CN108147612B

CN108147612B - Method for treating coal carbonization wastewater

Info

Publication number: CN108147612B
Application number: CN201611101853.XA
Authority: CN
Inventors: 于永辉; 孙承林; 赵颖
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2016-12-05
Filing date: 2016-12-05
Publication date: 2021-01-26
Anticipated expiration: 2036-12-05
Also published as: CN108147612A

Abstract

A method for treating coal carbonization wastewater adopts unit combination technologies of oil removal, rotational flow air flotation, filtration, extraction dephenolization, rectification ammonia distillation, biological oxygen deficiency, SBR oxidation, CWPO oxidation, coagulating sedimentation and the like, and can effectively remove organic pollutants such as tar, ammonia nitrogen, phenols and the like in the coal carbonization wastewater. Wherein the oil removal rate of the cyclone air flotation unit reaches 93.8 percent, and the removal rate of volatile phenol of the extraction dephenolization unit reaches 98.3 percent; the ammonia nitrogen removal rate of the rectification ammonia distillation unit reaches 95.8 percent. The method is mature in technology, stable and reliable, achieves the direct discharge requirement of 'emission standard of pollutants for coking chemical industry' GB16171-2012 after the coal dry distillation wastewater is treated, and has popularization value.

Description

Method for treating coal carbonization wastewater

Technical Field

The invention belongs to a method for treating coal chemical industry wastewater, and particularly relates to a method for treating coal dry distillation wastewater by oil separation, cyclone air flotation, filtration, extraction dephenolization, rectification ammonia distillation, biological oxygen deficiency, SBR oxidation, CWPO oxidation and coagulating sedimentation.

Background

The traditional processing method of coal is mainly divided into two methods of high-temperature coking and low-temperature dry distillation. High-temperature coking is commonly used for producing coke, coal tar and coal gas are additionally produced, and the high-temperature coking temperature can reach 900-1100 ℃ at most. And the low-temperature dry distillation is mainly used for producing semicoke and additionally producing coal tar and coal gas, and is generally controlled to be between 400 and 600 ℃. The main purpose of low-temperature carbonization is to obtain more coal tar, is more suitable for coal types with relatively high volatile matters such as lignite, bituminous coal and the like, and is one of the effective utilization ways of the low-quality coal in China.

The coal dry distillation process inevitably produces a large amount of waste water, which is mainly from oil gas washing water. In the coal dry distillation process, high-temperature oil gas generated by pyrolysis of the rotary reaction furnace enters the washing tower through the gas guide tube, the gas directly contacts with circulating ammonia water to carry out mass transfer and heat transfer, dust is washed away, and coal tar and pyrolysis water are condensed. In addition, the moisture contained in the coal and the pyrolysis water generated by the pyrolysis reaction in the reaction furnace at the temperature of 400-600 ℃ are also important sources of the coal carbonization wastewater. Removing tar from the wastewater generated in the coal carbonization process, and recycling the wastewater as washing water, wherein the wastewater is called as circulating ammonia water; the residual waste water is led to a waste water treatment plant for treatment, and the water is called residual ammonia water. Because the process is different from the traditional coal gasification or coking process, the generated residual ammonia water and the circulating ammonia water contain high-concentration phenols, ammonia nitrogen, COD, cyanides and other toxic and harmful substances. Wherein, the content of the phenolic compounds is the maximum, and the phenolic compounds comprise phenol, o-cresol, p-cresol, xylenol and other unit phenols, catechol, hydroquinone, pyrogallol and other polyhydric phenols. Meanwhile, the composite material also contains a plurality of heterocyclic compounds such as diazabenzene, pyridine, quinoline, indole and the like which are difficult to biodegrade and Polycyclic Aromatic Hydrocarbons (PAHs) such as biphenyl, naphthalene, benzopyrene, anthracene, phenanthrene and the like. In addition, coal gasification wastewater contains a large amount of inorganic pollutants, which are generally present in the form of ammonium salts, such as ammonium carbonate, ammonium bicarbonate, ammonium cyanide, ammonium sulfide, ammonium thiocyanate, and the like. The biodegradability of coal chemical wastewater is poor, and the lower the rank of coal is, the worse the water quality is. The tar in some high-pH coal gasification wastewater is seriously emulsified and is more difficult to treat.

Phenols in the coal dry distillation wastewater are cell protoplasm poisons, protein can be denatured at low concentration, protein can be precipitated at high concentration, various cells can be directly poisoned, and strong corrosion effect is realized on skin and mucous membrane epidermis; nitrite generated by the nitration of ammonia nitrogen under the aerobic condition has toxic action on human beings and can cause cancer or mutation. Cyanide belongs to a highly toxic substance and can cause central nervous poisoning, resulting in paralysis and asphyxia; some polycyclic aromatic hydrocarbons such as benzopyrene have strong carcinogenicity. After the coal gasification wastewater is discharged into a water body, the coal gasification wastewater has toxic and harmful effects on aquatic organisms. Meanwhile, the dissolved oxygen in the receiving water body is consumed, so that the dissolved oxygen in the water is reduced rapidly. In addition, the method can also cause water eutrophication, so that algae in the water excessively proliferate, generate peculiar smell to deteriorate the water quality, and bring great harm to drinking water sources, aquaculture industry, industry and tourism industry. If the coal carbonization waste water is directly discharged without being treated or is discharged due to insufficient treatment degree, serious environmental pollution is caused. At present, the activity of microorganisms is influenced by the low tar and phenol removal efficiency of most domestic coal chemical wastewater in the pretreatment stage, so that the wastewater is difficult to discharge up to the standard, and becomes a technical bottleneck of coal chemical industry and wastewater treatment.

Disclosure of Invention

Aiming at the problems of high treatment difficulty, high treatment cost, substandard effluent, environmental pollution and the like of coal carbonization wastewater, the invention aims to provide a method for treating coal carbonization wastewater, namely a method for treating coal carbonization wastewater by oil separation, cyclone air flotation, filtration, extraction dephenolization, pH adjustment, rectified ammonia distillation, biological oxygen deficiency, SBR oxidation, CWPO oxidation and coagulating sedimentation, wherein after coal carbonization wastewater is treated, the coal carbonization wastewater reaches the discharge standard of coking chemical industry pollutants GB 16171-2012.

In order to achieve the purpose, the coal dry distillation wastewater is treated by oil removal, cyclone air flotation, filtration, extraction dephenolization, pH adjustment, rectification ammonia distillation, biological oxygen deficiency, SBR oxidation, CWPO oxidation and coagulating sedimentation. Removing floating oil and ash slag in the coal carbonization wastewater by using an oil separation tank; removing emulsified oil and suspended oil by adopting a rotational flow air flotation oil remover; removing trace oil and suspended matters in the wastewater by using a filter; removing phenols in the wastewater by adopting an extraction tower; removing ammonia in the wastewater by adopting a rectification deamination tower; removing organic matters in the wastewater by using a biological anoxic tank-SBR oxidation tank to reduce COD; adopting a CWPO oxidation tower to decompose organic matters which are difficult to biodegrade in the wastewater; and removing suspended substances and adsorbing organic matters of the coiled belt part in the wastewater by adopting a coagulating sedimentation tank.

The method comprises the following specific steps:

1) oil removal: the coal dry distillation wastewater contains a large amount of coal tar which mainly exists in the form of oil slick, suspension oil and emulsified oil, and the oil separation tank is adopted to remove the oil slick and a small amount of heavy oil in the wastewater. Filling phi 50 plastic inclined plate filler in an oil separation tank by adopting an inclined tube sedimentation principle, keeping for 50-90 min, floating oil floats on the liquid surface and is collected by an oil collecting pipe, and heavy oil is sunk to the bottom of the tank and is recovered;

2) cyclone air flotation: the cyclone air-float oil remover is a device which integrates cyclone and air-float and can effectively remove oil, slag and sort. The effluent water in the step 1) contains suspended oil and emulsified oil, the suspended oil and the emulsified oil pass through a jet device through a lift pump, acid is added to perform demulsification, the pH is 2-4, the acid reacts with carbonate and bicarbonate in the wastewater to generate micro carbon dioxide bubbles, the dissolved air water enters a cyclone air flotation oil remover from a tangential inlet, and a cyclone is formed in a container through an inlet spiral sheet. Due to the centrifugal force generated by high-speed rotation, the water with high density moves to the wall of the tank, and light components such as oil drops and air bubbles are pressed to the anti-vortex inner cylinder in the middle of the tank and reach the inner cylinder wall. The oil droplets and the bubbles are combined and rise due to the density being less than that of the surrounding water, and the oil droplets are subjected to primary flotation by the rise of the bubbles. Meanwhile, secondary dissolved air water generated in the middle of the container through a reflux pump carries out secondary dissolved air flotation on sewage, oil-water separation is carried out on the sinking sewage, and separated oil drops rise in the inner cylinder. And other heavier particles sink along the tank wall to the bottom of the tank and are discharged as sludge from a sludge outlet at the bottom. The smaller oil drops adsorbed by the bubbles are gradually condensed to generate larger oil drops, a continuous layer of oil or emulsion is formed on the upper layer of the liquid in the air flotation chamber, and the generated oil-gas accumulation is continuously discharged through the outlet of the separation pipeline. The treated water is discharged from the gap between the cyclone separator and the outer cylinder through the overflow weir.

3) And (3) filtering: the filter adopts a walnut shell filter, so that residual oil in the wastewater is further removed, and the extractant is protected. And 2) filtering the effluent in the step 2) by using a walnut shell filter, and removing oil and suspended matters in the wastewater by using the hydrophilic and oleophobic properties of the walnut shells. The filtration speed is 5 m/h.

4) And (3) extraction dephenolization: and 3) passing the effluent of the step 3) through an ejector, simultaneously adding an acidic system extracting agent, fully mixing the extracting agent with the wastewater, and allowing phenols in the wastewater to enter an extraction phase in an extraction tower to achieve the aim of dephenolization. The volume ratio of the extracting agent to the waste water is 0.5-1, and the phase separation time is 10-20 min.

5) Regeneration of an extracting agent: adding the extractant in the step 4) into alkali liquor, stirring to fully mix the extractant and the alkali liquor, precipitating phenols in the extractant in a regeneration tower in the form of phenol salt, and recycling the regenerated extractant for extraction and dephenolization. The regenerant is 15-20% sodium hydroxide, the ratio of the extracting agent to the regenerant is 3-5, and the phase separation time is 30-50 min.

6) Rectifying and distilling ammonia: adding alkali into the water obtained in the step 4) to adjust the pH value to 12-13, feeding the water into a rectifying tower, heating the water by using steam, controlling the temperature to be 90-98 ℃, cooling by adopting circulating water, and recovering ammonia water; and controlling the pH value of the effluent of the rectifying tower to be 7-8.

7) Biological hypoxia: and 6) enabling the effluent to enter a biological anoxic tank, oxidizing and decomposing organic matters under the action of anaerobic bacteria, and simultaneously refluxing 50-100% of the solution in the SBR aerobic tank to realize short-range denitrification. HRT in the biological anaerobic tank is 12 h.

8) SBR oxidation: by utilizing the characteristics of high salt resistance, impact load resistance, toxic substance resistance and the like of the SBR process, the effluent in the step 7) automatically flows into the SBR aerobic oxidation tank, and meanwhile, the aeration head at the bottom is aerated to degrade organic matters through the metabolism of microorganisms. And simultaneously, the intermittent time is utilized to carry out high-efficiency denitrification. The aeration time is 26-32 h, and the intermittent time is 12-16 h.

9) CWPO catalytic oxidation: and (3) a certain amount of organic matters which are difficult to biodegrade are contained in the coal dry distillation wastewater and can only be decomposed through chemical oxidation, so that the effluent in the step 8) enters a CWPO oxidation tower, and meanwhile, a hydrogen peroxide oxidant is added to accelerate the oxidative decomposition process under the action of a catalyst, so that the concentration of the organic matters in the wastewater is reduced. Space velocity of CWPO oxidation tower is 1.

10) Coagulating sedimentation: and decoloring by using a coagulant and adsorbing organic matters in the wastewater by using a winding belt. And 9) enabling the effluent to flow into a coagulating sedimentation tank, adding an inorganic coagulant and an organic auxiliary agent in sequence to form flocs, precipitating in the sedimentation tank, and discharging the clear water after reaching the standard. The dosage of the inorganic coagulant is 100-150 mg/L, the dosage of the organic auxiliary agent is 3-5 mg/L, and the precipitation time is 1.5-2 h.

The invention has the following advantages:

the cyclone air flotation oil remover is a device which integrates cyclone and air flotation and has high efficiency in oil removal, slag removal and separation, and because the device has high efficiency and short retention time, the investment of wastewater treatment is reduced;

secondly, a large amount of micro bubbles are generated by utilizing the characteristic that the coal carbonization wastewater contains carbonate and bicarbonate and reacts with acid to generate carbon dioxide, and the micro bubbles are used for air floatation in a rotational flow air floatation device, so that the equipment investment of a bubble generator is reduced;

the autonomously developed DA type acidic system extractant is adopted for dephenolization, so that the extraction dephenolization efficiency is high, and the extraction and regeneration time is short;

and fourthly, the independently developed CWPO oxidation treatment process is adopted, organic matters, toxic inorganic matters and the like which are difficult to degrade biochemically can be effectively removed, and the method has high removal efficiency and mild operation conditions.

The method can effectively remove tar, ammonia nitrogen, phenols and other organic pollutants in the coal dry distillation wastewater. Wherein the oil removal rate of the cyclone air flotation unit reaches more than 90 percent, and the removal rate of volatile phenol of the extraction dephenolization unit reaches more than 95 percent; the ammonia nitrogen removal rate of the rectification ammonia distillation unit reaches more than 95 percent. The method is mature in technology, stable and reliable, achieves the direct discharge requirement of 'emission standard of pollutants for coking chemical industry' GB16171-2012 after the coal dry distillation wastewater is treated, and has popularization value.

Drawings

FIG. 1 is a treatment process of the present invention. The device comprises an oil separation tank, a rotational flow air flotation oil remover, a filter, an extraction dephenolization tower, an extractant regeneration tower, a rectification ammonia distillation tower, a biological anoxic tank, an SBR oxidation tank, a CWPO oxidation tower, a coagulating sedimentation tank and other units.

Detailed Description

The present invention will be described in detail with reference to the following examples and drawings.

As shown in figure 1, the method for treating the coal carbonization wastewater comprises units such as an oil separation tank, a cyclone air flotation oil remover, a filter, an extraction dephenolization tower, a rectification ammonia distillation tower, a biological anoxic tank, an SBR oxidation tank, a CWPO oxidation tower, a coagulation sedimentation tank and the like. The retention time of the oil separation tank is 60 min; adding sulfuric acid by rotational flow air flotation, and adjusting the pH to 3.8; the filter adopts a walnut shell filter, and the filtering speed is 5 m/L; adopting DA extractant for extraction dephenolization, wherein the volume ratio of the wastewater to the extractant is 2, and the extraction time is 10 min; the extractant regeneration adopts 15 percent sodium hydroxide, the volume ratio of the extractant to the sodium hydroxide is 5, and the regeneration is carried out for 30 min; adjusting the pH value of the rectification ammonia distillation wastewater to 13, 5% of condensed ammonia water; the retention time of the biological anoxic pond is 12 h; the aeration time of the SBR tank is 32 hours, the intermittent time is 16 hours, and the sludge backflow is 50 percent; the retention time of the sedimentation tank is 1.5h, and the sludge flows back by 10 percent; CWPO adopts DICP-C5 carbon catalyst, pH6.5, space velocity 1, oxidant adopts hydrogen peroxide, and dosage is 300 mg/L; the coagulating sedimentation adopts an externally purchased high-efficiency coagulant, the dosage of the inorganic coagulant is 160mg/L, the dosage of the organic auxiliary agent is 3mg/L, and the sedimentation time is 1.5 h.

The present invention will be described specifically by taking the water qualities shown in Table 1 as an example.

TABLE 1 coal carbonization wastewater quality

Example 1:

the coal dry distillation wastewater is treated by adopting oil removal, cyclone air flotation, filtration, extraction dephenolization, rectification ammonia distillation, biological oxygen deficiency, SBR oxidation, CWPO oxidation and coagulating sedimentation, the treatment amount is 3L/d, and the treatment result is shown in table 2.

TABLE 2 results of combined process treatment of circulating ammonia

As can be seen from the table 2, the oil content of the effluent water of the cyclone air flotation is reduced from 1215mg/L to 75.35mg/L, and the removal rate reaches 93.8 percent; the volatile phenol in the extracted dephenolized effluent is reduced from 5739mg/L to 98.82mg/L, and the removal rate reaches 98.3 percent; the ammonia nitrogen in the distilled ammonia effluent is reduced from 4156 to 174.2mg/L, and the removal rate reaches 95.8 percent. The COD, oil content, volatile phenol and ammonia nitrogen of the coagulating sedimentation effluent reach the direct discharge standard of pollutants for coking chemical industry GB 16171-2012.

Claims

1. A coal dry distillation wastewater treatment method comprises the following steps of sequentially connecting and combining wastewater through oil removal, cyclone air flotation, filtration, extraction dephenolization, rectification ammonia distillation, biological oxygen deficiency, SBR oxidation, CWPO oxidation and coagulating sedimentation technologies in series, and specifically comprises the following steps:

1) oil removal: the coal dry distillation wastewater contains a large amount of coal tar which mainly exists in the form of oil slick, suspension oil and emulsified oil, and the oil slick and part of heavy oil in the wastewater are removed by adopting an oil separation tank; the retention time is 50-90 min, the floating oil floats on the liquid surface and is collected by an oil collecting pipe, and the heavy oil sinks into the bottom of the pool and is recovered;

2) cyclone air flotation: enabling the effluent water obtained in the step 1) to pass through an ejector through a lift pump, simultaneously adding acid for demulsification, enabling the pH to be 2-4, enabling the effluent water to enter a cyclone air flotation oil remover from a tangential inlet, and forming a cyclone in a container through an inlet spiral sheet; due to the centrifugal force generated by high-speed rotation, water with high density moves to the wall of the tank, and light components containing oil drops and bubbles are pressed to the anti-vortex inner cylinder in the middle of the tank and reach the inner cylinder wall; the oil drops and the bubbles are combined and rise due to the fact that the density of the oil drops and the bubbles is smaller than that of the surrounding water, and the oil drops are subjected to primary flotation through the rising of the bubbles; meanwhile, secondary dissolved air flotation is carried out on the sewage in the middle of the container through secondary dissolved air water generated by a reflux pump, oil-water separation is carried out on the sinking sewage, and separated oil drops rise in the inner cylinder; other heavier particles sink to the bottom of the tank along the wall of the tank and are discharged from an oil sludge outlet at the bottom in the form of oil sludge; the oil drops adsorbed by the bubbles are gradually condensed and enlarged, a continuous layer of oil or emulsion is formed on the upper layer of the liquid in the air flotation chamber, and the generated oil-gas accumulation is continuously discharged through an outlet of the separation pipeline; the treated water is discharged from a gap between the cyclone separator and the outer cylinder through an overflow weir;

3) and (3) filtering: filtering the effluent in the step 2) by a walnut shell filter, and removing oil and suspended matters in the wastewater by utilizing the hydrophilic and oleophobic properties of the walnut shell; the filtering speed is 5 m/h;

4) and (3) extraction dephenolization: passing the effluent obtained in the step 3) through an ejector, simultaneously adding an acidic system extractant to fully mix the extractant with the wastewater, and allowing phenols in the wastewater to enter an extraction phase in an extraction tower to achieve the aim of dephenolization; the volume ratio of the extracting agent to the wastewater is 0.5-1, and the phase separation time is 10-20 min;

5) regeneration of an extracting agent: adding the extractant in the step 4) into alkali liquor, stirring, fully mixing the extractant and the alkali liquor, feeding the mixture into a regeneration tower, precipitating phenols in the extractant in the tower in the form of phenolic salt, and recycling the regenerated extractant for extraction and dephenolization; the regenerant is sodium hydroxide with the mass concentration of 15-20%, the volume ratio of the extracting agent to the regenerant is 3-5, and the phase separation time is 30-50 min;

6) rectifying and distilling ammonia: adding alkali into the water obtained in the step 4) to adjust the pH value to 12-13, feeding the water into a rectifying tower, heating the water by using steam, controlling the temperature to be 90-98 ℃, cooling by adopting circulating water, and recovering ammonia water; controlling the pH value of the effluent of the rectifying tower to be 7-8;

7) biological hypoxia: enabling the effluent obtained in the step 6) to enter a biological anoxic tank, oxidizing and decomposing organic matters under the action of anaerobic bacteria, and simultaneously refluxing 50-100% of the SBR aerobic tank solution to realize short-range denitrification; HRT in the biological anoxic tank is 10-16 h;

8) SBR oxidation: feeding the effluent obtained in the step 7) into an SBR aerobic oxidation tank, aerating by using an aeration head at the bottom, and degrading organic matters through metabolism of microorganisms; meanwhile, the intermittent time is utilized to carry out high-efficiency denitrification; the aeration time is 26-32 h, and the intermittent time is 12-16 h;

9) CWPO catalytic oxidation: introducing the effluent obtained in the step 8) into a CWPO oxidation tower, and simultaneously adding a hydrogen peroxide oxidant, under the action of a catalyst, accelerating the oxidative decomposition process, and reducing the concentration of organic matters in the wastewater; the space velocity of the CWPO oxidation tower is 0.5-21;

10) coagulating sedimentation: feeding the effluent obtained in the step 9) into a coagulating sedimentation tank, adding an inorganic coagulant and an organic auxiliary agent in sequence to form flocs, precipitating in the sedimentation tank, and discharging clear water after reaching the standard; the dosage of the inorganic coagulant is 100-150 mg/L, the dosage of the organic auxiliary agent is 3-5 mg/L, and the precipitation time is 1.5-2 h.

2. The method of claim 1, wherein: the oil separation tank adopts an inclined tube precipitation principle and is filled with a phi 50 cellular plastic inclined plate.

3. The method of claim 1, wherein: the acid in the cyclone air flotation is sulfuric acid.

4. The method of claim 1, wherein: alkali added in the rectification ammonia distillation is sodium hydroxide.

5. The method of claim 1, wherein: the concentration of the hydrogen peroxide oxidant for CWPO catalytic oxidation is 27-30%.