Patent Publication Number: US-2021164653-A1

Title: Gas swirling state determination system and gasification melting furnace

Description:
TECHNICAL FIELD 
     The present invention relates to a gas swirling state determination system and a gasification melting furnace provided with the gas swirling state determination system. 
     This application claims priority based on Japanese Patent Application No. 2018-103485 filed in Japan on May 30, 2018, the disclosure of which is incorporated herein. 
     BACKGROUND ART 
     There are known devices that swirl gas to perform appropriate treatments. For example, a gasification melting furnace that treats waste such as municipal waste, incombustible waste, incineration residues, and sludge is known as a device that swirls pyrolysis gas for combustion and melting. Such gasification melting furnace systems includes a gasification furnace that gasifies waste by pyrolysis, and a swirling melting furnace provided downstream of the gasification furnace, and configured to combust pyrolysis gas generated by the gasification furnace at high temperatures to produce combustion gas, and melts ash contained in the gas into slag (melting treatment) (refer to Patent Document 1, for example). 
     CITATION LIST 
     Patent Document 
     Patent Document 1: JP 2009-58216 A 
     SUMMARY OF INVENTION 
     Technical Subject to be Solved 
     “A stable swirling state of gas” is empirically known as one of barometers for performing smooth melting treatment in the swirling melting furnace. The swirling state of gas is considered to be stable, for example, when combustion gas continues to swirl in the same direction at the approximately same speed, and the swirling speed of the gas is higher than a predetermined speed. 
     A stable swirling state of the combustion gas does not necessarily mean that the smooth melting treatment is performed. However, when the swirling state is not stable, the smooth melting treatment has not been performed and thus, measures for improvement need to be taken. Therefore, it is necessary to know the gas swirling state as one barometer and determine the quality of the state, i.e. whether the state is stable. 
     In the gasification melting furnace described in Patent Document 1, a luminance meter disposed on a top portion of a secondary combustion chamber measures the luminance of the secondary combustion chamber, and the amount of combustion air and the supply amount of waste are controlled based on the luminance. 
     However, the luminance meter generally only provides information about the total amount of luminance over the entire field of view at a given time point, and it is difficult to know the gas swirling state and determine the quality with such information. 
     Although a camera is installed in place of the luminance meter to capture a video, and can acquire the changes in the luminance distribution over time from this video, since the luminance distribution irregularly changes, it is difficult to objectively know the gas swirling state and determine the quality. 
     An object of the invention is to provide a gas swirling state determination system and a gasification melting furnace provided with the gas swirling state determination system that can determine the quality of the stability of the gas swirling state based on a video captured by an imaging device (a plurality of still images captured at different times) and display a determination result. 
     Solution to Subject 
     According to a first aspect of the present invention, a gas swirling state determination system is a gas swirling state determination system for determining quality of a swirling state of gas swirling around a central axis, the system comprising: an imaging device configured to capture the swirling gas from a direction along the central axis to acquire still images; an information processing device including a calculation unit configured to calculate luminance distribution information for each of the plurality of still images captured at different times by the imaging device to acquire a swirling speed of a centroid of the luminance or a luminance difference at a specific location of the still image as a first calculation result, a smoothing unit configured to smooth a change in the first calculation result over time to acquire a second calculation result, and a determination unit configured to compare the second calculation result with a threshold and determine the quality of the swirling state to acquire a determination result; and a display device configured to display a determination result. 
     According to such configuration, the quality of the swirling state of the gas is automatically determined by using the luminance distribution information of the plurality of still images captured at different times to acquire the first calculation result and smoothing the change in the first calculation result over time, and the determination result is displayed on the display device. Thus, the quality of the swirling state of the gas can be easily recognized. 
     In the above-described gas swirling state determination system, a luminance difference at a specific location may be a difference between a maximum value and a minimum value of the luminance on a circumference having a predetermined radius around the central axis of the still image. 
     In the above-described gas swirling state determination system, the swirling speed may be an angular speed around the central axis of a centroid of the luminance acquired from the plurality of still images. 
     In the above-described gas swirling state determination system, the threshold may have a first threshold and a second threshold, the second threshold being larger than the first threshold, the determination unit may be configured to: compare an absolute value of the second calculation result with the threshold value, determine that the swirling state is unfavorable when the absolute value is smaller than the first threshold; determine that the swirling state is favorable when the absolute value is equal to or larger than the second threshold; and determine that the swirling state is semi-unfavorable when the absolute value is equal to or larger than the first threshold and smaller than the second threshold. 
     According to a second aspect of the present invention, a gasification melting furnace includes: a swirling melting furnace; a secondary combustion chamber connected to an upper portion of the swirling melting furnace; and any of the above-mentioned gas swirling state determination systems, the connection site and a vicinity of the connection site constitute a throat portion having a constricted-shape, and the imaging device is disposed on a top portion of the secondary combustion chamber and is oriented to capture the throat portion. 
     According to such configuration, since the quality of the swirling state of gas in the gasification melting furnace is automatically determined, and the determination result is displayed on the display device, the operator of the gasification melting furnace can easily recognize the quality of the gas swirling state. 
     Advantageous Effects of Invention 
     According to the present invention, a gas swirling state determination system configured to determine the quality of the gas swirling state stability based on images captured by the imaging device and display a determination result, and a gasification melting furnace provided with the gas swirling state determination system are provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration view of a gasification melting furnace provided with a gas swirling state determination system of the present invention. 
         FIG. 2  is a sectional view illustrating the shape of a vertical cyclone melting furnace  15  taken along a line II-II in  FIG. 1 . 
         FIG. 3  is an image (still image) captured by an imaging device  39  focusing on a cross section (throat portion) taken along a line in  FIG. 1 . 
         FIG. 4  is a graph in which the luminance distribution of a still image on a circumferential reference line in  FIG. 3  is linearly expanded. 
         FIG. 5  is a graph (image view) illustrating changes in the first calculation result (luminance difference at a specific location in a still image) over time calculated by a calculation unit using the luminance distribution on the reference line in  FIG. 4 . 
         FIG. 6  is a graph illustrating changes in a second calculation result over time acquired by smoothing the first calculation result in  FIG. 5 . 
         FIG. 7  is a flowchart illustrating steps of processing of the gas swirling state determination system according to the present invention, where a luminance difference at a specific location in a still image is a first calculation result. 
         FIG. 8  is a schematic view illustrating the luminance centroid CB, which is an image (still image) captured by the imaging device  39  focusing on a cross section (throat portion) taken along a line in  FIG. 1 . 
         FIG. 9  is a schematic view for describing the movement of the luminance centroid CB using the image in  FIG. 8 . 
         FIG. 10  is a graph illustrating changes in the first calculation result (swirling speed of the luminance centroid) over time calculated by the calculation unit using the luminance distribution of the entire viewing range in  FIG. 8  or  FIG. 9 . 
         FIG. 11  is a graph illustrating changes in a second calculation result over time acquired by smoothing the first calculation result in  FIG. 10 . 
         FIG. 12  is a flowchart illustrating steps of processing of the gas swirling state determination system according to the present invention, where the swirling speed of the luminance centroid is the first calculation result. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A gasification melting furnace provided with the gas swirling state determination system and the gas swirling state determination system according to a first embodiment of the present invention will be described in detail below with reference to the drawings. Note that the gas swirling state determination system of the present invention is a system for determining the swirling state of the gas. Therefore, the system is applicable to any device that involves gas swirling. However, here, the system is applied, for example, to a gasification melting furnace provided with a swirling melting furnace, as the device, and determines the swirling state of gas in the gasification melting furnace. 
     As illustrated in  FIG. 1 , a gasification melting furnace  1  in the present embodiment is a system in which a gasification furnace  2  (fluidized bed gasification furnace) pyrolyzes an object to be treated such as waste W 1  into gas (hereinafter referred to as pyrolysis gas) and a melting furnace  4  combusts the gas and melts ash contained in the gas into slag. 
     The gasification melting furnace  1  includes: the gasification furnace  2 ; a melting furnace  4  having a vertical cyclone melting furnace  15  that combusts and melts pyrolysis gas gasified in the gasification furnace  2 , and a secondary combustion chamber  17  connected to a top portion of the vertical cyclone melting furnace  15 ; a combustion air supply device  30  that supplies combustion air to the melting furnace  4 ; and a gas swirling state determination system  10  that determines the quality of the swirling state of combustion gas CG swirling in a throat portion  19 . 
     The throat portion  19  is a portion including the connection site between the vertical cyclone melting furnace  15  and the secondary combustion chamber  17 , and the vicinity thereof. When viewing a horizontal cross-section of the throat portion  19 , the connection site is the narrowest portion of the throat portion  19  (the portion having the smallest opening area which is substantially circular). As illustrated in  FIG. 1 , the throat portion  19  is shaped like a constriction (constricted shape) including a portion of a first inclined face portion  25   a  (described below) that gradually decreases in diameter upward and a portion of a diffuser portion  16  (described below) that gradually decreases in diameter downward. The throat of throat portion  19  means a narrow passage. 
     The gasification furnace  2  includes a gasification furnace body  5 , a waste injection port  6  provided on a side wall of the gasification furnace body  5 , and a waste discharge device  6   a  that discharges the waste W 1  injected through the waste input port  6  to the gasification furnace body  5 . 
     A pyrolysis gas discharge port  23  for discharging pyrolysis gas PG generated in the furnace is provided at the top of the gasification furnace body  5 . An incombustibles discharge port  7  for discharging incombustibles W 2  is provided at the bottom of the gasification furnace body  5 . The bottom of the gasification furnace body  5  is a fluidized bed with a fluidized medium  8  such as sand. 
     The melting furnace  4  includes the vertical cyclone melting furnace  15 , the secondary combustion chamber  17  connected to the upper portion of the vertical cyclone melting furnace  15 , and a boiler portion  18  connected to the downstream side of the secondary combustion chamber  17 . 
     The vertical cyclone melting furnace  15  includes a substantially cylindrical melting furnace body portion  24 , the first inclined face portion  25   a  that is connected to a top portion of the melting furnace body portion  24  and gradually decreases in diameter upward, a second inclined face portion  25   b  that is connected to a lower portion of the melting furnace body portion  24  and gradually decreases in diameter downward, and a cinder port  20  connected to a lower portion of the second inclined face portion  25   b.    
     The pyrolysis gas PG generated by pyrolyzing the waste W 1  in the gasification furnace  2  is fed through a pyrolysis gas duct  3 , and it is mixed with combustion air CA 1  supplied from the combustion air supply device  30  along the way. Then, the mixture is introduced into the vertical cyclone melting furnace  15 . 
     As illustrated in  FIG. 2  that is a sectional view taken along a line II-II in  FIG. 1 , the vertical cyclone melting furnace  15  includes a substantially cylindrical furnace wall  15   a  and a pair of pyrolysis gas introduction ports  21  through which pyrolysis gas PG is introduced. The pyrolysis gas introduction ports  21  are disposed such that the pyrolysis gas PG introduced through the pyrolysis gas introduction ports  21  is ejected in the tangential direction of a circle “C” around a central axis “A” of the vertical cyclone melting furnace  15 . With this configuration, the pyrolysis gas PG swirls in the vertical cyclone melting furnace  15 . The gas swirling in the vertical cyclone melting furnace  15  becomes the combustion gas CG, and its combustion heat melts ash. 
     The combustion gas CG is introduced from the vertical cyclone melting furnace  15  into the secondary combustion chamber  17 . Since the secondary combustion chamber  17  is formed in a substantially cylindrical shape that is concentric with the central axis “A” of the vertical cyclone melting furnace  15 , the combustion gas CG passes through the secondary combustion chamber  17  such that the central axis of the swirling coincides with the central axis “A” of the vertical cyclone melting furnace  15 . 
     The diffuser portion  16  that gradually decreases in diameter toward the vertical cyclone melting furnace  15  is provided at a lower end of the secondary combustion chamber  17 . In other words, focusing on the flow of the combustion gas CG, the secondary combustion chamber  17  includes the diffuser portion  16  that gradually increases in diameter from the vertical cyclone melting furnace  15  toward the downstream side. 
     The boiler portion  18  is provided downstream of the combustion gas, that is, exhaust gas of the secondary combustion chamber  17 , and heat is recovered by a superheater (not illustrated) or the like disposed on a flue. Exhaust gas EG, fed through the boiler portion  18 , is fed through a dust collector (not illustrated) at a later stage, and is discharged to the atmosphere through a chimney. 
     As illustrated in  FIG. 1 , the combustion air supply device  30  includes a blower  33  that supplies air to be combustion air CA 1  or CA 2 , a melting furnace air supply device  31  that supplies the combustion air CA 1  to the vertical cyclone melting furnace  15 , and a secondary combustion chamber air supply device  32  that supplies the combustion air CA 2  to the secondary combustion chamber  17 . 
     The melting furnace air supply device  31  includes a melting furnace air supply pipe  34  that connects the blower  33  to the pyrolysis gas duct  3 , and can regulate the flow rate of the combustion air CA 1  flowing through the melting furnace air supply pipe  34  by the melting furnace air amount regulation valve  35 . The combustion air CA 1  introduced into the pyrolysis gas duct  3  via the melting furnace air supply pipe  34  is mixed with the pyrolysis gas PG and supplied to the vertical cyclone melting furnace  15  via the pyrolysis gas introduction ports  21 . 
     The secondary combustion chamber air supply device  32  includes a secondary combustion chamber air supply pipe  36  that connects the blower  33  to the secondary combustion chamber  17 , and can regulate the flow rate of the combustion air CA 2  flowing through the secondary combustion chamber air supply pipe  36  by the secondary combustion chamber air amount regulation valve  37 . The combustion air CA 2  introduced into the secondary combustion chamber  17  via the secondary combustion chamber air supply pipe  36  is used for combustion of an unburned fraction contained in the combustion gas CG passing through the secondary combustion chamber  17 . 
     The pyrolysis gas duct  3  branches into two at a predetermined position in the flow of the pyrolysis gas PG from the upstream side (the side of the gasification furnace  2 ) to the downstream side (the side of the vertical cyclone melting furnace  15 ). The two branched pyrolysis gas ducts  3  are connected to the respective pyrolysis gas introduction ports  21 . Similarly, two branched melting furnace air supply pipes  34  are connected to the two branched pyrolysis gas ducts  3 , respectively. 
     Next, the gas swirling state determination system  10  will be described. The gas swirling state determination system  10  includes an information processing device  11  and an imaging device  39  that captures the combustion gas CG swirling around the central axis “A”. 
     The information processing device  11  includes: a calculation unit  40  that receives information about video captured by the imaging device  39 , that is, a plurality of still images “S” captured at different times (see  FIG. 3 ), extracts information about the luminance distribution of the still images “S”, calculates a first calculation result C 11  based on the information, and outputs the first calculation result C 11 ; a smoothing unit  41  that receives the first calculation result C 11 , smooths changes over time in the first calculation result C 11 , and outputs a second calculation result C 12 ; a determination unit  43  that receives the second calculation result C 12 , compares the second calculation result C 12  with a threshold to determine the quality of stability of the swirling state of the combustion gas CG, and outputs a result of the determination (hereinafter referred to as a “determination result”), and a display device  42  that receives the determination result and performs display corresponding to the determination result. The display device  42  may display the changes over time in the second calculation result C 12  simultaneously with or separately from the determination result. 
     The imaging device  39  is a device that captures the combustion gas CG swirling in the throat portion  19  from the direction along the central axis of the swirling of the combustion gas CG. The imaging device  39  is disposed at a top portion  17   a  of the secondary combustion chamber  17 , and on and in the vicinity of the central axis of the swirling of the combustion gas CG, and it is oriented to capture the throat portion  19 . In the present embodiment, since the vertical cyclone melting furnace  15  and the secondary combustion chamber  17  are configured as described above, the central axis “A” of the vertical cyclone melting furnace  15  coincides with the central axis of the swirling of the combustion gas CG in the secondary combustion chamber  17 . “Direction along the central axis” may be on or in the vicinity of the central axis of the swirling of gas. 
     The swirling combustion gas CG emits light by combusting the unburned fraction.  FIG. 3  illustrates a still image “S” captured by the imaging device  39  focusing on the narrowest portion in the throat portion  19  (cross section taken along a line in  FIG. 1 ) when viewing the throat portion  19  in the horizontal direction. In the still image “S”, a white portion has a higher luminance and a black portion has a lower luminance. 
     The imaging device  39  may be any devices such as a visible camera or an infrared camera, as long as it can acquire information about the distribution of luminance (luminance distribution information). The still image “S” is captured every predetermined time (for example, 0.1 seconds) and transmitted to the calculation unit  40 . 
     The calculation unit  40  acquires the luminance distribution information from each of the still images “S”, calculates a luminance difference D 1  (first calculation result C 11 ) at a specific location using the luminance distribution information, and outputs the result. 
     The specific location is a reference line “B” indicated by the dot-dash line in  FIG. 3 , and the reference line “B” is a circumference having a predetermined radius around the central axis “A” of the swirling of the combustion gas CG (identical to the central axis “A” of the vertical cyclone melting furnace  15  in the present embodiment). The luminance difference D 1  is a difference between a maximum value and a minimum value of the luminance on the reference line “B”. 
       FIG. 4  is a graph in which the luminance distribution of the still image “S” on the reference line “B” in  FIG. 3  is linearly expanded. In  FIG. 4 , a horizontal axis indicates the circumferential position on the reference line “B”, and a vertical axis indicates the luminance. The luminance at each position on the reference line “B” can be recognized from  FIG. 4 . 
     From the luminance distribution information illustrated in  FIG. 4 , the calculation unit  40  calculates, as the first calculation result C 11 , a difference (luminance difference D 1 ) between the maximum value (MAX) and the minimum value (MIN) of the luminance on the reference line “B”. The calculation unit  40  calculates the first calculation result C 11  for each of the plurality of still images “S” captured at different times. 
     The smoothing unit  41  smooths a set of the continuous first calculation results C 11  (luminance differences D 1 ) over time, which correspond to the still images “S”, and outputs the smoothed result (second calculation result C 12 ). 
     The importance of smoothing of the set of the continuous first calculation results C 11  over time will be described in detail. Smoothing is generally a technique used to remove noise. The first calculation results C 11  are calculation values and are not noise, but the inventor found that meaningful information about the swirling of gas could be acquired by smoothing the set of the first calculation results C 11 . 
       FIG. 5  is a graph illustrating changes in the first calculation results C 11  over time acquired by the calculation unit  40 . As apparent from the figure, no meaningful information about the swirling of gas can be read from the changes in the first calculation result C 11  over time itself. 
     However, a graph in which the changes in luminance difference over time are represented as one smoothly continuous line, as illustrated in  FIG. 6 , can be acquired by smoothing the set of the first calculation results C 11  illustrated in  FIG. 5 . Then, when historical driving data of the gasification melting furnace and knowledge experienced by the operator (time points when it is empirically recognized that the combustion gas in the gasification melting furnace is swirling stably and is in a favorable state, and when it is empirically recognized that the combustion gas in the gasification melting furnace is swirling unstably and is in an unfavorable state, for example) are compared with the graph of  FIG. 6 , a certain relationship can be derived about the swirling of the combustion gas in the throat portion  19 . That is, a following relationship can be derived: in comparing the luminance difference D 2  (second calculation result C 12 ) at a certain time with a first threshold A 1  or a second threshold A 2 , the swirling of the combustion gas is favorable when the second calculation result C 12  is equal to or larger than the second threshold A 2 , the swirling of the combustion gas is somewhat unfavorable (semi-unfavorable) when the second calculation result C 12  is equal to or larger than the first threshold A 1  and smaller than the second threshold A 2 , and the swirling of the combustion gas is unfavorable when the second calculation result C 12  is smaller than the first threshold A 1 . 
     Thus, as described below, the determination unit  43  of the gas swirling state determination system  10  automatically and mechanically executes the determination based on this relationship, and causes the display device  42  to display the determination result, thereby achieving optimal operation of the gasification melting furnace  1 . 
     Note that smoothing can be performed, for example, by calculating an average of the continuous  10  first calculation results C 11 . For each of the first calculation results C 11 , the smoothing unit  41  calculates an average of a plurality of previous first calculation results C 11  including the current first calculation result C 11  to acquire the second calculation result C 12  (the luminance difference D 2  after the smoothing). Changes in the first calculation results C 11  over time can be smoothed by sequentially performing this calculation. 
     The smoothing is not limited thereto, and any processing of smoothing data including fine fluctuations can be adopted as appropriate. 
     The determination unit  43  compares the absolute value of the second calculation result C 12  with the first threshold A 1 , determines that the swirling state of the combustion gas CG is unfavorable when the absolute value of the second calculation result C 12  is smaller than the first threshold A 1 , and outputs a determination result indicating that the swirling state is unfavorable. 
     The determination unit  43  compares the absolute value of the second calculation result C 12  with the second threshold A 2 , determines that the swirling state of the combustion gas CG is favorable when the absolute value of the second calculation result C 12  is equal to or larger than the second threshold A 2 , and outputs a determination result indicating that the swirling state is favorable. 
     The determination unit  43  compares the absolute value of the second calculation result C 12  with the first threshold A 1  and the second threshold A 2 , determines that the swirling state is somewhat unfavorable (semi-unfavorable) when the absolute value of the second calculation result C 12  is equal to or larger than the first threshold A 1  and smaller than the second threshold A 2 , and outputs the determination result indicating that the swirling state is semi-unfavorable. 
     The display device  42  receives the determination result output from the determination unit  43 , and distinguishably displays the determination results of favorable, unfavorable, and semi-unfavorable such that the operator can visually recognize the results. When distinguishably displaying the determination results of favorable, unfavorable, and semi-unfavorable, a difference in size and color of the characters may be provided. 
     Next, steps of the processing of the gas swirling state determination system  10  will be described using  FIG. 7 . 
     In a capture step S 1 , the imaging device  39  captures a video (constituted of a plurality of still images “S” captured at different times) of the throat portion  19 . 
     In a luminance distribution information acquisition step S 2 , the calculation unit  40  acquires luminance distribution information from each of the still images “S”. 
     In a first calculation step S 3 , the calculation unit  40  calculates the luminance difference D 1  (first calculation results C 11 ) at a specific location of the still images “S” by using the luminance distribution information, and outputs the first calculation results C 11 . 
     In a second calculation step S 4 , the smoothing unit  41  smooths changes in the first calculation result C 11  over time to output the second calculation result C 12 . 
     In a first comparison step S 5 , the second calculation result C 12  is compared with the second threshold A 2 , and when the second calculation result C 12  is equal to or larger than the second threshold A 2 , a first display step S 6  is executed. In the first display step S 6 , the display device  42  displays “favorable swirling” on a monitor or the like. 
     In a second comparison step S 7 , the second calculation result C 12  is compared with the second threshold A 2  and the first threshold A 1 , and when the second calculation result C 12  is smaller than the second threshold A 2  and is equal to or larger than the first threshold A 1 , a second display step S 8  is executed. In the second display step S 8 , the display device  42  displays “somewhat unfavorable swirling” on the monitor or the like. 
     When the second calculation result C 12  is smaller than the first threshold A 1  in the second comparison step S 7 , a third display step S 9  is executed. In the third display step S 9 , the display device  42  displays “unfavorable swirling” on the monitor or the like. 
     After the first display step S 6 , the second display step S 8 , or the third display step S 9 , in a graph display step S 10 , the display device displays the change in the second calculation result C 12  over time in the form of a graph on the monitor or the like. 
     Upon completion of the graph display step S 10 , the processing returns to the capture step S 1 , and the above-described steps are sequentially executed again. 
     When the determination result displayed on the display device  42  means “unfavorable swirling” or “somewhat unfavorable swirling”, it is likely that a smooth melting treatment has not been performed. Thus, to improve this situation, the operator of the gasification melting furnace  1  regulates, for example, the amount of combustion air and the input amount of the waste. In this manner, the optimal operation of the gasification melting furnace  1  can be achieved. 
     Second Embodiment 
     Next, a gas swirling state determination system and a gasification melting furnace provided with the gas swirling state determination system according to a second embodiment of the present invention will be described in detail with reference to the drawings. Note that, in the present embodiment, differences from the above-described first embodiment will be mainly described, and the description will be omitted for similar parts. 
     A large difference between the first embodiment and the second embodiment is that, the luminance difference D 1  of the still image “S” is the first calculation result C 11  in the first embodiment, while a swirling speed R 1  of a luminance centroid is a first calculation result C 21  in the second embodiment. 
     Accordingly, the content of the processing of the information processing device  11  and its constituents (the calculation unit  40 , the determination unit  43 , and the like) in  FIG. 1  vary between the first embodiment and the second embodiment, but for simplification of explanation, the following description will be given without changing the reference number of each of the devices and constituents in the first embodiment in  FIG. 1 . 
     Similar to  FIG. 3 ,  FIG. 8  is a still image “S” captured by the imaging device  39  focusing on the throat portion  19 . 
     As illustrated in  FIG. 8 , the calculation unit  40  calculates a luminance centroid CB of each still image “S” from the luminance distribution information of each still image “5”, and acquires position information (X, Y) of the centroid CB on the planar coordinates. 
     Note that, unlike the first embodiment, the display device  42  may display a video of the imaging device  39  on a monitor or the like. At this time, a centroid marking (nX, nY) acquired by multiplying the position (X, Y) of the luminance centroid CB by “n” may be displayed such that the operator can easily recognize the position of the luminance centroid. In  FIG. 8 , the centroid marking is illustrated as a double circle. 
     The swirling speed R 1  of the luminance centroid CB will be described. The swirling speed R 1  of the luminance centroid CB is the angular speed of the luminance centroid CB around the central axis of the swirling of the combustion gas CG. As in the first embodiment, the central axis of the swirling of the combustion gas CG is the same as the central axis “A” of the vertical cyclone melting furnace  15 . 
     The calculation unit  40 , by using the position information (X, Y) of the luminance centroid CB, acquires the swirling speed R 1  from an angular change φ in the luminance centroid CB between two continuous still images “S” that changes as illustrated in  FIG. 9 , and a time difference (Δt) between the still images “S”. That is, the calculation unit  40  acquires the swirling speed R 1  as the first calculation result C 21  according to a following expression (1). 
         R 1=φ/Δ t   (1)
 
     As in the first embodiment, the smoothing unit  41  in the present embodiment smooths changes in the first calculation results C 21  (swirling speed R 1 ) over time, and outputs a second calculation result C 22  (swirling speed R 2 ). 
       FIG. 10  is a graph illustrating changes in the first calculation results C 21  over time. As in the first embodiment, the first calculation results C 21  are calculation values and are not noise, but the Inventor found that meaningful information about the swirling of gas could be acquired by applying smoothing, which is the technique generally used to remove noise, to the set of the first calculation results C 21 . 
       FIG. 10  is a graph illustrating change in the first calculation results C 21  over time acquired by the calculation unit  40 . As shown in  FIG. 10 , not only the magnitude of the swirling speed R 1  changes over time, but also the swirling direction changes in the forward (+) or reverse (−) direction over time. That is, as apparent from the figure, no meaningful information about the swirling of gas can be read from the changes in the first calculation results C 21  over time itself. 
     However, a graph in which the swirling speed is represented in only one direction and changes in the swirling speed over time are represented as one smoothly continuous line, as illustrated in  FIG. 11 , can be acquired by smoothing the set of the first calculation results C 21  illustrated in  FIG. 10 . Then, when historical driving data of the gasification melting furnace and knowledge experienced by the operator (time points when it is empirically recognized that the combustion gas in the gasification melting furnace is swirling stably and is in a favorable state, and when it is empirically recognized that the combustion gas in the gasification melting furnace is swirling unstably and is in an unfavorable state, for example) are compared with the graph of  FIG. 11 , a certain relationship can be derived about the swirling of the combustion gas. That is, a following relationship can be derived: in comparing the swirling speed R 2  (second calculation result C 22 ) at a certain time with a first threshold B 1  or a second threshold B 2 , the swirling of the combustion gas is favorable when the second calculation result C 22  is equal to or larger than the second threshold B 2 , the swirling of the combustion gas is somewhat unfavorable (semi-unfavorable) when the second calculation result C 22  is equal to or larger than the first threshold B 1  and smaller than the second threshold B 2 , and the swirling of the combustion gas is unfavorable when the second calculation result C 22  is smaller than the first threshold B 1 . 
     Thus, as described below, the determination unit  43  of the gas swirling state determination system  10  automatically and mechanically executes the determination based on this relationship and causes the display device  42  to display the determination result, thereby, enabling optimal operation of the gasification melting furnace  1 . 
     The determination unit  43  compares the absolute value of the second calculation result C 22  with the first threshold B 1 , determines that the swirling state of the combustion gas CG is unfavorable when the absolute value of the second calculation result C 22  is smaller than the first threshold B 1 , and outputs a determination result indicating that the swirling state is unfavorable. 
     The determination unit  43  compares the absolute value of the second calculation result C 22  with the second threshold B 2 , determines that the swirling state of the combustion gas CG is favorable when the absolute value of the second calculation result C 22  is equal to or larger than the second threshold B 2 , and outputs a determination result indicating that the swirling state is favorable. 
     The determination unit  43  compares the absolute value of the second calculation result C 22  with the first threshold B 1  and the second threshold B 2 , determines that the swirling state is somewhat unfavorable (semi-unfavorable) when the absolute value of the second calculation result C 22  is equal to or larger than the first threshold B 1  and smaller than the second threshold B 2 , and outputs a determination result indicating that the swirling state is semi-unfavorable. 
     Next, steps of the processing of the gas swirling state determination system  10  in the present embodiment will be described using  FIG. 12 . 
     In a capture step S 11 , the imaging device  39  captures a video (constituted of a plurality of still images “S” captured at different times) of the throat portion  19 . 
     In a luminance distribution information acquisition step S 12 , the calculation unit  40  acquires luminance distribution information of all pixels from each of the still images “S”. 
     In a centroid calculation step S 13 , the calculation unit  40  calculates, from the luminance distribution information about each still image “S”, the luminance centroid CB for each still image “S” using the luminance of all pixels, and acquires position information (X, Y) of the luminance centroid CB on the planar coordinates. 
     In an angle calculation step S 14 , the calculation unit  40  calculates an angular change φ in the luminance centroid CB of two continuous still images “S” by using the position information (X, Y) of the luminance centroid CB. 
     In a first calculation step S 15 , the calculation unit  40  calculates the swirling speed R 1  (first calculation result C 21 ) from the angular change φ in the luminance centroid CB of two continuous still images “S” and a time difference (Δt) between the still images “S”, and outputs the first calculation result C 21 . 
     In a second calculation step S 16 , the smoothing unit  41  smooths the set of the first calculation results C 21  and outputs the second calculation result C 22 . 
     In a first comparison step S 17 , an absolute value of the second calculation result C 22  is compared with the second threshold B 2 , and when the absolute value of the second calculation result C 22  is equal to or larger than the second threshold B 2 , a first display step S 18  is executed. In the first display step S 18 , the display device  42  displays “favorable swirling” on a monitor or the like. 
     In a second comparison step S 19 , the absolute value of the second calculation result C 22  is compared with the second threshold B 2  and the first threshold B 1 , and when the absolute value of the second calculation result C 22  is smaller than the second threshold B 2  and is equal to or larger than the first threshold B 1 , a second display step S 20  is executed. In the second display step S 20 , the display device  42  displays “semi-unfavorable swirling” on the monitor or the like. 
     When the absolute value of the second calculation result C 22  is smaller than the first threshold B 1  in the second comparison step S 19 , the third display step S 21  is executed. In the third display step S 21 , the display device  42  displays “unfavorable swirling” on the monitor or the like. 
     After the first display step S 18 , the second display step S 20 , or the third display step S 21 , in a graph display step S 22 , the display device displays the changes in the second calculation result C 22  over time in the form of a graph in  FIG. 11  on the monitor or the like. 
     Upon completion of the graph display step S 22 , the processing returns to the capture step S 11 , and the above-described steps are sequentially executed. 
     As described in the first embodiment and the second embodiment, the gas swirling state determination system and the gasification melting furnace provided with the gas swirling state determination system according to the present invention can determine the quality of the stability of the gas swirling state based on the image captured by the imaging device, and display the determination result. Thus, based on the display, the operator can optimally operate a device that performs appropriate processing by swirling the gas, such as a gasification melting furnace. 
     Note that the gas swirling state determination system and the gasification melting furnace provided with the gas swirling state determination system according to the present invention may execute the processing steps in one of the first embodiment and the second embodiment in  FIGS. 7 and 12 , or may simultaneously execute the processing steps in both embodiments. 
     The embodiment of the present invention has been described above in detail with reference to the drawings, but the specific configurations are not limited to those embodiments, and design changes and the like that do not depart from the scope of the present invention are also included. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, a gas swirling state determination system that is configured to determine the quality of gas swirling state stability based on images captured by an imaging device and display a determination result, and a gasification melting furnace provided with the gas swirling state determination system are provided. 
     REFERENCE SIGNS LIST 
     
         
           1  Gasification melting furnace 
           2  Gasification furnace 
           3  Pyrolysis gas duct 
           4  Melting furnace 
           5  Gasification furnace body 
           6  Waste input port 
           6   a  Waste discharge device 
           7  Incombustibles discharge port 
           8  Fluidized medium 
           10  Gas swirling state determination system 
           11  Information processing device 
           15  Vertical cyclone melting furnace 
           15   a  Furnace wall 
           16  Diffuser portion 
           17  Secondary combustion chamber 
           18  Boiler portion 
           19  Throat portion 
           20  Cinder port 
           21  Pyrolysis gas introduction port 
           23  Pyrolysis gas discharge port 
           25   a  First inclined face portion 
           25   b  Second inclined face portion 
           30  Combustion air supply device 
           31  Melting furnace air supply device 
           32  Secondary combustion chamber air supply device 
           33  Blower 
           34  Melting furnace air supply pipe 
           35  Melting furnace air amount regulation valve 
           36  Secondary combustion chamber air supply pipe 
           37  Secondary combustion chamber air amount regulation valve 
           39  Imaging device 
           40  Calculation unit 
           41  Smoothing unit 
           42  Display device 
           43  Determination unit 
         C 11 , C 21  First calculation result 
         C 12 , C 22  Second calculation result 
         D 1  Luminance difference 
         EG Exhaust gas 
         PG Pyrolysis gas 
         R 1  Swirling speed 
         W 1  Waste 
         CG Combustion gas