STANDARDIZED FILTER TESTS OF METAL WORKING FLUID MIST SEPARATORS

Transcription

1 STANDARDIZED FILTER TESTS OF METAL WORKING FLUID MIST SEPARATORS Dipl.-Ing. Thomas Laminger Mechanical Process Engineering and Clean Air Technology

2 CONTENT 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 2

3 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. ( (2010): cutting process 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 the emission (droplets and vapor) [1] Betrieblicher Umweltschutz in Baden-Württenberg. (2010) (2010): full enclosed machining center 3

4 FULL ENCLOSED MACHINING CENTER material machining Oil Emulsion Oil + Emulsion Dust Oil + Dust Oil + Emulsion +Swarf Mist separator Dust Dust + Swarft (2010): air ventilation system

5 INTRODUCTION Types of mist separators Different separators can be distinguished by their filtration mechanism [2]: Filtering separators Electrostatic precipitators Centrifugal collectors Combinations 42% 52% 1% Types of mist separators[2] 5% Filtering separators Electrostatic precipitators Centrifugal collectors Combinations Clean gas Raw gas 1) Pre-separator (Inlet) 2) 1-stage filter 3) 2-stage filter 4) HEPA filter (2010): OEL SMOKE STOP Drainage [2] Riss, B.: Erfassung und Abscheidung von Kühlschmierstoff-Emissionen: Erhebung zum Stand der Technik in Österreich. In: Zusammenfassung der Vorträger der Fachveranstaltung Kühlschmierstoffe der AUVA Österreich; Wien, 20. November

6 INTRODUCTION To compare filtration specific parameters (e.g. e.g. pressure drop, separation efficiency) of MWF-mist separators no standards or norms, as they are available for cleanable dust filters or particulate air filters, exist. Purpose of the work Development of a standardized test procedure for metal working fluid mist separators (filtering separators) with emulsion as test substance. Filtering separators 1. Filter test rig 2. Measurement device for MWF emission 3. Test procedure 4. System for classification

7 ANALOGIES TO NORMS AND STANDARDS FOR DUST FILTER DIN EN 1822: High Efficiency Particulate Air Filters (HEPA and ULPA) US-Standard ANSI/ASHRAE Standard : 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 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 Filtration specific parameters Classification and characterization Stationary liquid equilibrium steady state condition Pressure drop, total holdup, oil holdup, fractional separation efficiency respective MWF 10-stage classification system respective the fractional separation efficiency of several particle sizes (ÖNORM Z1263) 7

8 FILTER TEST RIG Components 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 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

9 CYCL-FID-MEASUREMENT DEVICE 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 A2, US-Patent US B2 Components and measurement principle Emission (Droplet+Vapor) Sampling Droplets ( Ø<Cut-Off) +Vapor Evaporator FID Vapor Oil concentration measurement Cyclone Cut-Off-diameter Classifier The variation of the Cut-Off-Diameter ( µm) 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

10 FID-Concentration [ppm propane equivalent] FID-concentration [ppm propane equivalent] FID-concentration [ppm propane equivalent] FID-concentration [ppm propane equivalent] CYCL-FID-MEASUREMENT DEVICE: MEASUREMENT PRINCIPLE Raw gas <3.0 <10.0 Droplets Vapor and Droplets <0.3 µm <0.3 <1.0 Vapor Cut-Offdiameter [µm] Cut-Offdiameter [µm] Clean gas <10.0 <0.3 <1.0 <3.0 Cut-Offdiameter [µm] Cut-Offdiameter [µm] 10

11 FID-Concentration [ppm propane equivalent] Fractional separation efficiency [%] FID-Concentration [ppm propane equivalent] CYCL-FID-MEASUREMENT DEVICE: MEASUREMENT PRINCIPLE Raw gas Calculation of the fractional separation efficiency: C Ei 1 C Clean Raw (i) *100 (i) E i Fractional separation efficiency of the emission fraction i [%] C Clean (i)..clean gas concentration of the emission fraction i [mg/m³ or ppm] C Raw (i).raw gas concentration of the emission fraction i [mg/m³ or ppm] Cut-Offdiameter [µm] Clean gas Vapor and Droplets <0.3 µm Cut-Offdiameter [µm] Cut-Offdiameter [µm] 11

12 LIQUID STORAGE INSIDE A FILTER MEDIUM Within a filtering mist filter a complex dynamic system is forming consisting of separated and coalesced droplets, drained-off liquid, re-entrained droplets and the air which passes through the filter. Due to the rearrangement of liquid within the filter (=holdup), the air flow conditions within the filter, respectively further filtration specific parameters (e.g. pressure drop, separation efficiency), continuously change until the steady state equilibrium is achieved. Raw gas Droplets Mist filter Clean gas Droplets (Re-Entrainment) 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 Drainage Filtering separators

13 LIQUID STORAGE INSIDE A FILTER MEDIUM Balancing the emulsion mass flows of a filter medium allows the calculation of 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). Filter medium Total emulsion balance With t=infinite: Stationary total holdup Raw gas Clean gas Total holdup(t) t ( 0 m raw m clen m ) drainage total dt Water balance Stationary water holdup Holdup Drainage Water holdup(t) Oil balance Oil holdup(t) t ( 0 t ( 0 m m raw raw m m clean clean m m ) drainage water drainage ) oil dt dt Stationary oil holdup m (t) drainage, oil m(t) drainage, total * c(t) drainage, oil m (t) raw, oil m(t) raw,total * c(t) raw,total m (t) clean, oil m(t) clean,total * c(t) clean,total 13

14 Holdup [g] Pressure drop [Pa] LIQUID STORAGE INSIDE A FILTER MEDIUM Time evolution of the pressure drop and holdup Kühlschmier-Emulsion (10 Vol%) (10 Vol-%) Time [min] A high increase of the pressure drop within 100 minutes. Another 1000 minutes necessary to reach a steady state pressure drop Total holdup Oil holdup Water holdup Time [min] 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. 14

15 Pressure drop [Pa] LIQUID STORAGE INSIDE A FILTER MEDIUM Pressure drop vs. Holdup Pictures of the clean gas side 30 min min Total holdup [g] 120 min Four stages of the filter medium aging: 1. Wetting the fibers with drops 2. Coalescence of the droplets along the fibers 3. Rearrangement of the holdup inside the filter 4. Steady-state equilibrium 240 min 1800 min 15

16 Filter height Filter height FILTER MODEL TO SIMULATE THE LIQUID DISTRIBUTION WITHIN A FILTER To estimate the liquid distribution within a filter a simulation model was derived. 10x10 cell representing the cross area Assumptions: Air Liquid Liquid holdup Filter depth Air Liquid 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. Air flow 16

17 STEPWISE ITERATION LH A in Operation parameters L in,raw gas ( Liquid flow to the filter ) A in,raw gas ( Air flow to the filter ) L out A out Process parameters β Deviation angular of fiber orientation to vertical K Air flow constant ζ.minimum liquid retention number L in t0 (1) Start t1=t0+δt AH (2) Air and liquid flows (3) New air and liquid holdup Iteration steps etc. t2=t1+δt Iteration procedure 1) Start condition (t0) ( dry filter ) Air holdup (AH t0 )= Cell volume Liquid holdup (LH t0 )=0 2) Calculation for each cell Porosity ε i,j, Volume specific surface A V, Air flow resistance α i,j =f(lh) Air flow A out Filter pressure drop ( p Filter ) Liquid saturation S L out Filter liquid holdup (LH Filter ) 3) Calculation of the following air and liquid holdup (t1) AH t1 =AH t0 + L in,t0 L out,t0 FH t1 =FH t0 + F in,t0 F out,t0 17

18 STEPWISE ITERATION Stepwise development of the liquid holdup-profil of the model filter Mean Fluid accumulation at the filter clean gas side results in a pressure drop increase, despite an approximately equal holdup. 18

19 200x 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 nozzle up to 1g/( cm²/min) filter area specific mass flow (=filter loading) Ring with fine holes 200 Filter medium Top view Side view Emulsion pump 19

20 Pressure drop [Pa] ACCELERATED FILTER AGEING: TEST PROCEDURE A Filter medium: Wire/glass-fiber filter Test substance 10% Emulsion, mineral oil Filter face velocity: 5000m³/(m²/h) Filter loading: 0,05 and 0.45g/(cm²/min) B 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-FIDmeasurement device Time [min] The same stationary pressure drop is achieved with (A) A accelerated and (B) B non accelerated filter ageing procedure. Ageing time filter loading 0.45g/(cm²/min) With high filter loading values the ageing time respectively the filter test Ageing time time can be reduced to a few hours. filter loading 0.05g/(cm²/min) 20

21 Ageing time [min] CORRELATION BETWEEN THE AGEING TIME AND THE FILTER LOADING Ageing time = time to reach a stationary pressure drop Filter loading = filter area specific mass flow 1000 With increasing filter loading the ageing time decreases. The ageing time of the HEPA-filter depends mostly on the filter loading. 120 min ,01 0,10 1,00 Filter loading [g/(cm²min)] 0.5 g/(cm²min) 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. 21

22 CLASSIFICATION SYSTEM FOR METAL WORKING FLUID MIST SEPARATORS ÖNORM Z1263: 10-stage classification system Stationary fractional separation efficiency of several particle sizes after an accelerated filter ageing Filter-class <0.3µm (including vapor) Minimal requested separation efficiency (%) 0.3-1µm 1-3µm 3-10µm E3<35 0 E4< E3<45 50 E4< E2<35 45 E3<55 60 E4< E2<45 55 E3<65 70 E4< E2<55 65 E3<75 80 E4< E2<65 75 E3<85 85 E4< E1<5 65 E2<75 85 E3<90 90 E4< E1<10 75 E2<85 90 E3<95 95 E E1<20 85 E2<95 95 E3 95 E 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

23 dcm [mg/m³] Sum (dcm) [mg/m³] 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 Test aerosol: Particle size distribution (PCS 2010, Palas ) Aerosol generator: 7500rpm; 1.2l/min emulsion flow 1 0 0, Particle size[µm]

24 Oil concentration [%] Drainage [g/min]. Pressure drop [Pa] Holdup [g] TIME DEVELOPMENT AND STATIONARY VALUES OF THE PRESSURE DROP, TOTAL HOLDUP AND OIL HOLDUP Filter medium: Fine wire/glass-fiber filter Test substance: 10% Emulsion, mineral oil Filter face velocity: 5000m³/(m²h) Filter loading: 0,5 g/(cm²/min) Pressure drop Drainage Oil holdup Total holdup Time [min] Accelerated Ageing Stabilizing Measuring Raw gas emulsion Drainage emulsion Stationary pressure drop: 686Pa Stationary total holdup: 213g Stationary oil holdup: 125g 24

25 FID concentration [ppm] STATIONARY RAW GAS AND CLEN GAS CONCENTRATION AND THE FRACTIONAL SEPARATION EFFICIENCY IN FOUR FRACTIONS 2,0 1,6 1,2 0,8 0,4 0,0 Raw gas Clean gas <0.3µm 0.3-1µm 1-3µm 3-10µm Fractional separation efficiency Particle size range Filter reach Filter-class 7 Filterclass 100% 80% 60% 40% 20% 0% Fractional separation efficiency [%] Filter medium: Fine wire/glass-fiber filter Filter face velocity: 5000m³/(m²h) Test substance: 10% Emulsion, mineral oil Test aerosol concentration: 56mg/m³ Fractional Stationary fractional separation efficiency: <0.3µm: µm: µm: µm: 0.98 Minimal requested separation efficiency (%) <0.3µm 0.3-1µm 1-3µm 3-10µm E3<35 0 E4< E3<45 50 E4< E2<35 45 E3<55 60 E4< E2<45 55 E3<65 70 E4< E2<55 65 E3<75 80 E4< E2<65 75 E3<85 85 E4< E1<5 65 E2<75 85 E3<90 90 E4< E1<10 75 E2<85 90 E3<95 95 E E1<20 85 E2<95 95 E3 95 E E1 95 E2 95 E3 95 E4 25

26 (stationary pressure drop try pressure drop) /stat. total holdup [Pa/g] Stationary pressure drop [Pa] Stat. total holdup [g] Stat. oil holdup [g] 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 Filter face velocity: 2000 and 5000m³/(m²h) Test substance: 10% Emulsion, mineral oil Test aerosol concentration: 56mg/m³ Stat. Pressure drop [Pa] Stat. Total holdup [g] Stat. Oil holdup [g] rd stage 1 0,1 0,01 1 st stage 2 nd stage For economical reasons the 2 nd and 3 rd filter stage must be protected from large quantity of liquid mass. 26

27 Fractional separation efficiency [-] 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. Filter face velocity: 2000 and 5000m³/(m²h) Test substance: 10% Emulsion, mineral oil Test aerosol concentration: 56mg/m³ 1,0 Specified separation efficiency (solid particles) according to EN779: >99% 0,8 0,6 Baffle plate Coarse wire mesh CYCL-FID-Measurements includes also the vapour phase: 0,4 0,2 Coarse glass-fibre filter Fine wire/glass-fibre filter Low vapour reduction! 0,0 <0,3µm 0,3-1µm 1-3µm 3-10µm Particle size range Fine glass-fibre filter HEPA filter 27

28 Filter-class RESULTED FILTER-CLASSES OF THE SIX TESTED MWF MIST FILTERS Filter face velocity: 2000 or 5000 m³/(m²h) Filter loading: 0.5g/cm²/min (ageing nozzle) Test substance: 10% Emulsion, mineral oil Test aerosol concentration: 56mg/m³ Increasing filter-class Filters with finer structure reach higher filter-class values

29 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-measurement device 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