https://cementl.com/ This is a ZJTL Model Vertical roller mill coal pulverizer used in cement production line and power plant, the model is similar to babcock wilcox but it is actually developed by our own in 2002 and has over 2000 sets sold world wide. We also looking forward to be the supplier of Bobcock Wilcox, please contact us if possible.
Website: https://cementl.com/
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In thermal power plants that operate with pulverized coal firing, fuel preparation is one of the most important steps. The vertical roller mill (VRM) is widely used for this purpose, since it can dry, grind, and classify coal in a single unit. This type of mill replaces traditional ball tube mills or bowl mills in many modern installations, offering steady product quality and lower auxiliary power consumption.
A coal VRM handles raw coal with a particle size up to 50 mm and moisture content typically in the range of 10–15%. The mill consists of a rotating grinding table and two to four grinding rollers. Coal is fed to the center of the table, and centrifugal force moves it outward under the rollers. The grinding pressure is controlled hydraulically, with operating forces usually between 1000 and 2500 kN, depending on the mill size. Simultaneously, hot primary air from the boiler air preheater enters the mill housing at 250–300°C, drying the coal as it is ground.
The ground coal is lifted by the gas stream to the integrated classifier located above the mill. The classifier separates fine particles and sends them as pulverized fuel to the burners, while coarse particles return to the table for further grinding. The required fineness depends on the boiler design. In subcritical boilers, 70–75% passing 75 μm is common, while in supercritical and ultra-supercritical units, finer grinding is preferred to achieve 80–85% passing 75 μm.
The mill throughput depends on boiler load. A typical VRM in a 500 MW unit has a capacity of 55–65 tons per hour of pulverized coal at design fineness. The mill motor power ranges between 1200 and 2000 kW. Differential pressure across the mill (500–900 mm water gauge) is an important parameter for monitoring material circulation. Gas flow and damper settings are adjusted to maintain proper drying and classification.
Operation safety is a critical aspect in coal grinding. Since pulverized coal is highly combustible, the mill is designed with explosion vents, CO detection, and inertization systems. In many plants, nitrogen or CO₂ is used to purge the mill during startup and shutdown. The grinding housing is lined with wear-resistant segments, and the rollers are equipped with hardfaced surfaces to achieve 6000–8000 hours of service before refurbishment.
Coal VRMs are usually located in the mill bay under the boiler bunkers. The system layout includes raw coal feeders, mill body, classifier, primary air fan, pulverized coal piping, and burner distribution lines. The feeders (gravimetric belt or rotary type) control the coal flow into each mill, ensuring balanced supply to all boiler burners. The pulverized coal is transported pneumatically to the burner nozzles, where it mixes with secondary air for combustion. Flame temperature in the furnace can exceed 1800°C, and stable coal fineness from the mill ensures uniform flame shape and reduced unburnt carbon.
Overall, the coal vertical roller mill in a power plant is not just a grinding unit but a key part of the fuel firing system. It connects the raw coal supply to the boiler burners, and its performance directly affects boiler efficiency, emissions, and load response. For reliable plant operation, careful control of air-fuel ratio, mill differential pressure, and product fineness is required on a continuous basis.
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