Baghouse

Bag filter as filtering separators have prevailed in filter technology, gas purification and dust in many industrial processes. As one of their fathers of today virtually forgotten Wilhelm Beth is mentioned. That's the problem with compliance with current emission limits given in a one-step process - to establish - at the highest volume flows and dust loads. The filters were cleaned in previous years by knocking, shaking or in combination with low-pressure flushing, so come in today's filtration technology has been cleaned by compressed air - bag filter used.

Abreinigungsmethoden

In the first dust separators, the cleaning was done as manual cleaning, in the wake by vibration, via purge air to the development and establishment of the compressed air cleaning ( jet pulse cleaning ). With the oldest cleaning method, by motor or manually operated vibrators, an engine is started or a time-dependent on reaching a maximum filter resistor which enables the filter element to vibrate. The resulting movement of the accreted dust cake detaches from the filter surface and drops down into a dust collection container is emptied usually caused by dust discharge system. The mechanical cleaning is carried out after interruption of the filtration operation. When cleaning by shaking filter tubes are mechanically stressed and have relatively short service lives. A more gentle cleaning method consists in the periodic reversal of the flow direction ( back-flushing filter ). Here, the filter system is made of several separate chambers and chamber will be cleaned. In many cases the combination of both Abreinigungsmethoden was realized.

The in filter technology most commonly used and most modern form of cleaning is the pressure shock method ( jet pulse cleaning ). Meanwhile, this Abreinigungsart has largely prevailed as the standard. The filter is cleaned with jet pulse equipment by a cyclic, intense pressure air blast. This enables the filter hose during cleaning briefly in overpressure. The filter bags are inflated short, the flow direction is reversed and replaced the filter cake. In the filter phase is a supporting basket the hose the corresponding stability. The cleaning cycles depend inter alia on the filter surface load (volume flow per filter area and unit time), the gas density, the raw gas and the particle properties. The regeneration can be time-controlled or fixed filter differential pressures. The transition process of the reverse air for jet pulse cleaning has contributed through the effective removal of the periodically depositing filter cake significantly to increase energy efficiency.

Dedusting and filtering process

The raw gas is ideally performed in a cross flow to the filter bags to avoid up-current against the Partikelsedimentationsrichtung. The crude gas is directed through a distribution plate, to which a preliminary separation takes place, and the raw gas is made uniform in the filter housing. The deposition of the particles takes place at the surface of the filter medium or on the surface of the filter cake being deposited thereon. The corresponding flow resistances resulting from the pressure drop of the filter cake and the filter medium directly after jet pulse cleaning (residual pressure loss).

The cleaned gas flows upwards out of the tube. Especially with long tubes ( for example, a tube length of 8 m with a tube diameter of 160 mm) and high filter surface loading is the pressure drop across the tube bottom, ie, at the outlet from the tube over the inlet nozzle into the clean gas range, is also important. These and all other flow resistances of the filter housing ( the filter cake to raw gas inlet surface pure gas flow from the outlet tube to the clean gas outlet channel) are grouped in the case pressure loss. After the cleaning of the filter bags, the dust particles settle in the dust collecting chamber and the material is transported from there in most cases on the conveyor screw, and rotary valves. In the online mode, the present in the raw gas particles are continuously anfiltriert. Immediately after the jet pulse cleaning the particle concentration in the vicinity of the filter tube is very high. In this state, particularly with the finely dispersed dusts with little tendency to agglomerate, to Wiederanfiltrieren abgereinigter particles. This " inner" dust circulation can cause a significant portion of the filter cake mass and thus contributes to the loss of pressure. To increase energy efficiency, therefore, filter modules are offset by raw and / or pure gas side shut-off during the cleaning in a no-flow condition. In this so-called off-line mode, the immediate redeposition of dust on adjacent filter bags is prevented. Cleaning can also be done by an air pulse of much lower intensity.

Injektortechnologien

The compressed air injector system for the periodic regeneration of the flow-through from outside to inside the filter bags is crucial for energy-efficient operation. The cleaning has to be done so that the filter cake over the entire length of hose completely detached. In parallel, the repulse of the medium is to minimize the support basket by appropriate modulation of the pressure curve. Injector systems can for example consist of a simple blow tube holes, from which the compressed air flows. By the venturi nozzle downstream secondary air is drawn in and made ​​to increase the static pressure in the filter bag. The inlet nozzle represents an optimization with reduced flow losses dar. by necking of the nozzle to the "ideal nozzle " is reached, a further increase in efficiency in conversion of pneumatic energy into a cleaning pulse. A very efficient cleaning technology, the Coanda injector dar. This cleaning system uses the so-called Coanda effect in which the compressed air emerges from an annular gap and is guided over a curved surface. The primary air follows the boundary layer does not become detached due to the geometry of the Coanda injector. This creates within the first injector stage, an extremely high vacuum which draws additional secondary air, and a driving jet is formed which is opposed to the variants described above, has a significantly increased amount of air. This propulsion jet enters the inlet duct as a second injector stage is sucked into the further secondary air.

Cleaning control

The cleaning control system is carried out today on microprocessor technology and fieldbus systems. In addition to controlling the diaphragm valves pneumatically or electrically actuated raw and clean gas valves are controlled and signals from field sensors, such as "broken -bag guards " processed. At timing of the pressure pulses is made between a fixed timing, and the differential pressure control system with variable cycle times. A further control parameter, the continuous control of the tank pressure of the compressed air reservoir. By continuously adapting the Abreinigungsdrucks air demand is adjusted to the prevailing operating conditions. As a rule, the size of the so-called pre-pressure controlled cleaning of the filter differential pressure used. The operating data of the dedusting be kept at minimum air demand at the desired operating point and there is an equalization of the dust levels and better utilization of the capacity of the dust discharge organs achieved and achieved a lower mechanical load on the filter bags.