JPS61274714A - Method for washing filter apparatus - Google Patents

Abstract

PURPOSE:To remove adverse effect due to high conc. brine, in washing the filter apparatus having a packed bed comprising a particulate filter agent of a seawater desalting process, by substituting residual seawater with air or fresh water before washing the suspended substance of the packed bed with fresh water. CONSTITUTION:Seawater is allowed to flow in from a seawater inflow pipe 5 and sent to a reverse osmosis membrane through a valve 11, a filter tower 1 and a valve 12. When a suspended substance is caught by a filter packed bed and pressure loss increases, the valves 11, 12 are closed and valves 13, 14 are subsequently opened and air is flowed in from an air inflow pipe 6 to discharge seawater from a discharge pipe 9. The valve 14 is opened and the valve 13 is closed while a valve 15 is opened to allow fresh water to flow in from a fresh water inflow pipe 7 and, subsequently, the valve 14, 15 are closed and valves 13, 16 are opened to allow air to flow in from the air inflow pipe 6. Next, the valves 13, 16 are closed and valves 17, 18 are opened to allow air to flow in and, subsequently, the valves 17, 18 are closed and valves 19, 20 are opened to allow fresh water to flow in and the filter packed bed is expanded to perform backwashing.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for cleaning a seawater filtration device installed upstream of a seawater desalination device using a reverse osmosis membrane device.

<Prior art> A method of obtaining fresh water from seawater using a reverse osmosis membrane device has been practiced for some time, but in order to prevent contamination of the reverse osmosis membrane used in the reverse osmosis membrane device, it is generally necessary to Various filtration devices will be installed.

A filtration device in which a filtration tower is filled with a granular filter agent such as silica sand or anthracite is mainly used as the filtration device. The layer traps and filters suspended matter.

<Problems to be Solved by the Invention> As the filtration device continues to filter seawater, suspended solids are trapped in the voids of the filler layer, resulting in an increase in pressure loss, so that the pressure loss remains constant. When the value of is reached, the filler layer is cleaned as follows. That is, washing water flows upwardly at a relatively high flow rate from below the filler layer, expands the filler layer to some extent, and washes away suspended solids trapped in the voids of the filler from the upper part of the filtration tower. Note that air for stirring may be introduced from below the filler layer prior to or during the cleaning.

Although such cleaning generates cleaning wastewater containing a large amount of suspended solids, it may not be possible to discharge the cleaning wastewater as it is due to SS regulations. Therefore, in such a case,
Although it is necessary to treat the washing wastewater to concentrate suspended substances in the wastewater and take it out as solid matter, seawater filtration devices have the following problems.

That is, generally when treating the washing wastewater of a filtration device, a polymer flocculant is added to the wastewater to coagulate and precipitate suspended substances in the washing wastewater, and the precipitate is concentrated using a centrifuge or the like.
Solids are then obtained using various dewatering devices such as a belt press, but even if fresh water is used as the washing water, the washing wastewater in the seawater filtration device described above is contaminated with seawater remaining in the filtration tower at the end of filtration. Therefore, the salt M tl
jJ degree is high.

Therefore, in the case of such high salt concentration water, even if a polymer flocculant is added thereto, its flocculating action is inhibited, which impedes the coagulation-sedimentation operation. In addition, the materials used for the sedimentation tanks, concentrators such as centrifuges, and dehydrators must be made of materials that are resistant to corrosion against water containing high salt concentrations, resulting in a significant increase in manufacturing costs. be.

The present invention has been made in view of the problems in conventional seawater filtration equipment, and it reduces the salt concentration of the washing wastewater, and the above-mentioned method for concentrating suspended solids in the washing wastewater and extracting them as solids. The purpose of this project is to solve the following problems.

<Means for Solving the Problems> The present invention provides a method for producing seawater and fresh water by filtering seawater through a filtration device comprising a packed bed of granular filtering agents such as silica sand or anthracite, and treating the filtered water with a reverse osmosis membrane device to obtain freshwater. When cleaning the filtration device in the filtration process, the seawater remaining in the packed bed at the end of filtration is replaced with air or fresh water, and then the suspended solids trapped in the packed bed are washed with fresh water. The present invention relates to a method for backwashing a filtration device.

<Effect> The present invention will be explained below with reference to the drawings.

The drawing is an explanatory flow diagram showing an example of an embodiment of the filtration device used in the present invention, in which a filtration tower 1 is filled with silica sand 2 and anthracite 3 in two layers, and 4 indicates an inflow of the filtration tower 1. A pressure loss indicator and an alarm meter connected to the pipe and the outflow pipe, 5 indicates the seawater inflow pipe, 6 the air inflow pipe, 7 the freshwater inflow pipe, 8 the filtration water pipe, 9 the discharge pipe, 1o
11 and 22 respectively indicate cleaning waste water pipes, and 11 to 22 indicate valves, respectively.

First, when filtering seawater, open the valves 11 and 12, let seawater flow in from the seawater inflow pipe 5, pass through the two-layer filtration packed bed of anthracite 3 and silica sand 2, and filter water from the filtration water pipe 8. The filtered water is then passed through a filtered water storage tank (not shown) and treated with a reverse osmosis membrane device (not shown) to obtain fresh water and concentrated water.

As such filtration continues, suspended matter contained in the seawater is captured by the filtration packed bed, resulting in an increase in pressure loss, and the pressure loss indicator/alarm meter 4 is activated to close the valves 11 and 12, causing the filtration to proceed. end.

Next, the valves 13 and 14 are opened, air flows in through the air inflow pipe 6, the seawater in the filter tower 1 is replaced with air, and the seawater pushed out by the air is discharged through the discharge pipe 9 (cleaning preparation , extrusion). Next, close the valve 13 while leaving the valve 14 open, and open the valve 15 to allow fresh water to flow in through the fresh water inflow pipe 7 to wash away the seawater adhering to the filtration packed bed, and then transfer this wastewater to the discharge pipe 9 in the same way. (cleaning preparation, replacement). Next, the valves 14 and 15 are closed, and the valves 13 and 16 are opened, and air is introduced through the air inflow pipe 6 to push out the water in the freeboard of the filtration tower 1, which is then discharged through the discharge pipe 9. (preparation for cleaning, draining water).

The seawater etc. flowing out from each of the extrusion, displacement, and water removal steps for cleaning preparation described above does not contain suspended substances and can be discharged as is. Further, through the above steps, the seawater in the filter tower 1 including the filter packed bed is replaced with fresh water.

Next, the valves 13 and 16 are closed, and the valves 17 and 18 are opened to allow air to flow in through the air inflow pipe 6 to agitate the filtration packed bed with air (bubbling).

Next, valves 17 and 18 are closed, valves 19 and 20 are opened, and fresh water flows upward into the filtration tower 1 from the fresh water inflow pipe 7 to expand the filtration packed bed, which is called backwashing. , the cleaning wastewater is sent to a cleaning wastewater treatment facility such as a coagulation sedimentation tank (not shown) via the cleaning wastewater pipe 10 (cleaning 1
). Although the washing wastewater contains a large amount of suspended solids,
Since the inside of the filtration tower 1 including the filtration packed bed is replaced with fresh water before washing, the salt content is low.

Next, the valves 19 and 20 are closed, and the valves 21 and 22 are opened, and seawater flows upward from the seawater inflow pipe 5, replacing the fresh water in the filter tower 1 with seawater (washing 2). Note that the effluent from this process does not contain suspended substances, so the effluent can be discharged.

Next, the valves 21 and 22 are closed to perform settling, and then the valves 11 and 14 are opened to allow seawater to flow downward from the seawater inlet pipe 5 for washing (3), and after the filtrate has stabilized, the valve 14 is
is closed, and the valve 12' is opened to continue the above-mentioned filtration.

Table 1 summarizes the above steps. The time shown in the table is just a reference time.

Table 1: Operational Operation Table Note that the cleaning step 2 may be omitted depending on the case.

Furthermore, in the above explanation, the seawater remaining in the filtration tower was first pushed out with air at the end of filtration, but this step is omitted and fresh water is simply flowed downward into the filtration tower filled with seawater. There is no problem in replacing the inside of the filtration tower, including the packed bed, with fresh water.

<Effects> As explained above, in the present invention, before cleaning the filtration device, the inside of the filtration tower including the packed bed remaining at the end of filtration is replaced with air or fresh water. The concentration is low, so coagulation and sedimentation treatment of suspended solids in washing wastewater can be carried out without any problems, and the materials used for treatment equipment such as sedimentation tanks, centrifuges, and dehydrators must be particularly corrosion-resistant. Nor.

<Example> Seawater was filtered using a filtration device as shown in the drawing with diameter 280 (1+ m, height 3000 mm, silica sand packed bed height 60On+, anthracite packed bed height 500+n), and then fresh water of TD 32000 ■/l was filtered. When the operation was carried out according to the steps shown in Table 1, washing wastewater with a TDS of 2200/β containing a large amount of suspended solids was obtained in the washing 1 step, and the washing wastewater contained polymer agglomerates. When a coagulation and sedimentation treatment was carried out by adding the agent, a good floc was obtained and the treatment could be carried out without any problems.

[Brief explanation of the drawing]

The drawing is an explanatory diagram of a flow showing an example of an embodiment of the filtration device used in the present invention. ■...Filtering tower 2...Silica sand 3...Anthracite 4...Pressure loss indicator/alarm gauge 5...Seawater inflow pipe 6...Air inflow pipe 7...Fresh water inflow pipe
8...Filtering wood pipe 9...Discharge pipe 1o...
Washing waste water pipes 11-22...valve

Claims (1)

[Claims] When cleaning the filtration device in a seawater desalination process in which seawater is filtered through a filtration device consisting of a packed bed of granular filtering agents such as silica sand or anthracite, and fresh water is obtained by treating the filtrated water with a reverse osmosis membrane device, A method for cleaning a filtration device, which comprises replacing seawater remaining in a packed bed at the end of filtration with air or fresh water, and then using fresh water to wash suspended matter trapped in the packed bed.