In the treatment of micro polluted water, organic wastewater, sludge fermentation and dehydration, sterilization and disinfection of drinking water, and the scale inhibition and descaling of industrial water, the ultrasonic wave has made great achievements. However, the application of sonochemistry in water treatment has been expanding in the laboratory, but it has never been applied in industry. The reason is the lack of efficient ultrasonic reactors capable of mass processing and continuous operation. This paper introduces and analyzes several commonly used ultrasonic reactors in water treatment, and points out the future research directions of ultrasonic reactors.
1 several ultrasonic reactors for water treatment
The ultrasonic reactor is a container or system that has the ultrasonic wave to introduce and react under its action. It is a place to realize the sonochemical reaction. At present, the ultrasonic reactors used for water treatment can be summed up in two categories. One is the liquid whistle. It is used to produce ultrasonic waves by mechanical methods. The other is to use the electromechanical effect to produce ultrasonic waves, including the cleaning groove, the horn type, the cup type and the parallel plate.
1.1 liquid sentry ultrasonic reactor
The difference between this reactor and other reactors is that it produces ultrasonic waves from the jet impact reed in the medium, instead of introducing the ultrasonic wave from the external transducer into the medium, and the sound intensity in the reactor can be adjusted by changing the shape of the jet to regulate the [2i. In water treatment, liquid whistle reactor is mainly used for emulsification and homogenization of oily wastewater. In 1960, Singiser and others used different ultrasonic sources to emulsify mineral oil and water, peanut oil and water and safflower oil and water respectively. The results showed that the effect of liquid whistle treatment was better than that of other piezoelectric ultrasonic transducers.
1.2 cleaning groove ultrasonic reactor
The common cleaning tank is to put a group of parallel piezoelectric transducers at the bottom of the cleaning tank, and the coupling liquid is injected into the tank, and then the reaction container is placed in the coupling liquid. This kind of reactor is cheap and easy to operate, and its operation is simple and convenient. Most of the sonochemical reactions in the laboratory are carried out with it.
This kind of reactor has some disadvantages in industrial application: first, the acoustic impedance between the reaction container and the lotus root liquid is very different, the acoustic reflection is very serious. In the glass reactor, when the water is the lotus root liquid, the reflectivity is up to 70%; second, the sound intensity in the cleaning tank is small, generally not more than 5 W / cm: Third, counter. The efficiency of the reactor is related to the shape of the reaction vessel and the depth of the reaction vessel in the coupling liquid, so the reproducibility of the test results is poor. Fourth, the coupling fluid will increase the temperature in the reaction process because of absorbing ultrasonic energy, so it is not easy to control the reaction temperature. In view of the above shortcomings, in the actual large-scale water treatment, in order to obtain better ultrasonic treatment effect, we must use other types of ultrasonic reactors. At present, the cleaning groove ultrasonic reactor is mainly used in industrial cleaning. Compared with other cleaning methods, ultrasonic cleaning has the advantages of short cleaning time, little residue and good cleaning effect.
1.3 variable amplitude rod ultrasonic reactor
This is a very effective sonochemical reactor. The horn can make the ultrasonic energy concentrated on the smaller radiant surface, and can obtain hundreds of W / cm sound intensity on the end surface of the ultrasonic radiation, and the transmitter power of the probe is generally adjustable continuously. This reactor has the following advantages: high sound energy utilization, and the sound energy density greatly improved because of the energy fusion of the horn. It can continuously change the power to optimize the reaction conditions, and can accurately design the reactor according to the size of the sound energy density. In order to solve the shortcoming that some reactors can only run intermittently, some people have designed a swing rod immersed flow tank reactor, which can run continuously. Jorg Hofmann and other such reactors were used to study the effects of ultrasonic power, amplitude of the horn and immersion depth of the horn on the conversion degree of phenyl thiourea. The study of A.Kotronarou shows that, because of the smaller diameter of the probe (10~30 mm), the surface area of the sound wave is small, the energy efficiency is low, and its practical application is limited to the treatment of groundwater.
1.4 cup ultrasonic reactor
An ultrasonic reactor was combined with an ultrasonic tank to obtain a cup type ultrasonic reactor. Compared with the ultrasonic cleaning tank, the cup reactor has the following advantages: the energy density is high and can be adjusted; the frequency fixation can carry on the more quantitative and repeatable experiments; the temperature control is more accurate.
Compared with the horn type reactor, the cup reactor has an important advantage, that is, the tiny particles eroded by the cavitation surface of the probe will not pollute the reaction fluid. Hepher M J and.6: in 2000, 4 shapes of cup sonochemical reactors were designed, which were cylindrical, conical, circular cylindrical tower with peristaltic pump,.Prashant A with peristaltic pump cycle tapered tower in 2002, [7= combined the cup type acoustic chemical reactor with the acoustic swing bar counter, designed to synthesize two. A dual frequency reactor with the advantages of a reactor. The reactor improves the ultrasonic effect and energy utilization rate, and accelerates the reaction rate. But similar to the cleaning tank reactor, the sound intensity in the cup type ultrasonic reactor is also small. And the size of the container of the reacting liquid will be limited. Therefore, the cup type ultrasonic reactor is not very promising in the large water treatment facilities. At present, the reactor is also mainly used for water treatment in laboratories.
1.5 parallel plate near-field acoustic processor
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