Titanium white powder widely used in manufacturing coatings, aspects advanced white paint, white rubber, synthetic fiber, welding, rayon dimming agents, plastic fillers and the like, and fine paper, but also for telecommunications equipment, metallurgical, dyeing, printing, Enamel, aerospace and other industries.
The main raw material of titanium dioxide is a titanium iron ore sulfuric acid and sulfuric acid. The process is a continuous production mode, the process flow is long, and the three wastes are discharged in the production process. However, as long as effective environmental protection measures are adopted, the national emission standards can be reached. This paper mainly describes the technical measures for the treatment of titanium dioxide wastewater by sulfuric acid process. In the process of wastewater treatment, the production process realizes the logic control as a whole, realizes remote automatic control, saves a lot of labor, changes the production environment, realizes the reduction of staff and efficiency, and at the same time guarantees the quality of sewage treatment. . Thereby ensuring the healthy development of the titanium dioxide industry for the benefit of future generations.
I. Wastewater discharge
The sulfuric acid method produces titanium dioxide. The wastewater mainly comes from floor washing, equipment washing and acid hydrolysis, calcining tail gas flushing water. The wastewater discharge, water quality and sulfur content in ilmenite, the number of times of washing in the process, and the operation management level are Certain relationship. The discharge of titanium dioxide wastewater in general tons of products is about 80-250t/a, the pH value is about 1-5, and it contains trace amounts of FeSO 4 ·7H 2 O. The amount of water and water quality varies greatly.
Second, the commonly used wastewater treatment process
The treatment of titanium white industrial wastewater is usually carried out by neutralization method and is generally divided into three components: preparation and dosing of neutralizing agents, neutralization reaction and sedimentation, sludge disposal and the like. The traditional titanium white production wastewater treatment process requires a large number of personnel to actually operate on site, and the air pollution and dust pollution at the job site seriously damage the health of employees. The mechatronics wastewater treatment microcomputer control system can better solve this problem.
(1) Preparation and dosing of neutralizing agents
Since Ca(OH) 2 can neutralize any concentration of acidic wastewater, and it itself has a coagulation effect on impurities in the wastewater, Ca(OH) 2 can be used as a neutralizing agent for the treatment of titanium white acidic wastewater, and the method of application can be dried. The injection or wet injection, the wet-reaction reaction is rapid, thorough, and the dosage is small, so it is widely used. The preparation of Ca(OH) 2 emulsion can be prepared by various methods. Regardless of the raw materials used, the design of the dosing system should be as tightly sealed and automated as possible to avoid dust hazard and protect the health of employees. The concentration of Ca(OH) 2 emulsion should be 5-10%.
1. Process design considerations
1 Use the bucket elevator to raise the raw materials, and ensure that the raw material block is less than 30mm. 2 Raw material quantitative transportation is easy to use spiral air conveyor to avoid dust flying. The 3Ca(OH) 2 emulsion setting tank and the storage tank should be equipped with a stirring device. The stirring method can be mechanical stirring or compressed air stirring. Most of the mechanical stirring is used. The mechanical stirring line speed is generally about 3m/s, and the air stirring intensity is 8~10L. /(sm 2 ). The selection of 4Ca(OH) 2 pump should consider the corrosion resistance and wear resistance of the pump.
2. Precautions for pharmacy equipment and dosing design in mechatronics
1 The combination of the raw material hoist and the raw material position sensor control I/O module is connected to the PLC main unit (Japan MORONC200H type) through the internal system bus. On-site increase the raw material hoist manual start and stop control buttons. 2 raw material screw conveyor, emulsified water injection control solenoid valve, emulsion liquid level sensor, emulsion concentration measurement sensor, emulsion preparation pool, stirring five I / O control module through the internal system bus, connected to the PLC host (Japan MORONC200H type), the site Increase the increase of raw material screw conveyor, emulsified water injection control solenoid valve, emulsion equipped with pool stirring manual start, stop control button.
(2) Neutralization reaction and sedimentation
Titanium white acid wastewater pays attention to H 2 SO 4 and trace FeSO 4 ·7H 2 O. It reacts with Ca(OH) 2 emulsion to form CaSO 4 precipitate. When the pH value increases to above 8, the original in the wastewater The divalent iron salt (F2+) is oxidized to a ferric salt (F3+), and the iron hydroxide colloid is a surface active substance, which can act as an adsorption and accelerate the sedimentation rate.
The dosage of Ca(OH) 2 emulsion can be adjusted by pH online control valve, and the pH value is controlled at 6.5-8.5 to achieve the best effect. According to the operation experience, the neutralization reaction residence time should be 15~30min. . Since the neutralized product CaSO 4 is heavy, gravity sedimentation can be used to remove it from the wastewater. In order to achieve better sedimentation effect and reduce CaSO 4 fouling, a high-molecular flocculant polyacrylamide (PAM) can be added before the precipitation of wastewater, so that CaSO 4 and other suspended solids flocculate or suspend particles together to increase the sedimentation rate. To reduce CaSO 4 fouling. The dosage of PAM has a great relationship with the molecular weight of PAM. Generally, the molecular weight is 3 to 6 million units, and the dosage is 0.1% to 0.15% of the amount of sewage. The in-line mixer is used to achieve continuous mixing of wastewater and PAM.
1. Process design considerations
1 Neutralization and reflection tank should be equipped with a stirring device to make the reaction uniform and rapid. The stirring method can be mechanical stirring or compressed air stirring. The mechanical stirring line speed is generally about 9m/s, the air pressure is 0.1~0.2MPa, and the air stirring intensity is 0.2m 3 /(min.m 2 ). According to the operating experience, the air is stirred. The reaction rate can be greatly increased, thereby reducing the amount of Ca(OH) 2 emulsion. It is recommended to be preferred in the design, and a diaphragm type anti-blocking aeration head is used. 2CsSO 4 is more viscous. It adopts sloping plate and inclined tube sedimentation tank, which is easy to cause sloping plate and inclined pipe to be blocked. The maintenance workload is large, and should be avoided in the design. The vertical flow sedimentation tank and the radial flow sedimentation tank have large effective volume. The utility model has the advantages of small occupied area and convenient mud discharging, and is suitable for the separation of CsSO 4 . For small-flow wastewater, the design should use vertical flow sedimentation tank and intermittent operation; for large-flow wastewater, the design should use radial flow sedimentation tank for continuous operation. 3 Due to the high viscosity of CsSO 4 , the design of the sedimentation tank should fully consider the convenience of maintenance and maintenance of the sludge removal pipe. No matter what kind of sedimentation tank, it should be completely designed on the ground. The design of the drain pipe should also avoid burying, and set the flushing water pipeline to wash regularly to avoid blocking the pipe.
2, neutralization reaction and precipitation design considerations
1Ca(OH) 2 emulsion injection control, waste acid water injection control, neutralization level sensor control I/O module is connected to the PLC host (Japan MORONC200H type) through the internal bus. On-site increase of Ca (OH) 2 emulsion injection control solenoid valve, waste acid water injection control manual start, stop control button. 2 Compressed air control, PH measurement electrode sensor I / O module is connected to the PLC host (Japan MORONC200H type) through the internal bus. On-site increase the aeration tank compressed air solenoid valve manual start stop control button. 3 After neutralization, the upper neutral water and the lower sludge water are discharged through the I/O control module respectively, and connected to the PLC main unit (Japan MORONC200H type) through the internal bus. At the scene, increase the neutral water discharge in the upper layer and the manual start and stop control of the lower sludge water discharge.
(3) Sludge treatment
In order to improve the production efficiency of the dewatering equipment , the moisture content of the wet sludge is reduced as much as possible, and the sludge discharged from the settling tank is generally concentrated in a sludge concentration tank and then dehydrated by a dehydrator. The intermittent operation of the sludge concentration tank not only plays a role in concentration, but also has certain sludge storage and buffering effects. For small-flow wastewater, due to the intermittent operation of the sedimentation tank, it also plays a certain concentration, and can be directly dewatered by the sludge dewatering machine. At present, the sludge dewatering equipment commonly used in sewage treatment mainly includes a belt filter press, a plate and Frame filter press and a centrifugal dewatering machine. Among them, the belt type filter press and the centrifugal dewatering machine are capable of continuous operation due to their large amount of processing. Widely used in the sewage treatment industry. However, for industrial sewage treatment, the selection of equipment, the operating cost of the equipment also plays a decisive role in the normal operation of the entire device.
1. Precautions for electromechanical control of sludge water dehydration
1 Neutral sludge water into the plate filter press pump, neutral water recovery flow sensor I / O module, connected to the PLC host (Japan MORONC200H type) through the internal bus. On-site increase the neutral sludge water into the plate filter press pump, manually start and stop the control button. 2 plate frame filter press automatic empty plate hydraulic control, filter cake conveyor belt machine control I / O module, connected to the PLC host (Japan MORONC200H type) through the internal bus. On-site increase the plate blank filter press automatic empty plate, filter cake conveyor belt manual start, stop control button. In short: the sulfuric acid process titanium dioxide wastewater treatment technology will increasingly become the focus of the titanium dioxide industry, reducing environmental pollution caused by wastewater discharge, will have important social benefits.
references
[1]Qin Yipeng, Wang Guipeng, Ma Qing; Treatment of waste acid and wastewater in the production of titanium dioxide by sulfuric acid process [J]; Shandong Environment; 2002-06.
[2] Liu, Wang silver; waste acid treatment in Titanium Dioxide Production by Sulfuric Acid [J]; Chemical Production and Technology: 2003 01.
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