The candle filter of type CF is a filter that operates in a discontinuous manner. The candle-shaped filter elements are arranged vertically in a pressure vessel. The process steps typically performed with this unit are filtration, washing, drying and discharge. All these steps take place under pressure. The candle filter is used for the clarification of liquids with a low solids content. It is a compact unit, operates fully automatically and enables high throughput rates, dry cake discharge and a wide range of cake treatment options.
In order to meet the respective process engineering requirements, the filter cake can be treated in many ways. It can be washed or slurried once or several times. To achieve further dehumidification of the filter cake, it is possible to pass air, nitrogen or other gases through it. If necessary, precoat filtration can be performed using filter aids.
The candle filter works fully automatically. At the end of a process cycle, the filter cake is separated from the candle surface by means of a blow-back blast and discharged. Then, the next cycle begins.
The entire filtration process takes place under pressure – up to a differential pressure of 10 bar g – in a closed, gas-tight system. This enables the use of BHS candle filters even under stringent safety or hygienic requirements. Products can also be processed in an inert or sterile atmosphere.
The BHS candle filter has no moving parts. This increases operational reliability and reduces the need for maintenance. When discharging the cake, the special surface design of each candle ensures that the cake fully separates before it is discharged downwards.
We utilize different stainless steel grades as required by the specific application scenario (for example, also 316L, Super-Duplex, Hastelloy etc.) or coated designs as well as plastics. If required, ground and polished surfaces are also available.
We produce special-purpose filters according to GMP principles and equipped with CIP units, where necessary, for applications in the pharmaceutical, food and bioprocess industries. We are also ATEX certified.
BHS has developed a modular system of turnkey filtration plants using candle filters. The advantages of these proven system solutions include short delivery times and low installation costs on site. The modules are designed to facilitate transport to the construction site in ISO containers at low cost.
Candle filter design
The central pipe is designed as an immersion pipe that facilitates complete discharge of the filtrate.
The candle is connected to the register via a thread at the end of the central pipe.
The support structure for the filter cloth is heavily perforated, which enables high filtrate throughput rates.
The pleating bars cause the filter medium, and by extension the filter cake, to settle in a wave-like pattern. This results in stable, reliable cake formation.
The filtrate is led downwards inside the support structure to the filtrate collection chamber. From there, it leaves the candle upwards via the central pipe.
During filtration, the filter medium is brought into a convex-concave wave shape by the pleating bars in combination with the working pressure applied.
The solid matter (7) accumulates as a filter cake on the surface of the filter medium due to the pressure difference applied during the filtration cycle. The clear filtrate (8, blue arrow) flows upwards through the central pipe and is discharged through the register pipes.
Displacement or circulation washing can be implemented in the direction of the filtration.
Mechanical cake drying is implemented by blowing gas or steam through the filter cake. Alternatively, the cake can be discharged as sludge.
At the end of the process cycle, the container is no longer under pressure and the discharge flap opens. To eject the filter cake (9), the filter cloth is expanded by means of blowback (10, orange arrow). The filter cake is ejected from the filter medium, breaks into pieces and falls through the discharge flap.
BHS manufactures candle filter systems for a wide range of applications. The offering is based on a range of standardized modules for plants with filter surfaces from 1 m² to 50 m². BHS also manufactures individual candle filter plants tailor-made according to customer specifications. The four main components of the BHS candle filter plant are the candle filter, piping with fittings and measuring instruments, steel structure and control system. There are additional accessories to further supplement and expand the system.
In addition to machine technology, BHS also offers complete process engineering solutions in the field of solid-liquid separation. The actual filtration can be supplemented by upstream and downstream process steps, which we plan and implement.
All BHS candle filter plants feature a modular design. This reduces the planning effort, allows for factory pre-assembly and facilitates detailed testing before delivery (FAT). On-site installation is accelerated and short delivery times are generally possible. Depending on the technical process requirements, the modules can be combined flexibly.
The modules installed in the systems fit into ISO containers. This enables cost-effective and hassle-free transport worldwide.
It is part of our standard project planning protocol to fully clarify all interfaces early on. For this purpose, we draft foundation plans and detailed piping isometrics. All connection points are clearly defined.
BHS has extensive experience in the preparation of plant documentation according to international standards.
Residual filtration devices are used to process the residual volume at the end of the filtration cycle via an internally filtering candle on the tank cone. In this way, complete residual filtration can be achieved while minimizing the expenditure of compressed gas.
A CIP system is available for cleaning the filter interior, the register pipes and the filter candles. A special version of the candle filter with carefully designed surfaces allows safe cleaning of all parts that come in contact with the product.
A precoat or body feed system is required to stir powdered filter aids into a suspension. The precoat system works in batches, and the body feed system operates continuously. Both are of modular design and comprise a storage tank, agitator, piping, fittings, measuring instruments, steel structures and pumps.
In the case of wet discharge with plate, the candles are attached to a holding plate that separates the filtrate from the suspension chamber. The filter cake is discharged via filtrate counterflow. Under certain conditions, wet discharge with plate represents an economical solution.
To match your application needs, we can draw on our extensive experience to integrate other accessories into the candle filter systems, such as police filters or activated carbon filters.
|Type||Candle length||Candle area||Number of candles||Active filter area (total)||Vessel diameter||Vessel length|
|3 units||1 m²||419 mm||1,6 m|
|7 units||2,4 m²||508 mm||2 m|
|19 units||6,5 m²||800 mm||2,5 m|
|7 units||3,6 m²||508 mm||2,3 m|
|19 units||9,7 m²||800 mm||2,8 m|
|37 units||18,9 m²||1.100 mm||3,5 m|
|49 units||25 m²||1.300 mm||3,7 m|
|61 units||31,1 m²||1.500 mm||3,9 m|
|49 units||29,4 m²||1.300 mm||4 m|
|61 units||36,6 m²||1.500 mm||4,2 m|
|77 units||46,2 m²||1.600 mm||4,3 m|
|91 units||54,6 m²||1.800 mm||4,5 m|
|112 units||67,2 m²||2.000 mm||4,7 m|
|144 units||86,4 m²||2.200 mm||4,9 m|
|221 units||132,6 m²||2.600 mm||5,6 m|
|49 units||33,3 m²||1.300 mm||4,3 m|
|61 units||41,5 m²||1.500 mm||4,5 m|
|77 units||52,4 m²||1.600 mm||4,6 m|
|91 units||61,9 m²||1.800 mm||4,8 m|
|112 units||76,2 m²||2.000 mm||5 m|
|144 units||97,9 m²||2.200 mm||5,2 m|
|221 units||150,3 m²||2.600 mm||5,9 m|
|Operating pressure||up to 10 bar (g)|
|Operating temperature||up to 250 °C|
|Solids content (suspension)||up to 10 % (wt.)|
|Cake thickness||up to 30 mm|
|Particle size||0,5 µm and above|
|Filter performance – suspension||0,1 to 10 m³/m² h|
|Filter performance – dry solids||-|
|Active filter surface (total)||1 to 150 m²|