What is Candle Filter?
Candle filters, also known as Backwashing Tubular Filters, are industrial filters used for filtration, polishing, and thickening liquids, slurries, or solids. The candle filter provides us with a high yield discharge of dried filter cake. These filters are suitable for the treatment of various filtrates like flammable, toxic, or corrosive materials. They are explicitly designed to work in harsh environments. Candle Filters runs in batch cycles and can automatically recycle and filter the filtrate without direct operator supervision.
Candle Filters consist of three major components:
1. The vessel
Vessels are of two types: one with conical bottoms used for cake discharge, and the other with flat bottoms used for thickening of filters or slurries. In both types, the material is fed from the bottom to avoid settling of solids, and they have a safety valve at the top to prevent overflow. The vessel operates under the pressure of 6-10 bar. The candles plug into the header, which carries slurry out near the top of the filter.
2. Cake discharge system
In this system, the cake discharge occurs by:
- A controlled and calculated release of entrapped air or gas
- And manipulating the sludge Inlet, filtrate outlet, and slurry drain.
3. The candles
Candles are hollow tubes with a cap on the bottom and a threaded connector on the top. These threaded connectors connect with a header. Candles are named after their shape. These are the main filter elements. The outer face of the tube is mainly made of sintered metal, expanded metal, punch plate, or porous ceramic. The outer face provides support to the filter media.
The first filter media is stainless steel wire cloth. It provides good cake release and excellent withstanding pressure. The second media is a wedge-shaped wire. This triangular wire offers excellent abrasion resistance. There may be a fabric media also present. Fabric media allows a greater flow rate. Using this versatile media, polypropylene, Teflon, nylon, polyester, and cotton textiles can be woven in various styles to allow filtration ranging from 1-900 micron.
Working Principle of the Candle Filter
Candle Filters work on the famous principle of mechanical trapping and adsorption of toxic particles in the pores of candles. The candle filter work in three stages: filling, filtration, and discharge. But depending upon the circumstances, the following steps are included in most of the operations.
Pre-coating is not usually performed. This step occurs only in the following circumstances:
When the product is sticky or gelatinous. The pre-coat layer will act as a barrier that avoids cloth binding. In this way, the interface between cloth and pre-coat departs quickly, and the cake discharges, leaving the clean cloth behind.
When the clear filtrate is immediately required after one filtration cycle. Otherwise, recirculation must be needed until a clear filtrate is obtained.
As described previously, the slurry will enter the vessel from the bottom, release the air above the candles and headers.
After pre-coating and filling, the filtration will occur in the candles. The pressure is used to separate the forming cake from the filtrate. This forming cake will retain on candles, and filtrate will pass through headers for further processing.
If the filtration process is slow, you can add body-aid to enhance the cake permeability. But this addition may cause an increased formation of cake for disposal.
Spray bars are present near the headers. These spray bars clean the cake down the length of the candles.
The air or gas will pass through the cake until the moisture content becomes minimum. At this point, the cake will be considered dry. Moreover, this process may filter any leftover filtrate into the candles.
After the completion of the filtration cycle, the air or gas will blow through the vessel. Under the influence of air, the slurry heel around the candles will be pushed and displaced downwards until it reaches the lowest region of the candle stack. From here, the remaining heel slurry will go back to the evacuated tank by a special dip pipe. The dip pipe is located at the end of the vessel. The sole purpose of this pipe is to empty the vessel from any slurry.
The cake outlet will open during this step, and the candle will vibrate to discharge the cake. But keep in mind that the cake outlet opening must be integrated with the pressure sensors to avoid opening under pressure. In some cases, you might be required to clean the candles if any residue cake is present. If absent, then the filter is ready for another cycle.
Candle Filter Applications
Candle filters are available in different sizes and capacities, depending upon their usage. Different manufacturers launch different sizes of candle filters. But basically, all of them are designed to give a reliable performance. Candle filters mainly have applications as following:
- Pharmaceutical filters
- Fine Chemistry filters
- Food Industry filters requiring FDA approval
- Fuel and Oil Additive Filters
- Hazardous Materials Filters
- Precious Metal and other Catalyst Recovery Filters
- Solid content: up to 2%
How to Use a Candle Filter?
Candle filters are used to handle toxic and corrosive substances. They can efficiently handle titanium oxide, flue gas, brine clarification, red mud, China clay, fine chemicals, and many other materials. They are more suitable for substances that require low moisture content and a high degree of polishing.
Candle Filters remove turbidity, suspended particles, and microbial organisms from the material flowing through them. Removal action occurs by a physical process such as mechanical trapping and adsorption of particles in the micropores of the filter. Below is the series of steps that will happen in the candle filter system:
- The material is fed into a vessel through a proper system.
- This material will pass through the candles while simultaneously releasing the contaminants.
- The final cake will discharge into a storage tank for further processing.
- The candle filtration system both treats and store the media.
- The whole process is automatic and requires almost no intervention from the operator.
- Maintenance on a regular basis is mandatory. Otherwise, it will not work efficiently.
- After two weeks, the operator should clean the filters and keep a keen eye on other components for proper functioning.
Pros and Cons of Candle Filters
Advantages of using candle filters:
- Good cake discharge
- Effective in slurry thickening
- Minimum floor space required
- The whole process is mechanically simple because there is no complex sealing glands or bearings.
Disadvantages of the candle filter
- The high headroom is needed for dismantling the filtering elements.
- Emptying the vessel between cake filtration, washing, and drying requires close monitoring of the pressure inside the vessel.
- Frequently monitor the filter to ensure that cake holds onto the candle.
Candle Filter’s Maintenance
Candle filters require maintenance on a regular basis. Because of frequent particle build-up and the resulting decrease in fluid flow rates, candle filters must be cleaned with a handle. Use soft brushes and water to do the task. Ceramic candle Filters may lose walls thickness and become less efficient in removing microbes.
There should be a hoisting device and sufficient headroom to lift the candle easily and move it horizontally adjacent to the tank. There should be a special rig to hold the candle for maintenance. The major components of candle filter that require attention are:
- You should periodically check the filter tank as per the safety regulations.
- There is a pressure relief valve at the top of the tank. You must check it for emergency functioning.
- The clamps are used to seal the upper and lower ends of the filtering medium to the core.
- Large diameter caulking gasket of the dished top headcover. Its end must be cut at an angle that will ensure a perfect seal.
- The locking bolts of the headcover
- The interlock prevents the opening of cake discharge under pressure.
- Filtrate sight glass which visually enables inspection of the filtrate.
- The maintenance hoist above the filter must prevent the candles from hitting the tank wall.
- Inspection of the filter medium or cloth for any damage.
- Vent present on the top of the head. You should check it for free evacuation of air.
- The filters must not be overfilled with the cake. This may cause bending of the candle, so check it from time to time.
Top Candle Filter Manufacturers
Candle Filters are widely used in several industries all around the world. Candle filter suppliers are present in almost every world as they have high demand in the market. But not every supplier has top quality candle filters. You should buy a candle filter from a reliable manufacturer and supplier. Following are the list of some manufacturers who have top quality and long-lasting candle filters.
- Saifilter: Saifilter is a worldwide recognized company. This company has 12 years’ experience in industrial filters. They can also design and customize the filters for different variety of applications and industries. Their contact details are available on website. You can ask for more details by visiting their website.
- Maag group: Maag is also one of the popular companies among many candle filter manufacturing companies. They produce high-quality candle filters. Their products are famous worldwide. They have earned their name in this industry through hard work.
- Ningbo Jewin electrical appliances Co. Ltd: This company is also famous as superjewin. They are the leading manufacturer and exporters of candle filters.
- Bucher Unipektin: Bucher Unipektins are leading manufacturers of candle filters. They supply in various countries.
- Steri Technologies: Steri Technologies are reliable manufacturers that provide cost-effective candle filters. Their fine chemistry candle filters meet ASME standards or any other industry standards.
The candle filters should be selected in the following conditions:
When there is limited floor space, but large filtration areas are required.
When there are volatile materials that cannot be subjected to vacuum.
Candle Filters are needed for polishing applications where high filter clarity is required.
When there is a risk of an environmental hazard. This process has a secure discharge mechanism.
When the dry or thickened slurry cake is required.
Candle filters are best suited for flammable and hazardous substances. These filters can work efficiently in less floor space. Moreover, they can effectively filter the cake without leaving any impurities behind. The world’s top manufacturers supply good quality and highly affordable candle filters throughout the globe. But candle filters require close monitoring and periodic maintenance. You should look into all the pros and cons of a candle filter before buying one.