Vertical roller mill powder classifier Introduction

Powder classifier (also known as coarse powder separator) plays a vital role in the selection of powder during grinding. The ground material is brought up by the high-speed rotating airflow in the mill and enters the powder separator through the stationary blades. The material is screened under the high-speed rotation of the cage rotor, and the screened fine particle material is taken out by the exhaust gas and enters the cyclone. The coarse particle material falls into the grinding disc through the lower cone tube for re-grinding. The type of separator is composed of two parts, one cage rotor or impeller is fixed and another impeller is movable which will generate upstream air flow that delivers the fine powder to the finished product collector.

Strucuture of vertical roller mill

A vertical roller mill (VRM) is a type of industrial equipment used to crush or grind materials into small particles. It's widely used in the cement and mineral processing industries. The structure of a typical VRM includes the following components:

Grinding Disc: This is the main component that rotates and contains the grinding elements. The material to be ground is fed onto the grinding disc, and the grinding elements exert pressure and force to crush and grind the material.

Grinding Rollers: The grinding elements are typically rollers that are mounted on the grinding disc. These rollers can vary in size and shape, but they generally exert pressure on the material as the grinding disc rotates.

Table Liner: The grinding disc is usually lined with a replaceable table liner that helps protect the disc and maintain efficient grinding. The table liner is in direct contact with the material being ground and is subjected to wear.

Grinding Rollers shaft: A forged shaft could refer to various components such as the main shaft that supports the grinding rollers or other critical shafts within the mill's structure. These components need to withstand significant mechanical loads and stresses, and using forged shafts can ensure the necessary strength and durability.

Grinding Rollers wheel hub: The grinding roller wheel hub is a metal casting part that is mounted on the outside of the grinding roller shaft. The wheel hub refers to the central part of the grinding roller that connects it to the driving mechanism of the mill. 

Separator/classifier: A separator is used to separate the ground material from the airflow that carries it through the mill. The finer particles are lifted by the air and transported to the classifier for separation, while the coarser particles drop back onto the grinding disc for further grinding.

Middle shell: The middle casing of the vertical roller mill is a welded structural part, which supports the weight of the entire separator. There are 4 inspection doors on the middle casing for roll overhaul. The door is designed with a sealing sheath that is in close contact with the grinding rollerto Prevent air leakage. The inner wall of the middle shell is laid with a wear-resistant lining to protect the inner shell.

Drive System: A VRM is powered by a motor and a drive system that rotates the grinding disc and the rollers. The drive system can vary based on the size and design of the mill but typically involves gears or belts to transmit the rotational motion.

Base Frame: The support base of the vertical roller mill is generally four peripheral support pedestal and a central support base, and the support base and the installation foundation are connected and fixed by anchor bolts. All the vertical roller mills of Tongli will be pre-assembled and leveling calibrated before leaving the factory to ensure that the equipment can be installed smoothly on site.

Feed and Discharge System: The material to be ground is fed onto the grinding disc through a feed mechanism. Once the material is ground to the desired size, it is discharged from the mill through an outlet.

Pressure System: In Tongli VRMs, a hydraulic or pneumatic system is used to apply pressure to the grinding rollers. This pressure helps control the grinding process and ensures consistent grinding efficiency.

Design principles of vertical roller mill powder separator

Particle Classification: The primary function of the separator is to classify the ground particles from the grinding process into different size fractions. This classification is important to ensure that particles of the desired fineness are properly collected and transported out of the mill.

Coarse Material Return: The separator helps in directing the coarse particles that haven't reached the desired fineness back to the grinding zone. This recycling of coarse material allows for further grinding and ensures that only properly ground particles are collected as the final product.

Fine Particle Collection: The fine particles that have reached the desired fineness are collected and transported by air or an airflow into the product collection system.

Efficient Operation: By separating the particles of different sizes, the separator helps to maintain a stable and efficient grinding process. This prevents over-grinding and ensures that the mill operates within its optimal range, leading to improved energy efficiency and product quality.

Rotor: The separator rotor is a rotating component with vanes or blades that create an airflow within the mill. The rotor's rotation generates centrifugal forces that push the particles outward, separating them based on their size and density.

Cage or Louver System: The rotor is surrounded by a cage or louver system that directs the airflow and particles. The cage system helps to control the movement of particles and ensures effective classification.

Fines Exit: The fine particles are carried by the airflow through the rotor and exit the separator to be collected in the product collection system.

Coarse Material Exit: The coarse particles that have not reached the desired fineness are directed back to the grinding zone for further processing. This is typically achieved through a return duct or chute.

Drive Mechanism: The rotor is driven by a motor or other rotational mechanism, enabling the creation of the centrifugal forces required for particle separation.

Specifications of vertical roller mill powder classifier

Note: *The diameter is middle diameter of the grinding table

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Industry Knowledge extension

What is the difference between ball mill and vertical roller mill?

Both ball mills and vertical roller mills plays a vital role in the cement grinding plant. Ball mills are versatile and cost-effective, suitable for various materials and simple to maintain. On the other hand, vertical roller mills offer superior energy efficiency and particle size control, making them ideal for cement and ore grinding applications. The choice between the two depends on specific requirements, budget constraints, and technical expertise.

What is the relationship between vertical roller mill and rotary kiln?

The relationship between a vertical roller mill (VRM) and a rotary kiln lies in their roles within the cement manufacturing process. Both of these equipment are essential components of the cement production line and are used to facilitate the production of clinker, which is the intermediate product in the production of cement.

Vertical Roller Mill (VRM): A VRM is a type of industrial equipment used to crush or grind materials into small particles. It consists of a rotating table onto which materials (such as raw materials for cement production) are fed. The material is then ground between the grinding rollers and the grinding table, creating fine powder. In the context of cement manufacturing, the VRM is used to grind the raw materials (such as limestone, clay, shale, etc.) into a fine powder called raw meal. This raw meal is then fed into the rotary kiln for further processing.

Rotary Kiln: A rotary kiln is a large, cylindrical furnace that is inclined slightly from the horizontal and rotates on its axis. It is used to process raw materials at high temperatures to produce clinker, which is a fused, small, spherical nodules of intermediate product in cement production. The raw meal from the VRM, along with other additives like gypsum, is fed into the rotary kiln. Inside the kiln, the materials undergo a series of complex chemical and physical reactions, resulting in the formation of clinker. The clinker is then cooled and ground to produce cement.