The photographing system with an ultrahigh speed shutter camera has been developed at Kimitsu No. 3 blast furnace. In this system, the shutter speed can be raised up to about 1μs, and the actual raceway can be observed over a long time with high accuracy in on-line real time.
The raceway images obtained with this system contain two sorts of the basic information, i.e., brightness and particle size of coke. By using these two informations, the two phenomena occurring near the raceway were elucidated; melting down behavior of the root of cohesive zone and change in coke properties. As a result, the mechanism for the periodical change of raceway brightness has been considered, and the degradation mechanism of coke in the furnace has been elucidated by analyzing the results of test operations using coke with various high temperature properties. Besides, this system has been used effectively in the blowing-out operation of blast furnace by lowering the burden level to the tuyere level.
Based on the observation results obtained with this system, change in coke properties in the furnace has been investigated by using the model experiments and mathematical calculations. As a result, the following facts were guessed to be occurred.
(1) Coke has already been deteriorated before running into the raceway.
(2) Impact energy working on coke circulating in the raceway was not so great.
(3) There was few cases where coke was degraded in the raceway by the thermal stress generated in coke particle when it came into the raceway.