While a lot is written about tar in producer gas, very little attention is given to how the particulates of soot and ash behave in their passage through the gasifier components. Even less appreciation is given to how producer gas will revert to flocculated soot and CO2 if held above 500C once it leaves the gas making bed. With a mixture of soot ranging from plain carbon through to carbon blacks including C60> fullerines, and recently discovered soot attracted to magnets, it is important to understand this formation process to avoid mistakes in designing gas cooling systems.
In these tests, all the soot is dry, and can be blown off all surfaces with compressed air, or brush. No tar condenses on the soot at any time, but if cooled enough, water will condense and wet the surfaces and slurry the soot.
Included is a Report of how soot formation has been identified by one researcher back in 1984, the only one I have managed to collect close to my interest in soot formation as applied to engines. It is just readable, and can only apologise for the reproduced quality.
|Char dust collected from a hot cyclone with 200x magnification, showing stick like fragments of cell walls.|
|Char Dust from the hot cyclone with 1,000x magnification. In this photo, you can see the fuzzy edges of the cell walls in the process of shedding carbon to the gas making during the reduction phase.|
|Soot at 1,000x magnification. This is actually cyclone soot, and in size resembles talcum powder. It is extremely fluid in movement and easily becomes airborne.|
|Soot at 10,000x magnification. These fluffy balls were identified as having a graphite crystal lattice|
|In our latest 2008 testing of soot formations, these photos show differing formations inside our specially designed test rig, where hot dusty gas flows through a controlled tube assembly. The gas temperatures were about 470C at the inlet, and 195C at the outlet box shown in the top LH photo. Soot appears to behave in accordance to molecular type and size, with very fine particles on the tube walls in the hottest zones, and courser fluffy soot in the cooler zones, like seen in the outlet box. Of particular interest, was the soot that formed at the hot gas entry to the tubes on a spiral spinner hanging in a wire down the tubes. this was very black, fluffy, and was growing up the wire after forming a thick coating on the spiral. This is shown in the RH photo, and at this stage, only the soot behaviour is being studied, not it's type of molecular structure.|