GB2153055A

GB2153055A - Process and installation for the thermal treatment of granular materials

Info

Publication number: GB2153055A
Application number: GB08401844A
Authority: GB
Inventors: Holm Kruger
Original assignee: STRAHLVERFAHRENSTECHNIK BERND
Current assignee: STRAHLVERFAHRENSTECHNIK BERND
Priority date: 1984-01-24
Filing date: 1984-01-24
Publication date: 1985-08-14
Also published as: GB8401844D0; GB2153055B

Abstract

Granular material, in particular material for hardening or tempering of metallic blasting medium particles is thermally treated in a furnace by hot fuel gases by directing the material from the top of a furnace to the bottom along tortuous paths in counterflow to the hot fuel gases. The apparatus comprises a furnace (1) with metal plates (3) fitted obliquely opposite one another in cascade and inclined downwards. The plates are movably supported in the furnace wall and linked with a vibration device (7). Burners (8) provide hot fuel gases which travel upwards through the material and exit through a duct (12). Charge material enters the furnace at the top (10) and cascades downwards to the exit point (14) where there may be a tempering bath (15). <IMAGE>

Description

SPECIFICATION Process and installation for the thermal treatment of granular materials The invention relates to a process and an installation for the thermal treatment of granular materials, in particular for the hardening or tempering of metallic blasting medium particles in a furnace with the aid of hot fuel gases.

From German Patent Specification No.

1,227,045 a furnace for the heat treatment of workpieces is known in which a hollow cylinder runs centrally from bottom to top within the furnace and has a helical channel on its outer face. The hollow cylinder with the helical channel is securely joined at its bottom end to a bunker, which for its part is connected via elastic supports to a vibrator located underneath. In the operation of this known furnace, the bunker and the hollow cylinder with the helical channel situated upon it are set into oscillation with the aid of the vibrator, and the workpieces to be treated are delivered via the bunker to the helical channel from below. Under the action of the vibratory movement, the workpieces in the channel are conveyed from bottom to top and, during this process, are heated by means of electrical heating devices or gas burners.

In this known furnace for the heat treatment of workpieces it is a drawback that the conveying of the workpieces in the helical channel from bottom to top by means of vibration is associated with a relatively high energy consumption. In addition, in this process the degree of effectiveness of heat transfer to the workpieces is also relatively low, since the heating of the workpieces while they are moved from bottom to top in the helical channel is effected essentially through indirect heat transfer only. This also has a disadvantageous effect on throughput. Finally, this known furnace is also barely suitable for having granular substances or fluid material conveyed inside it from bottom to top with the aid of the helical channel and for subjecting them in course of this to a uniform heat treatment.

The object of the invention consists in providing a process for the thermal treatment of granular materials, in particular blasting medium particles, that makes possible an optimum heat transfer from the fuel gases to the granular materials with low energy consumption.

According to the invention there is provided a process for the thermal treatment of granular materials, in particular for the hardening or tempering of metallic blasting medium particles in a furnace by means of hot fuel gases, wherein the granular material is directed from top to bottom in a furnace, in counterflow to the hot fuel gases, along tortuous paths.

The process according to the invention may achieve a rotating motion in the material, by means of which optimum heat transfer from the hot fuel gases to the granular material is achieved and thereby a maximum exploitation of the heat present in the fuel gases for the heating of the material. In addition, through the fact that in accordance with the invention the granular material in the furnace is conveyed from top to bottom in counterflow to the fuel gases, the free gravity energy of the granular material in the furnace is exploited whereby in comparison with known processes the thermal treatment of the granular material in the furnace can be attained with significantly lower energy consumption.

According to a useful further development of the invention, the heating of the blasting medium particles in the furnace may be effected by direct and indirect heat transfer from the hot fuel gases to the blasting material particles. Through direct and indirect heat transfer from the hot fuel gases to the blasting medium particles, the heating of the blasting material particles is especially intensified. This is particularly the case when the direct heat transfer from the hot fuel gases to the granular material takes place in a crossflow, as in this situation the hot gases flow around the individual granules on all sides.

In a further useful development of the process according to the invention, the movement of the blasting medium particles along their tortuous paths is influenced by the action of vibration. By this means the time of transit of the blasting medium particles through the furnace can be controlled to great advantage.

In a further refinement of the process according to the invention, provision is made for the blasting medium particles to be separated into fractions of different particle size, which are passed through the furnace with the duration of stay of each fraction being adjusted to the particle size of the fraction. Thus it is possible for the blasting medium particles to be hardened etc. with advantage with a duration of stay adjusted to the size of particle, so that in a manner hitherto unrealized particles are obtained which, although hardened all the way through, exhibit no marginal decarbonisation and only a minimum of scaling.

The following is a detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a vertical section through a shaft furnace with installations fitted in cascade opposite one another, according to the invention, and Figure 2 is a section along the line AB of Figure 1.

As Figures 1 and 2 show, the installation consists of a shaft furnace 1, round in crosssection, which is fitted with an internal fireproof lining 2. In the furnace wall, metal plates 3 are located obliquely opposite one another in cascade and are held movably in bearings 4.

In place of the bearings 4, it can also be advantageous to provide resilient material in the connection between the metal plates 3 and the furnace wall. The metal plates 3 extend through the furnace wall and are mounted so as to be inclined downwards at an angle of some 15 to 20 with respect to the horizontal. Outside the shaft furnace 1 the metal plates 3 are connected at their ends, via joints 5, to a push rod 6, with which engages a vibration drive 7. In the embodiment shown, an eccentric drive is provided for as a vibration drive. However, an electromagnetic vibration drive can also be used with advantage.

To produce the hot fuel gases, four burners 8 (for example) are fitted in the central and lower area in the furnace wall, and their flames 9 are directed at the metal plates 3 located opposite them at any given time. The burners 8 are connected with feed conduits (not shown in detail in the drawings) for the supply of fuel and air. In addition, in the upper area of the furnace wall an opening 10 is provided for the delivery of g anular material. Through this opening 10 the charging of the furnace can very advantageously be effected, via a bucket wheel (not shown in detail in the drawings) which is fitted in a bunker outlet (also not shown). Finally, in the top wall of the shaft furnace 1 is provided an opening 11 to which a conduit 1 2 for exhaust gases is fixed.In the lower region, there is provided an outlet aperture 14 in the furnace wall for the discharge of the fully treated granular material the outlet being equipped with a hinged shutter 1 3. To receive the material exiting from the shaft furnace 1 via the outlet aperture 14 a tank 1 5 is provided in the circumstances of thermal treatment of blasting medium particles the tank 15 is in the form of a tempering bath. From the tempering bath, the blasting medium particles are removed (e.g. via a drainage elevator) after a time short enough for them still to exhibit a final temperature of over 1 00 C and thus to dry automatically.

In the operation of the shaft furnace 1 according to the invention, the metal plates 3 are set in vibration by switching on the vibration drives 7, and the burners 8 are ignited.

Thereupon the metallic blasting medium particles are delivered continuously to the shaft furnace 1 through the opening 10, from where they reach the uppermost metal plate 3. The metal plates 3 are, as shown in particular by Figure 2, advantageously provided with side edges 1 6 which are turned upwards to form flanges, so that the blasting medium particles cannot fall sideways over the edges of the metal plates and downwards through the furnace. The blasting medium particles are conducted, as indicated in Figure 1, from top to bottom in the furnace from metal plate to metal plate essentially in counterflow to the fuel gases (arrows 17) in somewhat tortuous paths, and in the process are particularly subject, by means of the vibrating metal plates 3, to a beneficial rotating motion.

Through this, to great advantage, indirect and direct heat transfer on all sides from the hot fuel gases to the metallic blasting medium particles is achieved. In particular, in the passage from metal plate to metal plate, intensive heating of the blasting medium particles on all sides is effected, for in these transitional areas the heat transfer from the hot gases to the blasting medium particles takes place in a cross4low. Additionally, the heat transfer from the fuel gases to the blasting medium particles is also effectively enhanced, to great advantage, by the burner flames 9 being directly aimed at the metal plates 3.For the purpose of better or (as the case may be) allround and uniform distribution of the blasting medium particles, especially on the metal plates mounted at the top in the shaft furnace, the metal plates 3 can advantageously be provided with upwardly directed projections distributed preferably evenly on the metal plates.

The metallic blasting medium particles, guided in this way in the shaft furnace 1 in counterflow to the hot fuel gases in a somewhat tortuous manner from top to bottom, are heated, with optimum heat transfer and low energy consumption, in a relatively short time, to the requisite hardening temperature of (for example) 900 to 1000"C and are led out of the furnace through the discharge aperture 14 into the tempering bath 1 5. The speed of transit and hence the duration of stay of the blasting medium particles in the shaft furnace 1 can be varied to great advantage by changing the inclination of the metal plates 3 relative to the horizontal and/or by altering the vibration, especially by altering the amplitude of oscillation.In this way the possibility exists of adjusting the thermal process optimally to coarse-grain or even fine-grain materials at any given time. Thus, for example, the thermal process can run also at the temperatures necessary for the tempering of the blasting medium particles (e.g. roughly 500"C). In this connection the shaft furnace 1 can, for example, also be operated very usefully with fewer than four burners or a smaller and/or shorter furnace can be used.

The installation for carrying out the process according to the invention is not limited to the embodiment shown in the drawings. Thus for example the shaft furnace 1 can also be provided with a gas exhaust aperture fitted in the side of the furnace wall. Also, the metal plates 3 can with great advantage, if required, be shaped in such a way as to become wider from top to bottom. Over and above this, the thoroughly advantageous possibility exists of configuring the shaft furnace, as indicated in dotted lines in Figure 2, with a rectangular cross-section. In this case the metal plates 3 are somewhat wider than shown in Figure 2, so that at the sides only a small cross-section is left free for the rising hot gases.

Claims

1. Process for the thermal treatment of granular materials in particular for the hardening or tempering of metallic blasting medium particles in a furnace by means of hot fuel gases, wherein the granular material is directed from top to bottom in a furnace, in counterflow to the hot fuel gases, along tortuous paths.

2. Process according to Claim 1, wherein the heating of the blasting medium particles in the furnace is effected through direct and indirect heat transfer from the hot fuel gases to the blasting medium particles.

3. Process according to Claim 1 or Claim 2, wherein direct heat transfer from the hot fuel gases to the blasting medium particles is effected in cross-flow.

4. Process according to any of Claims 1 to 3, wherein the motion of the blasting medium particles along their tortuous paths is influenced by the action of vibration.

5. Process according to any of Claims 1 to 4, wherein the blasting medium particles are separated into fractions of different particle size, which are passed through the furnace separately, with the duration of stay of each fraction being adjusted to the particle size of the fraction.

6. Process for the thermal treatment of granular materials substantially as hereinbefore described with reference to the accompanying drawings.

7. An installation to carry out the process according to any one of Claims 1 to 6 comprising a shaft furnace with a materials feed and at least one exhaust gas discharge aperture in the upper region of the furnace, with a materials outlet in the bottom region of the furnace and at least one fuel gas feed in the lower and central region of the furnace, as well as devices in the furnace which comprise metal plates, fitted obliquely opposite one another in cascade, which are mounted projecting from the inner wall of the furnace, are inclined obliquely downwards, and are supported movably in the furnace wall, the devices being linked with a vibration drive mounted outside the furnace.

8. An installation according to Claim 7, wherein, for the production of the hot fuel gases in the central and lower region of the furnace, several burners are fitted whose focal ellipses are directed on to the metal plates.

9. An installation according to Claim 7 or Claim 8, wherein the focal ellipses of the burners fitted in the central and lower region of the furnace are directed at the metal plates located opposite thereto.

10. An installation according to any of claim 7 to 9, wherein the metal plates are provided with upwardly directed projections.

11. An installation according to any of claims 7 to 10, wherein the metal plates are provided with flange-like lateral edges directed upwards.

12. An installation according to any one of Claims 7 to 11, wherein the metal plates are mounted inclined downwards at an angle of from 15 to 20 with respect to the horizontal.

13. An installation according to any one of Claims 7 to 12, wherein the shaft furnace is of rectangular cross-section.

1 4. An installation according to any one of Claims 7 to 12, wherein the shaft furnace has a circular cross-section with gas feed devices near the metal plates.

1 5. An installation for the thermal treatment of granular materials substantially as hereinbefore described with reference to the accompanying drawings.