Fig. 1 – Kalugin hot stove

       Jet vortex of gas and air in the pre-chamber (Fig. 2) ensures intensive and uniform mixing & combustion of gas and the process of combustion is over in the middle part of the dome before entering the checker-work. The optimum degree of jet vortex is obtained experimentally and can also be verified through theoretical calculations. Thus, unevenness of distribution of combustion products across the checker-work surface does not exceed 3-5%.

Fig. 2– Jet vortex of gases in the pre-chamber
           of Kalugin hot stove

       Jet vortex flow distribution may be different for Kalugin hot stoves of different thermal capacities. Research work carried out in the operating KSS with oxygen (O2) content in exhaust waste gas in the range of 0.3 to 5.1% during full thermal capacity operation have shown that the jet-vortex burner ensures the content of carbon monoxide (CO) of 0.0016%, or about 20 mg/m3, which is 5 times less than the European standards (Fig. 4). The Kalugin ceramic burner performs better than the most commonly used slot-hole ceramic burner of DME design (Germany).

       An example of pre-chamber burner 3D numerical calculation results is shown in Fig. 3. It is obvious that gas combustion starts in the pre-chamber and completes in the top part of the dome so that before entering the checker-work, the gas is almost burnt out having the content of carbon monoxide max 50 ppm. When gas is moving down the checker-work, after-burning of remaining carbon monoxide occurs and at the outlet of KSS the content of CO is less that 20 mg/m³. Hence, the ceramic burner system of the pre-chamber ensures a very intensive mixing and instant combustion of gas owing to the jet vortex flow of gas and air.

Fig. 3 – Location of the gas combustion zone in KSS. The content of carbon monoxide (CO) is determined based on 3D numerical computer calculation
           for full thermal capacity operation

Fig. 4 – Relation of the carbon monoxide (CO) concentration in exhaust waste gas
           on the oxygen concentration

       As obvious, there is no “short circuiting” in KSS and the hot blast stove will remain ecologically friendly throughout the entire service life.

At present, hot blast stove with internal combustion chamber (see Fig. 5), where both the checker chamber and the combustion chamber are located within the same steel shell, represent the most commonly used type of hot blast stoves in iron making around the world. This design was introduced by a British engineer and inventor E.A. Cowper more than 150 years ago. Operation of this type of stove has revealed a number of essential weaknesses as follows:

       - “Short circuit”, or direct leakage of fuel gases through the separation wall between the combustion chamber and the checker chamber through cracks and joints between bricks. During the gas period this leads to a substantial increase of CO content in the waste gases reaching 5000 mg/m³, while the European norms are 100 mg/m³ only resulting in a significant increase in CO emissions into atmosphere and to deterioration of the ecosystem. Due to the same short circuiting reason during blast cycle, part of cold blast leaks from checker-work chamber into combustion chamber and gets mixed with hot blast leading to reduction of hot blast temperature (sometimes by 100ºС)

       - Leaning of the combustion chamber towards the checker chamber (“banana” effect) that leads to damage of both combustion chamber and checker brickwork as well as to displacement of checkers and partial loss of open channels and to a significant increase in hydraulic resistance of hot blast stove;

       - High-temperature creep of refractory bricks under the influence of high temperatures and brickwork load in the bottom part of the combustion chamber that causes deformation and collapse of brickwork, especially of hot blast branch;

       - Uneven distribution of combustion products along the checker-work surface which may go up to ±15% and this reduces the efficiency of the checker-work performance and results in temperature fluctuation across the checker-work and in development of cracks in its bricks and in the checker supporting grid;

       - Pulsating combustion, which originates from the acoustic excitation of tall combustion chamber similar to that of organ pipe and leads to strong vibration of structures and to a collapse of its brickwork, which in turn deteriorates the performance of hot blast stoves;

       - Cracking of refractories in the bottom part of combustion chamber (in the area where the burner is installed) due to thermal shock caused to refractory bricks during the change-over from gas period to blast period and visa versa.

       These design deficiencies lead to frequent failures of the combustion chamber and, therefore, the combustion chamber is considered as the weakest element of the hot blast stove with internal combustion chamber. Long-term hot blast temperature operation of these stoves is limited to 1100ºС. The higher the operating hot blast temperature, the more frequent are shutdowns and relines of stoves which affect the blast furnace techno-economics.

Fig. 5 – Hot stove with the internal combustion chamber

     The most essential modification in hot blast stoves with internal combustion chamber was introduction of external combustion chamber where the latter is arranged in a separate shell (see Fig. 6). However, only two disadvantages are thus eliminated, namely- “short circuiting” and “banana” effects.

       These hot stoves have a much more complicated dome design and a complex system of temperature expansion compensation of the checker chamber shell and of the combustion chamber shell and therefore, their cost is 30-35% higher. Moreover, much more space is required for such stoves due to a larger footprint, which makes it impossible to introduce in operating shops. Besides, the shell of this type of stoves has a high tendency to Stress Corrosion Cracks (SCC). Nevertheless, these stoves have a more reliable structure and they are mainly installed in large capacity blast furnaces. Long-term maximum operating hot blast temperature of these stoves is 1250ºC.

Design by
Didier-Werke

Design by
Martin and Pagenstecher

Design by

Krupp Koppers

Design introduced in Japan and applied
           at the Bao Steel works (China)

Fig. 6 – Hot stoves with the external combustion chamber