Coal mining generated a lot of dust, not only seriously affect the health of the miners, but also has explosive coal dust, coal mine production safety threat. In recent years, with the increase in the intensity of coal mining, dust prevention issues have become increasingly prominent. At present, China’s significant coal mine dust control measures are spraying dust, use an air spray nozzle to clean, dust and spray as the primary element atomization (fog mist particle shape and size of the stream) directly determine the effect of spray dust.
Classification and characteristics of spray nozzle design
1,According to the shape of the nozzle flow, fog formation can be a solid cone nozzle into a hollow cone nozzle and nozzle into two categories.
Solid nozzle dust mainly dominated hollow nozzle dust barrier. Solid fog nozzle velocity tapered columns larger solid fog, mist particles of dust collision can down. But because big mist flow velocity, air entrainment around easily be smaller respirable dust particle vanishes objectively affected dust effects. Hollow cone nozzles mist curtain to dust resistance mainly to make fog screen area coverage increase, generally have a lot of fog curtain cone angle nozzle is relatively far away from the dust source. This also caused the large diameter end of the curtain fog, mist particle velocity has been reduced to a very small, except not capture dust particles, but also lost a dust barrier effect.
From the fog body shape analysis, in its full-length area, the density ratio of solid density spray mist spray large mist hollow in the effective range of solid spray, under normal circumstances is difficult to pass through the fog of coal dust curtain, so , solid conical mist fog over the hollow conical body effect is better.
2, according to the atomization method of classification
(1) mechanical atomization
Mechanical atomization mainly by a high-speed jet of liquid under pressure to make their action resulting atomized thus can be divided into a direct nozzle, centrifugal rotary nozzles, and nozzle.
Direct atomization and centrifugal atomization can be referred to as pressure atomization. Direct-injection nozzle mainly rely on water to achieve the purpose of atomized water pressure is relatively high, and the larger the diameter of the hole the more coarse spray atomization, the nozzle diameter is not too large, the flow adjustment range is relatively small. Centrifugal high-pressure water nozzle is the use of centrifugal force generated by the swirl device generates film was broken and spray air. Centrifugal atomization is better than direct atomization, but it also requires a higher water pressure, so the application conditions are somewhat limited.
Rotary nozzle body and rotating the rotary roughly divided into two categories vents. Rotating body is divided into a spinning cup and rotary disc. Atomizer front rotor is sprayed into the conical water rotor, the rotor using high-speed rotating exhibition of water into a thin film by “centrifugal spray” and “speed spray” comprehensive action atomized liquid. Similarly, relying on the high-speed rotary disc atomizer to atomize the liquid rotating disk.
(2) medium atomization
Depending on the mode of atomization is divided into a wide range of pneumatic nebulization and bubble atomization, pneumatic spray nozzle applications.
A pneumatic spray nozzle relying on gas pressure (compressed air or steam) is formed high-speed airflow, so that formation of a high relative velocity between the object to achieve the atomization air and water. The advantage is possible to obtain good results at lower atomization pressure, and the working conditions can be adjusted within a wide range. But not an only power source
First, a complex system.
(3) special nozzle atomization
Special nozzles use ultrasonic, electromagnetic, electrostatic interactions, such as the principle of atomization. Although in some other kind of industrial nozzle applications with good results, the coal mine harsh environment caused fewer applications.
Second, the factors that affect the ability of the spray nozzle.
A pressure nozzle
When using a pressure type spray nozzle (direct and centrifugal) implementation spray dust for determining the use of the occasion, dust efficiency depends mainly on the water pressure, different size of dust required water pressure is different, more subtle forces require dust higher. Water pressure is high, not only can get fine mist particles, but the particle velocity mist also makes substantial space large water content, which is the primary mechanism for the dust to collisions method is hugely beneficial. Based on the actual dispersion of dust particles and dust efficiency requirements, refer to the corresponding graph to select the appropriate pressure can achieve good results and the best value for money. This conclusion applies to any spray nozzle using pressure spray settlement coal dust in the workplace.
2, two-phase nozzle
For two-phase type nozzle atomization capacity affected by the following factors:
Impact of (1) mixing tube diameter and length
Mixing tube diameter becomes smaller, can increase the relative velocity of the gas-liquid two-phase, is conducive to fog, but it will also affect the cohesion and re-atomized particles. Because the mixing tube is too long, gas energy loss is much worse it would flow atomization; If the mixing tube is too short, the gas energy cannot be fully utilized, resulting in inadequate fluid atomization.
(2) Effect of nozzle
Because narrow exit area will increase exports drop, resulting in accelerated gas-liquid two mixed and matter significantly enhanced, while the gas-liquid relative velocity between the two phases increases, also contributed to more liquid fine crushing. However, exports will inevitably increase the pressure drop increases mixing tube, resulting in the relative velocity of the two-phase gas-liquid mixing tube is reduced, which in turn causes the fogging worse.
(3) the relationship between particle size and atomization gas-liquid ratio
With the gas-liquid ratio increases, the droplet size was decreasing trend. Therefore, increasing the relative speed of the gas-liquid ratio increase gas-liquid two-phase, so that more detailed breakup. However, the gas-liquid ratio is increased to a certain extent, but no significant change in particle size.
(4) changes in droplet concentration with the gas-liquid ratio
As the gas-liquid ratio increases, the particles tend to decrease the concentration of the water, because of reduced water content in the air caused.
Third, to improve the atomization nozzle design approach.
According to atomization mechanism and experimental studies, combined with the mine site experience, improving access to the nozzle atomization mainly in the following aspects:
(A) increasing the relative speed difference between the gas-liquid two-phase gas to increase power, the larger droplets in the aerodynamic effect, more finely crushed.
(2) Improve the liquid outlet nozzles to increase the speed of the collision, the relative discharge of the collision of the droplets can be further broken. It was found that, if the exit velocity of the droplet is small, the convergence of the droplets larger than if the exit velocity of the large droplet, to improve the degree of atomization. However, this would reduce the relative speed of gas and liquid, so aerodynamic atomized droplets worse.
(3) The results show a significant impact nozzles, mixing tube geometry and dimensions of the atomization performance. Therefore, in the design of the model, except that they were on considerations atomized, they should be considered together after the change of the overall performance.
(4) Research spraying water system flow, pressure and nozzle geometry, the relationship between structure and shape, improving atomization. In particular, the impact on the water supply system pressure atomization larger, the higher the pressure, the more water mist particles. But the problems caused by high water pressure is:
① energy consumption;
② water supply system components to withstand all the pressure, failure-prone, short life, especially mining
Dig the spray system on the device. This presents us with another research topic: how limited water pressure, improve the structure of the pressure type spray nozzle for fine mist particles.
By classification and characterization, pointing out that the scope of various types of nozzles and nozzle atomization in the analysis by factors that affect the ability to put forward ways to improve the nozzle atomization. To improve
Atomization nozzle and the nozzle characteristics must match the supply system, and improve water quality, enhance the accuracy of the spray water filtration