STANDARDIZED FILTER TESTS OF METAL WORKING FLUID …Development of a standardized test procedure for...

STANDARDIZED FILTER TESTS OF METAL WORKING FLUID MIST SEPARATORS

Dipl.-Ing. Thomas Laminger

Vienna University of Technology

Institute of Chemical Engineering

Mechanical Process Engineering and Clean Air Technology

Institute of Chemical EngineeringInstitut für Verfahrenstechnik, Umwelttechnik und Technische Biowissenschaften

Vienna University of TechnologyTechnische Universität Wien

CONTENT

2

Introduction

• Background information about Metal Working Fluid

• Usage of mist separators in enclosed machine centers

Standardized test procedure for metal working fluid mist separators

• Analogies of standardized test procedures for dust filter media

• Filter test rig for mist separators

• Set-up and main components

• Measurement device for metal working fluid mist emissions

• Liquid storage inside a mist filter

• Time evolution of the liquid storage and its effect on the pressure drop behavior

• Accelerated filter ageing procedure

Determination of filtration specific properties and classification of filter media

• Classification procedure

• Demonstrative measurement example

• Comparison of achieved results of different filter media

Summary

Outlook



INTRODUCTION

Background

Metal working fluid (MWF) is used in the metal working industry:

– Cooling and lubrication

– Removal of metal chips

Emission of droplet and vapor

About 50% of the oil is used as oil/water-emulsion [1].

- Mineral, synthetic or ester oil base

- Additives (emulsifier, stabilizer, biocides, fungicides, …)

MWF-mist emissions can cause

• skin disease (dermatitis, allergies, oil acne)

• disease of the respiratory path

• cancer, …

Measurement and monitoring of the working environment is necessary and regulated by law.

Preventive measures

• Proper working process and adequate metal working fluid

• Scheduled metal working fluid care and maintenance

• Use of exhausts

• Total enclosed machines with filter system to reduce theemission (droplets and vapor)

3

[1] Betrieblicher Umweltschutz in Baden-Württenberg. www.umweltschut-bw.de (2010)

www.zerspanungtechnik.at (2010): full enclosed machining center

(www.fuchs-oil.de, www.tradenote.net (2010): cutting process



FULL ENCLOSED MACHINING CENTER

material machining

Mist

separator

www.handte.de (2010): air ventilation system

Oil

Emulsion

Oil +

Emulsion

Dust

Oil +

Dust

Oil +

Emulsion

+Swarf

Dust

Dust +

Swarft



INTRODUCTION

Types of mist separators

Different separators can be distinguished by theirfiltration mechanism [2]:• Filtering separators• Electrostatic precipitators• Centrifugal collectors • Combinations

5

42%

52%

5%

1%

Types of mist separators[2]

Filtering separators

Electrostatic precipitators

Centrifugal collectors

Combinations

[2] Riss, B.: Erfassung und Abscheidung von Kühlschmierstoff-Emissionen: Erhebung zumStand der Technik in Österreich. In: Zusammenfassung der Vorträger derFachveranstaltung „Kühlschmierstoffe“ der AUVA Österreich; Wien, 20. November 2007.

Clean

gas

Raw

gas

Drainage

1

2

34

www.handte.de (2010): “OEL SMOKE STOP”

1) Pre-separator (Inlet)2) 1-stage filter3) 2-stage filter4) HEPA filter

2

3

4



INTRODUCTION


To compare filtration specific parameters (e.g. e.g. pressuredrop, separation efficiency) of MWF-mist separators nostandards or norms, as they are available for cleanable dustfilters or particulate air filters, exist.

Purpose of the work

Development of a standardized test procedure for metalworking fluid mist separators (filtering separators) withemulsion as test substance.

1. Filter test rig2. Measurement device for MWF emission3. Test procedure4. System for classification



ANALOGIES TO NORMS AND STANDARDS FOR DUST FILTER

Content/object transferable for mist separators

Filter test rig Filter test rig for mist separators + measurement devices

Test substance (s) MWF-emulsion (mineral oil, synthetic oil)

Test condition of the filter Stationary liquid equilibrium – steady state condition

Filtration specific parametersPressure drop, total holdup, oil holdup, fractional separation efficiency

respective MWF

Classification and characterization10-stage classification system respective the fractional separation efficiency

of several particle sizes (ÖNORM Z1263)

7

• DIN EN 1822: High Efficiency Particulate Air Filters (HEPA and ULPA)

• US-Standard ANSI/ASHRAE Standard 52.2-50007: Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size

• EN 779: Particulate air filters for general ventilation

• VDI 3926: Testing of cleanable filter media



FILTER TEST RIG

• Aerosol generator (Austrian Patent A 1658/2003) generation of a test aerosol conditioning of the sucked-off air

• Ageing nozzle• Filter holder• CYCL-FID-Measurement device Online detection of vapor and droplet

concentration

Components Measured and calculated values

• Pressure drop• Drainage flow• Oil concentration of the drainage flow and the

emulsion tank• Raw gas and clean gas concentration

Total holdup (stored emulsion inside the filter) Oil holdup (stored oil inside the filter) Separation efficiency

8



CYCL-FID-MEASUREMENT DEVICE

Components and measurement principle

The variation of the Cut-Off-Diameter (0.3-1.0-3.0-10µm)according to definitions of maximum workplace concentration values(e.g. PM10, PM4, PM2.5) creates several emission fractions.

The fraction with the smallest cut-off diameter includes per definition the vapor fraction of the mist emission.

9

Online-Measurement device for the detection of metal working fluid mist emission (concentration of droplet and vapor)Austrian Patent A 1390/2005; European Patent EP 1757927 A2, US-Patent US 7523642 B2

Emission(Droplet+Vapor)

Cyclone

Sampling

Classifier

Oil concentration

FIDEvaporator

measurement

Cut-Off-diameter

Vapor

Droplets( Ø<Cut-Off)+Vapor



CYCL-FID-MEASUREMENT DEVICE: MEASUREMENT PRINCIPLE

0.3 1.0 3.0

Vapor andDroplets <0.3 µm

10.0

Cut-Off-diameter [µm]

FID

-co

nce

ntr

atio

n

[pp

mp

rop

ane

equ

ival

ent]


FID

-co

nce

ntr

atio

n

[pp

mp

rop

ane

equ

ival

ent]

<1.0

<3.0

<10.0

<0.3

0.3 1.0 3.0 10.0

Vapor

Droplets

Raw gas


FID

-Co

nce

ntr

atio

n

[pp

mp

rop

ane

equ

ival

ent]

<1.0<3.0

<10.0

<0.3

0.3 1.0 3.0 10.0 0.3 1.0 3.0 10.0


FID

-co

nce

ntr

atio

n

[pp

mp

rop

ane

equ

ival

ent]

Clean gas

10



CYCL-FID-MEASUREMENT DEVICE: MEASUREMENT PRINCIPLE

0.3 1.0 3.0 10.0


FID

-Co

nce

ntr

atio

n

[pp

mp

rop

ane

equ

ival

ent]

0.3 1.0 3.0 10.0


FID

-Co

nce

ntr

atio

n

[pp

mp

rop

ane

equ

ival

ent]

Clean gas

Raw gas


Frac

tio

nal

sep

arat

ion

ef

fici

ency

[%

]

Vapor andDroplets <0.3 µm

Calculation of the fractional separation efficiency:

Ei……………Fractional separation efficiency of the emission fraction i [%]

CClean(i)…..Clean gas concentration of the emission fraction i [mg/m³ or ppm]

CRaw(i)…….Raw gas concentration of the emission fraction i [mg/m³ or ppm]

100*(i)C

(i)C1E

Raw

Cleani

11



LIQUID STORAGE INSIDE A FILTER MEDIUM


a. The behavior of pressure drop and holdup of a filter medium for MWF emulsion?

b. Where the stored liquid (holdup) is distributed inside a filter medium?

c. How can a steady state can be achieved in a relatively short time (accelerated aging filter media)? Test procedure

Within a filtering mist filter a complex dynamic system isforming consisting of separated and coalesced droplets,drained-off liquid, re-entrained droplets and the air whichpasses through the filter.

Due to the rearrangement of liquid within the filter (=holdup),the air flow conditions within the filter, respectively furtherfiltration specific parameters (e.g. pressure drop, separationefficiency), continuously change until the steady stateequilibrium is achieved.

Raw gas Clean gas

Drainage

Droplets Droplets(Re-Entrainment)

Mist filter




Balancing the emulsion mass flows of a filter medium allows the calculationof the total stored emulsion (total holdup). Balancing the oil mass (by the oil concentration) of the emulsion flows it is possible to calculate the stored oil mass (oil holdup).

Raw gasClean gas

Drainage

Filter mediumTotal emulsion balance

Water balance

Oil balance

Holdup

t

0

totaldrainageclenraw dt)mmm(holdup(t) Total

t

0

waterdrainagecleanraw dt)mmm(holdup(t) Water

t

0

oildrainagecleanraw dt)mmm(holdup(t) Oil

oildrainage,total drainage,oildrainage, c(t)*(t)m(t)m

raw,totalraw,totaloilraw, c(t)*(t)m(t)m

13

lclean,totalclean,totaoilclean, c(t)*(t)m(t)m

With t=infinite:

Stationary total holdup

Stationary water holdup

Stationary oil holdup



0

100

200

300

400

0 500 1000 1500 2000

Ho

ldu

p[g

]

Time [min]

Oil holdup

Water holdup

Total holdup


14

Time evolution of the pressure drop and holdup

A high increase of the pressure drop within100 minutes.Another 1000 minutes necessary to reach a steady state pressure drop.

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

Pre

ssu

red

rop

[Pa]

Time [min]

Kühlschmier-Emulsion (10 Vol-%)

Separation of MWF-emulsion within the filter medium:• Slow growth of the oil holdup.• The stationary pressure drop is linked to

the attainment of a stationary oil holdup.

Emulsion (10 Vol%)



400

600

800

1000

0 100 200 300 400

Pre

ssu

red

rop

[Pa]

Total holdup [g]


15

Pressure drop vs. Holdup Pictures ofthe clean gas side

60 min

120 min

240 min

1800 min

30 min

Four stages of the filter medium aging:1. Wetting the fibers with drops2. Coalescence of the droplets along the fibers3. Rearrangement of the holdup inside the filter4. Steady-state equilibrium

1

2 3

4



Air flow

Filter depth

Filt

er h

eigh

t

FILTER MODEL TO SIMULATE THE LIQUID DISTRIBUTION WITHIN A FILTER

Air

Liquid

Air

Liquid

Liquid holdup

Assumptions:

1. Filter is mounted vertical. Air

flow is horizontal.

2. Each cell has the same

properties.

3. No flow across the upper and

lower filter’s borders.

4. Air and liquid flows uniformly

to the filter.

5. Liquid becomes fully

separated within the first filter

layer.

16

10x10 cell representing the cross area

Filt

er h

eigh

t

To estimate the liquid distribution within a filter a simulation model was derived.



STEPWISE ITERATION

LH

Aout

AH

Lout

Ain

Lin

Operation parametersLin,raw gas (“Liquid flow to the filter“)Ain,raw gas (“Air flow to the filter“)

Process parametersβ…Deviation angular of fiber orientation to verticalK…Air flow constantζ….Minimum liquid retention number

Iteration procedure1) Start condition (t0) (“dry filter”)Air holdup (AHt0)= Cell volumeLiquid holdup (LHt0)=0

2) Calculation for each cell Porosity εi,j, Volume specific surface AV, Air flow resistance αi,j =f(LH) Air flow Aout Filter pressure drop (∆pFilter)Liquid saturation S Lout Filter liquid holdup (LHFilter)

3) Calculation of the following air and liquid holdup (t1)AHt1=AHt0 + ∑Lin,t0 –∑Lout,t0

FHt1=FHt0 + ∑ Fin,t0 –∑Fout,t0

……

17

t0 t1=t0+Δt

(1)Start

(2)Air and liquid flows

(3)New air and liquid holdup

Iteration steps

t2=t1+Δt

etc.



18

Stepwise development of the liquid holdup-profil of the model filter

Fluid accumulation at the filter clean gas side results in a pressure drop increase, despite an approximately equal holdup.

Mean

STEPWISE ITERATION



ACCELERATED FILTER AGEING: AGEING NOZZLE

The development of the stationary pressure drop relies on the relative slowly forming oil holdup. To shorten the time to form the stationary oil holdup more oil is needed to be brought to the filter in a shorter time.

Hence the time to reach a steady state pressure drop (=Ageing time) should be reduced by increasing the emulsion mass flow to the filter.

Ageing nozzleup to 1g/( cm²/min) filter area specific mass flow (=filter loading)

Top view

Side view

Ring with fine holes

Emulsion pump

Filter medium200

350

350

200x200

19



0

200

400

600

800

1000

1200

0 100 200 300 400 500 600

Pre

ssu

re d

rop

[P

a]

Time [min]

Filter medium: Wire/glass-fiber filterTest substance 10% Emulsion, mineral oilFilter face velocity: 5000m³/(m²/h)

B

A

0

200

400

600

800

1000

1200

0 100 200 300 400 500 600

Pre

ssu

re d

rop

[P

a]

Time [min]

Filter medium: Wire/glass-fiber filterTest substance 10% Emulsion, mineral oilFilter face velocity: 5000m³/(m²/h)Filter loading: 0,05 and 0.45g/(cm²/min)

ACCELERATED FILTER AGEING: TEST PROCEDURE

20

The same stationary pressure drop

is achieved with (A) accelerated

and (B) non accelerated filter

ageing procedure.

1) „Accelerated Ageing“transfer the filter in a stationary condition using the ageing nozzle and the aerosol generator

2) „Stabilizing“shut down of the ageing nozzle – using only the aerosol generator

3) „Measuring“measuring the stationary raw and clean gas concentration with the CYCL-FID-measurement device

AB

Ageing timefilter loading 0.45g/(cm²/min)

Ageing timefilter loading 0.05g/(cm²/min)

With high filter loading values the

ageing time respectively the filter test

time can be reduced to a few hours.



CORRELATION BETWEEN THE AGEING TIME AND THE FILTER LOADING

21

• With increasing filter loading the ageing time decreases.

• The ageing time of the HEPA-filter depends mostly on the filter loading.

• For an optimal filter loading the finest filter can be used:

Potential irreversible damage of the filter structure >1g/(cm²/min).

For about 2 hours maximum test time 0.5g/(cm²/min) is sufficient.

Ageing time = time to reach a stationary pressure dropFilter loading = filter area specific mass flow

10

100

1000

0,01 0,10 1,00

Age

ing

tim

e [

min

]

Filter loading [g/(cm²min)]

120 min

0.5 g/(cm²min)



Filter-class

Minimal requested separation efficiency (%)

<0.3µm

(including

vapor)

0.3-1µm 1-3µm 3-10µm

1 - - 0≤E3<35 0≤E4<50

2 - - 35≤E3<45 50≤E4<60

3 - 0≤E2<35 45≤E3<55 60≤E4<70

4 - 35≤E2<45 55≤E3<65 70≤E4<80

5 - 45≤E2<55 65≤E3<75 80≤E4<85

6 - 55≤E2<65 75≤E3<85 85≤E4<90

7 0≤E1<5 65≤E2<75 85≤E3<90 90≤E4<95

8 5≤E1<10 75≤E2<85 90≤E3<95 95≤E4

9 10≤E1<20 85≤E2<95 95≤E3 95≤E4

10 20≤E1 95≤E2 95≤E3 95≤E4

Filter-classes:1-3: Pre-Separators, Coarse wire mesh …4-6: Coarse glass-fiber filter, wire/glass-fibre filters …7-10: Fine glass-fiber filters, HEPA filters …

Further report values:Airflow rate, Test substance, stationary pressure drop, total holdup, oil holdup …

CLASSIFICATION SYSTEM FOR METAL WORKING FLUID MIST SEPARATORS

ÖNORM Z1263: 10-stage classification systemStationary fractional separation efficiency of several particle sizes after an accelerated filter ageing



DEMONSTRATIVE MEASUREMENT EXAMPLE

Test filter

Fine wire/glass-fiber filter, 200x200x40mm

Test parameters

Filter face velocity: 5000m³/(m²h)

Test substance: 10% emulsion, mineral oil

Filter loading (ageing nozzle): 0.5g/(cm²/min)

Test aerosol concentration: 56mg/m³

23

0

10

20

30

40

50

60

0

1

2

3

4

5

6

0,1 1 10

Sum

(d

Cm

) [m

g/m

³]

dC

m [

mg/

m³]

Particle size[µm]

Test aerosol: Particle size distribution (PCS 2010, Palas ®)

Aerosol generator: 7500rpm; 1.2l/min emulsion flow



0

100

200

300

400

500

0 50 100 150 200

Ho

ldu

p [

g]

Time [min]

Oil holdup

Total holdup

6

8

10

12

14

16

0 50 100 150 200Oil

con

cen

trat

ion

[%

]

Raw gas emulsion

Drainage emulsion

0

200

400

600

800

1000

1200

1400

0 50 100 150 200Dra

inag

e [

g/m

in].

Pre

ssu

re d

rop

[P

a]

Pressure drop

Drainage

Filter medium: Fine wire/glass-fiber filterTest substance: 10% Emulsion, mineral oilFilter face velocity: 5000m³/(m²h)Filter loading: 0,5 g/(cm²/min)

TIME DEVELOPMENT AND STATIONARY VALUES OF THE PRESSURE DROP,TOTAL HOLDUP AND OIL HOLDUP

StabilizingAccelerated Ageing Measuring

24

Stationary pressure drop: 686Pa

Stationary total holdup: 213g

Stationary oil holdup: 125g



STATIONARY RAW GAS AND CLEN GAS CONCENTRATION AND THE FRACTIONAL SEPARATION EFFICIENCY IN FOUR FRACTIONS

25

0%

20%

40%

60%

80%

100%

0,0

0,4

0,8

1,2

1,6

2,0

<0.3µm 0.3-1µm 1-3µm 3-10µm

Fraction

al sep

aration

efficie

ncy [%

]

FID

co

nce

ntr

atio

n [

pp

m]

Particle size range

Raw gas

Clean gas

Fractional separation efficiency

Filter medium: Fine wire/glass-fiber filterFilter face velocity: 5000m³/(m²h)Test substance: 10% Emulsion, mineral oilTest aerosol concentration: 56mg/m³

Fractionalseparationefficiency:<0.3µm: 0.240.3-1µm: 0.65

Filter medium: Fine wire/glass-fiber filterFilter face velocity: 5000m³/(m²h)Test substance: 10% Emulsion, mineral oilTest aerosol concentration: 56mg/m³

Stationary fractional separationefficiency:<0.3µm: 0.240.3-1µm: 0.651-3µm: 0.983-10µm: 0.98

Filter-

class

Minimal requested separation efficiency (%)

<0.3µm 0.3-1µm 1-3µm 3-10µm

1 - - 0≤E3<35 0≤E4<50

2 - - 35≤E3<45 50≤E4<60

3 - 0≤E2<35 45≤E3<55 60≤E4<70

4 - 35≤E2<45 55≤E3<65 70≤E4<80

5 - 45≤E2<55 65≤E3<75 80≤E4<85

6 - 55≤E2<65 75≤E3<85 85≤E4<90

7 0≤E1<5 65≤E2<75 85≤E3<90 90≤E4<95

8 5≤E1<10 75≤E2<85 90≤E3<95 95≤E4

9 10≤E1<20 85≤E2<95 95≤E3 95≤E4

10 20≤E1 95≤E2 95≤E3 95≤E4

Filter reach Filter-class 7



COMPARISION: STATIONARY PRESSURE DROP, TOTAL HOLDP AND OIL HOLDUP OF DIFFERENT FILTER MEDIA

Six filter media with different filter fineness were tested with the accelerated filter ageing procedure.Within 2-3 hours a steady state condition was reached and the stationary pressure drop, total holdup and oil holdup were determined.

0,01

0,1

1

10

100

(sta

tio

nar

y p

ress

ure

dro

p –

try

pre

ssu

re d

rop

)/s

tat.

to

tal h

old

up

[P

a/g]

26

1st stage

For economical reasons the 2nd and 3rd filter stage must be protected from large quantity of liquid mass.

2nd stage

3rd

stage

0

100

200

300

400

500

600

0

200

400

600

800

1000

1200

Stat

. to

tal h

old

up

[g]

Stat

. oil

ho

ldu

p [

g]

Stat

ion

ary

pre

ssu

re d

rop

[P

a]

Stat. Pressure drop [Pa]

Stat. Total holdup [g]

Stat. Oil holdup [g]

Filter face velocity: 2000 and 5000m³/(m²h)Test substance: 10% Emulsion, mineral oilTest aerosol concentration: 56mg/m³



0,0

0,2

0,4

0,6

0,8

1,0

<0,3µm 0,3-1µm 1-3µm 3-10µm

Frac

tio

nal

se

par

atio

n e

ffic

ien

cy [

-]

Particle size range

Baffle plate

Coarse wire mesh

Coarse glass-fibre filter

Fine wire/glass-fibre filter

Fine glass-fibre filter

HEPA filter

Filter face velocity: 2000 and 5000m³/(m²h)Test substance: 10% Emulsion, mineral oilTest aerosol concentration: 56mg/m³

27

COMPARISION: STATIONARY FRACTIONAL SEPARATION EFFICIENCY OF DIFFERENT FILTER MEDIA

• With increasing “filter fineness” the fractional separation efficiency increases.

• The largest differences of the fraction separation efficiencies are in the particle size range between 0,3-1µm.

Specified separation efficiency (solid particles) according to EN779: >99%

CYCL-FID-Measurements includes also the vapour phase:

Low vapour reduction!



0123456789

10

Filt

er-

clas

s

Filter face velocity: 2000 or 5000 m³/(m²h)Filter loading: 0.5g/cm²/min (ageing nozzle)Test substance: 10% Emulsion, mineral oilTest aerosol concentration: 56mg/m³

RESULTED FILTER-CLASSES OF THE SIX TESTED MWF MIST FILTERS

Increasing filter-class

Filters with finer structure reach higher filter-class values



SUMMARY

• In analogy to existing norms and standards for dust filters a standardized test procedure for metal working fluid mist filters was developed:

A filter test rig with its main components was presented. The CYCL-FID-measurementdevice and the principle to measure the droplet and vapor concentration of a mist emission in several particle size fractions was shown.

A three-step filter test procedure (accelerated filter ageing) was described using an ageing nozzle which allows the determination of the stationary filtration specific parameters which are pressure drop, total holdup, oil holdup and the fractional separation efficiency in a relative short test time.

A classification system with 10 filter-classes for MWF mist filters was proposed. The system includes four particle size ranges (<0,3µm/0.3-1µm/1-3µm/3-10µm) with minimal requested separation efficiencies. The particle size range “<0.3µm” includes also the vapor fraction of the mist emission.

• With the filter test rig, the developed accelerated filter ageing procedure and the classification system it is now possible to evaluate and compare different mist separators in a very short time.

29

STANDARDIZED FILTER TESTS OF METAL WORKING FLUID …Development of a standardized test procedure for...

Documents

Transcript of STANDARDIZED FILTER TESTS OF METAL WORKING FLUID …Development of a standardized test procedure for...