Online laser monitoring of metal chloride and oxygen concentration using Collinear Photofragmentation and Atomic Absorption Spectroscopy

Transcription

1 Online laser monitoring of metal chloride and oxygen concentration using Collinear Photofragmentation and Atomic Absorption Spectroscopy Jan Viljanen*, Juha Toivonen Tampere University of Technology, Laboratory of Photonics Liekkipäivät

2 Motivation Online Metal Chloride Monitoring in Gas Phase Metal Chloride associated problems Slagging and fouling Corrosion Desired properties for monitoring Non-intrusive In-situ Molecule specific Broad dynamic range Scalability

3 CPFAAS technique 1. IR laser transmission 2. KCl fragmentation 3. Vapor relaxation O 2

4 K Concentration Concentration curve formation Concentration proportional to depth of the absorption dip via Beer-Lambert law αl = ln[i(t)/i(t < 0)] [1] Potassium decay follows [K] = K 0 exp k 1 t + K 0 res exp k 2 t where k 1 corresponds reaction rate for K + O 2 + M KO 2 + M Time (μs) [1] T. Sorvajärvi et al. Appl. Spectrosc. 68, (2014) [2] T. Sorvajärvi et al. J. Phys. Chem. A 119, (2015)

5 Absorption Cross Section Molecule specific Molecules have broad absorption bands => interferences Atomic lines narrow and specific [4] [3] SO 2 KCl NaCl Wavelength (nm) [3] C. Forsberg et al. Rev. Sci. Instrum. 80, (2009) [4] T. Sorvajärvi et al. Opt. Lett. 37, (2012)

6 Dynamic range Tunable dynamic range A f E in L Fragmentation beam area Decrease => increase sensitivity Input fragmentation pulse energy Increase => increase in sensitivity Interaction length, overlap Increase => increase in sensitivity

7 Scalability Requirements: two view ports for optical access Visibility Demonstrated in 1 cm laboratory flame and in 10 m wide BFB boiler

8 Concentration (ppm) CPFAAS Applications Temporal potassium release Samples of fuels were combusted in a single particle reactor Probe beam positioned 7 mm above sample Interaction length for absorption was 10 mm Simultaneous detection of K, KCl and KOH [1] T. Sorvajärvi et al. Appl. Spectrosc. 68, (2014) Time (s)

9 CPFAAS Applications Reaction kinetics and conditions Potassium decay follows [K] = K 0 exp k 1 t + K res 0 exp k 2 t where k 1 corresponds reaction rate for K + O 2 + M KO 2 + M Sample: Black liquor droplet m = 13.6 g Set [O 2 ] = % Set temperature = 950 C Time (μs) Time (s) [5] J. Viljanen et al. Opt. Lett. 42, (2017)

10 Photodiode signal (V) CPFAAS Applications Corrosion studies Probing of gas phase corrosion intermediates, e.g. KOH, in different gas environments Combined studies with Api-ToF massspectrometer Monitoring of changes in reaction kinetics N 2 H 2 O O 2 Cr Fe Time (μs)

11 CPFAAS Applications PbCl 2 Wavelengths of 355 nm and 266 nm are used for photofragmentation of PbCl 2 and PbCl, respectively. Pb* is measured using CW laser at 405 nm. Measurement point Superheater tubes (660 C) Feedstock (demolition wood) Transmittance (%) I/I 0 PbCl signal (ppm) No limestone With limestone Measurement parameters and main results from PbCl 2 detection through a 10 m wide flue gas passage using mobile CPFAAS prototype

12 Future prospects Recent development in laser diodes enable online NaCl and NaOH measurements Reaction kinetics of K + SO 2 Measurement of other more complex molecules, e.g. ZnCl 2 Applications outside combustion, e.g. atmosphere

13 Highlights CPFAAS is versatile method for metal chloride monitoring in combustion environments molecule specific, scalable Sub ppm detection limits Simultaneous monitoring of K, KCl, KOH, O 2 and temperature PbCl 2 monitoring in full-scale BFB boiler

14 Jan Viljanen, M.Sc. (Tech.) Laboratory of Photonics Tampere University of Technology Acknowledgements J. V. would like to acknowledge the support by TUT Graduate school References [1] Sorvajärvi, T., DeMartini, N., Rossi, J., & Toivonen, J. (2014). In situ measurement technique for simultaneous detection of K, KCl, and KOH vapors released during combustion of solid biomass fuel in a single particle reactor. Applied spectroscopy, 68(2), [2] Sorvajärvi, T., Viljanen, J., Toivonen, J., Marshall, P., & Glarborg, P. (2015). Rate Constant and Thermochemistry for K+ O2+ N2= KO2+ N2. The Journal of Physical Chemistry A, 119(14), [3] Forsberg, C., Broström, M., Backman, R., Edvardsson, E., Badiei, S., Berg, M., & Kassman, H. (2009). Principle, calibration, and application of the in situ alkali chloride monitor. Review of Scientific Instruments, 80(2), [4] Sorvajärvi, T., Saarela, J., & Toivonen, J. (2012). Optical detection of potassium chloride vapor using collinear photofragmentation and atomic absorption spectroscopy. Optics letters, 37(19), [5] Viljanen, J., Sorvajärvi, T., & Toivonen, J. (2017). In situ laser measurement of oxygen concentration and flue gas temperature utilizing chemical reaction kinetics. Optics letters, 42(23),