Operators, furnace and fuel influence the dust emissions from small-scale furnaces. The present particles vary in size, shape and composition. As a reference method for dust emission measurements the gravimetric determination of dust load is used. This is a direct gravimetric measuring method. Size, shape and composition of the particles play only a subordinate role in this measuring method.
The accuracy of this reference method was not previously known for its use at small-scale furnaces for solid fuels. First, the process carried out for measurements on these furnaces has been adapted in this work. Subsequently, the uncertainty of the measurement method was calculated theoretically as well as determined practically under real flue gas conditions. In order to cover a wide range of practical combustion and measuring conditions different combustion systems and fuels have been used. About all combustions and measuring conditions the results for the measurement uncertainty is 7.3%. The accuracy of the measured values has been demonstrated during verification measurements on an emissions simulation facility. Based on the determined measurement uncertainty at real exhaust gas conditions under a wide range of combustion and measuring conditions uncertainty and accuracy of the measurements with the reference method for determining the concentration of dust at small-scale furnaces is established.
Based on statistical methods to assess the accuracy and the development of suggestions to improve current standards and guidelines, a methodology has been developed which allows the validation of new dust measurement systems in the future. As part of an exemplary validation of a new dust measuring instrument a measurement uncertainty of 15% was determined for this system. A new state of the art with respect to the accuracy of measurements for limit value monitoring at small-scale furnaces could be established.
Additionally, it was demonstrated by experimental studies on the isokinetic sampling that effects of non-isokinetic sampling at smal-scale furnaces can be neglected. To increase the accuracy of the measurements for the future it is recommended to do without isokinetic sampling, but rather to increase the mass of collected dust, and to use a maximum possible sample volume.