Pyrolysis of rubber crumb at around 500°C produces oil, char and gas in typical proportions of 50% oil, 35% char and 15% gas mixed with light hydrocarbon vapour. For this project, the oil is condensed and collected, and the char cooled and collected. The gaseous product is not required, and is disposed of by flaring.
The type of gas produced is high in heavier hydrocarbon gases, and also contains a substantial quantity of oil vapour so proved difficult to burn cleanly using a flare nozzle with natural mixing. This was a particular problem as the pressure available at the flare nozzle was only a few millibar, making it impossible to generate sufficient turbulence to entrain enough air using the velocity at the gas nozzle.
As can be seen from the picture at the left, the natural draught flare burned with a very dirty flame, producing a lot of soot and odour, and is clearly unacceptable.
This design of flare also had a propensity to go out once the gas feed rate fell to a low level, emitting odorous gas.
On the right is a picture of the new forced draught flare with clean burn. The gas flow is similar in both these pictures.
There was no scope to increase the gas pressure to improve mixing at the nozzle and the forced air system was designed to minimise the need for gas pressure. The original nozzle was used, but mounted inside a forced air mixing assembly comprising a primary swirl air and flame stabilisation plate, and a concentric secondary air register.