In the case of the size and structure of the cyclone, t […]
In the case of the size and structure of the cyclone, the key to the dust removal efficiency lies in the influence of operating factors.
The cyclone dust collector uses centrifugal force to remove dust. The greater the centrifugal force, the better the dust removal effect. In the circular motion (or curved motion), the centrifugal force of the dust is F = ma, where F, centrifugal force, N; m - the mass of the dust, kg; a - the centrifugal acceleration of the dust, m / s2. Because, a = VT2 / R, where VT - the tangential velocity of the dust particles, m / s; R - the radius of rotation of the airflow, m, so, F = mVT / R. It can be seen that in the case where the structure of the cyclone is fixed (R is constant) and the dust is the same (m is stable), the airflow speed of the cyclone dust collector is increased, and the centrifugal force of the cyclone is larger.
The inlet air volume of the cyclone is Q=3600AVT, where Q is the inlet gas volume of the cyclone, m3/h; A——the inlet cross-sectional area of the cyclone, m2. Therefore, in the case of fixed structure (R is constant, A is unchanged) and dust is the same (m stable), the airflow velocity of the dust collector population is proportional to the inlet gas volume, and the inlet gas volume of the cyclone dust collector is controlled by the induced draft fan. The amount of wind is determined.
It can be seen that increasing the airflow velocity of the air inlet can increase the tangential velocity of the airflow in the dust collector, so that the centrifugal force of the dust is increased, which is beneficial to improving the dust removal efficiency, and at the same time, improving the dust-containing air volume. However, the airflow velocity of the air inlet is increased, the radial and axial speeds are also increased, and the influence of turbulence is increased. For each specific dust cyclone, there is a critical air inlet velocity. When this wind speed is exceeded, the influence of turbulence is increased faster than the separation, so that some of the separated dust is taken away again, affecting the dust removal effect. . In addition, as the air inlet airflow increases, the dust removal resistance also rises sharply, the pressure loss increases, and the power consumption increases. Considering the dust removal effect and economy of the cyclone dust collector, the airflow speed of the air inlet is controlled between 12~20 m/s, and the maximum is no more than 25m/s. Generally, 14m/s is suitable.
Dust particle size is a key factor affecting the concentration of the outlet. The dust swirling outside the cyclone is simultaneously subjected to two forces in the radial direction. First, the centrifugal force generated by the tangential velocity of the swirling airflow causes the dust to be subjected to outward displacement; the other is caused by the swirling airflow. The centripetal force generated by the radial velocity causes the dust to be subjected to an inward displacement. At the interface between the inner and outer swirls, if the centrifugal force generated by the tangential velocity is greater than the centripetal force generated by the radial velocity, the dust is moved outward by the inertial centrifugal force and is separated; if the centrifugal force generated by the tangential velocity Less than the centripetal force generated by the radial velocity, the dust enters the inner swirling flow under the push of the centripetal force, and finally is discharged through the exhaust duct. If the centrifugal force generated by the tangential velocity is equal to the centripetal force generated by the radial velocity, that is, the external force acting on the dust particles is equal to zero, in theory, the dust should constantly rotate at the interface. In fact, due to the turbulent flow of the airflow and various random factors, 50% of the dust in this state may enter the internal swirl, and 50% may move to the outer wall, and the dust removal efficiency should be 50%. The critical dust particles separated at this time are referred to as split particle diameters. At this time, the interface between the inner and outer swirls is like a screen with a pore size of divided particles, and the dust larger than the divided particle size is trapped and trapped by the screen, and the dust smaller than the divided particle size passes through the screen. Discharge from the exhaust duct.
The smaller the particle size of the dust collected by the cyclone, the higher the dust removal efficiency of the dust collector. The magnitude of the centrifugal force is related to the dust particles. The larger the particles, the greater the centrifugal force. When the particle size and tangential velocity of the dust are larger, the radial velocity and the diameter of the exhaust pipe are smaller, and the dust removing effect is better. The ash concentration in the gas is also a key factor affecting the outlet concentration. When the dust concentration is increased, the dust tends to agglomerate, so that the smaller dust particles are gathered together and trapped. At the same time, the large particles are also separated from the wall or impact by the small particles moving toward the wall. However, due to the downwardly high-speed rotation of the airflow in the precipitator, the pressure at the top of the precipitator is lowered, and some of the airflow is also rotated along the outer wall to the top, and then rotated along the outer wall of the exhaust pipe to be discharged by the exhaust pipe, resulting in exhaustion. The dust removal efficiency of the cyclone can not be 100%.
According to the dust removal efficiency calculation formula η = (1- So / Si) × 100%, where η - dust removal efficiency; So - the amount of dust at the exit, kg / h; Si - dust at the entrance The amount of people, kg / h.
Because the dust removal efficiency of the cyclone dust collector cannot be 100%, when the amount of imported dust flow increases, the dust removal efficiency will increase, and the absolute amount of dust discharged from the exhaust pipe will also increase greatly. Therefore, in order to reduce the dust concentration of the discharge port, it is necessary to reduce the inlet dust concentration, and a multi-stage dust removal method in which a plurality of cyclone dust collectors are used in series can be adopted to achieve the purpose of reducing emissions.