Longer Working Life And Anti-Explosive Design Coal Vertical Roller
Mill
Working Principle of Coal Vertical Roller Mill
Coal is crushed and ground into fine size in the coal vertical
roller mill between the rotating horizontal grinding table and the
grinding rollers.
The axes of the tapered rollers are placed with about 15° angle to
the horizontal towards the center of the grinding table, which can
achieve optimum grinding efficiency.
Coal Vertical roller mill grinding rollers with large diameters are
placed on the grinding table surface. Coal vertical roller mill
with larger grinding rollers can brings a higher output with
increased grinding area. In addition to a rolling movement, the
coal vertical roller mill narrow rollers also bring a sliding
motion, as the roller axis and grinding table axis do not intersect
at the grinding table level. The shearing forces thus create
additional reduction of the grinding material.
Function and structure of Coal Vertical Roller Mill
Coal can be conveyed laterally or centrally onto the rotating
grinding table. Coal is crushed over here by the rollers and ground
through the action of the forces emanating from the hydraulic
roller spring assembly. When the coal vertical roller grinding mill
rollers follow the contour of the grinding bed, the roller will
also move up and down with the help of hydraulic cylinders
connected with roller arm.
The grinding coal is spun outwards by the rotation of the grinding
table. The hot gas current captures the material in the vicinity of
the louvre ring that surrounds the grinding table and conveys it to
the classifier.
Coal has an immediate contact with the hot gas in the coal vertical
roller mill, which can make the moisture contained in the coal
evaporate spontaneously, so that the desired coal vertical roller
mill outlet temperature of between 70°C to a max. of 130°C is had
been achieved in the grinding chamber.
Coarse coal powder is blocked by the classifier and falls onto the
grinding table again for renewed grinding. The qualified coal
powder passes through the classifier and goes into the pulse-jet
collector. The coal vertical roller mill is powered by a standard
motor via a vertical gearbox. Segment thrust bearings in the
gearbox absorb the roller forces. The grinding rollers are raised
hydraulically from the grinding table prior to commencing grinding.
This is realised by reversing the oil pressure exerted on the
spring assembly cylinders. The coal vertical roller grinding mill
can therefore be started in an empty or full state with a low
starting torque.
Metal to metal contact between the grinding rollers and grinding
table is prevented by the adjustable hydraulic station. And coal
vertical roller mill grinding components (such as roller, liners
and grinding tables roller) can be easily replaced.
Safety device of coal vertical roller mill
Coal powder can, under certain circumstances, combust, flash ignite
or explode as a result of:
• an increased O2 content (> 12 %) in the process room
• ignition sources being present
• large quantities of volatile material being present
• an increased CO content in the process air
• the fineness of the grinding material
• the temperature of the material and process air.
In order to prevent explosion, the follow steps are taken:
• internal operating status with max. O2 contents of approx. 10 %
• pressure-shock resistant structure
• adequate pressure relief surfaces
• O2 monitoring
• CO monitoring
• plant safety design in compliance with local regulations.
Nowadays, safety and monitoring measures are equipped with coal
vertical roller mill with a help of computer monitoring system.
Technical Data of Vertical Roller Grinding Mill:
Model
Modelo | Grinding table median diameter (mm)
Diámetro del Plato de la molienda (mm) | Capacity Capacidad (th) | Mining Slag Moisture Humedad de la escoria | Product specific surface area Superficie de area específica de escoria | Product Moisture Humedad del Producto terminado (%) | Power- (kw) |
| Hk30/2S | 2500 | 23-26 | <15% | ≥420m2/kg | ≤1% | 900 |
| Hk34/3S | 2800 | 50-60 | <15% | ≥420m2/kg | ≤1% | 1800 |
| Hk42/4S | 3400 | 70-83 | <15% | ≥420m2/kg | ≤1% | 2500 |
| Hk44/4S | 3700 | 90-110 | <15% | ≥420m2/kg | ≤1% | 3350 |
| Hk50/4S | 4200 | 110-140 | <15% | ≥420m2/kg | ≤1% | 3800 |
| Hk53/4S | 4500 | 130-150 | <15% | ≥420m2/kg | ≤1% | 4500 |
| Hk56/4S | 4800 | 150-180 | <15% | ≥420m2/kg | ≤1% | 5300 |
| Hk60/4S | 5100 | 180-200 | <15% | ≥420m2/kg | ≤1% | 6150 |
| Hk65/6S | 5600 | 200-220 | <15% | ≥420m2/kg | ≤1% | 6450/6700 |
