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State of the art gas measurements and diagnostics in furnaces
At RISE we are developing and implementing state of the art measurement and diagnostic techniques with tunable diode lasers to monitor and enhance the performance of thermochemical conversion processes. The techniques enable real-time, accurate measurements of difficult-to-quantify entities in hot and enclosed environments.
Gain deeper insight into combustion, gasification, and other thermochemical processes.
Advanced optical measurement techniques, specifically Tunable Diode Laser Absorption Spectroscopy (TDLAS) have developed and matured in recent years and can offer new and exciting alternatives for monitoring industrial processes. The technology relies on the fact that chemical species of interest will absorb infrared light at certain known frequencies, while not absorbing any light at "off" frequencies, a simple concept that allows for robust measurements in difficult environments. Residence time of TDLAS measurements is determined by the scanning rate of wavelength around the chemical species spectroscopic feature ( on and off the peak). Typically we work with 1-10 ms scanning intervals. Equipment for TDLAS is inexpensive compared to competing technologies such as FTIR.
RISE at the forefront
RISE is focused on both developing the TDLAS technology for new uses as well as implementing TDLAS technologies within industry. Current research focuses on using TDLAS to adjust fuel feedstock flows in real time to achieve better combustion efficiency. Implementations at industry are focused on measurements of temperature, soot, NO, CO2, H2O, CO, C2H2, CH4 as well as biomass flow and moisture content.
References and Research topics
- Following fuel conversion during biomass gasification using Tunable Diode Laser Absorption Spectroscopy diagnostics
- Simultaneous diagnostics of fuel moisture content and equivalence ratio during combustion of liquid and solid fuels
- Laser-based detection of methane and soot during entrained-flow biomass gasification
- Measuring NO and temperature in plasma preheated air using UV absorption spectroscopy
How RISE can help
Our expert researchers and engineers are enthusiastic about this technology and are available to aid in a successful implementation or research initiative.
TDLAS implementations offer an extremely robust method for capturing data in difficult environments, using non-invasive light beams for the measurements. Difficult environments such as sooty or gasified gas streams are no problem for TDLAS techniques, because the baseline measurement factors out the additional absorption. Additionally, the use of lasers emitting exact frequencies means that calibration is never required and results are repeatable.
Normally, two optical ports (sight glasses) are needed on opposite sides of the furnace or reactor vessel, in order to emit and detect the laser beam.
RISE can supply laser measurement equipment as well as software for signal interpretation. We offer the expertise needed for implementation, support, and development.
Methodology and Comparison
In TDLAS (see Figure 1) the wavelength of a narrowband laser is tuned across a specific absorption feature of the target species. The absorption of the laser intensity is measured with a photodetector and related to properties of targeted species (e.g. concentration, temperature (T), pressure (P)) using spectroscopic properties available from databases and the Beer–Lambert law. If the spectroscopic and gas properties (P, T) are known, the concentration can be evaluated from the measured absorption. For the temperature measurements, the laser is tuned over two or more lines of a species, the lines' (integrated or peak) absorbance ratio provides the temperature. It is important to note that the accurate detection of the parameters of the process (species concentration and T) is possible even at high level of laser light extinction due to particles, e.g. dust, soot, char and ash. The broadband reduction of the laser intensity can be used to evaluate particle concentrations. The lasers can easily be coupled to optical fibers, which constitutes a significant advantage for practical applications since the instrument can be located in a control room (or other safe places) with the light being transferred to the boiler in the fiber. The measured data is an integration (or average) over the entire absorption path and, therefore, provides information on the overall process condition and efficiency.
Currently, the monitoring and control of bio-based energy generation processes is carried out using feedback signals from conventional temperature measurements, flow rates and flue gas analysis. The main drawbacks of these methods are their poor temporal resolution, slow response time, invasiveness, etc. Due to these drawbacks, conventional methods are unfit for accurate and rapid detection of changes in process conditions that are needed for responsive control. In-situ diagnostics are measurements carried out directly in the reaction zone of the process, thereby reducing the response time of the feedback signal. Optical in-situ methods are non-invasive and operable for prolonged times in challenging environments. At present, TDLAS is one of the most promising and rapidly developing optical techniques for online in-situ diagnostics in thermochemical conversion systems. A comparison of TDLAS and conventional methods based on extractive sampling and invasive probing is given in Table 1 (Appendix).
