Online water vapor detection in the product gas from indirect gasification

Report, 2013

The integration of a gasifier into a complex synthesis process, such like SNG synthesis, with several process steps asks for a better monitoring of the gasifier performance. While the dry gas composition is often known, tar concentration and steam concentration in the raw producer gas are usually not available online. A set of standard analyzers for dry gas composition (GC or NDIR) and online tar measurement combined with an online water measurement could allow the continuous calculation of simple mass and energy balances. Those balances, that characterize the gasification process, could enable the operator to monitor the effects of varying fuel properties and eventually counter the effects on the downstream equipment. For the detection of steam concentration in raw gas electromagnetic waves of terahertz frequencies (hundreds of gigahertz) are promising with regard to develop a robust online measurement device for industrial application. Main reasons for the high potential are the low risk for interference with the wide range of other molecules and the fact that THz frequencies are rather insensitive to deposits and particulate matter in the course of the beam, compared to laser technology at IR. Aiming to test the feasibility of applying this measurement technique in the industrial scale, a gas cell was designed and constructed providing conditions close to the onsite operation (i.e. T, P, gas composition, etc.) for primary laboratory tests. The experiments were then followed with onsite tests at Chalmers power central. Within those experiments the application of THz spectroscopy as a promising technique for detection and measurement of steam and CO at real industrial processes was proven. Current report demonstrates the procedure of implementing a THz spectrometer to acquire data in both laboratory and industrial scale and discuss how those data could be interpreted to gain a precise measurement of desired gaseous components.