JP2014151278A - Method for cleaning sand filter apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten time required for a rinse step carried out during cleaning operation of a sand filter apparatus.SOLUTION: A method for cleaning a sand filter apparatus comprises: a liquid drain step of discharging raw sea water sw (water to be treated) from a filter sand layer 16 after filtering of the raw sea water sw; a gas cleaning step of introducing air a from the outlet side of a housing 14 after the liquid drain step and removing impurities captured in the filter sand layer 16 from the filter sand layer 16; an impurity discharge step of introducing concentrated sea water cs (cleaning water) from the outlet side of the housing 14 into the filter sand layer 16 and discharging the removed impurities together with the concentrated sea water cs from the filter sand layer 16; a cleaning water discharge step of flowing down the concentrated sea water cs from the filter sand layer 16 by a gravity force after the impurity discharge step; and a rinse step of introducing the raw sea water sw as rinse water into the filter sand layer 16 from the inlet side of the housing 14 and adjusting the layer state of the filter sand layer 16 while replacing the concentrated sea water cs remained in the filter sand layer 16 with the raw sea water sw.

Description

  The present invention relates to a cleaning method capable of shortening the time required for cleaning a filter sand layer in a sand filter provided in a seawater desalination plant, for example.

  In the seawater desalination plant, the process of desalinating seawater is a pre-treatment that removes impurities contained in the raw seawater with a sand filter, and then distills the seawater to produce fresh water, The salt content of seawater is concentrated and separated by applying a pressure to seawater and passing through a filtration membrane called a reverse osmosis membrane, and the salt content is removed from the seawater using a reverse osmosis method that produces fresh water. Patent Document 1 discloses a process for producing non-ionized water such as drinking water and industrial water from seawater. In this production process, after removing relatively large contaminants such as garbage and microorganisms in the raw seawater using a sand filtration device, the membrane is subjected to a membrane separation process using an ion exchange membrane or a reverse osmosis membrane and an evaporative concentration step, followed by a salt content. Non-ionized water from which water has been removed is produced.

  The trapped impurities are deposited on the filter sand layer provided in the sand filter and clogged if left as it is. Therefore, it is necessary to remove the deposited impurities from the filter sand layer. In order to remove impurities from the filter sand layer, a back-flow cleaning method is used in which washing water is introduced into the filter sand layer from the outlet side of the filter sand layer to remove impurities trapped on the surface or inside of the filter sand layer. Patent Document 2 discloses a backwashing method for such a sand filtration device.

JP 2009-95821 A Japanese Patent Laid-Open No. 2005- 211804

The washing operation of the sand filtration device requires less frequent backwashing because the accumulation of impurities in the filter sand layer is slow when the properties of the raw seawater, which is the main component of the washing water, are clear. In the case of dirty seawater containing a large amount of impurities, the accumulation of impurities in the filter sand layer is accelerated, and therefore the frequency of cleaning work must be increased.
On the other hand, in order not to interrupt the operation of the treatment facility during the cleaning of the sand filtration device, usually two or more sand filtration devices are provided in parallel to the introduction path of the water to be treated. The to-be-processed water here is the raw water processed with a sand filtration apparatus, and is a seawater in a seawater desalination plant. In addition, a large number of sand filtration devices are provided when the processing capacity of the processing equipment is large. In this case, if the cleaning time of one sand filter device becomes long, the operation time of the processing facility is affected, and the cleaning time of other sand filter devices cannot be taken sufficiently.

  Accordingly, the present inventors examined a cleaning method capable of shortening the cleaning time while maintaining the effect of removing impurities, and considered a cleaning method described below. This cleaning method will be described with reference to FIGS. FIG. 2A shows a case where clear seawater is handled in a seawater desalination plant, and FIG. 2B shows a case where dirty seawater containing a large amount of impurities is handled.

  In FIG. 2 (A), first, the liquid is removed to remove the raw seawater remaining in the filter sand layer (liquid draining step). Next, air is blown in from the outlet side of the filter sand layer, and impurities adhering to the inside of the filter sand layer and the inlet side surface are peeled off (air washing step). Furthermore, washing water is introduced from the outlet side of the filter sand layer to wash the filter sand layer (water washing step). As the washing water, for example, concentrated seawater separated in a subsequent separation step performed using a reverse osmosis device or the like, or filtered seawater from which impurities have been removed by a sand filtration device may be used. After the water washing process, the washing water remaining in the filter sand layer is replaced with rinse water (for example, sea water having sea water having the same quality as the raw sea water or the like) and the filter sand layer in which the layer state is disturbed by backwashing is prepared. Processing is performed (rinse process). According to this cleaning method, it is possible to remove impurities in a short time by using both the air cleaning step and the water cleaning step.

  However, in the rinsing process, the washing water (concentrated seawater, etc.) used in the water washing process and the rinsing water are mixed in the filter sand layer, so it takes a lot of time to completely replace the rinsing water. I understood. In particular, as shown in FIG. 2B, dirty seawater containing a large amount of impurities requires a longer rinsing time than clear seawater. On the other hand, if the time for the rinsing process is shortened, the replacement is insufficient and the washing water may flow out to the subsequent process. In that case, the reverse osmosis membrane provided in the security filter and the reverse osmosis device provided in the subsequent stage may be clogged, resulting in an increase in the differential pressure before and after the membrane and a decrease in the life. For this reason, it is necessary to replace the cleaning water with the rinsing water at an early stage to shorten the time required for the rinsing process.

  An object of this invention is to shorten the time which the rinse process performed in the washing | cleaning operation | work of a sand filter apparatus in view of the subject of this prior art.

  In order to achieve this object, the sand filtration device cleaning method of the present invention is a cleaning method using the backflow cleaning method, and after the water to be treated is filtered, the water to be treated remaining in the sand filtration device is discharged. A liquid draining process, a gas cleaning process for introducing gas from the filtered water outlet side of the sand filtration device after the liquid draining process, and separating impurities trapped in the sand filter layer from the sand filter layer; The washing water is introduced from the outlet side of the filtered water of the filtration device, and the separated impurities are discharged from the sand filtration device together with the washing water. After the impurity discharging step, the washing water is caused to flow down from the filtered sand layer by gravity. The washing water discharge process for discharging from the sand filtration device, the rinse water is introduced into the filter sand layer from the inlet side of the sand filter device, the washing water remaining in the filter sand layer is replaced with the rinse water, and the layer state of the filter sand layer is changed. A rinsing process to prepare

  In the present invention, after the impurity discharge step, a wash water discharge step is provided in which the wash water is dropped from the filter sand layer by gravity. After the washing water in the filter sand layer is discharged in the washing water discharging step, the rinsing step is performed, so that the washing water and the rinsing water are not mixed in the rinsing step. Thereby, since the replacement with rinsing water can be accelerated, the time required for the rinsing process can be shortened, and the operation of the sand filter can be resumed promptly. In addition, since mixing of washing water and rinsing water does not occur, even if the time required for the rinsing process is shortened, replacement does not become insufficient, and even after resuming operation of the sand filtration apparatus, washing water and separated impurities are not present. There is no risk of spilling into subsequent processes. Therefore, clogging of a filter or the like of the device arranged in the subsequent stage can be eliminated, and the life reduction can be prevented.

In one embodiment of the present invention, the time when the wash water flowing down from the filter sand layer is changed from a continuous water flow to intermittent water droplets in the wash water discharge step can be set as the time when discharge of the wash water is completed.
It can be easily observed from the outside of the sand filtration device that the washing water flowing down from the filter sand layer changes from a continuous water flow to intermittent water droplets. Therefore, it is possible to easily know from the outside of the sand filtration device when the washing water is completely discharged, and it is possible to quickly move to the rinsing process.

  In one aspect of the present invention, when a plurality of sand filtration devices are arranged in parallel to the introduction path of the water to be treated, after the washing of one sand filtration device is completed, the other sand filtration devices are washed. It is recommended to start work. In this case, the other sand filter can be operated while one sand filter is being cleaned. Moreover, since the rinsing time can be shortened according to the present invention, even when there are a plurality of sand filtration devices, the washing step can be performed with sufficient margin for each sand filtration device. Accordingly, it is possible to secure a sufficient operation time of facilities such as a seawater desalination plant in which a sand filtration device is incorporated, and the quality of filtered water after restart is not reduced.

  ADVANTAGE OF THE INVENTION According to this invention, in the washing | cleaning process of a sand filtration apparatus, the time which a rinse process requires can be shortened, without producing replacement short with washing water and rinse water. Therefore, the backwashing process can be carried out with a sufficient margin even in a facility in which a plurality of sand filtration devices are arranged without causing clogging of a safety filter, a reverse osmosis membrane, or the like provided in the subsequent stage.

It is a block diagram of the sand filtration apparatus concerning a 1st embodiment of the present invention. (A) And (B) is a flowchart of the cleaning process as an intermediate technique considered by the present inventors, and (C) is a flowchart of the cleaning process in the first embodiment. It is a block diagram of the sand filter apparatus which concerns on 2nd Embodiment of this invention. It is a diagram which shows the procedure of the backwashing process of the said 2nd Embodiment.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

(Embodiment 1)
1st Embodiment of this invention is described based on FIG.1 and FIG.2 (C). FIG. 1 shows a sand filtration apparatus according to the present embodiment incorporated in, for example, a seawater desalination plant. In FIG. 1, a sand filter device 10 </ b> A according to this embodiment includes a sand filter 12. The sand filter 12 has a housing 14 filled with a filter sand layer 16 over the entire cross section. A raw seawater introduction path 18 is connected to the housing wall above the filter sand layer 16, and a filtered seawater discharge path 22 for discharging the filtered seawater fs filtered by the filter sand layer 16 is connected to the bottom wall of the housing 14. Yes. The raw seawater introduction path 18 is provided with a pump 20 that sends the raw seawater sw to the sand filter 12.

  The bottom wall of the housing 14 is provided with an air introduction path 24 through which air a is introduced when an air cleaning process is performed in a cleaning operation. The bottom wall of the housing 14 is connected with a concentrated seawater introduction path 26 for introducing concentrated seawater cs as cleaning water from a reverse osmosis device 34 provided at a later stage when performing a water washing process in a washing operation. Yes. Further, a concentrated seawater discharge path 28 for discharging the concentrated seawater cs supplied to the sand filter 12 in the water washing step is connected to the upper wall of the housing 14. Further, a rinse water discharge passage 30 for discharging rinse water (raw seawater sw) is connected to the bottom wall of the housing 14 when the rinse process is performed.

  In such a configuration, during normal operation of the seawater desalination plant, the raw seawater sw is introduced into the housing 14 from the raw seawater introduction path 18 by the pump 20. The filter sand layer 16 removes relatively large contaminants such as garbage and microorganisms from the raw seawater sw. The filtered seawater fs from which impurities have been removed is sent to the subsequent stage through the filtered seawater discharge path 22. The rear stage side of the filtered seawater discharge path 22 is connected to the security filter device 32, and the impurities remaining in the filtered seawater fs are removed just in case.

  The filtered seawater discharge path 22 is connected to the reverse osmosis device 34 on the rear side of the security filter device 32. The reverse osmosis device 34 has a reverse osmosis membrane, and separates the filtered seawater fs into filtered water w from which salt is removed and concentrated seawater cs containing concentrated salt. The filtered water w is sent from the filtered water supply path 36 to the post-processing step, and the concentrated seawater cs is discharged to the concentrated seawater discharge path 38. In the water washing step at the time of a washing operation described later, a part of the concentrated seawater cs is introduced as cleaning water into the housing 14 from the concentrated seawater introduction path 26 to wash the filter sand layer 16.

  FIG. 2C shows the cleaning process of this embodiment. In the washing process, first, the raw seawater sw remaining in the filter sand layer 16 is discharged (liquid draining process). In the discharging method, the remaining raw seawater sw is naturally flowed down by gravity, and the liquid level is lowered to the vicinity of the upper surface of the filter sand layer 16.

  After the liquid draining step, air a is blown into the lower portion of the housing 14 from the air introduction path 24, and the air a is passed through the filter sand layer 16. Thus, impurities trapped in the filter sand layer 16 are peeled off from the filter sand layer 16 (air washing step). Next, the concentrated seawater (washing water) cs is introduced from the concentrated seawater introduction path 26 into the lower part of the housing 14 and passed through the filter sand layer 16. Thereby, the peeled impurities are removed, and the impurities are discharged from the concentrated seawater discharge passage 28 (water washing step).

  Next, the introduction of the concentrated seawater cs is stopped, and the process proceeds to the liquid discharge process. In the liquid draining step, the concentrated seawater cs remaining in the filter sand layer 16 is caused to flow down from the filter sand layer 16 by gravity. The time when the concentrated seawater cs flowing down from the filter sand layer 16 changes from a continuous water flow to intermittent water droplets is defined as the completion of the liquid discharge step. Next, the raw seawater (rinse water) sw is introduced into the filter sand layer 16 from the raw seawater introduction channel 18, and the concentrated seawater cs remaining in the filter sand layer 16 is completely replaced with the raw seawater sw and is disturbed in the backwash process. The sand layer 16 is prepared (rinse process). This completes the cleaning operation and returns to normal operation.

  According to the present embodiment, after the water washing process, the liquid discharge process is performed, and after the concentrated seawater cs remaining in the filter sand layer 16 is removed, the rinse step is performed, whereby the concentrated seawater cs and the raw seawater sw It is not mixed in the grit sand layer 16. Thereby, the time which can be replaced with the raw seawater sw can be accelerated, and the time required for the rinsing process can be shortened. Therefore, even when dirty seawater is handled, it can be shortened to the same time as the rinse time shown in FIG. 2 (A), and the operation of the plant is not hindered. Further, even if the rinsing time is shortened, the replacement does not become insufficient, and there is no possibility that the concentrated seawater or impurities will flow out to the subsequent safety filter device 32 or the reverse osmosis device 34. Therefore, the safety filter 32 and the reverse osmosis device 34 provided in the subsequent stage are not blocked, and the life of the filter or the like can be prevented from being reduced.

  Further, in the liquid discharge step, when the concentrated seawater cs flowing down from the filter sand layer 16 is changed from a continuous water flow to intermittent water droplets, the point in time when the discharge of the concentrated seawater cs is completed, thereby discharging the concentrated seawater cs. The completion time can be clearly identified from the outside of the sand filter 12. Moreover, since the concentrated seawater cs does not substantially remain in the filter sand layer 16 when the flow of the concentrated seawater cs changes from a water flow to a water droplet, setting this time as the completion time does not cause any trouble. Therefore, it is easy to grasp when the liquid discharge step is completed, and the transition to the rinse step can be quickly performed.

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to FIGS. In the sand filtration device 10B of the present embodiment, a large number of sand filters 12 are arranged in parallel to the raw seawater introduction path 18 to increase the pretreatment capacity of the seawater desalination plant. FIG. 3 shows the configuration. 3, a large number (three or more) of sand filters 12a, 12b, 12c,... Each filtered seawater discharge path 22 of each sand filter is provided with one security filter device 32a, 32b, 32c,. Similarly to the first embodiment, each sand filter is connected to a raw seawater introduction path 18, a filtered seawater discharge path 22, a concentrated seawater introduction path 26, and a concentrated seawater discharge path 28.

  Two reverse osmosis devices 34 a and 34 b are connected in parallel to the downstream end of the filtered seawater discharge passage 22. Other configurations are the same as those of the first embodiment. The filtered seawater fs filtered by each sand filter is removed from the reverse osmosis device 34a or 34b by opening and closing the switching valves 40a and 40b after the remaining impurities are removed by the respective security filter devices. Of reverse osmosis equipment. The filtered water w filtered by the reverse osmosis device is sent from the filtered water supply path 36 to a subsequent processing device (not shown).

The concentrated seawater cs whose salinity is concentrated by the reverse osmosis device 34 a or 34 b is discharged from the concentrated seawater discharge path 38. A part of the concentrated seawater cs is returned to the sand filter from the concentrated seawater introduction path 26 as cleaning water when any sand filter is cleaned.
FIG. 4 assumes a case where the cleaning time of one sand filter takes 2 hours. As shown in FIG. 2, in the cleaning process of each sand filter in the present embodiment, since one sand filter can be operated while one sand filter is being cleaned, one sand filter is used. Repeat for each vessel. That is, two or more sand filters are not washed at the same time, and after one sand filter has been washed, another sand filter is started to be washed.

  According to this embodiment, since the rinsing time can be shortened as in the first embodiment, even in a plant provided with a large number of sand filters, the washing operation is performed with sufficient margin for each sand filter. be able to. Therefore, the operation of facilities such as a plant in which the sand filtration device is incorporated can be continued without hindrance, and the quality of water to be treated existing in the sand filtration device is not lowered after the operation is resumed.

  According to the present invention, since the cleaning operation of the sand filtration device can be shortened, the water quality is poor, and even when dirty seawater containing a large amount of impurities is processed, the operation of the processing equipment is not hindered.

10A, 10B Sand filtration device 12, 12a, 12b, 12c Sand filter 14 Housing 16 Filter sand layer 18 Raw seawater introduction path 20 Pump 22 Filtration seawater discharge path 24 Air introduction path 26 Concentrated seawater introduction path 28, 38 Concentrated seawater discharge path 30 Rinse water discharge passage 32, 32a, 32b, 32c Safety filter device 34, 34a, 34b Reverse osmosis device 36 Filtrated water supply passage 40a, 40b Switching valve a Air (gas)
cs Concentrated seawater (wash water)
fs filtered seawater sw raw seawater (treated water, rinse water)
w Filtration water

Claims (3)

Washing from the outlet side of the filtered water of the sand filtration device to the sand filtration device that has a filtered sand layer provided in the housing, filters the treated water by passing through the filtered sand layer, and generates filtered water In the washing method of the sand filtration device for introducing impurities and removing the impurities trapped in the filter sand layer by backwashing,
A liquid draining step for discharging the treated water remaining in the sand filtration device after the treated water is filtered;
After the liquid draining step, a gas washing step of introducing a gas from the filtered water outlet side of the sand filtration device and separating impurities trapped in the filter sand layer from the filter sand layer;
Impurity discharging step of introducing cleaning water into the filtered sand layer from the filtered water outlet side of the sand filtering device, and discharging the separated impurities from the sand filtering device together with the cleaning water (cs),
After the impurity discharging step, the washing water is caused to flow down from the filter sand layer by gravity, and the washing water discharging step is discharged from the sand filtration device,
A rinsing step of introducing rinsing water (sw) into the filter sand layer from the inlet side of the sand filtration device, replacing the washing water remaining in the filter sand layer with the rinse water, and adjusting a layer state of the filter sand layer; A method for cleaning a sand filtration device, comprising: In the washing water discharge step,
2. The sand filtration device according to claim 1, wherein the time when the wash water flowing down from the filter sand layer is changed from a continuous water flow to intermittent water droplets is a time point when discharge of the wash water is completed. 3. Cleaning method. A plurality of the sand filtration devices are arranged in parallel to the introduction path of the treated water,
The method for cleaning a sand filter according to claim 1 or 2, wherein a cleaning process for another sand filter is started after the cleaning process for one sand filter is completed.

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