Filter Press Cycle: Introduction & Time Factors

A Brief Overview Of The Filter Press Cycle And Its Cycle Time

Filter Press Cycle: What Is It?

Filter presses dewater and detach liquids and solids in various applications. Due to their versatile and reliable nature, filter presses are one of the most widely used systems in solid-liquid separation. They drench material and separate solids and liquids by pumping the slurry into a series of chambers formed by a press's filter plates. Each plate is connected with filter media determining what particles are dewatered and separated from the liquid.

Filter press machine dewaters slurry material in a series of procedures known as press cycle. A press cycle comprises the closing of filter plates, filling up the chambers with slurry, opening filter plates, and filtration. The filter press dewatering cycle includes a series of process steps involved in completing the dewatering process.

Complete Process Of Plate Filter Press Cycle

A typical filter press cycle consists of the following steps:

• Filter plate closing
• Filling
• Filtration
• Crux or core blow
• Cake Drying
• Squeezing of membrane
• Filter pate opening

Filter plate closing – The filter plates are closed using a mobile plate or hydraulic cylinder. Initially, lower pressure is required to close the plate stack; extreme hydraulic pressure is applied to close the plates tightly together. The clamping pressure must be high-ended to withstand the pressure created by the feed pump pushing slurry into the chambers between the filter plates.

Filling – During the filling procedure, the slurry feed rate can be very high, and the feed pressure tends to be low. The feed pump is filled so that it can begin occupying the void spaces between the clamped filter plates.

Filtration – The feed pump speed is ramped up to increase the feed pressure over time as soon as the minimum feed pressure is reached in the fill stage. The speed of the feeding pump is kept on increasing level until the target filtration stage is reached. Meanwhile, the pressure is held constant for the balance of the ramp stage. The filtration process ends when the slurry flowing rate reaches a pre-determined level, and the feed pump is stopped.

Core Blow – Some amount of slurry remains in the core hole areas of the filter press plates after the feed pump is stopped. Though a core blow step is totally optional, the step removes the remaining slurry using flush water or compressed air.

Flush water is forced to push the slurry out; compressed air is forced through the core holes to push out the flush water and remaining slurry.

Cake drying – Compressed air is forced through the filter cakes to remove additional water while the cakes are still positioned in the filter plates. Also, this step of cake drying is optional and is typically used when the cake material is very penetrable and low moisture levels are required.

Squeezing of membrane – Squeezing the membrane includes removing additional water from the filter cakes after they have been formed. Membrane plates have flexible outside that is expanded with water or compressed air. The expanded plate compresses the cakes and forces additional water to be removed.

Filter plate opening – As soon as the complete dewatering procedure has been finished, the high hydraulic clamping pressure is relieved. The cylinder plate and mobile plate remain open to make space for all the filter plates that must be separated. A plate opening system indicates each plate to open, permitting the dewatered cake material to fall between the filter plates. Once all of the cakes have been discharged, a new fresh filter press cycle begins.

Factors Affecting The Cycle Time Of The Filter Press

Each step of the filter press cycle requires some time that will depend on the characteristics of the slurry materials being dewatered as well as the structural design of the filter press. The total time it takes for a press filter to complete one cycle depends on several processes and design factors. The significant press filter factors that influence the cycle time include:.

• The thickness of a chamber
• Slurry feed pump pressure
• Speed of filter plate opening and closing
• Filter plate cloth design
• Slurry feed density
• Slurry compositions
• Slurry particle size distribution
• Dewatering aids
• Compression of cake

The thickness of a chamber – Filter plates with a larger chamber thickness will require a longer filtration duration due to a higher volume of slurry that will be dewatered between the filter plates.

Slurry feed pump pressure – Filtration time typically can be reduced with extreme pressures for slurry feed pump pressures. Testing representative sample materials can determine the time reduction achieved with higher feed pressures at different feed pressures. Higher feed pressures are also available in the market for special dewatering applications.

Speed of filter plate opening and closing – The hydraulic power unit and size will determine how fast the filter press can open and close. Conventional hydraulic cylinder opening and closing speeds range from 1 to 10 minutes. The plate opening speed is dependent on the filter press plate shifting design, typically 1 to 5 seconds per plate.

Filter plate cloth design – Filter Cloth Selection are woven synthetic fabrics made from polypropylene or polyester filaments. However, many different types of cloth weaves, styles, and patterns can be used for dewatering. Filter cloths are designed to apprehend the solid particles and allow filtrate water to pass through.

More tightly woven cloth is required to capture the solid particles and allow filtrate water to pass through. The optimum cloth design is chosen based on dewatering characteristics, best cloth wear, and cake release factors.

Slurry feed density – High-density slurry feeds typically reduce the fill and filtration times. The number of solids being pumped into the filter press chambers occurs more quickly at higher percent slurry solids resulting in reduced cycle times.

Slurry compositions – The composition of slurry material being dewatered will impact the water removal rate. Materials that tend to absorb water can be very difficult to dewater and may require extended filtration times or filter aids. Materials that naturally repel water will dewater much more easily, reducing the filtration time.

Slurry particle size distribution – Slurries with larger, round particles are more easily dewatered than slurries with fine particles that can be packed easily together. Fine clay materials pack tightly together, making the water between them nearly impossible.

Dewatering aids – One can add dewatering aids and special chemicals to decrease the filtration time when slurry water is very difficult to dewater. The most common dewatering aids include perlite, diatomaceous earth i.e., DE, and high calcium hydrated lime. Perlite and DE are naturally occurring minerals that provide fine particles in the slurry permitting water to be removed more easily.

Adding hydrating lime can chemically make the slurry material release water more easily.

Compression of residual cake – Cake compression is normally achieved as a supplement to the filtration step to reduce the moisture of compressible cakes.

Membrane filter plate consider all of the above factors while designing a filter press machine to ensure optimum dewatering technique efficiency for each application and purpose. NMP has been a perceived pioneer in the Indian markets. We provide different types of filter presses for different industries.