Vacuum Filter Ceramic Filter
A vacuum ceramic filter is designed to facilitate the separation of liquids from solids, primarily for the dewatering of ore concentrates. This device comprises various components such as a rotator, slurry tank, ceramic filter plate, distributor, discharge scraper, cleaning device, frame, agitating device, pipe system, vacuum system, automatic acid dosing system, automatic lubricating system, valve, and discharge chute. While its operation and construction principles bear similarities to a conventional disc filter, the key difference lies in the use of a finely porous ceramic disc as the filter medium. This ceramic disc material exhibits inert properties, boasts a long operational lifespan, and demonstrates resistance to a wide range of chemicals. To optimize performance, it is crucial to consider the various factors that impact the overall efficiency of the separation process. Some of the key variables influencing the performance of a vacuum ceramic filter include solid concentration, the rotational speed of the disc, slurry level in the feed basin, the temperature of the feed slurry, as well as the pressure during dewatering stages and filter cake formation.
Applications
Vacuum ceramic filters find their applications in multiple industries, including:
- Paper manufacturing
- Metallurgy
- Water treatment
- Chemical processing
- Ore beneficiation in mining (such as iron, gold, nickel, copper, and quartz).
This process proves especially useful in large-scale continuous separation of free-filtering suspensions where washing isn’t necessary. Essentially, the filter works by separating solid-liquid mixtures, removing water from mineral concentrates, and shaping the feed slurries into pellets. This pelletization occurs through capillary action under low vacuum pressure. To aid in the process, solid matter is added to the sewage sludge, facilitating the easy removal of water. The end result is a final cake product with minimal moisture content, suitable for disposal as sewage. This process is often followed by bleaching and heating the cake, ultimately yielding a dry cake and a filtrate devoid of any solid product.
Advantages and Limitations
The primary advantage of vacuum ceramic filters over other filtration systems lies in their remarkable energy efficiency. These filters can reduce energy consumption by up to 90%. This significant savings stems from the utilization of capillary force acting on the pores, eliminating the need for air to flow through the discs. The fine pores of the filter prevent air breakthrough, enabling the retention of higher vacuum levels. Consequently, vacuum losses are minimized, resulting in a smaller vacuum pump requirement compared to conventional disc filters, thereby lowering operating costs. For instance, a vacuum ceramic filter with a 45 m2 filtration area consumes only 15 kW of power, whereas similar filters with cloth membranes consume 170 kW.
Conventional disc filters are often unsuitable for cake washing, as water quickly runs off the cake’s surface. When cake solids are sprayed with a wash liquid to remove impurities, conventional filtration systems may experience channeling or uneven distribution, leading to cake cracking. However, vacuum ceramic filters have proven more efficient in cake washing due to their steady flow profile and even cake distribution.
Another benefit of vacuum ceramic filters is their high output capacity, producing a very dry filter cake with low water content. In a comparative study, a VDFK-3 ceramic filter outperformed existing BOU-40 and BLN40-3 drum type vacuum filters in filtering aluminum hydroxide, resulting in an average moisture content that was 5% lower.
Furthermore, vacuum ceramic filters boast a longer service life compared to cloth filters, which need frequent replacement. This replacement not only increases the moisture content of the cake but also reduces productivity and disrupts production operations. The ceramic filter, on the other hand, is both mechanically and chemically robust, capable of withstanding regeneration processes.
Despite its many advantages, the vacuum ceramic filter has some operational limitations. One such limitation is the significant fluctuations in recoil washing pressure, ranging from 0.05 to 0.35 MPa. These fluctuations can elevate short-term negative pressure and induce dilute acid due to the “falling suck” phenomenon. Consequently, this can adversely affect the cleaning effectiveness of the ceramic plates and overall filter efficiency.
Designs Available
Design criteria for vacuum ceramic filters vary depending on the type of disc and the filtering capacity required. A standard iron extraction filter typically comprises 12 ceramic filtering plates, or discs, each with a diameter of approximately 2705 mm, providing a total filtering surface of 120 m2. This filter is ideally suited for filtering feed slurries containing high solid concentrations (ranging from 5-20% w/w) and particles sizes between 1–700 µm. Ceramic filters are available with filtering areas up to 45 m2, making them highly suitable for processing metal and mineral concentrates.
Ceramic discs come in two varieties: cast plate and membrane plate. The cast plate is a single-piece ceramic construction featuring a homogeneous surface and a granulated core. Its filter medium consists of thick walls separated by ceramic granules, creating a sturdy mechanical structure. Conversely, the membrane plate type sports a thin membrane atop a coarser core, crafted from a multi-layer porous structure of aluminum oxide. The coarser portion ensures mechanical strength, while the intermediate layer functions as a membrane carrier, and the outer layer serves as the filtering layer. The filtration layer of these ceramic filters boasts uniform pores, allowing for precise filtering of particles of a specific size.
Main Process Characteristics
- Cake Formation:
The discs rotate within a slurry trough, segmented to minimize the slurry volume held at any given time, thereby reducing residence time within the trough. The duration of this stage is influenced by the disc’s rotation speed and the slurry level in the basin. A vacuum is applied within the discs to facilitate cake filtration. - Cake Dewatering:
Washing primarily occurs in the upper portions where the cake surface is nearly horizontal, matching the feed temperature. The ceramic filter employs a sintered alumina disc to dewater the slurry under a low vacuum. Dewatering is achieved through capillary action, ensuring no air or particles clog the filter medium. However, excessive wash water can cascade down the cake and into the feed trough, diluting the slurry. - Cake Drying:
The final moisture content of the cake is controlled by passing dry air or gas (either cold or hot) through it. Drying time depends on various factors such as the distribution valve timing, slurry level in the basin, rotation speed, and scraper position. - Cake Discharge:
Typical operational conditions for a vacuum ceramic filter include:
- Slurry level must exceed the top of the sectors as they move through the trough to prevent air from passing through the cloth during cake formation.
- Solids throughput can reach up to 4,000 kg/m2h.
- Typical filtration capacity ranges from 200-5,000 L/m2h.
- Typical air consumption/flow rate is 50–80 m3/h·m2 at a 500 Torr vacuum.
- The pressure difference with the ceramic disc typically lies between 0.90 and 0.95 bar. However, pressure differences across the filter are generally limited to less than 85 kPa, enabling continuous processing of a wide variety of feed materials.
- Higher rotating speeds allow for greater solid production rates by forming thinner cakes. However, this may compromise washing efficiency and require more electrical power.
- The minimum cake thickness for effective discharge is 3/8-1/2 inch or 10–13 mm.
- Submergence required for cake discharge is 25% of the cycle.
- The effective maximum submergence of the disk is 28% of the cycle.