electrostatic precipitator

ESP´s are most commonly used for the dedusting of hot flue gas streams. They can operate with flue gas temperatures up to 400 °C and in some special cases even higher. This is why they are used in many industrial sectors, such as energy generation, metal processing industry, cement industry and several other sectors. A new field of application for the electrostatic precipitator has arisen due to the phosphorus shortage. The ash from the sludge incineration contains of a relatively high portion of phosphor.

The main application is the dedusting of hot gases or fumes. Due to the robust construction and the interior consisting almost entirely of steel, ESP`s are very well-suited for higher temperatures up to 400 ° C and in special cases even for higher temperatures. Due to these properties, electrostatic precipitators are used in various industries. They can be found in power generation in lignite power plants and biomass combustion, in the metal industry, in the production of cement and in many other industries.

The ash from the incineration of sewage sludge contains a relatively high percentage of phosphorus and therefore electrostatic filters are used as pre-separator for the phosphorus-rich fly ash in modern mono sludge incineration plants. The high temperature resistance is one of the main advantages over other fabric filters such as the bag filters and other fabric filters. Another advantage of ESP`s results from the low pressure drop across the filter and the low maintenance compared to filtering separators. Bag filters and fabric filters can generate better clean gas values depending on the filter medium, however. But also electrostatic precipitators are able to remove 99.9% of dust particles from the raw gas with proper design and dimensioning and are therefore often used as a pre-separator before desulphurisation or for removal of acidic pollutants. A high dust content in the flue gas has a negative impact on the reactivity of the acid pollutant components. As a result, both filter forms have found their place in the industry and the decision for the right type of filter must be taken depending on the specific application.

Principle of separation

The deposition of the particles or dust particles is achieved by the generation of an electric field. This is generated between the negatively charged corona electrode and the positively charged precipitation electrode. The dust particles existing in the gas stream are highly charged in this electric field and move through their charge across the flow direction to the positive precipitation plate of the electrostatic precipitator. Upon contact with the collecting electrode, the particles are discharged and adhere to this. Thus creates a layer of dust, which has an influence on the electric field at the collector electrode. For this reason the precipitation plates must be cleaned at regular intervals from the dust particles. This takes place in the electrostatic precipitator usually via a mechanical rapping. The hammer blows of rapping enable the precipitation plates to vibrate, thus separating the dust completely from the plates. The dust falls into the funnel and can be discharged from there. Depending on the funnel shape screw conveyors, rotary valves or different flaps can be used therefor. The dust may then be further processed or recovered, depending upon the application.

Design and components

The ESP is mainly composed of the housing, the electrode system including the high-voltage units and the rapping system. The housing consists of the filter chamber, the filter funnel and the gas inlet and gas outlet hood. In the hoods are installed gas distributor walls or baffles for the optimal distribution of gas flow over the cross section of the electrostatic precipitator. An uniform distribution of the flow rate on the precipitation system contributes significantly to the deposition of the electrostatic precipitator. The precipitation system consists of the emitting or discharge electrode system (SE) and the collecting electrode system (NE). The discharge electrodes may e.g. be designed as wires or rods with corona and collecting electrodes are plates which are folded in different forms. The electrode system is arranged in the form of lanes which extend in the flow direction. The air stream flows through the lanes and the particles can be deposited according to the principle described above. As already mentioned, the cleaning of the plates is generally carried out via a rapping system.