US3804339A

US3804339A - Method of fragmentizing metal strap

Info

Publication number: US3804339A
Application number: US00269594A
Authority: US
Inventors: W Laws; N Townsend; P Barham
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1971-07-29
Filing date: 1972-07-07
Publication date: 1974-04-16
Anticipated expiration: 1991-04-16
Also published as: NL7210408A; GB1381726A; BE786707A; DE2233255A1; SE375919B; FR2147755A5

Abstract

A process for the preparation of steel scrap either for charging to a furnace or for roll compaction. The scrap is pressed into bundles and cooled nitrogen is then passed through the bundle to reduce the temperature of the steel scrap so that it becomes brittle. The cooled bundle is then fragmented in a crusher. The cooled nitrogen is supplied from a heat exchanger into which a cooling agent, liquid methane, is fed, the methane emerging from the heat exchanger in the gaseous phase.

Description

United States Patent 11 1 1111 3,804,339

Laws et al. Apr. 16, 1974 [5 METHOD OF FRAGMENTIZING METAL 2,742,176 4 1956 l-leyl et a1. 62/62 x STRAP 3,072,347 l/1963 Dombrowski. 1 3,137,101 6/1964 Leliaert Inventors: William Robert Laws, Worcester 3,298,138 1/1967 McCormick 51/13 Park; Nicholas Arthur Townsend; Peter James Barham, both of OTHER PUBLICATIONS gexley, n f England Chattanooga Times, newspaper article on page 26 of Sept. 10, 1970 edition entitled Scrap Process Uses [73] Ass1gnee: British Steel Corporation, London, Freezing} 1 England Better Scrap Comes in from the Cold,- Business 22 Filed; July 7 1972 Week, Oct. 31, 1970, p. 54.

[21] Appl- 269,594 Primary Examiner-Charles W. Lanham Assistant Examiner-D. C. Reiley, Ill [30] Foreign Application Priority Data Attorney, Agent, & Thomas July 29, 1971 Great Br1ta1n 35692/71 ABSTRACT 7 52 11.8. 241/17, 29/403, 62/63, A Process for the Preparation f Steel Scrap either f 100 92 241 1 22 charging to a furnace or for roll compaction. The 51 1111.01. B02c 23/00 Scrap is Pressed into bundles and cooled nitrogen is 58 Field of Search. 29/403; 100/92; 62/62, then Passed through the bundle to reduce the p 2/63 4; 241/3 15 DIG 13 DIG 22 17 ature of the steel scrap so that it becomes brittle. The 1 cooled bundle is then fragmented in a crushenThe 56 R f r n Cited cooled nitrogen is supplied from a heat exchanger into a. Cooling agent, methane, is fed, the methane emerging from the heat exchanger in the gas- 3,666,l85 5/1972 Williams 241/17 eous hase 3,713,592 l/l973 Beike 241/17 p 2/1972 George 241/3 NATURAL GAS 13 Claims, 8 Drawing Figures FRUH GRID (90% METHANEl cumarssnn Hm I 11111100111 EXHAUST v GASES LIOUIFAETIUN 51111 PLANT -2 1 11m EXCHANEER i 1 SEEDNIJARY LIJUP (mourn) l SEW sum EUULING 7 TUNNEL 1 20 "4 m sum 1 CRUSHINB I 1 {9' PLANT 1 1 SCRAP 551W OUT PREHEATER I 1 L- -1 PATENTED M 6 1914 3; 804. 339

SHEEI 1 [1F 6 NATURAL GAS FROM mun (90% METHANE) GAS M6 -2 EUMPRESSUR V PRIMARY LUUHMETHANE) HOT I 1 EXHAUST NITRUGEN GASES LlumFAcnuN SUPPLY PLANT I N '10 4? HEAT EXEHANEER i SECONDARY LUUP (NITROGEN) l I f SCRAPCUULINB m TUNNEL ,/20 4 SCRAP 1 FAN 75 ERUSHINB PLANT SBRAL scNA'P 1 OUT PREHEATER REEUPERATUR 1 PATENTEB APR] 619M SHEET 2 BF 6 PAIENIEB PRIW 7 3,804,339

SHEET 5 0F 6 PATENTEUAPR 1 6 m4 3'. 804. 339

sum 6 BF 6 I v 1 FIG. 8.

SCRAP 0 cnusmuu 2 PLANT EXHAUST muse L m SECONDARY LIUDP (POST HEAT I EXCHANGER) cnu smsn SCRAP AUXILIARY SIZE cnuum: 1 m CHAMBER uuum I I mmuneu I SUPPLY g f I w: 78 50 I ll (105 (704 SIZE AUXILIARY 1 RECUPERATUR UMBER [:RUSl-IER 1 METHOD OF FRAGMENTIZING METAL STRAP Proposals have been made to fragment metal scrap, such as motor car bodies, by applying liquid nitrogen to the scrap so as to reduce its temperature and render it brittle, and then to crush the scrap. Carbon and low alloy steels are known to experience a dramatic loss in resistance to impact at low temperature. Such a method suffers from the disadvantage that to provide a continuous supply of liquid nitrogen is expensive.

According to the present invention there is'provided a process for preparing metal scrap including cooling the scrap by contacting thescrap with a cooled gas until the scrap is brittle and then fragmenting the scrap, in which the gas is cooled by passing the gas through a heat exchanger to'which cooling agent is fed in the liquid phase and from which the cooling agent emerges in the gaseous phase. Preferably the cooling agent emerging from the heat exchanger is compressed and liquified and fed back to the heat exchanger.

A cooling agent which is'readily available and which i has the desired thermodynamic properties of a low boiling point andhigh latent heat is natural gas which is approximatley 90 percent methane. Methane has better thermodynamic properties than nitrogen for the purposes of cooling metal scrap to a temperature at which it becomes brittle and has the potential to re move approximately three times the heat per unit weight of cooling agent from steel than nitrogen. However methane is inflammable and for safety reasons cannot therefore be brought into direct contact in the liquid or gaseous phases with the scrap to be cooled. In accordance with'the invention the methane cools the scrap indirectly by heat exchange with a gas which in turn directly contacts the scrap.

The thermal efficiency of the overall process can be improved if the hot exhaust gases from the heat engine that compresses and/or liquifies the cooling agent are used to heat the fragmented scrap. The heat engine i.e., a gas turbine can convenientlybe powered by methane.

The thermal efficiency can also be improved if the fragmented scrap, while still cold, is passed through a recuperator where the fragmented scrap receives heat from a gas which gas is used to cool scrap to be frag mented.

The brittleness of metal ata given temperature depends on the type of metal and it is possible that certain metals may not be fragmented as a result of cooling by contact with gas. To overcome this, after the scrap is fragmented, and'preferably before passing to the recuperator, scrap pieces larger than a desired size are separated from the remainder of the fragmented scrap, and are subjected to a liquifiednormally gaseous cooling agent to reduce their temperature and are then fragmented. I I

The scrap is preferably passed into bundles before being contacted by the cooled gas. Alternatively it can be contained in containers. Preferably each cooled bundle is fragmented by applying forces to the bundle at locations on opposite sides .of the bundle spaced along the length of the bundle, the locations on one side being offset with respect to the locations at the other side.

In one arrangement the scrap is passed continuously through .a chamber continuously fed with the cooled gas, the gas emerging from the chamber being fed back to the heat exchanger to be cooled again. In this arrangement the scrap temperature is lowered quickly.

In another arrangement the bundles of scrap are successively positioned in a store where they are contacted by the cooled gas and are successively removed after a period of time. Preferably each bundle is removed from the store as a result of the introduction of another bundle. In this arrangement the scrap temperature is lowered slowly.

Any non-hazardous gas can be used to contact the scrap but it should preferably be dry. In steelworks, waste nitrogen from tonnage oxygen plants is available and suitable. Alternatively dry air may be used.

The fragmented scrap can be fed directly to another crusher for further crushing. Alternatively the fragmented pieces can be rapidly heated so as to subject them to thermal shock, can be cooled again and then further crushed.

According to another aspect the invention consists of apparatus for carrying out the above processes.

In the accompanying drawings:

FIG. 1 is one arrangement for the process according to the invention shown schematically,

FIG. 2- is a cross sectional side view of part of the apparatus for the arrangement of FIG. 1, r

FIG. 3 is another arrangement for the process according to the invention shown schematically,

FIG. 4 is a plan'view of part of the apparatus for the arrangement of FIG. 3,

FIG. 5 is a perspective view of a detail of the apparatus of FIG. 4,

FIGS. 6 and 7 show apparatus for use with rangements, and

FIG. 8 shows a modification that can be included in the arrangement of FIGS. 1 or 3.

The arrangement for the process for preparing metal scrap shown in FIG. 1 includes a primary loop 2 for natural gas which is about percent methane and a secondary loop 4 for nitrogen. The methane is compressed by a compressor 6, liquified in a liquifaction plant 8, receives heat in a heat exchanger 10 from which it emerges as a gas, and passes back to the compressor 6. The compressoris driven by a gas turbine 12 which is powered by methane from the grid.

In the secondary loop 4 nitrogen cooled in the heat exchanger is continuously fed to a scrap cooling chamber or tunnel 14 to cool the scrap by direct contact with the scrap as shown more fully in FIG. 2. The nitrogen emerging from the tunnel 14 is driven by a fan 16 to a recuperator 18 where it gives off heat to fragmented scrap so as to precool the gas before it passes to the both arheat exchanger 10.

Cooled scrap emerging from the tunnel 14 is crushed in a crushing plant 20 and the fragmented scrap is then passed to the recuperator 18 where it receives heat from the gas that has left the tunnel 14. The scrap then passes to a scrap preheater 22 which is warmed by the exhaust gases from the turbine 12. The scrap can then be charged into a steelmaking vessel. 1

FIG. 2 shows the scrap cooling tunnel 14 in cross section. Bundles of scrap 24 are delivered by a conveyor 26 to an inclined roller table 28 which passes through the entry 30 of the tunnel 14. The entry 30 is provided with chain screens 32 to form an air lock. The roller table 28 delivers the bundles 24 on to a conveyor 34 which transports the bundles through the tunnel to an inclined roller table 36 passing through an exit air lock 38 also provided with chain screens 40. At the bundle exit end of the tunnel there is an inlet 42 for cooled nitrogen and at the bundle entry end there is an outlet 44 for nitrogen provided with the fan 16. The tunnel 14 is provided with baffles 46 above and below the upper run of the conveyor 34 with the upper baffles 46 being offset with respect to the lower baffles 46. Scrap can therefore be fed through the tunnel continuously in one sense and cooled nitrogen can flow through the tunnel in the opposite sense. The baffles 46 direct the cooled gas through the conveyor 34 from one side to the other and back again to promote exchange of heat between the scrap and the nitrogen. With the tunnel l4 bundles of scrap are cooled continuously and quickly.

The arrangement for the process shown in FIG. 3 has a primary loop similar to the primary loop of FIG. 1 except that the heat exchanger is a cold store 48. Bundles of scrap are successively positioned in the cold store 48 where they are contacted with a gas, such as nitrogen cooled by the methane flowing through coil in the store 48 and are then successively removed after a period of time.

Cooled scrap leaving the cold store 48 passes to a crushing plant ,20 and fragmented scrap passes to a recuperator 50 where it receives heat from gas in a loop 52. The scrap then passes to a scrap preheater 22 where it is heated by the exhaust gases from the turbine 12.

The gas in the loop 52 is driven around the loop by a fan 54. The gas. having given off heat to the scrap in the recuperator 50 is used to precool bundles of scrap in a pre-cooler 56 before the scrap is positioned in the cold store 48.

FIG. 4 shows that the cold store 48 and the scrap precooler 56 are an integral unit. Bundles of scrap 24 are conveyed by I a conveyor 58 through an airlock 60 formed by a pair of chain curtains 62. In line with the conveyor 58 is another conveyor 64 extending parallel to the cold store 48 which consists of a series of cubicles 70 in line. Nitrogen in the loop 52 is passed through the pre-cooler 56 from inlet 66 to outlet 68 so as to precool the'bundles 24 held on the conveyor 58 awaiting delivery to the cold store 48. On the opposite side of the cold store 48 is a discharge conveyor 72 for conveying cooled bundles away from the cold store 48. A charging machine 78 having a ram 80 is movable along a table 82 parallel to the conveyor '64 and cold store 48 and can be moved so that the ram 80 is opposite any desired cubicle 70.

In FIG. one cubicle 70 is shown. A coil 74 forming part of the methane loop 2 is disposed in the roof of each cubicle 70. The cubicle 70 has a door 76 at each end. To charge the cubicle a bundle is conveyed by the conveyor 64 until it is opposite the desired cubicle 70. The charging machine 78 isa'lso moved opposite the desired cubicle 70. The doors 76 are then opened and the ram 80 pushesthe bundle 24 into the cubicle thus discharging a cooledbundle 24 already in the cubicle on to the discharge conveyor 72. The doors 76 are then closed. To promote cooling of the bundles 24, fans may be provided in each cubicle to circulate the nitrogen within the cubicles 70. Since the cubicles 70 are in direct communication with the pre-cooler 56 they will receive nitrogen from the inlet 66.

The process of charging the cubicles 70 successively can be automatic and can be set so that each bundle 24 remains sufficiently long in its cubicle to be cooled adequately for subsequent fragmentation.

FIG. 6 shows a press 84 for lightly compressing loose scrap to bind it into compact bundles 24 before being contacted by the cooled nitrogen. The press 84 includes two

pressing members

86 and 88 operated by hydraulic rams 90. The member 86 squeezes the pieces to the required width. The bundles 24 do not have a density as high as those leaving a conventional baling process.

FIG. 7 shows a crusher 20 which is similar in construction to a forging hammer except that it has saw toothed plattens 92, 94. The lower platten 92 in fixed and the upper platten 92 is movable. The plattens 92, 94 have projections 96 which contact the cooled bundle 24 at locations spaced along the length of the bundle, the projections 96 on one platten being offset with respect to the projections on the other platten. The projections 96 impart highly localised bending momerits and shear forces to the scrap and thus promote fracture as preferred planes indicated by chain dot lines 98. The bundles 24 are fed intermittently through the crusher 20. There are practical considerations which limit the minimum pitch of the projections 96 and hence the particle size that can be obtained from the crusher 20. Further crushing is therefore necessary to achieve a'smaller particle size. In the case of plain carbon steels it is possible to use a conventional impacting machine, such as a hammer mill of the type used for crushing minerals, immediately after crushing in the primary crusher 20.

However low alloy steels, which are more resistant to impact than carbon steels, are best first subjected to thermal shock so as to cause surface crazing or cracking. The scrap is particularly susceptible to thermal shock because of its brittleness and poor conductivity at low temperatures. The crazing and cracking causes stress raisers in the scrap which promote fracture in a secondary crusher.

Plain carbon steel is ductile at temperatures above about 0C, and is very brittle below about 30C. In between there is a narrow transition region. Low alloy steels have a larger transition region and in general need to be cooled to a lower temperature than plain carbon steels to render them brittle. It is to be understood that in the performance of the process of the invention the metal to be crushed should preferably be cooled so as to be in the brittle region, although the process may be used with some of the metal at a temperature in the transition region.

FIG. 8 shows a modification that can be made to the arrangement of either FIGS. 1 or 3 so that scrap which has not been made adequately brittle can be further cooled. The fragmented scrap leaving the crusher 20, and before passing to the

recuperator

18 or 50 passes to a size grader 100 where scrap pieces larger than a desired size are separated from the remainder of the fragmented scrap and fed to an auxiliary cooling chamber 102. In the chamber 102 liquid nitrogen is directed onto the separated scrap pieces, which consequently are cooled below the temperature to which they were previously reduced. The scrap then passes to an auxiliary crusher 104 where the pieces are crushed. Any pieces still oversize are rejected in a size grader 106 and the remaining pieces rejoin the remainder of the scrap in the

recuperator

18, 50.

We claim:

1. In a process for producing fragmented metal scrap wherein the metal scrap is cooled in a secondary closed loop of gaseous atmosphere, which atmosphere is itself cooled by a closed primary refrigerant loop containing an appropriate cooling agent, said process comprising the steps of supplying metal scrap to a cooling enclosure; feeding the cooling agent in its liquid phase to a heat exchanger; supplying the gaseous atmosphere to be cooled through said heat exchanger; cooling said gaseous atmosphere in the heat exchanger through heat exchange with said cooling agent, thereby extracting from said gaseous atmosphere at least the heat required for evaporation of said cooling agent; compressing and liquifying the cooling agent emerging from the heat exchanger and feeding the liquified cooling agent back to the heat exchanger; supplying the cooled gaseous atmosphere emerging from the heat exchanger to said scrap cooling enclosure in which the scrap is cooled until it is brittle by contact with said cooled gaseous atmosphere; and fragmentizing the cooled metal scrap.

2. A process according to claim 1 in which the cooling agent is compressed by means driven by a heat engine, the hot exhaust gases from which are used to heat the fragmented scrap.

3. A process according to claim 1 in which the cooling agent is liquified by means driven by a heat engine, the hot exhaust gases from which are used to heat the fragmented scrap.

4. A process according to claim 1 in which the cooling agent includes methane.

5. A process according to claim 4 in which the scrap ispressed into bundles before being contacted by the cooled gas.

temperature and are then fragmented.

8. A process according to claim 1 in which the scrap is passed continuously through the cooling enclosure which is continuously fed with the cooled gaseous atmosphere, the atmosphere, the gas emerging from the enclosure being fed back to the heat exchanger to be cooled again.

9. A process according to claim 8 in which the scrap is fed through the cooling enclosure in one sense and the cooled gaseous atmosphere flows through the chamber in the opopsite sense.

10. A process according to claim 5 in which bundles of scrap are successively positioned in a store where they are contacted by the cooled gas and are succes sively removed after a period of time.

11. A process according to claim 1 in which the cooled gaseous atmosphere is air.

12. A process according to claim 1 in which the cooled gaseous atmosphere is nitrogen.

13. A process according to claim 1 in which the gaseous atmosphere emerging from the cooling enclosure is fed back to the heat exchanger to be cooled again.

* a: s a:

Claims

2. A process according to claim 1 in which the cooling agent is compressed by means driven by a heat engine, the hot exhaust gases from which are used to heat the fragmented scrap.
3. A process according to claim 1 in which the cooling agent is liquified by means driven by a heat engine, the hot exhaust gases from which are used to heat the fragmented scrap.
4. A process according to claim 1 in which the cooling agent includes methane.
5. A process according to claim 4 in which the scrap is pressed into bundles before being contacted by the cooled gas.
6. A process according to claim 1 in which the fragmented scrap is passed to a recuperator where the fragmented scrap receives heat from the gaseous atmosphere used to cool the scrap to be fragmented.
7. A process according to claim 1 in which, after the scrap is fragmented, scrap pieces larger than a desired size are separated from the remainder of the fragmented scrap, said larger pieces are subjected to a liquified normally gaseous cooling agent to reduce their temperature and are then fragmented.
8. A process according to claim 1 in which the scrap is passed continuously through the cooling enclosure which is continuously fed with the cooled gaseous atmosphere, the atmosphere, the gas emerging from the enclosure being fed back to the heat exchanger to be cooled again.
9. A process according to claim 8 in which the scrap is fed through the cooling enclosure in one sense and the cooled gaseous atmosphere flows through the chamber in the opopsite sense.
10. A process according to claim 5 in which bundles of scrap are successively positioned in a store where they are contacted by the cooled gas and are successively removed after a period of time.
11. A process according to claim 1 in which the cooled gaseous atmosphere is air.
12. A process according to claim 1 in which the cooled gaseous atmosphere is nitrogen.
13. A process according to claim 1 in which the gaseous atmosphere emerging from the cooling enclosure is fed back to the heat exchanger to be cooled again.