DE2552741A1 - Batch operated vacuum band filter - having cycle controlled by limiting reduced pressure in hook - Google Patents

Abstract

Control system for a batchwise vacuum filter process involves evacuating a filter chamber and then using the reduced pressure as a control parameter for the filtration and filter sealing operation. The vacuum is only produced by the vacuum pump connected to the filter unit. The rate of change of pressure in the vacuum chamber during the filtration is determined by a manometer the signal from which is used to control the feed value into the filter. After reaching a certain value, the inlet value is opened to commence the filtration. After the pressure in the filter chamber has dropped to a certain minimum value, the value is closed and the filtration terminated. The process ensures controlled feed, allows filtration even when seal is imperfect, keeps ingress of air to a minimum and ensures reliable termination of the sequence.

Description

CONTROL OF A BAND FILTER

The invention relates to the control of a chamber filter, which as Filter medium preferably uses a paper belt conveyed in cycles.

One known embodiment of this type of filter essentially exists from a filter plate (i) with a vacuum pump (2) connected at the bottom and one at the top lying cover (3), which is operated by a pressure cylinder (4).

The function of the sealing cap is to place one on the filter plate resting filter tape medium section sealingly on the edges of the filter plate to press. The filter plate consists of a recessed drain space on which the horizontal perforated support plate (5) is on top. On the frame (6) is located a filter tape roll (7), which by means of take-off rollers () with a connected discharge motor (9) is passed between the filter cover and the filter plate. In the immediate A scraper for the filter cake is attached near the pulley (10). from An air line in which a ventilation valve (12) is arranged goes off the filter cover is.

The following well-known series of functions takes place fully automatically: The filter tape take-off rollers (B) guide a clean section of tape onto the filter plate (1).

Filter sealing: The filter cover is closed by means of the pressure cylinder (3) pressed onto the clean filter belt and sealed the filter.

Filtration: The vacuum pump (2) switches on and the one to be filtered Liquid is sucked into the filter chamber (11) and over the filter belt distributed. The filtrate is sucked through the filter belt and taken to the desired one ## uVc # ' Collection location promoted.

Filter chamber emptying and cake drying: After filtration, the ventilation valve (12) opens automatically.

This interrupts the negative pressure in the filter chamber (11) and atmospheric air is sucked through the filter cake and filter belt.

The filter cover (3) is then lifted.

Cake discharge: The discharge motor (9) is switched on and the take-off rollers (n) slowly pull the filter belt out of the filter chamber (11). The filter cake is lifted off the filter belt by the scraper.

The work cycle is then repeated automatically.

The series of functions described under "Filtration" and "Filter sealing" above has some disadvantages: 1. Too fast suction or supply of what is to be filtered Liquid in the filter chamber can cause the filtration differential pressure to rise too quickly to lead. This often causes poor filtration results and short filtration cycles with an uneven specific filtration throughput.

2. It can happen that before the suction or delivery process the filter chamber is not sufficiently sealed for mechanical reasons.

This leads to excessive penetration of outside air into the Filter chamber during filtration.

3. The known procedures for terminating the filtration process are carried out carried out either by time relay or differential pressure gauge.

Either the filtration differential pressure or the negative pressure generated under the filter plate are used as the values for the completion of the filtration. However, these values are also heavily dependent on the respective Pumping speed the vacuum pump, the filter chamber sealing ratio, the filter inlet dimensioning and facility. In practice, incorrect switching cannot be ruled out.

The purpose of the present invention is to create a controller the 1st - the possibility of a too rapid increase in the filtration differential pressure excludes during the filtration and even a control of this differential pressure and thereby enables the specific throughput over a certain period of time.

2. - the possibility of carrying out a filtration process without eliminates the presence of an adequate filter chamber seal.

3. - the penetration of outside air into the filter chamber during Filtration reduced to a minimum.

4. - a reliable termination of the filtration process guaranteed.

According to the invention, to achieve these objects is the generation an initial vacuum in the filter chamber (11) is a prerequisite. After the filter chamber sealing process and before or during the supply of the liquid to be filtered, the filter chamber put under vacuum.

The presence of a certain negative pressure value in the filter chamber (11) before the filtration process shows that the filter chamber is adequately sealed and that this negative pressure is the minimum value of the existing vacuum below the The filter plate (1) must be observed during the filtration.

The presence of a negative outlet pressure in the filter chamber creates this is the prerequisite for a gradual increase in the filtration differential pressure during the filtration. By controlling this negative pressure during a certain Period, e.g. through a control valve (13) in the supply line, is a uniform, specific throughput during a given To achieve the period.

The presence of negative pressure in the filter chamber (11) during the Filtration also ensures that the filter lid is a significant additional Is subjected to sealing pressure. This results in a significant reduction the outside air entering during the filtration.

The presence of a certain maximum initial negative pressure value in the filter chamber also means that when a minimum vacuum value is reached and by the cooperation of a corresponding control valve (13) in the supply line the filtration process is ended.

According to the invention, the following series of functions takes place fully automatically instead of: Filter chamber sealing: as described above Filter chamber ventilation: The Vacuum pump (2) turns on and air (or gas) is closed with a Control valve (13) sucked out of the filter chamber. When a fixed negative pressure value is not reached in the filter chamber, a corresponding signal switches the Filter system off.

Filtration: When a fixed negative pressure value in the filter chamber is reached, the control valve (13) is opened. When the sealed filter belt surface from the liquid to be filtered is completely covered, the actual filtration begins. The presence of the negative pressure in the filter chamber ensures that there is a gradual increase in the filtration differential pressure takes place. When the control valve (13) with a corresponding feedback the contact manometer (14) is equipped, a certain increase in the filtration differential pressure can be achieved over any period of time.

When the negative pressure in the filter chamber reaches a minimum value the control valve (13) is closed by the contact pressure gauge (14) and the air valve (1?) open.

Filter chamber emptying and cake drying: as described above.

Cake discharge: as described above.

The work cycle is then repeated automatically.

Claims (5)

PATENT CLAIMS Tine Control of the filtration and filter chamber sealing processes a cyclically operating vacuum chamber filter, characterized in that the Filter chamber (11) is placed under vacuum and that the negative pressure value in the filter chamber used as a control variable for the filtration and filter chamber sealing processes will. 2. Control processes according to claim 1, characterized in that the negative pressure in the filter chamber (11) only connected from the existing from below Vacuum pump (2) is achieved. 3. A control of the filtration processes according to claim 1. thereby characterized in that the rate of change of lowering the negative pressure in the filter chamber during filtration, by coupling a pressure gauge (14) with the control valve (13) in the supply line determined. 4. A control of the filter chamber sealing process according to claim 1. characterized in that after reaching a certain negative pressure value the control valve (13) in the filter chamber is opened by the pressure gauge (14) and only then is the actual filtration process carried out. 5. A control of the filtration process according to claim 1 and 3. characterized in that, after reducing the negative pressure in the filter chamber (11) and reaching a minimum value, the control valve (13) closed and the Filtration process is ended.