This paper delineates the improvements of a measuring system to prevent hunting of blast flow, one of the factors that decreases productivity of melted pig iron in the steel-making process. The analysis on the cause of hunting air flow arising in blast furnaces shows that the profile of the general flow rate is poorly formed due to a short and straight part of the pipe in the upstream of orifice plate which is a device to generate differential pressure for measuring air flow rate. In order to resolve the problem, several measuring devices applicable to compressed gas in high temperature are considered, and the properties of AVM(Annular Ventury Meter) and thermal mass flow meter are elucidated.
Based on the properties in this study, a new type of AVM is developed which has guide vanes installed in the external part of the cone so as to give the AVM flowmeter the ability to produce uniform flow. As the result, it became possible to prevent hunting of blast flow.