MEASUREMENT OF TIME-DEPENDENT FUME RELEASE RATE DURING BLACK LIQUOR PYROLYSIS

An electrical low-pressure impactor (ELPI) connected to a grid heater apparatus was used to implement real-time measurement of fine particle s formed in black liquor pyrolysis. The measurements gave information on the time variation of the mass of the released condensable material in black liquor pyrolysis. In addition to the ELPI-measurement, parti cles were also collected on a teflon filter and further analyzed for s odium. A small sample (of the order of 10 mg) was used on the grid in order to avoid excessive swelling and unequal temperature distribution in the sample. The ELPI was found to be suitable and very sensitive f or measuring the small amounts of particles resulting from a small sam ple. The sample mass losses in the measuring system, i.e., the condens ation of particles into the reactor and sampling lines, were found to be less than 10% of the total released material. The comparison of the fine particle mass based on ELPI measurements with the gravimetric an alysis of filter samples gave quite a good correlation, which indicate s that no or very few coarse particles were produced by mechanical dis integration of the sample. These experiments demonstrated that, below a certain temperature limit, between 600 degrees and 700 degrees C, pa rticles were formed in the beginning of pyrolysis, and the formation q uickly stopped after the first few seconds. According to chemical anal ysis, these particles contained no sodium. Above this temperature rang e, the formation of particles took place throughout the whole measurin g period. In these tests, two distinctly different stages of particle production were observed. Varying amounts of sodium were found in the particles produced here.