Abstract
Improving the heat efficiency in converter is very important for the development of high scrap ratio operation and scrap melting process in BOF and also in-bath smelting reduction processes.
Essential conditions to improve heat efficiency in an in-bath smelting reduction furnace, SRF, are described, based on the integrated operation with 5t scale SRF directly connected to a pre-reduction furnace, PRF, in NKK Fukuyama Works. Control method of the SRF operated under the high level of post-combustion and the performance of the bubbling bed type PRF are also mentioned.
Under post-combustion in the SRF, slag is considered to be a major heat transfer medium. To obtain high heat transfer efficiency from hot gas to slag,
(1)the height adjustment of a top blowing lance.
(2)intensive stirring of slag layer by bottom blowing are essentially important.
For the sake of high post-combustion degree, operation should be carried out under ultra soft blowing of oxygen through a double flow lance. Pressurized operation of the SRF is also effective to increase post-combustion degree.
As the result, post-combustion degree of 50% with high heat transfer efficiency of more than 85% was attained.
