Holger Teichert

Simultaneous in situ measurement of CO, H2O, and gas temperatures in a full-sized coal-fired power plant by near-infrared diode lasers

We present what is to our knowledge the first near-infrared diode-laser-based absorption spectrometer that is suitable for simultaneous in situ measurement of carbon monoxide, water vapor, and temperature in the combustion chamber (20-m diameter, 13-m path length) of a 600-MW lignite-fired power plant. A fiber-coupled distributed-feedback diode-laser module at 1.56 microm served for CO detection, and a Fabry-Perot diode laser at 813 nm was used to determine H2O concentrations and temperature from multiline water spectra. Despite severe light losses (transmission, <10(-8)) and strong background radiation we achieved a resolution of 1.9 x 10(-4) (1sigma) fractional absorption, equivalent to 200 parts in 10(6) by volume of CO (at 1450 K, 10(5) Pa) with 30-s averaging time.

SIMULTANEOUS DIODE-LASER-BASED IN SITU DETECTION OF MULTIPLE SPECIES AND TEMPERATURE IN A GAS-FIRED POWER PLANT

We have developed a diode-laser (DL)-based spectrometer and demonstrated, to our knowledge, the first simultaneous in situ detection of all major combustion species and the temperature in the same measurement volume for active combustion control purposes and to ensure a safe ignition procedure of large-scale multi-burner gas-fired combustion systems. Two distributed-feedback DLs at 760 nm and 1.65 μ m were used to detect O 2 , CH 4 , and CO 2 , while a Fabry-Perot DL at 812 nm served to extract absolute H 2 O concentrations and the temperature from multiline water spectra. Permanent alignment of the laser beams could be ensured, despite strong wall deformation, with a new active alignment control loop. We analyzed the instationary ignition procedure of a full-scale gas-fired power plant with a 10 m furnace diameter using the spectrometer. A time resolution of 1.6 s and a minimum detectable absorption better than 10 −3 OD could be achieved. CH 4 could be detected with a dynamic range of more than two orders of magnitude and a detectivity in the 100 ppm range. A strong dependence of the CH 4 signal on the burner height was found. This spectrometer is well suited to enable an on-line control of the furnace atmosphere and a rapid detection of ignition delays by unburned CH 4 .

In situ detection of potassium atoms in high-temperature coal-combustion systems using near-infrared-diode lasers

Direct tunable diode laser absorption spectroscopy at 769.9 and 767.5 nm was used to measure potassium (K) atom concentrations in situ in the high temperature (up to 1650 K) flue gas of two different pulverized coal dust combustion systems (atmospheric or pressurized (12 bar)). Two laser types (Fabry-Pérot (FP) and vertical-cavity surface-emitting lasers (VCSEL)) were used for the spectrometer and characterized with respect to the magnitude and linearity of their static and dynamic wavelength tuning properties. The wide continuous current-induced tuning range of the VCSEL of 20 cm(-1) (compared to 1 cm(-1) for the FP) make this laser ideal for species monitoring in high pressure processes. Two VCSELs were time-multiplexed to realize the simultaneous detection of the potassium D1 and D2 lines. Several oxygen absorption lines in the A-band, which are in close spectral vicinity of the K lines, were detected simultaneously, showing the possibility of multi-species detection with one laser. Using the FP-DL for the atmospheric process and the VCSEL for the high pressure process, the pressure-dependent coefficients for spectral broadening as well as a shift of the K line in the flue gas were determined to be (0.18 +/- 0.01) and (-0.060 +/- 0.003) cm(-1) per atm (at 1540 K and 11.2 bar). The total width and shift of the D1 line (11.2 bar/1540 K) were 60 and -20 GHz, respectively. The K atom concentration was determined continuously for several days in both plants under various operation conditions. Typical concentrations in the atmospheric plant were around 2 microg m(-3) with a range of 50 ng m(-3)-30 microg m(-3). Averaging 100 scans for each concentration value, we achieved a time resolution of 1.7 s and a detection limit of 10 ng m(-3), which corresponds to a fractional absorption in the 10(-3)-10(-4) range. A strong anti-correlation with the oxygen concentration could be verified. At the 12 bar plant, the concentration was again typically around 2 microg m(-3) but K levels up to 60 microg m(-3) were observed. Here, a strong dependence of the K-signal on the type of fuel could be verified.

Fasergekoppeltes In-situ-Laserspektrometer für den selektiven Nachweis von Wasserdampfspuren bis in den ppb-Bereich (Fibre-Coupled In-situ Laser Absorption Spectrometer for the Selective Detection of Water Vapour Traces down to the ppb-Level)

Abstract Ein neues, glasfasergekoppeltes In-situ-Absorptionsspektrometer auf Basis von Nah-Infrarot(NIR)-Diodenlasern eröffnet im Hinblick auf den in Industrie und Forschung bedeutenden In-situ-H2O-Nachweis neue Möglichkeiten, da es erstmals auch in mehrphasigen Gasströmungen die schnelle, selektive, probennahme- und kalibrationsfreie Feuchtemessung gestattet. Aufwändige Tests in der cryogenen Aerosolkammer AIDA ermöglichten mit einer gefalteten Absorptionstrecke von 82 m selbst in dichten Eiswolken eine Nachweisgrenze von 15 ppb (1σ, Δt = 2 s) und demonstrierten gleichzeitig die erste präzise Bestimmung der dynamischen Übersättigung der Gasphase während der Wolkenbildung.

Diodenlaserbasierte, probennahmefreie Multikomponenten-Gasanalyse in einem 1000 MWth-Gaskraftwerk (Diode-Laser Based In-situ Detection of Multiple Gas Species in a Power Plant)

Ein NIR-Diodenlaser-gestütztes Absorptionsspektrometer zum simultanen In-situ- Nachweis mehrerer Spezies und der Temperatur und die erstmalige simultane In-situ- Erfassung aller Majoritätsspezies und der Temperatur im Brennraum eines industriellen Verbrennungsprozesses wird beschrieben. Haupteinsatzzweck des Gerätes ist die aktive Kontrolle chemischer Prozesse oder z.B. die Überwachung der schnellen Lastwechsel in Verbrennungsanlagen. Im Spektrometer werden insgesamt drei Diodenlaser bei 760nm, 812nm und 1,65µm eingesetzt um O2, H2O, CH4 und CO2 innerhalb des gleichen Messvolumens zu erfassen. Die Temperatur wird simultan aus dem Mehrlinienspektrum von Wasser bei 812 nm bestimmt. Um die starken Deformationen der Kesselwände zu korrigieren, wurde zusätzlich ein in-situ-taugliches System zur automatischen Nachführung und Stabilisierung der Laserstrahllage entwickelt und erfolgreich eingesetzt. Mit diesem Spektrometer gelang es, einen kompletten An- und Abfahrvorgang eines 1000- MWth-Gaskraftwerkes mit einem Brennraumdurchmesser von 10m zu überwachen. Die Zeitauflösung betrug dabei 1,6s, die kleinste nachweisbare molekulare Absorption lag im Bereich von 10–4 bis 10–3 optische Dichte. Methan, das für die schnelle Erfassung von Zündverzögerungen entscheidend ist, konnte unter Verbrennungsbedingungen mit einer Nachweisgrenze unter 100 ppmV und einem dynamischen Bereich von mehr als zwei Größenordnungen nachgewiesen werden.