Patent Publication Number: US-2009238737-A1

Title: Apparatus for sterilizing and smoothing fine sands

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for sterilizing and smoothing fine sands, and more particularly, to an apparatus that sterilizes and polish ultra fine sands, which are used, for example, water purification, by heating the ultra fine sands and rubbing the surface of ultra fine sands each other. 
     2. Discussion of the Related Art 
     For example, a low speed filtrating method and a high speed filtrating method have been generally known as a method of producing drinking water from raw water. The low speed filtrating method is a method of purifying raw water by performing a microbial treatment with an ultra fine sand filter layer and filtrating foreign substances. The low speed filtrating method slowly performs a treatment as compared to the high speed filtrating method that performs a treatment by using chemicals such as chlorine, but is excellent for drinking water in terms of less chemical flavor (Japanese Patent Application Publication No. 07-308518 and Japanese Patent No. 3406258). 
     Specifications of the turbidity of water, which is purified by filter sands, are provided. It is required that turbidness is low and saprophytic bacteria or foreign substances such as organic impurities are as few as possible. Filter sands used for low speed filtration uses sea sands, river sands, and mountain sands as raw material sands. However, since foreign substances such as organic impurities and saprophytic bacteria are attached to the surfaces of grains of the raw material sands, the foreign substances or saprophytic bacteria need to be removed when the sands are used. 
     There have been known a method of sterilizing raw material sands, such as collected sea sands, river sands, and mountain sands by heating the raw material sands to high temperature in a kiln while the raw material sands are fed by a conveyor, such as a screw conveyor or a net conveyor (Japanese Patent Application Publication Nos. 10-234831 and 07-289613). There have been known a method of sterilizing raw material sands by supplying hot air to the raw material sands from below side to heat the raw material sands while the raw material sands fall into a vibration box (Japanese Patent Application Publication No. 2002-65815). 
     However, as for the method of sterilizing raw material sands by heating the raw material sands in a kiln while the raw material sands are fed by a conveyor, since the raw material sands are ultra fine sands, grains of the sand cohere to each other due to moisture or organic impurities, thereby forming a clod. For this reason, there has been a concern that the grains of sand in the clod are not sterilized even though heated. 
     As for the method of sterilizing raw material sands by supplying hot air to the raw material sands from below side to heat the raw material sand while the raw material sands fall into a vibration box, since hot air is supplied to the grains of sand, a clod of sands is less formed. However, unless the grains of sand are in contact with hot air for a sufficiently long time so as to be heated, there is a concern that the saprophytic bacteria remain. As a result, the bulk of the vibration box tends to be large. 
     SUMMARY OF THE INVENTION 
     The present inventor developed an apparatus for sterilizing fine sands that supply raw material sands to a sterilization chamber having a closed cross-sectional shape, apply vertical vibration and forward feed vibration to the sterilization chamber so that the raw material sands are fed forward while jumping, throws burner flame to the raw material sands from above so that the raw material sands are heated to high temperature and attachments are separated from fine sand to sterilize the fine sands, thereby being capable of reliably sterilizing sands through the dispersion of sands without increasing bulk of the apparatus (PCT/JP2007/066748). 
     However, it has been proved that the fine sands sterilized in the above-mentioned apparatus for sterilizing fine sands have few things to worry about foreign substances or saprophytic bacteria but variation occurs in efficiency of water purification if the filter sands of the low speed filtrating method are used. 
     The present inventor has repeated various experiments about filter sands used in the low speed filtrating method, and have found out the following knowledge. That is, in some locations where raw material sands are collected, grains of fine sand have a sharp shape and foreign substances or saprophytic bacteria are attached thereto in the shape of mud. 
     It has been proved as follows: in the case of the above-mentioned muddy raw material sands, foreign substances or saprophytic bacteria may be removed by heating the raw material sands to high temperature. However, if the fine sands still have a sharp shape, gaps between the grains of the fine sand may have variation and capillarity is difficult to occur. For this reason, a variation of the function of the fine sands as a water purifying membrane occurs and causes a variation of the efficiency of purification. 
     An object of the present Invention is to provide an apparatus for sterilizing and smoothing fine sands that can reliably sterilize sands through the dispersion of sands without increasing bulk thereof, and can make the shape of sand become round to ensure high efficiency of purification in a low water-speed filtration. 
     An apparatus for sterilizing and smoothing fine sands according to the invention separates fine sands and attachments such as foreign substances and saprophytic bacteria from raw material sands, heats the fine sands to sterilize the fine sands, and makes sharp fine sands round by rubbing each other. The apparatus includes a feed chamber, a raw material sands feeding device, heating burners, and receiving means. The feed chamber includes an upstream receiving port and a downstream discharge port at both ends of a body that is composed of a floor and a cover and has a closed cross-sectional shape, receives the fine sands through the upstream receiving port, feeds the fine sands to the downstream discharge port by applying forward feed vibration to the floor while making the fine sands bounce by applying vertical vibration to the floor, and makes the raw material sands be rubbed against each other by the vertical vibration and forward feed vibration so that sharp portions of the fine sands become round. The raw material sands feeding device feeds the raw material sands to the upstream receiving port of the feed chamber in the shape of a curtain. The heating burners throw burner flame, of which the lateral width is substantially equal to that of the curtain-shaped raw material sands, into the feed chamber in a lateral direction, make the raw material sands be in contact with hot air having high temperature by making the burner flame cross the curtain-shaped raw material sands in order to separate dust of attachments from the fine sands, and heat the fine sands to sterilize the fine sands. The receiving means receives the sterilized fine sands, of which sharp portions are removed, from the downstream discharge port of the feed chamber. 
     In the above-mentioned apparatus for sterilizing fine sand (PCT/JP2007/066748), while vertical vibration and forward feed vibration are applied to raw material sands, burner flame was thrown to the raw material sands. Accordingly, attachments were not completely or sufficiently separated, and grains of fine sand were rubbed against each other in this state. As a result, it is thought that the fine sands still had a sharp shape. 
     According to an aspect of the invention, the raw material sands fall in the shape of a curtain and crosses the burner flame thrown in a lateral direction, and the attachments such as foreign substances or saprophytic bacteria of the raw material sands are quickly burnt and separated from the fine sands. 
     In this way, the attachments such as foreign substances or saprophytic bacteria are completely separated from the raw material sands, and the fine sands are fed by applying forward feed vibration thereto while bouncing by applying vertical vibration to the fine sands from which the attachments are removed. Accordingly, the grains of the fine sand are reliably rubbed against each other by the vertical vibration and forward feed vibration. As a result, the sharp portions of the fine sand are removed and the fine sand have a round shape that is optimum for water purification. 
     Further, the curtain-shaped raw material sands crosses the burner flame thrown in a lateral direction and the attachments such as foreign substances or saprophytic bacteria of the raw material sands are quickly burnt and separated from the fine sands. Therefore, it is possible to reliably sterilize and smooth the surface of fine sands. 
     Furthermore, since the raw material sands fall in the shape of a curtain and crosses the burner flame, it is possible to quickly and reliably heat the raw material sands to high temperature. In addition, since the bulk of the apparatus does not need to be significantly increased, it is possible to easily install the apparatus in a building having a common height. 
     If the blast volume of the burner is adjusted, it is possible to feed the fine sands on the floor in the feed chamber, and to separate dust from the fine sands in an inner space of the feed chamber and then send the dust to the downstream discharge port. 
     That is, the fine sands may be fed to the downstream discharge port on the floor in the feed chamber by the forward feed vibration, and the dust separated from the fine sand may be fed to the downstream discharge port through an inner space of the feed chamber by a force of the burner flame. 
     In this case, if a dust suction port for sucking the dust is formed at the downstream discharge port of the feed chamber and a suction duct and a dust collector are connected to the dust suction port, it is possible to efficiently collect and treat only dust without polluting the atmosphere. That is, it is preferable that a dust suction port for sucking the dust be formed at the downstream discharge port of the feed chamber and a suction duct be connected to the dust suction port so as to suck the dust. 
     The feed chamber may include a floor and a cover has a closed cross-sectional shape, and the material thereof is not particularly limited. However, considering that a high temperature atmosphere is formed in the chamber, at least inner walls thereof may be produced using a heat-resistant material, for example, a stainless steel plate and a heat-resistant resin. The reason why the feed chamber is formed to have a closed cross-sectional shape is to suppress the scattering of the dust, which is separated from the raw material sands, to the environment. The feed chamber can feed the fine sands by the forward feed vibration. However, if the feed chamber is inclined so that the front portion descends, it is possible to reliably feed the fine sands. 
     It is possible to quickly heat the raw material sands to high temperature by making the curtain-shaped raw material sands cross the burner flame. Accordingly, it is possible to expect that the clod of the raw material sand fragments into small pieces. However, it is preferable that the clod of the fine raw material sands fragment into small pieces before being fed to the feed chamber. Further, rock grains may be contained in the fine sands of the collected sea sands, river sands, and mountain sands. 
     The apparatus may further include a vibration feeder that receives unsterilized raw material sands and applies vertical vibration so as to make a clod of sand fragment into small pieces and feeds the small pieces to a raw material feeding device. The vibration feeder may include a mesh filter that filters rock grains. 
     If a large amount of fine sands are fed to the raw material feeding device at one time, it is not possible to feed the raw material sands to the feed chamber in the shape of a thin curtain having a constant thickness and there is a concern that variation may occur in the sterilization of the fine sands or in making the fine sands round. 
     The vibration feeder may be formed to feed a predetermined amount of fine sand. For example, a vibratory fixed quantity shooter may be provided in the vibration feeder, and the fixed quantity shooter may be formed in a planar shape to load a predetermined amount of fine sand thereon and to slowly feed the fine sands loaded on the fixed quantity shooter to the sterilization chamber. 
     The high temperature atmosphere formed in the chamber may correspond to temperature where the sterilized fine sands are not contaminated again, specifically, the temperature range of 150 to 300° C. 
     The sterilized and smoothed fine sands are used in the low water-speed filtration, the fine sands may have a mean diameter in the range of 0.08 to 1.8 mm. 
     It is preferable that the vibration feeder and the feed chamber vibrate in a vertical vibration and a forward direction. The vibration generating method may use an eccentric rotor, but it is preferable that the vibration generating method use electromagnetic vibration in consideration of the accurate vibration control. A known vibration mechanism may be used for the electromagnetic vibration. For example, it is preferable that the vibration generating method be a method of attracting a vibrating body against the spring force of a spring member by magnetism and returning the vibrating body by the spring force while the attraction is stopped. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         FIG. 1  is a schematic view showing the configuration of an apparatus for sterilizing fine sand according to a preferred embodiment of the invention. 
         FIG. 2  is a plan view showing the configuration of the apparatus according to the embodiment. 
         FIG. 3  is a schematic perspective view showing the closed cross-sectional shape of a sterilization chamber of the embodiment. 
         FIG. 4  is a view showing the shapes of unsterilized raw material sand and sterilized fine sand in the embodiment. 
     
    
    
       10  Apparatus for sterilizing fine sand 
       11  Hopper 
       12  Vibration feeder 
       12 A Shooter 
       13  Feed chamber 
       13 A Upstream receiving port 
       13 B Downstream discharge port 
       14  Heating burner 
       15  Shooter 
       17  Receiving container for sterilized fine sand 
       18  Water tank 
     THE PREFERRED EMBODIMENTS OF THE INVENTION 
     The invention will be described in detail below with reference to a specific embodiment shown in drawings.  FIGS. 1 to 4  show an apparatus for sterilizing and smoothing fine sands according to a preferred embodiment of the invention. In the drawings, a hopper  11 , which receives raw material sands W, such as collected sea sands, river sands, or mountain sands, are provided on a table  19  of a sterilizing apparatus  10 . A discharge port is formed at the bottom of the hopper  11 , and a feeder  11 A is disposed below the discharge port. Further, a vibration generator  11 B is provided below the hopper  11  to apply vertical vibration to the hopper  11  and the feeder  11 A and to apply forward feed vibration to the feeder  11 A. 
     A vibration feeder  12  is provided on the front side of the feeder  11 A of the hopper  11 . The vibration feeder  12  includes a tank of which the upper surface is opened, and a mesh filter  12 A is stretched on the tank so that rock grains are separated from the raw material sands. A pan  12 B for fine sands is provided on the lower side of the mesh filter  12 A. The pan  12 B receives forward feed vibration from a vibration generator  12 C and measures the amount of the raw material sands so as to allow the feeder  11 A to feed a predetermined amount of raw material sands. 
     A raw material feeding device  15  is provided on the lower side of the vibration feeder  12 , and the raw material feeding device  15  includes a forked horizontal feeder. Raw material sand is load on the horizontal feeder with a constant thickness, is fed by the forward feed vibration applied by the vibration generator  15 A, and falls in the shape of a curtain. 
     An upstream receiving port  13 D of a feed chamber  13  is disposed on the front side of the raw material feeding device  15 . For example, a cover  13 C formed of a stainless steel plate covers a floor panel  13 B formed of a stainless steel plate so as to form a closed cross-sectional shape, so that the feed chamber  13  is formed. An upstream receiving port  13 D is formed on the upstream side of the feed chamber  13 , and a downstream discharge port  13 E is formed on the downstream side thereof. Further, a dust suction port  13 F is formed on the downstream side of the cover  13 B. 
     A vibration generator  13 A is provided on the lower side of the feed chamber  13 , and applies vertical vibration and forward feed vibration to the floor panel  13 B of the feed chamber  13 . 
     Further, a support  14 A is mounted on the table  19  so as to stand up, and heating burners  14  are laterally mounted on the support  14 A in the shape of a 2×2 matrix. Accordingly, the heating burners  14  throw burner flame, of which the lateral width is substantially equal to that of the curtain-shaped raw material sands, into the feed chamber  13  in a lateral direction. 
     A receiving container  17  for sterilized fine sand is disposed on the front side of the downstream discharge port  13 E of the feed chamber  13 , and the receiving container  17  is immersed in a cooling water tank  18 . Further, a suction duct  16  is connected to the dust suction port  13 F of the feed chamber  13  and the suction duct  16  is connected to a dust collector. Accordingly, the suction duct sucks dust in the feed chamber  13 . 
     In this case, it is preferable that vertical vibration and forward feed vibration be vibration having, for example, a triangular waveform, an amplitude of 1 mm, and a frequency of 60 times/sec. 
     When sea sands, river sands, or mountain sands are collected, these raw material sands are input to the hopper  11 . When the sterilization begins, the vibration generator  11 B applies vertical vibration to the hopper  11 , the raw material sands of the hopper  11  falls onto the feeder  11 A little by little, the vibration generator  11 B applies forward feed vibration to the feeder  11 A, and the raw material sands on the feeder  11 A falls onto the vibration feeder  12  little by little. 
     In the vibration feeder  12 , the mesh filter  12 A is adjusted to have an aperture of, for example, 1.8 mm and the vibration feeder  12  vibrates in a vertical direction so that the raw material sands fall onto the mesh filter  12 A. If the raw material sands fall, sands having a size of 1.8 mm or more are sorted. Sand grains or rock grains having a size of 1.8 mm or more are filtered by the mesh filter  12 A. 
     The pan  12 B applies vertical vibration to the sorted fine sands having a size of 1.8 mm or less so as to disperse the sorted fine sands, and measures the amount of the sorted fine sands so as to allow the feeder  12 A to feed a predetermined amount thereof to the raw material feeding device  15 . 
     The vibration generator  15 A applies forward feed vibration to the sands in the raw material feeding device  15 . The fine raw material sands are spread on the entire surface of the forked horizontal feeder with a uniform thickness, and falls onto the upstream receiving port  13 D of the feed chamber  13  in the shape of a curtain that has a predetermined width in a lateral direction. 
     In this case, the heating burners  14  throw burner flame, of which the temperature is high, for example, in the range of 150 to 300° C., in a lateral direction. The curtain-shaped raw material sands are in contact with the burner flame while crossing the burner flame, so that the raw material sands are quickly heated to high temperature. Accordingly, attachments, such as foreign substances of saprophytic bacteria of the raw material sands are burned and become dust, and are then sent into the feed chamber  13 . Then, the fine sands sterilized through the separation of the attachments are loaded from the upstream receiving port  13 D onto the floor  13 B of the feed chamber  13 . 
     The vibration generator  13 A applies vertical vibration and forward feed vibration to the floor  13 B of the feed chamber  13 . Accordingly, while bouncing from the bottom  13 B due to the vertical vibration, grains of the fine sand loaded onto the floor  13 B of the feed chamber  13  are fed to the downstream discharge port  13 B. As a result, the grains of the fine sand are rubbed against each other so that sharp portions of each grain of the fine sand become round. 
     Since dust contained in the fine sands are sucked by the suction duct  16 , the sterilized and rounded fine sands having a mean diameter in the range of 0.08 to 1.8 mm are received in the receiving container  17  and then cooled. 
     When applied to low water-speed filtration, the fine sands are sorted into first fine sands having a mean diameter in the range of 0.08 to 0.3 mm and second fine sands having a mean diameter in the range of 0.4 to 1.8 mm and may be used for upper and lower filter sand tanks. 
     When the present inventor observed unsterilized raw material sands and sterilized fine sands by a microscope, it was confirmed that the raw material sands have sharp portions in the grains of the fine sand  20 , and saprophytic bacteria  21 , dust  22 , dirt  23 , foreign substances  24 , and mud  25  existed between the grains of the fine sand  20  as shown in  FIG. 4A . In contrast, when the present inventor observed sterilized fine sands  20 ′, it was confirmed as follows: sharp portions of each grain of fine sand were removed and became round, saprophytic bacteria  21  were not shown between the grains of the fine sand  20 ′ as shown in  FIG. 4B , and the sterilized fine sand was optimum for filter sand of low water-speed filtration. 
     INDUSTRIAL APPLICABILITY 
     According to the invention, it is possible to reliably sterilize raw material sands collected from a river or a mountain and to make the shape of sand be optimum. Therefore, since being capable of being used as filter sand for purifying drinking water, the sterilized sands are very useful.