What is the difference between dewatering and drainage?

In the context of coal washing plants, the terms “dewatering” and “drainage” are often used to describe processes related to the removal of water. While they are related and sometimes used interchangeably in casual conversation, they refer to distinct processes with specific goals, techniques, and implications for coal processing. Understanding the difference is crucial for optimizing both water management and the quality of the coal product.


Dewatering Screen in a coal washing plant refers to the process of removing water from the coal itself after it has been washed. The primary objective is to reduce the moisture content of the coal to improve its calorific value, reduce transportation costs, and meet the specifications required by the end-users or to adhere to environmental regulations. Dewatering is a critical step in the coal preparation process, as it directly affects the efficiency and economics of coal production and utilization.

Techniques and Equipment Used in Dewatering:

  • Centrifugation: Centrifugal dewatering utilizes the principle of centrifugal force to separate water from coal particles. This method is especially effective for fine coal dewatering, where other methods might be less efficient.
  • Filtration: Employing filter presses or vacuum filters to remove water through a filter medium. This method is suitable for various coal sizes and can achieve low moisture content.
  • Thermal Drying: Applying heat to evaporate moisture from coal. While effective in reducing moisture to very low levels, it is energy-intensive and less commonly used due to its high operational costs.
  • Screening:Screening involves the use of vibrating or stationary screens to separate water from coal particles. It is particularly effective for coarse coal dewatering.

Dewatering is a comprehensive process that may involve several stages of moisture reduction, from initial bulk water removal to fine coal dewatering. The choice of dewatering technique depends on factors such as coal particle size, initial moisture content, and the desired final moisture level.

Centrifugal and screening dewatering techniques offer valuable solutions for moisture reduction in coal washing plants. While centrifugal methods excel in handling fine coal with high efficiency, screening methods are lauded for their simplicity, energy efficiency, and effectiveness in coarse coal dewatering. The choice between centrifugal and screening dewatering will depend on various factors, including the coal particle size distribution, desired moisture content, energy considerations, and economic constraints. By leveraging these techniques appropriately, coal washing plants can significantly enhance the quality and value of the processed coal, ensuring it meets market demands and environmental standards.


Drainage, on the other hand, refers to the process of removing water from the surrounding environment or from within the coal piles before the actual coal washing process begins. It is primarily concerned with managing water that accumulates from rain, groundwater, or as part of the mining process. Effective drainage is essential for maintaining the operational integrity of the coal washing plant and for preventing excessive water from interfering with the coal cleaning and preparation processes.

Techniques and Equipment Used in Drainage:

  • Ditches and Channels: Constructed around or within the coal storage areas to divert surface water away from the coal.
  • Sumps and Pumps: Used to collect and pump water away from the coal preparation areas. Sumps act as collection points for water, which is then removed by pumping.
  • Settlement Ponds: Designed to collect runoff and sediment from the coal storage and preparation areas. These ponds allow for the sediment to settle out of the water, which can then be reused or safely discharged.

Drainage is more about water management and control on the site, ensuring that the coal washing processes can proceed efficiently without being hindered by excessive water. It is a critical aspect of the overall water management strategy of a coal washing plant, focusing on preventing water-related issues before they affect the coal processing operations.

Key Differences

  • Objective: Dewatering aims to reduce the moisture content of the coal itself to improve its quality and reduce handling and transportation costs. Drainage, however, focuses on managing water in the plant’s environment to prevent operational disruptions and facilitate the coal washing process.
  • Process Stage: Dewatering is a post-washing process, applied after the coal has been cleaned. Drainage is a continuous requirement that addresses water management needs before and during the coal washing process.
  • Techniques and Equipment: While there is some overlap in the equipment (e.g., pumps) that may be used, dewatering techniques are primarily focused on moisture reduction in coal, using methods like centrifugation and filtration. Drainage techniques, however, involve water diversion and removal strategies, such as ditches and sumps, to manage water in the plant area.
  • Impact on Coal Quality: Dewatering directly impacts the quality and commercial value of the coal by reducing its moisture content. Drainage does not directly affect coal quality but is essential for efficient plant operation and preventing water-related issues in coal storage and processing areas.

Both dewatering and drainage are integral to the operation of a coal washing plant, but they serve different purposes and are characterized by distinct processes and outcomes. Dewatering enhances the quality of the coal by removing moisture, making it more efficient for transportation and use. Drainage, meanwhile, ensures that excess water does not impede the coal washing process or damage infrastructure. Together, these processes ensure that coal washing plants can operate efficiently, producing high-quality coal that meets the requirements of the market while managing environmental and operational challenges effectively.

Umair Akram

Umair Akram

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