A bag filter of ETM GmbH is designed as a fully automatic, heavy-load filter with online Pulsjet-Jet cleaning. The filter housing is designed as a welded steel construction with profiled steel stiffeners. The welded hole plate for bags separates the raw and clean gas space. Under the raw gas dust collection hopper are arranged. Each of the hoppers is equipped with a repair slide valve on dust discharge. It is recommended a slide size of at least 400 x 400 mm. The dust-loaded flue gas is distributed over the raw gas in the filter chambers. The housing is designed in multi-chamber design with butterfly valves. In the filter chamber the cylindrical filter bags are arranged. The filter bags are flowed through from outside to inside. As it flows through the filter bags, the dust content of flue gases is largely retained and accumulates as a filter cake on the surface of the filter bags. Support cages, used in the bags used prevent the collapse of the filter bags. The cleaned flue gas flows from the unfiltered gas side of the bag filter into the interior of the filter bags and thence into the clean gas chamber and the subsequent clean gas channel. For uniform distribution of smoke and dust on the filter surface and to protect the filter bags against abrasion distribution and guide walls are provided in the entry area. The cleaning is done by the pressure surge process (pulse-jet cleaning) by a cyclic, intensive pneumatic shock. This enables the filter bag briefly in overpressure during cleaning. The filter bags are inflated briefly, the flow direction is reversed and replaced the filter cake. The support cage gives the filter bag the appropriate stability in the filtration phase. The cleaning cycles depend inter alia on the filter surface load (flow rate per filter area and unit time), the gas density, the raw gas and the particle properties. The regeneration can be time-controlled or via fixed filter differential pressures. Today, the cleaning control in the baghouse is done on microprocessor technology and fieldbus systems. In addition to controlling the membrane valves, the pneumatically or electrically actuated raw and clean gas flaps are controlled and signals from field sensors (level, temperature, etc.) are processed. At timing of the pressure pulses there is a distinction between a fixed timing and the differential pressure control with variable cycle times.
The material for filter bag depends on the aggressiveness of the flue gas medium and the temperature of the flue gas. Mostly needle felts (PI / PTFE needle felt or PI-needle felt PTFE supporting tissue) with PTFE surface equipment are used, as these materials achieve a longer life than "naked" fabric. The filter bags are made up according to the conditions in the bag filter. They get a double bottom and below a lateral duplication. Above the filter bags are provided with a snap ring and double bulge. The expansion of bags will be upwards. If it is necessary to change the filter bags during operation, the affected chamber of the filter, in which the defective bags are situated, has to be insulated from the exhaust at the raw gas side and at the clean gas side by special shut-off devices. The clean gas chamber lids are lifted by means of lifting gear and driven with a geared trolley aside. The defective filter bag can be changed or filter bags can be closed by covers. To change the filter bags of a complete chamber or of the entire bag filter the downtime for maintenance of the boiler system should be used or the boiler plant has to be shut down.
When commissioning and during each start-up from the cold state a precoating of the filter bags must be carried out with hydrated lime. Basically, there will be a separation of the filter medium and dust to be deposited by a protective layer by precoating. The precoating serves an additional protection of the filter media against chemical attacks and to improve the separation behavior of the bag filter at low raw gas and very fine dust particles. It is particularly important to distribute the precoating material (hydrated lime) evenly on the not yet loaded filter medium at startup, to left this material on the filter bag and to store it there. The cleaning of filter bags is therefore inadmissible during this time. It is recommended to apply 200 to 250 g / m² filter area with running induced draft fan on the raw gas side but with switched of control. Only after the warming up of the system via the gas or oil burner the cleaning is to put into operation according to the setting. For precoating a hydrated lime / calcium hydroxide should be used with a fineness of dx50 < 9 µm.