Various technologies are suggested to ensure the precipitation of particles and aerosols. ENVIROTHERM has the capacity to resort to all proven filtration technologies and will select the most effective and cost-efficient one in dependence of the respective application.
Dry-type electrostatic precipitators
… are used in power stations and incineration plants right downstream of boilers to clean flue gas of dust.
In this context, the capacity ranges from 20,000 m³/h to several millions m³/h.
Wet-type electrostatic precipitators
… are employed in saturated gas atmospheres and ensure precipitation of aerosols to reach minimum pollutant levels in the cleaned gas.
SO₃, TiO₂ and tar can be reliably removed. For cleaning purposes, the mass flow is horizontally routed through wet-type electrostatic precipitators which are manufactured from high-quality corrosion-resistant materials.
Dust particles or drops contained in the gas flow collect a negative electrical charge from discharge electrodes connected to a high voltage (T/R) block. Under the influence of a strong electrical field the particles migrate to the grounded collecting electrodes where they adhere to the surface and get discharged. Regular cleaning of the electrodes is ensured by appropriate cleaning devices. Accumulated deposit layers fall or flow into bunkers or trays arranged beneath the collecting chamber. From this place, discharge and further transportation is carried out by mechanical or pneumatic devices and pumps respectively.
The raw gas flows through the gas distribution internals arranged within the conical inlet hood and is routed into the active separation section. In accordance with the required collection efficiency of the electrostatic precipitator the dust-laden gas flows through several sequentially arranged collection zones. Cleaned gas contents of less than 10 mg/m³ will be reached.
Characteristic features of ENVIROTHERM-designed horizontal dry-type electrostatic precipitators are:
- Adaption of gas velocity and discharge electrodes to height and length changes within the electrostatic precipitator.
- Optionally, top-rapping design with patent-registered collecting electrodes with nearly ideal electrical and mechanical features as well as rigid and unbreakable discharge electrodes may be provided.
- Modular configuration designated to insure quick and easy assembly.
- Minimization of the quantity of wear parts is given.
- Maximum precipitation efficiency and maximum saving of energy of up to 90 % thanks to the application of precipitator voltage controllers based upon microprocessor technology. The self-optimizing variable pulse operation mode constitutes a special feature of these controllers.
On an optional basis, a superior-level control system will be installed designated to control and optimize the entire dedusting process and to yield energy saving effects simultaneously.
Amongst others, the above-mentioned features imply the following benefits for the customer:
- Low investment costs.
- Maximum precipitation efficiency (efficiency levels of more than 99,99 % can be achieved).
- Highest levels of plant availability.
- Short delivery and assembly times.
- Low maintenance costs.
- Minimization of operational costs.
Since, by now, more than 13,000 electrostatic precipitators based upon LURGI and ENVIROTHERM technology have been manufactured, we are in a position to resort to the experience contained in one of the biggest manufacturer-owned data bases in the world.
Due to raw gas saturation which normally takes place in upstream processes a liquid film is formed on the collecting electrodes under the influence of an electrical field. This liquid film runs down continuously with the separated dust particles being discharged as a suspension subsequently. Cleaning of the precipitators is ensured by the use of flushing nozzles to be put into operation after certain time intervals. Thus, no mechanical cleaning devices are needed. The achievable dust contents in the cleaned gas amount to less than 1 mg/m³.
ENVIROTHERM offers the entire range of wet-type electrostatic precipitators:
- Horizontal wet-type electrostatic precipitators may enclose several collection zones and are suited for the cleaning of large-volume gas flows within the limits of one precipitator enclosure.
- Vertical wet-type electrostatic precipitators, in most cases, are equipped with collecting electrodes shaped as honeycomb bundles and the gas generally flows from the bottom up. The modular configuration of these precipitators permits a cost-effective cleaning of large-volume gas flows. Vertical wet-type electrical precipitators may, for example, be also used in conjunction with desulfurization units as aerosol separators.
- Condensation-type electrostatic precipitators are self-cleaning units within the limits of which dust is continuously running down the water-cooled collection electrodes within the limits of a condensate film.
Fabric filters (also called “baghouse filters”) are based upon filtration by the use of textile fabric materials.
In this case too, dust particles are removed from the gas. However, the addition of auxiliary substances provides the possibility to attain a simultaneous adsorption of gaseous pollutants. SO₂, HCl, HF and heavy metals can be reliably removed. The respective technical textile materials will be selected in exact accordance with gas composition and temperature.
These filters were, first of all, designed for the treatment of large flow rates amounting to app. 50,000 cbm per hour up to several millions of cbm per hour. The most characteristic feature of the low-pressure pulse jet technology is the low pressure of the blowing air vessel which is less than 1 bar whereas conventional systems are operated at 2 to 6 bar. For this reason, far less mechanical precautions need to be taken and the primary energy needed for the cleaning process is significantly less.
For cleaning the flue gas is routed to separate raw gas chambers via the raw gas duct and the raw gas butterfly valves. In order to prevent wearout and local deposits the flow is routed downwards into the hopper via deflectors with a preliminary removal of large particles taking place right there. The pre-cleaned gas, then, is brought to the filter bag from below and passes the filter media from outside to inside. During this stage the remaining impurities are removed. The supporting cages located inside the filter bags prevent collapsing of the bags during the filtration phase. The cleaned flue gas leaves the filter bags moving up into the clean gas chamber and is routed to downstream units via the clean gas header line.
Characteristic features of the ENVIROTHERM-designed pulse jet baghouse filter which is basing upon LURGI technology are:
- High-volume dust loads in the raw gas.
- Low residual dust contents.
- High-intensity loads on filter surfaces can be handled.
- Long service lifetime of filter bags.
- Low loss of pressure.
- Low energy consumption.
- Quick change of filter bags without any interruption of operation allowed.
- Small number of diaphragm valves.
- Easy-to-maintain modular configuration.
Due to the above-mentioned features low-pressure pulse jet baghouse filters provide the following benefits:
- Low investment costs.
- High filtration efficiency (filtration efficiency levels of more than 99,99 % can be achieved).
- High equipment availability.
- Short delivery and assembly times.
- Low maintenance costs.
- Low operational costs.
Up to now, flue gas flows from various processes are subject to dedusting procedures by low-pressure pulse jet filters at a rate of more than 40,000,000 cbm of per hour.
The dust-laden gases pass the filter bags from outside to inside. Dust deposits are removed from the bag’s surface by compressed air pulses (on-line cleaning). To this end, the gas flow is re-routed for a short time whereby the filter bags get swelled and the removed filter cake, as an agglomeration of dust, will fall into the filter bunker.
At the same time, the compressed air blowing pulse ensures a thorough cleaning of the filter. The cleaning phase is started by an electronic control device whereby the cleaning procedure can be performed in dependence of differential pressure or following a preset time schedule.
The baghouse filters are equipped with several chambers which provides the possibility to cut off plant sections from the gas flow for maintenance and inspection purposes or for the substitution of bags during plant operation.
ENVIROTHERM designed and delivered complete flue gas cleaning plants fitted for incineration plants of its own design and for customer-defined processes.Learn more
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