Safety device for conveying installation

Abstract

To provide a safety device of a conveying facility capable of preventing the occurrence itself of dust explosion.SOLUTION: A safety device for avoiding dust explosions in a chain conveyor 2 for transporting wood pellets 1 through a closed space 3a surrounded by a conveyor case 3 includes electrostatic meters 15 (electrostatic detectors) disposed in respective connected sections of the conveyor case 3, infrared cameras 19, 20 (temperature detectors) for detecting at least one of a surface temperature of the wood pellets 1 in the conveyor case 3 and a temperature of a transport path (a transport chain 10 and a scraper 11), an anemometer 21 (wind speed detector) for detecting a speed of wind flowing through the closed space 3a, and a control device 16 for activating a danger avoidance mode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a safety device for preventing dust explosions in conveying facilities that transport powder and granular material through a closed space surrounded by a casing. [Background technology]

[0002] A chain conveyor, such as that shown in Patent Document 1, is known as a conveying equipment for transporting powdered and granular materials such as coal. This type of chain conveyor comprises a long conveyor case that encloses a transport path for the powdered and granular materials, a conveying chain with scrapers that runs in a circular motion within the closed space within the conveyor case, an inlet provided at the top of one longitudinal side of the conveyor case, and a discharge outlet provided at the bottom of the other longitudinal side of the conveyor case. The powdered and granular materials fed from the inlet are transported by the chain scrapers toward the discharge outlet.

[0003] On the other hand, in recent years, the expansion of renewable energy has become an important issue in terms of promoting measures against global warming, and the effective use of biomass (organic matter derived from plants and animals) as renewable energy is being considered. As a result, the handling of wood pellets as an alternative power generation fuel to coal has increased, and there are more opportunities to transport these types of wood pellets by chain conveyor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-227103 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because wood pellets have a high rate of pulverization and are easily ignited, measures are needed to prevent dust explosions and resulting fires in transport equipment. However, the common dust prevention measure of spraying water on wood pellets is difficult to adopt for this type of wood pellets (because there is a concern that they may harden or ferment after being sprayed with water).

[0006] To date, measures have been developed to minimize the damage caused by dust explosions, such as the installation of explosion relief vents and flame vents, as well as explosion suppression systems that open sealed sections or spray fire extinguishing agents the moment pressure is detected.However, none of these measures prevent dust explosions from occurring in the first place; they only serve to minimize damage immediately after an explosion occurs.Given that wood pellet transport equipment is generally often used for power generation, there is a need for measures that can prevent dust explosions from occurring in the first place, to avoid the long downtime that would occur if damaged.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a safety device for a conveying facility that can prevent the occurrence of a dust explosion in advance. [Means for solving the problem]

[0008] The present invention is a safety device for avoiding dust explosions in conveying equipment that transports powdered or granular material through a closed space surrounded by a casing, and is characterized by comprising: a static electricity detector that detects the amount of static electricity and is arranged in each connected section of the casing; a temperature detector that detects the temperature of at least one of the powdered or granular material in the casing and the transport path; a wind speed detector that detects the speed of wind flowing through the closed space in the casing; and a control device that activates a danger avoidance mode when the detected value of at least one of the static electricity detector and the temperature detector exceeds an allowable value and the detected value of the wind speed detector is lower than a wind speed that can avoid a dust explosion.

[0009] Furthermore, in implementing the present invention more specifically, it is preferable that the conveying equipment has an opening / closing section in the middle of the casing that can open the closed space as appropriate, and that the control device opens the opening / closing section when the danger avoidance mode is activated, and it is also possible that the control device stops the conveying equipment when the danger avoidance mode is activated.

[0010] Furthermore, in the present invention, the temperature detector may be an infrared camera that photographs at least one of the powder and granular material and the transport path through a window portion of the casing to detect the temperature, and the powder and granular material transported by the conveying equipment may be wood pellets. [Effects of the Invention]

[0011] The safety device for conveying equipment of the present invention monitors ignition sources that could trigger dust explosions, and determines whether or not there is a possibility of a dust explosion under conditions where the wind speed is lower than that at which a dust explosion can be avoided. This makes it possible to prevent dust explosions from occurring in the first place without excessively interrupting the operation of the conveying equipment, thereby avoiding situations where long periods of downtime occur due to dust explosions. It can also have the excellent effect of being applicable as a highly effective safety measure for power generation equipment that uses wood pellets as fuel, for example. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an overall configuration diagram showing an embodiment of a safety device for a conveying facility according to the present invention; [Figure 2] 2 is an explanatory view of the air cylinder of FIG. 1 as viewed from a horizontal direction perpendicular to FIG. 1. [Figure 3] 2 is a flowchart illustrating a specific control procedure in the control device of FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0014] Figure 1 shows one embodiment of the present invention, illustrating a safety device for a chain conveyor 2 (transportation equipment) that transports wood pellets 1 (granular material) as power generation fuel to a power generation facility (not shown).The chain conveyor 2 transports the wood pellets 1 through a closed space 3a surrounded by a long conveyor case 3 (casing).An inlet 4 for the wood pellets 1 is provided at the top on one longitudinal side of the conveyor case 3, and an outlet 5 is provided at the bottom on the other longitudinal side.

[0015] Sprockets 6 and 7 are arranged at both longitudinal ends of the conveyor case 3, and an endless conveying chain 10 that circulates along a lower forward path 8 and an upper return path 9 is wound around both sprockets 6 and 7, and scraping plates 11 are provided at a predetermined interval on both sides of the conveying chain 10 to scrape out the wood pellets 1 that have been fed into the conveyor case 3 from the inlet 4 to the outlet 5.

[0016] Here, the sprocket 6 on the discharge port 5 side serves as a driving sprocket that is driven by a drive unit 12 with a reducer, and the sprocket 7 on the input port 4 side serves as a driven sprocket.

[0017] The outgoing path 8 is arranged along the longitudinal direction at the center of the upper surface of the bottom of the conveyor case 3, and the returning path 9 is arranged along the longitudinal direction at the upper center inside the conveyor case 3, but the latter returning path 9 is supported by each cross member 13 that is placed horizontally at appropriate intervals along the longitudinal direction of the conveyor case 3 on the upper side inside the conveyor case 3.

[0018] In addition, wood pellets 1 unloaded by an unloader are fed into the inlet 4, and in this case, a chute 14 is connected to feed the wood pellets 1 in the conveying direction of the conveyor chain 10 so that the wood pellets 1 are fed evenly across the width of the conveyor case 3 and are not concentrated in the center of the width.

[0019] In this embodiment of the chain conveyor 2 having such a structure, each connected section of the conveyor case 3 is equipped with an electrostatic meter 15 as a static electricity detector to detect the amount of static electricity, and the detected values ​​from each of these electrostatic meters 15 are input to the control device 16.

[0020] That is, the long conveyor case 3 is made by connecting parts that are divided into each compartment, and since it is expected that each compartment will be charged with a different amount of static electricity due to the presence of gaskets and coatings at the connecting points, each compartment is equipped with an electrostatic meter 15 to detect the amount of static electricity.

[0021] Furthermore, observation windows 17, 18 (window portions) are provided on the side and ceiling surfaces of the conveyor case 3 midway along its length, and infrared cameras 19, 20 are installed as temperature detectors so that the interior of the conveyor case 3 can be photographed through the observation windows 17, 18, and the detected values ​​from these infrared cameras 19, 20 are also input to the control device 16. Note that if observation windows 17, 18 of this type already exist, they can be effectively reused, and if no existing windows exist in the required locations, new ones can be installed.

[0022] That is, the surface temperature of the wood pellets 1 during transport is detected based on infrared images taken by an infrared camera 19 through an observation window 17 on the side of the conveyor case 3, while the temperature of the transport path (conveyor chain 10 and scraper 11) is detected based on infrared images taken by an infrared camera 20 through an observation window 18 on the ceiling surface of the conveyor case 3.

[0023] Furthermore, an anemometer 21 is installed in an appropriate excess portion of the conveyor case 3 as a wind speed detector to detect the wind speed flowing through the closed space 3a, and the detected value from the anemometer 21 is also input to the control device 16.

[0024] In addition, an opening / closing section 22 capable of opening the closed space 3a as needed is provided in a required range on the ceiling surface midway along the longitudinal direction of the conveyor case 3, and an air cylinder 23 for opening and closing the opening / closing section 22 is mounted on the side of the conveyor case 3 via a bracket 24 (see Figure 2), so that the control device 16 operates the air cylinder 23 to open the closed space 3a when a danger avoidance mode, which will be described later, is activated.

[0025] On the other hand, on the control device 16 side, a danger avoidance mode is activated when the detection value (static electricity amount or temperature) of at least one of the electrostatic meter 15 and the infrared cameras 19, 20 exceeds an allowable value and the detection value of the anemometer 21 is lower than the wind speed at which a dust explosion, which will be described later, can be avoided. More specifically, when the danger avoidance mode is activated, a contraction operation command is output to the air cylinder 23 to open the closed space 3a, and a stop command is output to the drive unit 12.

[0026] The above-described electrostatic meter 15, infrared cameras 19 and 20, anemometer 21, control device 16, opening / closing unit 22, and air cylinder 23 constitute a safety device that prevents dust explosions from occurring on the chain conveyor 2.

[0027] Here, to add a bit more information about the conditions for a dust explosion, the three elements that are said to be the cause of a dust explosion are dust concentration, oxygen, and an ignition source (static electricity or temperature). However, in powder and granular material transport equipment where dust explosions are a concern, it is not realistic to completely control the dust concentration in the closed space to a level that will prevent a dust explosion. In many cases, it is unavoidable that the dust concentration in the closed space will fall within the range where a dust explosion is possible during normal operation, and it is also not realistic to completely block the intrusion of oxygen into the closed space.

[0028] Therefore, the inventors focused on making the ignition source that could trigger a dust explosion a realistic target for monitoring, and decided to have the control device 16 monitor using the electrostatic meter 15 and infrared cameras 19 and 20 to see if the amount of static electricity or temperature exceeded an allowable value. However, since it is already known that dust explosions will not occur if the wind speed in the closed space 3a exceeds a predetermined value, the lower limit of the wind speed at which a dust explosion can be reliably avoided is set as a threshold, and the control device 16 also monitors whether the value detected by the anemometer 21 is below this threshold.

[0029] More specifically, as shown in the flowchart in Figure 3, after operation is started in step S1, it is determined in step S2 whether the detection value of the electrostatic meter 15 exceeds the allowable value and a static electricity amount greater than the minimum ignition energy of dust is detected, while in step S3 it is determined whether the surface temperature of the wood pellets 1 during transport or the temperature of any of the transport paths (conveyor chain 10 or scraper 11), detected based on the infrared images of each infrared camera 19, 20, exceeds the allowable value and is detected to be greater than the minimum ignition temperature of dust.

[0030] Furthermore, in step S4, it is determined whether the detection value of the anemometer 21 is below the lower limit of the wind speed at which a dust explosion can be avoided. If the determination in at least one of the previous steps S2 and S3 is YES and at the same time the determination in step S4 is also YES, it is determined in step S5 that there is a possibility of a dust explosion, a danger avoidance mode is activated, and a contraction operation command is output to the air cylinder 23 to open the closed space 3a, and a stop command is output to the drive unit 12.

[0031] Then, in the next step S6, the determinations in steps S2, S3, and S4 are made again, and if there is no possibility of a dust explosion, the process returns to step S1 and operation resumes. However, if there is still a possibility of a dust explosion, the process proceeds to step S7, where a timer is used to confirm that a certain period of time has passed, and then the process returns to step S6 and the determinations in steps S2, S3, and S4 are made again.

[0032] In this way, when the detection value (static electricity amount or temperature) of at least one of the electrostatic meter 15 and the infrared cameras 19, 20 exceeds the allowable value and the detection value of the anemometer 21 is lower than the wind speed at which a dust explosion can be avoided, the control device 16 determines that there is a possibility of a dust explosion and activates a danger avoidance mode. When this danger avoidance mode is activated, a contraction operation command is output to the air cylinder 23 to open the closed space 3a, and a stop command is output to the drive unit 12 to stop operation, thereby preventing the occurrence of a dust explosion.

[0033] Therefore, according to this embodiment, ignition sources that could trigger dust explosions are monitored, and the possibility of a dust explosion is determined under conditions where the wind speed is lower than that at which a dust explosion can be avoided. This makes it possible to prevent a dust explosion from occurring without excessively interrupting the operation of the chain conveyor 2, thereby avoiding situations where a dust explosion would result in long-term downtime. This can be applied as a highly effective safety measure, particularly for power generation facilities that use wood pellets 1 as fuel, as in this embodiment.

[0034] Furthermore, the safety device for the conveying equipment of the present invention is not limited to the above-mentioned embodiment, and as long as the conveying equipment transports powdered or granular material through a closed space surrounded by a casing, it does not necessarily have to be in the form of a chain conveyor, and temperature detectors other than infrared cameras may be used, and further, the powdered or granular material transported by the conveying equipment is not limited to wood pellets, and of course various other modifications can be made within the scope that does not deviate from the gist of the present invention. [Explanation of symbols]

[0035] 1. Wood pellets (granular material) 2 Chain conveyor (transport equipment) 3 Conveyor case (casing) 3a Closed space 15 Electrostatic meter (static detector) 16 Control device 17 Observation window (window part) 18 Observation window (window part) 19 Infrared camera (temperature detector) 20 Infrared camera (temperature detector) 21 Anemometer (wind speed detector) 22 Opening and closing section 23 Air cylinder 24 Bracket

Claims

1. A safety device for avoiding dust explosions in conveying equipment that transports powdered or granular material through a closed space surrounded by a casing, comprising: a static electricity detector that detects static electricity and is arranged in each connected section of the casing; a temperature detector that detects the temperature of at least one of the powdered or granular material in the casing and the transport path; a wind speed detector that detects the speed of wind flowing through the closed space in the casing; and a control device that activates a danger avoidance mode when the detected value of at least one of the static electricity detector and the temperature detector exceeds an allowable value and the detected value of the wind speed detector is lower than the wind speed at which a dust explosion can be avoided.

2. 2. A safety device for a conveying facility according to claim 1, wherein the conveying facility is provided with an opening / closing section in the middle of the casing that can appropriately open the closed space, and the control device opens the opening / closing section when a danger avoidance mode is activated.

3. 3. The safety device for a transport facility according to claim 1, wherein the control device stops the transport facility when the danger avoidance mode is activated.

4. 2. A security device for a conveying facility according to claim 1, wherein the temperature detector is an infrared camera that photographs at least one of the powder and granular material and the conveying path through a window in the casing to detect the temperature.

5. 2. A safety device for a conveying facility according to claim 1, wherein the powdery or granular material transported by the conveying facility is wood pellets.

Images