The core mission of pumps dedicated to filter presses (mostly of the plunger pump, diaphragm pump, or screw pump type) is to convey the slurry to be filtered to the filter chambers of the filter press at a stable high pressure, providing power for filter cake formation and dehydration. Their working principle can be broken down into two major dimensions: "power transmission" and "flow rate regulation".
Taking the most widely used plunger-type pump dedicated to filter presses as an example, its power transmission process follows the logic of "mechanical conversion - pressure superposition - directional conveying":
- The motor drives the crankshaft to rotate, which drives the plunger to reciprocate in the pump cylinder; when the plunger extends outward, the volume inside the pump cylinder increases to form negative pressure, the suction valve opens, and the slurry is sucked into the pump cavity.
- When the plunger pushes inward, the volume of the pump cavity shrinks, and the pressure rises sharply (up to more than 30MPa in extreme cases). The suction valve closes, the discharge valve opens, and the high-pressure slurry is forced to be conveyed to the filter chambers of the filter press through pipelines.
- Under the action of high pressure, the moisture of the slurry entering the filter chambers penetrates and is discharged through the filter cloth, while solid particles accumulate in the filter chambers to form filter cakes, completing the initial stage of "solid-liquid separation".
Compared with ordinary centrifugal pumps, the key advantage of dedicated pumps lies in pressure stability: through the uniformity of the plunger's reciprocating motion and the sealing design of the pump cavity and valves, uneven filter cake formation caused by pressure fluctuations can be avoided, ensuring consistent filling degree of the filter chambers.
The filter press process has significant differences in flow rate requirements at different stages (e.g., large flow rate is required in the filter chamber filling stage, while small flow rate is needed in the filter cake compaction stage). Dedicated pumps achieve adaptive matching through a "variable regulation" mechanism:
- For plunger pumps, stepped flow rate regulation can be realized by adjusting the motor speed, changing the plunger stroke, or increasing/decreasing the number of working plungers.
- For diaphragm-type dedicated pumps, continuous fine-tuning of the flow rate can be achieved by adjusting the pneumatic/hydraulic driving pressure to change the deformation range of the diaphragm.
- Some high-end dedicated pumps are also equipped with the "pressure-flow linkage control" function: when the pressure in the filter press chamber increases (as the filter cake gradually forms), the pump automatically reduces the flow rate to avoid filter cloth damage or equipment overload caused by excessive pressure, forming a dynamic balance of "pressure priority and flow rate adaptation".
The filter press process is generally divided into four stages: "Filter Chamber Filling - Filter Cake Compaction - Filter Cake Washing - Filter Cake Discharging". The pressure and flow rate requirements vary significantly in each stage. The matching of dedicated pumps must follow the principle of "stage-specific adaptation" to avoid efficiency waste or equipment damage caused by a "one-size-fits-all" selection approach.
The core goal of this stage is to fill the filter press chambers with slurry in a short period (usually accounting for 30%-40% of the total process time), requiring the dedicated pump to meet the demand for "large flow rate and medium-low pressure":
- Matching Key Points: Select a dedicated pump with large displacement (such as a multi-plunger parallel pump). The flow rate should be calculated based on the total volume of the filter chambers and the filling time (Example: For a filter chamber volume of 100 m³ requiring filling within 30 minutes, the pump flow rate must be no less than 200 m³/h).
- Pressure Control: The pressure in this stage does not need to be too high (usually 0.5-1.5 MPa). This avoids the premature formation of a thin filter cake on the filter cloth surface due to early pressure rise, which would hinder subsequent slurry filling and prolong the process time.
After the filter chambers are filled, high pressure is needed to squeeze the filter cake to reduce its moisture content (from over 80% initially to below 30%, depending on material properties). In this stage, the dedicated pump needs to switch to the "high pressure and small flow rate" mode:
- Matching Key Points: Select a dedicated pump with prominent high-pressure performance (such as a single-plunger long-stroke pump). The pressure must be higher than the "critical pressure" required for filter cake formation (Example: 3-5 MPa for filter pressing in the coal industry, and 8-12 MPa for high-viscosity materials in the chemical industry).
- Flow Rate Control: The flow rate in this stage should be reduced to 1/5-1/10 of that in the filling stage. Only the space generated by the volume shrinkage of the filter cake during dewatering needs to be supplemented, so as to prevent excessive slurry injection from causing a sudden pressure rise and damaging the filter press main beam or filter plates.
For materials with "high viscosity and high solid content" such as mining tailings slurry and chemical sludge, the matching of dedicated pumps needs to additionally focus on "anti-clogging" and "wear-resistant" performance:
- Material Adaptation: The pump cavity, plungers/impellers should be made of wear-resistant materials (such as high-chromium alloy and ceramic coating) to avoid erosion and wear of the pump body by particle-containing materials.
- Structural Adaptation: Adopt a "large-diameter feed inlet + dead-angle-free flow channel design" to reduce the retention and accumulation of slurry in the pump and prevent pump clogging.
- Pressure Adaptation: High-viscosity materials have high flow resistance, so the dedicated pump must have a higher "initial pressure" (usually 20%-30% higher than that for ordinary materials) to ensure that the slurry can smoothly enter the filter chambers.
In addition to optimally matching the filter press process, it is also necessary to further improve solid-liquid separation efficiency and reduce energy consumption and costs through the linkage of three aspects: "pump parameter optimization", "process coordination", and "daily maintenance".
Based on material properties and filter press specifications, determine the "optimal operating parameters" of the dedicated pump through experiments:
- For easily filterable materials (e.g., coal slime): Appropriately increase the flow rate during the filling stage (to shorten filling time); the pressure during the compaction stage can be controlled at 3-4 MPa to avoid energy waste caused by excessive pressurization.
- For difficult-to-filter materials (e.g., chemical sludge): Reduce the flow rate during the filling stage (to prevent filter cloth clogging); gradually increase the pressure to 8-10 MPa during the compaction stage, and extend the high-pressure holding time (5-10 minutes) to ensure sufficient dehydration of the filter cake.
- Equip with an intelligent control system: Link the filter press and the dedicated pump through PLC (Programmable Logic Controller), collect real-time data such as filter chamber pressure and filter cake thickness, and automatically adjust the pump's pressure and flow rate to achieve "unattended" optimal operation.
The efficiency of the dedicated pump needs to be coordinated with the filter press's "filter plate spacing", "filter cloth selection", and "discharging speed":
- Excessively wide filter plate spacing: Requires the dedicated pump to provide a larger flow rate to fill the filter chamber, which easily leads to reduced efficiency. It is recommended to adjust the filter plate spacing according to the filter cake thickness (usually 20-50 mm) to match the pump's displacement.
- Inappropriate filter cloth mesh size: Overly dense filter cloth increases slurry flow resistance, requiring the dedicated pump to increase pressure (increasing energy consumption); overly sparse filter cloth causes solid particle loss. It is necessary to select filter cloth with an appropriate mesh size based on material particle size to reduce the pump's operating load.
- Synchronized discharging speed: If the filter press's discharging speed is slower than the pump's feeding speed, the pump will start and stop frequently (automatic shutdown when pressure is too high), shortening the pump's service life. It is recommended to adjust the speed of the discharging device to ensure consistent "feeding-discharging" rhythm.
Failures of the dedicated pump (e.g., liquid leakage, insufficient pressure) will directly interrupt the filter press process, so a "regular maintenance-fault early warning" mechanism must be established:
- Seal maintenance: Inspect the seals of the pump's suction valve and discharge valve weekly; replace them promptly if liquid leakage occurs (seal wear will cause pressure loss and reduce conveying efficiency).
- Lubrication and maintenance: Add special lubricating oil to moving parts such as plungers and crankshafts monthly to avoid flow fluctuations caused by mechanical wear.
- Spare 易损件 (vulnerable parts): Reserve wear-resistant parts (e.g., plunger sleeves, diaphragm sheets) in advance. When the pump malfunctions (such as decreased flow rate or sudden pressure drop), these parts can be replaced quickly to reduce downtime.
The core of the working principle of pumps dedicated to filter presses lies in "stable high-pressure conveying + dynamic flow rate regulation", while the essence of their matching with the filter press process is "optimal response to phased requirements". Whether it is parameter calculation during the selection stage or parameter optimization during operation, efforts must be carried out around the linkage of three factors: "material properties - process requirements - equipment performance". Only by achieving in-depth coordination among "pump - machine - material" can the solid-liquid separation efficiency be maximized, providing core support for enterprises to reduce energy consumption and improve production capacity.
