According to Directive 2000/76/EC of the European parliament and of the council, of 4 December 2000, on the incineration of waste, plants for incineration of waste must raise gas temperature to 850oC, and in some cases 1100oC, for two seconds. Furthermore, the directive states that these properties shall be subjected to appropriate verification, in the form of measurements. How these measurements shall be performed, however, have not been clarified. Consequently, there is a need for a new method that is cost-effective and fairly simple to use in different furnace geometries, as well as generally applicable and available to consultant companies at a reasonable cost.

The method proposed in this paper injects a pulse of helium into the furnace by using an injection lance, and then continuously samples the flue gas with a suction pyrometer to measure the temperature. The residence-time distribution is obtained by analysing the helium concentration in the sampled flue gas with a portable mass spectrometer as a function of time.

We successfully tested this method in a 40 MW pulverised wood fired boiler at Kalmar Energi Värme AB, Kalmar, Sweden. The results indicate that it is sensitive to conditions influencing residence-time distribution and thus can be used to verify implementation of European Union requirements. Additional advantages of this method are that it is fairly inexpensive, simple, and can also be used to determine mixing-rate.