Application of Crushing and Screening Plant in the Coal Conveying System
Introduction
The Crushing and Screening Plant, as the core pre-treatment equipment of the coal conveying system in thermal power plants, is mainly responsible for crushing the raw coal entering the plant. It processes oversized chunks of raw coal to a size that meets the requirements for boiler combustion, ensuring the stability of subsequent coal conveying processes, coal grinding operations, and boiler combustion conditions. Compared to mobile crushing stations, the Crushing and Screening Plant has a fixed installation location, a more rigid overall structure, and stable processing capacity, making it suitable for long-term continuous operation in coal conveying scenarios such as thermal power plants and large-scale coal transportation hubs in coal mines. To receive coal from open-pit mines and process it into a particle size specification suitable for belt conveyors and simple storage, the Crushing and Screening Plant is installed at the beginning of the coal conveying system project. The open-pit mine incoming coal is crushed to the specified particle size.
Layout of Crushing and Screening Plant
The processing capacity of the Crushing and Screening Plant is designed according to the requirements of the client’s project. It mainly consists of the receiving hopper, the feeding chute, the apron feeder, the roller screen, the mineral sizer, the discharge chute, the second steel platform, the belt conveyor, the electrical system, etc. Its process flow is as follows: incoming coal is transported by dump trucks to the unloading platform of the crushing station, and then passes through the receiving hopper → apron feeder → roller screen → mineral sizer → discharge chute → belt conveyor.
The incoming coal from the open-pit coal mine is transported by dump trucks to the unloading platform of the crushing station for unloading. Multiple unloading positions can be set. The incoming coal is buffered by the receiving hopper and sent into a mineral sizer for crushing by the apron feeder. The coal that meets the specifications is discharged by the belt conveyor.
Most of the crushing station is arranged below the platform floor. A shed is set on the upper part of the crushing station to prevent rainwater from accumulating in the pit of the crushing station.
Equipment configuration and functions of the Crushing and Screening Plant
Receiving hopper
Accepts raw coal unloaded from dump trucks during open-pit coal mining, stores the material, is a large steel structure piece, wear-resistant and impact-resistant, including the hopper body, receiving chute, legs, and supported by the legs and plate feeder frame. The steel plate thickness of the receiving hopper is not less than 10mm, the material is Q235, with additional reinforcing plates, and the inner wall and receiving chute of the receiving hopper are equipped with 16mm thick 16Mn wear-resistant linings.
Apron feeder
It is horizontally or inclinedly arranged under the receiving hopper, pulling the materials in the receiving hopper to the roller screen for pre-sieving. The drive device of the apron feeder includes a motor, a reducer, and a hydraulic coupling. It can adjust the feeding speed according to the working conditions to achieve uniform and controllable material transportation. The chain adopts the track chain used in bulldozers and excavators, which has a large pitch, high tensile strength, and good self-lubrication performance. The conveyor chain plate is made of high-strength and wear-resistant steel plates, and the adjacent chain plates are connected by hinging or overlapping forms to form a sealed load-bearing surface, which can withstand the impact of large pieces of materials and prevent the leakage of materials.
Roller screen
It is installed at the discharge end of the apron feeder to pre-sieve the raw coal that is being conveyed, separating out the fine-grained materials. This reduces the amount of fine coal entering the crusher, improves the crushing efficiency and reduces the wear of the crusher. The roller screen adopts a modular design, consisting of multiple groups of parallel-mounted screen shafts, each group of screen shafts being independently driven. On the screen shafts, wear-resistant screen discs and retaining sleeves are alternately installed. The screen discs are cast or welded from high manganese steel or 16Mn wear-resistant materials, with high surface hardness and good impact resistance. The gap between adjacent screen shafts forms a screen slot, and the size of the screen slot is determined according to process requirements (usually 30-80mm). When the materials move on the screen surface, particles smaller than the screen slot fall into the underflow chute below and directly enter the subsequent belt conveyor; while the coal blocks larger than the screen slot move forward along the screen surface and enter the crusher for crushing.
Mineral Sizer
This equipment is used to break the materials sent by the roller screen into materials with qualified particle size. It is the main equipment of the crushing station and consists of a power system, a main frame, a lubrication system and an electrical control system. It has reliable performance and a large processing capacity.
The power system consists of an electric motor, a hydraulic coupling, a coupling and a reducer. The torque generated by the electric motor is transmitted to the working toothed rollers through the torque-limiting hydraulic coupling, the coupling and the reducer to form the power for crushing the materials. The hydraulic coupling can effectively protect the startup and overload of the main motor during operation, preventing the motor from burning out due to excessive current. The reducer adopts a heavy-duty reducer, which has the characteristics of high transmission efficiency and large torque transmission. The main frame is the supporting component of the crusher, supporting the working pair to realize the process of crushing materials.
The automatic lubrication system mainly lubricates and protects each bearing position. It adopts automatic oil replacement lubrication, that is, adding clean and clean lubricating oil to the bearings regularly while discharging the impure oil in the bearings through the oil discharge hole outside the bearing housing, which can more fully ensure the lubrication of the bearings and thereby extend the service life of the bearings.
The electrical control system can protect the motor from overcurrent, overload, reduced voltage startup and stall protection, and has the functions of measuring the temperature and vibration of the main bearing. The motor startup adopts a solid-state soft starter, which can minimize the starting current of the main motor of the crusher as much as possible and reduce the impact on the power grid during the startup of the crusher.
Belt conveyor
It is placed below the chute of the roller screen and the discharge port of the mineral sizer, used to centrally transfer the fine coal screened out and the qualified materials after crushing to the subsequent storage area or loading equipment. The belt conveyor is arranged with a large inclination angle or horizontally, and is flexibly designed according to the on-site terrain and process requirements.
Electrical system
It is responsible for the operation and control of the entire crushing station, having the functions of measuring temperature, vibration, and rotational speed of each electrical equipment in the crushing station, providing protection for the crusher, monitoring and controlling the oil temperature of each reducer, and achieving interlock control functions with the discharge belt and subsequent equipment. An on-site control room is set up on the ground beside the crushing station to realize local control of the normal operation of all equipment in the crushing station.
Conclusion
The Crushing and Screening Plant is applied at the beginning of the coal conveying system for pre-treatment in open-pit coal mines. It can stably and efficiently complete the crushing operation of raw coal, meeting the requirements of subsequent belt conveyance, silo storage, and boiler combustion for the particle size of raw coal. Relying on mature modular configuration and a complete control system, the Crushing and Screening Plant can meet the long-term continuous operation needs of thermal power plants and large centralized transportation stations. The equipment has strong reliability and is easy to maintain. It can not only ensure the overall stable operation of the coal conveying process, but also reduce equipment wear through the pre-screening process, balance processing capacity and operating costs, and is a reliable raw coal pre-treatment solution for large fixed coal conveying systems.
