RU2383836C2 - Rotary kiln internal heat exchanger - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: invention relates to calcination of stock, for example oil or pitch coke, or hard coal in rotary kilns. Proposed device comprises heat exchange elements to mix up material. Said elements represent tooth with triangular part extending beyond kiln lining, triangle larger side being oriented in direction opposite to kiln unloading face. Angle between triangle larger side and adjacent sides makes at least 45°. Said tooth are located in the kiln material heating zone and arranged staggered in parallel rows relative to each other and adjacent sections.

EFFECT: higher efficiency and expanded operating performances.

3 cl, 3 dwg

Description

The invention relates to a process technology for firing raw materials, for example, “raw” coke, in rotary kilns, and can be used, for example, in the metallurgical industry in the production of anode mass for self-burning anodes of aluminum electrolytic cells, in the production of refractory materials, as well as in the electrode industry.

Known internal heat transfer device of rotary kilns, which is a curtain in the form of steel chains attached at one end to the lining of the furnace or at both ends, forming a chain of "garlands" [1, 2].

The disadvantages of the known heat exchange device are a significant increase in dusting of the material and, consequently, an increase in dust removal from the furnace, as well as a decrease in the service life of the lining. Another disadvantage can be considered the inability to use the device in the high temperature zone of the furnace, namely in this zone, the heat transfer process to the greatest extent affects the efficiency of the furnace. During the operation of the furnace, quick wear of the chains occurs.

Known internal heat transfer device of rotary kilns, which is located along the length of the furnace heat exchange elements attached by bases to its inner surface and made in the form of trough-shaped blades articulated at the base with a convex surface facing the gas stream [3].

A disadvantage of the known heat exchange device is the inability to use the device in rotary kilns of the aluminum industry, since it has a rather complex structure. The structure is made of metal and welded to the lining, which is unacceptable under the existing temperature conditions of rotary kilns for calcining the material and the physical and chemical processes occurring in them.

Closest to the technical nature of the present invention is an internal heat exchanger of rotary kilns of the aluminum industry, lined with refractory bricks, with loading and unloading ends, including heat exchange elements for mixing the material. The heat exchange elements are brick shelves installed in two rows in the calcination zone of the furnace on a 6.7 m long section and designed to intensify the heat exchange of the material with the gas stream and lining [4].

The prototype device has the following disadvantages.

Brick shelves made in the form of protrusions in the lining of a rotary kiln and located directly in the calcination zone are subjected to significant thermal and mechanical stress, which is the reason for their rapid wear. This leads to a significant increase in the cost of the lining of the furnace calcination zone, which in itself is the weak point of the lining of the rotary kiln as a whole and requires frequent repairs. The inevitable destruction of the lining leads to contamination of the product with silicon oxide. Fragments later also pass into the anode mass and degrade the quality of the anode.

Another drawback of brick shelves is their shape, which contributes to a significant increase in dust entrainment from a rotary kiln. When the shelves move through the material layer, some of it is captured by the side wall of the shelf and begins to rise with it as the rotary kiln rotates. Further, this material reaches the upper part of the rotary kiln, slides off the side wall of the shelf under the action of gravity and enters the gas stream, is picked up by it and leaves the rotary kiln together with the exhaust gases. Moreover, dust entrainment often amounts to a value comparable to the productivity of a rotary kiln.

In addition, it should be noted that the prototype device does not contribute to the active mixing of the material and the change in particle size distribution along the layer height, and these technological factors negatively affect not only the quality of the finished product, but also reduce the productivity of the rotary kiln.

The objective of the invention is to increase the productivity of a rotary kiln, improve the heat engineering parameters and increase the dust suppression ability.

The technical result that can be obtained using the proposed device is to intensify the process of mixing the material, its heat transfer, to increase the reliability of the rotary kiln and the durability of its lining.

This goal is achieved by the fact that in the internal heat exchanger for rotary kilns of the aluminum industry, lined with refractory bricks, with loading and unloading ends, including heat exchange elements for mixing the material, according to the claimed solution, the heat exchange elements are made in the form of teeth with a base in the shape of a triangle, the big side which is oriented in the opposite direction to the discharge end of the rotary kiln, and the angle between the larger side and adjacent to it is at least 45 °, and the heat exchange elements are located in areas in the material heating zone in the rotary kiln in parallel rows in a checkerboard pattern relative to each other and neighboring sections.

The device is complemented by private distinctive features aimed at solving the problem.

The heat exchange elements are located in two sections in four parallel rows in each section, in a checkerboard pattern, with five teeth in two opposite rows, and four teeth in the other two.

The sharp corners of the teeth of the heat exchange elements are cut to avoid chipping during operation of the furnace.

The essence of the invention lies in the fact that the design of the heat exchangers and their configuration in the furnace are designed in such a way as to ensure the maximum possible mixing of the material as it moves in the furnace, thereby ensuring the intensification of heat transfer while minimizing dust formation.

With active mixing of the material, its particle size distribution and temperature are aligned with the height of the layer, high dust-suppressing ability of heat-exchange elements is provided to prevent dust removal from the furnace and reduce its productivity.

A comparative analysis of the features of the proposed solutions and the characteristics of analogues and prototype indicates that the solution meets the criterion of "novelty."

In Fig.1 shows a diagram of the installation of heat exchangers in the furnace, Fig.2 - scan of the furnace with the location of the heat exchange elements on it, Fig.3 - the shape of the tooth of the heat exchange element.

The proposed internal heat exchange device of a rotary kiln 1 with bandages 2 and a ring gear 3 installed on it consists of separate heat exchange elements 4, the bases of which are part of the overall lining of the furnace. The heat exchange elements 4 are made in the form of teeth made with bases in the shape of triangles. The large sides of which are directed so that when the rotary kiln rotates, the material falling on them is discarded in the direction opposite to its movement. The lateral side of the tooth of the heat exchange element is at an angle to the moving flow of material. Inside the rotary kiln, the heat exchange elements are located in two sections of the lining 5 (Fig. 1) located in the heating zone of the material, in four parallel rows in each section at an angle of 90 ° to each other (Fig. 2). The teeth of the heat exchange elements in rows in the direction of rotation of the rotary kiln are staggered and distributed evenly along each section. In two opposite rows, 5 teeth are located, in the other two - 4 teeth. The location of the heat exchange elements directly in the calcination zone would lead to a significant reduction in their service life due to high temperatures and the mechanical impact of the material on them, and this is associated with additional costs for replacing the lining.

A specific example of the installation of heat exchange elements in two areas is given. The number of sections, heat exchange elements and their number may vary depending on the design characteristics of rotary kilns.

When the rotary kiln 1 is operating, the heat exchange elements 4 are immersed in the material layer and moved in it as the kiln rotates. At the same time, the material moves between parallel rows alternately around the circumference of the rotary kiln and at an angle relative to the generatrix of the kiln and the moving material is discarded to the loading end of the rotary kiln (against the movement of the material), which helps increase the residence time of the material in the rotary kiln.

When the furnace rotates, the teeth of the heat exchange elements move through the layer of material and its main layer is divided into pulsating flows. Moreover, given the complex arrangement of heat exchange elements in parallel rows around the circumference, accelerated multi-threaded movement of the material is observed, which contributes to an increase in the chord of the segment and the area of the material layer, and the presence of a variable layer shape helps to intensify the mixing process, evens out the temperature of the material in the layer, which ensures a decrease in heterogeneity in calcining small and large material, improving heat transfer and increasing productivity of a rotary kiln.

In the proposed heat exchange device, the heat exchange elements are made of refractory reinforced concrete (figure 3). The lower part of the heat exchange element is part of the overall lining, therefore, made in the form of a trapezoid. Inside the brick there is a metal anchor to give strength to the tooth of the heat exchange element. The sharp corners of the tooth are pre-cut to avoid chipping when exposed to temperature and mass of material. In addition, at the teeth of the heat-exchange elements, the angle between the larger side and adjacent side is at least 45 °, which ensures a delay of the material in the rotary kiln for a while, and at the same time there is active impulse-supporting mixing. In this case, there is a positive effect of this angle on the dust suppression ability. It was found that a significant reduction in dusting of the material is achieved when the angle of inclination of the side of the tooth of the element is not less than 45 ° to the material flow.

Literature

1. Khodorov E.I. Furnaces of the cement industry. - L .: Publishing house of building literature, 1968.

2. Khodorov E.I. The movement of material in rotary kilns. - M .: Promstroyizdat, 1957.- 64 p.

3. RF patent No. 2035022. M.cl. F27B 7/18, 1995.

4. V.G. Lisienko, Ya.M. Shchelokov, M.G. Ladygichev. Rotary kilns: heating technology, management and ecology. - M.: Heat engineer, 2004 .-- 592 p.

Claims (3)

1. The internal heat exchange device of rotary kilns lined with refractory bricks and made with loading and unloading ends, including heat exchange elements for mixing the material, characterized in that the heat exchange elements are made in the form of teeth with a triangle-shaped protruding part of the lining, the larger side of which is oriented in the opposite direction to the discharge end of the rotary kiln, and the angle between the larger side and adjacent to it is at least 45 °, and the heat exchange elements you are arranged at sites in the preheating zone the material in the rotary kiln parallel rows staggered relative to each other and adjacent sections. 2. The internal heat exchange device according to claim 1, characterized in that the heat exchange elements are arranged in two sections in four parallel rows in each section in a checkerboard pattern, with five teeth in two opposite rows and four teeth in the other two. 3. The internal heat exchange device according to claim 1, characterized in that the sharp corners of the teeth of the heat exchange elements are cut to avoid chipping during operation of the furnace.

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