Abstract:
A reaction apparatus for producing vapor-grown carbon fibers (VGCF) and a continuous production system for producing VGCF are disclosed. The VGCF reaction apparatus is featured in installing a plurality of holes on the upper portion of inner tubes; and filling thermally conductive material in the areas between the inner tubes and the outer tube. The continuous production system includes the reaction apparatus, a product collection system and a carrier-gas collecting system, wherein carbon fibers produced by the reaction apparatus fall into the product collection system, and in the product collection system, a collection bin full-loaded with carbon fibers is pushed out and an empty bin is pushed into the collection chamber under PLC control as well as atmosphere replacement with inert gas, thereby continuously producing VGCF.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a reaction apparatus for producing vapor-grown carbon fibers (VGCF) and a production system for producing the same, and more particularly, to the VGCF reaction apparatus and continuous production system that can prevent carbon fibers from attaching to inner tube walls with high thermal conduction efficiency. 
     BACKGROUND OF THE INVENTION 
     VGCF has excellent material properties of a unique onion-ring micro-structure, a high aspect ratio, a high thermal-conductive coefficient, a low thermal-expansion coefficient, high strength, high elasticity and high corrosion resistance. In addition, carbon fibers made by the vapor-growing method can have the structure similar to the single-crystal graphite structure, thereby forming excellent multi-wall carbon tubes having excellent electrical conductivity, wherein the thermal conductivity thereof is better than that of the thermally-conductive material such as copper or aluminum. The success of VGCF study has added quite an important product to the carbon fiber industry in which OPCF (Organic Precursor Carbon Fibers) such as PAN, Pitch carbon fibers have been the major products for quite a long time. 
     The VGCF production process mainly uses low boiling hydrocarbon compounds as raw material (carbon source) having pyrolysis reaction in reductive carrier gas (H2) atmosphere, thus directly forming VGCF via the special catalysis of transition metals such as iron, nickel or cobalt in nano-particles thereof as nucleation, wherein the reaction temperature is between 800° C. and 1300° C. The VGCF fabrication process has the advantage that the fabrication skill is simple and does not need to perform the steps of spinning, pre-oxidation, carbonization, etc. required in the OPCF fabrication process, so that the VGCF fabrication process can form carbon fibers directly from cheap low-boiling hydrocarbon material via pyrolysis and catalysis. 
     Referring to  FIG. 1A  and  FIG. 1B ,  FIG. 1A  and  FIG. 1B  are schematic diagrams showing conventional VGCF reaction apparatuses respectively, wherein a conventional VGCF reaction apparatus is composed of tubular reactor and a heater  50 , and the tubular reactor can be formed solely from an outer tube  40  (such as shown in  FIG. 1A ) or from an inner tube  30  inserted into the outer tube  40  (such as shown in  FIG. 1B ). 
     Such as the tubular reactor shown in  FIG. 1A , raw material gas enters the outer tube  40  via an guide tube  10  mounted on one end of the outer tube  40 , and the heat generated by the heater  50  is passes through the outer tube  40  to the gas mixture of the raw material gas and carrier gas for increasing the temperature of the gas mixture, thereby pyrolyzing the raw material gas to form carbon fibers. Thereafter, the carbon fibers generated fall into a collection bin  60 . However, in the aforementioned process, the temperature near the tube wall is quite higher than the central area of the reaction tube and the situation becomes worse when the reactor diameters increase, so that aforementioned process is merely suitable for use in the tubular reactors with small diameters and is not suitable for mass production. Meanwhile, there are carbon fibers frequently attached to the tube wall, thus lowering productivity, and the reaction often needs stopping for cleaning, thus disadvantaging continuous production. 
     Such as the tubular reactor shown in  FIG. 1B , raw material gas enters the outer tube  40  via a guide tube  10 , and carrier gas (H 2 ) enters the outer tube  40  via a gas inlet  20  mounted on one end of the outer tube  40 , and inert gas enters from the bottom of the outer tube  40  as guide gas. After mixing, the raw material gas, and the carrier gas enter the inner tube  30 , wherein the heat generated by the heater  50  is passed through the outer tube  40  to the inner tube  30  and then to the gas mixture of the raw material gas, the carrier gas and inert gas for increasing the temperature of the gas mixture, thereby enabling the raw material gas to be pyrolyzed to form carbon fibers. Thereafter, the carbon fibers generated fall into a collection bin  60 . Generally, the inert gas passing between the inner tube  30  and the outer tube  40  is used as guide gas for reinforcing the heat transfer efficiency between the inner tube  30  and the outer tube  40 . However, since the thermal conductive coefficient of the guide gas is not large, the heating efficiency of the heater  50  on the gas mixture is not good, and the energy provided by the heater  50  thus cannot be well utilized, and the VGCF formed from carbon source under inert atmosphere is inferior to that formed under pure reductive atmosphere (H 2 ). Further, there are carbon fibers frequently attached on the tube wall of the inner tube  30  in the conventional tubular reactor, thus lowering productivity and disadvantaging continuous production due to frequent tube wall cleaning. 
     On the other hand, a conventional continuous production system for producing VGCF is mainly composed of a gas-supplying apparatus, a tubular reactor and a collection bin. After the carbon fibers generated fall into a collection bin and fill up the collection bin, the reaction has to be first stopped, and then a gas-swapping step is performed for replacing the carrier gas (H 2 ) in the collection bin with inert gas (such as nitrogen) so as to prevent carrier gas from resulting in explosion. Thereafter, the collection bin is moved out and replaced with another empty collection bin. Then, after the air in the empty collection bin is expelled and replaced with inert gas, the carrier gas is introduced into the reaction system for starting another reaction cycle. Therefore, the conventional continuous production system has the following disadvantages. Besides replacing the collection bin and the atmosphere therein, a lot of manpower have to be consumed and further the reaction system has to be stopped for quite a period of time, thus resulting production interruption and lower productivity; and there is no carrier-gas recycling system, not only resulting in pollution but also increasing production cost. 
     Hence, there is a need to develop a reaction system for producing VGCF in a continuous manner, thereby effectively utilizing the energy provided by the heater; preventing carbon fibers from attaching to the tube wall of the inner tube; continuously collecting products (VGCF) without stopping the reaction apparatus; and effectively recycling carrier gas, thus increasing productivity; easily cleaning the reaction tubes; preventing pollution and workforce waste; and lowering production cost. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to provide a reaction system for producing VGCF with effective utilization of the energy provided by a heater, thereby lowering production cost. 
     Another aspect of the present invention is to provide a reaction apparatus for producing VGCF by directing carrier gas to the center of reaction tube so as to increase the efficiency for mixing carrier gas and raw material gas and to prevent carbon fibers from forming on the tube wall, thereby increasing productivity and saving time of cleaning the reaction tubes. 
     Another aspect of the present invention is to provide a reaction apparatus for producing VGCF for effectively utilizing the overall heating capacity and forming an excellent effect in which gas is cooled on both ends of the reaction tube and heated with reaction at the central portion of the reaction tube. 
     Another aspect of the present invention is to provide a reaction apparatus for producing VGCF and a continuous production system for producing the same, thereby continuously collecting products (VGCF) without stopping the reaction apparatus for increasing productivity. 
     Another aspect of the present invention is to provide a reaction apparatus for producing VGCF and a continuous production system for producing the same, thereby effectively recycling the carrier gas for preventing pollution and lowering production cost. 
     According to the aforementioned aspects, a reactor for producing VGCF is provided. According to an embodiment of the present invention, the reactor comprises a vertical tubular reactor and a heater, wherein the vertical tubular reactor is composed of an outer tube and an inner tube. The inner tube is located inside the outer tube, and the top end of the inner tube has a guide tube mounted thereon for introducing reaction gas, and a thermal-conductive material is filled between the inner tube and the outer tube. The inner tube is divided into upper and lower inner tubes via a division plate, wherein the upper inner tube is a first inner tube, and the lower inner tuber is a second inner tube. One end of the first inner tube is aligned with one end of the outer tube, and there are a plurality of first holes distributed on the tube wall of the first inner tube, and there is an gas inlet between the first inner tube and the outer tube for introducing a second carrier gas to cool down the upper end of the outer tube and the first inner tube. The second inner tube is located below the first inner tube in the outer tube, wherein there are a plurality of second holes distributed on the tube wall of an upper portion of the second inner tube, and the thermal-conductive material is filled in a filler portion extending from the area between the first inner tube and the outer tube to the area between the second inner tube and the outer tube, and the length of the filler portion corresponding to the second inner tube is greater than the length of the second holes corresponding to the second inner tube. The outer tube has a second gas inlet located on below the thermal-conductive material for introducing first carrier gas. Further, both ends of the heater are respectively spaced from both ends of the outer tube at a first predetermined distance and a second predetermined distance, and the heater is corresponding to a portion of the first inner tube and a portion of the second inner tube, thereby heating a portion of the outer tube. 
     Moreover, according to the aforementioned aspects, a continuous production system for producing VGCF is provided. The continuous production system comprises the aforementioned reactor, a product-collecting system and carrier-gas collecting system, wherein reaction gas formed by mixing raw material gas (including carbon source and catalyst) with carrier gas is introduced into the reactor for producing the VGCF via pyrolysis with residual reaction gas remaining. The product-collecting system is connected to the lower end of the second inner tube in the aforementioned reactor for continuously collecting the VGCF by using a dry-collection method. The product-collecting system comprises: a circulating rooms set and a collection-bins set. The circulating rooms set is divided into an air atmosphere area and an inert atmosphere area, and the collection-bins set has a plurality of bins, wherein the bins move circulatively in the air atmosphere area and the inert atmosphere area. Moreover, the carrier-gas collecting system is connected to the product-collecting system for collecting and purifying recyclable carrier gas from the effluent gas expelled from the product-collecting system by using a water-washing vessel. The carrier-gas collecting system comprises a water-washing vessel, wherein a water flow is introduced into the water-washing vessel for washing the effluent gas so as to obtain a residual product and the recyclable carrier gas. 
     Further, the product-collecting system further comprises a circulating rooms set, a first gate, a second gate, a third gate, a fourth gate, a collection-bins set, a first push-equipment set, a second push-equipment set and a gas-swapping apparatus. 
     Further, the circulating rooms set is divided into a first air-atmosphere sub-area, a second air-atmosphere sub-area and a third air-atmosphere sub-area; and a first inert-atmosphere sub-area, a second inert-atmosphere sub-area and a third inert-atmosphere sub-area each having an inert atmosphere, wherein both opposite sides of the second air-atmosphere sub-area are open respectively to the first air-atmosphere sub-area and the third air-atmosphere sub-area, and the second inert-atmosphere sub-area is isolated from the second air-atmosphere sub-area, and the second inert-atmosphere sub-area is open to the reaction apparatus for collecting the VGCF. 
     Further, the first gate is mounted between one side of the second inert-atmosphere sub-area and the first inert-atmosphere sub-area; and the second gate is mounted between the third inert-atmosphere sub-area and the other side of the second inert-atmosphere sub-area opposite to the first inert-atmosphere sub-area, wherein the first gate and the second gate are opened simultaneously. The third gate is mounted between the first inert-atmosphere sub-area and the first air-atmosphere sub-area; and the fourth gate is mounted between the third inert-atmosphere sub-area and the third air-atmosphere sub-area, wherein the third gate and the fourth gate are opened simultaneously. 
     Further, the collection-bins set moves circulatively in the circulating rooms set, wherein the collection-bins set is composed of a first bin, a second bin adjacent to the first bin, a third bin and a fourth bin adjacent to the third bin, wherein the first bin is spaced from the third bin with a first division, and the second bin is spaced from the fourth bin with a second division. When the first inert-atmosphere sub-area is referred as the first division, the third air-atmosphere sub-area is the second division. When the first air-atmosphere sub-area is referred as the first division, the third inert-atmosphere sub-area is the said second division. 
     Further, the first push-equipment set is respectively mounted on the first inert-atmosphere sub-area and the third air-atmosphere sub-area for pushing the bins of the collection-bins set to the second inert-atmosphere sub-area and the second air-atmosphere sub-area. The second push-equipment set is respectively mounted on the first air-atmosphere sub-area and the third inert-atmosphere sub-area for pushing the bins of the collection-bins set to the first inert-atmosphere sub-area and the third air-atmosphere sub-area. The gas-swapping apparatus is used for replacing the atmosphere in the inert atmosphere area with the inert atmosphere. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1A  and  FIG. 1B  are schematic diagrams showing conventional VGCF reaction apparatuses respectively; 
         FIG. 2  is a schematic diagram showing a VGCF reaction apparatus according to a preferred embodiment of the present invention; 
         FIG. 3  is a schematic top view showing a vertical tubular reactor according to the preferred embodiment of the present invention; 
         FIG. 4  is a schematic diagram showing various types of thermal-conductive material according to the present invention; 
         FIG. 5  is a SEM(JEOL JSM6360) diagram of the product manufactured in accordance with the process example of the present invention; 
         FIG. 6  is a SEM(JEOL JSM6360) diagram of the product manufactured in accordance with the conventional comparison example; 
         FIG. 7  is a schematic diagram showing a VGCF production system according to the preferred embodiment of the present invention; and 
         FIG. 8A  to  FIG. 8C  are schematic diagrams showing the steps for collecting VGCF according to the preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is featured in installing a plurality of holes on a portion of the tube wall of an inner tube in a vertical tubular reactor and filling a thermal-conductive material between the inner tube and an outer tube, thereby increasing the efficiency for mixing carrier gas and raw material gas, preventing carbon fibers from forming on the tube wall of the inner tube, and increasing heat conduction efficiency. 
     Referring to  FIG. 2  and  FIG. 3 ,  FIG. 2  is a schematic diagram showing a VGCF reaction apparatus according to a preferred embodiment of the present invention; and  FIG. 3  is a schematic top view showing a vertical tubular reactor according to the preferred embodiment of the present invention. According to the present invention, the vertical tubular reactor (not labeled) is the major part of the reaction apparatus  100  for producing VGCF, and is composed of an outer tube  110  and an inner tube  120 . The inner tube  120  is located inside the outer tube  110 , and is divided by a division plate  122  into upper and lower inner tubes  120   a  and  120   b , wherein the top end of the inner tube  120   a  is aligned with the top end of the outer tube  110 , and has a guide tube  170  mounted thereon for introducing reaction gas, and the reaction gas includes the raw material gas such as hydrocarbons (for example, aromatic/aliphatic hydrocarbons), the catalyst such as ferrocene (Fe(C 5 H 5 ) 2 ) and the carrier gas such as hydrogen, wherein the aliphatic hydrocarbons include methane, ethylene, styrene, acetylene, propane, liquefied petroleum gas, butane, butene and butadiene, etc., and the aromatic hydrocarbons include benzene, toluene and xylene, etc. 
     The top end between the inner tube  120   a  and the outer tube  110  has a gas inlet (not labeled) used for introducing carrier gas (such as hydrogen) via a pipeline  320  for cooling down the top end of the outer tube  110  and the inner tube  120   a , thereby preventing sealing material therein from being damaged. Further, the inner tube  120   b  is located inside the outer tube  110  and below the inner tube  120   a , and is spaced from the inner tube  120   a  at a predetermined distance (i.e. the division plate  122 ). Besides, the heater  150  is installed externally to the outer tube  110 , and both ends of the heater  150  are spaced from both ends of the outer tube  110  respectively at a distance  124  and a distance  126 , wherein the heater is only corresponding to a portion of the inner tube  120   a  and a portion of the inner tube  120   b , i.e. the heater  150  merely heats a portion of the outer tube  110 . The power of the heater  150  can be such as about 10-50 kW. 
     One of the features of the present invention is to fill the thermal-conductive material  140  between the inner tube  120   a  and the outer tube  110 ; and between the upper portion of the inner tube  120   b  and the outer tube  110 , and a gas inlet (not labeled) is installed on the outer tuber  110  below the thermal-conductive material  140  for introducing carrier gas (such as hydrogen). The thermal conductive material  140  can be such as ceramic, metal, quartz glass or the mixtures thereof. Another feature of the present invention is to install a plurality of holes  130   a  on the tube wall of the lower portion of the inner tube  120   a , and to install a plurality of holes  130   b  on the tube wall of the upper portion of the inner tube  120   b . The length of the filler portion of the thermal-conductive material  140  filled in the inner tube  120   b  is greater than the length of the holes  130   b  corresponding to the inner tube  120   b.    
     After the carrier gas enters the area between the inner tube  120   b  and the outer tube  110  via the pipeline  330 , the carrier gas moves upwards into the inner tube  120   b  through the holes  130   b . At this time, since the heat-absorption and heat-transfer rate of the thermal-conductive material  140  are far greater than those of the conventional guide gas, the heat provided by the heater  150  can be effectively utilized. On the other hand, the cold carrier gas from a pipeline  320  enters the inner tube  120   b  through the holes  130   a , wherein the area as shown by the distance  124  is not heated by the heater  150 . After reaction gas is formed by mixing the carrier gas from the holes  130   a , the raw material gas from the guide tube  170  and the hot carrier gas from the holes  130   b , the reaction gas moves downwards to a reaction zone to form carbon fibers by pyrolysis. At this time, the downward reaction gas and the upward hot carrier gas form a counter-flow heat exchange, thereby further effectively utilizing overall heating capacity to heat the carrier gas, thus greatly increasing the temperature of the carrier gas. Thereafter, the carbon fibers generated and the effluent gas move downwards through the cooling zone as shown by the distance  126  (which is not heated by the heater  150 ), so as to be cooled down properly. Then, the carbon fibers and the effluent gas fall into a bin  414  of a product-collecting system  400 , wherein the bin  414  is under inert atmosphere. Since the carrier gas is gradually heated from room temperature between the outer tube  10  and the inner tube  120   a / 120   b , and the reaction gas moves from top to bottom in the inner tube  120   a / 120   b  for exchanging heat with the carrier gas, and additionally the aforementioned cooling zone is employed, the temperature of the carbon fibers and effluent gas in the bin  414  of the product-collecting system  400  is effectively lowered. 
     To sum up, the present invention provides an excellent heat transfer effect in which reaction gas is cooled on both ends of the vertical tubular reactor and heated with reaction at the central portion thereof. It is worthy to be noted that the holes  130   a  and  130   b  can direct the carrier gas to the center of the inner tube of the reaction apparatus  100 , thereby increasing the effect for mixing carrier gas, raw material gas (hydrocarbons, catalyst and carrier gas), and meanwhile, the carrier gas injecting through the holes  130   a  and  130   b  can effectively avoiding carbon fibers growing on the tube wall of the inner tube. 
     The product-collecting system  400  is connected to a carrier-gas recycling system  500  via a pipeline  420  for recycling the carrier gas in the effluent gas. The carrier gas recycled then enters a pipeline  302  via a pipeline  510 . After mixing with the carrier gas provided from a carrier gas source  300 , the carrier gas is divided into three portions respectively entering a mixer  210  and the vertical tubular reactor via pipelines  310 ,  320  and  330 . The carrier gas entering the mixer  210  is mixed with the mixture gas provided by a raw material/catalyst gas source  200  so as to form reaction gas, wherein the reaction gas can be pre-heated by a pre-heater  160  before entering the inner tuber  120   a.    
     Further, the inner and outer tubes of the vertical tubular reactor can be circular tubes as shown in  FIG. 3 , and the material thereof can be such as aluminum oxide, silicon carbide, quartz, mullite or silicon nitride. However, the inner and outer tubes of the vertical tubular reactor also can be in the other shapes such as square tubes, and the material thereof also can be other material. Therefore, the present invention is not limited thereto. 
     Further, referring to  FIG. 4 ,  FIG. 4  is a schematic diagram showing various types of thermal-conductive material according to the present invention. 
     Hereinafter, a process example of the present invention and a conventional comparison example are used for explanation. 
     Process Example of the Present Invention 
     In the VGCF reaction apparatus  100  as shown in  FIG. 2 , VGCF is fabricated under the following conditions. 
     At first, raw material gas is delivered from the raw material/catalyst gas source  200  to the mixer  210  and is uniformly mixed with a portion of carrier gas, the reaction gas composed of the raw material gas and the carrier gas is delivered to the pre-heater  160  for pre-heating to 300° C. Thereafter, the reaction gas pre-heated is introduced into the reaction tube via the guide tube  170  for reaction, and meanwhile, the other portions of the carrier gas are delivered respectively to the area between the inner tubes  120   a / 120   b  and the outer tube  110 ; to the thermal-conductive material  140  between the inner tube and the outer tube  110  via the pipelines  320  and  330 , while the heater  150  is heating the outer tube  110  and the thermal-conductive material  140 . After being heated by the thermal-conductive material  140 , the carrier gas injects into the inner tubes  120   a  and  120   b  through the holes  130   a  and  130   b . The VGCF product generated is collected by the product-collecting system  400 , and the effluent gas is recycled by the carrier-gas recycling system  500 . 
     The specification and operation conditions of the reaction apparatus  100  and the results thereof are listed as follows: 
     (1) inner tube  120 : a quartz tube of 20 cm inner diameter; 24 cm outer diameter; and 200 cm long; 
     (2) outer tube  110 : a quartz tube of 30 cm inner diameter; 34 cm outer diameter; and 200 cm long; 
     (3) holes  130   a : location: spaced from the top end of the reaction tube at the distance of 35 cm; extending downwards for 15 cm; hole size: 2 mm diameter; hole distance: 1 cm; 
     (4) holes  130   b : location: spaced from the top end of the reaction tube at the distance of 51 cm; extending downwards for 30 cm; hole size: 2 mm diameter; hole distance: 1 cm; 
     (5) division plate  122 : a quartz ring of 20 cm inner diameter; 30 cm outer diameter; and 1 cm thick; location: spaced from the top end of the reaction tube at the distance of 50-51 cm; 
     (6) thermal-conductive material  140 : quartz material; filler type-a as shown in  FIG. 4  (0.8 cm inner diameter; 1.0 cm outer diameter; and 1.2 cm long); 
     (7) heater  150 : 1200° C. control temperature; 
     (8) Raw material gas supply: reaction material composition: 96 wt % xylene and 4 wt % ferrocene; reaction material flow rate: 60 ml/min (liquid phase at 25° C., 1 ATM; entering the reaction system after vaporization); 
     (9) carrier gas: hydrogen; flow rates: 20 L/min (via the guide tube  170 ), 30 L/min (via the holes  130   a ); and 100 L/min (via the holes  130   b ); reaction time: two hours; 
     (10) products: 2.52 Kg (45% yield; no carbon fibers attached to the tube wall); wherein the average diameter of the carbon fibers is 200 nm. 
     Referring to  FIG. 5 ,  FIG. 5  is a SEM(JEOL JSM6360) diagram of the product manufactured in accordance with the process example of the present invention. It can be known from  FIG. 5  that the purity of the products generated in the process example of the present invention is quite high. 
     Conventional Comparison Example 
     In the reaction apparatus as shown in  FIG. 1A , raw material gas and a portion of carrier gas are introduced into the reaction tube via the guide tube  10 , and meanwhile, the other portions of the carrier gas are introduced to the reaction tube via the gas inlet  20 , and the heater  50  heats the tube externally, and the product generated is collected by the collection bin  60 . 
     The specification and operation conditions of the conventional comparison example and the results thereof are listed as follows: 
     (1) reaction tube  40 : a quartz tube of 20 cm inner diameter; 24 cm outer diameter; and 200 cm long; 
     (2) heater  50 : 1200° C. control temperature; 
     (3) Raw material gas supply: reaction material composition: 96 wt % xylene and wt % ferrocene; reaction material flow rate: 60 ml/min (liquid phase at 25° C., 1 ATM; entering the reaction system after vaporization); 
     (4) carrier gas: hydrogen; flow rates: 20 L/min (via the guide tube  10 ) and 130 L/min (via the gas inlet  20 ) 
     (5) reaction time: two hours; 
     (6) products: 0.84 Kg (about 15% yield; a lot of carbon fibers attached to the tube wall); wherein the average diameter of the carbon fibers is 300 nm. 
     Referring to  FIG. 6 ,  FIG. 6  is a SEM(JEOL JSM6360) diagram the products manufactured in accordance with the conventional comparison example. It can be known from  FIG. 6  that there are quite a lot of non-fiber impurities existing in the products generated in the conventional comparison example. 
     Moreover, other important features of the present invention reside in the product-collecting system  400  and the carrier-gas recycling system  500 . Referring to  FIG. 7 ,  FIG. 7  is a schematic diagram showing a VGCF production system according to the preferred embodiment of the present invention. The carrier-gas collecting system  500  is connected to the product-collecting system  400  via the pipeline  420  for collecting and purifying carrier gas from the effluent gas expelled from the product-collecting system  400  by water-washing. In the carrier-gas collecting system  500 , a water-washing vessel  510  is used to provide a water flow for washing the effluent gas therein via a spray head  530  and a distribution plate  520 , so as to separate a residual product from carrier gas in the effluent gas. Then, the residual product enters a filter  570  connected to the bottom of the water-washing vessel  510  so as to separate residual solids from water. Thereafter, the water filtered out returns to a water-storage vessel  580 . If the water level in the water-storage vessel  580  is too low, water source  560  supplies water to bring back the water level. On the other hand, a fan  540  is installed on the top of the water-washing vessel  510  for withdrawing the effluent carrier gas formed after water washing. The fan  540  is connected to a switching device  550  used for determining the ultimate treatment of the effluent carrier gas: either recycling the recyclable carrier gas back to the reaction apparatus  100 , or burning the effluent carrier gas with a combustion device  552  connected to the fan  540 . 
     As to another feature of the present invention with respect to continuously collecting the products of carbon fibers by a dry-collection method, please refer to  FIG. 8A  to  FIG. 8C , wherein  FIG. 8A  to  FIG. 8C  are schematic diagrams showing the steps for collecting VGCF according to the preferred embodiment of the present invention. The product-collecting system  400  is to move a collection-bins set circulatively in a circulating rooms set, wherein the circulating rooms set is divided into an air atmosphere area and an inert atmosphere area. At first, the air atmosphere area is divided into an air-atmosphere sub-area  422 , an air-atmosphere sub-area  424  and an air-atmosphere sub-area  426 ; and the inert atmosphere area is divided into an inert-atmosphere sub-area  432 , an inert-atmosphere sub-area  434  and an inert-atmosphere sub-area  436 . Both opposite sides of the air-atmosphere sub-area  424  are open respectively to the air-atmosphere sub-area  422  and the air-atmosphere sub-area  426 , and the inert-atmosphere sub-area  434  is isolated from the air-atmosphere sub-area  424 , and the inert-atmosphere sub-area  434  is open to the reaction apparatus  100  (shown in  FIG. 7 ) for collecting the VGCF generated from the reaction apparatus  100 . The inert-atmosphere sub-area  434  is also open to the carrier-gas collecting system  500  for recycling the carrier gas in the effluent gas. 
     Such as shown in  FIG. 8A , the collection-bins set is composed of a bin  412 , a bin  414 , a bin  416  and a bin  418 , wherein the bin  412  is adjacent to the bin  414 , and the bin  416  is adjacent to the bin  418 , and the bin  412  is spaced from the bin  416  with the air-atmosphere sub-area  422 , and the bin  414  is spaced from the bin  418  with the inert-atmosphere sub-area  436 . On the other hand, the positional relationship among those four bins also can be such as shown in  FIG. 8B , wherein the bin  412  is spaced from the bin  416  with the inert-atmosphere sub-area  432 , and the bin  414  is spaced from the bin  418  with the air-atmosphere sub-area  426 . 
     Further, a gate  446   b  is mounted between one side of the inert-atmosphere sub-area  434  and the inert-atmosphere sub-area  432 , and a gate  446   a  is mounted between the inert-atmosphere sub-area  436  and the other side of the inert-atmosphere sub-area  434  opposite to the gate  446   b , wherein the gate  446   a  and the gate  446   b  can be opened simultaneously. A gate  444   b  is mounted between the inert-atmosphere sub-area  432  and the air-atmosphere sub-area  422 , and a gate  444   a  is mounted between the inert-atmosphere sub-area  436  and the air-atmosphere sub-area  426 , wherein the gate  444   a  and the gate  444   b  can be opened simultaneously. 
     Further, pushers  442   a  and  442   b  (one push-equipment set) are respectively mounted on the inert-atmosphere sub-area  432  and the air-atmosphere sub-area  426 , and pushers  440   a  and  440   b  (the other push-equipment set) are respectively mounted on the inert-atmosphere sub-area  436  and the air-atmosphere sub-area  422 . The pushing directions of the pushers  442   a  and the  442   b  are opposite to each other, and so are the pushing directions of the pushers  440   a  and the  440   b . All four pushers  442   a ,  442   b ,  440   a  and  440   b  form a cross shape, and can adopt such as hydraulic tanks to move the bins. 
     Further, a gas-swapping apparatus  490  (shown in  FIG. 7 ) is used for replacing the atmosphere in the inert atmosphere area with the inert atmosphere such as nitrogen atmosphere, wherein the gas-swapping apparatus  490  is composed of a vacuuming device and an inert-gas input device (not shown). 
     Hereinafter, the steps for operating the product-collecting system  400  are explained with reference to  FIG. 8A  to  FIG. 8C . 
     Referring to  FIG. 8A , when the bin  414  located at the inert-atmosphere sub-areas  434  is loaded with VGCF (at this point, the gates  446   a  and  446   b  are closed), since the bin  414  has been filled with the carrier gas such as hydrogen susceptible to explosion, the inert-atmosphere sub-areas  432  and  436  have to be vacuumed by using the vacuuming device so as to expel the air therein before the gates  446   a  and  446   b  are opened. Then, the inert-gas input device is used to fill the inert gas in the inert-atmosphere sub-areas  432  and  436 . 
     Thereafter, the gates  446   a  and  446   b  are opened, and then the pusher  442   b  is used to push and move the bin  412  from the inert-atmosphere sub-area  432  to the inert-atmosphere sub-area  434 , thereby causing the bin  412  to push the bin  414  from the inert-atmosphere sub-area  434  to the inert-atmosphere sub-area  436 ; and meanwhile, the pusher  442   a  is used to push and move the bin  418  from the air-atmosphere sub-area  426  to the air-atmosphere sub-area  424 , thereby causing the bin  418  to push the bin  416  from the air-atmosphere sub-area  424  to the air-atmosphere sub-area  422 , wherein the positional relationship of the four bins is such as shown in  FIG. 8B . 
     Please continuously referring to  FIG. 8B . Thereafter, the gates  446   a  and  446   b  are closed, and then the vacuuming device is activated to vacuum the inert-atmosphere sub-areas  432  and  436  so as to expel the atmosphere therein, and then the inert-gas input device is used to fill the inert gas in the inert-atmosphere sub-areas  432  and  436 . Thereafter, the gates  444   a  and  444   b  are opened, and then the pusher  440   b  is used to push and move the bin  416  from the air-atmosphere sub-area  422  to the inert-atmosphere sub-area  432 ; and meanwhile the pusher  440   a  is used to push and move the bin  414  from the inert-atmosphere sub-area  436  to the air-atmosphere sub-area  426 , wherein the positional relationship of the four bins is such as shown in  FIG. 8C . Consequently, the bin  414  loaded with the VGCF is moved out and the empty bin  412  is moved into the collection room (i.e. the inert-atmosphere sub-area  434 ), thereby keeping the collection room on the status ready for collecting the products. 
     After the bin  412  is loaded with the VGCF, the aforementioned steps can be repeated for moving the loaded bin  412  out of the collection room and moving another empty bin  416  into the collection room, thereby achieving the purpose of continuously collecting the VGCF (products). The product-collecting system of the present invention can be further operated with appropriate instrumentation and control facility for continuously collecting the VGCF (products), thereby not only promotion productivity but also greatly enhancing factory safety. 
     It is worthy to be noted that the shapes and allocation of the circulating rooms set are merely stated as examples for explanation, and the present invention is not limited thereto. 
     Hence, it can be known from the aforementioned embodiments that the present invention has the advantages of effectively utilizing the energy provided by the heater; preventing carbon fibers from attaching to the tube wall of the inner tube; continuously collecting products (VGCF) without stopping the reaction apparatus; and effectively recycling carrier gas, thus increasing productivity; easily cleaning the reaction tubes; preventing pollution and workforce waste; and lowering production cost. 
     As is understood by a person skilled in the art, the foregoing preferred embodiments are illustrations rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.