7/28/2019 Low Dust Emission With ESP Ver 2

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Technical DescriptionTechnical Description

Low dust emissionLow dust emissionwithwith

Electrostatic PrecipitatorsElectrostatic Precipitators

Small dust particlesSmall dust particlesis a health risk.is a health risk.Decreasing dustDecreasing dustemission has aemission has asignificant healthsignificant healthimpact on the pop-impact on the pop-ulation.ulation.A new inventionA new inventionfor reduction offor reduction ofthe number ofthe number ofsmall particles issmall particles isdescribed in thisdescribed in thispaper.paper.

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7/28/2019 Low Dust Emission With ESP Ver 2

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Small particles is a health problemSmall particles is a health problemIn recent years, adverse health effects of fine particles have increasinglybeen brought into focus. Particles can be measured in different size frac-tions. The fine particle fraction PM2.5 (particle diameter less than 2.5microns) has proved to be the particle fraction most closely associated withadverse health effects in epidemiological studies.

For fine particulate matter, the present level of regulatory protection israther weak. The present levels of these pollutants, and the present limitvalues, imply risk of significant health impacts - even deaths - on the popu-

lation.

One third reduction of annual PM2.5 levels in Danish urban areas willexpectedly result in about 400 fewer deaths per one million people peryear.

In order to reduce the level of particles with a diameter less than 2.5microns, a reduction of total dust emission from collecting equipment mustbe carried out.

Future requirementsFuture requirementsThe European Commission ambient air quality regulations require that a 24 hour average ofparticles PM10 should be less than 50 g/m3. This value is not to be exceeded more than 35times per calendar year, decreasing to 7 times per calendar year in 2010.

This means that the future design of dust emission control equipment must meet lower emis-sion values than required today.

Best Available TechniquesBest Available TechniquesThe European Commission recommendElectrostatic Precipitators, Fabric Filters orin some industries Wet Scrubbers as thepreferred air pollution control equipment.

The basic principle of fabric filtration isthe use of fabric membrane which is per-meable to gas, but retains the dust. Thefabric filter should have multiple compart-ments which can be individually isolated

in case of bag failure, and that should besufficient to allow adequate performanceto be maintained if a compartment istaken off line. The use of modern fabricfilters can reduce dust emissions to below5 mg/Nm3.

Sufficiently dimensioned electrostatic pre-cipitators, together with good gas condi-tioning and optimised ESP cleaning regime,can reduce levels down to 5-15 mg/Nm3 onmonthly average. Existing EP installationscan often be upgraded without the needfor total replacement, thereby limitingcosts.

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7/28/2019 Low Dust Emission With ESP Ver 2

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Choosing the correct con-Choosing the correct con-trol equipmenttrol equipmentSelection of the appropriatecontrol equipment must bedone with consideration tomany factors in the daily opera-tion of the main productionmachines. The influences on theoperation of the main produc-

tion machines from the air pol-lution equipment are shown inthe table.

The Sneakage problemThe Sneakage problemConventional electrostatic precipitators are normally notable to maintain dust emission levels below 30 mg/Nm3. Inan electrostatic precipitator the dust is collected by electri-cal forces between the collecting plates, but because of theinternal mechanical construction some gas and dust willby-pass the electrical field either below or above the field.This means that even when the electrostatic precipitatorhas a 100 % collection efficiency, dust will be emitted to

the stack.

This example shows how serious the stack emission iseffected by gas by-passing the electrical field:

ParameterParameter Fabric FilterFabric Filter PrecipitatorPrecipitatorRisk of disturbance of production Medium Low

Efficiency sensitivity from the process Low Medium

Sensitivity to process upset condition Low High

Cold start-up capability Sensible High

Power consumption including ID fan High Low

Maintenance costs High LowMaximum operating temperature oC 260 oC 400 oC

Inlet dust load: 30 g/Nm3

Outlet dust emission designed to: 20 mg/Nm3

Only 0,1% of the gas by-passing the fields

Outlet dust emission will increase to: 50 mg/Nm3.

Example of SneakageExample of Sneakage

An Ideal flow patternAn Ideal flow patternThe ideal configuration of an electrostatic precipi-tator is a simple pipe (the collecting plate) and inthe centre of the pipe the discharge electrode ispositioned. With this configuration all gas flows inthe electrical field, and it has been proven that acollection efficiency of 100 % can be achieved. In anindustrial size precipitator it is not possible to imple-ment the ideal design. But it is possible to design

devices by which an almost ideal flow pattern canbe achieved.

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Conventional Solution to the sneakageConventional Solution to the sneakageproblemproblemWith installation of simple steel plates before eachelectrical field the gas can be forced to flow betweenthe collecting plates.

In many types of electrostatic precipitators theseplates (anti sneakage plates) are manufactured fromperforated plate. Placed in a heavy dust loaded gasflow, the holes will over time be blocked with dust.

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7/28/2019 Low Dust Emission With ESP Ver 2

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VELOCITY MAGNITUDE

M/S

2.000

1.800

1.600

1.400

1.200

1.000

0.8000

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The FLSmidth Airtech Solution to the sneakage problemThe FLSmidth Airtech Solution to the sneakage problemFLSmidth Airtech has performed several tests with different designs ofthe anti sneakage plates and performed computer simulations of theinternal flow. The results have proven that installation of perforatedplates create a relatively strong vortex behind the plate and belowthe electrical field. The trick is to design the anti sneakage plates in away where recirculation of gas behind the plates is eliminated and atthe same time ensure that no gas is by-passing the electrical field.

FLSmidth Airtech has invented a Vortex Free Anti sneakage Device.It turns out that recirculation of the flow behind the anti sneakageplates has been eliminated compared to standard hole plate design,and that the gas is now guided to flow between the collecting plates.

Nord Kalk, Sweden

Uppsala, Sweden

Posco, South Korea

Sidmar, Belgium

LKAB, SwedenEnci, Holland

OCI, USA

MSila, Algeria

FLSmidth Airtech InstallationsFLSmidth Airtech Installationswith Low Dust Emissionwith Low Dust Emission

With a well designed precipitator equippedwith the Vortex Free Anti sneakage Device it isproven that a low emission can be achieved and,therefore, the future demand for reduction offine particles can be met.

0.1 1 10Micron

WithSneakage

plate

WithoutSneakage

plate

Emission

Sneakage plate

Collecting plates

Flow pattern. Conventional designed Anti Sneakage plates

Sneakage plate

Collecting plates

Flow pattern. FLSmidth Airtech Vortex Free Anti Sneakage plates

With this devicethe flow patternin an industrial size precipitator is very close to the ideal flowpattern in a pipe precipitator.

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Ramsingsvej 30DK-2500 Valby

Tel. +45 3618 2000Fax. +45 3618 2030

E-mail: info@flsairtech.comwww.flsairtech.com

F.L.Smidth Airtech supplies Air Pollution Control equipment: Electrostaticprecipitators FabriClean pulse-jet fabric filters Gas conditioning towers Desulphurization systems COROMAX pulse systems PIACS microprocessorcontrollers and other advanced electrical control systems Dust transportand storage equipment All kinds of auxiliary equipment like fans, fluegas ducts, cyclones etc. We supply new equipment or upgrading of existingequipment no matter whether the existing equipment is supplied by us or not. Re

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