How to Select the Right Primary Mineral Sizer for ROM Coal Crushing
Introduction
Raw coal refers to the unprocessed coal material directly extracted from mines or open-pit sites, without any screening or pre-treatment. It features large and uneven particle sizes, complex composition, high moisture content with significant fluctuations—especially during the rainy season, when moisture levels can reach 20% or higher. The material exhibits characteristics of high humidity and high viscosity. Traditional coal crushing equipment such as hammer crushers or impact crushers are prone to clogging in the crushing chamber when handling raw coal with these properties, leading to production interruptions.
The Primary Mineral Sizer adopts a dual-roller design with low rotational speed and high torque, breaking materials through a three-point loading mechanism involving shearing, tensile, and bending forces. This enables efficient processing of large, wet, and sticky raw coal, while effectively controlling product size, reducing dust generation, and minimizing over-crushing.
Characteristics of Raw Coal
Feed Size of ROM Coal
Mining methods (such as blasting parameters and excavator bucket capacity) and transportation methods (such as mine truck load capacity) directly determine the maximum lump size of raw coal, which is a decisive factor in selecting the inlet size and roll center distance of the Mineral Sizer, enabling it to handle feed material up to 1500 mm in size.
During normal operation, the average particle size of the material and the proportion of different size fractions—especially large lumps—help more accurately predict processing capacity and power requirements. The higher the proportion of large lumps, the greater the demands on the Mineral Sizer’s gripping capability and crushing torque.
Coal Hardness and Crushing Characteristics
Uniaxial compressive strength (UCS) is an indicator of a material’s “hardness.” The Mineral Sizer can process materials ranging from soft coal (approximately 30 MPa) to hard rock (up to 250 MPa). The Hardgrove Grindability Index (HGI) reflects how easily coal can be ground; although primarily used for selecting coal mills, it also indirectly indicates coal brittleness and serves as one of the reference indicators for crushing performance.
Coal types vary significantly in characteristics—for example, lignite is typically softer and higher in moisture content, while anthracite is harder. The Mineral Sizer, utilizing low-speed shearing action, is particularly suitable for breaking medium- to low-hardness materials and can accomplish crushing tasks with relatively low specific energy consumption.
Moisture Content and Clay Content
High-moisture and sticky materials tend to adhere to the inner walls of the crushing chamber and discharge openings in conventional crushers, leading to a sharp decline in processing capacity or even complete blockage. Wet and sticky materials after crushing are also prone to clogging screen meshes during subsequent screening processes.
The unique advantages of the Mineral Sizer lie in its open structure and self-cleaning function. The two counter-rotating toothed rollers feature specially designed teeth that not only crush material but also scrape against each other, effectively preventing material buildup. Its open-bottom discharge channel further reduces the risk of material accumulation.
Why Choose the Primary Mineral Sizer as the Primary Coal Crushing Equipment?
High Capacity for Large Coal Lumps
With large-diameter toothed rollers and high-torque hydraulic or direct-drive systems, the equipment generates strong gripping and shearing forces, forcibly drawing large coal lumps into the crushing chamber. It can easily handle coal blocks with side lengths exceeding 1000 mm, and even up to 1500 mm—sizes that many traditional crushers struggle to process.
Precise Product Size Control and Extremely Low Over-Pulverization Rate
The maximum product size is primarily determined by the gap between the two toothed rollers and their tooth design. Additionally, our Mineral Sizer is equipped with Breaker Bars; by adjusting the distance between the Breaker Bar and the rollers, the discharge particle size can be precisely controlled. Typical primary sizing output from the Sizer can be stably maintained at ≤300 mm.
The low-speed shear crushing method of the Mineral Sizer causes materials to break along their natural fracture planes rather than being “crushed” by high-speed impact. The screening action between the rollers allows already qualified fine particles to pass directly through the gaps and sides of the teeth, avoiding repeated crushing and grinding within the chamber, thereby significantly reducing the production of fine coal dust.
Detailed Explanation of Key Selection Parameters for the Primary Mineral Sizer
| Parameters | Function and Description |
| Capacity （t/h） | The key indicators that determine the specifications and models of the equipment. Peak production capacity needs to be considered, usually verified at 120% of the nominal production capacity. |
| Max Feed Size（mm） | The selection of the machine opening size, the diameter of the toothed rollers and the center distance of the machine are the primary limiting factors in the design process. |
| Product Size（mm） | Determine the tooth shape, tooth height, tooth pitch and tooth roller gap. Some Sizers have the function of hydraulically adjusting the product size. |
| Bulk Density（t/m³） | This parameter is used to convert volumetric flow rate into mass flow rate (t/h) and is an important factor for calculating the actual processing capacity and power. |
| Moisture Content（%） | It affects the fluidity and adhesion of the materials. Therefore, the maximum value under the worst conditions (such as during the rainy season) should be considered to ensure that the equipment does not get clogged. |
| Clay Content（%） | The interaction with water determines the “stickiness” of the material, which is the key to evaluating the adaptability of the Sizer. |
| Compressive Strength (UCS)（MPa） | The core indicator for measuring the hardness of materials directly affects the required crushing force and motor power. The UCS values of coal and gangue need to be provided. |
| Tooth Roller Diameter（mm） | It is directly related to the maximum feed particle size. The larger the diameter, the more favorable the bite angle is, and the stronger the processing capacity is. The model range is usually from 800mm to 1500mm. |
Performance Comparison of Primary Mineral Sizer with Traditional Coal Crushing Equipment
| Comparison | Primary Mineral Sizer | Hammer Crusher |
| Handling large-scale capabilities | Up to 1500mm | Usually < 1000mm |
| Adaptability to wet and sticky coal | Very good, not prone to clogging | Poor quality. The grating bars are prone to getting clogged. |
| Resulting in pulverization and the generation of dust | Low, shear breakage, less dust | High, high-speed impact crushing, with a lot of dust |
| Product particle uniformity | Better, with adjustable size | Generally, the hammer head is more prone to wear and tear. |
| Wear and tear of vulnerable parts | Lower, low-speed operation, with replaceable tooth crowns | Higher, the hammer head and the mesh bars wear out quickly |
| Maintenance | Relatively simple. Some models can be removed as a whole for maintenance. | More complicated. It takes time to replace the hammer head and the liner plate. |
| Unit energy consumption | Lower | Relatively high |
Conclusion
Choosing the right Primary Mineral Sizer for your coal mine determines the efficiency, stability and economy of the entire raw coal processing system. All key characteristics of raw coal, such as its maximum particle size, particle size distribution, hardness, moisture content and clay content, directly affect the final outcome of the equipment selection.
