US2880069A - Manufacture of calcium carbide in shaft furnace - Google Patents

Description

March 31,1959 s. KOOPAL 2,880,069

MANUFACTURE OF CALCIUM CARBIDE IN SHAFT FURNACE FIGJ INVENTOR.

BY A M 8 v- W.

S. KOOPAL March 31, 1959 MANUFACTURE OF CALCIUM CARBIDE IN SHAFT FURNACE 2 Sheets'-Sheet 2 Filed May 5, 1955 INVENTOR.

Sp'e d8 Kypp al YW M '1 M444, ATTORNEYQ.

United States Patent MANUFACTURE OF CALCIUM CARBIDE IN SHAFT FURNACE Sieds Koopal, Sittard, Netherlands, assignor to Stamicarbon N. Heerlen, Netherlands Application May 5, 1955, Serial No. 506,333

application Netherlands May 7, 1954 6 Claims. (Cl. 23-208) Claims priority,

The present invention relates to novel improvements in the manufacture of calcium carbide in a shaft furnace by burning therein, i.e., heat reacting, a solid fuel which consists essentially of carbon, preferably coke, and lime or limestone which is also referred to hereinafter as lime. The high temperature and energy needed for the carbide formation is produced by burning part of the carbon present with an oxygen-rich blast which is injected into the hearth of the furnace through tuyeres, the carbide formed being discharged in the liquid state from the bottom of the furnace, while the gas produced therein is discharged through the furnace top. (See, for example, U.S. patent application Serial No. 302,614, filed August 4, 1952, now abandoned.)

When operating in the manner described above, using thoroughly mixed charges of, for example, one part of lime and two parts of coke, it has been found that carbide with a CaC content of 60-70% can be continuously prepared if a small furnace (such as one having an internal diameter of 56 cm. and a bed height of 2.5 m.) is used. However, when using a larger furnace (e.g., internal diameter 80 cm., height of bed 2.5 m.) under otherwise identical operation conditions, certain unexpected difii- Culties are encountered. For instance, it has been found that due to a shell formation consisting substantially of lime over, and partly in front of, the burners, the condition of the hearth is deteriorated to such an extent that hardly any carbide can be produced.

Accordingly, the principal object of the present invention is to provide novel improvements in the abovementioned process whereby said difiiculties, and particularly undesired shell formation, are avoided. Other objects will also be hereinafter apparent from the ensuing description and accompanying drawings.

According to the present invention, the manufacture of calcium carbide by heat reacting lime, as such or in the form of limestone, and a fuel consisting essentially of carbon, in a shaft furnace using a gas blast containing a high oxygen content to gasify the fuel and give the temperature and energy necessary for carbide formation is improved by building up the charge of lime and fuel in the furnace in such a way that the concentration of the lime in a plane immediately above the tuyere mouths will increase from the furnace wall towards the center of the furnace. Preferably, the furnace is so charged that the proportion of lime to coke in the charge increases slowly from the furnace wall inwards to a point located at some distance beyond the tuyere mouths after which the lime concentration rises sharply to a maximum at the center of the furnace.

Variation of the lime concentration in the manner discussed effectively eliminates the undesired shell formation mentioned above. Additionally, it has been found that a substantially more efficient reaction is obtained. These improved results can perhaps be explained by the following discussion. Three distinct regions may be noted in a shaft furnace with tuyeres through which an oxygen-rich blast is infilled with solid fuel and equipped.

2,880,009 Patented Mar. 31, 1959 jected as a result of the combustion and gasification of the solid fuel. These regions are (l) combustion zone in the vicinity of the tuyeres; (2) an adjacent reduction zone where the CO formed is reduced to CO by the carbon that has been raised to a high temperature, and (3) an adjoining preheating zone where the rising hot gases heat the descending cold solid fuel by passing in countercurrent relation thereto.

By providing the tuyeres with sight holes, the temperature of the glowing fuel surfaces in ends may be optically measured and the temperature at the end of the reduction zone (where the temperature of the gas phase is taken to be equal to the temperatureof the solid fuel) may then be calculated. It has been found that when coke is gasified in a furnace of this type with a blast composed of 47%, by volume, technical oxygen (i.e. by volume of O and 10% by volume of N and 53%, by volume, of steam, the optically measured temperature of the glowing fuel surface in front of the burners amounts to about 1600 C., while a calculation shows that the temperature at the end of the reduction zone will be about 875 C. At higher oxygen contents this temperature difference decreases.

It is, therefore, surprising to find that if the gasification is elfected using an oxygen-steam blast with a very high oxygen content, e.g. 65% to oxygen, by volume, or a blast consisting of oxygen enriched air with at least 35% oxygen the temperature at the end of the reduction zone is considerably higher than the measured temperature of the glowing fuel surface immediately in front of the tuyeres. For example, in a test wherein the blast consisted solely of technical oxygen, the temperature measured at the glowing fuel surface in front of the tuyeres amounted to about 3400 C., while the temperature at the end of the reduction zone was 4000 C. Accordingly, if a mixed charge of coke and lime is fed to the furnace and a blast with a very high oxygen content is applied thereto, a lime particle located in the immediate vicinity of the tuyeres may have a temperature of many hundreds of degrees below that of a lime particle in the reduction zone, dependent upon the diameter of the furnace. This can be more clearly understood by reference to the accompanying drawings wherein:

Figures 1 and 2 are diagrammatic views of the effect of furnace diameter on the arrangement of the combustion, reduction and preheating zones; and

Figures 3 and 4 are sectional elevations of furnaces provided with means for controlling the distribution of the charge according to the invention.

Referring more particularly to Figure l, the furnace shown therein has a small diameter, e.g., one up to 0.5 m., and the space between the tuyeres is shown to be entirely occupied by the combustion zone which is overlain by the reduction zone. Figure 2 shows a furnace with a larger internal diameter, e.g., one of the order of 0.5 m. to 2 m. Consequently, in this case, there is a larger distance between the ends of two opposed tuyeres and, as shown, the space between the tuyeres, in contrast to the situation shown in Figure l, is not entirely occupied by the combustion zone. Thus, in Figure 2, oxygen supplied through the tuyeres is entirely consumed before reaching the center of the furnace and the reduction zone extends downwards into the region between the two opposed tuyeres.

In the situation illustrated by Figure l, substantially all descending lime particles will first pass through the entire reduction zone, and they are allowed sufiicient time to be heated up to a temperature high enough to react with the carbon at a similar temperature to form the desired carbide. However, in the case shown in Figure 2, part of the lime particles, viz., the particles located over the tuyere ends, do not pass through the reduction zone where front of the tuyere the temperature is highest. Furthermore, the stay of these particles in the combustion zone is relatively short due to the fact that this zone is so small. As a result, the lime particles are not heated up to the high temperature (e.g., 2000 to 2200" C.) needed for the carbide formation. Some carbide is formed at the surface of the lime operating troubles. fuel combustion will 7 increased.

usual gross composition of, for example, 20-30% by Weight of CaO and 80-70% by weight of C (in the form of coke) the lime content may rise, slowly at first and then more rapidly, from 0 furnace wall to 85% of high lime-content in the vicinity of the tuyere mouths. Additionally, no unreacted cumulate at the furnace center.

The desired increase in the lime content of the towards the center of the furnace may be effected in variin Figure 3 wherein 1 denotes the furnace. The hearth of the furnace is provided with tuyeres 2 connected to a feed pipe for the blast. The walls of the hearth are so designed that they may be protected against unduly high temperatures by means of cooling water.

On the top of the furnace there is mounted a hopper 3 whose contents can be discharged into the furnace by lowering a bell closure 4. Under closure 4 is a distributing device 5, the position of the closure with respect to the distributing device 5 determining the place to which the charge will be delivered. For example, with the bell in position a, the charge will descend from the hopper along the outer edge of the bell and the outer wall of the device 5 and will accumulate in an outer region against the furnace wall. when the bell is in position b, the tween the outer edge of the bell and the curved inner wall of the distributing device and accumulate in the central region around the center line. When the bell is put in position 0, the charge is delivered to the medial region between the central and outer regions aforesaid. By releasing successive quantities of material differing in slowly and then rapidly, from the furnace wall towards the center.

The same result may alternatively be obtained in another way, namely, by making use of the segregation which occurs when the charge is composed of carbon particles and lime particles of different sizes. The specific gravity of carbon in the form of coke is considerably different from that of lime, namely, 0.5 for coke and 1.5 for lime. Accordingly, if a coke-lime mixture, in which the lime particles are smaller than the coke particles, is supplied from a hopper through a centrally arranged vertical feed pipe into a furnace with an internal diameter segregation will be. The relationship of the diameter of the centrally arranged feed pipe and the furnace diameter also has an influence on the ultimate coke-lime distribution in the furnace charge. For example, to obtain the outer region The effect of Composition of the blast:

35% by volume of steam 65% by volume of technical oxygen (contaminated with by volume of N Reaction mixture: 1 part by weight of lime and 2 parts by weight of coke Amount of blast: 500 m. per hour Entering velocity of the blast: 80 m./sec.

Height of bed over the tuyere mouths: times larger than the coke diameter In contrast to the foregoing, the above operations were repeated, except that the furnace was fed with a charge comprising coke having a particle diameter of -60 mm. and lime with a particle diameter of 10-20 mm. The resulting filling was such that the lime concentration increased inwardly towards the center of the furnace and a carbide with a CaC -content of by weight was continuously produced without any difficulty.

Various modifications in the invention as described above can be made without in any way deviating from the scope thereof as defined in the following claims wherein I claim:

1. In a process for the production of calcium carbide in a vertical shaft furnace in which a charge of lime and carbonaceous fuel is heat reacted while passing downwardly therethrough with a gas blast of high oxygen con tent introduced into the lower part of said furnace through tuyeres so as to gasify said fuel and provide the temperature and energy necessary for carbide formation, the improvement which comprises maintaining, in a zone immediately above said tuyeres, a distribution of lime in said charge which gradually and continuously increases from a minimum concentration of lime adjacent the furnace wall to a maximum concentration of lime in the region of the axial line of said furnace by axially feeding a charge of intermixed lime and carbonaceous fuel particles into said furnace wherein the average maximum dimension of said lime particles is less than onehalf the size of said fuel particles whereby disposition of a shell formation of lime on the furnace wall adjacent said tuyeres is substantially avoided. I 2. The improved process of claim bonaceous fuel is coke.

3. The improved process of claim 1 wherein the concentration of lime gradually increases from substantially zero concentration at the sides of the furnace to about by weight at the center.

4. The improved process of claim 1 wherein the concentration of lime increases slowly from the sides of the furnace for a distance and then increases rapidly to about 85% concentration at the center.

5. The improved process of claim 1 where the oxygen content of said blast is from 65 to by volume by using oxygen-steam blast.

6. The improved process of claim 1 wherein the oxygen content of said blast is at least 35% by using as blast oxygen-enriched air.

1 wherein said car- Belgium Feb. 15, 1954 Canada Aor. 13. 1954

Claims (1)

1. IN A PROCESS FOR THE PRODUCTION OF CALCIUM CARBIDE IN A VERTICAL SHAFT FURNACE IN WHICH A CHARGE OF LIME AND CARBONACEOUS FUEL IS HEAT REACTED WHILE PASSING DOWN WARDLY THERETHROUGH WITH A GAS BLAST OF HIGH OXYGEN CONTENT INTRODUCED INTO THE LOWER PART OF SAID FURNACE THROUGH TUYERES SO AS TO GASIFY SAID FUEL AND PROVIDE THE TEMPERATURE AND ENERGY NECESSARY FOR CARBIDE FORMATION, THE IMPROVEMENT WHICH COMPRISES MAINTAINING, IN A ZONE IMMEDIATELY ABOVE SAID TUYERES, A DISTRIBUTION OF LIME IN SAID CHARGE WHICH GRADUALLY AND CONTINUOUSLY INCREASES FROM A MINIMUM CONCENTRATION OF LIME ADJACENT THE FURNACE WALL TO A AXIAL LINE OF SAID FURNACE BY AXIALLY IN THE REGION OF THE AXIAL LINE OF SAID FURNACE BY AXIALLY FEEDING A CHARGE OF INTERMIXED LIME AND CARBONACEOUS FUEL PARTICLES INTO SAID FURNACE WHEREIN THE AVERAGE MAXIMUM DIMENSION OF SAID LIME PARTICLES IS LESS THAN ONEHALF THE SIZE OF SAID FUEL PARTICLES WHEREBY DISPOSITION OF A SHELL FORMATION OF LIME ON THE FURNACE WALL ADJACENT SAID TUYERES IS SUBSTANTIALLY AVOIDED.

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