Bag Filter vs EP Information

CTP Team Technologies Bag filter Vs Electrostatic Precipitator

1 CTP Team S.r.l. - Sede operativa: Via S.Maria in Campo, 1 - 20040 Cavenago Cavenago di Brianza Brian za (MB) (MB) -Tel.: +39-02-9591981 -

Fax +39 + 39-02-95919846 -02-95919846 --- E-ma E-mail: il: info@ i [email protected] ctp.mi.it

1.0 INTRODUCTION CTP team has the technologies and know how to manufacture electro static precipit ator and bag filter. Electrostatic Precipitator (ESP) was common in coal/lignite fired power plants until 30 years ago. Nowadays in Europe ESP is not a desirable choice for a new installation, and moreover many existing ESPs have been converted into Fabric Filters. This is due to the changing limitation of the value of admitted dust emissions. Also for gas emissions like SO2, dioxin etc., the fabric filter can reach significant abatement with the injection of particular reactants directly on the bags 1.1.

Emiss ion Guarantees

With ESP technology the guarantees for the achievable emission levels are currently more than 80 mg/m3, especially for the old plants. Now with the new Electrostatic precipitator the emission could be get 20 the mg/m3 but with more than 4 fields. Sizing of an ESP is not an exact science. Extensive reference knowledge for similar applications is required, or design margins will increase Fabric Filters are actually the best available technology in particulate control With Fabric Filter technology the guarantees for the achievable emission levels are less than 10 mg/m3, but the real expected value could be around 4/5 mg/m 3 PM10/2,5 likely to be regulated more specific in the near future, Fabric Filter is more efficient on fine particulate collection 1.2.

Process Requirements

ESP-sizing using the classic “Deutsch”-formula:

where: η collection efficiency [%] f(SCA) specific collecting area A/V [s/m] wD migration velocity [cm/s] A collecting area [m2] V volume flow rate [m3/s]

Indicates that the collection efficiency increases with the logarithmic increasing of the collecting area, so for having an high efficiency it is required to estimate a big plant. Also there is a big dependence from the type of coal/Lignite used.

2 CTP Team S.r.l. - Sede operativa: Via S.Maria in Campo, 1 - 20040 Cavenago di Brianza (MB) -Tel.: +39-02-9591981 -

Fax +39-02-95919846 -- E-mail: [email protected]

With Fabric Filter the situation is completely different because there is nearly no dependence on coal/ash properties with regard to emission limits Stations need to cope with wider range of fuels without being limited by particulate control, maintaining full operational flexibility. Low emission guarantees demanded by utilities available for FF at more competitive cost compared to ESP. Investment for bag filter considerably less than for ESP at low emission levels. 1.3.

Economical selection crit eria

Capital cost of Fabric Filter and ESP vs. SCA to achieve the same ELV in different applications may differ considerably Increasing ash resistivities require a larger ESP-Specifíc Collecting Area (SCA) to achieve a certain emission value Fabric Filters are insensitive to ash resistivity, thus their SCA is a constant for the same emission value These considerations can be clearly seen in the following graph.

Bag life guarantee usually ranges between 2 years and 4 years, subject to specific guarantee conditions, but actual bag life may exceed guarantee considerably.



1.4.

Layout and site specific crit eria

The number of compartments is crucial for operational flexibility and availability, in a well designed Fabric Fitter almost all the checks, most of the maintenance operations (>99%) and bag change should be possible during operation (on-line) Many retrofit systems have only few separate compartments due to limitations from the existing ESP-casing. In those cases, load reduction is required if maintenance is required. A system with multiple compartments also allows offline cleaning if specific dust properties make cleaning difficult In addition Fabric Filter retrofit shows limited space requirements compared to ESPs because Fabric Filters need a reduced footprint compared with ESP 2.0 CTP Team Techno log ies 2.1 SWAP bag filt er pist on valve cleaning sy stem made by CTP TEAM Two special features distinguish CTP Shock Wave Pulse technique from conventional filter systems: its active gas distribution and effective pulse cleaning. Due to its superior cleaning principle with compressed air pulse, the Shock Wave Pulse filter can operate with over 10-meter-long bags cleaned ON-LINE. Raw gas goes through the filter's inlet duct for primary collection of large dust particles, after that it is distributed up towards the upper section of the filter. This arrangement creates a downward flowing (gravimetric) gas stream along the filter bags, that helps to transport the dust particles towards the dust hopper. With traditional systems where the particles had only fallen because of the force of gravity, it is produced almost incredibly low settling rate. For example, it takes 28 hours for a dust particle of 1 μm size to fall 8 meters in still air. When a certain amount of dust has been collected a quick and powerful pulse of compressed air is injected through the bags. The pulse of air has major cleaning effect within a brief time because it closes almost as quickly as it opens. When the filter material contracts, the dust particles are exposed to acceleration forces of up t o 100g. The high collecting efficiency of the filter will also depend on the choice of bag, bag cages and the tolerance between them. While conventional sy stems demand a compressor pressure of 600- 700 kPa to

CTP SWAP System can cl ean 10 m bags with a comp ressed pressure of only 350 kPa



clean Filt er bags 6,5 m long , in ON-LINE The fabric bags are cleaned by means of compressed air pulses which are directed down through the bag's opening. The compressed air expands the bag with a shockwave effect, with such a strong acceleration that dust particles on the outside of the bag are loosened when the bag later contracts. The compressed air is directed down into the bags via a tube provided with nozzles. The nozzles are specifically designed to reduce flow losses to a minimum.

The compressed air pulse is extremely short (approximately 0.05s). The entire cleaning operation, which occurs while the bags are in full operation, consumes little energy. The compressed air is usually supplied by a separate compressor. The distribution of air in short pulses is done by means of a piston valve. The pulse repetition frequency can either be constant or controlled by the resistance over the filter bags. The practical solution to the problem of pulse regulation involves, among other elements, a unique piston valve design for which a patent has been applied. The collected dust falls into dust hoppers located under the bags and is transported away by conveyor.

Both mechanical and pneumatic conveyors are available, and the type selected can be adapted to different types of dust.



2.2 Electro static precipitator CTP Team technolog ies Electrostatic precipitator The fundamental principle of operation of an ESP is that the particles are passed through an electrical field where they receive an electrical charge. Charged particles are then deflected across the field and collected on grounded plates. In practice, the ESP normally takes the form of a series of vertical parallel plates, usually named “receiving (or collecting) electrodes”, which are normally at ground potential, having insulated discharging elements positioned midway between them. Adjacent to the electrode elements, the resultant high electrical field ionizes the gas molecules, forming both positive and negative ions. The positive ions are immediately captured by the negatively charged electrodes, while the negative ions and any electrons, generally referred to as a corona discharge, migrate under the influence of the electric field into the inter electrode space. As the gas-borne particles pass through the inter-electrode space, the larger particles receive an electric charge either by collision with the ions/electrons or by induction charging for the smallest particles. The charged particles then move under the influence of the electric field and migrate to the collecting electrodes, where the charge subsequently leaks away t o the ground.

Working principles ESPs’ working principles can be roughly divided in the three following phases:



phase n. 1: transfer of th e electrical charge to particl es of dust; phase n. 2: capture of the particles; phase n. 3: removal of the captured particl es. The electrical charge is transferred to dust particles in accordance to the principles of the “Crown Effect”; this phenomenon is carried out in presence of non-uniform electric fields, obtained by applying high voltages to small sizes conductors. Electrons are highly accelerated by the magnetic field produced by electricity and this causes the ionization of flowing gasses; solid particles in suspension in the flue gas are electrically charged and captured by the collecting electrodes according to the below scheme:

All the particles can be charged by the described electrical and magnetic effect, and the charge level is strictly related to the particles resistivity.



3.0 B.A.T. (Best Avail able Technol ogi es ) Project p rop osed by CTP Team CTP chosen Fabric Filter fabric filter technologies for the follows reasons: 

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The reduction in emissions in order to meet the more stringent requirements from the Authorities, with the possibility of control also the gas emission like Sox,Hcl,Hf. The footprint required, approx 1/2-1/3 than an "equivalent" ESP and the opportunity of recovering of the existing foundations and sometime the ESP structure and casing. The lower investment compared with an equivalent ESP Almost no limitations in coal/Lignite range Possibility to do the maintenance during the filtration without stop of the kiln and therefore the nickel production No limitation of Co inlet (For ESP is necessary to avoid high concentration of Co gas inlet to prevent explosion) Less electrical power consumption at the equal dust emission. Possibility to absorbed in the future acid pollutants like Sox with alkaline reagent injection PM10/2,5 likely to be regulated more specific in the near future, Fabric Filter is more efficient on fine particulate collection



Bag Filter vs EP Information

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