Application of a Diode-Laser-Based Ultraviolet Absorption Sensor for in Situ Measurements of Atomic Mercury in Coal-Combustion Exhaust

Abstract

A diode-laser-based ultraviolet absorption sensor was successfully demonstrated for both in situ and extractive sampling atomic mercury measurements in a laboratory-scale 29.3 kWt (100 000 BTU/h) coal combustor and in situ measurements in a flow reactor at Texas A&M University. Laser sensor measurements were compared to measurements from a commercial mercury analyzer (CMA). A 375 nm single-mode laser and a 784 nm distributed feedback (DFB) laser are sum-frequency-mixed in a nonlinear β-barium borate crystal to generate a 254 nm beam. By tuning the frequency of the DFB laser, the ultraviolet beam frequency was tuned across the transition frequency of mercury at 253.7 nm. The tuning range was large enough that an off-resonant baseline was clearly visible on both sides of the Hg transition. No pretreatment is required for elemental mercury measurements, and the effects of broadband absorption can be effectively eliminated during data analysis. Extractive sampling was demonstrated to improve the detection limit of the sensor and demonstrate the feasibility of total mercury concentration measurements in the future through extractive sampling. Significant variation in the atomic mercury concentration of coal-combustion exhaust was observed over short time periods during our in situ measurements. The sensor detection limits for in situ and extractive sampling are 0.3 and 0.1 parts per billion over a 1 m path length, respectively.

On-line spectroscopic and spectrometric methods for the determination of metal species in industrial processes☆

“…In recent years, a sum-frequency mixing (SFM) system has been developed and demonstrated for the detection of mercury and applied in coal combustion [264,265]. Light at 254 nm was generated by sum-frequency mixing a 375 nm laser and a 784 nm distributed feedback (DFB) laser in a non-linear b-barium borate crystal.…”

“…Light at 254 nm was generated by sum-frequency mixing a 375 nm laser and a 784 nm distributed feedback (DFB) laser in a non-linear b-barium borate crystal. Initially [264], an ECDL was used, but this was then replaced by a single-mode DL at 375 nm [265]. About 4 nW of UV radiation could be generated in the mixing process.…”

“…The TDLAS UV-sensor described in Section 4.1.3 was applied for measurements of atomic mercury in both in-situ and extractive modes in a laboratory-scale 29.3 kW (thermal power) coal combustor and in-situ measurements in a flow reactor [265]. Measurements by TDLAS were compared to measurements from a commercial mercury analyser (CMA).…”

Measurement Enhancement on Two-Dimensional Temperature Distribution of Methane-Air Premixed Flame Using SMART Algorithm in CT-TDLAS

“…On the other hand, there have been several approaches to using laser technology. It has been proven that the TDLAS (tunable diode laser absorption spectroscopy) is able to measure the temperature and concentration with fast response time [5][6][7][8][9][10][11][12][13][14][15][16]. Yamakage et al [7] showed that the TDLAS could measure transient changes of temperature and concentration in a combustion engine under various operation loads.…”

2D Temperature Detection Characteristics of Engine Exhaust Gases Using CT Tunable Diode Laser Absorption Spectroscopy

“…Recently, tunable diode laser absorption spectroscopy (TDLAS) as a for temperature and species concentration measurement technique with high sensitivity and high response in combustion environments has been researched and applied to the actual combustors [1][2][3][4][5][6][7][8][9][10][11][12]. With these engineering developments, transient phenomena such as start-ups and load changes in engines have been gradually elucidated in various conditions [3].…”