Hot blast stove
.jpg)
A wind heater is a regenerator with a fixed storage mass. It serves to provide the hot blast for the blast furnace process . With the use of flue gas heat for air or gas preheating, considerable fuel savings are achieved.
Cowper
The mostly used wind heaters are named after the inventor and developer of regenerative heat exchange Edward Alfred Cowper . Cowper work with a change in time (heating - cooling). They consist of cylinders with a height of about 50 m and a diameter of 10 m. These containers consist of a combustion chamber, a storage room lined with fire-resistant bricks, and the dome. The furnace gas is enriched with natural gas or other high-strength gases in the combustion chamber and burned afterwards, the hot exhaust gas that arises is passed over the storage stones and discharged. The stones are heated and give off this heat again when the boiler is switched to fresh air. The air heated in this way is called a hot wind, which is then passed into the rest of the blast furnace at a temperature of around 1300 ° C. The production of some types of pig iron such as ferro- manganese and ferro-silicon has only become possible with the hot blast technology.
By far the most important and largest part of the Cowper are the stones, the latticework. This latticework forms the storage mass for the heat and is made up of refractory bricks. These lattice stones have channels through which the heat is supplied and released. The thicker the walls of the lattice blocks, the more heat can be stored. However, a greater wall thickness also means a smaller diameter of the channels, which means that the warm-up phase has to be selected longer due to the smaller heat exchange surface. If the wall thickness is thinner, the heat storage capacity decreases due to the reduced mass, but the larger ducts ensure faster heat exchange. The optimal lattice stone is designed so that it represents the best compromise between heat storage mass and heat exchange surface.
Next to the lattice shaft is the significantly smaller, mostly lens-shaped or round combustion shaft, in which, with the help of an internal, ceramic burner or an external machine burner, for example, furnace gas burns and a hot combustion gas is generated. This flows up through the combustion shaft, is deflected in the dome and then flows from above through the latticework, giving off its heat to the latticework. After switching, air, called "cold wind" in the iron and steel industry, flows through the latticework from bottom to top and is heated to high temperatures in the process. The cold wind heated in this way is in turn deflected in the dome, flows through the furnace and leaves the heater as a “hot wind” that is blown into the furnace via the ring line. When blowing into the blast furnace, a constant hot blast temperature of around 1200 ° C is necessary. In order to guarantee this in the case of a wind heater that is constantly cooling down, a mixed wind is generated by adding unheated cold winds. Here, a part of the cold breeze, which is constantly decreasing over time, is led past the heater through a bypass and mixed with the hot breeze. In this way, an adjustable and almost temperature-constant wind power reaches the blast furnace. At the end of each wind season, the hot wind from the heater should still be sufficient for the required temperatures without the addition of cold wind.
Types of cowpers
There are Cowper with internal and external firing shafts. In one design, the combustion shaft is located next to the lattice shaft in the same container; in the other design, it is located outside and separately. The wind heaters with an external combustion shaft can be clearly recognized by their two cylindrical structures and the connecting dome, which protrude up to 50 m into the air.
The alternative design is the integration of the combustion shaft into the jacket of the heater to form an internal combustion shaft. The advantage of an internal firing shaft is the reduced heat radiation into the environment and the compact design. On the other hand, the maintenance of the built-in combustion shaft is more difficult. A decisive disadvantage of the internal combustion shaft is the frequent formation of cracks in the masonry between the combustion shaft and the latticework. These “short circuits” mainly occur in the lower part of the partition wall, because this is the area on the furnace side where the highest temperatures are reached during heating. On the other hand, on the latticework side, the wall is cooled most strongly in the wind phase. These thermal stresses can lead to the formation of cracks, which seriously disrupt Cowper operation.
Also because the requirements for very high wind temperatures became more and more important over time, the construction of an external combustion shaft was increasingly used. This construction has the advantage that significantly more trimming stones can be accommodated in the lattice shaft, the heating surface becomes larger and the wind output can be increased again.
prehistory
.png)
Wilhelm von Faber du Faur had installed a tubular coil heater in the Wasseralfingen ironworks that worked as a heat exchanger. The German chemist Robert Wilhelm Bunsen , together with the British chemist Lyon Playfair, carried out analyzes of the gases that occur in or escape from the blast furnace. In their final report, published in 1847, they had pointed out the “appropriate use of furnace gases as fuel” and thus contributed to the development of effective wind heaters.
Individual evidence
- ^ Robert Bunsen, Lyon Playfair: Investigations on the process of the English pig iron preparation . In: Otto Linné Erdmann, Richard Felix Marchand (Hrsg.): Journal for practical chemistry . tape 42 , no. 1 . Johann Ambrosius Barth, Leipzig 1847, p. 145–188, 257–275 and 385–400 , doi : 10.1002 / prac.18470420123 ( 1st part online , 2nd part online doi: 10.1002 / prac.18470420136 , 3rd part online , doi: 10.1002 / prac.18470420153 ) .