Injection of Reducing Gas into Blast Furnace (FTG Process)

Abstract

Since the lack of coking coal is a serious problem for steel industry, various studies have been carried out for saving coking coal, such as the way of decreasing coal consumption in blast furnace process, the research and development of formed coke process and of direct iron making process etc. Among them fuel injection through blast tuyere is a very effective process because coke is directly replaced by injected fuel, and recently coke rate of 360kg/t level was obtained by several blast furnaces under fuel oil injection of approximately 100kg/t in combination with the oxygen enrichment. However, the capacity of race way is limited as gasifying chamber to burn injected fuel from tuyere. In order to save coal moreover, it may be a good idea to produce reducing gas from fuel oil outside blast furnace and to inject it into blast furnace.
Reducing gas injection processes have long been subjects of investigation, where reducing gas is produced from fuel by cracking in an exclusive gasifying chamber and is injected into blast furnace, and recently reports of some performances with actual experimental equipment were published. On this subject authors have carried out several fundamental studies such as investigation of reducing gas production process, estimation of the effect of reducing gas injection by a mathematical model of blast furnace, examination on mixing of injected gas inside blast furnace using air-CO₂ model, and plant engineering for dealing with hot reducing gas. As for reducing gas production a joint research has been conducted with Texaco Inc. who has many experiences in this technology.
A commercial scale experiment (FTG process) has been carried out using a blast furnace of 1691m³ inner volume with which a Texaco-type generator of fuel oil gasifying capacity of 5 t/hr was installed, and the following results were obtained;
(1) Partial oxidation process was considered to be optimum in order to produce hot reducing gas of high reducing power from the available fuel oil.
(2) Cok saving was 0.9-1.0kg per gasified fuel oil of 1.0kg when hot reducing gas was injected into lower part of blast furnace shaft under following conditions;
Fuel oil rate injected through tuyere:<70kg/t
Fuel oil rate gasified by FTG process:<30kg/t
R. R. value of injected gas: 6-8
where; R. R.(CO+H₂)/(CO₂+H₂O)
(3) The fuel oil gasifying system and the hot reducing gas transfer system were kept under good conditions, and the blast furnace was operated smoothly.