CN213294951U - Defluorination system for drainage of coal bed gas - Google Patents

Abstract

The invention discloses a defluorination system for drainage of coal bed gas. The system comprises a first precipitation device, a flocculation device, a second precipitation device, a pH value adjusting device and a sludge collecting device; the first precipitation device, the flocculation device, the second precipitation device and the pH value adjusting device are sequentially communicated through a pipeline; the sludge collection device is respectively communicated with the first sedimentation device, the flocculation device and the second sedimentation device; the pH value adjusting device discharges the wastewater reaching the standard through an external discharge pipeline, and a valve for opening or closing the external discharge pipeline is arranged on the external discharge pipeline. This system carries out preliminary sedimentation to coal bed gas drainage through first sediment device, throws the medicament in the flocculation device, adsorbs the flocculation to fluorine pollutant and suspended solid, and the flocculation is further precipitated to flocculation thing in the second sediment device and discharges, and this system treatment simple process adsorbs modes such as flocculation and discharge mud through throwing the medicament to fluorine pollutant and suspended solid, and the high efficiency is got rid of and is handled fluorine pollutant and suspended solid in the coal bed gas drainage.

Description

Defluorination system for drainage of coal bed gas

Technical Field

The invention relates to the technical field of underground water pollution ex-situ remediation, in particular to a defluorination system for drainage of coal bed gas.

Background

Elemental fluorine is widely present in mineral rocks, such as fluorite, cryolite, calcium fluorophosphate, etc., all of which contain a certain amount of fluorine. The fluorine wastewater mainly comes from the production industries of steel production, electrolytic aluminum industry, coal power, phosphate fertilizer, glass cement, coal bed gas exploitation and the like, the materials used in the industries also contain a part of fluorine-containing minerals, and the fluorine concentration of the produced fluorine-containing wastewater is different and can reach 700mg/L at most and is only 5mg/L at least. The demand of fluorine element for human body is not very high, and excessive intake of fluorine element can cause various human diseases.

Coal bed gas drainage is used as main pollution generated in coal bed gas exploitation, fluorine is a main harmful substance, and the content of fluorine is 5-20 mg/L drainage. The underground water pollution sources are various, the coal bed gas drainage is a byproduct associated in the fracturing and exploitation processes in the coal bed gas production process, the water quality and water quantity characteristics of the coal bed gas drainage are shown as the water quality and water quantity characteristics that the fluorine concentration is higher and the single-well drainage is not very large, the fluorine concentration is generally 5-20 mg/L, and the single-well drainage is only 0-30 m³And the water discharge quantity is gradually reduced along with the mining time, and the treatment application specially aiming at the coal bed gas water discharge is less at present. In the coal bed gas exploitation technology, fracturing fluid is needed when a fracturing technology is adopted, the fracturing fluid contains high salinity, and in addition, some easily-dissolved salts in a coal bed can enter a water body, so that the salinity in the coal bed gas drainage is high and can reach 2000-4000 mg/L, and the recovery of the salinity in the coal bed gas drainage is less at present.

In the prior art, the wastewater is subjected to fluorine removal by generally adopting a chemical precipitation method or an ion exchange method, wherein the chemical precipitation method is to add a chemical agent into fluorine-containing wastewater to generate a corresponding precipitate with fluorine ions in water so as to achieve the purpose of removing fluorine, but the concentration of the fluorine in the coal bed gas pumping drainage water is 5-20 mg/L, and if the chemical precipitation method is adopted, the dosage of the agent is very large; the ion exchange method is a good method for treating fluorine pollutants, has good fluorine removal effect, generates few byproducts in the treatment process, and has more complex ion exchange resin regeneration operation process and difficult actual operation.

In China, most of treatment methods for coal bed gas drainage only carry out treatment through infiltration and evaporation, are greatly influenced by seasons and climate, are unstable in fluorine removal effect, and have certain influence on the surrounding environment and underground water, so that the water quality characteristics of coal bed gas drainage need to be fully considered, and a fluorine removal system suitable for coal bed gas drainage in China is designed.

Disclosure of Invention

The invention aims to provide a defluorination system for drainage of coal bed gas, which has the advantages of simple process, good defluorination effect on fluorine pollutants and suspended matters and simultaneous recovery of salinity, aiming at the defects in the prior art.

The purpose of the invention can be realized by the following technical scheme:

a defluorination system for drainage of coal bed gas comprises a first precipitation device, a flocculation device, a second precipitation device, a pH value adjusting device and a sludge collection device; the first precipitation device, the flocculation device, the second precipitation device and the pH value adjusting device are sequentially communicated through a pipeline; the sludge collection device is respectively communicated with the first sedimentation device, the flocculation device and the second sedimentation device through pipelines; the pH value adjusting device discharges standard-reaching wastewater through an external discharge pipeline; and a valve for opening or closing the outer discharge pipeline is arranged on the outer discharge pipeline.

Preferably, the defluorination system further comprises a filtering device, the filtering device is communicated with the pH value adjusting device through a water inlet pipeline, and a valve for opening or closing the water inlet pipeline is arranged on the water inlet pipeline.

Preferably, the filtering device comprises a quartz sand filter, a loaded biochar filter, a resin softener and a nanofiltration membrane filter which are sequentially communicated through a pipeline; the quartz sand filter passes through the water intake pipe with pH valve adjusting device intercommunication, be equipped with the third water pump on the water intake pipe, be equipped with the fourth water pump on the pipeline section between resin softener and the nanofiltration membrane filter.

Preferably, the filtering apparatus further comprises a cartridge filter located on a pipeline section between the nanofiltration membrane filter and the resin softener.

Preferably, the first sedimentation device comprises a first sedimentation tank, the upper end of the first sedimentation tank is provided with a first water outlet communicated with the interior of the first sedimentation tank, the bottom end of the first sedimentation tank is provided with a first sludge discharge port communicated with the interior of the first sedimentation tank, the first water outlet is communicated with the flocculation device through a pipeline, a first water pump is arranged on a pipeline section between the first water outlet and the flocculation device, the first sludge discharge port is communicated with the sludge collection device, and a first sludge discharge valve is installed on the first sludge discharge port.

Preferably, the flocculation device includes flocculation basin and medicine unit, add the medicine unit with the flocculation basin passes through the pipeline intercommunication, be equipped with first mixer in the flocculation basin, the flocculation basin upper end is equipped with the second delivery port rather than inside being linked together, the flocculation basin bottom is equipped with the second row mud mouth rather than inside being linked together, the second delivery port with the second deposits the device and passes through the pipeline intercommunication, the second delivery port with be equipped with the second water pump on the pipeline section between the second deposits the device, the second row mud mouth with mud collection device intercommunication, install the second on the second row mud mouth and arrange the mud valve.

Preferably, the dosing unit includes a plurality of dosing ponds, and is a plurality of all be equipped with the second mixer in the dosing pond, it is a plurality of the dosing pond all through add the medicine pipeline with the flocculation basin is linked together, all be equipped with the dosing pump on the medicine pipeline.

Preferably, the dosing unit comprises three dosing tanks, one dosing tank is used for adding active aluminum salt, one dosing tank is used for adding PAC, and the other dosing tank is used for adding PAM.

Preferably, the second sedimentation device comprises a second sedimentation tank, an inclined plate group is arranged in the middle of the second sedimentation tank, and the inclined plate group comprises a plurality of inclined plates arranged at intervals; every the both ends of swash plate are fixed respectively two relative lateral walls of second sedimentation tank, and the contained angle of horizontal direction is 50 ~ 65, second sedimentation tank upper end is equipped with the third delivery port rather than inside being linked together, the second sedimentation tank bottom is equipped with the third mud discharging mouth rather than inside being linked together, the third delivery port with pH valve adjusting device passes through the pipeline intercommunication, the third mud discharging mouth with sludge collection device intercommunication, install the third mud valve on the third mud discharging mouth.

The invention relates to a defluorination system for drainage of coal bed gas. The first sedimentation device is used for carrying out preliminary sedimentation on the drainage water of the coal bed gas, so that pollutants with larger particles, such as fly ash, gravel and the like, are removed, and the sedimentation load of a subsequent flocculation device is reduced; adsorbing and flocculating fluorine pollutants and suspended matters in a coal bed gas row in a mode of adding a medicament in a flocculation device, precipitating a part of the fluorine pollutants and suspended matters at the bottom of the flocculation device, discharging precipitates to a sludge collection device through a pipeline, mixing the rest of the fluorine pollutants and suspended matters with the medicament, then feeding the mixture into a second precipitation device, further precipitating the flocculated suspended matters formed by the fluorine pollutants, the suspended matters and the medicament in the second precipitation device, discharging the precipitates to the sludge collection device through the pipeline, further removing the fluorine pollutants and the suspended matters in a water body, feeding supernatant of the second precipitation device into a pH value adjusting device, and adjusting the pH value in the pH value adjusting device to reach a discharge standard; and deeply removing fluorine pollutants in the water body through a filtering device. The system has simple structure and simple treatment process, and has good effect of removing fluorine pollutants and suspended matters when the system is used for treating the coal bed gas drainage.

Drawings

Fig. 1 is a schematic structural diagram of an overall defluorination system for drainage of coal bed methane according to an embodiment of the present invention.

The notation in the figure is:

1. a first precipitation device; 11. a first sedimentation tank; 111. a first water outlet; 112. a first sludge discharge port; 12. a first water pump; 13. a first mud valve; 2. a flocculation device; 21. a flocculation tank; 211. a first mixer; 212. a second water outlet; 213. a second sludge discharge port; 22. a dosing unit; 221. a medicine adding pool; 222. a second mixer; 223. a dosing pipeline; 224. a dosing pump; 23. a second water pump; 24. A second sludge discharge valve; 3. a second precipitation device; 31. a second sedimentation tank; 311. a third water outlet; 312. A third sludge discharge port; 32. a swash plate group; 321. a sloping plate; 33. a third sludge discharge valve; 4. a pH value adjusting device; 5. a sludge collection device; 6. a filtration device; 61. a quartz sand filter; 62. a biochar-loaded filter; 63. a resin softener; 64. a nanofiltration membrane filter; 65. a third water pump; 66. A fourth water pump; 67. a cartridge filter; 7. an outer discharge pipeline; 8. a water inlet pipeline; 9. and (4) a valve.

Detailed Description

The following are specific embodiments of the present invention and are further described with reference to the drawings, but the present invention is not limited to these embodiments.

Example 1

As shown in fig. 1, the overall structure of a defluorination system for drainage of coal bed gas is schematically shown. The system comprises a first sedimentation device 1, a flocculation device 2, a second sedimentation device 3, a pH value adjusting device 4 and a sludge collecting device 5; the first precipitation device 1, the flocculation device 2, the second precipitation device 3 and the pH value adjusting device 4 are sequentially communicated through a pipeline; the sludge collecting device 5 is respectively communicated with the first sedimentation device 1, the flocculation device 2 and the second sedimentation device 3 through pipelines; the pH value adjusting device 4 discharges the wastewater reaching the standard through an external discharge pipeline 7; and a valve 9 for opening or closing the outer discharge pipeline 7 is arranged on the outer discharge pipeline.

The invention relates to a defluorination system for drainage of coal bed gas. The first sedimentation device is used for carrying out preliminary sedimentation on the drainage water of the coal bed gas, so that pollutants with larger particles, such as fly ash, gravel and the like, are removed, and the sedimentation load of a subsequent flocculation device is reduced; through the mode of throwing the medicament in flocculation device, fluorine pollutant and the suspended solid of arranging in the coal bed gas adsorb the flocculation, partly fluorine pollutant and suspended solid deposit in the flocculation device bottom, the precipitate is discharged to mud collection device through the pipeline, the fluorine pollutant of surplus portion and suspended solid get into the second after mixing with the medicament and deposit the device, the flocculation suspended solid that fluorine pollutant and suspended solid and medicament formed reaches further sediment in the second precipitation device, the precipitate is discharged to mud collection device through the pipeline, further get rid of fluorine pollutant and suspended solid in the water, the supernatant of second precipitation device gets into pH valve adjusting device, reach emission standard after adjusting pH value in pH valve adjusting device. The system has simple structure and simple treatment process, and has good effect of removing fluorine pollutants and suspended matters when the system is used for treating the coal bed gas drainage.

This defluorination system can also include filter equipment 6, and filter equipment 6 can be through 8 and 4 intercommunications of pH valve adjusting device of inlet channel, can be equipped with the valve 9 of opening or closing it on the inlet channel 8, and the water in the pH valve adjusting device 4 passes through inlet channel 8 and gets into filter equipment 6, and filter equipment 6 is used for further desorption coal bed gas to arrange fluorine pollutant and suspended solid in the water.

The type of the filtering device 6 may be various, and is not limited herein, and the filtering device 6 in this embodiment may include a quartz sand filter 61, a loaded charcoal filter 62, a resin softener 63, and a nanofiltration membrane filter 64, which are sequentially communicated through a pipeline; the quartz sand filter 61 can be communicated with the pH value adjusting device 4 through a water inlet pipeline 8, a third water pump 65 can be arranged on the water inlet pipeline 8, and a fourth water pump 66 can be arranged on a pipeline section between the resin softener 63 and the nanofiltration membrane filter 64; the quartz sand filter 61 and the loaded charcoal filter 62 can further remove suspended matters in the water body, the resin softener 63 can remove calcium and magnesium ions in the water, and the nanofiltration membrane filter 64 can adopt a mode of arranging a plurality of nanofiltration membranes in parallel so as to improve the removal rate of fluorine ions and sodium ions in the water body. The wastewater in the pH value adjusting device 4 is treated by the filtering device 6, so that the concentration of fluorine pollutants and suspended matters is greatly reduced, and the deep treatment of the fluorine pollutants and suspended matters in the coal bed gas drainage is realized.

The filtration apparatus 6 may further comprise a cartridge filter 67, and the cartridge filter 67 may be located on a line section between the nanofiltration membrane filter 64 and the resin softener 63; to ensure water quality filtration accuracy and to protect nanofiltration membrane elements in the nanofiltration membrane filter 64 from damage by large particulate matter. The type of the first sedimentation device 1 may be various, and is not limited herein, in this embodiment, the first sedimentation device 1 may include a first sedimentation tank 11, the upper end of the first sedimentation tank 11 may be provided with a first water outlet 111 communicated with the inside of the first sedimentation tank, the bottom end of the first sedimentation tank 11 may be provided with a first sludge discharge port 112 communicated with the inside of the first sedimentation tank, the first water outlet 111 may be communicated with the flocculation device 2 through a pipeline, a pipeline section between the first water outlet 111 and the flocculation device 2 may be provided with a first water pump 12, the first sludge discharge port 112 is communicated with the sludge collection device 5, the first sludge discharge valve 13 is installed on the first sludge discharge port 112, and sludge at the bottom of the first sedimentation tank 11 is discharged to the sludge collection device 5 by opening the first sludge discharge valve 13; because the action of gravity, the great pollutants of granule such as fly ash, gravel in the coal bed gas drainage can subside in the bottom of first sedimentation tank 11, through opening first mud valve 13, mud collection device 5 can be discharged to the precipitate of first sedimentation tank 11 bottom, through the mode that mud discharged for the great pollutants of granule such as fly ash, gravel in the coal bed gas drainage reaches to get rid of, has reduced follow-up flocculation device's sediment load.

The flocculation apparatus 2 may be of various types, and is not limited herein, in this embodiment, the flocculation apparatus 2 may include a flocculation tank 21 and a dosing unit 22, the dosing unit 22 may be communicated with the flocculation tank 21 through a pipeline, to add a medicament into the flocculation tank 21, a first stirrer 211 may be disposed in the flocculation tank 21, so that the medicament is fully dissolved and uniformly mixed in the flocculation tank 21, the upper end of the flocculation tank 21 can be provided with a second water outlet 212 communicated with the inside of the flocculation tank, the bottom end of the flocculation tank 21 can be provided with a second sludge discharge port 213 communicated with the inside of the flocculation tank, the second water outlet 212 can be communicated with the second sedimentation device 3 through a pipeline, a second water pump 23 can be arranged on the pipeline section between the second water outlet 212 and the second sedimentation device 3, the second sludge discharge port 213 is communicated with the sludge collection device 5, the second sludge discharge port 213 can be provided with a second sludge discharge valve 24, discharging sludge at the bottom of the flocculation tank 21 to the sludge collection device 5 by opening the second sludge discharge valve 24; throw the medicament in to flocculation basin 21 through adding medicine unit 22, the medicament adsorbs the flocculation to fluorine pollutant and suspended solid in the coal bed gas row, some fluorine pollutant and suspended solid deposit in flocculation basin 21 bottom under the action of gravity, arrange to mud collection device 5 through the pipeline, the fluorine pollutant and the suspended solid of surplus portion get into second precipitation device 3 after mixing with the medicament, the flocculation suspended solid that fluorine pollutant and suspended solid and medicament formed reaches further the sediment in second precipitation device 3, and arrange to mud collection device through the pipeline, further get rid of fluorine pollutant and suspended solid in the water.

The type of the dosing unit 22 may be various, and is not limited herein, the dosing unit 22 in this embodiment may include a plurality of dosing tanks 221, a second stirrer 222 may be disposed in each of the plurality of dosing tanks 221, each of the plurality of dosing tanks 221 may be communicated with the flocculation tank 21 through a dosing pipeline 223, and each of the dosing pipelines 223 may be provided with a dosing pump 224; by arranging the plurality of dosing tanks 221, it is convenient to add different kinds of medicaments into the flocculation tank 21.

For example, in this embodiment, the dosing unit 22 may include three dosing tanks 221, and one dosing tank 221 may be filled with an active aluminum salt, which has a good fluorine adsorption effect; PAC can be added into a dosing tank 221, and the PAC is beneficial to agglomeration of active aluminum salt particles for adsorbing fluorine and rapid formation of precipitates; PAM can be added into the remaining dosing tank 221, and the PAM enables suspended matters with charges in the wastewater to flocculate, so that the rapid formation of precipitates is facilitated; through the three dosing tanks 221, three different medicaments are added into the flocculation tank 21, which is helpful for efficiently removing suspended matters and fluorine pollutants in the water body.

The type of the second settling device 3 can be various, and is not limited herein, the second settling device 3 in this embodiment can include a second settling tank 31, an inclined plate group 32 is disposed inside the second settling tank 31, the inclined plate group 32 can include a plurality of inclined plates 321 arranged at intervals, both ends of the inclined plates 321 can be respectively fixed on two opposite side walls of the second settling tank 31, the included angle between the inclined plate 321 and the horizontal direction can be 50-65 degrees, the second sedimentation tank 31 is divided into a plurality of sedimentation areas by the inclined plates 321 arranged at intervals, the effective sedimentation area of the second sedimentation tank 31 is increased, the sedimentation efficiency of flocculates is improved, the turbulence of water can be reduced by the arrangement of the inclined plates 321, the flocculates are easily adsorbed on the inclined plates 321, under the action of gravity, the flocculate sinks to the bottom of the second sedimentation tank 31 along the inclined plate 321, so that the sedimentation effect is greatly improved; the upper end of the second sedimentation tank 31 can be provided with a third water outlet 311 communicated with the inside of the second sedimentation tank, the bottom end of the second sedimentation tank 31 can be provided with a third sludge discharge port 312 communicated with the inside of the second sedimentation tank, the third water outlet 311 can be communicated with the pH value adjusting device 4 through a pipeline, the third sludge discharge port 312 can be communicated with the sludge collecting device 5, and the third sludge discharge port 312 can be provided with a third sludge discharge valve 33.

The system provided by the invention is used for carrying out defluorination treatment on the coal bed gas drainage, and the specific application steps are as follows:

1. extracting the coal bed gas drainage water to be treated to a first precipitation device 1, wherein the concentration of fluorine in the coal bed gas drainage water to be treated is 6.2mg/L, and the turbidity value is 80 NTU; the pollutants with larger particles in the coal bed gas drainage sink to the bottom of the first sedimentation tank 11 under the action of gravity, the first sludge discharge valve 13 is opened, the sediment at the bottom of the first sedimentation tank 11 enters the sludge collection device 5, and the pollutants with larger particles in the coal bed gas drainage are removed; starting a first water pump 12, and pumping the supernatant of the first sedimentation tank 11 into the flocculation device 2;

2. a dosing pump 224 is opened, the active aluminum chloride in a dosing tank 221 enters the flocculation tank 21 through a dosing pipeline 223, the concentration of the aluminum element in the flocculation tank 21 is 50mg/L, the first stirrer 211 in the flocculation tank 21 is started, after stirring for 5min, the other dosing pump 224 is opened, the PAC medicament in the other dosing tank 221 enters the flocculation tank 21 through the dosing pipeline 223, so that the concentration of PAC in the flocculation tank 21 is 50mg/L, after continuously stirring for 10min, the remaining one dosing pump 224 is opened, the PAM chemical in the remaining one dosing tank 221 enters the flocculation tank 21 through the dosing pipeline 223, keeping the concentration of PAM in the flocculation tank 21 at 0.5mg/L, continuing stirring for 1min, opening a second sludge discharge valve 24, enabling sediment at the bottom of the flocculation tank 21 to enter a sludge collection device 5, opening a second water pump 23, and pumping supernatant in the flocculation tank 21 into a second sedimentation device 3;

3. after the coal bed gas drainage water is settled in the second settling device 3 for 4 hours, the third sludge discharge valve 33 is opened, and the sediment at the bottom of the second settling tank 31 enters the sludge collection device 5; the supernatant in the second sedimentation tank 31 enters a pH value adjusting device 4;

4. and (4) adjusting the pH value to 7 in a pH value adjusting tank, opening a valve 9 on an external discharge pipeline 7, and discharging the wastewater reaching the standard.

And detecting the concentration and turbidity of the fluorine ions in the liquid in the pH value regulating tank, wherein the concentration of the fluorine ions is 2.3mg/L, and the turbidity is 5NTU, so that the wastewater discharge standard is reached.

Example 2

The present example is substantially the same as the step in example 1, except that the concentration of fluorine in the coalbed methane wastewater to be treated in step 1 in the present example is 10mg/L, and the turbidity value is 90 NTU; in the step 2, the concentration of aluminum ions in the flocculation tank 21 is 100mg/L, the stirring time of active aluminum salt is 8min, the concentration of PAC in the flocculation tank 21 is 70mg/L, the stirring time of PAC is 8min, the concentration of PAM in the flocculation tank 21 is 1.0mg/L, and the stirring time of PAM is 2 min; the settling time in the step 3 is 5 hours; and 4, regulating the pH value to be 8 in a pH value regulating tank.

And detecting the concentration and turbidity of the fluorine ions in the liquid in the pH value regulating tank, wherein the concentration of the fluorine ions is 1.9mg/L, and the turbidity is 3NTU, so that the wastewater discharge standard is reached.

Example 3

The present example is substantially the same as the step in example 1, except that the concentration of fluorine in the coalbed methane wastewater to be treated in step 1 in the present example is 20mg/L, and the turbidity value is 100 NTU; in the step 2, the concentration of aluminum ions in the flocculation tank 21 is 180mg/L, the stirring time of active aluminum salt is 10min, the concentration of PAC in the flocculation tank 21 is 100mg/L, the stirring time of PAC is 10min, the concentration of PAM in the flocculation tank 21 is 1.5mg/L, and the stirring time of PAM is 3 min; the settling time in the step 3 is 6 hours; in the step 4, the pH value is adjusted to 8.5 in the pH value adjusting tank, a valve 9 on an external discharge pipeline 7 is closed, the valve 9 on a water inlet pipeline 8 is opened, the wastewater in the pH value adjusting device 4 enters a filtering device 6, suspended matters in the water body are sequentially removed through a quartz sand filter 61, the suspended matters in the water body are further removed through a loaded biochar filter 62, calcium and magnesium ions in the water are removed through a resin softener 63, fluorine ions and sodium ions in the water body are removed through a nanofiltration membrane filter 64, and concentrated water and defluorinated water are discharged through pipelines.

Through detection, the concentration of fluorine ions in the defluorinated water discharged from the nanofiltration membrane filter 64 is 0.22mg/L, the conductivity of the concentrated water discharged from the nanofiltration membrane filter 64 reaches 8mS/cm, the concentrated water is discharged to a concentration water collecting tank, solar salt drying is carried out under the illumination condition, and the salt content is recycled.

The above is not relevant and is applicable to the prior art.

While certain specific embodiments of the present invention have been described in detail by way of illustration, it will be understood by those skilled in the art that the foregoing is illustrative only and is not limiting of the scope of the invention, as various modifications or additions may be made to the specific embodiments described and substituted in a similar manner by those skilled in the art without departing from the scope of the invention as defined in the appending claims. It should be understood by those skilled in the art that any modifications, equivalents, improvements and the like made to the above embodiments in accordance with the technical spirit of the present invention are included in the scope of the present invention.

Claims (9)

1. A defluorination system for drainage of coal bed gas is characterized by comprising a first sedimentation device (1), a flocculation device (2), a second sedimentation device (3), a pH value adjusting device (4) and a sludge collecting device (5); the first precipitation device (1), the flocculation device (2), the second precipitation device (3) and the pH value adjusting device (4) are communicated in sequence through pipelines; the sludge collecting device (5) is respectively communicated with the first sedimentation device (1), the flocculation device (2) and the second sedimentation device (3) through pipelines; the pH value adjusting device (4) discharges standard-reaching wastewater through an external discharge pipeline (7); and a valve (9) for opening or closing the discharge pipeline (7) is arranged on the discharge pipeline.

2. The defluorination system for drainage of coal bed gas as claimed in claim 1, further comprising a filtering device (6), wherein said filtering device (6) is communicated with said pH value regulating device (4) through a water inlet pipeline (8), and a valve (9) for opening or closing said water inlet pipeline (8) is arranged on said water inlet pipeline (8).

3. The defluorination system for drainage water of coal bed gas as claimed in claim 2, wherein said filtering device (6) comprises a quartz sand filter (61), a loaded biochar filter (62), a resin softener (63) and a nanofiltration membrane filter (64) which are communicated in sequence by pipelines; quartz sand filter (61) pass through inlet channel (8) with pH valve adjusting device (4) intercommunication, be equipped with third water pump (65) on inlet channel (8), be equipped with fourth water pump (66) on the pipeline section between resin softener (63) and nanofiltration membrane filter (64).

4. A defluorination system for drainage water from coal bed methane as claimed in claim 3, wherein said filtration device (6) further comprises a cartridge filter (67), said cartridge filter (67) being located on the line section between said nanofiltration membrane filter (64) and said resin softener (63).

5. The defluorination system for drainage of coal bed gas according to claim 3 or 4, wherein said first sedimentation device (1) comprises a first sedimentation tank (11), said first sedimentation tank (11) is provided at an upper end thereof with a first water outlet (111) communicated with an interior thereof, said first sedimentation tank (11) is provided at a bottom end thereof with a first sludge discharge port (112) communicated with an interior thereof, said first water outlet (111) is communicated with said flocculation device (2) through a pipeline, a first water pump (12) is provided on a pipeline section between said first water outlet (111) and said flocculation device (2), said first sludge discharge port (112) is communicated with said sludge collection device (5), and said first sludge discharge port (112) is provided with a first sludge discharge valve (13).

6. The defluorination system of drainage water of coal bed gas as claimed in claim 5, wherein said flocculation device (2) comprises a flocculation basin (21) and a dosing unit (22), the dosing unit (22) is communicated with the flocculation tank (21) through a pipeline, a first stirrer (211) is arranged in the flocculation tank (21), the upper end of the flocculation tank (21) is provided with a second water outlet (212) communicated with the inside of the flocculation tank, the bottom end of the flocculation tank (21) is provided with a second sludge discharge port (213) communicated with the inside of the flocculation tank, the second water outlet (212) is communicated with the second sedimentation device (3) through a pipeline, a second water pump (23) is arranged on the pipeline section between the second water outlet (212) and the second sedimentation device (3), the second sludge discharge port (213) is communicated with the sludge collecting device (5), and a second sludge discharge valve (24) is installed on the second sludge discharge port (213).

7. The defluorination system for drainage of coal bed gas as claimed in claim 6, wherein said dosing unit (22) comprises a plurality of dosing pools (221), each of said dosing pools (221) is provided with a second stirrer (222), each of said dosing pools (221) is communicated with said flocculation tank (21) through a dosing pipeline (223), and each of said dosing pipelines (223) is provided with a dosing pump (224).

8. The defluorination system for drainage of coal bed methane according to claim 7, wherein said dosing unit (22) comprises three dosing tanks (221), one dosing tank (221) for active aluminum salt, one dosing tank (221) for PAC, and the remaining one dosing tank (221) for PAM.

9. The defluorination system for drainage of coal bed methane according to claim 8, wherein said second settling device (3) comprises a second settling tank (31), a sloping plate group (32) is arranged in the middle of said second settling tank (31), and said sloping plate group (32) comprises a plurality of sloping plates (321) arranged at intervals; every the both ends of swash plate (321) are fixed respectively two relative lateral walls of second sedimentation tank (31), and be 50 ~ 65 with the contained angle of horizontal direction, second sedimentation tank (31) upper end is equipped with third delivery port (311) rather than inside being linked together, second sedimentation tank (31) bottom is equipped with third mud discharging port (312) rather than inside being linked together, third delivery port (311) with pH valve adjusting device (4) pass through the pipeline intercommunication, third mud discharging port (312) with mud collection device (5) intercommunication, install third mud discharging valve (33) on third mud discharging port (312).

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