Development and application of a "one-minute" probe for measuring carry-over in a recovery boiler

Recovery boilers that are being upgraded such as air systems or liquor firing modifications, particularly those that are running above the design load, need to understand the impacts of these changes on carry-over. Traditional air-cooled carry-over probes, while excellent for research and longer term studies, do not lend themselves readily for use by mill operators. The main objective of with this work was to develop and calibrate an un-cooled short-time probe that could easily be used by plant operating personnel to quickly estimate the amount of carry-over in a recovery boiler. The deposits on the probe were photographed after exposure and the photos were analyzed with image processing software. The degrees of particle hit coverage on the probe surface were converted to correspond to the air-cooled probe results, thus it was possible to obtain the rate of the deposit growth in mm/h and to also calculate the amount of carry-over as g/Nm³. Depending on the flue gas temperature and the carry-over amount 10 -30 s exposure times showed to be suitable. Exposure times were set to 20 s in this work. It was also possible to estimate the particle size variations from the images. It was assumed that there were no particles overlapping on the probe surface, when the coverage was relatively low. However when the degree of coverage for particle hits increased to around 50 % of the probe surface, it was clearly observed that particle hits overlapped each other. A reference image series was created; so that future recovery boiler personnel can use the series to evaluate the results of own "one-minute" probe measurements.