It has been reported in the literature that raceway measurement made
during the decreasing gas velocity is relevant to operating blast
furnaces. However, no raceway correlation is available either for
decreasing or increasing gas velocity which is developed based on a
systematic study and none of the available correlation take care of
frictional properties of the material. Therefore, a systematic
experimental study has been carried out on raceway hysteresis. Based on
experimental data and using dimensional analysis, two raceway
correlations, one each for increasing and decreasing gas velocity, have
been developed. Also, in the present study the effect of stresses has
been considered along with pressure and bed weight terms mathematically.
These three forces are expressed in mathematical form and solved
analytically for one-dimensional case, using a force balance approach.
Based on the force balance approach a general equation has been obtained
to predict the size of the cavity in each case, i.e., for increasing and
decreasing velocity. Results of these correlations and model have been
compared with the data obtained from literature on cold and hot models
and plant data along with some experimental data. An excellent agreement
has been found between the predicted (using correlations and model) and
experimental values. The proposed theory is applicable to any packed bed
systems. It has been shown that hysteresis mechanism in the packed beds
can be described reasonably taking into consideration the reversal of
sign in frictional forces in increasing and decreasing velocity cases.