Advanced treatment process of smelting flue gas acid-making wastewater
The existing industrial wastewater treatment technologies include chemical method, redox method, extraction method, ion exchange method, adsorption method, membrane separation method, etc. Pollutant Discharge Standard” requirements, but the total hardness of the effluent is 3~5g/L, the mass concentration of chloride ions is 500~7000mg/L, and the TDS is 6~8g/L.
Also contains a certain concentration of iron, zinc, copper and other ions. According to the water quality characteristics, the advanced treatment project of 600m3/d production wastewater plans to adopt the combined treatment process of chemical method and membrane separation method, chemical method is used for pretreatment, and membrane separation is used for advanced treatment.
The pretreatment mainly removes calcium and iron, so that the total hardness of the wastewater is reduced to less than 300mg/L, and the mass concentration of iron ions is less than 0.1mg/L, which meets the water quality index requirements of advanced membrane treatment.
The membrane advanced treatment system mainly removes the salts and various ions dissolved in the water, so that the water quality of the effluent meets the water quality requirements for recycling water.
The principle and process of advanced wastewater treatment process
2.1 Preprocessing
The high-hardness industrial wastewater is pumped into the adjustment tank through the raw water pump, and the water quality and quantity of the influent are uniform; an oxidation air duct is set in the adjustment tank to oxidize the Fe2+ ions in the raw water quality to Fe3+ ions.
The oxidized wastewater enters the decalcification tank, and the pH value is adjusted to 10-12 by adding w(NaOH) 30% sodium hydroxide solution; the soda ash solution with a mass fraction of 10% is continuously and uniformly added through the dosing pipeline to make Precipitation reaction of calcium, magnesium, copper, zinc, iron and other ions in wastewater occurs.
The reacted wastewater flows into the flocculation tank by itself, and PAC and PAM are continuously and uniformly added to the flocculation tank through the dosing pipeline for flocculation reaction, and a large number of gelatinous objects are formed in the wastewater.
Then it flows into the inclined tube sedimentation tank for solid-liquid separation, the mud in the sedimentation tank is sent out by pressure filtration, and the pressure filtrate is returned to the flocculation tank. The supernatant is sent to the clear water tank, and after testing the water quality reaches the water inlet conditions of the membrane treatment system, it is sent to the membrane treatment system for treatment.
The pretreatment reaction equation is as follows:
2.2 Film advanced treatment
The pretreated wastewater enters the multi-media filter and ultrafiltration device to remove fine particulate matter that cannot be naturally settled, such as suspended solids, colloids, organic matter, turbidity, etc.
After filtering, it enters the primary reverse osmosis device, the concentrated water reverse osmosis device, and the secondary reverse osmosis device respectively. The whole system realizes automatic control of the equipment startup, operation, backwashing, shutdown, and standby operations through PLC.
A sterilization device is installed in front of the ultrafiltration device to kill bacteria and microorganisms in the water.
As the main desalination equipment of the system, the reverse osmosis system adopts imported DOW low-pressure membrane elements, and is also equipped with pneumatic butterfly valves and measuring instruments such as flow, conductivity, pH, ORP, SDI, etc., and is automatically controlled by PLC.
In order to obtain high-quality product water and reuse it in the circulating cooling water system and improve the circulating water quality, a two-stage reverse osmosis treatment process is selected to make the product water quality index close to the boiler water quality index.
In order to reduce the amount of concentrated water and ensure that the water production rate of the system reaches more than 80%, on the basis of the two-stage reverse osmosis treatment process, the concentrated water reverse osmosis process is adopted to recycle the first-stage reverse osmosis concentrated water.
2.3 Ways to reuse concentrated water
The concentrated water produced by this project is about 120m3/d, which is used for slag slow cooling and water quenching system.
The slow cooling of converter slag consumes 10m3/d of concentrated water, the slow cooling of electric furnace slag consumes 20m3/d of concentrated water, and the water consumption of electric furnace slag water quenching system is 300m3/d.
About 120m3/d of concentrated water produced by this project can be completely consumed, realizing zero discharge of waste water recycling.
2.4 Brief description of the technological process
The high-hardness industrial wastewater is pumped into the adjustment tank by the raw water pump, and then the ferrous ions are oxidized and then sent to the decalcification tank to remove calcium; after the effluent is flocculated and precipitated, the supernatant liquid enters the multi-media filter to remove the suspended solids.
Then it enters the ultrafiltration system, and the ultrafiltration system further removes smaller particles, and the produced water enters the RO1 system, and then enters the RO2 system, and is reused after reaching the process circulating cooling water standard.
The RO1 and RO2 concentrated water enters the RO3 and RO1 systems respectively for recovery, the RO3 produced water enters the RO2 system for reprocessing, and the RO3 concentrated water is opened for slow cooling and water quenching of the slag.
The water production rate of the entire system is set to be greater than or equal to 80%, and the amount of concentrated water is less than 20%. After the membrane system is treated and the concentrated water is reused, the entire system achieves the effect of zero discharge. The process flow of 600m3/d production wastewater is shown in Figure 1.
Operation effect
After the project was put into operation, it was gradually debugged to reach full production.
The company has carried out a statistical analysis on the full-load production situation. The production time is 72 hours in total. During the test run, the raw water volume is 1990m3, and the system processing water volume is 633.33m3/d, of which the water production volume is 1673m3, the concentrated water volume is 317m3, the water production rate is 84%, and the concentrated water rate 16%. The wastewater treatment effect, equipment operation and chemical usage are as follows.
3.1 Effluent quality
The raw water has high hardness, high salinity and complex components. The ion content in the effluent after treatment is very low, which is far better than the reclaimed water quality indicators in GB50050-2007 “Design Specification for Industrial Circulating Cooling Water Treatment”. After being reused in the circulating water system, The quality of circulating water has been greatly improved. The indexes before and after treatment are shown in Table 1.
3.2 Equipment Operation
See Table 2 for the operation of the equipment after it is put into operation.
3.3 Drug use
The full-load trial production of the device is as follows: polyaluminum chloride 90kg/d, sodium carbonate 1666.7kg/d, coagulant aid 0.6kg/d, oxidizing bactericide 8kg/d, sodium bisulfite 11kg/d, hydrochloric acid 400kg/d, sodium hydroxide 58.3kg/d, primary and secondary RO scale inhibitor 2.5kg/d, concentrated acid RO scale inhibitor 1.7kg/d. The dosage of the drug is consistent with the basic dosage of the design.
Conclusion
This high-hardness smelting flue gas acid-making industrial wastewater, after oxidation, decalcification, flocculation, precipitation and desalination, reaches the industrial circulating cooling water reclaimed water quality index and then reuses it to achieve “zero” discharge of wastewater recycling.
The advanced wastewater treatment project has achieved the predetermined goals of project construction in terms of treatment load, water production rate and index control, and has been running stably and up to the standard, which has reference significance for the same industry.