CN115974311A - Treatment method of coal gasification wastewater - Google Patents
Treatment method of coal gasification wastewater Download PDFInfo
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Abstract
The invention relates to a method for treating coal gasification wastewater, which comprises the steps of adjusting the pH value of the coal gasification wastewater to 10.0-12.0, and adding a medicament into the coal gasification wastewater to convert calcium, magnesium and silicon ions in the coal gasification wastewater into precipitates; and the supernatant enters a softening deamination tower, and sludge particles generated by softening are filtered and removed through an ultrafiltration membrane device at the bottom of the tower while ammonia gas is removed, so that wastewater after softening deamination and pure ammonia water or ammonium sulfate solution are obtained. And recycling part of the softened and deaminated wastewater to a grey water system for carrying out lock bucket flushing or slag tank flushing of a gasification furnace, or feeding the softened and deaminated wastewater into a subsequent biochemical system for carrying out advanced treatment. The sewage blockage of the equipment can be avoided when the softened deaminated wastewater is recycled. After the coal gasification wastewater is treated by the method, and then is subjected to biochemical treatment, the additional carbon source required by denitrification of a subsequent biochemical system can be greatly reduced.
Description
Technical Field
The invention relates to the field of sewage treatment, in particular to a method for treating coal gasification wastewater.
Background
Different coal gasification technologies have great water quality difference of coal gasification wastewater. The low-temperature gasification technology, the quality of the sewage is characterized by high chemical oxygen demand, high phenol, high ammonia nitrogen, high oil and high turbidity; by adopting the technology of coal water slurry high-temperature and dry powder pressurized gasification, the sewage quality is characterized by high ammonia nitrogen, high hardness, low organic pollution degree and easy biodegradation of organic matters. The technology is mainly used for the coal gasification wastewater of organic matters with high ammonia nitrogen, high turbidity, high hardness and low concentration.
As an important branch of the novel coal chemical industry, the coal gas chemical industry can generate a large amount of wastewater in actual operation, so that the coal gasification wastewater needs to be efficiently treated.
The coal gasification wastewater mainly refers to grey water quality overflowing from a gasification furnace, and is gasification grey water containing excessive coal elements directly discharged by a gasification furnace and a washing tower, and is mainly characterized by high hardness, high ammonia nitrogen and high suspended matters, and most of the operation of the existing gasification grey water system is faced with the blockage phenomena of a heat exchanger, a washing tower, a pipeline and the like caused by the high hardness and the high suspended matters; meanwhile, a flocculating agent is added into the settling tank to precipitate suspended matters during internal circulation of the gasified grey water, a dispersing agent has to be added into the effluent of the settling tank to prevent equipment and pipelines from being blocked, and the two agents have completely opposite effects and are difficult to find a proper adjusting point, so that the gasified grey water system is unstable in operation; the gasification wastewater is discharged to a sewage treatment plant, and a series of problems such as scaling, high ammonia nitrogen and the like are brought to the sewage system. The addition of the dispersant will also cause the treatment load of the total phosphorus of the sewage treatment plant to increase. High ammonia nitrogen in the gasified wastewater usually needs a large amount of carbon sources added into a sewage system for denitrification to control the TN of the effluent of the sewage system not to exceed the standard; if total nitrogen TN is not controlled, nitrate in the total nitrogen TN can enter a subsequent zero-emission system to generate sodium nitrate (hazardous waste), so that the operation of the zero-emission system is influenced, and the disposal cost of the miscellaneous salts is increased.
Because the coal gasification wastewater contains a certain amount of dispersant, the dispersant can form a stable soluble complex with calcium and magnesium ions to influence the chemical reaction of the softening agent and calcium and magnesium, so that the traditional softening method (alkali-soda method and lime-soda method) has poor effect on hardness removal of the coal gasification wastewater. The existing treatment technology of coal gasification wastewater generally comprises the steps of directly adding a softening agent, then carrying out chemical precipitation, and then carrying out denitrification treatment, wherein the influence of a dispersing agent in water is not considered, and meanwhile, the traditional precipitation separation process has poor effect and unstable separation effect. The precipitation separation and the deamination nitrogen separation are treated separately, the process flow is longer, and the treatment cost is increased.
Disclosure of Invention
The operation of the gasified grey water system is faced with the blockage phenomenon of a heat exchanger, a washing tower, a pipeline and the like caused by high hardness and high suspended matters; meanwhile, a flocculating agent is added into the settling tank to precipitate suspended matters during internal circulation of the gasified grey water, a dispersing agent has to be added into the effluent of the settling tank to prevent equipment and pipelines from being blocked, and the two agents have completely opposite effects and are difficult to find a proper adjusting point, so that the gasified grey water system is unstable in operation; the gasification wastewater is discharged to a sewage treatment plant, and a series of problems such as scaling, high ammonia nitrogen and the like are brought to the sewage system.
The invention provides a method for treating coal gasification wastewater, which can be reused in a grey water system to carry out lock bucket flushing or slag pool flushing of a gasification furnace after the coal gasification wastewater is treated by the method, so that the pollution and blockage of equipment are avoided, and the extra carbon source required by denitrification of a subsequent biochemical system can be greatly reduced when the coal gasification wastewater is treated by the method and then is subjected to biochemical treatment.
The purpose of the invention can be realized by the following technical scheme:
the invention provides a method for treating coal gasification wastewater, which comprises the following steps:
(1) Controlling or adjusting the pH value of the coal gasification wastewater to be 10.0-12.0, adding a softening agent and a flocculating agent into the coal gasification wastewater in a drug adding reaction box (2), and uniformly mixing by using a stirrer (1) to convert calcium, magnesium and silicon ions in the coal gasification wastewater into solid or colloid particles;
(2) Enabling the supernatant treated in the step (1) to enter a softening deamination tower through a mixed liquid feeding pump (3), filtering and removing sludge particles generated by softening through an ultrafiltration membrane device at the bottom of the tower while removing ammonia gas to obtain wastewater of softening deamination, and purifying and absorbing the ammonia gas by using an ammonia gas absorption tank to obtain a pure ammonia water solution or an ammonium sulfate solution;
(3) And recycling part of the softened and deaminated wastewater to a grey water system for carrying out lock bucket flushing or slag tank flushing of a gasification furnace, or conveying the softened and deaminated wastewater to a sewage treatment system for further biochemical treatment according to design requirements. In one embodiment of the invention, the coal gasification wastewater has high hardness, high ammonia nitrogen and high SiO 2 High salt content. Compared with high-salt wastewater, coal gasification wastewater contains more and complicated impurity components, and the removal effect of directly adding the medicament on hardness is poor.
In one embodiment of the invention, the method for controlling or adjusting the pH value of the coal gasification wastewater to 10.0-12.0 in step (1) is to add a conventional pH adjusting agent to the coal gasification wastewater, and the purpose of adjusting the pH value of the coal gasification wastewater to 10.0-12.0 is to improve the softening and ammonia nitrogen removal effects of the softening and deamination process. The pH value is within the range of 10-12, ammonia nitrogen often exists in the form of free ammonia, the pH value is forward related to the pH value, the softening and ammonia nitrogen removing effects are poor, and the treatment effect cannot be achieved; since too high pH value leads to large dosage and high cost, the pH value of the coal gasification wastewater is controlled or adjusted to 10.0-12.0, preferably 10.0-11.0 based on the special composition of the coal gasification wastewater.
In one embodiment of the present invention, in step (1), an appropriate amount of softening agent is added according to the composition of the coal gasification wastewater, so that calcium, magnesium and silicon ions in the coal gasification wastewater are converted into precipitates.
In one embodiment of the present invention, in step (1), a softening agent and a flocculant are added to the coal gasification wastewater to convert calcium ions in the coal gasification wastewater into calcium carbonate, magnesium ions in the coal gasification wastewater into magnesium hydroxide, and silicon ions in the coal gasification wastewater into silicate precipitates.
The softening agent comprises sodium carbonate and sodium hydroxide, the flocculating agent comprises aluminum salt, iron salt and other agents,
the flocculant has the main functions of replacing calcium and magnesium ions by a complexing mechanism to be combined with a dispersing agent, so that the chemical reaction can be well carried out by adding a sodium carbonate medicament into the coal gasification wastewater according to theoretical approximate data, effective solid or colloidal particles are generated, and the calcium and magnesium hardness is removed by a membrane filtration mode;
the dosage of the softening agent is 100-500ppm, and the dosage of the softening agent in the coal gasification wastewater is adjusted according to the hardness of the wastewater and the scaling tendency of a system.
The addition amount of the flocculating agent is 1-100ppm, preferably 20-50ppm.
And (2) adding a chemical into the chemical reaction box in the step (1), arranging a stirring device in a circular conical bottom structure, ensuring that the liquid and the added chemical are completely mixed and react uniformly, discharging the bottom precipitate after the reaction is completely finished through gravity, conveying the bottom precipitate to a sludge treatment system for treatment, and conveying the supernatant to a softening deamination tower.
In one embodiment of the invention, in the step (2), the softening deamination tower consists of a tower body, a tower plate, a membrane component, an aeration device, an ammonia absorption tank and a water production system,
a membrane component is arranged at the bottom of the tower body of the softening deamination tower, an aeration device is arranged at the bottom of the membrane component, tower plates are installed on the upper part of the tower body in a staggered mode, water is retained by the tower plates, water distribution holes are evenly distributed, the contact area of a gas phase and a liquid phase is increased, and meanwhile the mass transfer efficiency between the two phases can be improved; in addition, the temperature of the waste liquid entering the tower is 60-70 ℃, the escape speed of ammonia gas can be better maintained, and the removal rate of ammonia nitrogen is improved.
The upper part of the tower body is made of light materials, and can be made of glass fiber reinforced plastics or other corrosion-resistant materials; the lower part is made of stainless steel, and the lower part is provided with a membrane component; the upper part and the lower part of the tower body are connected in a sealing way by flanges, and the tower body is divided into an upper part and a lower part, so that the membrane assembly is more convenient to disassemble and assemble.
The tower plate is made of CPVC, ABS, PP and other corrosion-resistant or high-strength organic composite materials. Meanwhile, the bottom of the tower plate is assisted by a stainless steel reinforcing rib and a framework.
The tower plate is provided with water retaining holes and water distribution holes uniformly, so that the contact area of a gas phase and a liquid phase is increased, and the mass transfer efficiency between the two phases can be improved.
The water production system is led out from the membrane module.
The aeration device is used for carrying out aeration treatment on wastewater in the tower body of the softening deamination tower, and liquid in the tower body is uniformly mixed by aeration, so that the surface of the membrane is washed away, and the pollution of the membrane is reduced. The temperature of the waste liquid entering the tower is 60-70 ℃, the pH value is 10-12, ammonia nitrogen usually exists in the form of free ammonia, and the aeration device simultaneously improves the removal rate of the ammonia nitrogen. Under the alkaline condition, at the temperature of 60-70 ℃, the ammonia gas is easily taken out from the liquid phase due to the arrangement of the aeration device, and the gas-liquid contact interface is enlarged through the distribution of the multistage tower plates, so that the deamination efficiency is further improved.
The ammonia absorption tank is connected with a glass fiber reinforced plastic pipeline led out from the top of the tower body, and ammonia is fully absorbed in the ammonia absorption tank. The ammonia gas that utilizes dilute sulphuric acid or water absorption tower top to collect in the ammonia absorption tank to the cooperation sets up the circulating pump and keeps certain circulation proportion in the absorption tank, so that better even absorption liquid improves absorption efficiency.
When the ammonia gas absorption tank takes dilute sulfuric acid as an absorbent, the pH at the end of absorption is generally 3.5-5.5, and the pH is preferably 4-5.
When the ammonia absorption tank takes water as an absorbent, the concentration of the obtained ammonia water is generally 1-20%, and the concentration range of the ammonia water can be determined according to the recycling requirement.
In one embodiment of the invention, in the step (2), the softening deamination tower further comprises a backwashing system and a cleaning system, and the backwashing system and the cleaning system are connected with the membrane module of the softening deamination tower and used for backwashing or cleaning the membrane.
In one embodiment of the invention, in the step (2), the water production system of the softening deamination tower comprises a water production pipeline led out from the membrane module, and a water production pump arranged on the water production pipeline.
In one of the preferred embodiments of the present invention, a backwash system and a cleaning system are provided on the water production line, the backwash system comprising a backwash water tank and a backwash line between the backwash water tank and the water production line. And the backwashing water in the backwashing water tank enters the membrane separation device through the backwashing pump to clean the membrane so as to ensure the separation efficiency of the membrane. According to the requirement, the water in the backwashing water tank can be produced water or a certain acid, alkali, sodium hypochlorite solution and the like are prepared regularly for backwashing.
In one embodiment of the invention, the membrane component is made of a high polymer material, has good acid resistance and alkali resistance, can endure long-term operation in a pH range of 1-14, has no requirement on chloride ion concentration, and does not have the problem of chloride ion corrosion.
In one preferred embodiment of the invention, the pore diameter of the membrane module is 0.05-0.1 μm, and different pore diameter ranges are selected according to requirements, so that the use requirements of various particle sizes of particles can be met. By utilizing the principle of screening and filtering, solid or colloidal particles generated by reaction are directly retained outside the membrane wire without considering the influence of the settling time and water quality fluctuation of precipitation separation in the traditional softening process (reaction-precipitation-filtration-ultrafiltration) on precipitated particles.
In one preferred embodiment of the invention, in the step (2), an absorption distributor is arranged at the bottom of the ammonia gas absorption tank, and the normal operation liquid level is controlled to be about 2-3m, so that the ammonia gas absorption efficiency is improved; the absorbent is pure water or dilute sulfuric acid, and the pH value of the absorption end point is controlled so as to supplement the absorbent in time. The ammonia absorption tank is assisted by a circulating pump, so that the solution in the ammonia absorption tank is uniformly mixed, reaches a certain recycling concentration and is absorbed by water or dilute sulfuric acid to be converted into ammonia water or ammonium sulfate solution with the highest concentration of 20%.
Removing the precipitate suspended matters in the wastewater by a softening deamination process, and synchronously softening deamination to obtain softened deaminated wastewater and pure ammonia water or ammonium sulfate solution.
In one embodiment of the invention, in the step (2), the gas-water ratio of the softening deamination tower is directly related to the ammonia nitrogen content in the wastewater, the water temperature and the pH; the water temperature is 60-70 ℃, and the pH value is 10-12, the gas-water ratio of the softening deamination tower is 50-2, preferably 20-5.
In one embodiment of the present invention, in step (2), preferably, the frequency of the softening deamination tower backwash is 1min per 2h, the online cleaning period is 7 days, and the offline cleaning period is 6 months.
In one embodiment of the invention, in the step (3), most of the softened and deaminated wastewater is recycled to the grey water system for lock bucket flushing or slag pool flushing of the gasification furnace, and ammonia water or ammonium sulfate solution can be recovered.
In the step (3), when the softened and deaminated wastewater is conveyed to a sewage treatment system for further biochemical treatment according to design requirements, compared with the original gasification wastewater, the ammonia nitrogen in produced water is greatly reduced, and the treatment cost of the biochemical system can be greatly reduced (electricity consumption is saved by 40-50%, the service life of a biochemical aerator is prolonged, and aeration holes are prevented from being blocked by calcium and magnesium particles).
The ammonia water or ammonium sulfate solution obtained based on the method has high purity and can be used for reproduction.
Compared with the prior art, the beneficial effects of the invention are embodied in the following aspects:
1) Softening and deamination nitrogen are integrated into one device, and the effects of softening and deamination nitrogen are synchronously realized;
2) Only adding a softening agent into the coal gasification wastewater can not achieve the effect of removing hardness, and the complex calcium and magnesium ions which are difficult to treat by the traditional softening method can be treated by adding a flocculating agent simultaneously;
3) The total hardness of the effluent of the softening deamination tower is less than or equal to 1mmol/L, the removal rate of silicon is more than or equal to 80 percent, the removal rate of ammonia nitrogen is more than or equal to 80 percent, the water treatment effect is stable, and the effluent of the softening deamination tower returns to a lock bucket of a gasification furnace for flushing or a slag pool for flushing, so that the stable operation of the system is ensured;
4) After the total hardness of the effluent of the softening deamination tower is reduced, the effluent enters a subsequent biochemical system, so that the pollution and blockage of aeration equipment of the biochemical system are avoided, and the stability of the biochemical system is ensured;
5) The ammonia nitrogen concentration of the softened deamination effluent is reduced, the additional carbon source required by denitrification of a subsequent biochemical system is greatly reduced, and the running cost of the biochemical system is saved;
6) The concentration of ammonia nitrogen in the softened deamination effluent is reduced, the tank capacity of a biochemical system is reduced, and the cost is further saved;
7) The bottom of the softening deamination tower is provided with an aeration device, thus slowing down the pollution of the bottom membrane component. Meanwhile, under the alkaline condition, at the temperature of 60-70 ℃, ammonia gas is easily taken out from the liquid phase by aeration, so that the deamination efficiency is improved; the softening deamination tower is provided with a plurality of stages of tower plates, so that a gas-liquid contact interface is increased, and the deamination efficiency is further improved;
8) The top of the softening deamination tower is provided with a gas collecting pipeline connected with an ammonia absorption tank, the bottom of the tank is provided with an absorption distributor, ammonia collected from the top of the ammonia absorption tank is absorbed by dilute sulfuric acid or water, and a circulating pump is arranged in the absorption tank in a matching manner to keep a certain circulating proportion, so that a better uniform absorption liquid can be used for improving the absorption efficiency.
Drawings
In order to more clearly illustrate the invention, the softening deamination tower of the figure is briefly described below.
FIG. 1 is a schematic diagram of a softening deamination process;
in fig. 1, a stirrer; 2. adding a medicine reaction box; 3. a mixed liquid feeding pump; 4. a tower body; 5. a column plate; 6. the system comprises a membrane component, 7, a water production system, 8, a circulating pump, 9, an ammonia gas absorption tank, 10 and an aeration device.
Detailed Description
The present invention will be described in detail with reference to specific examples.
The softening deamination process related in the following embodiment is shown in fig. 1, and comprises a stirrer 1, a dosing reaction box 2, a mixed liquid feeding pump 3, a tower body 4, tower plates 5, a membrane assembly 6, a water production system 7, a circulating pump 8, an ammonia gas absorption tank 9 and an aeration device 10;
the chemical feeding reaction box is of a circular conical bottom structure, a stirring device is configured, liquid and added chemicals are guaranteed to be completely mixed and uniformly reacted, sediment at the bottom is discharged through gravity after complete reaction and is sent to a sludge treatment system to be treated, and supernatant is sent to a softening deamination tower.
The softening deamination tower consists of a tower body, tower plates, a membrane component, an aeration device, an ammonia absorption tank and a water production system.
A membrane component is arranged at the bottom of the tower body of the softening deamination tower, an aeration device is arranged at the bottom of the membrane component, tower plates are installed on the upper part of the tower body in a staggered mode, water is retained by the tower plates, water distribution holes are evenly distributed, the contact area of a gas phase and a liquid phase is increased, and meanwhile the mass transfer efficiency between the two phases can be improved; in addition, the temperature of the waste liquid entering the tower is 60-70 ℃, the escape speed of ammonia gas can be better maintained, and the removal rate of ammonia nitrogen is improved.
The upper part of the tower body is made of light materials, and can be made of glass fiber reinforced plastics or other corrosion-resistant materials; the lower part is made of stainless steel, and the lower part is provided with a membrane component; the upper part and the lower part of the tower body are hermetically connected by flanges, and the tower body is divided into an upper part and a lower part, so that the assembly and disassembly of the membrane module are more convenient.
The tower plate is made of organic composite materials such as CPVC (chlorinated polyvinyl chloride), ABS (acrylonitrile butadiene styrene), PP (polypropylene) and the like, which are corrosion-resistant and have higher strength. Meanwhile, the bottom of the tower plate is assisted by a stainless steel reinforcing rib and a framework.
The tower plate is provided with water retaining holes and water distribution holes uniformly, so that the contact area of a gas phase and a liquid phase is increased, and the mass transfer efficiency between the two phases can be improved.
The water production system is led out from the membrane module.
The aeration device is used for carrying out aeration treatment on wastewater in the tower body of the softening deamination tower, the ammonia gas absorption tank is connected with a glass fiber reinforced plastic pipeline led out from the top of the tower body, and ammonia gas is fully absorbed in the ammonia gas absorption tank.
The bottom of the ammonia absorption tank is provided with an absorption distributor, and the normal operation liquid level is controlled to be about 2-3m, so that the ammonia absorption efficiency is improved conveniently; the absorbent is pure water or dilute sulfuric acid, and the pH value of the absorption end point is controlled so as to supplement the absorbent in time. The ammonia absorption tank is assisted by a circulating pump, so that the solution in the ammonia absorption tank is uniformly mixed, reaches a certain recycling concentration and is absorbed by water or dilute sulfuric acid to be converted into ammonia water or ammonium sulfate solution with the highest concentration of 20%.
The ammonia gas absorption tank takes dilute sulphuric acid as an absorbent, and the pH value of the absorption end point is generally 3.5-5.5, preferably 4-5.
The ammonia gas absorption tank takes water as an absorbent, the concentration of the obtained ammonia water is generally 1-20%, and the concentration range of the ammonia water can be determined according to the recycling requirement.
And the backwashing system and the cleaning system are connected with the membrane module and are used for backwashing or cleaning the membrane module.
Specifically, the water production system comprises a water production pipeline led out from the membrane module and a water production pump arranged on the water production pipeline. A backwashing system and a cleaning system are arranged on the water production pipeline, the backwashing system comprises a backwashing water tank and a backwashing pipeline between the backwashing water tank and the water production pipeline, and a backwashing pump is arranged on the backwashing pipeline; the cleaning system comprises an acid metering tank, an acid dosing pump, an alkali metering tank, an alkali dosing pump, a sodium hypochlorite metering tank, a sodium hypochlorite dosing pump and other equipment. And the backwashing water in the backwashing water tank enters the membrane component through the backwashing pump to clean the membrane so as to ensure the separation efficiency of the membrane. According to the requirement, the water in the backwashing water tank can be produced water or a certain acid, alkali, sodium hypochlorite solution and the like are prepared regularly for backwashing.
In the following embodiments, the membrane module is made of a high polymer material, has good acid resistance and alkali resistance, can withstand long-term operation in a pH range of 1-14, has no requirement on chloride ion concentration, and does not have the problem of chloride ion corrosion.
In the following embodiments, the membrane module has a pore size of 0.05-0.1 μm, and different pore size ranges are selected as required, so that the use requirements of various particle sizes can be met. By utilizing the principle of screening and filtering, the particles generated by the reaction are directly trapped outside the membrane filaments without considering the influence of the settling time and water quality fluctuation of the precipitation separation in the traditional softening process (reaction-precipitation-filtration-ultrafiltration) on the precipitated particles.
For the convenience of understanding, the present invention will be described more fully and in detail below with reference to the following examples, which are not intended to limit the scope of the present invention.
Example 1:
a method for treating coal gasification wastewater comprises the following steps:
(1) Taking 40L of coal gasification wastewater;
(2) 148.9g of 30 percent sodium hydroxide solution is added to adjust the pH value to 11, 20mg/L of flocculating agent and 70g of anhydrous sodium carbonate are added into a dosing reaction box to be fully mixed and reacted.
(3) The supernatant of the mixed liquid is treated in a softening deamination tower, and the parameters of the softening deamination tower are controlled: gas-water ratio of 50.
(4) And (5) measuring the values of calcium, magnesium, silicon and ammonia nitrogen in the effluent.
As can be seen from the data in the table, after the coal gasification wastewater is subjected to softening and deamination treatment, the total hardness (calcium + magnesium) =0.28+0.03=0.31mmol/L, the removal rate of the hardness is 98%, the removal rate of silicon is 84.1%, and the removal rate of ammonia nitrogen is 82.2%.
Example 2: a method for treating coal gasification wastewater comprises the following steps:
(1) Taking 40L of coal gasification wastewater;
(2) After 156.3g of 30% sodium hydroxide solution was added to adjust the pH to 10, 30mg/L of a flocculant and 70g of anhydrous sodium carbonate were added to the solution and reacted sufficiently in a chemical-addition reaction tank.
(3) The supernatant of the mixed liquid is treated by a softening deamination tower, and the parameters of the softening deamination tower are controlled: the gas-water ratio is 30.
(4) And (5) measuring the values of calcium, magnesium, silicon and ammonia nitrogen in the effluent.
| Ca | Mg | Si | NH3-N | |
| Raw water | 16.55mmol/L | 0.76mmol/L | 2.14mmol/L | 20.79mmol/L |
| Discharging water | 0.39mmol/L | 0.01mmol/L | 0.32mmol/L | 3.25mmol/L |
| Removal rate of | 85.0％ | 84.4％ |
From the data in the above table, after the coal gasification wastewater is subjected to softening deamination treatment, the total hardness (calcium + magnesium) =0.39+0.01=0.4mmol/L, the removal rate of silicon =85.0%, and the removal rate of ammonia nitrogen =84.4%.
Example 3:
a method for treating coal gasification wastewater comprises the following steps:
(1) Taking 40L of coal gasification wastewater;
(2) Adding 30% sodium hydroxide solution to adjust pH to 12, adding anhydrous sodium carbonate and 50mg/L flocculant, and reacting in a chemical reaction tank.
(3) The supernatant of the mixed liquid is treated by a softening deamination tower, and the parameters of the softening deamination tower are controlled as follows: gas-water ratio of 40, hydraulic retention time of 30min.
(4) And (5) measuring the values of calcium, magnesium, silicon and ammonia nitrogen in the effluent.
From the data in the table, after the coal gasification wastewater is subjected to softening and deamination treatment, the total hardness (calcium + magnesium) =0.5+0.01=0.51mmol/L, the removal rate of silicon =90.0%, and the removal rate of ammonia nitrogen =85%.
The embodiments described above are described to facilitate an understanding and use of the invention by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.
Claims (10)
1. The method for treating coal gasification wastewater is characterized by comprising the following steps of:
(1) Controlling or adjusting the pH value of the coal gasification wastewater to be 10.0-12.0, adding a softening agent and a flocculating agent into the coal gasification wastewater in a drug adding reaction box (2), and uniformly mixing by using a stirrer (1) to convert calcium, magnesium and silicon ions in the coal gasification wastewater into solid or colloidal particles;
(2) The supernatant treated in the step (1) enters a softening deamination tower through a mixed liquid feeding pump (3), ammonia gas in the supernatant is removed, and simultaneously sludge particles generated by softening are filtered and removed through an ultrafiltration membrane device at the bottom of the tower, so that wastewater after softening deamination is obtained; purifying and absorbing ammonia gas by using an ammonia gas absorption tank to obtain a pure ammonia water solution or an ammonium sulfate solution;
(3) And recycling part of the softened and deaminated wastewater to a grey water system for carrying out lock bucket flushing or slag tank flushing of a gasification furnace, or conveying the softened and deaminated wastewater to a sewage treatment system for further biochemical treatment according to design requirements.
2. The coal gasification wastewater treatment method according to claim 1, characterized in that in the step (1), under the alkaline condition of pH value of 10.0-12.0, softening agent and flocculant are added into coal gasification wastewater to remove calcium and magnesium ions and scaling pollutants including silicon dioxide in wastewater, and sludge generated after softening partially settles at the bottom of the dosing reaction tank (2) and is discharged to a sludge treatment system; the supernatant of the dosing reaction box (2) enters a softening deamination tower for further solid-liquid separation and ammonia nitrogen removal;
the softening agent comprises sodium carbonate and sodium hydroxide, the flocculating agent comprises aluminum salt and ferric salt, and the adding amount of the softening agent in the coal gasification wastewater is adjusted to be 100-500ppm according to the hardness of the wastewater and the scaling tendency of a system.
3. The coal gasification wastewater treatment method according to claim 1, wherein in the step (2), the softening deamination tower comprises a tower body (4), tower plates (5), a membrane module (6), an aeration device (10), an ammonia gas absorption tank (9) and a water production system (7);
a membrane component (6) is placed at the bottom of a tower body (4) of the softening deamination tower, an aeration device (10) is arranged at the bottom of the membrane component (6), tower plates (5) are installed on the upper part of the tower body (4) in a staggered mode, water is retained by the tower plates (5) and water distribution holes are uniformly distributed, the contact area between a gas phase and a liquid phase is increased, and meanwhile, the mass transfer efficiency between the two phases can be improved;
the upper part of the tower body (4) is made of light materials, the lower part of the tower body is made of stainless steel materials, and the lower part of the tower body is provided with a membrane component (6); the upper part and the lower part of the tower body (4) are hermetically connected by flanges; the tower plate (5) is made of organic composite material;
the membrane component (6) adopts an ultrafiltration membrane;
the water production system (7) is led out from the membrane module (6);
the aeration device (10) is used for carrying out aeration treatment on wastewater in the tower body (4) of the softening deamination tower, the ammonia absorption tank (9) is connected with a pipeline led out from the top of the tower body (4), and ammonia is fully absorbed in the ammonia absorption tank (9).
4. The coal gasification wastewater treatment method according to claim 3, wherein in the step (2), the softening deamination tower further comprises a backwashing system and a cleaning system for the membrane modules (6), and the backwashing system and the cleaning system are used for backwashing or cleaning the membrane modules (6) at the bottom.
5. The method for treating coal gasification wastewater according to claim 3, wherein an absorption distributor is arranged at the bottom of the ammonia gas absorption tank (9), and the normal operation liquid level is controlled to be 2-3m, so that the absorption efficiency of ammonia gas is improved; the absorbent in the ammonia absorption tank (9) is pure water or dilute sulfuric acid, and the pH value at the absorption end point is controlled so as to supplement the absorbent in time.
6. The method for treating coal gasification wastewater according to claim 5, wherein the ammonia gas absorption tank (9) is assisted by a circulating pump (8) to ensure that the solution in the ammonia gas absorption tank (9) is uniformly mixed and reaches a certain recycling concentration;
when the ammonia gas absorption tank (9) takes dilute sulfuric acid as an absorbent, the pH value of the absorption end point is 3.5-5.5, and the pH value is preferably 4-5;
when the ammonia gas absorption tank (9) takes water as an absorbent, the concentration of the obtained ammonia water is 1-20%.
7. The coal gasification wastewater treatment method according to claim 1, wherein in the step (2), the softening deamination process is used to remove the precipitated suspended matters in the wastewater, and the ammonia nitrogen is purified and absorbed synchronously, so as to obtain the softened deaminated wastewater and a pure ammonia water solution or an ammonium sulfate solution.
8. The method for treating coal gasification wastewater according to claim 1, wherein in the step (2), when the water temperature of the supernatant is 60-70 ℃ and the pH is in the range of 10-12, the gas-water ratio of the softening deamination tower is 50-2, preferably 20-5.
9. The coal gasification wastewater treatment method according to claim 1, wherein in the step (2), the backwashing frequency of the ultrafiltration membrane in the softening deamination tower is 1min per 2h backwashing, the online cleaning period is 30 days, and the offline cleaning period is 6 months.
10. The coal gasification wastewater treatment method according to claim 1, wherein the total hardness of the effluent of the softening deamination tower is less than or equal to 1mmol/L, the removal rate of silicon is greater than or equal to 80%, and the removal rate of ammonia nitrogen is greater than or equal to 80%.
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| CN117088522A (en) * | 2023-10-19 | 2023-11-21 | 中国农业科学院农业环境与可持续发展研究所 | Black ash water treatment equipment with low maintenance cost |
| CN117088522B (en) * | 2023-10-19 | 2024-02-06 | 中国农业科学院农业环境与可持续发展研究所 | Black ash water treatment equipment with low maintenance cost |
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