Laser-based IR spectroscopy for measuring sulfur trioxide in the exhaust gas of gas power plants

A measuring system for determining a sulfur trioxide content in a combustion gas also containing sulfur dioxide at <50 ppm and water, comprising:

• a first gas line from a gas take-off point to a measuring cell,
• a pressure regulation device for the measuring cell,
• a wave number tunable monochrome light source in the region of a sulfur trioxide absorption band,
• a control for carrying out a transmission measurement in the measuring cell, and
• an evaluation unit for determining the sulfur trioxide content,
• wherein the light source is suited to generate monochromatic light in a window around 1365.5 cm−1, and
• the evaluation unit determines the sulfur trioxide content by compensating sulfur trioxide absorption at 1365.49 cm−1 for a cross-influence of sulfur dioxide absorption between 1365.52 and 1365.54 cm−1.