Calibration Standard& for XRFA of Emitted Aerosol Particles Collected on a Newly Developed Filter Band with an Automated Sampler

Transcription

1 760 Calibration Standard& for XRFA of Emitted Aerosol Particles Collected on a Newly Developed Filter Band with an Automated Sampler Olaf Haupt, Rtidiger Harmel and Walter Dannecker University of Hamburg, Institute of Inorganic and Applied Chemistry, Martin-Luther-King-Platz 6, D Hamburg, Germany INTRODUCTION An important field in environmental analysis is the monitoring of stack gas emissions from industrial furnaces. The ecological harm and toxic effects to man s health are well known and reflected in the German law (TA-Luft and 17.BImSchV) with low emission limits for elements like V, Cr, Mn, Co, Ni, Cu, As, Sb, Sn, Cd, Tl and Pb [l]. For the monitoring of these emission limits an automated and continuously working sampling and analyzing device had to be created. After evaluation of the optimum operating parameters for the monitoring system by manual sampling at the stack gas channel of an incineration plant [2] the new combined automatic and isokinetic sampling unit was built up and installed at the same plant near Hamburg. Figure I shows a picture of the prototype while sampling at the plant in May 1997.

2 This document was presented at the Denver X-ray Conference (DXC) on Applications of X-ray Analysis. Sponsored by the International Centre for Diffraction Data (ICDD). This document is provided by ICDD in cooperation with the authors and presenters of the DXC for the express purpose of educating the scientific community. All copyrights for the document are retained by ICDD. Usage is restricted for the purposes of education and scientific research. DXC Website ICDD Website -

3 761 A heated titanium probe (Paul Gothe, Germany) was used to take a split sample flow isokinetically out of the stack gas channel. The hot stack gas aerosols with temperatures of about 120 to 140 OC were collected on a quartz fibre filter band MK 370 developed by our working group in cooperation with Munktell Filter AB (Swede). The filter band was locked between two heated titanium blocks in the automatic emission sampling device developed in cooperation with Verewa (Germany). The new filter band material has very low blanks shown later in this paper. It is suitable for the analysis of low element concentrations and it has all desired mechanical properties like resistance to hot and aggressive gases up to 200 C and high loading capacities [3]. Figure2 shows a 2500 magnification of a MK 370 blank scanned by electron microscopy (SEM Model 44 Cam Scan, UK). After a sampling period of 30 min. the filter band position was moved 10 cm forward and the next unloaded position can be used. With the 20 m long quartz fibre filter band approximately 200 samples can be collected automatically.the whole sampling section can be heated up to 130 OC to prevent the temperature in the split sample from falling below the dew-point of the gaseous contents. Back of the sampling device the hot gas can be cooled by a titanium cooler down to 10 OC to get a total condensation. Processing of measured data, adjustment and control of the sampling device, like sampling time and filter changes were performed by a personal computer. To analyze such a great number of samples the nondestructive multielement method of x- ray fluorescence is very usefull. The spectrometer used was an energydispersive XRFspectrometer X-LAB (Spectra AI., Germany)[4]. The filter samples with a diameter of 32 mm were fixed in a rotating cup positioned on an autosampler with 18 cups. Primary source was a rhodium side window tube, an Iso Debyeflex 300 generator (Seifert, Germany) producing high voltage potentials (8-60 kv). Secondary targets for optimal excitation of different element ranges were imployed. The fluorescence radiation was detected by a Si(Li) semiconductor detector (active area 10 mm2, effective thickness 3mm, energy resolution 150 ev). Table I displays the applied secondary targets and measuring parameters.

4 762 Tab.1. Applied secondary targets and operation parameters Target Filter Tube voltage Measuring range Measuring time Analyzed elements WI WI ISI Pd Pd (K), 72-92(L) Sm Sm Co Fe Cd Calibration of the x-ray fluorescence spectrometer was achieved via artificial standard filters, prepared at our institute. EXPERIMENTAL Calibration standards The spectrometer was calibrated with self developed multi-element quartz fibre standard filters. To obtain suitable calibration standards, quartz fibre filters MK 360 (Munktell Filter AB) were treated with dried multielement standard solutions collected on the surface of the filter media by using different aerosol generators. Figure 3 shows the three different types of aerosol generators built up in our institute. Type 1 Type 3 Berner-Impact filter head high volume samoler reaction pipe ( 1 m long, 250 mm in diameter ) rel humidity c 10 % atmospheric pressure plume of aerosol t reaction pipe ( 1 m long, 100 mm in diameter ) ret. humidity < 10 % atmospheric pressure standard solution 1 I + purified, dry air 13.5 llmin + purified, dry air 13.5 llmin spray chamber (Scott) I 1 syphon cross flow nebulizer drain Fig. 3. Three different types of aerosol generators. Different diameters of reaction pipes and filters were used, depending on the needed number of uniform standard filters. Usualy cross flow nebulizers were used to produce the aerosol (type 1 and 2). After separation in the spray chamber (Scott) the droplets were dried in the reaction pipe (1 m high, 100 mm in diameter) by purified dry air (13.5 L/min.).

5 763 On top of the drying pipe a filter head with a diameter of 100 mm or a Berner-Impactor for particle size analysis was installed.with the,,multi-spray chamber (type 2), four cross flow nebulizers can be used simultaneously. Hydrochloric, sulphuric and nitric acid multielement standard solutions with different salt contents can be nebulized at the same time onto the same filter. An ultrasonic nebulizer (type 3) was applied for the big reaction pipe (250 mm diameter) to obtain a homogeneous covered filter with a filter area of 519 cm2. 40 identical filters with a diameter of 32 mm were cut out of the main filter. Each filter was analyzed by XRFS and the obtained standard deviation of element distribution over the whole filter area was < 6%. Table 2 displays the aerosol generator parameters. Tab. 2. Aerosol generator parameters Type of nebulizer max. used std. solutions reaction pipe diameter (height 100 cm) number of uniform filters with 32 mm diameter 1 cross-low 1 5orlOcm 1 or4 2 cross flow 4 3 ultrasonic 1 1 ultrasonic nebulizer USN-100 (SPECTRO A.I.) 10cm 4 25 cm 40 In the Scott spray chamber (type 1) all coarse droplets > 20 pm were separated and run off through the drain. The mean particle sizes of the dried droplets were about 2 pm depending on the nebulizing and drying parameters, especially on the concentrations of the standard solutions [5]. The Particle mass distribution depending on the salt concentration of the standard solution was obtained by a Berner impactor LPI 25 (Fa. Hauke, Germany) [6]. Solutions with salt concentrations from 0.05 % up to 5 % were tested and the percental mass distribution was plotted against the Berner cut-diameter. For the 0.05 % salt concentration the resulted particle size maximum is between and 0.48 pm. Higher salt concentrations in the standard solution causes a shift to greater particle diameters up to particles with a maximum between 1 and 4 pm for solutions with 5 % salt content. Usually we used standard solutions with salt concentrations of 0.2 % because of the best cross-flow nebulizer efficiency. Therefore the maximum particle size was in the range between 0.5 and 1 pm, but also particles up to 4 pm occur. With the ultrasonic nebulizer, salt concentrations up to 2 % in the standard solutions can be nebulized without any problems. The dried standard aerosol particles (< 2 pm) deposited on the filter surface and in the first 100 pm of the quartz fibre filter with a total mean thickness of 600 pm, similar to the aerosol particles sampled from the stack gases [7]. The diameters of the quartz fibres are in a range between 0.1 and 2.5 pm. The following pictures shows dried standard aerosol particles on quartz fibre filters MK 360 scanned by electron microscopy SEM 115 (Philips, Dutch). Figure 4 shows particles generated in the,,multi spray chamber and collected on MK 360. Multi-element standard solutions with hydrochloric and nitric acid were used simultaneously and crystals resulted. Figure 5 shows the SEM picture of dried droplets performed out of a nitric mulielement standard solution with the ultrasonic nebulizer and the Scott spray chamber. Obviously rounded but,,dry particles stick on the quartz fibres.

6 Copyright (C) JCPDS International Centre for Diffraction Data 1999 Fig.4. SEM picture of standard aerosol particles generated by the,,multi spray chamber. Fig.5. SEM picture of standard aerosol particles generated by the ultrasonic nebulizer and the Scott spray chamber Spectrometer Calibration For calibration the multielement standard filters were measured by x-ray fluorescence with the energy dispersive x-lab spectrometer. After evaluation of the spectra the normalized intensities (imp se1ma_ ) were obtained. After that the filters were dissolved by oxidative digestion [S] and the obtained solutions were analyzed by reference methods like optical emission spectrometry using inductive coupled plasma (ICP-OES), mass spectrometry using inductive coupled plasma (ICP-MS) and atomic absorption spectroscopy (AAS). The normalized intensities from the XF2F spectrometer were plotted against the determined elemental concentrations (ng/cm2). 764

7 765 Figure 6 shows the resulting calibration graph for the element Pb. For the clibration range of 20 to 5330 ng/cm2 a correlation coefficient of was obtained Calibration curve of Pb on quartz fibre filters MK 360 s * -_ u) E a = $4 b=0.014 Table 3 displays the calibration ranges with their correlation coefficients, limits of detection and the blank values of the new developed quartz fibre filter band MK 370 for 28 elements. Oi rig I cm2 Fig. 6. Calibration curve of Pb on MK 360 Tab. 3. Calibration parameters for 28 elements Limits of detection, calibration ranges, correlation coefficients and blank values for EDXRFA of aerosol particles precipitated on the quartz fibre filter band MK 370 Elements Limits of detection Calibration ranges Corr. coefficients Blank values ( ng/cm2) ( ng/cm2) R (ng/cm ) Al 108, ,9998 <210,0 S 22, , ,8 Cl 21, ,973o 95,8 Ca 30, , ,8 Ti 54, ,9972 <54,2 V 11, ,999o <12,0 Cr , ,9 Mn 11, ,9995 <12,0 Fe 41, , ,3 co , ,5 Ni , ,0 cu , ,5 Zn 13, , ,0 As , Se 2,5 1 l-650 0, ,2 Br 5, ,9996 5,5 Ag ,9946 <3,6 Cd 12, ,998O <12,2 Sn 29, ,9936 <29,4 Sb 25,l ,9663 <25,1 Ba 100,o , ,3 Tl 22, ,9999 <22,5 Pb , ,8 Sampling In May 1997 the combined sampling device with the filter band was installed at an incineration plant near Hamburg (Germany). Within three days 135 samples with a sampling time of 30 minutes were collected. Table 4 shows the sampling parameters.

8 766 Tab. 4. Sampling narameters Date and time Sample numbers Sampling period Sampling volume Flow Temperature in stack gas Furnace temperature Dust ahead ACF Dust behind ACF Total normalized volume ACF: Active carbone filter, installed in Nov /5/1997 lo:31 to 7/5/ : minutes /- 188 litre 2,41 +/- 0,18 m3/h 141,6 C 730 OC 7,8 mg/nm3 0,l mg/nm Nm3ih 7/5/ :52 to : minutes 1220 litre 2,41 m3/h 139,5 C 730 C 8 mg/nm3 0,02 mg/nm3 98 OOONm3/h The averaged sampling volume was about 1220 liters, due to the sample flow of 2.41 m3/h obtained by isokinetic sampling in the stack gas channel with a gas velocity of 7.1 m/s. The aerosols sampled on the quartz fibre filter band were automtically covered with a Mylar foil to prevent them from contamination. The sealed samples were stored on a second role for further investigations. The obtained samples with a diameter of 32 mm were cut out of the band for multielementanalysis in the laboratory x-ray fluorescence spectrometer. In November 1996 an active carbon filter (ACF) packed bed reactor was installed at the plant and a reduction of a factor 10 was observed for the particulate emissions. Figure 7 shows a 2000-times magnification of stack gas particles collected on MK 370 after the installation, The diameter of the particulate matter is approximately < 3 pm, a few agglomerates up to 10pm. Despite of the low loading due to the short sampling time and small sample amount, good results could be achieved for most samples. Fig. 7. Stack gas particles collected on MK 370

9 767 Figure 8 depicts mean values and standard deviations of waste incineration plant (WIP) samples (including blank values) and MK 370 blanks l-29. IO4 h - Means and standard deviations of WIP samples including blanks Means and standard deviations of blanks l-29 V 1 Crl 1 FeICo/ NilCul blse/brl /CdISn/SblBalTI/PblBi 1 Elements Fig. 8. Mean values and standard deviations of WIP-samples and MK 370 blanks This method of sampling and analyzing enables the monitoring of stack gas emissions for many elements. In Figure 9 the Pb concentration (ng/cm2) on the filter was plotted versus the sampling date and time. Obviously sample 72 and 91 showed the highest Pb concentrations caused by the substitution of the carbon bed reactor. Figure 10 shows the XRF-spectra of a MK 370 blank and a real WIP-sample in the background. For each peak the affiliated elements were given Pb Filter 91 i :ilter Si FeU WP sample precipitated on MK 370 MK 370 blank Sampling date and time Fig. 9. Concentrations in ng/cm2 versus sampling date and time Energy [ kevj Fig. 10. XRF spectra of MK370 blank and a real WIP sample

10 Copyright (C) JCPDS-International Centre for Diffraction Data The achieved XRFA results in ng/cm2 were converted into ng/m3 by equation 1: concentration (3) - concentrarion (s) * filter area ( cm2 sample volume ( m3 ) (1) with a filter area of 8.06 cm2. The calculated averages, minima and maxima of emission at the WIP were given in ng/m3 for each measured element in Table 5. Tab. 5. Limits of detection and emission concentrations from a waste incineration plant Elements Limits of detection I) -hit Min Max Elements Limits of detection ) *vg Min Max Al S Cl Ca Ti V Cr ml Fe co Ni CU [ng/m31 [ng/m3] [ng/m ] [ng/m ] [ng/msl [ng/m ] [ng/m ] [ng/m3] 350,5 112,2 2131,4 SO,5 3747,l 123,7 604,9 67,0 890,5 18,7 24,8 36,4 868,9 4815,7 33,l 22,0 43,4 64,0 841,O 3654,5 151,4 6004,2 1749,2 147,l 2720,6 40,6 56,0 869,s ,3 133,5 Zn AS Se Br As Cd Sn Sb Ba Tl Pb 78,5 2112,7 21,5 168,l 14,6 28,6 108,l ,5 65,2 35,5 599,2 16,7 42,9 600,5 1) calculated from LOD [ng/cmz] for a flow of 2.44 ms/h, 0.5 h sampling on the quartz fibre filter band MK 370 (area 8.04 cm2) 151,9 3784,4 615,4 17,9 166,6 162,8 208,2 130,s 636,4 34,9 3515,9 Additionally the calculated limits of detection in ng/m3 were shown. Table 6 reflects the limits of emission for the different element classes set in the German law [l] compared to the summarized maximum element concentrations obtained by EDXRF of the analyzed samples. The summarized maximum of emission were 0.5 and 1 percent of the limits of emission. Tab. 6. Limits of emission, set in the German law 17. BImSchV Cd and Tl and their compounds Sb, As, Pb, Cr, Co, Cu, Mn, Ni, V, Sn and their compounds Limits of emission [ndm l Z of Max bdm l total < total < HR and their compounds total < not measured

11 Copyright (C) JCPDS-International Centre for Diffraction Data CONCLUSIONS The new developed isokinetic sampling device was succesfully tested at a stack gas channel of a waste incineration plant. The aerosol samples were collected,,out of stack on a new developed quartz fibre filter band material MK 370 with low blanks and high resistance to hot and aggressive gases. 135 samples with a sampling time of 30 minutes were collected within 3 days in May The samples were analyzed by an x-ray fluorescence spectrometer calibrated for aerosol filter samples with selfdeveloped standard filters. For the production of 40 identical standard filters a aerosol generator with 250 mm diameter and an ultrasonic nebulizer was built up. For special use a multi-spray chamber with four cross flow nebulizer interfaces was developed either. Determination with a Berner-impactor showed a particle size distribution depending to the salt content of the nebulized standard solution. Standard filters with particle sizes similar to real stack gas particles (< 3 pm) were used for spectrometer calibration. The calculated emission concentrations in ng/m3 were 100 times below the limits of emission, set in the German law. Nevertheless it was possible to make a quantitative analysis. The next step will be the use of the combined sampling and measuring device. Further investigations must show if there are any problems by particle losses or depositions through the sampling device. Therefore parallel sampling with,,in stack methods [9] will be carried out. REFERENCES [l] Bundes-Immissionsschutzgesetz- Verordnung, 17. BImSchV, Bundesminister fir Umwelt und Reaktorsicherheit, Bonn [2] O.Haupt, K.Linnow, R.Harmel, W.Dannecker, X-Ray Spectrom (1997). [3] T.Stahlschmidt, O.Haupt, MSchulz W.Dannecker, Gefahrstoffe Reinhaltung der Luft; Air Quality Control, in press. [4] Spectra X-Lab Handbook, Spectra A.I., Kleve, Germany (1993). [5] O.Haupt, C.Schafer, S.Strauss, W.Dannecker, Fresenius 2. Anal. Chem. 355, 375 (1996). [6] A.Berner, C.Lurzer, L.Pohl, O.Preining, P.Wagner, Sci. Total Environ. 13, 245 (1979). [7] O.Haupt, B.Klaue, C.Schafer, W. Dannecker, X-Ray Spectrom (1995). [S] M. Kriews, Ph. D. Thesis, University of Hamburg, Germany (1992) [9] VDI-Handbuch Reinhaltung der Luf, Richtlinie 2066 Blatt 1, Beuth Verlag GmbH, Berlin (1975) ACKNOWLEDGEMENT Many thanks for the financial support to the DLR (Deutsche Forschungsanstalt fur Luft- und Raumfahrt ev), to the BMBF (Bundes-Ministerium ftir Bildung und Forschung) and to Spectra A.I..