Bag filter In fluid technology, a filter (surface filter, in which the filter medium) is formed.  As a filter separator, bag filter has the upper hand in filtration technology, gas cleaning and dust removal in various industrial processes.
Just as its inventor applied William Beth from Lubeck, if the filter had been cleaned earlier by knocking, shaking or combining with low-pressure flushing, then today it uses compressed air for cleaning.
The feed gas of bag filter is fed into the filter bag in the form of cross flow to prevent upward flow and resist the settling direction of particles. The raw gas is guided through the distribution plate, and the pre separation is carried out at the distribution plate, and the raw material air flow in the filter shell is uniform. The actual deposition of particles occurs on the surface of the filter medium or on the surface of the filter cake deposited on it. The cleaned gas flows upward out of the hose. The corresponding flow resistance is caused by the pressure loss (residual pressure loss) of filter cake and filter medium after the removal of jet pulse. In particular, it has a long hose (for example, a pipe length of 8 meters is a pipe diameter of 160 mm) and a high filtration surface load, and the pressure loss through the hose floor, D. Hours. It is also important when leaving the hose through the inlet nozzle in the clean gas area. This is grouped with the pressure loss of all other flow resistances of the filter housing (feed gas inlet, with the clean gas flow from the tube outlet to the clean gas channel on the surface of the filter cake).
Classification of filter bag cleaning
Vibration cleaning method
In the old cleaning method, by manual operation or electric vibrator (vibrator), the engine starting depends on the time or when reaching the large filter resistance to make the filter element vibrate. The movement resulting from separating and annealing the filter cake from the filter surface falls into the dust collection container and is normally emptied through the dust discharge system. Mechanical cleaning after interruption of filtration operation. The disadvantage of cleaning by shaking is that the filter bag is subject to mechanical stress, so its service life is relatively short.
The filter belt cleaning mode is shown on the left side
A milder cleaning process involves periodically reversing the flow direction by blowing air (backwashing). Here, the filtration system is designed in several separate chambers, which are individually cleaned. In many cases, the combination of vibration and backwashing of cleaning method is realized
Pressure fluctuation method
Hose filter with pressure fluctuation cleaning, and the commonly used filtering technology is pressure pulse method (jet pulse cleaning), which is now widely used as a standard and modern cleaning form. In this method, the filter bag, unlike the two O.G., flows through the filter from the outside in, so the basket needs to be supported to provide the required stability. Through the periodic strong compressed air impact into the hose for cleaning, this temporarily makes the filter hose overpressure. And now, the filter cake is separated from the outside by a short flow direction. After cleaning the filter bag, the dust particles deposit in the dust collection chamber, and the materials are usually transported away by screw conveyor and rotary valve. It must be cleaned in such a way that the cake is completely separated over the entire length of the hose. In parallel, the repulsion of the medium on the support basket is minimized by modulating the corresponding pressure curve. The cleaning cycle is suspended. One. Upper filter surface load (volume flow and time unit per filter surface)
The transition from purge air cleaning to jet pulse cleaning significantly improves energy efficiency by effectively removing regularly deposited filter cake.
In online mode, the particles in the feed gas chamber are continuously filtered. After the jet pulse cleaning, the particle concentration near the filter bag is very high. In this state, especially fine dispersed dust with oligomeric tendency, is used to re penetrate the cleaned particles. This "internal" dust cycle results in a considerable proportion of cake mass, resulting in pressure loss.
In order to improve energy efficiency, the filter module is therefore offset by the original and / or clean gas shut-off device during cleaning without flow. In this offline mode, dust is prevented from accumulating immediately on the adjacent filter bags. This can also be achieved by cleaning the filter with a significantly lower intensity of compressed air pulse.
Today, cleaning is controlled by microprocessor technology and Fieldbus systems. The "chtern" and "chtern" gas sensors are operated in addition to the diaphragm control valves.
Another control parameter is the continuous control of the tank pressure of the compressed air reservoir. In this case, the compressed air demand adapts to the respective operating conditions by continuously adjusting the cleaning pressure. Therefore, the filter differential pressure is used as a controlled variable for preloading control cleaning (see Figure). Advantages of this method: the operating data for dust removal are maintained at the desired operating point of small air demand, dust becomes more uniform, dust discharge mechanism is better utilized, and filter hose is less mechanically loaded.
Comparison of ejector systems for compressed air controlled cleaning of bag filters
The two-stage ejector system, which introduces compressed air during periodic regeneration, plays a decisive role in the energy-saving operation of the bag filter.
The ejector system may consist of, for example, a blowpipe with a simple hole from which compressed air flows (left portion of Fig. 1). The secondary air is inhaled through the downstream venturi inlet nozzle, and the static pressure in the filter hose is increased. The inlet nozzle is an optimized flow loss reduction.
When the compressed air energy is converted into a cleaning pulse (middle part of the figure), the inlet hole is extracted into the "ideal nozzle" to further improve the efficiency.
A very effective cleaning technique is the Coanda syringe (shown on the right side). The cleaning system uses the Kodak effect, in which compressed air comes out of the annular gap and is directed to the curved surface. The main air follows the boundary layer, which does not separate due to the geometry of the Kodak injector. In this process, a very high negative pressure is generated in the ejector stage, which sucks in additional secondary air and forms a propulsion jet with a significantly increased air volume compared to the previously described variant. The propulsion jet enters the inlet nozzle as a second ejector, in which additional secondary air is drawn in.