EP0327650B1 - Apparatus to clear the flame area in a rotary drum furnace using direct heating, and arrangement and construction of the shovels - Google Patents

Abstract

The invention relates to a process to clear the coaxially running flame area of a directly fired rotary drum furnace (1) for drying and heating bulk material (5), in particular grain-graded mineral substances or granulates made of mineral substances and bituminous binders by means of shovels (3) which are arranged in the direction of rotation, are partially open to the inner circumference (2) of the rotary drum furnace (1) and the edge limits of which form scooping edges (3.5), as well as the design and arrangement of shovels (3) in a directly fired rotary drum furnace (1) with uniform separation over its inner circumference (2). Criteria of these inventions are a) the reduction of the degree of filling of the shovels (3), occurring at constant material feed, to a given filling volume which allows greater mobility of the material inside the shovels and thus promotes heat transmission by contact to the material; b) prevention of shovel emptying until quadrant II of the rotary drum furnace (1) is reached; c) the special design of the rear wall (3.1) of the respectively leading shovel (3) with an indentation forming a channel (3.2) which receives the discarded residual volume of the bulk material (5), avoiding development of spraying grain and d) the necessary free space for the development of the coaxially running flame area is produced. <IMAGE>

Description

The invention relates to a device for keeping the essentially coaxial flame region of a directly fired cylindrical rotary kiln for drying and heating bulk materials, in particular grain-graded minerals or granules from minerals and bituminous binders, by means of an approximately trapezoidal design, arranged in the direction of rotation, partially to the inner circumference of the rotary kiln open lifting vanes, the edge boundaries of which form scooping edges, the bulk material being picked up in the area of the fourth and first quadrants over the scooping edge of each lifting scoop and being released onto the rear wall of the leading lifting scoop as the rotary kiln continues to rotate in the direction of the outlet opening of the lifting scoop.

In LUEGER, Gesamtlexikon der Technik, roro edition 1972, volume 37, page 511, it is stated that the installations in drying drums have the purpose of mixing the material and distributing it evenly over the drum cross-section in small quantities.

A device of the type mentioned is known from BE-A 858 730.

Another version for keeping the flame area free is known for example from DE-PS 26 17 839. In a rotary kiln of this type, screw flights are provided in the feed area running parallel to the drum casing, which have overlapping boundaries, while the internals that follow later are approximately trapezoidal Shaped blades, which, viewed in the direction of rotation of the rotary kiln, raise the material relatively far, beyond the first quadrant, and thus enable good heat transfer as well as a large surface area for the addition of the dispersed binder.
Due to the profiles of the mixing area connecting the internals, the drum cross section is kept free of more or less controlled ejection of good particles, so that in this area of the drum there is a practically undisturbed heating gas flow, which on the one hand allows the mineral material to be brought together with the binder in a controlled manner and on the other hand enriches it of the gas flow with rock particles that have not yet been completely enveloped (see column 2, lines 39-55).

EP-A 48 952, page 5, shows a diagram of the discharge behavior of the material in a drum cross section equipped with angle profiles, which is to be regarded as the basis of the prior art.
There is no serious change if the free legs of the angles are angled briefly in the direction of the drum wall as a "trapezoid".

In summary, it should be noted that the current The internals used essentially have trapezoids or trapezoidal shapes, the leg located at the front in the direction of rotation of the drum not being connected to the wall, but rather leaving an inlet or outlet opening for the material to be heated.

In these conventional installations, a small part of the material falls through the flame area and prevents the flame from burning out, which is required by environmental regulations, and additionally pollutes the exhaust gas flow with entrained fines from the passage area.

Taking this into account, it is the object of the invention to design a device for keeping the flame area clear of falling bulk material in a cylindrical rotary tube furnace, and the arrangement and design of lifting blades in a directly fired, cylindrical rotary tube furnace for keeping a coaxially directed flame area free, with which the take-up is evened out and the spray grain development is prevented when the goods are handed over.

The object is achieved by the features specified in the main claim. Further refinements of the invention can be found in the subclaims.

When using the device according to the invention, the bulk material is picked up in the area of the fourth and first quadrants over the scooping edge of each lifting vane, while avoiding complete filling and reduction of the inlet cross-section by means of an installation or a baffle which engages in it and upon further rotation of the rotary kiln in the direction of the outlet opening of the lifting blades through the chicane, initially no emptying of the lifting blade contents takes place until the second quadrant of the rotary kiln is reached, while approximately at the beginning of the III. Quadrants of the bulk material occur with a delay on the rear wall of the leading lifting vane, each of which is provided with a channel-shaped indentation, which takes up the remaining volume of the previous lifting vane and prevents the spray grain development and in the further decline down to the fourth quadrant, approximately coaxially with the radius of the lifting vane limit , emptied.

The restriction of the degree of bulk filling of the lifting bucket due to the installation or the chicane, with a uniform supply of material, ensures a uniform pick-up and thus an increased mobility of the bulk material within the heated lifting bucket. Associated with this is an increase in heat transfer through movement,
by exchanging the goods with the contact surfaces of the lifting blade. Until the second drum quadrant is reached, there is initially no emptying of the blades - at least not to a considerable extent - and only when the goods enter III. Quadrants use the outlet delayed by the intended chicane, which is received by the groove-shaped bulge of the rear wall of the leading lifting blade, the spray grain development being prevented due to the shape of this bulge.

To keep a coaxially directed flame area free from falling bulk material, it is further provided that each lifting vane, with its rear wall attached to the inner circumference of the drum wall, has a trough-shaped indentation which, starting from the tangent to the fastening line, points with about a third of its radial extent and in the direction of rotation , 10 - 20 ° angled and bent back at approximately the same angle with about two thirds of the radial extent, the two mutually directed folding planes forming the side surface of a channel that the rear wall then merges into the bottom of the lifting blade, which is about 90 ° with a width of more than 50% related to the unwinding length of the rear wall is such that the bottom is transferred into a further section which is angled outward by approx. 135 ° and which transitions into the scooping edge at an angle of 150 ° in its upper boundary , and that between the scoop edge and the inner circumference of the drum wall, an installation for the bulk material is arranged, the distance between the installation and the scoop edge being approximately one third of the length between the fastening line of the rear wall and the radian measure formed perpendicular to the line of the scoop edge.

The formation of the lifting vane wall in the context of a uniform process, which includes the rear wall with a channel or bulge, the adjoining floor, which leads into an upwardly angled section and which forms a scooping edge in its upper edge, slightly angled backwards rational prefabrication of these internals.

The chicane arranged within the lifting vane boundary comprises various embodiments. Thus, it can be provided that the chicane is an equal or unequal leg angle profile with its legs on the inner circumference, or has another suitable cross section.

From the multitude of possible lifting vane arrangements within the rotary kiln, it should only be pointed out that the lifting vanes, for example, are arranged offset with respect to the circumference and the length of the rotary kiln and delimited on both sides by cover plates, or that these are arranged in rows with different center distances continuously on the inner circumference of the rotary kiln and are each provided with a cover plate that closes at the end.

Of course, the lifting blades can be adapted to the requirements of the process in a wide range.

Figur 1

stellt einen partiellen Schnitt durch die Quadranten II und III eines rechtslaufend angetriebenen Drehrohrofens dar.

Die Figuren 2 und 3

zeigen aus der Vielzahl der Anordnungsmöglichkeiten der Hubschaufeln im Drehrohrofen zwei Ausführungsbeispiele.

The method according to the invention, as well as the arrangement and design of the lifting blades are explained for example by the accompanying drawings.

Figure 1

represents a partial section through quadrants II and III of a right-handed rotary kiln.

Figures 2 and 3

show two embodiments from the variety of arrangement options of the lifting blades in the rotary kiln.

The rotary kiln 1 is equipped over the area of its circumference and its functional length either with offset staggered lifting blades 3 or provided with lifting blades 3 arranged in a row and in a gap (FIGS. 2 and 3).

In the first case (Figure 2), the lifting blades 3 are closed at the end of the inclined rotary kiln 1 by a cover plate 1.1, while in the second case (Figure 3) the lifting blades 3 are arranged in rows, each lifting blade 3 being closed at both ends by a cover plate 1.1 .

In the lifting blades 3, an installation reducing the filling volume of the lifting blades 3 or a baffle 4 is arranged at an approximate distance of a third of the length of the arc dimension formed between the fastening line of the rear wall 3.1 and the perpendicular to the line of the scooping edge 3.5, which also the emptying speed of the bulk material 5 is delayed out of the lifting blades 3.

The cross section of the lifting blades 3 is determined by the shape of the rear wall 3.1, which, starting from the tangent to the fastening line, has approximately one third of its radial extension (3.11) and in Direction of rotation is angled 10 to 20 ° and is bent back at approximately the same angle with about two thirds of the radial extent (3.12), the two mutually directed buckling planes forming the side surface of a channel (3.2), the rear wall 3.1 subsequently being in the floor 3.3 the lifting vane 3 merges, which is angled by approximately 90 ° with a width of more than 50% related to the unwinding length of the rear wall 3.1, the base 3.3 transferring into a further section 3.4 angled outwards by approximately 135 °, the in its upper boundary with an angle of 150 ° into the scooping edge 3.5.

From II. Quadrants of the rotary kiln 1, a discharge of the material 5 taking place parallel to the drum periphery over the scooping edge 3.5 takes place to a limited extent, while approximately at the beginning of III. Quadrant the bulk material 5 hits the rear wall 3.1 of the leading lifting blade 3 with a delay and is initially received here by the groove-shaped indentation 3.2. This leading lifting vane 3 thus takes up the remaining volume of the trailing lifting vane 3 in its trough-shaped indentation 3.2 and gives this in the further decline via the III. down to the fourth quadrant - roughly coaxial to the radius of the lift paddle boundary.

This ensures that the essentially coaxially directed flame region is kept free from grain falling through the flame, so that it is not carried away by the exhaust gases.

Thermal overload of the granules is also prevented.

Claims (5)

1. Apparatus for clearing the substantially coaxially extending flame area of a directly heated cylindrical rotary drum furnace (1) for drying and heating bulk material (5), especially mineral materials in graduated grain sizes or granulates of mineral materials and bituminous bonding agents, using trapezoidal shovels (3) which are arranged in the direction of rotation, which are partially open towards the inner circumference (2) of the rotary drum furnace (1) and whose limiting rims form scooping edges (3.5), with the bulk material (5), in the region of the quadrants IV and I, being received via the scooping edge (3.5) of each shovel (3) and, upon further rotation of the rotary drum furnace (1), being released in the direction of the outlet aperture of the shovel (3) on to the rear wall (3.1) of the preceding shovel (3)
   characterised in
   that an insert (4) is arranged in the running-in cross-section of the shovel (3); and
   that the rear wall (3.1) of the shovel (3) is provided with a channel-shaped indentation (3.2).
2. Apparatus according to claim 1,
   characterised in
   that the rear wall (3.1) fixed to the inner circumference (2) of the drum wall comprises a channel-shaped indentation (3.2) which, starting from the tangent on the fixing line and over approximately one third of its radial extension (3.11), is angled by 10 to 20° pointing in the direction of rotation and over approximately two thirds of its radial extension (3.12), bent back at approximately the same angle, with the two bent planes facing one another forming the side face of a channel (3.2);
   that the rear wall (3.1) subsequently changes into the base (3.3) of the shovel (3), which base, with a width of more than 50% with reference to the developed length of the rear wall (3.1), Is angled by approximately 90° from the latter; that the base (3.3) changes into a further portion (3.4) which is angled outwardly by approximately 135° and which, in its upper limiting rim, changes into the scooping edge (3.5) at an angle of 150°; and
   that between the scooping edge (3.5) and the inner circumference (2) of the drum wall, there is arranged an insert (4) for the bulk material (5), the distance between the Insert (4) and the scooping edge (3.5) amounting to approximately one third of the length between the fixing line of the rear wall (3.1) and the arched dimension (3.6) formed perpendicularly relative to the line of the scooping edge (3.5).
3. Apparatus according to any one of the preceding claims,
   characterised in
   that the insert is formed by an equal-sided angle section whose sides are positioned on the inner circumference.
4. Apparatus according to any one of the preceding claims,
   characterised in
   that the shovels (3) are arranged so as to be offset across the circumference and along the length of the rotary drum furnace (1) and limited by cover plates (1.1) on both sides.
5. Apparatus according to any one of claims 1 to 3,
   characterised in
   that the shovels (3) are arranged continuously on the inner circumference of the rotary drum furnace (1) in rows with different axial distances and that they are each provided with a cover plate (1.1) closing their ends.

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