01 dedusting equipment

8/10/2019 01 Dedusting Equipment

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Dedusting Equipment


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Dedusting Equipment

Bag filter

Electrostatic precipitator


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Electrostatic Precipitators


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The electrode system

Gasflow

Gap width

250400 mm

Max. field

height12,5 m

Discharge electrodes


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3 steps for particle collection

Chargingprecipitationrapping

mA

kV

Migration

velocity(~6-14 cm/s andthus ~60% of dust

collected within first 3 m

~84% in 6 m,

~94% in 9 m,

~98% in 12 m)


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ChargingPrecipitation - Rapping

Charging you need mA


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More power input improves the dust emission

DustEmission

kW

Potential for improvement

kW ~ kVavgx

mAavg

Curve from test


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Precipitation

you need kV


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Conditioning with water improves EP efficiency

0

20

40

60

80

100

120

140

160

180

45 47 49 51 53 55 57 59 61

Dew point [C]

Cleangasdustcon

tentr[mg/Nm3d

ry]

design point

Potential for improvement

Example

e.g.: 38 g/Nm3more water

(5.4 m3/h for a 2000 tpd kiln)or 63C lower CT exit temp.


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Exponential impact of flow on dust emission

0

10

20

30

40

50

60

70

80

90

100

80 85 90 95 100 105 110 115 120

Relative gas flow Q [%]

Cleangasdustcon

tentr[mg/Nm3dry]

design point

12% more gas can double dust emissions

Example


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Local condensation when false air enters


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Rapping


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The rapping system


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Without grounding still 3000 Volt in a shut off filter

Remove fuses from controller

Local grounding of T/R-set and EP roof isolator

Local grounding of each electrical field directly at

inspection door

T/R-set

Almost good

Discharge electrodes


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CO Trip


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Zero Dust Clouds

If above 6% O2, thenexplosion risk already at lowCO concentrations

In presence of H2or CH4from incomplete combustionthe critical CO limit is very

low H2/CO ratio up to 2

[normal: 0.11.0]

Explosion limit in any casearound 2.0 vol-% CO

Explosive

Range (200C)

O2[vol-%]

CO[vo

l-%]

0 vol-% H2

1 vol-% H2

2 vol-% H2

3 vol-% H2


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An EP is a selective dust collector

Dust that is easy to collect is mainly in the first zones,

while difficult dust is concentrated in the last zones Difficult dust:

Very fine dust


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Changed conditions due to AFR can have

an impact on EP performance

More CO peaks due to instable combustion (fuel feed,

net calorific value) Higher gas flow rate (due to higher heat consumption or

additional water)

More Cl, SO3, NH3can lower the EP performance:

sublimates bypassing the electrical zones space charge suppressing the filter current

sticky material builds-up and lowers the field strength

Organic matter can lower the conductivity of dust and

cause effects that look like back corona


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Dedusting: Bag Filters


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Bag Filter Technologies

Reverse Gas Bag Filter

Pulse Jet Bag Filter High or Low pressure online cleaning

Offline cleaning

Quasi offline cleaning

Hybrid Filters

Serial EP/BF-part

Parallel EP/BF-part

(advanced hybrid from Elex, discontinued)


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Velocities have main impact on function

1. Filtration

(Formation of dust cake)

2. Cleaning

(Moving cake into hopper)

Critical parameters

air-to-cloth ratio (~1 m/min) can(yon)-velocity (~1 m/s)

= gas flow rate / fabric area = gas flow rate / tubesheet area w/o bag area

Critical for pressure difference Critical for dust accumulation


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Cleaning Principles of Bag Filters

a, b: manual or mechanical, by rapping or shaking

c: mechanical, by vibrating

d: pneumatic, by reverse air flow (often combined with shaking or vibrating)

e: pneumatic, by compressed air (pulse jet)

Vibrator


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Reverse Gas Bag Filter: The Vacuum Cleaner

Dust emission


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Cleaning Cycles Reverse Gas Bag FilterPurge AirValve

Deflation ValveOutlet Valve

Clean Ga

Outlet

Purge Air

ShakingMechanism

Tubesheet

Dust Extraction

PurgingMaintenance

BypassValve

DirtyFlue

Gas Inlet

Filtering

InletValve

Null Deflation Cleaning(Shake)

Thimble

Deflation Ga


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Pulse Jet

Holcim State of the art

Dust emission


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Pulse Jet Cleaning

Compressed Air

Inlet Valve

Tubesheet

Clean Gas

outlet

Cage

Compressoor Blower

Outlet Valve

Dust Disposal

BypassValve

Gas Inlet

Filtering Maintenance Pulse-JetCleaning

Filtering


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Pulse Jet Cleaning Mode: Online

Standard mode (the most

common filter and cleaning type)

No compartmentalization

required

No division walls required and

thus dust transport from

converted EPs can be reused

Can velocity is limiting the filter

geometry


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Pulse Jet Cleaning Mode: Offline

Unusual mode, but good whenintensive cleaning required (helps onlyfor a short time, if root cause notsolved)

Can velocity has no impact on cleaningoperation

On-line maintenance possible (seldomused in kiln filters; safety issue)

Requires new dust transport whenconverting EPs

Requires additional inlet dampers

Allows to shut-off compartment with

broken bag


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Pulse Jet Cleaning Mode: Quasi Offline

No can velocity impact

Low air consumption and lowcleaning pressure

Allows to shut-off compartment

with broken bag

No division walls required andthus dust transport from

converted EPs can be reused


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Hybrid Filter

Up to 90% pre-collection ofdust in EP part, thus lowerbag load

Electrically charged residualdust forms permeable dustlayer resulting in low diff.pressure

Possibly better for PM2.5

High investment, lowoperating costs

Attractive if system fan andEP parts can be reused

Short CO shut-down of EPpart has no big impact on

operation Both filter parts need

maintenance (two systems)


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Needle Felt

Penetration of fine dust

particles into fabric and thus

continuously increasing diff.pressure during bag life

Cleaning pulse dust peaks

Average:


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Woven glass fiber with PTFE Membrane

Slightly higher fabric

resistance during first few

month

Negligible dust penetration

and negligible dust peaks from

cleaning pulses

Average: < 10 mg/Nm3

Careful installation required

High gas velocities can cause

bag damage more easily

Life guarantee from 4 y to

4 y + 2 y pro rata

B Lif


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Bag Life

Differential Pressure over Filter fabric

0

2

4

6

8

10

12

14

16

18

1 10 100 1000 10000 100000

Operating time [hr]

Fabricdifferential

pressure[mbar]

Early clogging phase Bag midlife phase End

Logarithmic time scale

Diff ti l P R ti


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Differential Pressure Reaction

Bag filter reaction to gas flow increase

0

5

10

15

20

25

0 20 40 60 80 100 120 140 160 180 200

Gas flow [% from design]

Filterdifferentialp

ressure[mbar]

0

2

4

6

8

10

Cleaningcycles

perhour[1/h]

Sufficient dust cake for bag protection

(Distance arrow proportional to cake thickness)

Continuous cleaning,

no bag protection

High can-velocity

hinders dust settling,

filter out of controlCleaning cycle

Diff. pressure

Design

Filt P t ti


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Filter Protection

Chemical attack

Acid or water condensation (bag blinding)respect dew points (water & acid) and do pre-coating

Mechanical attack

Erosion (holes, rips, high emissions)

respect velocity guidelines

Penetration of finest dust (high Dp, high emissions))do pre-coating

Thermal attack

respect fabric temperature range

and use emergency cooling

P ti


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Pre-coating

First Filter Start-up:

Do Pre-coating with approx. 200 g/m2inert material

(e.g. CaCO3, Ca(OH)2)e.g. bag filter with 5000 m2bag surface 1 ton raw meal being

injected upstream of the bag filter into the gas duct by a rented

silo truck equipped with an on-board compressor

Short Stop (hours up to max. a few days):deactivate cleaning cycle before stopping the filter

Long Stop (several days to weeks):

clean down the filter as much as possible and do pre-coating before

restarting the filter

Guide Values for Bag Filters (Pulse Jet)


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Guide Values for Bag Filters (Pulse Jet)

Inlet velocities (central duct): < 10 m/s

Can velocities: < 1.2 m/s

A/C ratios: < 1.0 m/min

Experience with bag length up to 7m

State of art cleaning:


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Corrosion Protection


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Corrosion Protection

Filter for combustion gas dedusting

Minimum 30C above acid dew point

Gas temperature 150C:

Flue Guard 225

Avoid using stainless steel in

presence of Cl and not required ifgas temperature always >180C

Filter for air dedusting

Minimum 20C above water dew

point

FlueGuard 225

Prerequisite

Good insulation (100 mm, rain water

tight) when combustion gas

Avoid cold spots/bridges

01 dedusting equipment

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