DK141992B - PROCEDURE FOR THERMAL TREATMENT OF A FINE CORN MATERIAL FOR BURNING CEMENT IN MULTIPLE STEPS - Google Patents

Description

(11) PUBLICATION REPORT 1 U 1 992 DENMARK (S ”lnt cl · 'c 04 B 7/44 § (21) Application no. 1509/76 (22) Filed on 51 Mar · 1976 (23) Running day 51 Mar. I976 (44) The application presented and the petition published on 4 Aug · 1 980

DIRECTORATE OF

PATENT AND TRADEMARK (3 °) priority requested from it

Apr 21 1975, 2517552, DE

(71) KXOECKNER — HUMBOItDT — DEUTZ SHAREHOLDERS> LSCHAFT, Deutz-Muelheimer-Strasse Ti 1, 5 Cools 80, DE.

(72) Inventor: Kunibert Brachthaeuser, An der Schmitten 18, 506 Bensberg, DE: Hubert Ramesohl, MoEnweg 22, 506 Bensberg-Refrath, DE: Klaus Beisner, Holunderweg 9, 5062 Hoffnungsthal, DE: Horst Herchenbach, SleTengebirgs-allee 15, 521 Troisdorf, DE.

(74) Plenipotentiary in the proceedings:

Hofman-Bang & Boutard engineering firm. (54) Process for thermal treatment of a fine-grained material by multi-stage cement burning.

The invention relates to a method of the kind set forth in claim 1.

In the conventional methods for the thermal treatment of cement feedstock by burning cement, the cement feed is preheated in a fluidizing gas heat exchanger to approx. 800 ° C, after which the material is introduced into the oven, usually a rotary oven. In such a process, the cement barrel in the heat exchanger is calcined to 35-4-0 ^. This means that approximately half of the rotary kiln must be used for final calcining of the material, while the other half of the furnace serves to sinter the material. Thus, in the preheater, only a small part of the total heat energy is transferred to the material, while by far the largest part of the heating work must be carried out in the rotary kiln. For installations with high performance in the unit of time, due to the unequal distribution of heat work in the rotary kiln, its thermal efficiency and performance will be limited. Also, the durability of the refractory casings in the stove's firing zone is significantly reduced, so that not only the investment cost but also the cost of maintaining the rotary kiln is disproportionately high.

The further development of modern heat exchangers and heat exchange methods is based on allowing the feedstock particles to float in the hot gas and calcining them as far as possible in a separate preliminary burning zone in the floating gas heat exchanger, whereas the material sintering is carried out later in the rotary kiln.

Such a newer heat exchanger or heat exchange method is known from DE Publication No. 23 24 519. The operation of this known heat exchanger with pre-calcining apparatus is explained in the publication "Zement Data Book",

Bauverlag GmbH, Wiesbaden, 1976, page 355, column 1, second paragraph: "That the cement feed introduced into the heat exchanger is pre-calcined to 90-96% at an air excess number of approximately 2.05".

Furthermore, the "Zement Data Book" states that using a so-called "Moment calcining chamber", the raw flour can be calcined up to 90% (SF process).

In this heat exchange method, a conventional heat exchanger interacts with a fluidized bed calciner (MFC method). In this process, the raw flour is acidified in the separately heated fluidization reactor interposed between the cyclone heat exchanger and the rotary kiln, so that the work in the rotary kiln itself is limited to the actual sintering process in the same way as in the "SF process", ie. that at least 90% of the raw flour is calcined in the reaction in the fluidizing bed.

In all cement plants of the latter type with floating gas heat exchanger, rotary kiln and with a supplementary zone for preliminary burning of the material between them, the cement raw flour is pre-calcined to above 70% and as far as possible up to 90-95%, cf. eg. German publication publication 23 44 056.

, 141992 3

In the various known heat exchanger systems with pre-calcining devices, the raw flour introduced into the preheater can be calcined almost completely in the separate combustion zone.

However, within this roasting zone, the desired maximum temperature is uncontrollably exceeded so that the rice-resistant, powdery material, upon initial formation of coarser granules and incipient plasticity due to melt phase formation, enters an undesirable state, whereby a proper flow of the calcined material from the preliminary burn zone and into the rotary kiln can no longer be secured. This applies to all calcination grades above 70%. This defect is due to the fact that the acidification of a lime particle is mainly dependent on three parameters: I. The deacidification temperature, II. Particle residence time in the combustion zone, III. The particle size.

Only within narrow boundaries can the grain size and grain size distribution of an industrially produced raw material be changed. The production of cement flour with only one grain size is not possible. Furthermore, agglomeration processes in the heat exchanger cannot be avoided.

The residence time of the particles at the calcination stage of a fluidization gas heat exchanger cannot be extended for more than up to a few seconds. However, the coarse fraction of the flour requires, at a temperature of 850-900 ° C, an acidification time which is at least the power factor 10, ie. an order of magnitude longer than these few seconds there. A recirculation of the large, yet un-acidified particles would require their separation from the fine material fraction of the over 800 ° C heat, which is not achievable for energy consumption.

Thus, a high degree of calcination of more than 70% in the known systems of heat exchangers and pre-calcination devices can only be achieved by increasing the deacidification temperature above 900 ° C, however, whereby the waste of heat with the waste gas becomes disproportionately large.

4 141992

In the prior art, as mentioned above, the maximum temperatures for the material are exceeded in the pre-calcination part of the plant, as the material loses its scratching ability as mentioned.

It is an object of the present invention to reduce the specific investment cost of a rotary kiln as a sintering kiln by heat treating cement raw materials by a method of the kind set forth in claim 1 *, and to avoid the generally known difficulties of deacidification of the cement kiln in a pre-heater and located in the rotary kiln for preliminary burning of the material, namely the difficulty of keeping the material in a rice-resistant state, in which it can be properly transferred to the rotary kiln without stopping due to the clumping of the material particles. These two objectives are achieved by the two measures specified in the characterizing part of the main claim. Due to the continued ability of the material to disperse finely in the hot gas stream, an optimal heat transfer from the hot gas to the material particles is achieved. This avoids the formation of clinker minerals and alkali vapors and the risk of material deposits in the pre-calcination apparatus.

According to the invention, the preheated material can be de-acidified to a degree of de-acidification of 60%. Hereby an optimization of the advantages of the process is achieved as far as there is a reduction in the amount of fuel needed to carry out the separate preliminary calcination process, thereby reducing the heat losses with the waste gas and reducing the total heat consumption in the plant.

In the embodiment according to claim 3, the following advantages are obtained: When the furnace flue gas e.g. contains 8-13% of oxygen, and when the degree of acidification in the separate calcination process is set to just over 50%, the oxygen content of the flue gas will usually be sufficiently large for stoichiometric combustion of the required amount of fuel so that supplementation of supplemental oxygen is not necessary. At the same time, at this degree of calcination, the exothermic high temperature zone in the rotary kiln is relieved so much that the durability of the refractory wall in this zone of the rotary kiln is substantially increased.

5 141992

By the measure of claim 4, it is achieved that the combustion of the fuel supplied starts immediately when the ignition temperature is reached and that the distribution of the fuel in the material and gas flow is not to be expected first. On the contrary, combustion begins during the distribution of the material in the gas stream.

Because of this measure, the firing zone can be kept particularly small and the degree of deactivation correspondingly exactly adjusted as needed.

Finally, in the embodiment according to claim 5, the total amount of fuel is lit before the fuel is introduced into the material stream, so that the firing zone can be designed far independently of the material stream. In this way, even and controlled combustion is ensured with a particularly good utilization of the fuel, thereby promoting the desired partial calcination of the cement raw material.

In the following, the invention is explained in more detail with reference to the drawing, in which fig. 1 is a schematic, partly side view and partly in vertical section, showing an embodiment of a plant for carrying out the method; and FIG. 2 shows another embodiment of the plant.

In FIG. 1, the material supply end portion of a rotary kiln 1 shown in relation to the other parts of the plant is shown with a material inlet chamber 2, in which a material supply line 3 from a lower cyclone 4 in a heat exchanger, which in addition to the cyclone shown, includes several superimposed and in series coupled cyclones, however not shown in the drawing. From the cyclone 4, a flue gas line 5 leads to the other cyclone preheat stage of the heat exchanger. The cyclone 4 is connected to the rotary furnace 1 by means of a substantially gas-upwardly directed smoke gas conduit 6, into which a material supply conduit 7 and a fuel supply conduit 9, which preferably open into the flue gas conduit 6, flows through one or more nozzles located above it. where the material supply conduit 7 opens into the flue gas conduit 6 having a portion which extends upwardly and serves as a pre-oxidation chamber 8 against which the orifices of the fuel nozzles are directed obliquely downwards, i.e., opposite to the gas flow up through the flue gas conduit 6. Instead for only one lower cyclone 4, several symmetrically located cyclones can be found. · In that case, instead of only one conduit for cyclones 4, the flue pipe 6 has one corresponding to the number of tubes of the cyclones.

In the following, the method according to the invention is explained by means of Fig. 1.

From the rotary furnace 1, the flue gas passes into the material inlet chamber 2, from which the flue gas flows up through the flue gas line 6 and into the first, lower cyclone of the heat exchanger 4. The material to be burned is introduced through the conduit 7 into the flue gas line 6 below the burners 9. The material may be desired. is supplied through only one or more wires, the outlet of which is provided with distributing means for evenly distributing the flow of material into the gas stream. As distribution means, e.g. baffles or guitars are used.

f

The material in the gas stream evenly and finely distributed is fed by the gas upwards in the flue gas line 6, reaching in the form of a continuous, uniform stream of material and gas into the firing zone at the level of the plane of the burner nozzle openings. As mentioned, the burner nozzles are directed downwardly towards the material and gas flow to ensure a good penetration of the fuel into said flow. Downwards, the firing zone is precisely bounded by the burner plane. while the boundary of the firing zone is reached upwards by appropriate setting of the flame. Due to the simple form of the pre-oxidation compartment, advantageous firing conditions can be provided, under which the material particles each pass the firing zone only once, so as to be able to precisely adjust the degree of acidification of the preheated material to the desired value between 50 and 70%, preferably 60%.

However, the method is also applicable in connection with the one shown in FIG. 2, inserted between the rotary furnace 1 and the material preheating heat exchanger. Here too, the material inlet end of the rotary furnace is through one of it initially beginning with vertically upward flue gas line 6 in connection with cyclone 7 14. In Fig. 2, the material supply pipe 7 in the flue pipe 6 opens above burner nozzles 9, the vertical distance between the level of the fuel being introduced through the nozzles 9 ' and the place where the material is supplied through the conduit 7 is selected so large that no material introduced through the conduit 7 into the flue gas conduit 6 can reach down to the burn zone. In this way, an exact desired setting of the degree of acidification of the preheated material can be obtained.