circulating bed material from the combustion unit to the gasification unit, thus transferring combustion energy to gasification,

In a fourth aspect of the present invention, a method of operation of the module described above is described, which comprises the following steps:

- introducing biomass, steam and solid heat transfer particles from a first storage tank and/or an internal stream of heat transfer material from the combustion unit, into the gasification unit,

- convert, in the gasification unit, said biomass into an output syngas and into a residual char generated after the volatilization of said biomass, in a residence time of the char in said gasification unit that comprises from 1 to 30 minutes giving lead to char conversions of between 15-80% depending on the thermal load of the heat transfer particles of the external current,

- feeding the lower sealing chamber with steam, and circulating a stream of solids comprising heat transfer particles from the external stream, heat transfer particles from the internal stream, and unconverted char, from the gasification unit to the combustion unit through of said lower sealing chamber,

- maintain a constant flow of solids passing through the lower supply chamber,

- adjust the temperature of the combustion unit depending on the thermal load of the heat transfer particles of the external current to meet the energy demand of the gasification unit,

- combust the char in the combustion unit with a minimum oxygen excess over the stoichiometric of 5%,

- introducing steam into the second sealing chamber by circulating the internal flow of heat transfer material from the combustion unit to the gasification unit, thus transferring the energy from combustion to gasification.

Mode of operation two is carried out under a constant circulation of heat transfer solids from the gasification unit to the combustion unit, varying the temperature of the combustion unit as the external heat input through the heat transfer solids is varied. coming from the first storage tank (this operation is convenient since, for any external heat load, not only is the current required to satisfy the energy demand for the combustion of char circulated to the combustor, but the heat transfer solids that are go to the second storage tank).

Both proposed methods are alternatives to solve the same problem, namely, allowing the operation of a dual fluidized module with a fluctuating solar input. In other words, the methods described above, as well as the proposed module, allow operating at the same time as:

(i) a conventional, autothermal DBFG, in which the heat required for gasification comes solely from the combustion of the char, resulting in char conversions in the gasification unit of less than 30% resulting in char residence times in the gasification unit low (1-5 minutes);

(ii) a highly allothermic DBFG, in which most of the heat required for gasification comes from an external source (solar energy in the form of hot particles) and only a small fraction is obtained from the combustion of char; This implies that most of the char (-80%) is converted to syngas in the gasification unit, therefore requiring a high residence time, for example 20-35 minutes (being values much higher than those achieved in DFBG conventional);

(iii) In addition, the gasification unit must be capable of operating at all intermediate points of external heat input located between the two extremes defined in sections (i) and (ii).

Compensated pressure losses in the sealing chamber are carried out by modifying the relative gas-solid velocity in the SC, for example, by varying the solids circulation of the system (operation mode 1) and/or by varying the steam feed/ air. However, the sealing chamber must be sized to allow maximum and minimum pressure losses in a reasonable range, for example, between 10 mbar-300 mbar.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, in accordance with a preferred example of its practical implementation, a set of drawings is attached as an integral part of said description. where, for illustrative and non-limiting purposes, the following has been represented:

Figure 1.- Shows a schematic view of a preferred embodiment of the dual fluidized bed module according to the present invention, showing the gasification unit, the combustion unit, each sealing chamber and the cyclone.

Figure 2.- Shows a schematic view of the installation of a preferred embodiment of the present invention, showing the storage tanks and the concentration solar energy unit with heliostats.

Figure 3.- Shows a schematic view of two different methods of operation of the dual fluidized bed module according to the present invention.

PREFERRED EMBODIMENT OF THE INVENTION

Next, with the help of Figures 1-3, a dual fluidized bed module, an installation for producing syngas with thermal storage of solar energy, and an operation method associated with said module are described.

As described in Figure 1, a first aspect of the present invention has as its object a dual fluidized bed module (2) for obtaining syngas by gasification of biomass with a solar energy contribution, which comprises a gasification unit (3) which operates as a bubbling fluidized bed and is fed by biomass (17), steam (18) and by solid heat transfer particles from an internal circulation (24) and, in the case of non-autothermal operation, also with a current external (13) of heat transfer particles that are previously heated in a concentrating solar energy unit (10), thus generating an output syngas (4) and a carbonaceous residue or char.

The dual fluidized bed module (2) also comprises a combustion unit (5) provided with a combustion riser tube (5') that operates by circulating fluidized bed, configured to burn the char generated in the gasification unit. (3) through combustion with air/enriched air (15).

Likewise, a lower sealing chamber (6) internally connects the gasification unit (3) with the combustion unit (5), sealing both units (3.5) of gas-tight form, where said lower sealing chamber (6) is fed with steam/air (23) to circulate the char and heat transfer solids from the gasification unit (3) to the combustion unit (5) through of a lower supply chamber (6') and a lower recycle chamber (6"),

An upper sealing chamber (7) that connects the combustion unit (5) with the gasification unit (3) sealing both units (3.5) in a gas-tight manner, in which said upper sealing chamber (7 ) is fed with steam (25) to circulate an internal stream (24) that comprises solid heat transfer material from the bed of the combustion unit (5), to the gasification unit (3) through an upper supply chamber (7 ') and an upper recycle chamber (7”),

Figure 1 further shows that the dual fluidized bed module in the preferred embodiment being described, comprises a cyclone (16) operatively connected to the combustion unit (5) and to the second sealing chamber (7), where said cyclone ( 16) separates the combustion gases (19) from the solid materials from the bed of the combustion unit (5).

The lower supply chamber (6') must have a geometric configuration that makes it possible to compensate for variations in pressure losses as a result of fluctuations in the external heat input (solar energy), and the gasification unit (3) must be wide enough for conversions. of up to 80% of the char in residence times of between 1 and 30 minutes, with maximum pressure losses of 200 300 mbar.

Figure 2 shows a second aspect of the present invention that has as its object an installation (1) comprising the dual fluidized bed module (2) and the concentrating solar energy unit (10) described above.

Additionally, the installation includes:

- a first storage tank (11) that receives a joint flow of solid heat-transfer particles once they have been heated in the concentrating solar energy unit (10),

- a second storage tank (12) that receives solid heat-transfer particles (13) at the outlet of the gasification unit (3) or at the outlet of the combustion unit (5), and

As shown in Figure 2, the solar concentration unit (10) comprises a plurality of heliostats (20) that concentrate the radiation in a receiver of a solar tower (22) where the solid heat-carrying particles (13) from the second storage tank (12).

Figure 3 shows a block diagram to illustrate two modes of operation of the dual fluidized bed module, according to the present invention. These modes of operation will be described in detail below.

In a first mode of operation, the method comprises the following steps:

- introducing biomass (17), steam (18), the solid heat-transfer particles (13) from a first storage tank (11) and/or the internal stream (24) of heat-transfer material from the combustion unit (5), in the gasification unit (3),

- convert, in the gasification unit (3), said biomass (17) into an output syngas (4) and into a residual char generated after the volatilization of said biomass (17), in a residence time of the char in said gasification unit (3) that lasts from 1 to 30 minutes giving rise to char conversions of between 15-80% depending on the thermal load of the heat transfer particles (13),

- introducing a gas (23) into the lower sealing chamber (6) and transporting a stream of solids which in turn comprises unconverted char, and the internal stream of heat-transfer particles (24),

from the gasification unit (3) to the combustion unit (5) through said lower sealing chamber (6),

- maintain the temperature of the combustion unit (5) constant,

- adjust the flow rate of said stream of solids depending on the thermal load of the heat transfer particles (13) to meet the energy demand of the gasification unit (3),

- combust the char in the combustion unit (5) with a minimum oxygen excess over the stoichiometric of 5%,

- introduce steam (25) into the second sealing chamber (7) by circulating the internal current (24) from the combustion unit (5) to the gasification unit (3), thus transferring the energy from combustion to gasification .

Preferably, the pressure losses are compensated by the variation of the solids flow rate in the lower supply chamber.

In a second mode of operation, the operation method comprises the following steps:

- introducing biomass (17), steam (18) and the solid heat-transfer particles (13) from a first storage tank (11) and an internal stream (24) of heat-transfer material from the combustion unit (5), into the gasification unit (3),

- convert, in the gasification unit (3), said biomass (17) into an output syngas (4) and into a residual char generated after the volatilization of said biomass (17), in a residence time of the char in said gasification unit (3) that lasts from 1 to 30 minutes giving rise to char conversions of between 15-80% depending on the thermal load of the heat transfer particles (13),

- feeding the lower sealing chamber (6) with a gas (23) that is steam, and circulating the stream of solids that also includes the heat transfer particles (13) from the gasification unit (3) to the combustion unit (5) through said lower sealing chamber (6),

- maintain a constant flow of solids that passes through the lower supply chamber (6),

- adjust the temperature of the combustion unit (5) depending on the thermal load of the heat transfer particles (13) to meet the energy demand of the gasification unit (3),

- combust the char in the combustion unit (5) with a minimum oxygen excess over the stoichiometric of 5%,

- introduce steam (25) into the second sealing chamber (7) by circulating the internal current (24) from the combustion unit (5) to the gasification unit (3), thus transferring the energy from combustion to gasification .

Preferably, any of the proposed methods comprises a step of varying the gas flow rate (23) fed to the lower sealing chamber (6) to compensate for pressure losses. As has been detailed throughout the document, the gas flow (23) can be steam or air in certain cases, preferably under the first mode of operation.

EXAMPLES

The following application examples serve to illustrate an example of the dual fluidized bed module object of the present invention, but do not limit, in any case, the scope of the present invention.

As an example to illustrate the invention, the main design and operation parameters of a dual fluidized bed module (2) for the gasification of biomass (17) with steam hybridized with solar energy are shown, as shown in Figure 1, in an operating mode according to the first option of Figure 3 where the solid heat-transfer particles (13) are extracted from the gasification unit (3). The example gasification unit (3) has a capacity of 10 MWt of biomass (17), which represents a biomass flow rate of 1800 kg/h with a higher calorific value of 20 MJ/kg.

Table 1 shows the main geometry parameters that allow the unit to operate under external heats of between 2.4 and 0 MJ per kg of biomass (dry and ashless). It is considered that the “l oop sea! " upper (7) can have a cross section that is half that of the lower “loop seal” (6) and that for the same loop seal the supply chamber and the recycle chamber have the same section. The height of the “riser” ” of the combustion unit must be such that it allows the entrainment of the required solid flows under any external heat load, a height of 7.5 m can be taken as a reference for the example case.

Gasification unit section (m2) 12

Combustion unit section (m2) 0.44

Lower loop seal section (m2) 0.22

Lower loop seal height (m) 1.38

Table 1. Main geometric parameters of the example unit

The operation is carried out for temperatures of 850 0C in the gasification unit (3) and 905 0C in the combustion unit (5). The solid heat transfer particles (13) from the solar field or thermal storage enter the gasification unit (3) at 9500C.

The gasification unit (3) is fluidized with preheated steam at 500oC under a steam/biomass ratio of 0.44. Air at room temperature is fed into the combustion unit (5). The amount of air fed to the combustion unit (5) must be such that it allows the complete combustion of the char that reaches the combustion unit (a minimum excess over the stoichiometric air of 5% is set) and at the same time allows the entrainment of the required solids flow.

The “loop seais” or sealing chambers (6,7) are fed with steam at 500oC. In the upper "loop sea!" the amount of steam fed must always be the minimum that allows solids to circulate and avoid dredging of gas from the supply chamber to the recycle chamber.

The lower "loop sea!" , under the mode of operation mentioned above, according to a design example, will operate in the same way since the change in the velocity of the solids in the supply chamber when varying the heat load external is sufficient to compensate for changes in pressure loss of the gasification unit.

Sand with an average particle size of 200 pm, density of 2500 kg/m3 and sphericity of 0.87 is used as solid heat-transfer particles of inert material.

Table 2 shows data of the proposed dual fluidized bed module under different operating conditions, where it is shown to be flexible enough to adapt the operation under a wide range of external heat input to the system. As the amount of heat supplied increases, it is observed that the char conversion in the gasification unit increases from 15 to 73%. Under the lower amount of heat supplied by the solid heat-carrying particles (13), less char is converted, and, as a consequence, a greater mass of solid particles is recirculated to the combustion unit (5). On the contrary, under conditions of high heat energy available from the solid heat-carrying particles of inert material, a smaller amount of heat transfer material will need to be recirculated to the combustion unit (5).

To achieve the maximum possible conversion (approximately 73%), an inventory of inert material of solid heat transfer particles is required in the gasification unit (3), 16.5 times greater than that of autothermal operation (without contribution). Furthermore, it is interesting to observe how the pressure loss of the supply chamber (SC) of the lower "loop sea!" decreases as the external heat input increases, to compensate for the increase in pressure loss of the gasification unit (5). , allowing the operation to be satisfied hydrodynamically for the entire range of external heat input.

Table 2. Operating parameters of the example unit under different levels of external heat input

Considering the above, particularly the necessary width of the gasification unit, the height of the supply chamber and its cross section, considered key parameters, and the considerations related to the configuration selected for the extraction of solids, the following geometric parameters are obtained that allow SDFBG units to be scaled:

Parámetros adimensionales y alturas propuestas a modo de ejemplo para una realización de la invenciónTable 3.

Dimensionless parameters and exemplary proposed heights for an embodiment of the invention

**The height of the riser must be such that it allows the entrainment of the required solid flows under any external heat load, a height of 7.5 m can be taken as a reference.

Where:

Ariser: combustion riser section

Agasifier: section of the gasification unit,

ASC.LLS: lower supply chamber section,

ARC.LLS: lower recycle chamber section,

ASC.ULS: upper supply chamber section,

ARC.ULS: upper recycling chamber section,

hSC,LLS: height of the lower supply chamber,

hriser: height of the combustion riser.

According to the above, reasonable design parameters for the first mode of operation can be:

- Mass consumption of biomass: 150 kg h'1 mgasifier2

- Maximum pressure loss in the gasifier: 200 mbar

- Minimum pressure loss in the gasifier: 10 mbar

- Minimum char conversion: 16% (resulting in a minimum char residence time of 1.1 min*)

- Excess oxygen (above the stoichiometric necessary to completely burn the char) minimum in the combustor: 5%

- Fluidizing agent: air

- Surface speed in the riser during autothermal operation: 5 m/s

While for operation mode two, they can be:

- Mass consumption of biomass: 150 kg h'1 mgasifier2

- Maximum pressure loss in the gasifier: 185 mbar

- Minimum pressure loss in the gasifier: 25 mbar

- Minimum char conversion: 25% (resulting in a minimum char residence time of 2.1 min*)

- Excess oxygen (above the stoichiometric necessary to completely burn the char) minimum in the combustor: 5%

- Fluidizing agent: enriched air 40% O ² v/v and air

- Surface speed in the riser during autothermal operation: 7 m/s.

*Residence times based on the same operating conditions used in the previous example.

Claims (13)

1.- Dual fluidized bed module (2) for obtaining syngas through biomass gasification with a solar energy contribution materialized through heat transfer particles (13) whose heat contribution is fluctuating, where said module (2) comprises: - a gasification unit (3) that operates as a bubbling fluidized bed and is fed by biomass (17), steam (18), an internal recirculation stream (24) of heat transfer bed material, and, when operating under a non-recirculating mode autothermal, by solid heat-transfer particles (13) that are previously heated in a concentrating solar energy unit (10), thus generating an output syngas (4) and an unconverted char, - a combustion unit (5) provided with a combustion riser tube (5') that operates as a circulating fluidized bed, configured to burn the char generated in the gasification unit (3) through combustion with air/enriched air (15 ), - a lower sealing chamber (6) that connects the gasification unit (3) with the combustion unit (5) sealing both units (3.5) in a gas-tight manner, where said lower sealing chamber (6) It is fed with a gas (23) to circulate a stream of solids from the gasification unit (3) to the combustion unit (5) through a lower supply chamber (6') and a lower recycle chamber (6). "), where said solids stream comprises at least unconverted char and the internal stream (24), - an upper sealing chamber (7) that connects the combustion unit (5) with the gasification unit (3) sealing both units (3,5) in a gas-tight manner, in which said second sealing chamber ( 7) is fed with steam (25) to circulate the internal current (24) of the combustion unit (5) to the gasification unit (3) through an upper supply chamber (7') and a recycle chamber top (7”), said module being characterized in that it is configured to be used with heat transfer particles (13) with a fluctuating thermal load that generate variable pressure fluctuations in the gasification unit (3) that are compensated by the lower supply chamber (6'). which is sized for this purpose, and where the gasification unit (3) is wide enough to achieve conversions of up to 80% of the char in residence times of between 1 and 30 minutes. 2. - The module (2) of claim 1, wherein the lower supply chamber (6) has a height (h) between 0.7 to 2 m. 3. - The module (2) of claim 1, wherein the combustion unit (3) operates at a constant temperature and the lower sealing chamber (6) compensates for pressure fluctuations by: - a variation of the solids stream comprising unconverted char and the internal heat transfer material stream, and/or - a variation in the flow rate of the gas (23) that comprises steam and/or air. 4. - The module (2) of claim 3, wherein the lower supply chamber (6) has a cross section that is between 0.03 and 3% of the cross section of the gasification unit (3). 5. - The module (2) of claim 1, wherein the stream of solids that passes through the lower sealing chamber (6) is constant and also comprises heat transfer particles (13), and the combustion unit (5 ) is configured to operate at a variable temperature. 6. - The module (2) of claim 5, wherein the lower supply chamber (6) has a cross section that is between 0.07% and 7% of the cross section of the gasification unit (3) . 7. - The module (2) of claim 1, which comprises a cyclone (16) operatively connected to the combustion unit (5) and the upper sealing chamber (7), where said cyclone (16) separates the gases from combustion (19) of the solid materials from the bed of the combustion unit (5). 8. - The module (2) of claim 1, which comprises first extraction elements, connected to or forming part of the gasification unit (3), which are configured to extract the solid heat-transfer particles (13). 9. - The module (2) of claim 1, which comprises second extraction elements, connected to or forming part of the combustion unit (5), which are configured to extract the solid heat-transfer particles (13). 10. - Method of operation of the dual fluidized bed (2) of any one of claims 1 to 9, which comprises the steps of: - introducing biomass (17), steam (18), the solid heat-transfer particles (13) from a first storage tank (11) and the internal flow (24) of heat-transfer material from the combustion unit (5), into the gasification unit (3), - convert, in the gasification unit (3), said biomass (17) into an output syngas (4) and into a residual char generated after the volatilization of said biomass (17), in a residence time of the char in said gasification unit (3) that lasts from 1 to 30 minutes giving rise to char conversions of between 15-80% depending on the thermal load of the heat transfer particles (13), - introducing a gas (23) into the lower sealing chamber (6) and transporting the stream of solids from the gasification unit (3) to the combustion unit (5) through said lower sealing chamber (6), - maintain the temperature of the combustion unit (5) constant, - adjust the flow rate of said stream of solids depending on the thermal load of the heat transfer particles (13) to meet the energy demand of the gasification unit (3), - combust the char in the combustion unit (5) with a minimum oxygen excess over the stoichiometric of 5%, - introduce steam (25) into the second sealing chamber (7) by circulating the internal current (24) from the combustion unit (5) to the gasification unit (3), thus transferring the energy from combustion to gasification . 11. Method of operation of the dual fluidized bed (2) of any one of claims 1 to 9, comprising: - introducing biomass (17), steam (18) and the solid heat-transfer particles (13) from a first storage tank (11) and an internal stream (24) of heat-transfer material from the combustion unit (5), into the gasification unit (3), - convert, in the gasification unit (3), said biomass (17) into an output syngas (4) and into a residual char generated after the volatilization of said biomass (17), in a residence time of the char in said gasification unit (3) that lasts from 1 to 30 minutes giving rise to char conversions of between 15-80% depending on the thermal load of the heat transfer particles (13), - feeding the lower sealing chamber (6) with a gas (23) that is steam, and circulating the stream of solids that also includes the heat transfer particles (13), from the gasification unit (3) to the combustion (5) through said lower sealing chamber (6), - maintain constant said stream of solids that passes through the lower supply chamber (6), - adjust the temperature of the combustion unit (5) depending on the thermal load of the heat transfer particles (13) to meet the energy demand of the gasification unit (3), - combust the char in the combustion unit (5) with a minimum oxygen excess over the stoichiometric of 5%, - introduce steam (25) into the second sealing chamber (7) by circulating the internal current (24) from the combustion unit (5) to the gasification unit (3), thus transferring the energy from combustion to gasification . 12. - The method of claim 11, comprising a step comprising varying the flow rate of gas (23) fed to the lower sealing chamber (6) to compensate for pressure fluctuations. 13. - Installation (1) comprising the dual fluidized bed module (2) of any one of claims 1 to 9, the concentrating solar energy unit (10), and, furthermore: - a first storage tank (11) that receives a joint flow of solid heat-transfer particles (13) once they have been heated in the concentrating solar energy unit (10), - a second storage tank (12) that receives solid heat-transfer particles (13) at the outlet of the gasification unit (3) or at the outlet of the combustion unit (5), where the solar concentration unit (10) comprises a plurality of heliostats (20) that concentrate the radiation in a receiver of a solar tower (22) where it is They heat the solid heat-transfer particles from the second storage tank (12).