GB2198507A - Stock heating furnaces - Google Patents

Stock heating furnaces Download PDF

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Publication number
GB2198507A
GB2198507A GB08629427A GB8629427A GB2198507A GB 2198507 A GB2198507 A GB 2198507A GB 08629427 A GB08629427 A GB 08629427A GB 8629427 A GB8629427 A GB 8629427A GB 2198507 A GB2198507 A GB 2198507A
Authority
GB
United Kingdom
Prior art keywords
stock
heating chamber
burner
furnace
tunnel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB08629427A
Other versions
GB8629427D0 (en
Inventor
Neil Fricker
Kevin Fred Pomfret
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
British Gas PLC
Original Assignee
British Gas PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by British Gas PLC filed Critical British Gas PLC
Priority to GB08629427A priority Critical patent/GB2198507A/en
Publication of GB8629427D0 publication Critical patent/GB8629427D0/en
Publication of GB2198507A publication Critical patent/GB2198507A/en
Withdrawn legal-status Critical Current

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Classifications

    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/0037Rotary furnaces with vertical axis; Furnaces with rotating floor
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27BFURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/14Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment
    • F27B9/16Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity characterised by the path of the charge during treatment; characterised by the means by which the charge is moved during treatment the charge moving in a circular or arcuate path
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27FURNACES; KILNS; OVENS; RETORTS
    • F27BFURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/30Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/3005Details, accessories, or equipment peculiar to furnaces of these types arrangements for circulating gases
    • F27B9/3011Details, accessories, or equipment peculiar to furnaces of these types arrangements for circulating gases arrangements for circulating gases transversally

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Tunnel Furnaces (AREA)

Abstract

A furnace for rapid heating of stock such as billets, comprises a tunnel burner assembly having at least one burner and a heating chamber 1 of at least part annular form, support means for supporting the stock, and means for causing relative rotary movement in opposite directions between the tunnel burner and the support means, wherein the heating chamber and at the least one burner are adapted and arranged such that in use said at least one burner emits a stream of burned gas which moves through the heating chamber in a direction counter to the direction of relative movement of the stock thereby to effect transfer of heat predominantly by convection through the heating chamber to the stock. <IMAGE>

Description

"STOCK HEATING FURNACES" The present invention relates to furnaces, and more particularly to continuous furnaces.
Pre-cut metal stock, for example short billets or bars, often need to be reheated before undergoing forming operations such as forging, pressing or extrusion. These operations may be carried out by using fossil fuel fired batch furnaces, or continuous furnaces such as rotary hearth furnaces, all of which depend overwhelmingly for their heating effect on thermal radiation from the combustion gases both to the furnace walls and to the stock. The furnace walls are heated mainly by hot gas radiation whereas the stock is heated by a combination of wall radiation and hot gas radiation. In order to achieve acceptable heating rates, these furnaces have been designed with large working chambers and therefore use large quantities of refractory material which have substantial thermal inertias.This leads to difficulties in controlling stock temperature, and to scaling and decarburisation problems, particularly for steel stock. In an attempt to alleviate such problems the furnaces needed to be kept hot irrespective of whether or not stock is present in the furnace, resulting in significant thermal inefficiency.
In the past, thermal efficiency has been improved by employing a continuous counterflow method whereby the combustion gas flow is counterflow with respect to the direction of stock movement through the furnace thereby preheating the stock before exhausting the waste combustion gases to a flue. However, such a system has a lower specific output (eg. weight of stock heated per unit hearth area per unit) than a non-counterflow furnace, and in order to save space and reduce capital costs, it has been practice to fire such furnaces with a plurality of burners along substantially the whole length of the furnace. Although this has the desired effect of increasing the output from a given furnace hearth, it reduces the effectiveness of the stock preheat zone.
An object of the invention is to alleviate or substantially eliminate at least some of the problems associated with knwon furnaces.
To this end the present invention provides a furnace for rapid heating of stock such as billets, comprising a tunnel burner assembly having at least one burner and a heating chamber of at least part annular form, support means for supporting the stock, and means for causing relative rotary movement in opposite directions between the tunnel burner and the support means, wherein the heating chamber and at the least one burner are adapted and arranged such that in use said at least one burner emits a stream of burned gas which moves through the heating chamber in a direction counter to the direction of relative movement of the stock transfer thereby to effect transfer of heat predominantly by convection through the heating chamber to the stock.
In known burners the tunnel dimensions are chosen such that the burner can emit a high-velocity stream of burned gas at the tunnel exit.
Burners of this kind have generally been termed in the art as "high-velocity tunnel burners" or "jet burners" or "high-intensity combustors".
Compared with known furnaces the inner widthwise cross-sectional areas or the inner lateral dimensions of the heating chamber of tunnel burner furnaces maybe sufficiently small to enable a relatively high combustion gas velocity within the chamber to be obtained to limit mixing between hot gases from the burner or burners and cooler gases within the furnace; and to reduce the transmission of heat by radiation from the "hot" and (or burner gas discharge end) of the furnace to the other end. As a result heat transfer occurs in the heating chamber predominantly by convection and temperature differentials along the length of the heating chamber are reduced.These advantages together with the lower thermal inertia which accompanies a furnace having a reduced mass and the promotion of convective heating also leads to better control of stock temperature and significant reductions in scale and decarburisation of the stock.
Preferably, the heating chamber is of complete circular or toroidal form so that the burned gas can circulate and recirculate around the heating chamber, thereby increasing the velocity of the gases around the heating chamber and further promoting convective heat transfer while at the same time reducing gas temperatures. This arrangement is particularly suitable for the re-heating of metals having a relatively low surface emissivity and a relatively low melting point, such as aluminium.
The recirculation may be produced by the jet or stream of hot gases leaving the burner, or by using combustion air supplied to the burner to induce gases from the charging zone.
The means for supporting and moving the stock through the heating chamber may be a rotary hearth.
In one embodiment the heating chamber may have a stock charging station via which stock is loaded into the furnace and onto the support means and a separate stock discharging station via which stock is removed from the support means and the furnace.
In order that the invention may be more readily understood, reference will now be made by way of example, to the accompanying drawings, in which : Figure 1 is a view in elevation of one embodiment of a furnace according to the invention, Figure 2 is a top plan view of the arrangement shown in Figure 1; Figure 3 is a sectional view on the lines III-III in Figure 2.
Referring to figures 1 to 3 of the drawings the furnace has a circular or toroidal heating chamber 1 defined by cast refractory circular inner 2 and outer 3 side walls respectively; the upper support surface of a rotary hearth; and a ceramic fibre roof 4 which bridges the tops of the side walls. The roof and side walls are supported on a frame 5 having inner and outer side members connected to a roof member. The frame supports the roof and side walls and provides part of water seals 7 and 8 which extend around the heating chamber between the rotary hearth and the inner and outer side walls. The roof includes an opening 9 which communicates with a flue for venting burned gases and another opening 10 which serves to vent exhaust gases from tunnel burner (not shown).
The tunnel burner is mounted above the chamber and is arranged to fire downwardly, and at an angle, to initiate high combustion gas velocity within the heating chamber. The outer side wall is provided with charging door 11, disposed generally beneath the vlue, via which stock can be introduced into the heating chamber, and a discharging door 12 via which stock can be removed from the furnace.
The rotary hearth 13 includes a support frame with a circular drive tract 15 to enable the hearth to rotate (whilst supported on bearing 16).
The angle through which stock loaded via charging door travels to the discharging door is about 3300.
By way of example, the inside width of the heating chamber between the inner surfaces of the side walls may be 0.4m and the height between the stock supporting surface of the rotary hearth and the underside of the roof may be 0.15m. The outside diameter of the inner side wall may be 1.8m whilst the inside diameter of outer side wall may be 2.6m. The size of the billets which for example can be used with a furnace of such dimensions may be of the order of 5cm x 5cm x 7.5cm.
The tunnel burner and heating chamber arrangement and dimensions are such that in operation the burner emits into the heating chamber a stream of high velocity burned gas which circulates anti-clockwise (when viewed from the top) around the chamber whilst the rotary hearth transports billets, e.g. aluminium billets, in the opposite (clockwise) direction from the charging door to the discharging door. The stream of burned gas thus moves counterflow to the direction of movement of the billets which are heated predominantly by convection via the circulating gases.
The circulation of hot gases allows the temperature differential between the load charging and discharging regions to be reduced and also reduces radiant heat change between "hot" billets and "cold" billets within the heating chamber.
Furnaces in accordance with the invention are particularly suitable for reheating metals such as aluminium which have a low surface emissivity and a relatively low melting point.
Whilst a particular embodiment of the invention has been described above, it will be understood that various modifications may be made without departing from the scope of the invention. For example, contoured refractory surfaces to further promote convective heat may be incorporated to into the furnace. The flue being located near to the burner, whilst the major portion of the circumference is used to form the furnace chamber, allows the furnace to include recuperators to provide preheated air to the burners. This arrangement avoids having long ducts to transport hot air or flue gases from the flue zone to the burner zone.

Claims (4)

1. A furnace for rapid heating of stock, comprising a tunnel burner assembly having at least one burner and a heating chamber of at least part annular form, support means for supporting the stock, and means for causing relative rotary movement in opposite directions between the tunnel burner and the support means, wherein the heating chamber and at the least one burner are adapted and arranged such that in use the at least one burner emits a stream of burned gas which moves through the heating chamber in a direction counter to the direction of relative movement of the stock thereby to effect transfer of heat predominatly by convection through the heating chamber to the stock.
2. A furnace as claimed in Claim 1 wherein the heating chamber is of circular or toroidal form.
3. A furnace as claimed in Claim 1 or Claim 2 wherein the furnace includes a rotary hearth for supporting and moving the stock through the heating chamber.
4. A furnace as claimed in Claim 1 and substantially as hereinbefore described.
GB08629427A 1986-12-09 1986-12-09 Stock heating furnaces Withdrawn GB2198507A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB08629427A GB2198507A (en) 1986-12-09 1986-12-09 Stock heating furnaces

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB08629427A GB2198507A (en) 1986-12-09 1986-12-09 Stock heating furnaces

Publications (2)

Publication Number Publication Date
GB8629427D0 GB8629427D0 (en) 1987-01-21
GB2198507A true GB2198507A (en) 1988-06-15

Family

ID=10608714

Family Applications (1)

Application Number Title Priority Date Filing Date
GB08629427A Withdrawn GB2198507A (en) 1986-12-09 1986-12-09 Stock heating furnaces

Country Status (1)

Country Link
GB (1) GB2198507A (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2236277A (en) * 1989-08-01 1991-04-03 Charles Roger Mortimore Producing laminated sheet glass

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB957077A (en) *
GB351740A (en) * 1930-04-23 1931-07-02 Russell Pearce Heuer Improvements in continuous copper melting furnace
GB693221A (en) * 1950-03-10 1953-06-24 Rotary Hoes Ltd Forging furnace
GB693118A (en) * 1950-08-23 1953-06-24 Joseph Samuel Lowe Improvements relating to rotary hearth furnaces
GB862991A (en) * 1958-12-16 1961-03-15 Salem Brosius S A Holding Improvements in or relating to rotary hearth heating furnaces
US4111644A (en) * 1977-04-19 1978-09-05 Selas Corporation Of America Rotary hearth furnace with preheat conveyor

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB957077A (en) *
GB351740A (en) * 1930-04-23 1931-07-02 Russell Pearce Heuer Improvements in continuous copper melting furnace
GB693221A (en) * 1950-03-10 1953-06-24 Rotary Hoes Ltd Forging furnace
GB693118A (en) * 1950-08-23 1953-06-24 Joseph Samuel Lowe Improvements relating to rotary hearth furnaces
GB862991A (en) * 1958-12-16 1961-03-15 Salem Brosius S A Holding Improvements in or relating to rotary hearth heating furnaces
US4111644A (en) * 1977-04-19 1978-09-05 Selas Corporation Of America Rotary hearth furnace with preheat conveyor

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2236277A (en) * 1989-08-01 1991-04-03 Charles Roger Mortimore Producing laminated sheet glass

Also Published As

Publication number Publication date
GB8629427D0 (en) 1987-01-21

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