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A blast furnace consists of a throat (furnace stack distributor), a shaft (cone-shaped part of the furnace for heating and recovery of the iron), a belly (cylindrical part of the furnace for softening and melting of the iron), a bosh (cone-shaped part where reducing gas is produced) and a hearth (a cylindrical part of the furnace for the accumulation of molten iron and slag).
The top of the hearth is equipped with the tuyeres representing the channels for feeding the heated air blasting (the mixture of compressed air enriched with oxygen and hydrocarbon fuel). The temperature in this part of the hearth can reach up to 2000 °C. Thus, the tuyeres are used in extreme conditions but the oxygen supply to the combustion zone of the hearth is required for the provision of the high temperature and efficient iron melting. Up to 4 500 m3 of the air can be supplied to the blast furnace through the tuyeres per day.
The first tuyeres were used in 1740 in the blast furnace of Nevyanskiy plant. The use of the tuyeres in the blast furnace practice gained widespread currency in the beginning of the ХХth century. Then this tuyere design has been slightly changed although its manufacturing technique has been improving constantly.
A tuyere unit consists of a nozzle transferring the blast air into the tuyere, a bootleg and a fixed elbow, a tuyere sleeve for connection with the blast pipe inlet through the clamp and tension screw fastening with a spring. The main components of the tuyere unit, such as tuyere and nozzle, nozzle and bootleg, bootleg and fixed elbow are tightly connected with the polished tapered surfaces by means of the consequent close arrangement of the next part in the previous one. Thus the closed-fitted tapered surfaces provide the leak-tight integrity of the joint. Any disturbance of operating heating cycle and leakage of the one of the joints in the tuyere unit results in the burning of the construction elements and failures.
The tuyere, tuyere cooler and nozzle operate in case of the heaviest temperature conditions. The tuyere cooler is placed the breast of the furnace lining, the nozzle is coupled with the tuyere which is already 250 – 350 mm deep inside the furnace body.
The nozzles are usually made of steel with coating from the special ceramic refractory lining. The tuyeres are made of copper. The prior art-type tuyere was made of pressed copper sheets, wall thickness up to 8 mm. Nowadays the tuyeres are usually made of centrifugally cast copper which ensures maximum operating life of the tuyere by means of the high manufacturability that provides the highest material homogeneity and the absence of micropores. However this method is a bit more expensive than the tuyeres manufacturing by the means of vacuum casting. The latter is also sometimes applied in the production of the tuyeres and has a smaller conversion cost but there is a possibility of the slight non-homogeneity of material. Anyway, the casting method of the tuyeres production has almost superseded the application of the welded construction of the tuyeres due to its lower operating capacity despite of the lower production cost which is also associated with the hollow copper tuyere cooler casting. The tuyere cooler is also manufactured by means of casting and is made of copper (less often of bronze). It is mounted in the breast of the furnace lining and fixed through the flange with the additional welding to the hearth jacket.
The blast furnace tuyere is cooled by the water supplied at a rate of 15 – 25 m3/hour directly to the inner face of the tuyere. At that the heating temperature of the discharged cooling water shall not exceed 15 °C. The pressure of the cooling water supplied to the face of the tuyere and tuyere cooler shall not exceed 5 – 10 atm. The use of the copper (with content min. 99,5% Cu) as the material of construction allows to remove heat effectively from the cone body of the tuyere operating in the extremely hot conditions.
Engineering company LCC "INTECH GmbH" has great experience in producing the centrifugally cast tuyeres and tuyere coolers according to the customer’s drawings. The company LCC "INTECH GmbH" performs the quality control of the work and material used at each stage of production from the feed stock analysis to the control of the finishing machining.
Another application of the tuyeres is the oxygen converter which is a pivoted pear-shaped tank with inner lining and a top inlet for supplying the oxygen through the tuyere, feeding cast iron, scrap, slag-formers; and equipped with a tap-hole for steel discharge.
A special water-cooled tuyere required for supplying oxygen to converter is placed in its neck strictly along the axis. The depth of the tuyere insertion into the converter above the bath tank may vary in the process of melting. The tuyere is transferred at the rate of max. 1 m/s by means of a special device integrated with the converter rotating mechanism. The pressure of oxygen supplied to the tuyere doesn’t usually exceed 16 bar.
The tuyere consists of two parts – copper head for operation in the extremely high temperature conditions up to 2600 °C and feeding pipeline which is out of the high temperature zone and doesn’t require extremely fast heat removal. The pipeline with a length of up to 27 meters consists of three coaxially fastened heat resistant steel pipes. The oxygen is usually supplied into the central pipe. The middle cavity formed by the central and middle pipe is filled with the cooling water which then is removed through a specially designed flow channel in the tuyere head via the cavity between the middle and outer pipe. As a result of such cooling water flow arrangement the heat is removed from the tuyere head and three pipes situated in the extremely hot zone. The rate of water supply is determined by the condition that the inlet and outlet temperature difference does not exceed 30°C. To compensate dissimilar thermal expansions of the pipe elements in the outlet pipe due to the great difference of the heating level in the inner pipes the corrugated metal expansion joints are used; in the pipes attachment points the gland seals are used which allow the pipes to move along the axis. The copper tuyere head is mounted on the outlet pipe in the converter zone. The copper tuyere head is equipped with nozzles distributing oxygen inside the converter.
The tuyere heads are usually made of pure copper to provide maximum heat transfer to the flowing cooling water and preserve the strength properties and prevent material overheating. Initially the copper heads were fabricated from a welded construction which was not reliable enough and the weld seams reduced the service life of the head greatly. Nowadays the casting design of the tuyere heads is mainly used. However the service life of the tuyere head does not usually exceed 150 melting cycles.
The heads in the first converters had one nozzle at rather low rate of oxygen supply. As the demand for the increase of the oxygen flow rate and converter capacity grew, the use of one single nozzle resulted in splash of the melted metal during the blow down. At present the tuyere heads are equipped with up to seven nozzles while the strength and service life of construction remained the same. The nozzles are mounted equally spaced around the tuyere head axis at a definite angle to this axis. This angle is determined depending on the converter free volume and the distance to the converter walls so that the oxygen coming out the nozzle doesn’t burn out the refractory wall material. This provides more uniform blow down without metal splashing and increases the finished metal output by a few percent.
Engineering company LCC "INTECH GmbH" can also provide the customers of the metallurgical production facilities with a number of special parts fabricated according to the customers’ technical assignments using special stainless steels of higher mechanical strength and durability, heat-resistant steels, stellen, bronze, ceramic and coated steels:
Technical department: info@intech-gmbh.ru, tel. +7 (499) 261-08-45.
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