US2143905A - Process for burning cement and similar raw material - Google Patents

Description

Jan. 17, 1939. N. AHLMANN 2,143,905

PROCESS FOR BURNING CEMENT AND SIMILAR RAW MATERIAL Filed July 1, 1958 INVENTOR lV/KOZ 4/ #194 MAN/V ATTORNEY5 Patented Jan. 17, 1939 UNITED STATES PROCESS FOR BURNING CELIENT AND SIMILAR RAW MATERIAL Nikolai Ahlmann, Fredriksberg, near Copenhagen, Denmark, assignor to F. L. Smidth & 00., New York, N. Y., a corporation of New Jersey Application July 1, 1938, Serial No. 216,895 In Great Britain July 14, 1937 8 Claims.

This invention relates 'to the burning of cement, or the sintering of similar raw materials, by forming a porous layer of a mixture of the raw material and coke, or other solid fuel, and

5 drawing or forcing gas capable of supporting combustion through the layer'after igniting the fuel.

Researches have shown that if cold air is drawn or forced through such a layer the burning is unsatisfactory, even if the mixture contains a relatively large quantity of fuel. This may be accounted for by the fact that the raw material, which as a rule is moistened'in order to render the mixture porous, must not only be burned or sintered, but also must be dried and preheated, and at least in the case of cement raw materials, mustbe calcined. All of these processes together require a considerable quantity of heat.

According to the present invention the amount of heat that must be produced by the fuel per unit volume of the mixture is reduced, without the'necessity of employing more than a relatively small amount of external heat, by drawing or forcing heated gas through the layer to dry and preheat it and thereafter igniting the fuel and carrying on the burning or sintering process by drawing or forcing further gas through the layer. Preferably the gas for drying and preheating the layer is drawn or forced transversely through the layer of material twice, namely, first through the layer at a point where the burning or sintering is complete, so that the gas is heated, and then through the layer at a point'in advance of that at which the fuel is ignited. The evaporation of the moisture contained in the raw material, I

and all or part of the preheating, are thus effected by means of hot gas so that the whole of the heat generated by the fuel 'is available for the remainder of the process. With materials that must be calcined the process may .be so carried on that some of the calcination is also effected by the hot gas. Whether the process is so carried on that only some of the preheating, or all a of the preheating, or all preheating and part of the calclnation,'is effected by the hot gas, it is only a single-stage process, in that all of the fuel that is burnt is combined in the initial layer of raw material and fuel. It is, immaterial whether .the gas that is passed through the layer before the ignition of the fuel is-capable of supporting combustion or not. 1

When the fuel is ignited the gas must, of course, be capable of supporting combustion, and 5 the fuel may be ignited simply by passing through the layer-gas which is rich in oxygen and heated to a sufliciently high temperature. Alternatively the layer may be ignited by a flame, which may be a gas or oil flame, and which need consume only a small amount of fuel. In general, it is 5 convenient to combine the two methods so that the amount of. heat contained in the gas passed through the layer is increased on passing the flame.

The gas that is passed through the layer after the ignition may simply consist of ordinary atmospheric air, but it is better either to add oxygen to the air or to preheat the air. Of course, hot gaseous products of combustion may be used if they are rich enough in oxygen. For example, 15 the gases coming from a furnace working with a high excess air coeflicient may be used. Preferably the gas that is passed through the layer after the ignition is air that has first been passed through the layer at a point where the burning or sintering is complete.

The incoming gas that is passed through the layer where the burning or sintering is complete is preferably divided into two streams after its passage through the layer, namely, a stream that has passed through an earlier and hotter part of the layer and a stream that has passed through a later and cooler part. The former stream is then passed through the layer a second time at a point where the ignition begins, or has begun, andthe latter stream is passed through the layer at a point where ignition has not begun and thus serves as the drying and preheating gas.

Apparatus suitable for carrying out the process is illustrated diagrammatically in the accompanying drawing but it will be understood that any appropriate apparatus capable of carrying out the process may be used. In order that the invention may be clearly understood and readily carried into effect one process in accordance 0 therewith will nowbe described by way of example with reference to the drawing.

a The apparatus may comprise an endless travelling grate carried by drums 2 and 3. The grate is preferably protected from the action of very, hot gases by,a layer 5 of any suitable material that has already been sintered, this material being supplied from a hopper 4. The mixture of raw material and fuel in porous form is fed from a hopper 6 onto the layer 5 and forms thereon a top layer 1. Atmospheric air is drawn through a pipe 8, the end of which is shown in the drawing, and passes upwards through the grate and the layers 5 and I into passages 9 and I0, and then passes downwards through the layers and the grate into a pipe I 9. During its first passage through the layer 1 the air is heated so that that part of it which passes through the portion iii of the layer and the passage 8 and then arrives at the portion ll of the layer 1, serves to dry and preheat the material, and may even calcine it to some extent. That part of the incoming air which passes through the portion l5 of the layer 1 and the passage l passes by a flame l3 to the portion 12 of the layer 1, and is hotter than that part of the air which passes through the passage 9, both because it is heated by the flame l3 and because the portion l of the layer 1 is hotter than the portion Hi. This air is in fact so hot that it aids the flame l3 in igniting the fuel in the portion l2 of the layer. Burning of the fuel proceeds as the grate travels and is complete when the rear edge of a wall [4 is reached. This wall is provided just above the surface of the layer I and forms one wall of the passage In so that no air passes longitudinally through the layer'directly from the portion l5 thereof to the portion 12.

It will now be seen that one portion of the incoming air passes through the layer 1 at a point where the burning or sintering is complete and immediately adjacent the burning or sintering zone and this portion of air, which is the hotter portion, is passed again through the layer at the ignition or burning and sintering zone. The other portion of incoming air is also first passed through the layer at a point where burning or sintering is complete but more remote from the burning or sintering zone and nearer to the discharge end of, the apparatus, and-this part of the air is again led through the layer in advance of the ignition zone to dry and preheat the incoming material.

The air thatpasses through the portions I 5 and [8 of the layer 1 cools the material to such an extent that both the pre-sintered and preburnt material in the layer 5 and the material in the layer 1 may be conducted directly to clinker silos or grinding machinery. The layers can easily be separated from each other'as the material in the layer 5 remains unchanged during the whole process and simply drops oi the rate as indicated at H, whereas the material in the layer 1 sinters together to form a compact mass which when its direction of travel is changed at the drum 3 drops off in large lumps I 8 I claim:

1. A process for burning cement or sintering similar raw materials which comprises forming a porous layer of a mixture of the raw material and solidfuel, passing hot gas through the layer to dry and preheat the material, thereafter igniting the fuel, and passing further gas through the layer by which the burning or sintering proper is carried on.

2. A process for burning cement or sintering similar rawmaterials which comprises forming a porous layer of a mixture of the raw material and solid fuel, igniting the fuel, passing gas through the layer twice, namely, first through the layer at a point where the burning or sintering is substantially complete so that the gas is thereby heated and then through the layer at a point in advance of that at which the fuel is ignited to dry and preheat the material, and

passing further gas through the layer by which the burning or sintering proper is carried on.

3. A process for burning cement or sintering similar raw materials which comprises forming a porous layer of a mixture of the raw material and solid fuel, passing hot gas through the layer to dry and preheat the material, and passing further gas through the layer by which the burning or sintering proper is carried on, said further gas being suificiently rich in oxygen and heated to a sufficiently high temperature to effect ignition of the fuel.

4. A process in accordance with claim 1 in which the ignition of the fuel is effected bya flame.

5. A process in accordance with claim 1 in which the gas for carrying on the burning or sintering is preheated and rich in oxygen and ignition of the fuel is effected by passing said gas by a. flame and directly thereafter passing it through the layer at the point where ignition is to begin.

6. A process for burning cement or sintering similar raw materials which comprises forming a, porous layer of a mixture of the raw material and solid fuel, igniting the fuel at a burning or sintering zone, passing gas through the layer at a zone where the burning or sintering is substantially complete to cool the layer and heat the gas, and passing the heated gas a second time through the layer at the burning or sintering zone.

7. A process for burning cement or sintering similar raw materials which comprises forming a porous layer of a mixture of the raw material and solid fuel, igniting the fuel at a burning or sintering zone, passing gas through the layer at a zone where the burning or sintering is substantially complete to cool the layer and heat the gas, and passing the heated gas a second time through the layer in advance of the burning or sintering zone to dry and preheat the material.

8. A process for burning cement or sintering similar raw materials which comprises forming a porous layer of a mixture of, the raw material and solid fuel, igniting the fuel at a burning or sintering zone, passing gas through the layer at a. zone where the burning or sintering is substantially complete to cool the layer and heat the gas, dividing said gas after its passage through the layer into two streams, namely, a stream that has passed through the'hotter portion of the layer adjacent the burning or sintering zone and a stream that has passed through a cooler portion of the layer more remote from the burning or sintering zone, passing the first mentioned stream a second time through the layer at the burning or sintering zone, and passing the last mentioned stream a second time through the layer at a point in advance of the burning or sintering zone to dry and preheat the material.

NIKOLAI AHLMANN.

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