MODELING THE PRESSURE DROP OF

CLEANABLE DUST FILTER MEDIA DURING

AGING IN LABORATORY TEST RIGS

Markus Stecher

Gerd Mauschitz

Wilhelm Höflinger

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of Technology

Introduction

Study Purpose

Aging Chamber

ModelModel Subject

Model Concept

Model Mathematics

Results

Summary

Contents

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyIntroduction

Cleanable dust filter media are widely-used for dedusting.

They have reached a high filtering-related level of development due to consequent increasing

technical requirements and environmental protection legislation.

The aging procedure is the key to significant results as far as the long

term operation behaviour of cleanable dust filter media is concerned.

To simulate a long operation time, an (artificial) aging procedure is included in standardized

filter tests.

The aging procedure has been (and will be?) adapted multiple times to improve the

predictability of the long term filtration behaviour (history of VDI 3926[5] to DIN ISO 11057[1]).

The selection of a filter medium for a certain filtration task is still a matter of empiricism due to

numerous influencing factors (e.g. filter face velocity, composition of raw gas,...).

Results of standardized filter tests (e.g. DIN-ISO 11057[1], ASTM D6830-2[2], JIS Z 8909-1[3], GB

12625[4]) help to reduce the risk of choosing an unsuitable filter media.

[1] DIN-ISO 11057: „Emissionen aus stationären Quellen – Prüfverfahren für die Charakterisierung des Filtrationsverhaltens abreinigbarer Filtermedien“, VDI/DIN-Handbuch Reinhaltung der Luft, Band 6, Dezember (2011).

[2] ASTM D6830-2: „Standard test method for characterizing the pressure drop and filtration performance of cleanable filter media“, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, USA

[3] JIS Z 8909-1: „Testing methods of filter media for dust collection“, Japanese Industrial Standard.

[4] GB 12625, Draft 2005: „Technical requirements of fabric and bag for bag filter“, National Standard of the People´s Republic of China, (2005)

[5] VDI-Richtlinie 3926: “Prüfung von Filtermedien für Abreinigungsfilter“, Blatt 1, Teil 2: Prüfung von abreinigbaren Filtermed ien unter anwendungstechnischen Bedingungen, VDI-Handbuch Reinhaltung der Luft, Band 6, (1994), 44 S.

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyIntroduction

Multiple assessment criteria may lead to ambiguous results – which of two filter media “A” or

“B” is the better. Filter medium “A” with a lower residual pressure drop after aging, or “B” with a

longer cycle time after aging?

To get explicit results a new aging-procedure and corresponding assessment criterion was

developed by Schubert[6] at the TU Vienna.

DIN-ISO 11057 overview:

Test rig: type 1 or equivalent

5 phases: (conditioning, artificial aging, stabilising, measurement, optional measurement)

Assessment criteria: residual pressure drop increase, cycle time evolution, residual dust

mass, clean gas concentration

Aging TU Vienna overview:

Test rig: aging chamber (less complicated/expensive/required space than type 1)

Time controlled, until complete clogging of filter medium

Assessment criterion: aging time (time of complete clogging – easy to detect by extreme

pressure drop increase)

[6] Höflinger, W., Schuberth, J., Mauschitz, G.: "Untersuchung des Alterungsvorgangs von abreinigbaren

Staubfiltermedien bei zeitgesteuerter Abreinigung", Gefahrstoffe Reinhaltung der Luft, 5, (2009), S. 180 - 188.

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyStudy Purpose

Modelling the pressure drop development during time controlled aging would

help to get a better understanding of the clogging processes during aging

be the basis for a time efficient calculation of the pressure drop

development, substituting time consuming aging tests.

Within the scope of the present work, a mathematical model

shall be developed which is capable of describing the pressure

drop slope during time controlled aging in the aging chamber.

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyAging Chamber

Vertical raw gas duct for complete dust cake removal into the dust hopper

Screw feeder for constant dust mass dispersed into raw gas

Jet-pulse cleaning system for filter medium regernation

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyModel Subject

Cleaning pressure drop ∆pA

Residual pressure drop ∆pR

Maximum cleaning pressure drop ∆pA,max

Cake pressure drop ∆pK

Initial pressure drop ∆p0 Aging time = Number of

Cycles x Cycle time

Cycle number N [-]

Pressure drop [hPa]

The aging procedure starts at the initial pressure drop

∆p0 and is regarded finished, when the maximum

cleaning pressure drop ∆pA,max, that goes along with an

extreme rise of the pressure drop across the filter

medium, is reached.

Combinations of depth filtration, patchy cleaning and

cake filtration may appear together in one cycle and

have to be covered by the model.

Pre

ss

ure

dro

p

Time

Depth filtration

Pre

ss

ure

dro

p

Time

Patchy cleaning

Pre

ss

ure

dro

pTime

Cake filtration

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyModel Concept

In terms of the model, the different filtration/clogging mechanisms are covered by an

adjustable particle deposition area.

Depth filtration Particle deposition area: high

Cake filtration Particle deposition area: medium

Red line: Particle deposition area

Grey area: Dust depositions that block particle deposition area

Schematic profile of filter medium – jagged line represents

specific inner particle deposition area (e.g. pores, flow

channels) of filter medium.

Directio

n o

f flow

Surface areaSpecific inner particle

deposition area

Schematic drawings show the situation after cleaning:

(Inner) Patchy

cleaning

Particle deposition area: low

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyModel Concept

The particle deposition area as well as the flow velocity distribution are perpetually altering

during the filtration process as the filtration/clogging mechanisms are changing.

For the calculation of the pressure drop the medium particle deposition area is introduced.

By means of the model the averaged, original flow velocity distribution of a cycle is redistributed

perfect evenly across the medium particle deposition area of that specific cycle. In terms of the

model the differential area between the medium and the total particle deposition area isn’t

subject to the flow.

Area A = Area B + Area C

Medium particle deposition area

Flow velocity

distribution

Total particle deposition area

Particle

deposition area

Original flow velocity distribution

Newly distributed flow velocity distribution

Model-wise the whole filtration process during aging is traced back to cake filtration with an

adjustable medium particle deposition area to cover the above-mentioned filtration/clogging

mechanisms.

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyModel Mathematics

∆𝑝𝐴 𝑁 = ∆𝑝𝑅 𝑁 + ∆𝑝𝐶 𝑁 = ∆𝑝0 + ∆∆𝑝𝑅(𝑁)

𝑁

𝑁=0

+ ∆𝑝𝐶 𝑁

∆pR(N=0) ≡ ∆p0

∆pR(N=2)

∆pR(N=1)

N=2N=1N=0

∆pA(N=1)

∆pA(N=2)

∆∆pR(N=1)

∆pK(N=2)

∆pC(N=1)

Cycle number N [-]

Pressure drop [hPa]

∆p0 Initial pressure drop

∆pA Cleaning pressure drop

∆pR Residual pressure drop

∆pC Pressure drop of the cleaned off dust cake

∆pK Cake pressure drop

∆∆pR Increase of residual pressure drop

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyModel Mathematics ∆pC

Mathematically the pressure drop ∆pC is described by a basic cake law with an adjustable

medium particle deposition area:

𝑚𝐶 𝑁 = 𝑚𝐶,𝑚𝑎𝑥 ∗ (1− 𝑒−𝑘1∗𝑁) 𝑨 𝑪 𝑵 = 𝑨 ∗ (𝑵 − 𝑵𝒎𝒊𝒏)𝟐 + 𝒌𝟐

∆𝑝𝐶(𝑁) =𝑉 ∗ 𝜂 ∗ 𝛼𝐶 ∗ 𝑚𝐶(𝑁)

𝑨 𝑪(𝑵)𝟐

Δ𝑝𝐶(𝑁) = 𝑘0𝑉 (1− 𝑒−𝑘1∗𝑁)

𝑁 − 𝑁𝑚𝑖𝑛 2 + 𝑘2 2

The cleaned off dust mass mC grows towards a

maximum mC,max as the aging process becomes

quasi-stationary.

The medium particle deposition area runs

through a minimum at Nmin to include a

flow equalization during the aging

process.

N Cycle number [-]

Nmin Cycle number at minimum particle deposition area [-]

mC,max Maximum cleaned off dust mass per cycle [kg]

k0 Combining-coefficient [-]

k1 Mass-coefficient [-]

k2 Area-coefficient [-]

∆pC Pressure drop of the cleaned off dust cake [Pa]

V Volume throughput per second [m³/s]

η Air viscosity [kg/m*s]

αC Medium specific cake resistance [m/kg]

mC Cleaned off dust mass [kg]

AC Medium particle deposition area [m²]

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyModel Mathematics ∆pR

Δ𝑝𝑅 𝑁 = Δ𝑝0 + ∆∆𝑝𝑅 𝑁

𝑁

𝑁=1

= Δ𝑝0 +𝑉 ∗ 𝜂 ∗ 𝛼𝑅 ∗ 𝑚𝑅(𝑁)

𝑁0

𝑨 𝑹(𝑵)𝟐𝑵

𝟎𝑵

𝑚𝑅 𝑁

𝑁

0

= 𝑚𝐴 − 𝑚𝐶,𝑚𝑎𝑥

𝑁

0

∗ 1− 𝑒−𝑘1∗𝑁 𝑑𝑁

= 𝑚𝐴 − 𝑚𝐶,𝑚𝑎𝑥 ∗ 𝑁 +𝑚𝐶,𝑚𝑎𝑥

𝑘1∗ (1− 𝑒−𝑘1∗𝑁)

𝑨 𝑹(𝑵)𝟐𝑵

𝟎

𝑵= 𝑨𝟎 ∗ (𝟏 − 𝒌𝟒 ∗ 𝑵𝟐)

Δ𝑝𝑅(𝑁) = Δ𝑝0 +𝑉 ∗ 𝑘3 ∗ 𝑁 + 𝑘5(1− 𝑒−𝑘1∗𝑁)

(1− 𝑘4 ∗ 𝑁2)2

Mathematically the pressure drop ∆pR is described by a basic cake law with an adjustable

medium particle deposition area:

The medium particle deposition area

declines perpetually due to the ongoing

clogging of the filter medium during the

aging procedure.

The residual dust mass in and on the filter medium

ads from all dust masses that stick to the filter

medium in each cycle.

A0 Initial particle deposition area [m²]

N Cycle number [-]

mC,max Maximum cleaned off dust mass per cycle [kg]

k0 Combining-coefficient [-]

k1 Mass-coefficient [kg]

k4 Area-coefficient [-]

k5 Combining-coefficient [-]

∆pR Residual pressure drop [Pa]

∆∆pR Increase of residual pressure drop [Pa]

V Volume throughput per second [m³/s]

η Air viscosity [kg/m*s]

αR Medium specific cake resistance [m/kg]

mR Residual dust mass per cycle [kg]

mA Dust mass brought to filter medium per cycle [kg]

AR Medium particle deposition area [m²]

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyResults

∆ pC (N)

∆ pR (N)

Filter medium: PI-Needle felt

Test dust: Pural NF (d50,3 = 8.6µm)

Cycle time: 100 s

Tank pressure: 0.5 MPa

Valve opening time: 60 ms

Raw gas concentration: 5.5 g/m³Filter face velocity: 2.5 m/min

To obtain the model’s coefficients (values for ki), needed to draw the model pressure

drop slopes, the model formulas for ∆pC(N) and ∆pR(N) were implemented into

“OriginPro 8G” and then fitted with the corresponding experimental data.

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologyResults

Aging time = 7.5h

∆ pA(N) - Model ∆ pR(N) - Model Pressure drop - Experiment

Pre

ssure

dro

p [hP

a]

Cycles N [-]

Maximum cleaning pressure drop

Cycle time: 50 s

Aging time = 5.4h

Pre

ssure

dro

p [hP

a]

Cycles N [-]

Cycle time: 100 s

Aging time = 3.7h

Pre

ssure

dro

p [h

Pa]

Cycles N [-]

Cycle time: 150 s

Aging time = 7.5h

∆ pA(N) - Model ∆ pR(N) - Model Pressure drop - Experiment

Pre

ssure

dro

p [hP

a]

Cycles N [-]

Maximum cleaning pressure drop

Cycle time: 50 s

Aging time = 5.4h

Pre

ssure

dro

p [hP

a]

Cycles N [-]

Cycle time: 100 s

Aging time = 3.7h

Pre

ssure

dro

p [h

Pa]

Cycles N [-]

Cycle time: 150 s

Aging time = 7.5h

∆ pA(N) - Model ∆ pR(N) - Model Pressure drop - Experiment

Pre

ssu

re d

rop [hP

a]

Cycles N [-]

Maximum cleaning pressure drop

Cycle time: 50 s

Aging time = 5.4h

Pre

ssu

re d

rop [h

Pa]

Cycles N [-]

Cycle time: 100 s

Aging time = 3.7h

Pre

ssu

re d

rop

[h

Pa]

Cycles N [-]

Cycle time: 150 s

Coefficient

Cycle time

Constant test parameters

Filter medium: PI needle-felt Test dust: Pural NF (d50,3 = 8.6µm)

Tank pressure: 0.5 MPa Valve opening time: 60 ms

Raw gas concentration: 5.5 g/m³ Filter face velocity: 2.5 m/min Initial pressure drop: 0.3 hPa

Filter face area: 0.0177 m²

50 s 100 s 150 s

∆pC(N)

k0 1.034E+13 1.404E+11 9.457E+09

k1 1.967E-02 2.145E-01 1.606E-01

k2 2.831E+05 3.448E+04 1.036E+04

∆pR(N)

k1 5.670E-03 2.765E-02 7.533E-02

k3 3.813E-04 9.181E-07 3.326E-08

k4 1.617E-06 1.420E-05 7.169E-05

k5 2.270E+05 2.433E+07 3.360E+08

Institute of Chemical

EngineeringTechnischen Universität Wien

Vienna University of TechnologySummary

A new mathematic model that is capable of describing the pressure drop slope of an

aging procedure was developed.

As a fundamental concept of the model, the depth filtration content of an aging

procedure is mathematically traced back to a surface filtration mechanism.

Therefore, the medium particle deposition area is introduced by means of the model.

The medium particle deposition area of a specific filtration cycle reflects the medium

airflow velocity distribution during this cycle and thus the dust distribution on the filter

medium.

When the model equations, respectively the model coefficients, where fitted to the

experimental data by “OriginPro 8G”, the model proofed its capability of describing the

pressure drop slope during aging for a wide set of operation parameters (e.g. different

cycle time).

Besides the now better understanding of the filtration and clogging process during

the aging procedure the new developed model is the basis to substitute time-

demanding tests in the laboratory by mathematical extrapolations with the developed

model.