Coal vertical roller mill Introduction

Coal vertical roller mill also known as vertical grinding mill is an equipment widely used in the cement production plant and cement grinding station. Coal vertical mill is a kind of grinding equipment integrating powder drying, powder selection and transportation. It is widely used in cement building materials, mineral processing, metallurgy and other industries. The fineness of coal powder produced can reach 80μm, and the fineness is stable, the particle size is uniform, and it has efficient gradation and excellent combustion performance. Coal vertical mills are widely used in cement plants, and the pulverized coal is sent to the burner of the rotary kiln through the rotor scale for combustion. Considering the flammable and explosive characteristics of coal powder, Tongli’s coal vertical mill has set up multiple protection measures, including nitrogen safety protection system, multi-point gas analysis, real-time temperature monitoring, etc. Tongli coal vertical roller mill is also suitable for grinding a variety of material such as clinker, coal, blast furnace slag, steel slag, furnace slag, manganese slag, nickel slag, metallurgical slag, limestone, dolomite, calcite, gypsum, pozzolan, clays, silica sand, non-metallic minerals, and other raw materials.

Coal vertical roller mill structure

The main components of the coal vertical roller mill include the grinding table, grinding rollers, grinding roller shaft, grinding roller wheel hub, grinding roller tyre, rocker arms, separator, transmission system, base frame. 

Grinding Table: The grinding table is a rotating part of the coal vertical roller mill responsible for grinding materials. It is mounted on a gearbox-driven spindle and can be tilted to control the product fineness and optimize the grinding process. The detailed structure of the grinding table includes guide ring, air ring, retaining ring, liner, disc body, scraper.

Grinding Rollers: Grinding roller is the main part for crushing and grinding materials. The grinding roller is composed of cast steel roller sleeve, forging shaft and wear-resistant surfacing bushing. The grinding roller is installed on the rocker arm of the coal vertical roller mill, under the action of external force, it is pressed tightly on the material of the grinding table, as the grinding table rotates the material is crushed. The grinding roller is equipped with a limit device to ensure that it does not directly contact the grinding table during operation

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. The term "forged shaft" refers to a shaft that has been manufactured using a forging process, this process enhances the mechanical properties of the metal, such as strength, durability, and resistance to impact and fatigue.

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. The wheel hub is designed to transmit the rotational motion and force from the mill's drive system to the grinding roller, allowing it to rotate and exert pressure on the material.

Grinding roller tyre: The grinding roller tire of a vertical roller mill is a crucial component that directly contacts the material being ground during the milling process. It's also commonly referred to as the grinding roller or roller shell. This component is made up of a cylindrical shell or tire-like structure that rotates around a central shaft. The grinding roller tire is typically equipped with segments or studs that aid in grinding and pulverizing the material as the mill's table or bowl rotates.

Rocker Arms: The function of the rocker arm device of the coal vertical roller mill is to transmit the pressure provided by the hydraulic cylinder to the grinding roller, so that it can be transformed into the grinding force act on the material bed. The rocker arm device is mainly composed of upper rocker arm, lower rocker arm, rocker arm shaft, bearing and bearing housing and other components. The upper rocker arm is used to install the grinding roller, the lower rocker arm is connected to the hydraulic system, and the two rocker arms are connected as a whole through shafts, taper sleeves and taper pins.

Classifier: Powder classifier (also known as coarse powder separator) of the coal vertical roller mill plays a vital role in the selection of powder during grinding. The ground material is carried by the high-speed rotating airflow in the mill and enters the powder classifier 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.

Middle shell: The middle casing of the coal 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 roller to Prevent air leakage. The inner wall of the middle shell is laid with a wear-resistant lining to protect the inner shell.

Base Frame: The support base of the coal 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 coal 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.

Transmission device: The transmission device of the coal vertical roller mill is composed of a planetary gear reducer, a motor and a coupling in the middle of 4 supporting beams. The planetary gear reducer is a reduction device with a vertical output shaft, and the output end is connected to the grinding table with a flange. The vertical downward force is supported by the hydraulic thrust bearing on the top of the reducer during operation.

PLC control system: A PLC is a digital computer-based system that is designed to control various industrial processes automatically. In the context of a vertical roller mill, a PLC is used to monitor and control parameters such as temperature, rotation speed, air flow, fuel flow, and other critical variables that affect the performance of the kiln and the quality of the products being processed. Tongli vertical roller mill is controlled with PLC control system which is capavle of monitoring temperature, vibration, filling rate, output rate. Tongli vertical roller mill also equipped with CO, O2 real-time gas analyzer to ensure save production.

Design principles of coal vertical roller mill

Working principle: The raw material is lifted by the bucket elevator and then pass through the iron remover to remove the other object, after that the raw material is fed into the coal vertical roller mill through a star airlock valve, once the material drops down form the top of the coal vertical roller mill landed at the center of the grinding table, through centrifugal force, the raw material will be thrown to the edge of the grinding table.

A hydropneumatics spring tension cylinder pulls on the rocker arm and exert a vertical force on the grinding roller and the grinding table, as the grinding table rotates cause the material to be crushed under the compressive force and the shear force. Fine particle will be taken to the classifier by a upstream, coarse particle will return to the grinding table for regrinding, also there is a exit chute on the edge of the grinding table for iron to exit in case it is not removed by the iron remover in the previous step. Foreign object and bulks of raw material exit from the chute will be sent to the bucket elevator and pass through the iron remover again. This raw material vertical roller mill system also integrates drying, it has a portal that can utilize the waste gas from the rotary kiln, or if no heat source it also can connect to the hot air generator through this portal.

Advanced design: As one of the leading vertical roller mill manufacturers, Tongli coal vertical roller mills are advanced in design, integrating the functions of crushing, drying, grinding, classifying, conveying. Adapt to fluctuating raw material qualities, adapt to different product qualities.

High grinding efficiency: The stand-alone production capacity of the coal vertical roller mill is large, low energy consumption compared with ball mills, the energy consumption is usually 40%-50% lower than the ball mill;

Dust-free operation: The coal vertical roller mill system adopts a fully enclosed system, and the whole system operates under negative pressure without dust spillage, which can meet the requirements of clean production

Customized deisgn: Tongli’s coal vertical roller mill has two types of grinding rollers, one is cone-shaped and the other is tire-shaped. According to different materials and different technological processes, we customized the equipment that meet your specific need.

Adaptability: Tongli coal vertical roller mill can process kaolin, barite, fluorite, talc, water slag, lime calcium powder, wollastonite, gypsum, limestone, phosphate rock, marble, potassium feldspar, quartz sand, bentonite, Manganese ore and other materials with a hardness below 7 on the Mohs scale.

Compact layout: the occupation area is only 50% of that of a ball mill and It can be arranged outside, no workshop needed. Due to this reason, it can effectively reduce construction costs and helping enterprises reduce initial investment costs.

Pre-assembling: the base frame is pre-assembled in our workshop and marked with number so that when it comes to installation on site, it is a lot of more easier, the owner can put it together like Lego.

Separator Balance test: All the separator need to pass the balance test before assemble, we have a balance test machine that test the vibrate and concentricity when the cage rotor rotates, Tongli make sure all the separator is running smooth.

Gas sealing system: Tongli coal vertical roller mill is equipped with a high-speed centrifugal blower to send high-speed air into the seal of the roller bearing to form a gas seal to prevent dust from entering the roller bearing. By doing this we can greatly improve the bearing service life.

Water spray system: The coal vertical roller mill of Tongli is equipped with a water spray system, one is to reduce the outlet temperature of the mill, and the other is to speed up the accumulation of the material layer on the grinding table.

Lubrication system: Tongli coal vertical roller mill is equipped with a forced lubrication device to ensure the service life of bearings and key components during operation.

PLC control system: Real-time monitoring of the coal vertical roller mill with operating parameters. Highly automatic, features remote control and touch screen control, Siemens control system.

Easy Maintenance: Swing-out feature allows the maintenance of the grinding roller to be easy and fast. Grinding roller can be rolled out of the machine by hydraulic device, and the replacement of the roller sleeve liner and the maintenance of the mill is very convenient; No need to arrange material layer on the grinding table before starting the machine, Tongli coal vertical roller mill can be started without load.

Specifications of coal vertical roller mill

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

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Zhejiang Tongli Heavy Machinery Manufacturing Co., Ltd (Formerly known as Tongxiang Coal&Mining Machinery Factory) established in year 1958 is a member of the Chinese National Building Material Machinery Association. Tongli is on the vendor list of designated production enterprise of the Ministry of Coal Industry. ISO9001、ISO14001、ISO45001 certified, accredited as High-tech & new technology enterprise of Zhejiang Province. With 65+ years of experience, Tongli has earned first class R&D and manufacturing capabilities, dedicated to provide satisfactory manufacturing equipments for global customers.   

Industry knowledge extension

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

Both coal ball mills and coal vertical roller mills plays a vital role in the coal pulverizing plant. Coal ball mills are versatile and cost-effective, suitable for various materials and simple to maintain. In the coal powder pulverizing industry, the vertical mill is more widely used, because the vertical roller mill occupies a small area and has a drying function. Generally, the raw coal needs to be sprayed with water to prevent spontaneous combustion during transportation, so the moisture content is very large, so the drying function is particularly important. Another reason is that vertical mills have a high safety factor and are equipped with nitrogen explosion-proof systems and gas detection, so vertical mills are more widely used than ball mills in the coal powder preparation industry. 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 rotary kiln is usually used as an intermediate process. The large raw materials are crushed by the crusher and then enter the grinding equipment for grinding. After being mixed with other raw materials, they are added to the rotary kiln for redox reactions. The calcined finished products need to enter the vertical roller mill or ball milling for secondary grinding to get the finished product. In the cement production line, it is usually equipped with a coal powder vertical roller mill. After the raw coal is ground by the vertical roller mill, it is evenly sent to the burner of the rotary kiln through the rotor scale for combustion, and then the tail gas generated by the rotary kiln enters the vertical roller mill to dry the raw coal, thereby achieving a cycle which saves energy while improving resource utilization.