EP0047755A1 - Arrangement for cooling metal workpieces - Google Patents

Abstract

A device, Fig. 1, for cooling metal workpieces (7), bars (7) or others and recovering their cooling heat, comprises a fluidized bed in which solid particles (3) are intended to be transported by a gas. The device further comprises a substantially horizontal conveyor (8) capable of transporting these workpieces (7) through the bed, and tubes (16, 30) for transporting an energy absorbing medium, for example water and/or steam. The device is characterized in that these tubes (16, 30) are positioned between distributors (13) or similar gas inlets in the bed, which are arranged at the bottom (4) of the device, and said conveyor (8). The device is further characterized in that at least one grid (19) or the like is placed between the pipes (16, 30) and the conveyor (8), which grid (19) is able both to protect the tubes (16, 30) against improperly transported workpieces (7) and crushing air bubbles in the mass of particles (3), thereby effecting a more uniform heat transfer between the bed material (3 ) and the tubes (16, 30).

Description

Arrangement for cooling metal workpieces

This invention relates to an arrangement for cooling metal workpieces, for example billets, bars or the like, and for recovering the cooling heat thereof, which arrangement comprises a so-called fluidized bed, a substantially horizontal conveyor for transporting said workpieces etc. through said bed and pipes for transporting an energy-absorbing medium, for example water and/or steam.

At the manufacturing of steel, but also of other metal, large amounts of metal, hereinafter exemplified as steel, are cooled from high temperature to room temperature. This applies a.o. to billets, cast continuously or rolled, which are intended to be worked to desired products, as well as to hot-rolled bars or the like. The cooling heat at rolling from about 100Θ C to room temperature corresponds to an energy amount of about 165 kWh/ton steel. Depending on the mill size, the annual output of each mill normally is from below 100 000 up to several millions of tons. This renders a clear conception of the total amounts of energy involved. Each ton of commercial steel, besides, normally is cooled more than once during its manufacture.

It seems today to be a matter of special urgency to recover the energy emitted and to convert it to some other form, for example to steam for the production of electricity, to hot water for room heating, or the like. Billets, bars or the like normally are cooled on a so-called cooling bed, which consists of a substantially rectangular support of substantial size, to one end of which hot billets, bars or the like are supplied and by screen means or the like transported transversely to their longitudinal direction over the bed while being cooled by air, and thereafter are discharged from the bed at the opposite end thereof. At cooling beds of this kind, which is the conventional kind, it is generally not possible to recover the cooling heat in an economic way. The reason of this is, that the heat transferfrom the billet, bar etc. to the surrounding medium, i.e. the air, proceeds relatively slowly both at free, but also at forced air colling. The cooling, therefore, proceeds slowly, and large cooling bed surfaces are required when the work pieces are transported over the bed at uniform speed. The large surface implies the necessary installation of expensive devices for the recovery and contributes to a low efficiency degree owing to low energy density.

It was found that a very good and uniform heat transfer can be achieved in a so-called fluidized bed. In principle, a fluidized bed comprises a container, which partly is filled with solid small particles, and in which by injection of gas, usually through the container bottom, the greater part of the particles is maintained suspended, and where the suspended particles together with the gas constitute a system, which has many of the properties of a fluid. Certain conditions, of course, are required for establishing and maintaining fluidization. The heat transfer takes place between the bed, i.e. the suspended particles and the gas, and objects being in the bed and having a temperature different from that of the bed. For this reason, fluidized beds are utilized a.o. for the heat treatment of, for example, large forged workpieces of steel, which require well-controlled and uniform heating in order a.o. to prevent distortion of the workpieces.

Fluidized. beds can also be used as "cooling beds" for the cooling of cast or hot-worked, for example hot-rolled, products at the manufacture of steel. Several advantages are obtained hereby, for example reduced bed size due to more rapid heat transfer, and improved environment in conn-ection to the bed, compared with cooling by applying free or forced air cooling, i.e. conventional cooling beds. Fluidized beds, furthermore, render it possible to control the cooling process whereby the same material properties as at conventional cooling can be obtained at a shorter time.

The reduced bed size implies high energy density and at the same time relatively moderate dimensions of the equipment for cooling heat recovery. The effective rapid heat transfer can be utilized at the energy conversion in connection with the recovery.

Fluidized beds are known, for example, for the cooling of hot-rolled wire where the wire is positioned in coils on a conveyor and transported thereby through the bed, which comprises pipes for the transport of an energy-absorbing medium.

The solution of cooling the aforesaid cast or hot-rolled products in a fluidized bed and recovering the cooling heat is, in principle, relatively simple, but a realization on an industrial scale does not yet exist, because the establishment of an operating cooling bed of this kind involves considerable problems.

The said pipes, for example, must be arranged so as to effect good heat transfer to them,but the pipes must not infringe with the bed and thereby deteriorate the heat transfer between the bed and the products. The pipes also must be protected against mechanical damage by said products. The bed, furthermore, inclusive of said pipes, must be arranged so as to yield easy access to the bed which is necessary, for example, at faulty operation of the conveyor means or when workpieces or the like which are transported incorrectly must be removed or The present invention relates to an arrangement, at which the aforesaid problems are eliminated.

The invention, thus, relates to an arrangement for the cooling of metal billets, bars and the like and for the recovery of their cooling heat, comprising a fluidized bed, in which solid particles are intended to be carried by a gas, a substantially horizontal conveyor for transporting said billets, bars or the like through the bed, and pipes for transporting an energy-absorbing medium, for example water and/or steam.

The invention is characterized in that said pipes are located between distributors or similar gas inlets to the bed, which are provided in the bottom of the arrangement, and said conveyor, and a grating or corresponding means is located between the pipes and the conveyor, which grating is carpable to protect the pipes against, for example, incorrectly transported workpieces etc. and to crush air bubbles in the particle mass and thereby to effect a more uniform heat transfer between the bed material and the pipes.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which

Fig. 1 is a vertical section through a schematically shown first embodiment of an arrangement according to the invention, in parallel with the direction, in which Billets,bars or the like are intended to be trans ported through the arrangement,

Fig. 2 is a horizontal section A-A according to Fig. 1, Fig. 3 is a vertical section through a schematically shown second embodiment of an arrangement according to the invention, in parallel with the direction, in which billets, bars or the like are intended to be transported through the arrangement, and Fig. 4 is a horizontal section B-B according to Fig. 3. The arrangement shown schematically in Fig. 1, comprising a fluidized bed, consists of a lower portion 1 and an upper portion 2, which portions 1,2 enclose the main part of the bed. The bed has horizontal cross-section which, for example, is substantially rectangular or square. The said portions 1,2 constitute a substantially parallelepipedic unit 1,2.

Said unit 1, 2 is partially filled with solid small particles 3, which are intended to be maintained suspended by means of a carrier gas, which usually is introduced at the bottom4 of the bed, i.e. of portion 1, as indicated by arrows in Fig. 1. Outlets 6 for carrier gas having passed through the bed are located preferably in the roof 5 of the bed, i.e. in the upper surface 5 of portion 2, as indicated by arrows in Fig. 1.

A conveyor means 8 of a suitable kind for the transport of products or workpieces 7 intended to be treated in the bed is located so as at an opening 9, for example in the form of a horizontal gap 9 in one of the vertical outer walls 10 of said unit 1,2 to introduce products 7 into the bed, to transport said products through the bed and to remove said products out of the bed through an opening 11, which corresponds to the opening 9 and is located in a second outer wall 12, which preferably is opposed to the outer wall 10 including the opening 9, as shown in Fig. 1.

The said products 7 here consist of oblong products such as billets, bars or the like, which are intended to be transported through the bed transversely to their longitudinal direction, as indicated in Fig. 2 where a billet 7 or the like is marked.

In connection to the bed bottom 4 gas inlets 13 in the form of so-called distributors 13 or the like are located. Each distributor 13 comprises a distribution chamber 14 and an upper surface 15, which constitutes a perforated partition wall 15 between the distributor 13 and the bed, through which partition wall 15 gas is introduced into the bed.

Between said gas inlets 13, i.e. distributors 13, and said conveying means, pipes 16 for transporting an energy-absorbing medium, for example water and/or steam, are located. Said pipes 16 preferably are arranged -as schematically shown in Figs. 1 and 2, i.e. in the form of coils reciprocating in a substantially horizontal plane. In Fig. 1 two horizontal coil arrangements are shown, but, of course, more such arrangements can be applied. Furthermore, the arrangements of coils can be interconnected with or separated from each other with respect to energy-absorbing medium. In Fig. 2, the coils by way of example are separated from each other, i.e. each horizontal coil arrangement for energy-absorbing medium has an inlet 17 of its own and an outlet 18 of its own. The pipes 16 preferably are capable to transport the energy-absorbing medium, for example water, according to the counter-flow principle, i.e. in a direction through the bed which is opposite in relation to the transport direction of said products 7 through the bed, as shown in Fig. 2.

The volume of the pipe system(s), of course, must be adapted to the tonnage per time unit to be passed through the bed, etc.

Between said pipes 16 and said conveyor means 8 one or several preferably horizontal net(s) 19, gratings 19 or corresponding means are provided. Said units' 19 are intended and capable both to protect said pipes 16, for example against incorrectly transported products, and to crush possible air bubbles in the mass of particles 3, thereby bringing about a more uniform heat transfer between the bed material, i.e. particles 3, and the pipes 16 as well as between the bed material and the products 7. By means, of said nets 19, thus, the possible interfer ing effect of the pipes 16 on the flow of gas and particles 3 in the bed is eliminated.

The said upper portion 2 can be removed, lifted off, from the remaining part of the arrangement, and preferably is located in its entirety above the horizontal plane of the conveyor, in which plane the products 7 are transported. The upper portion 2, of course, can be imagined assembled of several parts, which are removed together or individually.

In connection to the bed bottom 4, for example slightly above said distributors 13, one or several drain holes 20 are located, by means of which the solid particles 3 to the extent necessary can be removed rapidly from the arrangement when the upper portion 2 thereof is to be lifted off. Each drain hole 20 can be opened and closed by a valve 21 of a suitable kind, indicated by dashed lines in Fig. 2.

In Figs. 3 and 4 a second embodiment of an arrangement according to the invention is shown, where the bed is divided into two zones 22,23 in parallel with the longitudinal direction of the products 7 by means of a partition wall 24 or the like, which includes an opening 25 in connection to the conveying means. Figs. 3 and 4 do not show the conveying means, products, bed material and drain holes. Each zone 22.23 has a separate upper portion 26,27, each of which preferably can be removed separately, when required, and each of which is provided with outlets 28,29 for carrier gas.

Each zone 22,23 preferably is provided, with a separate system of pipes 30, which are arranged in parallel with the longitudinal direction of said products 7. An energy-absorbing medium is intended to be supplied to the pipes 30 on one side 33 of the bed via a feed conduit 31 and an end wall 32 common for the. pipes 30, and the energy-absorbing medium is intended to be removed from the bed via a corresponding end wall 34 and a drain conduit 35 on the side 36 of the bed opposed the side 33 thereof, as shown in Fig. 4. The systems of pupes 30 for energy-absorbing medium of the zones 22.23 are capable, if required, to be connected through a connecting conduit 37, whereby the systems can operate in series.

The arrangement according to the invention operates as follow Hot billets 7 or the like are transported through the bed by the conveying means 8. The billets hereby emit with high efficiency part of their heat content to the particles 3 and carrier gas. By the movements of the particles in the bed, preferably the main part of this heat content is transferred also with high efficiency to said energy-absorbing medium via the pipes 16 in the lower portion of the bed. The heat content, energy content, in said medium can be utilized outside the bed for room heating, electricity production or the like. As already mentioned, the pipes 15 are protected by means of the nets(s) 19, and at the same time possible air bubbles are crushed and thereby contribute to a uniform high heat transfer between the particles on one hand and the pipes and workpieces on the other hand.

When required, for example in order to adjust incorrectly transported workpieces or to inspect devices and details in the lower portion of the bed, particles are drained through the holes 20, preferably after the carrier gas flow has been interrupted. The upper portion 2 is lifted off and thereby provides easy access by an overhead crane or the like, because the pipes 16 are located beneath the conveyor 8.

The arrangement according to the embodiment shown in Figs. 3 and 4 has substantially the same main function. Due to the division into zones, which, of course, can be more than two in number, and a separate system of pipes 30 for each zone, it is possible to control the cooling process for said products 7. The pipes with energy-absorbing medium cool the bed in their zone, and by adjustment and a suitable choice of the temperature of the medium and its flow rate per time unit». the temperature of each zone can be controlled. The length of the zones perpendicularly to the longitudinal direction of the pipes also can be varied relative to each other, thereby increasing the degree of adjustability.

Two embodiments of an arrangement according to the invention have been described above. The invention eliminates a plurality of problems. Owing to the location of the pipes 16,30 in the lower portion of the bed, a very good access in the bed is obtained. The net(s) 19 further provide a uniform distribution of particles and carrier gas over horizontal cross-sections in the bed, whereby uniform heat transfer and high efficiency degree are achieved. The location of the net(s) 19 further protects the pipes 16,30. The upper portion(s) 2,26,27 of the bed being designed removable, the out-of-service period at faults is shortened substantially, which of course is very important.

The arrangement also is well adapted for use when a controlled cooling process is desired. The object thereof is in most cases to bring about a direct heat treatment of the material in said products.

The arrangement according to the invention, thus, provides high efficiency degree, operation reliability and easiness of access.

It is, of course, possible to imagine several more embodiments and alterations without abandoning the idea of the invention.

A plurality of pipe and zone arrangements, for example, can be imagined. The embodiment shown in Figs. 3 and 4 is one which is preferred for many applications. The pipe system in the zone 23 is maintained on a temperature level lower than zone 22, in order to obtain a suitable temperature of the products leaving the bed. The zone 23 with its pipe arrangement in this case is a preheating unit alternative a cooker for the energy-absorbing medium. The zone 22 with its pipe arrangement is maintained at a higher temperature and is a cooker alternative a superheater where the energy-absorbing medium is passed to the zone 22 after having passed through the zone 23. The function of the zone in question is chosen in view of the energy-absorbing medium and of the desired energy level of the medium when it is leaving the zone 22. For the cooling of workpieces and for the production of steam from the recovery system, a two-zone arrangement according to Figs. 3 and 4 is suitable. At the production of hot water, one zone would be sufficient.

The said openings 9,11, of course, can be placed so as to be located above the upper level 24 of the bed, in which case the products are to be moved down into the bed on* the feed side thereof and upwa-rd out of the bed on the discharge side thereof.

The carrier gas, furthermore, flowing out through the outlet 6,28,29 can be returned to the bed, as indicated by dashed lines and arrows in Fig. 3. The energy content in the carrier gas hereby can be utilized a.o. for controlling the bed temperature. Bed material, which possibly may have been taken along, also can be returned.

The invention, thus, must not be regarded restricted to the above embodiments, but can be varied within the scope of the attached claims.

Claims

Claims

1. An arrangement for the cooling of metal workpieces, bars and the like and for the recovery of their cooling heat, which arrangement comprises a fluidized bed, in which solid particles are intended to be carried by a gas, a substantially horizontally arranged conveyor capable to transport said workpieces, bars or the like through the bed, and pipes for transporting an energy-absorbing medium, for example water and/or steam, c h a r a c t e r i z e d i n that said pipes (16,30) are located between distributors (13) or similar gas inlets to the bed, which are arranged in the bottom (4) of the arrangement, and said conveyor (8), and that at least one grating (19) or corresponding means is located between the pipes (16,30) and the conveyor (8), which grating (19) is capable both to protect the pipes (16,30) against, for example, incorrectly transported workpieces (7) etc. and to crush air bubbles in the mass of particles (3), thereby effecting a more uniform heat transfer between bed material (3) and the pipes (16,30).

2. An arrangement as defined in claim 1, c h a r a c t e r i z e d i n that the pipes (16,30) are arranged lying in parallel(30) or alternatively in the form of coils (16) reciprocating substantially in a horizontal plane.

3. An arrangement as defined in the claims 1,2, c h a ra c t e r i z e d i n that at least the arrangement portion (2) located above the plane of the conveyor (8) can be lifted off from the remaining part of the arrangement, either as one unit or divided into several units in order to provide access to the conveying means without moving or dismantling said pipes (16,30).

4. An arrangement as defined in claim 3, c h a r a c t e r i z e d i n that drain holes (20) are located in connection to the bottom (4) of the arrangement, by means of which holes the solid particles (3) rapidly can be emptied from the arrangement when its said upper portion (2) is to be lifted off.

5. An arrangement as defined in claim 1,2, 3 or 4, c h a ra c t e r i z e d i n that the pipes (16) are capable to transport the energy-absorbing medium according to the counter-flow principle.

6. An arrangement as defined in claim 1,2, 3 or 4, c h a ra c t e r i z e d i n that the bed is divided into at least two zones (22,23) by means of partition wall(s) (24) extending perpendicularly to the transport direction of said conveyor, and that a separate system of pipes (30) is provided in each zone (22,23).