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Many existing pulverized coal (PCF) power plants operate at a fixed, steady load (i.e., base load operation). However, there is a growing need for load following or flexible operation, which requires flexibility in most components of the plant. Flexibility and efficiency can be improved by tightly controlling the coal grinding plant. Below we present a few facts to give you an idea of the importance of ACM to grind coal into powder form.
l How to Achieve Optimal Performance?
l What are the constraints?
l Combustion system requirements
As with any high-performance thermal machinery, achieving optimal performance depends on the quality of the fuel supplied to the plant. For PCF, it is not only the calorific value of the pulverized coal that affects performance, but also the size and shape of the particles. So does the rate at which the coal is blown into the furnace. This is all controlled by the coal mill or pulverizer and its associated feeder equipment. The operation of a coal mill affects the climb rate of a power plant and its ability to handle rapid changes in output. For coal-fired power plants, the response time of the mill is critical to the overall response time to changes in demand.
Flexible operation or load tracking requires that the output of the plant can vary based on demand and allowable ramp rates. The electrical output can be varied by changing the mechanical output of the turbine. There are several ways to do this, but all depend on the ability of the fuel supply and combustion system to respond to changes in demand.
A typical PCF plant can operate as low as 40% to 50% of maximum capacity, but new flexibility requirements call for operation as low as 20% or less. The limiting factor may be the coal mill itself. This is usually addressed in multi-mill operations by shutting down some mills and burners, but this usually requires modifications to the furnace burner arrangement to ensure that the flame can be sustained at low loads. Improvements to the coal mill and tighter controls allow operation at lower load levels.
The fineness of the pulverized coal and the uniformity of the coal stream fed to the burner are key parameters for achieving efficient combustion in coal-fired power plants. The coal pulverizer or mill is the heart of the PCF boiler. Often, the root cause of non-optimized combustion is the pulverizer. Capacity, reliability and environmental issues such as slagging, fouling and higher than expected CO or NO emissions; superheater and reheater tube metal overheating, and slag fouling of selective catalytic reduction catalysts and air heaters are sometimes associated with poor pulverizer performance.
Conclusion
Air classification mills operate in the medium to fine particle size range, providing guaranteed accurate particle size and achieving steep particle size distribution with a minimum of ultrafine particles thanks to highly efficient, variable speed dynamic integral air classifying.
Our continuous improvements have created a broad product range suitable for processing a wide variety of even difficult materials. With no potentially damaging product temperature rise, the ACM is even suitable for grinding viscous, fatty or oily materials and has achieved considerable success in chocolate grinding.
This type of mill operates on the impact grinding principle with high rotor speeds and impact edge speeds of up to 120 m/s. Size reduction is achieved by the influence of material particles on the rotating grinding surface (hammer or pin) and the fixed liner or grinding track. With the integral classifying design, particle size, distribution and cutting point can be precisely controlled by variable classifying speed.
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