JPH0134457B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating and removing plastics mixed in wood chips. In particular, the present invention actively utilizes the electrical charge that the mixed plastics have and detects this with an electrometer. It is intended to automatically separate and remove plastics based on a signal. In recent years, as plastics have come into widespread use, the degree to which these plastics are mixed into wood chips has increased, and as long as wood chips are used as a raw material for papermaking, these plastics must be removed prior to pulping. The need is increasing. In other words, wood chips currently contain plastic bags, strings, name tags, fragments of containers, toys, other plastic contaminants, and rubber (in this specification, these are collectively referred to as plastics). These plastics often contain a mixture of remains as is. These mixed plastics are further broken down into fine pieces by various mechanical actions such as pumps and beaters during the pulping process, and can hardly be separated by conventional screens. Furthermore, even if cleaners that apply centrifugal force are used, the difference between pulp and foreign matter is small, and plastics usually have a lower specific gravity than pulp, so the separation efficiency is low even though they consume a large amount of power. There was an inconvenience that the amount was extremely low. On the other hand, if paper is made from pulp containing such minute foreign matter, the foreign matter will enter the paper layer and cause dust, pinholes, holes, and even paper breaks. We are struggling to find a way to remove the plastics mixed inside, and the reality is that we are forced to separate them manually. In view of these circumstances, the inventors of the present invention first filed a patent application in 1983.
As the invention of No. 113564, wood chips mixed with plastics are subjected to electrical discharge treatment, and the presence of plastics is detected with an electrometer using the difference in chargeability between the wood chips and plastics. We proposed a method to eliminate this problem. However, as a result of subsequent research, it was confirmed that plastics mixed in wood chips could be separated without performing the electrical discharge treatment as in the earlier application. In other words, plastics are
Even before and after they are mixed into the chips, they become electrically charged due to friction during various processes such as transportation, storage, and processing, and this charge often remains without attenuating. In particular, wood chips are often transported using belt conveyors, etc.
It was confirmed that the plastics mixed in the materials are easily charged due to friction during transportation, whereas the wood chips themselves are hardly charged. Here, the present invention actively utilizes the electrical properties imparted or possessed by wood chips and plastics mixed therein during the distribution process, detects the surface potential difference, and uses the detection signal to detect the difference in surface potential. Plastics are removed or a removal means is activated. Regarding this point, in detail, wood chips generally contain a large amount of water, so their dielectric loss tangent is extremely large, and as a result, charge decay is extremely fast and it is difficult to charge, whereas plastics are Generally, the dielectric loss tangent is low, so the charge decay is slow, and therefore, it is extremely easy to be charged. Furthermore, as mentioned above, wood chips, along with plastics, are subject to friction due to various factors during the distribution or transportation process, which results in significantly different degrees of electrostatic charge.
The gap between the two is getting wider and wider. Now, to give a concrete example, the following table shows the surface potential of plastics in wood chips stored in chip silos or piled up in the open, and the surface potential after they are transferred. , there are considerable differences between them.

【table】

[Table] As described above, the present invention focuses on the difference in surface potential between wood chips and the plastics mixed therein, and actively utilizes the frictional effect during the distribution process of wood chips as necessary to mutually interact them. The difference in surface potential between the two is increased to facilitate detection with an electrometer. To be more specific, wood chips contain a large amount of water and therefore have high electrical conductivity; on the other hand, plastics are insulators and their electrical conductivity is an order of magnitude lower than that of wood chips. In addition to this property, when frictional action is added during the transfer process as described above, the difference in potential between the two becomes larger.
Furthermore, the absolute value of the measured surface potential is much larger than that of wood chips. The present invention utilizes this effect to eliminate the need for discharge treatment prior to measurement. By the way, the present invention is designed to transport wood chips with plastics mixed therein (usually not evenly mixed, but often locally unevenly distributed) on a conveyor belt that has a relatively flat conveying surface, such as a belt conveyor. The surface potential of the plastics mixed in the wood chips is measured using the surface electrometer by distributing and moving the plastics on the wood chips and installing the electrode part of a surface electrometer above the transfer band. At this time, a comparator (potential comparator) is connected to the electrometer, and if necessary, the output of this comparator is introduced to a display device such as a lamp or an alarm, and a timer is activated by the signal from the comparator. Then, after the set time of the timer has elapsed, the belt conveyor is stopped by the output signal of the timer,
Alternatively, as will be described later, it is configured to operate a plastics removal device. The timer is used to cause a certain time delay after the plastics mixed in the chip are detected based on their surface potential. Hereinafter, specific means for separating and removing plastics from wood chips using this method will be generally listed. (1) The output of the surface electrometer is introduced into a comparator, and the output signal of the comparator is introduced into a display device such as an alarm. In such cases, if the surface potential detected by the electrometer exceeds a certain value, a lamp will light or an alarm will sound. On the other hand, since the output signal of the comparator is also supplied to a separately provided timer, the belt conveyor is stopped after a predetermined time delay through the timer. In other words, when plastics are mixed in wood chips, the presence of plastics is detected by a surface electrometer, and when the absolute value of the surface potential exceeds a certain value, a comparator is activated and an alarm sounds and a pilot lamp is activated. In this method, the belt conveyor is stopped after a certain period of time has elapsed via a timer, and only the plastic in the wood chips is manually removed. (2) When the presence of plastic is detected by a comparator connected to an electrometer, the pilot lamp lights up, an alarm sounds, and a timer is activated. After a short delay, the wood chip remover moves on the belt conveyor and removes the plastic. To automatically remove contained wood chips in the lateral direction of a belt conveyor. (3) As a device for removing plastics from wood chips, this device is installed at the discharge end of a belt conveyor, and after it is moved automatically at the right time to remove the wood chips containing the plastic, Another method is to remove plastics by moving them to another location. Note that the comparator used in the present invention is operated so that the lower limit of the absolute value of the measured potential is set in advance and it automatically determines whether the measured value is greater than the lower limit, and is used as a type of potential comparison. It is a vessel. Furthermore, in order to be able to effectively detect the surface potential of plastics in wood chips that are being transferred on a belt conveyor, it is preferred that the wood chips be made into a thin layer and flowed on the belt conveyor.
By the way, the plastics whose presence can be detected with a surface electrometer include polystyrene, polyethylene, polyvinyl chloride, polycarbonate, polyethylene terephthalate, polytetrafluoroethylene, polypropylene, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, epoxy resin, There are synthetic polymer compounds including polyacrylic resins, polyamides, melamine resins, polybutadiene, etc., and copolymers thereof, as well as cellophane, rubbers, etc., and the rate of charge decay is slower than that of wood chips. The size of detectable plastics is 1
Even plastics with a size of 1 mm ^{2 or} more, but with extremely good chargeability, such as polystyrene, polyethylene, and polyester, can be sufficiently detected with an electrometer. Further, it is preferable that the electrode of the surface electrometer be placed as close to the flowing layer of wood chips as possible, and at a position where it does not come into contact with the wood chips. of course,
Since the value of the surface potential differs depending on the electrode position of the electrometer, it is necessary to make corrections. Furthermore, extremely small plastic pieces can also be screened out beforehand using a coarse mesh wire conveyor. The present invention will be specifically described below with reference to the accompanying drawings. Example 1 As shown in FIG. 1, wood chips are continuously dropped from a storage container 1 containing wood chips onto a metal belt conveyor 2 with a mesh of 32 meshes, and the wood chips are indicated by reference numeral 3. Level the chips into a single layer on the conveyor using a leveling rod. The conductive belt conveyor is
This is grounded as shown in the figure, and the moving speed is set to, for example, 10 m/min. Further, the electrode section 5 of the surface electrometer 4 is installed above the belt conveyor 2. When using three scanning type electrodes 5a to 5c as shown in FIG. 5c are arranged so as to each take charge of 1/3 of the width of the belt conveyor,
The conveyor is scanned back and forth at a speed of 20 m/min perpendicular to the transport direction of the conveyor. Note that the scanning type electrode portions 5a to 5
c may be arranged in two or three stages, front and rear. In this manner, the surface potential of the wood chips is detected and measured by the surface potentiometer 4. The output measured by the surface electrometer 4 is
The voltage is introduced into the comparator 7 shown in the figure, and the comparator detects whether or not the potential is higher in absolute value than the reference potential. For example, if the lower limit potential of the comparator 7 is set to -10 volts, and a higher potential than this is detected in absolute value, the pilot lamp 8 is turned on by the detection signal, or the alarm 9 is sounded at the same time. . As mentioned above, when the detection signal of the comparator is emitted, it indicates that plastics are contained in the wood chips. In response to this signal, a separately installed timer 10 is activated, and the driving drum 2a of the conveyor 2 is stopped after a certain period of time has elapsed. Thereafter, the plastics contained in the chips on the belt conveyor are manually removed. Thus, the present invention also includes a method for automatically detecting plastics contained in wood chips and manually removing them. Example 2 Next, an example will be presented in which wood chips containing plastics are automatically and locally removed without manual intervention. In the apparatus shown in FIG. 1, a hopper 11 is attached to the discharge end of the belt conveyor 2, branch pipes 13a and 13b having a sorting damper 12 are disposed in the hopper, and the drive source 14 of the damper 12 is connected to the above-mentioned drive source 14. A signal for timer 10 is supplied. Therefore, the damper 12 is normally set at the position shown by the dashed line in the figure, so that the chips discharged from the conveyor 2 are transported to the receiver 1.
5. If plastics are mixed in the wood chips, their presence is automatically detected as described above, the timer 10 is activated, and after a predetermined period of time, the damper 12 is cut to the position shown by the solid line in the figure. Change. In such a case, the chips containing plastics are stored in the plastic receiver 16 via the branch pipe 13b. Embodiment 3 As a method for removing plastics mixed in wood chips, it is also possible to use the means shown in FIGS. 3-4 or 5. In the former case, a scraper 17 that can be raised and lowered is installed diagonally above the belt conveyor 2 that transfers the chips, and the switching valve of the lifting cylinder 18 is operated by the above-mentioned detection signal and the output signal of the timer 10. This is an example of trying to force someone to do something. That is, the scraper 17 is normally raised as shown by the solid line in FIG. 3, and when the chips containing plastics reach a predetermined transfer position, the scraper is lowered by each of the signals described above. This is automatically removed as shown by the arrow in FIG. In the example shown in FIG. 5, a reciprocating plastic receiver 20 attached to the piston rod of the cylinder 19 is disposed at the discharge end of the conveyor 2.
In this case, an electromagnetic solenoid spool valve 21 is switched via the output signal of the timer 10, whereby the plastics are automatically removed. Embodiment 4 Figure 6 shows an example of transformation when detecting the surface potential of wood chips and plastics mixed therein.As a non-scanning surface potential meter, model SSV- manufactured by Kawaguchi Electric Co., Ltd. is used. 40 is placed 4cm above the belt conveyor, 1
Since the detection area of each electrode 5d is 7 to 8 cm wide, when this is applied to a belt conveyor with a width of 60 cm, it is sufficient to arrange 8 electrodes in the horizontal direction.
In some cases, the electrodes may be arranged in a staggered manner in two rows, front and rear, as shown in the figure. Further, when a plurality of electrodes are used, when any one of the electrodes detects a potential higher than the set potential of the comparator 7, an output signal of the comparator is generated. Note that since the belt conveyor needs to serve as a counter electrode to the electrode portion of the surface electrometer, it is necessary to use a conductive material and to ground it. The time from detecting the presence of mixed plastics to activating the damper 12, scraper 17, reciprocating plastic receiver 20, etc. depends on the transfer speed of the belt conveyor 2 and the electrodes 5, 5a to 5a. Since it is related to the mounting position of 5d and also depends on the distance to the end of the conveyor, it is set appropriately taking these into consideration. The relative relationships in each of the above embodiments are listed below.

[Table] Incidentally, the surface potential of plastics varies depending on the size, shape, composition, etc. of the plastic. Furthermore, even if wood chips or plastics become wet due to rain, etc., the difference in their surface potentials can be sufficiently detected. Example 5 Figure 7 shows an example in which the surface potential of plastics mixed in wood chips is detected after positively charging them. This is an example in which the surface potential increases due to frictional action, etc., so this action is utilized and the chip transfer operation required for pulping is also carried out. The thing indicated by the reference numeral 22 in the figure is a screw conveyor, and the wood chips C are piled up in the open.
As an example, a screw conveyor 22 with a length of 5 m
is supplied to the belt conveyor 2 disposed above it by the conveying action of the conveyor.
Send it to 3. At this time, by appropriately controlling the transfer speed of the screw conveyor, the chips can be transferred onto the belt conveyor in a thin layer, so there is no need to take the trouble of attaching a leveling rod to make the layer thin. By the way, it is desirable that the screw conveyor in this case is not grounded and is electrically insulated. The construction of the belt conveyor 23 and the electrode section for detecting surface potential placed above it is the same as in the first embodiment except for the leveling bar. The values of the surface potential of plastics when using the screw conveyor shown in FIG. 7 are shown below.

【table】 [Brief explanation of drawings]

Fig. 1 is a skeletal side view of an example of an apparatus for implementing this method, Fig. 2 is a skeletal cross-sectional view showing a scanning electrode in the same device, and Fig. 3 is a skeletal cross-sectional view showing a scanning electrode used in the above device. 4 is a plan view of a portion of the same as above; FIG. 5 is a vertical sectional view of a portion of another embodiment of the plastics removal device; FIG. 6 is a surface potential diagram. FIG. 7 is a side view schematically showing an embodiment in which a screw conveyor is used. 1: Wood chip storage device, 2, 23: Metal belt conveyor, 3: Bar for leveling, 4: Surface electrometer, 5, 5a to 5d: Electrode, 6: Guide rod,
7: Comparator, 8: Lamp, 9: Alarm, 1
0: Timer, 11: Hopper, 12: Damper, 13
a, 13b: Branch pipe, 14: Damper drive device, 1
5: Wood chip receiver, 16: Plastics receiver, 17: Scraper, 18, 19: Cylinder, 20: Reciprocating plastic receiver, 21:
Spool valve, 22: Screw conveyor.

Claims (1)

[Claims] 1. In separating plastics from wood chips in which plastics are mixed,
The mixture of wood chips and plastics is distributed in a single layer on the surface of the transport zone, and while it is being transferred, the electrodes of the surface electrometer placed above it are used to measure the surface of the wood chips and plastics. detecting a potential difference and stopping the movement of the transport band based on the detection signal;
Alternatively, a method for separating plastics mixed in wood chips, comprising activating a plastics removing means attached to the transfer zone. 2. Wood chips mixed with plastics are guided to a conveyance mechanism, and the conveyance mechanism applies a frictional effect, thereby charging the plastics so that they have a higher electric potential in absolute value than the wood chips. Then, the relative potential difference between the wood chips and plastics is increased, the potential difference is detected by a surface electrometer, and the detection signal is used to stop the contaminant transport mechanism or to stop the transport mechanism. 2. A method according to claim 1, further comprising activating means for removing plastics attached to the plastic. 3. The scope of claims that comprises transporting wood chips mixed with plastics on a conveyor having a conductive belt, and disposing a scanning or fixed surface potential detection electrode above the conveyor. The method according to item 1 or 2. 4 Introduce the output of the surface electrometer to the comparator,
The output signal of the comparator operates a display device such as a pilot lamp or an alarm, and
4. A method as claimed in claim 1, 2 or 3, characterized in that said output signal is passed to a timer to activate a device for removing plastics after the time set by said timer has elapsed. 5. A hopper having a branch pipe is disposed at the discharge end of the belt conveyor, and a damper for sorting is attached to the branch part of the branch pipe. The method described in Section 4. 6. A method as claimed in claim 1, 2, 3 or 4, characterized in that a reciprocating plastic receiver is attached to the discharge end of the belt conveyor.