KR20230030318A - Carbon nanotube bead for directly-irradiated particle receiver and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a carbon nanotube bead (CNT bead) that can be used as a heat transfer medium (heat absorber) in a solar fluidized bed heat absorbing device and a manufacturing method thereof. The carbon nanotube bead particles produced by the manufacturing method of the present invention maintains characteristics of carbon nanotube raw material particles with excellent heat transfer characteristics and characteristics of a Geldart A area that improves fluidity in a fluidized bed, thereby having good fluidity on a surface of the fluidized bed and showing homogeneous characteristics due to formation of small bubbles even when the particles are ejected above the fluidized bed. Accordingly, the carbon nanotube bead particles of the present invention can be usefully used as a heat transfer medium (heat absorber) in a solar fluidized bed particle heat absorbing device. The manufacturing method comprises the steps of: mixing cresol and carbon nanotubes into a paste; first agitating the paste with water and stabilizing the same; secondly agitating the same; obtaining a CNT aggregate; first drying the CNT aggregate; washing the CNT aggregate; and obtaining beads in a particulate form.

Description

Carbon nanotube bead heat absorber for particle-based solar heat absorber and manufacturing method thereof {Carbon nanotube bead for directly-irradiated particle receiver and manufacturing method thereof}

The present invention relates to a carbon nano tube bead (CNT bead) that can be used as a heat transfer medium (heat absorber) in a solar fluidized bed heat absorber and a method for manufacturing the same.

Solar energy is the most plentiful energy resource on Earth. It is a technology that converts sunlight into energy. PV (Solar photovoltaic energy) technology directly converts into electricity, CSP (Concentrating Solar Power) technology that produces power through condensing, and It is classified as SHC (Solar Thermal Collectors for heating and cooling) technology that applies direct or indirect heating and cooling using solar energy. To date, a lot of progress has been made, mainly with PV technology and CSP technology, to reduce carbon dioxide emissions in the power sector, which accounts for a very high percentage of fossil fuel consumption. However, in the recent primary and secondary industries (agriculture, chemistry, papermaking, etc.) as well as in the production of medium and low temperature energy of 250 - 300 degrees Celsius or less, such as preheating of combustion air in coal power generation and oil refining industry, new and renewable [0003] Attention is focused on the use of solar energy as an energy source.

The SHC technology for utilizing solar energy can be largely divided into a concentrating technology (lens area) that collects sunlight and a receiver technology that transmits the collected sunlight to an energy carrier. The heat absorber system can be divided into a direct irradiation method and an indirect irradiation method. Until now, the heat transfer method for power generation indirectly heats salt or water vapor in the tube by heating the tube (heat exchanger method), or sunlight A method of heating steam or gas in a transparent tube to be irradiated is mainly adopted. However, in the indirect heat exchanger method, heat transfer efficiency may decrease due to an increase in resistance in heat transfer. In the direct irradiation method for water vapor or gas, it is difficult to efficiently transmit the energy of the irradiated sunlight due to poor heat absorption.

Therefore, by using a fluidized particle receiver that directly irradiates sunlight to particles in a fluidized bed having smooth mixing of solid particles and thereby high heat transfer characteristics by using a fluidization phenomenon in which particles are suspended by gas, A method of transferring the heat absorbed by the gas has been proposed.

Sand, etc. is mainly used as an energy absorber (media particle) used inside the solar fluidized bed particle absorber, but there is a problem in that the heat transfer efficiency to gas is low due to low emissivity as a black body. . On the other hand, when the tower type is operated at a high gas flow rate, fine particles are generated due to collision and friction between the particles or between the particles and the wall of the heat absorber, and these fine particles are absorbed into the solar light transmission tube by the electrostatic phenomenon. There is a problem of sticking and significantly lowering the transmittance of sunlight. In addition, there are cases in which black silicon carbide (SiC) particles are applied to improve thermal emissivity, but the particle hardness is high, causing scratches on the solar tube tube to lower the solar transmission or damage the device. cause Accordingly, a new development of a solar energy absorber is required.

On the other hand, carbon nanotube particles have high thermal conductivity and high thermal emissivity as a black body, high electrical conductivity, so that particles do not stick to the heat absorber wall surface due to static electricity, and low hardness, so there is no damage to the wall surface by particles, and when fine powder is generated, van der Waals It was confirmed that the particles were re-aggregated into the parent particles by van der Waals force and physical entanglement. Accordingly, it is likely to be very suitable for solar heating systems. However, as shown in the Geldart diagram indicating the flow properties of the particles, carbon nanotube particles exist in an area other than the classification area of the existing particles and show a unique behavior. Specifically, when applied to a fluidized bed heat absorber, between particles Due to the entanglement phenomenon, when gas is injected, a channeling phenomenon in which gas flows only in a specific area appears, and the fluidity of the particles is very low, so it is not suitable for fluidized bed application. This means that it is necessary to adjust the physical properties of the particles to have new properties suitable for the fluidized bed. In this regard, large-particle research is being conducted for the application of carbon nanotube particles to electronic materials, and various methods have been proposed (Bryning et al., 2007; Kang and Moon, 2014). However, the size reported in recent literature research results is at the maximum level of 20 micrometers. In this case, the fluidity in the fluidized bed is not improved due to the cohesive force between the particles with the particles of the Geldart C region (see FIG. 1). In addition, Lee and Kim (2020) suggested molding into giant particles using carbon nanotubes, but the average particle diameter was too large, exceeding 1 mm, and there were limitations in the application of fluidized beds, such as the generation of giant bubbles or gas slugs.

Under this background, the present inventors have proposed a manufacturing method having optimal physical properties as a solar energy absorber by molding particles of at least 40 micrometers or more in consideration of particle fluidity suitable for a fluidized bed heat absorber through spheroidization of carbon nanotubes.

Korean Patent Publication No. 10-2019-0087908

Accordingly, an object of the present invention is to provide a method for manufacturing carbon nanotube beads that can be used as a heat transfer medium (heat absorber) in a solar fluidized bed particle absorber.

Another object of the present invention is to provide carbon nanotube beads that can be used as a heat transfer medium (heat absorber) in a solar fluidized bed particle absorber manufactured by the above method.

In order to achieve the object of the present invention as described above,

The present invention comprises the steps of a) preparing a paste by mixing cresol and carbon nanotubes; b) first stirring by adding water together with the paste to a stirrer and then stabilizing; c) secondarily stirring the mixed solution that has undergone the first stirring process; d) obtaining carbon nanotube (CNT) aggregates by filtering the mixed solution after the secondary stirring process while washing with water; e) firstly drying the carbon nanotube (CNT) aggregate; f) adding water to the carbon nanotube (CNT) aggregate that has undergone the primary drying process, stirring, and then washing; and g) obtaining beads in the form of fine particles through vacuum drying.

In one embodiment of the present invention, after step d), d') absorbing cresol using oil absorbent paper may be further included.

In one embodiment of the present invention, the primary stirring in step b) may be performed at 5000 to 7000 rpm for 5 to 20 minutes.

In one embodiment of the present invention, the secondary stirring in step c) may be performed at 5000 to 7000 rpm for 5 to 20 minutes.

In one embodiment of the present invention, the primary drying in step f) may be performed for 40 to 50 hours at a temperature of 180 to 190 ° C and a pressure of 0.2 atm.

In one embodiment of the present invention, the vacuum drying in step g) may be performed at a temperature of 160 to 170 ° C and a pressure of 0.9 to 1.0 atm.

In addition, the present invention provides a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber manufactured by the above method.

In one embodiment of the present invention, the carbon nanotube bead heat absorber may have a particle size of 200 to 600 μm.

In one embodiment of the present invention, the carbon nanotube bead heat absorber may have a particle density ranging from 0.2 to 0.3 g/cm3.

In one embodiment of the present invention, the carbon nanotube bead heat absorber may correspond to the Group A range of Geldart classification.

The carbon nanotube bead particles produced by the manufacturing method of the present invention maintain the properties of the raw material particles of the carbon nanotubes with excellent heat transfer properties and maintain the properties of the Geldart A region that improves the fluidity in the fluidized bed, so that they have good fluidity on the surface of the fluidized bed. In addition, due to the formation of small bubbles, homogeneous characteristics can be exhibited even when the particles are ejected to the top of the fluidized bed. Accordingly, the carbon nanotube bead particles of the present invention having the above characteristics can be usefully used as a heat transfer medium (heat absorber) in a solar fluidized bed particle heat absorber.

Figure 1 shows the Geldart classification table.
Figure 2 shows a method for producing the emulsified carbon nanotube beads of the present invention using an agitator ((a): emulsification and dispersion in water using an agitator, (b): washing process to remove residual organic solvent)
3 is a flowchart showing a method for manufacturing carbon nanotube beads according to Example 1 of the present invention.
4 is a flowchart showing a manufacturing method of carbon nanotube beads of Comparative Example 1 of the present invention ((a) manufacturing method flowchart, (b) pestle and mortar, (c) syringe for extrusion).
5 is an image showing the shape of carbon nanotube beads manufactured through the manufacturing method of Example 1 and Comparative Example 1 of the present invention ((a) Comparative Example 1, (b) Case 1 of Example 1, (c) ) case 2 of Example 1).
6 is an image showing the surface of carbon nanotube beads prepared through the manufacturing method of Example 1 and Comparative Example 1 of the present invention ((a) Comparative Example 1, (b) Case 1 of Example 1, (c) ) case 2 of Example 1).
7 shows the particle size distribution of carbon nanotube beads prepared through the manufacturing methods of Example 1 and Comparative Example 1 of the present invention.
Figure 8 shows the position in the Geldart diagram for carbon nanotube beads (CNT beads) prepared through the manufacturing method of Example 1 of the present invention.
9 shows the structure of a solar fluidized bed heater of direct irradiation type used in Example 2 of the present invention.
10 shows the gas absorption efficiency of the solar fluidized bed heater of the direct irradiation type used in Example 2 of the present invention ((a) effect of increasing flow rate, (b) comparison by particle at approximate flow rate).

The present invention provides a method for manufacturing a carbon nanotube bead heat absorber for a solar fluidized bed particle heat absorber.

The manufacturing method of the carbon nanotube bead heat absorber of the present invention includes: a) preparing a paste by mixing cresol and carbon nanotubes; b) first stirring by adding water together with the paste to a stirrer and then stabilizing; c) secondarily stirring the mixed solution that has undergone the first stirring process; d) obtaining carbon nanotube (CNT) aggregates by filtering the mixed solution after the secondary stirring process while washing with water; e) firstly drying the carbon nanotube (CNT) aggregate; f) adding water to the carbon nanotube (CNT) aggregate that has undergone the primary drying process, stirring, and then washing; and g) obtaining beads in particulate form through vacuum drying.

Step a) of the present invention is a step of preparing a paste by mixing cresol and carbon nanotubes, and in detail, by mixing 40 mg of carbon nanotubes (CNT) per 1 mL of m-cresol using a pestle and a mortar to make a paste. It can be manufactured in condition.

The term "carbon nanotube" referred to in this specification refers to a single-walled carbon nanotube (SWCNT) having a single-walled structure, a double-walled carbon nanotube having a double-walled structure, or a multi-walled carbon nanotube having a multi-walled structure. Various types of carbon nanotubes from multi-walled carbon nanotubes (MWCNTs), bundled carbon nanotubes, and combinations thereof may be used, but are not limited thereto. In addition, the carbon nanotubes may be prepared by a method known in the art, such as a chemical vapor deposition method, an arc discharge method, a plasma torch method, and an ion bombardment method, and may be subjected to a pretreatment step by a conventional method known in the art, There is no need to go through a pre-processing step. For example, the carbon nanotubes may be multi-walled carbon nanotubes (MWCNTs).

Step b) of the present invention is a step of putting the CNT paste and water into a stirrer, first stirring, and then stabilizing. This is a step of dispersing to form emulsion droplets (mixture of m-cresol and CNT) in micrometer units by mechanically stirring at 7000 rpm for 5 to 20 minutes. At this time, sufficient stabilization time may be given so that the hydrophilic groups of m-cresol in the emulsified droplets are activated so that the CNT agglomerates exhibit high sphericity.

Step c) of the present invention is a step of secondary agitation of the mixed solution, and in detail, mechanical agitation of the mixed solution that has undergone the primary agitation process at 5000 to 7000 rpm for 5 to 20 minutes.

Step d) of the present invention is a step of obtaining carbon nanotube (CNT) aggregates through the process of washing and filtering the mixed solution, and in detail, the mixed solution that has undergone the secondary stirring process through step c) is filtered with a filter paper This step is to obtain a bead-shaped carbon nanotube (CNT) aggregate by washing the obtained CNT aggregate including m-cresol with water to remove m-cresol.

Step e) of the present invention is a step of primary drying the carbon nanotube (CNT) aggregate, and in detail, the carbon nanotube (CNT) aggregate obtained through step d) is dried at a temperature of 180 to 190 ° C. and 0.2 atm. It is a step of primary drying for 40 to 50 hours under a pressure condition of .

The step f) of the present invention is a step of adding water to the carbon nanotube (CNT) aggregate that has undergone the primary drying process, stirring, and then washing. Specifically, the carbon nanotube (CNT) aggregate that has undergone the primary drying process through the After adding pure water to the tube (CNT) aggregate, mechanical stirring is performed at 6000 rpm for 10 minutes using an agitator, followed by washing with pure water.

Step g) of the present invention is a step of obtaining beads in the form of fine particles through vacuum drying, and the vacuum drying may be performed at a temperature of 160 to 170 ° C and a pressure of 0.9 to 1.0 atm.

In one embodiment of the present invention, after step d), d') absorbing cresol using oil absorbent paper may be further included. As the concentration of residual m-cresol per unit volume in the step e) increases in the carbon nanotube (CNT) agglomerate, the sphericity decreases and the particle diameter increases through additional bonding with external CNT powder or fine CNT particles. phenomenon could be confirmed. If step d') is added after step d) in the manufacturing method of the present invention, residual cresol on the outer surface of the CNT agglomerate can be sufficiently removed during the washing process, resulting in redispersion of CNT particles and aggregation of CNT and fine CNT particles. It is possible to maintain a low average particle size that is advantageous for excellent sphericity and fluidity.

In addition, the present invention provides a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber manufactured by the above method.

As the carbon nanotube bead heat absorber of the present invention has a particle size of 200 to 600 μm and a particle density in the range of 0.2 to 0.3 g/cm ³ , it may correspond to Group A of the Geldart classification.

In general, particles can be classified into four types according to the Geldart classification method based on particle size and density. Group A is a material with a small particle diameter and low density (<1.4 g/cm ³ ), which is easy to flow at a low flow rate. Group B is a sand-like material with a particle size of 40 to 500㎛ and a density of 1.4 to 4 g/cm ³ at the same time. It flows smoothly, but the size of the bubbles generated is larger than that of Geldart A. there is. Group C is a material that is difficult to flow due to strong cohesiveness due to a very small particle size or apparent density, such as wheat flour or starch. Group D is a material with a large or heavy particle size, such as coal, and requires a high gas velocity for fluidization, and in this case, gas slugging easily occurs, causing large pressure fluctuations in the system. Therefore, Group A or B type particles are suitable for application to the fluidized bed, and it is preferable to use Group A particles for optimum fluidization.

As a heat transfer medium (heat absorber) in the solar fluidized bed particle absorber, silicon carbide particles or sand, which have been used previously, correspond to the particles in the Geldart B area, so the particles do not sufficiently absorb sunlight at the top of the fluidized bed, and It is disadvantageous as a layer material of a fluidized bed particle heat absorber because it causes solar light loss by reflecting sunlight reflected from the outside. In addition, since the carbon nanotube (CNT) raw material corresponds to the particles in the Geldart C region and the particles are too fine and light, the fluidized layer is not formed, so even if the particles are absorbed on the surface of the fluidized bed, they are efficiently transferred into the fluidized bed. Otherwise, the solar heat absorption area of the transmission window is unfavorable for heat transfer into the heater by being absorbed at the surface. In addition, the non-uniformity of ejection into the top of the particle is evident.

On the other hand, the carbon nanotube bead heat absorber of the present invention maintains the properties of the CNT raw material particles with excellent heat transfer properties and the Geldart A area that improves the fluidity in the fluidized bed, so it has good fluidity on the surface of the fluidized bed, Due to the formation of small bubbles, even when the particles are ejected to the top of the fluidized bed, homogeneous properties can be exhibited.

Hereinafter, the present invention will be described in more detail through examples. These examples are intended to explain the present invention in more detail, and the scope of the present invention is not limited to these examples.

<Example>

experimental material

The particles used as the absorber in this experiment were silicon carbide (SiC) and MWCNT, and based on the particle size and density, the Geldart classification for classifying the fluidity of the particles in the fluidized bed was shown as shown in FIG. 8. Two types of silicon carbide (SiC) were used: fine SiC (F100, Showadenko, Tokyo, Japan) with a particle size of 0.052 mm and coarse SiC (F220, Showadenko, Tokyo, Japan) with a particle size of 0.123 mm. MWCNT particles include entangled carbon nanotubes (ENCNT, FloTube ^TM 9000, C-Nano) in which relatively short nanotubes are irregularly entangled with each other on the particle surface, and vertically aligned nanotubes (VACNT, FloTube) in which nanotubes are vertically grown on the particle surface. ^TM 7000, C-Nano) were used.

<Example 1>

CNT bead production according to the present invention

In this experiment, CNT beads were prepared using an agitator. The main manufacturing method used for manufacturing is shown in FIG. 2, and the specific manufacturing process is shown in FIG. VACNT (Vertical Aligned CNT) particles were used as the particles used to prepare the CNT beads. After initial pulverization of the CNT particles, a cresol solution (m-Cresol; Cas No. 108-39-4) was used for physical bonding between the CNTs.

Specifically, after preparing a paste by mixing m-Cresol and VACNT at 40 mg/mL using a mortar and pestle, cold water (8° C.) was poured into the CNT paste (mass ratio, paste: water = 1 :100). After first stirring the CNT paste solution for 10 minutes at 6000 rpm using a stirrer to disperse it to form micrometer-sized emulsified droplets (m-Cresol and CNT mixture), the hydrophilic properties of m-Cresol in the emulsified droplets It was activated and stabilized for 5 minutes so that the CNT agglomerates could have a high spherical shape, and then the CNT paste solution was agitated a second time at 6000 rpm for 10 minutes. Subsequently, as a first example (Case 1), in order to obtain beads from droplets, the mixed aqueous solution of droplets was filtered with filter paper, and water was used to remove m-Cresol from the obtained CNT aggregates containing m-Cresol. By washing, aggregates in the form of beads could be obtained. Thereafter, the agglomerates were subjected to a primary drying process (185° C., 0.2 atm, 48 hr), and after adding 200 mL of water, they were stirred for 10 minutes at 6000 rpm using a stirrer, and then washed with water. Finally, beads in the form of fine particles were obtained through vacuum drying (162.7 ° C., 0.92 atm). However, in the case of the first example (Case 1), as the concentration of residual m-cresol in the CNT agglomerate per unit volume increases in the first drying step, the sphericity decreases and additional contact with the external CNT powder or fine CNT particles occurs. It was confirmed that the particle diameter increased through bonding. To control this, the result of the second example (Case 2) was obtained by additionally introducing a cresol absorption step using an organic solvent absorbing paper (OAP) to lower the residual cresol concentration on the outer surface of the CNT agglomerate during the cleaning process. . This can sufficiently remove the aqueous solution and residual m-cresol in the particles in the drying step, thereby preventing redispersion of CNT particles and aggregation of CNT and fine CNT particles, thereby maintaining a low average particle size advantageous for excellent sphericity and fluidity. An organic solvent absorbent paper purchased from Pt Parisindo Pratama (Indonesia, Oil blotting paper) was used.

<Comparative Example 1>

Preparation of CNT beads using a syringe

In this comparison, CNT beads were prepared using a pitcher. A specific manufacturing process is shown in FIG. 4 .

Specifically, m-Cresol and VACNT were directly mixed at 30 mg/mL using a mortar and pestle to prepare a paste, and then water was poured into the CNT paste and mixed for 10 minutes (mass ratio, paste: water = 1.41:1.00). The initial shape of the CNT microbeads was formed by extruding the CNT paste into a water container through a nozzle having an inner diameter of 5 mm. The initial CNT beads were mechanically rolled and rounded in a water bath. A water container containing initial beads was placed on a plate of a shaker (SH30; FINEPCR, Gunpo-si, Korea) and mechanical rolling was performed at 100 rpm for 10 minutes. Then, the final CNT beads were prepared by drying in a vacuum oven at 162.7 ° C and 0.92 atm for 36 hours (Reference: Materials 2020, 13, 1289; doi: 10.3390/ma13061289, 'Preparation of MWCNT Microbeads for the Application of Bed Materials in a Fluidized Bed Heat Exchanger').

<Experimental Example 1>

Characteristics of CNT beads according to the present invention

In order to confirm the characteristics of the CNT beads of the present invention prepared through Example 1, the particle shape, particle size distribution, and position in the Geldart diagram were investigated.

SEM images of CNT beads were obtained using a Bruker Model Quanta-400 scanning electron microscope (Billerica, Middlesex, USA). The particle size of the CNT beads was obtained using a particle size analyzer (PSA: LA-950 V2, Horiba, Kyoto, Japan). The average particle size of the CNT beads was measured by a screening method using a sieve screen. The apparent density of the CNT bead particles was measured by porosity analysis (Autopore 9605, Micromeritics, USA).

As a result, as shown in FIGS. 5 to 7, it was confirmed that the CNT beads of the present invention prepared in Example 1 maintained low particle size and surface uniformity. The average particle size of the CNT beads of the present invention is 521 μm. In particular, the CNT beads prepared through the second example (Case 2) of the present invention showed excellent sphericity and a low particle size distribution in the range of 200-600 μm. On the other hand, in the case of the CNT beads prepared through Comparative Example 1, it was confirmed that the average particle diameter was too large to be 1 mm or more.

In addition, as shown in FIG. 8, the CNT beads of the present invention prepared in Example 1 showed a low particle diameter and high particle density compared to the MWCNT particle group, and were classified into the Geldart A group.

Through the above results, in the case of CNT as a raw material, it belonged to the Geldart C group (see the figure below) having an apparent diameter of 200 micrometers and a density of 0.25 g / cc due to physical entanglement, but Example 1 It was found that the CNT beads of the present invention prepared through this were improved to the Geldart A group.

<Experimental Example 2>

Application of solar particle absorber of CNT beads according to the present invention

In order to confirm that the CNT beads of the present invention prepared through Example 1 can be effectively used as a layer material (absorber) for a solar fluidized bed particle absorber, it is applied to a solar fluidized bed heater in the form of direct irradiation and applied to the fluidized bed absorber. The endothermic efficiency by gas was investigated. In this experiment, coarse SiC (silicon carbide particles), ENCNT (carbon nanotube particles), and CNT beads (carbon nanotube beads) of the present invention prepared in Example 1 were selected as absorbers. For reference, fine SiC, which has a small particle size and exhibits large particle carry-over, in which particles are discharged to the outside of the reactor, was excluded from the experiment.

The shape of the solar fluidized bed heater of the direct irradiation type used in the experiment was designed as shown in FIG. The experimental device was made of two Pyrex-glass (5T) columns to measure the temperature change and heat absorption efficiency of the gas. The fluidized bed apparatus consisted of a main column (50mm I.D. X 150mm high) (5) and a transmission window (9). The main column (5) was extended to a width of 0.08m (8) to minimize carryover for ejection of particles and deposition and scratches on the transmission window (9). The transmission window 9 was made of quartz glass (transmittance: 92%) and was installed at the top of the expansion tube 8 to guide sunlight to the surface of the inner particle layer material. This heater is operated in a state in which internal particles are suspended or fluidized. In order to suspend layer materials in the heater, the gas to be heated was injected through the compressor (1), which was blown by a mass flow meter (RK1150, Kojima instrument, Kyotanabe Kyoto, Japan) (2) for gas flow control. Injected into box (3). The gas was uniformly distributed to the particle layer in the heater (5) through the porous dispersion plate (4) located on the top of the windbox (3). At this time, the porous dispersion plate 4 is made of sintered metal of a staninless material. The particle layer is suspended at a gas flow rate higher than the minimum fluidization speed, which is a speed at which the gravity of the particles and the drag force due to the gas are equal by the injected gas, and at this time, the injected gas comes into contact with the particles heated by sunlight and is heated. The heated gas was injected through the heater outlet (10) into the process where the gas was used. A thermocouple (6) was installed in the reactor to measure the temperature of the heated gas, and a pressure gauge (7) was installed on the wall of the reactor to check the degree of fluidization of the particles.

In order to evaluate the thermal efficiency of the solar fluidized bed heater, the amount of heat absorbed by the gas per solar energy supplied from the outdoors was evaluated as follows.

- Thermal efficiency of receiver, η _receiver = Q _gas /Q _solar

- Q _gas = ρ _g U _g Ac _p,g (T _outlet -T _inlet )

where η _receiver is the thermal efficiency of the fluidized bed heater, Q _solar is the solar energy supplied per solar radiation by the installed collector, Q _gas is the solar thermal energy absorbed by the gas, ρ _g is the gas density, U _g is the gas flow rate, and A is is the cross-sectional area of , C _p,g is the gas heat capacity, T _outlet is the outlet temperature, and T _inlet is the gas inlet temperature.

As a result, as shown in FIG. 10, the thermal efficiency of the CNT beads of the present invention compared to the conventional representative silicon carbide particles (coarse SiC) at a gas velocity or higher at which the particles are fluidized increased up to 53% in the same section tested. This is the result of an increase of up to 53% compared to silicon carbide particles (based on gas velocity of 0.16 m/s). In addition, the CNT beads of the present invention showed 14% (based on gas velocity of 0.09 m/s) and 21% (based on gas velocity of 0.11 m/s) higher thermal efficiency than CNT particles (VACNT), which is a raw material. In particular, as shown in FIG. 10a, the raw material CNT particles could not operate at 0.13 m/s or more due to unstable fluidity, and thus the manufactured CNT beads exhibited high thermal efficiency and stable fluidity.

So far, the present invention has been looked at with respect to its preferred embodiments. Those skilled in the art to which the present invention pertains will be able to understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative rather than a limiting point of view. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the equivalent scope will be construed as being included in the present invention.

Claims (10)

a) preparing a paste by mixing cresol and carbon nanotubes;
b) first stirring by adding water together with the paste to a stirrer and then stabilizing;
c) secondarily stirring the mixed solution that has undergone the first stirring process;
d) obtaining carbon nanotube (CNT) aggregates by filtering the mixed solution after the secondary stirring process while washing with water;
e) firstly drying the carbon nanotube (CNT) aggregate;
f) adding water to the carbon nanotube (CNT) aggregate that has undergone the primary drying process, stirring, and then washing; and
g) obtaining beads in particulate form through vacuum drying;
Manufacturing method of carbon nanotube bead heat absorber for solar fluidized bed particle absorber. According to claim 1,
The method of manufacturing a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber, characterized in that it further comprises the step of absorbing cresol using d') oil absorbent paper after step d). According to claim 1,
In step b), the first stirring is performed at 5000 to 7000 rpm for 5 to 20 minutes, a method for producing a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber. According to claim 1,
In step c), the secondary stirring is performed at 5000 to 7000 rpm for 5 to 20 minutes, a method for producing a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber. According to claim 1,
In step f), the primary drying is performed for 40 to 50 hours at a temperature of 180 to 190 ° C and a pressure of 0.2 atm. Method for producing a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber. According to claim 1,
In step g), the vacuum drying is performed at a temperature of 160 to 170 ° C and a pressure of 0.9 to 1.0 atm. Method for producing a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber. A carbon nanotube bead heat absorber for a solar fluidized bed particle heat absorber manufactured by the method of any one of claims 1 to 6. According to claim 7,
The carbon nanotube bead heat absorber is a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber, characterized in that it has a particle size of 200 ~ 600μm. According to claim 7,
The carbon nanotube bead heat absorber is characterized in that it has a particle density in the range of 0.2 ~ 0.3g / cm ³ , carbon nanotube bead heat absorber for solar fluidized bed particle absorber. According to claim 7,
The carbon nanotube bead heat absorber is a carbon nanotube bead heat absorber for a solar fluidized bed particle absorber, characterized in that it corresponds to the Group A range of the Geldart classification.

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