FI62042B - SCHAKTUGN FOER SMAELTNING AV MINERALISKA RAOVAROR - Google Patents

Description

ADVERTISEMENT PUBLICATION r 0 Γ \ AO jt & A LBJ (11) UTLÄGCNINOSSKRIFT 6 2 042 C (* 5) Patent granted 10 11 1932 Patent neddelat ^ v -> / (51) Kv.lk?/lnt.CI.3 GB 5/12 ENGLISH —FINLAND (21) P *** "ttll» k * mu · - PKamam »knln« 780161 (22) HikamltplWt - An * 6knln (* d »f 13-02.78 (23) Alkuptlvt — GIKlfhatadtg 13.02.78 (41) Tullut Julkbwkal - Blhrlt offantllj 27. 01.79

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Patent- och registerstyrelsen AihMim utkpi «eh uti.ikrHtM pibiinnd 30.07.82 (32) (33) (31) hry4 * t * y« woiiwu * —β «« Μ priority 26.07.77

Sweden-Sweden (SE) 7708572-8 (71) Rockwool Aktiebolaget, Skövde, Sweden-Sweden (SE) (72) Olof Kjell-Berger, Skövde, Sweden-Sweden (SE) (7I) Berggren Oy Ab (5I +) Mineral raw materials -shaft smelting furnace -Sehaktugn för smältning av mineraliska ruvälor

The present invention relates to a shaft furnace for smelting mineral raw materials. Such shaft furnaces are used in particular for the smelting of mineral raw materials for the production of rock wool. In this case, the mineral is melted by charging the furnace with a mixture of mineral and fuel, the fuel usually being coke. The melt is assembled at the bottom of the furnace, from where it is removed to a suitable spinning unit, often formed by a rapidly rotating wheel or a cascade of rapidly rotating wheels, from which the melt is ejected as fine yarns which, when solidified, form mineral fibers. However, there are many types of spinning units, and the invention is, of course, not limited to a shaft furnace used in connection with a particular type of spinning unit. When making mineral wool from stone or slag, shaft furnaces form the most common smelting plant.

For economic reasons, high production efficiency is sought. Production capacity is determined on the basis of self-evident factors in the part of the plant with the lowest capacity per se. This part may be the spinning unit itself or a collecting device arranged behind the spinning unit or one of the following devices intended to perform s r, r,.

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post-treatment for spinning mineral wool mat. However, experience has shown that, in general, the part that limits production efficiency as a whole can be a shaft furnace. Therefore, efforts have often been made to increase the efficiency of the mineral smelting plant. The characteristics of the shaft furnace that lead to its power limitation are directly related to the way the shaft furnace operates. Namely, such a furnace operates by feeding a mixture of mineral and fuel at its upper end through a suitable charging device, usually as a batch process, so that such a mixture containing non-combustible fuel particles exists up to the furnace layer with a melt of the correct temperature and viscosity. Of course, combustion also occurs above this layer, but non-combustible particles of fuel remain up to this layer. As a result, the combustion air must be supplied at the level of the shaft furnace, which is located at a relatively low level, usually only slightly above the melt discharge level. The air is supplied through so-called flues, through which air is compressed under pressure. This pressure can be adjusted in a suitable way, but even when the pressure at which the combustion air is compressed is best adjusted, an uncontrolled flow of combustion air takes place inside the shaft furnace.

It can be shown that the air inside the shaft furnace has to change its direction so that it has an even stronger force component in the upward direction.

It has now been proposed to increase the diameter of the furnace in order to improve the efficiency of shaft furnaces which have too little power compared to the following parts of the plant. However, it was found that above a certain diameter, the power of the furnace increased to a decreasing extent in proportion to the increase in diameter, and when the prescribed diameter of the furnaces was reached, the expected increase in the power of the furnace remained almost non-existent. Instead, the melt received inferior properties, which in turn affected the quality of the product produced, especially mineral wool.

In this situation, instead, it was proposed to use two or more shaft furnaces in one and the same plant, which would be connected to the common production parts following them in the plant, so that each shaft furnace could be given a suitably adapted shark. would give a melt from which good quality mineral wool could be made. Of course, instead, each shaft furnace could be allowed to feed its own plant, adapted to the power of the shaft furnace. However, this solution to the present problem is far from an ideal solution. It means embarking on a path where production is divided into several smaller units and which is the exact opposite of what should be pursued for industrial and economic reasons. This solution increases the need for space and leads to an increase in both plant and staff costs.

The problems associated with this have been solved by the present invention. The invention is based on a series of experiments which have sought to find the reason why, by increasing the diameter or cross-sectional area of a shaft furnace, the production efficiency of the furnace cannot be increased while maintaining the quality of the melt. In this case, special attention has been paid to the question of how the combustion air moves inside the shaft furnace.

As mentioned above, it is expected that the air, once penetrating the bottom of the furnace through the flues, will gradually deviate in the upward direction. The inwardly directed motion component then gradually decreases, as a result of which a situation is easily created in which a core area is formed in which there is no combustion air at all. Of course, it is not very important if such a core area is located in the part of the furnace where the melt has already been prepared, so that it has a high quality. However, it has been found that the core area without combustion air or with insufficient combustion air not only increases in diameter but also in height as the diameter of the shaft furnace is increased. This disadvantageous core area, to which the combustion air is not supplied or is insufficiently supplied, therefore rises higher and higher in the furnace as the diameter of the shaft furnace is increased, with the result that combustion increasingly fails.

The purpose of combustion is not only to cause the mineral to melt, but also to raise its temperature so that the mineral becomes light-flowing to such an extent that it is suitable for subsequent spinning and certain chemical processes involving reduction of existing iron oxides and homogenization of the final melt. All these processes do not take place momentarily, but gradually in the height of the furnace 4 62042, and they are even partially intertwined. Other processes may also occur that may be relevant to melt quality.

The purpose of the studies has therefore been, inter alia, to determine the maximum permissible furnace diameter for a shaft furnace of circular cross-section in which the melt has the desired quality at the bottom of the furnace. In this case, the monitoring of the specific melting expressed in kg / h.m has been a good help. For the above-mentioned shaft furnaces, it was found that the maximum allowable diameter was 1.2-1.6 meters. Of course, the exact value cannot be determined at all, as it depends on a number of different factors, such as the quality of the raw material and the piece size.

The invention is based the idea that the cross-sectional area of the furnace is increased at the same time increasing the inside of the furnace wall, and the center distance between. This is done by giving the oven an oval or similar elongate cross-section at least in the area where defrosting and post-defrosting overheating take place.

The efficient and at the same time technically and economically advantageous cross-sectional shape of the shaft furnace in the melting zone is assembled from two semicircular parts connected to each other by flat wall parts. This is the so-called the initial type of a parallelepiped oval. Said cross-sectional shape is particularly advantageous when it comes to converting the circular cross-section of an already existing shaft furnace into a cross-section according to the present invention. Namely, the shaft furnace can then be divided by two vertical sections into two semicircular sections, which are moved apart and connected by flat wall sections.

With such a structure, the existing cross-sectional area can be considerably enlarged without the distance between the furnace wall and the furnace center having to exceed at any point the critical value determined by a circular furnace diameter of 1.6 meters, preferably 1.2 meters. The length of the oval cross-section of the furnace can be considerably longer, and it has been found suitable in experiments to give this dimension 1.8-2.4 meters. As a rule of thumb, it has been found that very advantageous results are obtained if the oven is dimensioned so that the ratio between the maximum width of the cross-section and the smallest width is between 1.1 and 1.5.

5,62042

It will then be clear from the above that the said rules apply to the part of the shaft furnace where melting takes place in the broadest sense, ie where not only the raw material softens but also its temperature rises, iron oxide and other harmful constituents are reduced and homogenization. In particular, the homogenization takes place very close to the bottom of the shaft furnace. The upper parts of the shaft furnace, on the other hand, do not necessarily have to have said oval shape. In view of the quality of the charging devices and the flue gas exhaust ducts, it may in many cases be suitable to make the furnace gradually change from said oval shape of the melting zone to a shape of circular cross-section or close to such a cross-sectional shape.

However, the tests performed have also given certain rules for the distribution of chimneys around the perimeter of the shaft furnace. As already mentioned above, the flues must be fitted to the bottom of the furnace. Combustion air is forced in through these flues at a certain pressure. This combustion air therefore tends, at least initially, to take in the furnace a direction inside its flat wall portions perpendicular to its wall portions, but which passes radially or almost radially inside its circular wall portions. As a result, if the flues were evenly distributed along the circumference of the furnace, condensation of combustion air would occur at or near the center of the circular portions of the furnace wall, whereas less combustion air would exist in front of the flat portions of the furnace wall. However, for obvious reasons, it is desirable that melting in the broadest sense mentioned above occurs evenly throughout the furnace. Since melting depends on the supply of combustion air, the combustion air must also be evenly distributed inside the cross-section of the furnace. For this reason, the flues are preferably fitted more frequently to the flat parts of the furnace and with a larger radius of curvature, but less frequently to those parts of the furnace wall where the radius of curvature is smaller. Following this explanation, one skilled in the art should be able to easily calculate how the density of the flues should be distributed around the perimeter of the furnace. If there are difficulties in this respect, the distribution can also easily be determined purely experimentally.

The invention will be explained in more detail below in connection with the exemplary embodiment shown in the accompanying drawing. It is clear, however, that the invention is not limited to this particular embodiment, but that all kinds of different modifications may occur within the scope of the invention.

In the drawing, Fig. 1 shows a vertical section through the center of the furnace according to the invention or a section line comparable to the center, while Fig. 2 shows a section through the melting zone of the same furnace in the horizontal direction. To clarify the sectional plane, the sectional plane of Fig. 2 is indicated by a line II-II in Fig. 1, and the corresponding sectional plane of Fig. 1 is indicated by a line I-I in Fig. 2.

The furnace casing 10 is coated on the inside with a refractory material, e.g. a lining 11 of chamotte bricks. These flues are connected to a source of pressurized combustion air, so that air is blown into the furnace in melting zone 16. In fact, zone 16 contains a mixture of coke, partially molten mineral and highly molten mineral, whereby the well melted and properly viscous heated mineral is collected in 16 , so that it can be removed in a suitable manner by means of the bottom hatches 14 schematically shown in the drawing. Coke in Zone 16 is commonly referred to as coke. The coke in the upper parts of the furnace is referred to herein as the coke charge. Thus, a mixture of smelting material and coke charge is stored above the bottom coke. The coke batch then means the amount of coke that is fed to replace the part of the coke that is burned in the form of bottom coke. The coke batch must therefore be fed continuously. The area with the mixture of melting material and coke charge is indicated in Figure 1 by reference numeral 17. The boundary area between the two zones 16 and 17, which cannot in fact be accurately located at all, is indicated by line 18.

However, as the coke batch is transferred to form coke, it must be replaced. This is done by charging the furnace at its upper end with a mixture of lump mineral and coke, which is usually fed intermittently to the hopper 20. The hopper 20 should preferably be continuously filled, but the intermittent feeding of coke and mineral takes place by a barrier schematically shown in Figure 1. guides 7 62042 by a rod 22 extending upwardly through a hopper 19 in the hopper 20.

Flue gas removal takes place via duct 23.

Figure 2 shows how the chimneys are divided into four groups with different divisions. In both groups, located in the semicircular crossheads in the present embodiment of the furnace, the flues are sparser, as shown by the flues 15 ', while the flues 15 "are located on the flat cross sides 26 and 27 of the much more densely illustrated embodiment.

Thanks to this arrangement, the combustion air is distributed more evenly over the entire area 16 through which the cutting plane according to Fig. 2 is placed, as described in more detail above.

Claims (6)

8 62042 A shaft furnace for melting mineral raw material for the production of mineral wool, the shaft furnace (10) comprising a vertical furnace shaft (12) closed at the bottom by means (14) for discharging mineral melt, the flues (15) near the bottom of the furnace supplying blowing air in addition to the mineral raw material for the combustion of the fed fuel, preferably coke, characterized in that the furnace (10, 11) has at least the area where melting and post-melting overheating take place, hereinafter referred to as the "melting zone" (16), given an oval or equivalent elongated cross-section. Shaft furnace according to claim 1, characterized in that its cross-section in the melting zone (16) consists of two at least approximately semicircular parts (24, 25) arranged at each end and having at least approximately parallel axes, and on each side and between them two from at least an approximately parallel, flat portion (26, 27). Shaft furnace according to Claim 1 or 2, characterized in that the minimum internal width of the cross-section in the melting zone is at most 1.6 meters and preferably at most 1.2 meters. Shaft furnace according to Claim 3, characterized in that the ratio between the maximum length and the maximum width of the cross section in the melting zone (16) is at most 1.5 and at least 1.1. Shaft furnace according to one of the preceding claims, characterized in that the cross-section in the shaft furnace parts (17) above the melting zone (16) is made such that it gradually approaches a circular shape or an oval shape with less eccentricity in the height direction of the furnace. in the form in the melting zone. Shaft furnace according to one of the preceding claims, characterized in that the flues (15) for supplying combustion air through the furnace wall (10, 11) are arranged more frequently in those parts (26, 27) of the furnace cross-section in the melting zone. (16) with a larger radius of curvature, and less frequently turning the cross section to those parts (24, 25) in the melting zone where the radius of curvature is smaller.