Tuyere injection

The simultaneous splitting and distribution of solids-gas mixtures for applications requiring multipoint injection, where the mixtures are transported usually under positive-pressure conditions. Some common examples include tuyere injection for blast furnaces, large burner nozzles for pulverized coal-fired boilers, small coal-fired plasma torches providing startup and support energy for boilers, injection of pulverized fuel into calciners, etc. 

Methods used to introduce oxygen into the cupola or blast furnace can be classified into two main categories diffuser enrichment and tuyere injection... 

Divided blast operation with a direct enrichment of blast air, results in an increase in the tapping temperature of 85 °C compared to cold blast operation. In divided blast operation, neither well injection nor tuyere injection give any greater benefit than the simple method of direct injection. 

The recirculation of dust through agglomeration and charging is much less common than tuyere injection. This is because the process is much more difficult to automate. Furthermore, good control and knowledge of the pelletisation process is needed to give the pellets the necessary... 

Figure 4.33 Zinc distribution for tuyere injection, npon injection during 20 days [156, Godinot, 2001]...

The analysis of the input and output flows do not allow a full closure of the zinc balance. This indicates that a considerable part of the zinc (20 % for tuyere injection, 10 % for pellet charging) remains and accumulates in the system. Upon recirculation, the dust gets sticky and deposits in the combustion chamber, heat-exchanger and filters. The recirculation will therefore require increased cleaning efforts and will result in a material for disposal at this cleaning stage. 

From the practical data from two foundries in France, additional operational costs were calculated. Tuyere injection showed an additional operational cost of EUR 0.35/tonne cast iron pellet injection EUR 0.90/tonne cast iron. This calculation does not take into account any extra costs for slag disposal or maintenance works. 

Figure 3 - Diagram of the Tuyere Injection Plant at Avonmouth...

Control of tuyere injection is facilitated by the use of oxygen injection boosting the tuyeres showing low blast flow rates. When injection rates become higher, it is anticipated that oxygen will be used continuously at the rate of 2% enrichment for an injection rate of 1.5 t/h... 

The tuyere injection plant at Duisburg was installed in 1996. It is capable of handling 35,000 t/y of secondary materials and was described in the paper by Schneider and Schwab (8). Later developments with this plant are likely to be discussed by these authors in their paper Zinc Recycling via Imperial Smelting Technology - Latest Developments and Possibilities to be presented at this conference. 

Compared with hot briquetting, tuyere injection would appear to have a number of advantages as a method of feeding secondary materials to the ISF ... 

Tuyere injection is an excellent method of treating fine dusts with the minimum... 

The raw materials costs for hot briquetting and tuyere injection are attractive and can be negative if the supplier would otherwise be facing dumping costs. If the smelter is at its limit for sinter production, both processes are very attractive because they offer the opportunity to increase metal output without proportional increases in operating costs. 

A.R. Musson, M.W. Gammon, I.M. Hitchens and S.P. Mathew, The Development of Tuyere Injection Technology for the ISF at Britannia Zinc Ltd , Zinc and Lead Processing. J.E. Dutrizac, J.A. Gonzalez, G.L. Bolton and P. Hancock, Eds., Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, Canada, 1998,265-276. 

Computer controls are likewise used for stove operation, to control deUvery of the hot blast. High hot blast temperatures are generally desirable, as these reduce the coke rate. Control of the flame temperature in the raceway is effected by controlled additions to the hot blast, primarily of moisture. Injectants into the tuyeres such as coal, oil, and natural gas are often used to replace some of the coke. The effect of these injectants on flame temperature must be accounted for, and compensation is performed by lowering moisture or adding oxygen. 

A heat balance for the blast furnace produced by Michard et al. (1967), shows tlrat nearly 80% of the heat generated in tire furnace is used to produce and melt the iron and slag. The gas which emerges from tire first zone is further used to pre-heat the ah injected in the tuyeres in large stoves. The process thus runs at a vety high efficiency, botlr from tire point of view of tire amount of metal and slag produced and from the heat generation and utilization. 

The flow pattern of gas through blast furnaces was studied by VDEh (Veren Deutscher Eisenhiittenleute Betriebsforschungsinstitut) by injecting Kr-85 into the air stream entering the tuyeres of the 688 m furnace. A sketch and listing of pertinent quantities for run 10.5 of 9.12.1969 is shown in Fig. P13.1. Assuming that the axial dispersion model applies to the flow of gas... 

---