JPH04345687A - Indirect heating rotary dryer for powder - Google Patents

Abstract

PURPOSE:To reduce the maximum bending stress of a heating pipe at points at which it is supported with support plates to thereby make it possible to prolong the life of the heating pipe by increasing the wall thickness of at least the heating pipes arranged in an innermost circular line only at one or more parts thereof near the support plates. CONSTITUTION:An indirect heating rotary dryer for powder, having heating pipes arranged in multiple lines in the form of concentric circles inside a rotating cylinder and supported with a plurality of support plates vertically arranged in ring form inside the rotating cylinder, wherein at least the heating pipes arranged in the innermost circular line have an increased wall thickness only at one or more parts thereof near the support plates. For example, the part 1a of the heating pipe 1, with a total length l1 including portions on both sides of a support plate 13, has a wall thickness t2; l2 is the length of a graded part. When welding is made at a point A at which the bending stress (a) of the pipe 1 in the lengthwise direction equals zero on the way of changing from plus (tension) to minus (compression), a breakage from a welded spot can be prevented, and the stress at a supported point can be greatly reduced by a slight increase in the weight of the pipe as a whole.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an indirect heating type rotary dryer for powder and granular materials.

0002

[Prior Art] Generally, a multi-tube bundle rotary dryer using steam is used as an indirect dryer for powder and granular materials [Chemical Engineering Society of Japan, "Chemical Engineering Handbook", May 20, 1972,
Maruzen Co., Ltd., p. 569 ; “Drying device” edited by Ryozo Kiri
June 25, 1972, Nikkan Kogyo Shimbun, p. 137]
. As shown in FIGS. 2 and 3, a large number of heating tubes 1 are arranged concentrically inside a rotating cylinder or drum 10.
When the rotary drum 10 is rotated, the granular material 14 inside rotates and flows, and at this time, the granular material is dried by heat transfer from the heating tube. The granular material 14 is supplied to the supply section 11 in FIG.
The liquid enters the tank and exits through the discharge section 12.

Further, as shown in FIG. 3, the heating tube 1 is supported in its longitudinal direction by a number of support plates 13 that are erected in a ring shape on the inner periphery of a rotating cylinder. Therefore, the heating tube 1 corresponds to a "continuous burr" that is subjected to the force F due to the flow of the powder material 6 shown in Fig. 2, and its bending moment diagram is approximately as shown in Fig. 4, with the maximum at the support plate part. becomes.

0004

[Problems to be Solved by the Invention] In the heating tubes of the conventional indirect heating type rotary dryer, the heating tube 1e (shown in FIG. 2) located closest to the center is directly hit by the flow force, and the maximum bending moment (i.e., bending Failure may occur at the support point where stress is generated. As a countermeasure against this problem, there is a method of increasing the section modulus of the heating tube 1e, that is, increasing the diameter and/or thickening the tube. However, enlarging the diameter of the existing equipment means enlarging the hole in the support plate of the heating tube, which is not practical from the viewpoint of construction and the strength of the support plate. Therefore, the method of increasing the thickness is taken, but since materials with high strength, wear resistance, and corrosion resistance, and therefore high prices, are generally used for heating tubes, it is necessary to increase the thickness uniformly over the entire length. is not economical. Furthermore, the increased weight due to the thicker overall length not only causes inconvenience in handling during modification, but also increases the rotational load on the drum.

The object of the present invention is to provide an indirect heating type rotary dryer for powder and granular materials, which solves all of the above-mentioned problems at once.

[0006]

[Means for Solving the Problems] The present invention provides a plurality of heating tubes arranged concentrically in multiple rows inside a rotating cylinder, and a plurality of heating tubes erected in a ring shape on the inner periphery of the rotating cylinder. In an indirect heating rotary dryer for powder and granular materials supported by a support plate, the wall thickness is increased at least in the vicinity of the support plate at one or more locations of the heating tubes arranged in the innermost row. This is an indirect heating type rotary dryer for powder and granular materials, preferably in which the thick and thin parts of the heating tube are welded at a position where the bending stress is approximately 0, and more preferably in the A tapered tube section whose wall thickness changes continuously from a thick section to a thin section is separated from the heat affected zone of the welded section.

[0007]

[Function] According to the present invention, the outer diameter of the heating tube near one or more support plate portions located at least on the innermost circumferential side is made thicker than other parts without changing the outer diameter of the heating tube. The present invention can be applied without any modification to the support plate of the rotating drum, and if the present invention is applied to the heating tube on the innermost circumference of the rotating drum, where the largest bending moment occurs due to the flow force of the powder or granular material,
The maximum bending stress at the point where the heating tube is supported by the support plate can be reduced, and the life of the heating tube can be extended.

[0008] Furthermore, the material cost is lower than in the case where the entire heating tube is made of a thick-walled tube, and the increase in rotational load due to the increase in the weight of the rotating drum can be reduced. In addition, the outside diameter is the same as that of other heating tube sections, with a thick wall section in the center, a sloped section (tapered tube section) where the wall thickness changes continuously from thick wall to thin wall on both sides, and thin wall section at both ends. By welding a pipe with a fleshed part to a thin-walled pipe, for example, at a point where the calculated bending stress becomes 0, the present invention can be easily applied to an existing rotary dryer, and the welded part can be welded. This is desirable because the stress applied can be substantially reduced and no damage will occur from the weld.

Furthermore, separating the sloped part (tapered pipe part) where the wall thickness changes continuously from thick to thin from the weld heat affected zone reduces stress concentration in the tapered pipe part and the effect of welding (residual This is desirable because it prevents damage caused by stress, etc.).

0010

[Embodiment] An embodiment of the present invention will be explained with reference to the drawings. FIG. 1(a) is a sectional view of a main part of an embodiment of the present invention. In this figure, 13 is a support plate that supports the heating tube. The heating tube portion 1a having a total length of l1 on both sides of the supporting plate 13 is made to have a wall thickness of t2.

[0011] The length l1 is preferably shorter than the length l5, which will be described later, and specifically, it is desirable that the tapered pipe portion be sufficiently separated from the heat-affected zone of welding. l2 is the gradient length. If the thickness of the thin wall portion 1b of the heating tube is t1, then l2 is more than three times the difference in wall thickness (l2 ≧3×(
It is desirable to set it to t2 - t1 )). Also, Figure 1
(b) shows the distribution of bending stress σ in the longitudinal direction of the heating tube 1. From this, since there are points A on both sides of the support plate 13 where the bending stress σ always becomes 0 while changing from + (tension) to - (compression), the length between both points A (=l5) A thick-walled pipe 1a is prepared and welded to a thin-walled pipe 1b at point A.

FIG. 5 shows a comparison of the axial stress distribution σ on the lower surface of the heating tube when the thickness t1 of the thin wall portion is constant and the thickness t2 of the thick wall portion is varied. The axial stress σ at the support point is reduced by increasing the thickness of t2. At this time, the "point where stress is 0" A remains almost unchanged. Also, Figure 5
In this case, the gradient was set to 3×(t2 - t1), but there is almost no stress concentration on the gradient part.

FIG. 6 shows a comparison of the stress between the partially thick-walled pipe of the present invention and the case where the entire length is made of a thick-walled pipe. This shows that there is almost no difference between the two in terms of the overall level as well as the maximum stress (at the support plate). As described above, in the present invention, the heating tube near the support plate is made thicker, the other parts are made thinner, and the welding point is brought to the point where the stress becomes 0, thereby preventing damage from the welding point. In addition, the stress at the supporting points can be significantly reduced with a slight increase in overall weight.

[0014] Incidentally, the conventional diameter is 2.8 m and the length is 21 m.
m indirect heating type rotary dryer for coal, the outer diameter of the heating tube closest to the center is 65A, the pitch of the support plates is 3.0m,
The thickness of the heating tube was uniformly t1 = 2.5 mm, while the material of the heating tube according to the embodiment of the present invention was the same as before.
Thickness of thin part t1 = 2.5mm, thickness of thick part t
2 = 5.5mm, gradient length l2 = 20mm
, thick wall length l1 = 800mm, length between welding points l
5 = 950mm (calculated value), operated under exactly the same conditions as before, and compared the stress at the support point by measuring strain on the heating tube.
It was found that the stress decreased significantly at a stress value of %.

[0015] Furthermore, the absolute value of the stress value at the welding point is 0.32.
kgf/mm2, and this stress value is so small that it can be ignored. In this example, the lengths l1 and l in FIG.
The above values were used for 2, l3, l4, and l5, but these may be determined based on the shape and dimensions of the dryer, the supply rate of powder and granular material, the rotation speed of the rotating drum, etc. Further, although the present invention is applied only to the innermost heating tube, it may be applied to heating tubes at other positions. Where the wall becomes thicker,
All the support plate parts may be used, or if the flow of powder or granules is particularly poor,
It may be sufficient to have only one or two locations on the supply side where it is easy to accumulate.

[0016]

[Effects of the Invention] The present invention thickens only the area near the support plate without changing the outer diameter of the heating tube, and the welding point is placed at a location where the stress value in the axial direction of the heating tube becomes 0. produce an effect. (1) It was possible to reduce the stress value at the support point, eliminating damage to the heating tube.

(2) Since there is no need to enlarge the holes in the support plate, there are no problems with construction or strength of the support plate when modifying existing equipment. (3) Weight increase is slight due to thickening of parts. (4) The weight increase is small, and it is relatively inexpensive compared to full-length thick-walled. (5) The weight increase per piece is small and handling is easy.

(6) The overall weight increase is small and the rotational load on the rotating drum is small.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of the present invention and an axial stress distribution diagram on the lower surface of a heating tube in the vicinity of a support plate.

FIG. 2 is a sectional view of a rotating drum.

FIG. 3 is a side view of the rotating drum.

FIG. 4 is a bending moment diagram acting on the heating tube.

FIG. 5 is a comparison diagram of axial stress when the wall thickness of a thick-walled pipe is changed.

FIG. 6 is a comparison diagram of axial stress in the case of partial thickening and overall thickening.

[Explanation of symbols]

1 Heating tube 10 Drum 11 Supply section 12 Discharge section 13 Support plate 14 Powder

Claims (3)

[Claims] 1. Powder particles in which heating tubes are arranged concentrically in multiple rows inside a rotating cylinder, and the heating tubes are supported by a plurality of support plates standing upright in a ring shape on the inner circumference of the rotating cylinder. In the indirect heating type rotary dryer for the body, only in the vicinity of one or more support plate portions of the heating tubes arranged at least in the innermost circumferential row,
An indirect heating type rotary dryer for powder and granular materials, which is characterized by its thick wall. 2. An indirect heating type rotary dryer for powder and granular material, characterized in that the thick walled portion and the thin walled portion of the heating tube are welded at a position where bending stress is approximately zero. 3. The joint of powder or granular material according to claim 2, characterized in that the tapered pipe portion whose wall thickness continuously changes from a thick wall portion to a thin wall portion is separated from a heat affected zone of a welded portion. Heated rotary dryer.