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.
BHS candle filters are available in a standardized range with a variety of modules. 15 sizes with filter areas ranging from one to 87 square meters cover all common applications and market requirements - a flexible and cost-efficient solution for clarification filtration.
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 6 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.
ATEX-certified versions of the BHS candle filter are available for potentially explosive processes.
Candle filter design
A Pressure vessel
B Suspension feeding
C Filtrate discharge
E Compressed gas infeed
F Solids discharge
G Residual volume discharge
H Register pipes
I Filter candle
K Safety valve
L Pressure transducer
M CIP unit
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.
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 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.
|Type||Candle length||Candle area||Number of candles||Active filter area (total)|
|3 units||1 m²|
|7 units||2,4 m²|
|19 units||6,5 m²|
|19 units||9,7 m²|
|37 units||18,9 m²|
|61 units||31,1 m²|
|7 units||4,1 m²|
|61 units||36,0 m²|
|91 units||53,7 m²|
|127 units||74,9 m²|
|19 units||12,9 m²|
|37 units||25,2 m²|
|61 units||41,5 m²|
|91 units||61,9 m²|
|127 units||86,4 m²|
|Operating pressure||up to 6 bar (g)|
|Operating temperature||up to 80 °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 86,4 m²|