The system facilitated entry of raw coal and exit of pulverized fuel from same end simultaneously.
These liners are made in different shapes so that the counter inside surface of the mill is suited for requirement of a particular application.
In addition to raising the coal temperature inside the mill for drying and better grinding, the same air works as the transport medium to move the pulverized coal out of the mill: it travels through the annular space between the fixed trunnion tubes and the rotating hot air tube onwards to the classifier.
Furthermore, to ensure sufficient velocity of pulverized fuel to avoid settling in the pipes, an additional quantity of primary air is fed into a mixing box on the raw coal circuit.
This by-pass air tapped from the primary air duct going into the mill makes an appreciable contribution to the drying of raw coal, by a flash drying effect, in addition to picking up the pulverized fuel from the mill outlet for its transportation towards the classifiers.
The tube mill output (responding to boiler load demand) is controlled by regulating the primary air-flow.
The size of the pulverized particles released from the grinding section of the mill is determined by a classifier separator.
This frame is connected by vertical tension rods to three hydraulic cylinders secured to the mill foundation.
Depending on the required coal fineness, there are two types of classifier that may be selected for a vertical roller mill.
In addition, adjusting the speed of the rotating cage can easily change the intensity of the centrifugal force field in the classification zone to achieve coal fineness control real-time to make immediate accommodation for a change in fuel or boiler load conditions.
For the applications where a micrometer-fine pulverized coal is not necessary, the static classifier, which consists of a cone equipped with adjustable vanes, is an option at a lower cost since it contains no moving parts.
For example, in 10 hours of milling, specific surfaces of 40 and 25 m2/g were obtained for alumina and barite, corresponding to 38 and 56 nm equivalent spherical diameter, respectively.
Size reduction rates for relatively coarse particles were first-order and increased linearly with power input to the mill.
Slurries of fine powders exhibited the same linear power-average density dependence as single-phase liquids.
Beater wheel mill maintenance program requires special attention due to operation under non-stationary conditions.
The purpose of this paper was to identify pulverizing process parameter that affect the beater wheel mill vibration level and severity at the same time by using statistical principles under a wide range of operating conditions.
This paper[clarification needed] intends to establish the foundations to investigate correlation of pulverizing process parameter with beater wheel mill vibration in order to set up a better predictive maintenance program.
To achieve this goal, the beater wheel mill vibration under different combinations of selected pulverizing process parameters are analyzed using statistical tools.
The results have demonstrated that the selected pulverizing process parameters do not have significant influence on beater wheel mill vibration severity.