Tapio Sorvajärvi

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:

A quantitative and simultaneous measurement of K, KCl, and KOH vapors from a burning fuel sample combusted in a single particle reactor was performed using collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) with a time resolution of 0.2 s. The previously presented CPFAAS technique was extended in this work to cover two consecutive fragmentation pulses for the photofragmentation of KCl and KOH. The spectral overlapping of the fragmentation spectra of KCl and KOH is discussed, and a linear equation system for the correction of the spectral interference is introduced. The detection limits for KCl, KOH, and K with the presented measurement arrangement and with 1 cm sample length were 0.5, 0.1, and 0.001 parts per million, respectively. The experimental setup was applied to analyze K, KCl, and KOH release from 10 mg spruce bark samples combusted at the temperatures of 850, 950, and 1050 °C with 10% of O2. The combustion experiments provided data on the form of K vapors and their release during different combustion phases and at different temperatures. The measured release histories agreed with earlier studies of K release. The simultaneous direct measurement of atomic K, KCl, and KOH will help in the impact of both the form of K in the biomass and fuel variables, such as particle size, on the release of K from biomass fuels.

Fluorescence cross sections of bioaerosols and suspended biological agents

Laser-induced fluorescence is used to investigate fluorescence properties of unwashed Bacillus thuringiensis and Bacillus subtilis spores, ovalbumin, and washed bacteriophage MS2. A fluorescence detector is calibrated to obtain absolute fluorescence cross sections. Fluorescence maps of biological aerosols and suspensions are measured at a wide excitation range from 210 to 419 nm and a wide detection range from 315 to 650 nm. The dominant features of the measured spectra are the amino acid peaks, having excitation maxima at 220 and 280 nm. The peaks are similar for the bacterial spores, both for aerosols and suspensions, whereas the peaks are shifted toward the shorter emission wavelengths for the suspended ovalbumin and MS2. Moreover, the fluorescence emission, excited above 320 nm is more intensive for the aerosols than the suspensions.

Phase-sensitive method for background-compensated photoacoustic detection of NO2 using high-power LEDs

A photoacoustic (PA) sensor has been developed for the detection of nitrogen dioxide (NO(2)). Ten amplitude-modulated high-power light emitting diodes (LEDs), emitting a total optical power of 9 W at 453 nm, are used to excite the photoacoustic signal in NO(2). The LEDs are attached to the circumference of a cylindrical PA cell. The induced longitudinal acoustics waves are detected using two electromechanical film stacks, located at the ends of the cell. Background signal cancelation is achieved by using phase-sensitive detection of the difference signal of the two pressure transducers. The phase-sensitive approach allows for improved dynamic range and sensitivity. A detection limit of 10 parts per billion by volume was achieved for flowing NO(2) gas sample in an acquisition time of 2.1 s, corresponding to a minimum detectable absorption coefficient of 1.6 × 10(-7) cm(-1) Hz(-1/2). The developed sensor has potential for compact, light-weight, and low-cost measurement of NO(2).

Wavelength modulation waveforms in laser photoacoustic spectroscopy

Different wavelength modulation waveforms were studied comprehensively in tunable diode laser photoacoustic spectroscopy. The generation of the photoacoustic signal was studied by way of simulations and experiments. A cantilever-enhanced photoacoustic detector and CO(2) sample gas were used in the experiments. The modulation waveforms compared in this study were sinusoidal, triangular, shaped, and quasi-square waves. All four waveforms allow background-free detection of trace gases. Compared to the conventionally used sinusoidal modulation, the triangular, shaped, and quasi-square waves enhanced the photoacoustic signal by factors of 1.12, 1.42, and 1.57, respectively.

Resonant photoacoustic cell for pulsed laser analysis of gases at high temperature

A new approach to high temperature gas analysis by means of photoacoustic (PA) spectroscopy is presented. The transverse modes of the resonant PA cell were excited with a pulsed laser and detected with a microphone. Changes in the properties of the PA cell resulting from a varying temperature are discussed and considered when processing the PA signal. The feasibility of the proposed method was demonstrated by studying PA response from saturated vapor of potassium chloride (KCl) in the temperature range extending from 410 to 691 degrees C. The PA spectrum, the detection limit, and the signal saturation of KCl vapor are discussed. At 245 nm excitation wavelength and 300 microJ pulse energy, the achieved detection limit for KCl is 15 ppb.

Transversely Excited Multipass Photoacoustic Cell Using Electromechanical Film as Microphone

A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in an optical multipass configuration. A detection limit of 22 ppb (10−9) was achieved for flowing NO2 in N2 at normal pressure by using the maximum of 70 laser beams between the resonator plates. The corresponding minimum detectable absorption and the normalized noise-equivalent absorption coefficients were 2.2 × 10−7 cm−1 and 3.2 × 10−9 cm−1WHz−1/2, respectively.

Electromechanical film as a photoacoustic transducer

An electromechanical film, EMFi, is utilized as a transducer in a photoacoustic (PA) gas sensor. The film is a sensitive acoustic transducer, it is easily formable, and it exhibits a wide frequency response regardless of its large surface area. As a demonstration of its capabilities, the EMFi-based PA detector is used to measure NO(2) with pulsed excitation at 436 and 473 nm. The minimum detectable absorption coefficient is extrapolated to be 5.10(-7) cm(-1). Improvements for EMFi-based PA detector are discussed.

In situ laser measurement of oxygen concentration and flue gas temperature utilizing chemical reaction kinetics

Laser spectroscopy allows authentic nonintrusive analysis of combustion chemistry. Various methods based on absorption spectroscopy have shown to be simple and effective for chemical analysis in combustion environment [1]. However, these methods have not been able to deliver localized information on flame temperature or O2 concentration. Multiple methods, in addition to conventional probe method, have been proposed to provide the desired localized temperature information on combustion flames and some of these techniques have also shown capability to map O2 concentrations [2], but these are generally complex and cannot be extended to large scale.

Detection of PbCl2 using Collinear Photofragmentation and Atomic Absorption Spectroscopy

PbCl2 causes corrosion in waste combusting power plants and there is no method to monitor it. We demonstrate the use of collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) to successfully detect PbCl2 in-situ in a hot furnace.