JP2021084040A - Coal wastewater treatment method and device - Google Patents

Abstract

To provide a coal wastewater treatment method and device that can effectively control the concentration of solids in wastewater under membrane filtration treatment and can effectively use the solids drawn out from the wastewater.SOLUTION: This coal wastewater treatment device is provided with: a membrane treatment tank 20 into which wastewater is introduced that is discharged from a device (conveyor C) for handling coal or coal ash; and a porous membrane 22 which is arranged inside of the membrane treatment tank 20 and which filters wastewater. Solids in the wastewater are concentrated and drawn out in the form of slurry, and in a case where the concentration of the solids in the slurry drawn out from the wastewater is equal to or higher than a threshold value, the slurry is returned to the device C.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method and apparatus for treating coal wastewater.

Generally, in equipment that handles coal and coal ash, water may be sprinkled on the equipment. For example, in a coal-fired power plant lifting facility, coal as fuel is transported from a coal storage yard using a conveyor, crushed by a mill, supplied as pulverized coal to a boiler burner, and burned. In such a coal lifting facility, water is sprinkled on a conveyor, which is one of the devices, for the purpose of suppressing the temperature rise of coal and the diffusion of pulverized coal, and maintaining the function of the device. After the water is sprinkled, the washing water is recovered, the pulverized coal is removed, and the water is reused.

The following Patent Document 1 describes an example of a conveyor cleaning facility and a wastewater treatment device in such a coal lifting facility. The coal wastewater treatment apparatus described in Patent Document 1 includes a settling tank and a membrane treatment tank, and the wastewater collected from the conveyor is stored in the settling tank, and the pulverized coal or the like in the wastewater is settled. After removal, the supernatant is transferred to the membrane treatment tank and filtered through a porous membrane.

JP-A-2019-130450

In the treatment apparatus as described above, the concentration of solid matter is adjusted in the sedimentation tank before filtration is performed in the membrane treatment tank. Here, the processing capacity of the settling tank depends on the volume of the tank in principle. In particular, when natural sedimentation is performed in a sedimentation tank, the drainage must stay in the tank for a reasonable period of time in order to sufficiently sediment the pulverized coal, etc., so the volume required for the sedimentation tank is treated per unit time. It is proportional to the amount. That is, when considering adjusting the concentration of solid matter by the sedimentation tank, the larger the amount of wastewater, the larger the volume and volume of the entire equipment. Therefore, it has been required to realize a mechanism for adjusting the concentration of solid matter in the membrane treatment tank regardless of the sedimentation tank.

The concentration of the solid matter can be adjusted by concentrating and extracting the solid matter from the wastewater to be subjected to the membrane filtration treatment. That is, if the solid matter is removed from the wastewater of the membrane treatment tank by membrane filtration, the concentration of the solid matter in the remaining wastewater becomes higher accordingly, so if the solid matter is removed from the wastewater remaining in the tank, the inside of the tank The solid matter concentration can be maintained.

Here, when wastewater that has not undergone sedimentation treatment is treated in a membrane treatment tank, the amount of solid matter extracted as a result of adjusting the concentration of solid matter in the membrane treatment tank is considerable, but coal wastewater is subject to purification treatment. If so, the solid matter recovered here may be reused as coal for fuel depending on the condition.

In view of such circumstances, the present invention effectively adjusts the concentration of solid matter in wastewater to be subjected to membrane filtration treatment, and can effectively utilize the solid matter extracted from the wastewater. It is intended to provide a device.

The present invention comprises a membrane filtration step of filtering wastewater collected from equipment handling coal or coal ash with a porous membrane, a concentration step of concentrating solid matter in wastewater, and a solid matter in slurry that has undergone the concentration step. The present invention relates to a method for treating coal waste including a slurry recycling step of reusing the slurry in the apparatus when the concentration is equal to or higher than a threshold value.

The method for treating coal wastewater of the present invention may include a slurry recirculation step of returning the slurry to the membrane filtration step or the concentration step when the concentration of solids in the slurry that has undergone the concentration step is less than the threshold value. ..

In the method for treating coal wastewater of the present invention, in the membrane filtration step, wastewater having a solid matter concentration of 20 g / L or more and 100 g / L or less can be filtered.

In the method for treating coal wastewater of the present invention, a porous membrane having an average pore diameter of 0.4 μm or less may be used as the porous membrane.

In the method for treating coal wastewater of the present invention, as the porous membrane, a porous membrane having an average pore diameter of 1/20 or less of the average particle size of the pulverized coal in the wastewater may be used.

In the method for treating coal wastewater of the present invention, the equipment can be a conveyor for coal lifting equipment.

Further, the present invention includes a membrane treatment tank into which wastewater discharged from equipment for handling coal or coal ash is introduced, and a porous membrane arranged inside the membrane treatment tank to filter the wastewater, and is in the wastewater. A coal wastewater treatment device configured to concentrate and extract the solid matter as a slurry and return the slurry to the equipment when the concentration of the solid matter in the slurry extracted from the wastewater is equal to or higher than the threshold value. Is.

The coal wastewater treatment apparatus of the present invention can be configured so that the slurry can be reconcentrated when the concentration of solids in the slurry is less than the threshold value.

The coal wastewater treatment apparatus of the present invention may include a concentration tank for extracting wastewater from the membrane treatment tank and concentrating it.

In the coal wastewater treatment apparatus of the present invention, the membrane treatment tank may be provided with a coarse particle remover for removing particles having a relatively large particle size.

In the coal wastewater treatment apparatus of the present invention, the membrane treatment tank can filter wastewater having a solid matter concentration of 20 g / L or more and 100 g / L or less.

In the coal wastewater treatment apparatus of the present invention, the average pore size of the porous membrane may be 0.4 μm or less.

In the coal wastewater treatment apparatus of the present invention, the average pore size of the porous membrane may be 1/20 or less of the average particle size of the pulverized coal in the wastewater.

In the coal wastewater treatment apparatus of the present invention, the apparatus can be a conveyor of a coal lifting facility.

According to the method and apparatus for treating coal wastewater of the present invention, the concentration of solid matter in the wastewater to be treated by membrane filtration can be effectively adjusted, and the solid matter extracted from the wastewater can be effectively used. Can produce the effect.

It is an overall schematic diagram which shows an example of the coal wastewater treatment apparatus by carrying out this invention. It is a schematic block diagram which shows an example of the purification unit which comprises the coal wastewater treatment apparatus. It is a graph which shows the particle size distribution of solid matter in coal wastewater. It is a graph which shows the relationship between the concentration of solid matter in coal wastewater, and the viscosity of wastewater. It is a flowchart which shows an example of the treatment method of coal wastewater by carrying out this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1 and 2 show an example of a coal wastewater treatment apparatus according to the implementation of the present invention. As shown in FIG. 1, a watering pump 1 is provided around the conveyor C, which is an equipment of the coal lifting facility, and the washing water boosted by the watering pump 1 is discharged to the required points of the conveyor C at a watering nozzle (a watering nozzle (). Watering is started from (not shown). The washing water containing pulverized coal after being sprinkled on the conveyor C is collected and sent to the purification unit 10 as wastewater. After the solid matter is separated and removed by the purification unit 10, the wastewater is again sprinkled from the watering pump 1 as cleaning water. Further, in the case of this embodiment, the solid matter separated from the wastewater is returned to the conveyor C as described later.

The configuration of the purification unit 10 is shown in FIG. The purification unit 10 of this embodiment includes a membrane treatment tank 20 that performs membrane filtration treatment on wastewater, a treatment water tank 30 that stores wastewater after the membrane filtration treatment, and a concentration tank 40 that concentrates solid matter in the wastewater. I have.

The raw wastewater collected from the conveyor C is once stored in the drainage tank 50 and then first sent to the membrane treatment tank 20. A coarse particle remover 21 and a porous membrane 22 are installed in the membrane treatment tank 20.

The coarse particle remover 21 is configured as a mesh-like metal member having an appropriate pore diameter of, for example, 0.5 mm or more and 1 mm or less, and is provided at a drainage introduction portion in the membrane treatment tank 20. The drainage led from the drainage tank 50 is first passed through a coarse particle remover 21 to remove particles having a large particle size. Then, the wastewater is passed through the porous membrane 22 and filtered to remove solid matter having a smaller particle size.

The porous film 22 includes, for example, cellulose acetate (CA: Cellulose Acetate), polyethylene (PE: Polyethylene), polyacrylonitrile (PAN: Polyacrylonitrile), polysulfone (PS: Polysulfone), polyethersulfone (PES: Polyethersulfone), polyamide (PES). One or more selected from resins such as PA: Polyamide), Polyvinyl Alcohol (PVA), Polyvinylidene Difluoride (PVDF), Polytetrafluoroethylene (PTFE), or other types of resins. It is a film formed porously using resin as a material. The porous membrane 22 is formed as, for example, a hollow fiber membrane, and guides drainage from the outside to the inside of the porous membrane 22 having a tubular shape, and when the drainage passes through the material of the porous membrane 22, a substance such as pulverized coal is used. To capture. Generally, the porous membranes used for filtration include reverse osmosis membranes (RO membranes: Reverse Osmosis Membrane, NF membranes: Nanofiltration Membrane) and ultrafiltration membranes (UF membranes: Ultrafiltration Membrane), depending on the size of the particles that can be captured. ), Microfiltration Membrane (MF membrane), but when targeting coal effluent, the microfiltration membrane 22 is suitable as a microfiltration membrane or an ultrafiltration membrane that can capture finer particles. ing.

A filtration pump 61 is connected to the porous membrane 22 via a filtration line 60 on the downstream side. The filtration pump 61 sucks the wastewater in the membrane treatment tank 20 from the inside of the porous membrane 22 which is a hollow fiber membrane via the filtration line 60. That is, for the porous membrane 22 which is a tubular hollow fiber membrane, the space in the membrane treatment tank 20 which corresponds to the outside of the tube corresponds to the upstream, and the inside of the tube corresponds to the downstream. The drainage in the membrane treatment tank 20 is guided to the inside of the porous membrane 22 by the suction force of the filtration pump 61, and is filtered when passing through the material of the porous membrane 22 to remove substances such as pulverized coal and remove them. The resulting substance is trapped on the surface of the porous membrane 22. The filtered wastewater is sent to the treated water tank 30, stored there, and further sent to the sprinkler pump 1 (see FIG. 1) as washing water, and reused for washing the conveyor C.

Here, the concentration of the solid matter in the wastewater discharged from the conveyor C is about 0.1 to 20 g / L, but in the case of this embodiment, the concentration of the solid matter in the wastewater in the membrane treatment tank 20 is here. It is adjusted to 20 g / L or more and 100 g / L or less. Generally, when wastewater or the like is treated by membrane treatment, the concentration of solid matter in water is controlled up to around 15 g / L. If the concentration of solid matter is too high, the porous membrane will be clogged at an early stage, the differential pressure will increase, the amount of wastewater treated by membrane filtration will decrease, and the porous membrane will need to be cleaned frequently. This is because it is said that the processing efficiency is lowered. In order to avoid such a situation, for example, as described in Patent Document 1, a settling tank is provided in front of the membrane treatment tank, and the solid matter in the wastewater is removed by the settling treatment in advance, and then the membrane treatment is performed. It has been done.

However, as a result of diligent research, the inventors of the present application have found that even if the concentration of solid matter in the target wastewater is set higher than before, purification by membrane treatment can be sufficiently efficiently performed. What makes this possible is firstly the selection of the membrane to be used for the porous membrane, and secondly the properties peculiar to coal wastewater.

In this embodiment, the porous membrane 22 is assumed to be, for example, a microfiltration membrane or a membrane having a pore size smaller than that. Specifically, it is preferable to use a porous membrane having an average pore diameter of 0.4 μm or less. If the pore size of the porous membrane 22 is sufficiently small with respect to the particle size of the pulverized coal particles contained in the target wastewater, the pulverized coal particles can be captured without leakage and many of the particles do not penetrate deep into the pores. Therefore, the captured particles can be removed by a simple operation and the purification performance can be restored (in the case of this embodiment, as will be described later, with the porous membrane 22 still installed in the membrane treatment tank 20, the reverse is true. The porous membrane 22 is cleaned by cleaning and surface cleaning. The mechanism for performing back cleaning and surface cleaning will be described in detail later). Since it can be assumed that the diameter of the pulverized coal contained in the wastewater differs depending on the type of coal handled by the conveyor C (see FIG. 1) and the crushed state of the coal, the porous membrane 22 can be used in the wastewater. Membranes having different pore diameters may be selected depending on the particle size of the pulverized coal contained. Specifically, a membrane having an average pore size of 1/20 or less of the average particle size of pulverized coal in wastewater (drainage after removing pulverized coal particles having a large particle size by the coarse particle remover 21). Is adopted as the porous membrane 22.

Table 1 below shows the results of experiments in which the particle size (particle size) of solids in actual coal wastewater was measured. For 10 types of coal wastewater (samples 1 to 10) collected under different conditions (coal type, production area, crushed state, target equipment, etc.), the particle size of the solid matter contained is measured and the average value is calculated. did. As a result, the particle size of the solid matter contained in the coal wastewater was about 10 μm to 80 μm on average.

The distribution of particle size is shown in FIG. Here, the particle size distribution of the solid matter in Sample 4 in Table 1 above is shown. Sample 4 (average particle size 27.5 μm) contained solid particles ranging from 0.9 μm to around 200 μm, with the largest number of particles having a particle size of around 10 μm. The selection of the porous membrane 22 as described above can be performed based on such measurements. That is, when it is desired to purify the coal wastewater of sample 4, for example, a membrane having an average pore size of about 1.375 μm or less. Alternatively, an ultrafiltration membrane or a membrane having an average pore size of 0.4 μm or less may be used.

Here, wastewater other than coal wastewater, such as sewage, contains a large amount of organic components in addition to inorganic components as solid components, and the ratio thereof is not constant. However, in the case of coal wastewater, the types of substances contained in the wastewater are extremely limited, and the COD component (Chemical Oxygen Demand) exists in a state of being bound to SS (Suspended Solid). It has been clarified by the research of the inventors of the present application. Therefore, when the operation of removing SS from the waste water (for example, filtration by a microfiltration membrane) is performed, the COD component is also removed at the same time. Therefore, if a membrane having a pore size capable of removing SS is adopted as the porous membrane 22, sufficient purification performance can be obtained for coal wastewater, and substances contained in the wastewater can be efficiently removed. ..

Further, when cleaning the porous membrane 22, if SS can be removed from the porous membrane 22, COD will be removed at the same time. Therefore, as described above, if the porous membrane 22 having a pore size suitable for the particle size of the pulverized coal is selected, the purification performance of the porous membrane 22 can be sufficiently regenerated by surface cleaning or back cleaning. is there.

By the way, the viscosity of wastewater affects the efficiency of the membrane filtration treatment and the efficiency of cleaning the porous membrane 22, and the viscosity of wastewater depends on the concentration of solid matter contained therein. Therefore, an experiment was conducted to investigate the relationship between the concentration of solid matter in the wastewater, the viscosity of the wastewater, and the membrane filtration differential pressure (pressure difference before and after the porous membrane 22).

FIG. 4 shows the results of an experiment investigating the relationship between the concentration of solid matter contained in coal wastewater and the viscosity of wastewater. The higher the concentration of solid matter contained in the wastewater, the higher the viscosity of the wastewater, and in particular, when the concentration exceeds 100 g / L, the viscosity tends to increase remarkably. That is, the higher the viscosity of the wastewater, the lower the fluidity, and the efficiency of stirring and surface cleaning of the wastewater in the membrane treatment tank 20 decreases.

Table 2 below shows the results of an experiment investigating the relationship between the concentration of solid matter and the differential pressure of membrane filtration. The higher the solid matter concentration, the larger the differential pressure before and after the porous membrane 22 tended to be.

That is, if the concentration of solid matter in the membrane treatment tank 20 is too high, the high drainage viscosity may hinder the cleaning of the porous membrane 22, and the membrane required to obtain the same flux and amount of treated water. The filtration differential pressure becomes high, and the energy efficiency related to the membrane treatment also decreases. In the demonstration experiment, when the operation was performed under the condition that the solid matter concentration in the membrane treatment tank 20 exceeded 100 g / L, the solid matter that could not be completely removed by the surface cleaning adhered to the porous membrane 22 and caused clogging. Continuous operation became difficult. For these reasons, as described above, it is preferable to control the solid matter concentration in the membrane treatment tank 20 up to about 100 g / L.

As described above, in this embodiment, by adjusting the solid matter concentration in the membrane treatment tank 20 to be higher (specifically, 20 g / L or more and 100 g / L or less) as compared with the conventional one, the conventional one can be used. For example, the configuration corresponding to the settling tank provided in the front stage of the membrane treatment tank 20 is abolished. By eliminating the settling tank, which requires a volume corresponding to the purification performance for the settling of solid matter, the space required for installing the purification unit 10 can be significantly reduced.

Further, the small installation space of each purification unit 10 contributes to more effective use of the site and space. That is, when trying to install a purification unit including a settling tank as in the conventional case, a large space is required for the installation, but the place where such a large area can be secured is limited. That is, for example, a small space vacant beside the conveyor cannot be used for installing the purification unit. Therefore, for example, it is necessary to install a purification unit at an appropriate location and lay various pipes between the purification unit and a plurality of locations on the conveyor. However, if the purification unit 10 does not include a settling tank as in the present embodiment, it is possible to disperse and arrange a plurality of purification units 10 in an empty space beside the conveyor C. Therefore, the limited space can be used more effectively, and at the same time, the cost and space required for piping and the like can be reduced.

By the way, when the settling tank as described in Patent Document 1 is not provided and the wastewater that has not undergone the settling treatment is stored in the membrane treatment tank 20 for the membrane treatment, the solid in the wastewater in the membrane treatment tank 20 is performed. A separate device for controlling the concentration of substances is required. That is, it must be adjusted so that the concentration of solid matter in the membrane treatment tank 20 does not rise too much. For this purpose, it is effective to concentrate the solid matter in the wastewater and pull it out as a slurry. In the case of this embodiment, a concentration tank 40 is provided in addition to the membrane treatment tank 20 as an apparatus that plays this role.

A part of the wastewater in the membrane treatment tank 20 is extracted and guided to the concentrating tank 40 as needed. In the case of this embodiment, when the concentration of solid matter in the wastewater in the membrane treatment tank 20 exceeds a certain value, a part of the wastewater flows into the concentration tank 40 and is stored. Inside, solids in the stored wastewater settle and accumulate at the bottom. A slurry extraction line 70 is connected to the bottom of the concentrating tank 40, and a slurry extraction pump 71 is installed in the slurry extraction line 70. Then, the slurry extraction pump 71 operates periodically or according to the water level in the concentration tank 40, and the slurry (drainage containing a large amount of solid matter) accumulated at the bottom of the concentration tank 40 is extracted from the slurry extraction line 70. It is designed to be drained.

Further, also in the membrane treatment tank 20, solid matter in the wastewater settles and accumulates at the bottom. The slurry extraction line 70 is also connected to the bottom of the membrane treatment tank 20, so that the solid matter accumulated at the bottom of the membrane treatment tank 20 is also extracted from the slurry extraction line 70 by the operation of the slurry extraction pump 71. It has become.

The slurry drawing lines 70 connected to the bottoms of the concentrating tank 40 and the membrane treatment tank 20 are merged into one on the downstream side of the concentrating tank 40 and the membrane treatment tank 20, and the slurry is drawn downstream from the confluence point. The pump 71 is installed. Further, in the case of this embodiment, the slurry extraction line 70 is branched into two branch pipes on the downstream side of the slurry extraction pump 71, and the outlets of the branched branch pipes are the conveyor C (see FIG. 1) or the outlets, respectively. It is connected to the drainage tank 50. On-off valves 72 and 73 are installed in the middle of the branch pipes, respectively, and by switching these on-off valves 72 and 73, the slurry extracted from the concentrating tank 40 or the membrane treatment tank 20 is transferred to the conveyor C for reuse. It is possible to select whether to return to the drainage tank 50 as drainage. Then, in the case of this embodiment, it is assumed that this switching is performed according to the concentration of the solid matter in the slurry. That is, when the concentration of solid matter is high, the on-off valve 72 is opened and the on-off valve 73 is closed, and the slurry is transferred to the conveyor C for reuse as coal. On the other hand, when the concentration of solid matter is low, the on-off valve 72 is closed and the on-off valve 73 is opened, the slurry is returned to the drainage tank 50, and the membrane filtration treatment in the membrane treatment tank 20 and the membrane filtration treatment in the concentration tank 40 are performed again. Use for concentration. Specifically, for example, the threshold value of the concentration of solids in the slurry is set to 200 g / L, and if the concentration of solids is equal to or higher than this threshold, it is transferred to the conveyor C, and if it is less than the threshold, it is sent to the drainage tank 50 as drainage. Just put it back.

As described above, in this embodiment, the solid matter is concentrated in the membrane treatment tank 20 and the concentration tank 40 and pulled out as a slurry to bring the concentration of the solid matter in the membrane treatment tank 20 to a concentration suitable for the membrane treatment. I try to adjust. At this time, instead of concentrating only in the membrane treatment tank 20, by separately providing a concentration tank 40 for taking out and concentrating the wastewater in the membrane treatment tank 20, the solid matter can be concentrated more efficiently and the concentration can be increased. Slurry can be collected.

Further, in this embodiment, when the concentration of the solid matter in the slurry is high, it is returned to the conveyor C and reused. The slurry containing the solid matter which is pulverized coal at an appropriate concentration can be returned to the conveyor C as it is and used as pulverized coal. Since the membrane treatment tank 20 treats wastewater containing a high concentration of solid matter and further concentrates the wastewater in the concentration tank 40, a high concentration slurry can be efficiently obtained and can be reused as it is. It is.

Further, in this embodiment, when the concentration of solid matter in the slurry is low, the slurry is returned to the drainage tank 50 again. The slurry returned to the drainage tank 50 is sent to the membrane treatment tank 20 and the concentration tank 40 again as wastewater and concentrated. In this way, when the slurry to be extracted has a low concentration, it can be effectively used by concentrating it again. Although the low-concentration slurry is returned to the drainage tank 50 in this embodiment, it may be returned to the membrane treatment tank 20 or the concentration tank 40.

Further, in the case of this example, since the wastewater is subjected to the membrane treatment without being settled by the flocculant or the like, the sol collected from the membrane treatment or the like 20 or the concentration tank 40 does not contain the flocculant. Therefore, the sol and the washing water can be effectively reused while avoiding problems such as clogging of the pipes caused by the coagulant.

Further, in this embodiment, as a mechanism for preventing the pulverized coal from sticking in the concentration tank 40 and the membrane treatment tank 20, inclined portions 40a and 20a are provided below the concentration tank 40 and the membrane treatment tank 20, respectively, and the concentration is concentrated. Stirring nozzles 90 and 91 are installed inside the tank 40 and the membrane treatment tank 20.

The concentrating tank 40 and the membrane treatment tank 20 each have a cylindrical shape, and the lower portions thereof form inclined portions 40a and 20a whose diameters decrease toward the bottom. That is, the inclined portions 40a and 20a have a downward gradient toward the inside of the concentration tank 40 or the membrane treatment tank 20, respectively, and the angle formed by the gradient is preferably about 30 ° or more and 45 ° or less with respect to the horizontal. Is.

The stirring nozzles 90 and 91 are installed in the lower part of the concentrating tank 40 and the membrane treatment tank 20, and an appropriate gas (for example, air) is sent from the stirring blower 92 to the concentrating tank 40 and the membrane treatment tank 20. The wastewater stored in the tank 20 is agitated. A stirring pump may be provided instead of the stirring blower 92, and water may be injected from the stirring nozzles 90 and 91 to stir the drainage.

As described above, the membrane treatment tank 20 stores high-concentration wastewater containing about 80 g / L of solid matter, so that the solid matter easily adheres in the tank. This is even more so in the concentrating tank 40 because the solid matter is further concentrated. Therefore, in this embodiment, the drainage in the tank is agitated by the air sent from the stirring nozzles 90 and 91 to prevent the drainage from staying and prevent the solid matter from sticking. In addition, since solids in water settle due to their own weight and the water flow may not reach the corners, solids tend to collect particularly in the corners of the bottom. Therefore, the concentration tank 40 and the membrane treatment tank 20 By providing the inclined portions 40a and 20a in the lower part of the above, the sticking is prevented more efficiently.

When concentrating or drawing out the slurry in the concentrating tank 40, the operation of the stirring nozzle 90 may be appropriately switched on and off. This is because it is more efficient to allow the wastewater to stand still in the concentrating tank 40 without stirring in order to obtain a slurry having a high concentration of solid matter. For example, while the wastewater is being introduced from the membrane treatment tank 20 into the concentration tank 40, the stirring nozzle 90 is operated to stir the wastewater, and the stirring nozzle 90 is stopped at the stage of concentration. Can be done.

Here, in the case of this embodiment, the coarse particle remover 21 is provided in the membrane treatment tank 20, and after removing particles having a relatively large particle size, filtration is performed by the porous membrane 22. Coarse particles have lower fluidity than fine particles and are difficult to pull out with a pump or the like. In addition, the sedimentation speed in water is high, and it easily sticks to the corner. Therefore, in this embodiment, after removing particles having a relatively large particle size in advance by the coarse particle remover 21, wastewater is stored in the membrane treatment tank 20 or the concentration tank 40, and the coarse particles are fixed in the tank. The situation such as hindering the drawing by the slurry drawing pump 71 is prevented. Here, the “particles having a relatively large particle size” refers to a group of particles having a particularly large particle size among the particles contained in the wastewater, and more specifically, the particles are removed by the coarse particle remover 21. It is a particle with a particle size of about.

A mechanism for performing surface cleaning and back cleaning of the porous membrane 22 will be described. A membrane cleaning nozzle 80 is arranged below the porous membrane 22 inside the membrane treatment tank 20, and an appropriate gas (for example, air) is sent from the membrane cleaning blower 81 to the membrane cleaning nozzle 80, and is above. It is designed to be sprayed onto the porous membrane 22. The air ejected from the membrane cleaning blower 81 scrapes off the solid matter trapped on the surface of the porous membrane 22. The membrane cleaning nozzle 80 also has a function of stirring the waste water in the membrane treatment tank 20 (note that, as described above, a stirring nozzle 91 is separately provided in the membrane treatment tank 20 as a mechanism for stirring. That is, in this embodiment, the wastewater in the membrane treatment tank 20 is agitated by the action of the membrane cleaning nozzle 80 and the stirring nozzle 91). The membrane cleaning blower 81 may be replaced with a pump, and the surface cleaning may be performed with water.

Further, a backwash line 101 for performing backwash is connected to the filtration line 60. The backwash line 101 branches from the treated water tank 30 to the conveyor C (see FIG. 1) from the middle of the treated water line 100 that guides the purified wastewater (treated water) to reach the filtration line 60, and then to the filtration line 60. It is designed to guide treated water. A backwash pump 102 is provided in the middle of the backwash line 101, and an on-off valve 103 is provided at a position downstream of the branch point to the backwash line 101 in the treated water line 100 and in the middle of the backwash line 101, respectively. , 104 are provided. When the backwash of the porous membrane 22 is performed, the filtration pump 61 is stopped, the on-off valve 103 is closed, the on-off valve 104 is opened, and the backwash pump 102 is operated. Is guided from the treated water line 100 to the backwash line 101, the treated water is pushed into the porous membrane 22 in the membrane treatment tank 20 from the filtration line 60 on the downstream side, and the solid matter captured by the porous membrane 22 is collected. It is removed by being extruded. Here, the case where treated water is used as the water for backwashing is illustrated, but for backwashing, water of any origin is used as long as it is water suitable for washing the porous membrane 22, such as industrial water. You may.

The frequency of surface cleaning and back cleaning may be set as appropriate, but as an example, the membrane treatment by the filtration pump 61 is performed intermittently, and the operation and stop of the filtration pump 61 are repeated at an appropriate cycle while the filtration pump 61 is stopped. It is advisable to perform backwashing. For example, after the membrane treatment is performed for 27 minutes, the filtration pump 61 is stopped, the backwash pump 102 is operated, and the backwash is performed for the next 3 minutes, and so on. Further, the membrane cleaning blower 81 is constantly operated to perform surface cleaning, in which the filtration pump 61 is stopped for, for example, one hour in a day's operation, and during that time, an operation of enhancing the cleaning effect by surface cleaning is performed. In this way, by combining surface cleaning and back cleaning with the intermittent operation of the filtration pump 61 and incorporating cleaning into the operation cycle, blockage of the porous membrane 22 is suppressed. In this embodiment, as described above, the membrane treatment with the porous membrane 22 is performed on the high-concentration wastewater, but if a porous membrane 22 having an appropriate pore size for coal wastewater is selected, such a membrane treatment is performed. The clogging of the porous membrane 22 can be sufficiently removed by cleaning by surface cleaning or back cleaning. In fact, according to a demonstration experiment by the inventors of the present application, it has been confirmed that the purification performance of the porous membrane 22 can be sufficiently restored by surface cleaning and back cleaning, and efficient wastewater purification can be continued.

That is, in the purification unit 10 as in this embodiment, while purifying the high-concentration coal wastewater by the porous membrane 22, the particles such as pulverized coal trapped in the porous membrane 22 are only surface-cleaned and back-cleaned. In some cases, it is possible to eliminate the need for cleaning with a chemical, for example. When cleaning with chemicals is not performed, it is not necessary to separately install a tank for cleaning or a tank for storing chemicals, so the space required for installing the device can be reduced, and for cleaning with chemicals. Efficient operation is possible because there is no need to move the porous membrane 22 to another tank. Here, an apparatus having both a mechanism for performing surface cleaning and a mechanism for performing back cleaning is illustrated, but if either one can sufficiently recover the performance of the porous membrane 22, only one of them is provided. May be provided.

The method for treating coal wastewater according to the present embodiment described above will be described with reference to the flowchart of FIG. The method for treating coal wastewater in this embodiment includes a membrane filtration step (step S2), a concentration step (step S8), and a slurry reuse step (step S10) as main steps.

The recovery step (step S1) is a step of recovering wastewater from the equipment (conveyor) C that handles coal or coal ash (see FIG. 1). The wastewater collected in the drainage tank 50 (see FIG. 2) is transferred to the membrane treatment tank 20 of the purification unit 10 and the membrane filtration step (step S2) is executed. In the membrane treatment tank 20, wastewater containing solid matter at a concentration of 20 g / L or more and 100 g / L or less is purified by filtration. The wastewater in the membrane treatment tank 20 is sucked through the porous membrane 22 by the operation of the filtration pump 61 installed in the downstream filtration line 60, and the solid matter is removed by filtration.

The wastewater purified through the membrane filtration step (step S2) is sent to the treated water tank 30 (see FIG. 2) through the filtration line 60, and is sent from the treated water line 100 to the sprinkler pump 1 (see FIG. 1) to the equipment (see FIG. 1). It is used as washing water for (conveyor) C (step S7, treated water reuse step).

Further, during a series of steps from the recovery step (step S1) to the treated water reuse step (step S7), the back cleaning step (step S4) and the surface cleaning step (step S60) are executed under certain conditions. In the case of this embodiment, it is assumed that the back cleaning step and the surface cleaning step are executed according to the passage of time. While the recovery step, the membrane filtration step, and the treated water reuse step are sequentially executed, the time is counted, and the passage of time is determined in steps S3 and S5. The timing of executing steps S3 and S5 may be any time (for convenience of illustration, steps S3 and S5 are displayed immediately after step S2, but in reality, each step of steps S1, S2 and S7 is executed. Is executed continuously in parallel, so steps S3 and S5 may be executed at an appropriate time in an appropriate cycle).

In step S3, it is determined whether or not a predetermined time has elapsed since the operation of the purification unit 10 was started or the previous reverse cleaning step (step S4) was performed. When a predetermined time (for example, 30 minutes) has elapsed, the process proceeds to the backwashing step (step S4), the filtration pump 61 (see FIG. 2) is stopped, the backwashing pump 102 is operated, and the backwashing is performed. Treated water is sent from the line 101 to the porous membrane 22, and the porous membrane 22 is backwashed.

In step S5, it is determined whether or not a predetermined time has elapsed since the operation of the purification unit 10 was started or the previous surface cleaning step (step S6) was performed. When a predetermined time (for example, 24 hours) has elapsed, the process proceeds to the surface cleaning step (step S6), the membrane cleaning blower 81 (see FIG. 2) is operated, and the porous membrane 22 is operated from the membrane cleaning nozzle 80. Water or gas is sprayed onto the porous membrane 22 to clean the surface of the porous membrane 22.

Further, in parallel with the operation of the membrane treatment tank 20, the concentration step (step S8) is performed. In the concentration step, the solid matter in the wastewater transferred from the membrane treatment tank 20 to the concentration tank 40 is accumulated in the concentration tank 40 and concentrated, and is drawn out as a slurry from the slurry drawing line 70 at the bottom. Further, the solid matter accumulated at the bottom of the membrane treatment tank 20 is also pulled out as a slurry in the same manner.

In the slurry extraction line 70, the concentration of solid matter in the wastewater extracted as a slurry is measured by a densitometer or the like (not shown) (step S9), and depending on this concentration, a slurry reuse step (step S10) or a slurry reflux step. (Step S11) is executed. That is, in step S9, when the concentration of the solid matter in the slurry is equal to or higher than the threshold value, the slurry is transferred to the conveyor C (see FIG. 1) and reused as pulverized coal (step S10, slurry reuse step). .. On the other hand, when the concentration of the solid matter is less than the threshold value, the slurry is returned to the drainage tank 50 (see FIG. 1) (step S11, slurry recirculation step), and again purified by membrane filtration (step S2, membrane filtration step). ) And the subsequent concentration in the concentration tank 40 (step S8, concentration step). Here, the slurry having a low concentration may be returned to the membrane treatment tank 20 instead of the drainage tank 50, or may be returned to the concentration tank 40. Further, steps S9 to S11 may be executed in the concentration tank 40 at the timing when the water level reaches a certain threshold value or higher, and in the membrane treatment tank 20, for example, it seems that a certain amount of slurry has accumulated at the bottom. It should be executed at the timing.

As described above, the coal wastewater treatment method of the present embodiment includes a membrane filtration step (step S2) in which the wastewater collected from the equipment (conveyor) C that handles coal or coal ash is filtered by the porous membrane 22, and the wastewater. When the concentration of the solid matter in the slurry that has undergone the concentration step (step S8) and the concentration step (step S8) is equal to or higher than the threshold value, the slurry is reused in the device C. The utilization step (step S10) is included.

Further, the coal wastewater treatment apparatus of this embodiment is arranged inside the membrane treatment tank 20 into which the wastewater discharged from the equipment (conveyor C) that handles coal or coal ash is introduced, and the membrane treatment tank 20. Equipped with a porous film 22 for filtering wastewater, the solid matter in the wastewater is concentrated and extracted as a slurry, and when the concentration of the solid matter in the slurry extracted from the wastewater is equal to or higher than the threshold value, the slurry is transferred to the device C. It is configured to be revertable.

In this way, the concentration of solid matter in the membrane treatment tank 20 can be efficiently controlled. In addition, the slurry concentrated to an appropriate concentration can be reused.

Further, in the method for treating coal wastewater in this embodiment, when the concentration of solid matter in the slurry that has undergone the concentration step (step S8) is less than the threshold value, the slurry is subjected to a membrane filtration step (step S2) or a concentration step (step S2). The slurry recirculation step (step S11) of returning to step S8) is included.

Further, the coal wastewater treatment apparatus of this embodiment is configured so that the slurry can be reconcentrated when the concentration of solid matter in the slurry is less than the threshold value.

In this way, the high-concentration slurry can be recovered more efficiently.

Further, the coal wastewater treatment apparatus of this embodiment includes a concentration tank 40 for extracting wastewater from the membrane treatment tank 20 and concentrating it. In this way, the solid matter in the wastewater can be concentrated more efficiently and recovered as a high-concentration slurry.

Further, in the coal wastewater treatment apparatus of this embodiment, the membrane treatment tank 20 is provided with a coarse particle remover 21 for removing particles having a relatively large particle size. In this way, since the wastewater is stored in the membrane treatment tank 20 and the concentration tank 40 after removing the particles having a large particle size in advance, the coarse particles may stick to the inside of the tank or hinder the drawing. Can be prevented.

Further, in the coal wastewater treatment method and apparatus of this embodiment, in the membrane filtration step (step S2) and the membrane treatment tank 20, wastewater having a solid matter concentration of 20 g / L or more and 100 g / L or less is filtered. .. By doing so, the space required for the installation of the equipment can be significantly reduced by eliminating the settling tank and subjecting the wastewater containing a high concentration of solid matter to the membrane treatment with the porous membrane 22.

Further, in the coal wastewater treatment method and apparatus of this example, the average pore size of the porous membrane 22 is 0.4 μm or less, or 1/20 or less of the average particle size of the pulverized coal in the wastewater. In this way, coal wastewater in which the COD component is bound to SS can be effectively purified.

Further, in the method and apparatus for treating coal wastewater in this embodiment, the apparatus is a conveyor for coal unloading equipment.

Therefore, according to the present embodiment, the concentration of the solid matter in the wastewater to be subjected to the membrane filtration treatment can be effectively adjusted, and the solid matter taken out from the wastewater can be effectively used.

It should be noted that the method and apparatus for treating coal wastewater of the present invention are not limited to the above-mentioned examples, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

1 Sprinkler pump 10 Purification unit 20 Membrane treatment tank 20a Inclined part 21 Coarse particle remover 22 Porous membrane 30 Treatment water tank 40 Concentration tank 40a Inclined part 50 Drainage tank 60 Filtration line 61 Filtration pump 70 Slurry extraction line 71 Slurry extraction pump 72 Opening and closing Valve 73 On-off valve 80 Membrane cleaning nozzle 81 Membrane cleaning blower 90 Stirring nozzle 91 Stirring nozzle 92 Stirring blower 100 Treated water line 101 Backwash line 102 Backwash pump 103 On-off valve 104 On-off valve C Conveyor

Claims (14)

A membrane filtration process that filters wastewater collected from equipment that handles coal or coal ash with a porous membrane,
Concentration process to concentrate solids in wastewater,
A method for treating coal wastewater, which comprises a slurry reuse step of reusing the slurry in the equipment when the concentration of solid matter in the slurry that has undergone the concentration step is equal to or higher than a threshold value. The method for treating coal waste according to claim 1, further comprising a slurry recirculation step of returning the slurry to the membrane filtration step or the concentration step when the concentration of solid matter in the slurry that has undergone the concentration step is less than the threshold value. The method for treating coal wastewater according to claim 1 or 2, wherein in the membrane filtration step, wastewater having a solid matter concentration of 20 g / L or more and 100 g / L or less is filtered. The method for treating coal wastewater according to claim 3, wherein a porous membrane having an average pore diameter of 0.4 μm or less is used as the porous membrane. The method for treating coal wastewater according to claim 3, wherein as the porous membrane, a porous membrane having an average pore diameter of 1/20 or less of the average particle size of the pulverized coal in the wastewater is used. The method for treating coal wastewater according to any one of claims 1 to 5, wherein the equipment is a conveyor of a coal unloading facility. Membrane treatment tanks that introduce wastewater discharged from equipment that handles coal or coal ash,
It is provided with a porous membrane that is arranged inside the membrane treatment tank and filters wastewater.
A coal wastewater treatment device configured so that the slurry can be returned to the equipment when the concentration of solid matter in the slurry drawn from the wastewater is equal to or higher than the threshold value. The coal wastewater treatment apparatus according to claim 7, wherein the solid matter in the wastewater is concentrated and extracted as a slurry, and the slurry can be concentrated again when the concentration of the solid matter in the slurry is less than the threshold value. The coal wastewater treatment apparatus according to claim 7 or 8, further comprising a concentration tank for extracting wastewater from the membrane treatment tank and concentrating the wastewater. The coal wastewater treatment apparatus according to any one of claims 7 to 9, wherein the membrane treatment tank is provided with a coarse particle remover for removing particles having a relatively large particle size. The coal wastewater treatment apparatus according to any one of claims 7 to 10, wherein in the membrane treatment tank, wastewater having a solid matter concentration of 20 g / L or more and 100 g / L or less is filtered. The coal wastewater treatment apparatus according to any one of claims 7 to 11, wherein the average pore size of the porous membrane is 0.4 μm or less. The coal wastewater treatment apparatus according to any one of claims 7 to 11, wherein the average pore diameter of the porous membrane is 1/20 or less of the average particle size of the pulverized coal in the wastewater. The coal wastewater treatment apparatus according to any one of claims 7 to 13, wherein the apparatus is a conveyor of a coal unloading facility.

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