GB1601329A

GB1601329A - Cooling gases from cupola furnaces

Info

Publication number: GB1601329A
Application number: GB49148/76A
Authority: GB
Original assignee: Lodge Cottrell Ltd
Current assignee: Lodge Cottrell Ltd
Priority date: 1978-02-27
Filing date: 1978-02-27
Publication date: 1981-10-28

Description

(54) IMPROVEMENTS IN OR RELATING TO COOLING GASES FROM CUPOLA FURNACES (71) We, LODGE-COTTRELL LI MITED, a British Company, of George Street Parade, Birmingham B3 1QQ, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with improvements in or relating to cooling gases from cupola furnaces.

In cupola furnaces, a hot dirty gas is Produced, which is required to be cleaned before discharge to the atmosphere. Often, the gas stream is too hot for the operation of the gas cleaning apparatus, and it must be cooled before cleaning.

It is an object of the present invention to provide an improved method of cooling a hot dirty gas emanating from a cupola furnace.

The present invention provides a method of cleaning, for discharge to the atmosphere, a hot dirty gas emanating from a cupola furnace comprising an upright furnace shaft leading to a duct which, adjacent its junction with the shaft, extends transversely of the shaft, which method comprises (a) passing the gas from the shaft into the duct; (b) cooling the gas by diluting the gas with a cooler gas introduced into the duct downstream of where the gas to be cleaned becomes clear of the shaft cross-section the cooler gas being introduced in a direction unopposed to the general direction of gas flow along the duct; (c) carrying out a gas cleaning operation on the cooled gas; and (d) discharging the cleaned gas to the atmosphere.

The invention also provides a method of cleaning, for discharge to the atmosphere, a hot dirty gas emanating from a cupola furnace comprising an upright furnace shaft leading to a duct which, adjacent its junction with the shaft, extends transversely of the shaft, which method comprises (a) passing the gas from the shaft into the duct; (b) cooling the gas by diluting the gas with a cooler gas introduced into the duct downstream of where the gas to be cleaned becomes clear of the shaft cross-section the cooler gas being introduced in a direction unopposed to the general direction of gas flow along the duct and so that it initially provides a cool outer gas layer protecting the duct from the hot gas and mixes into the hot gas as the gases flow downstream along the duct; (c) carrying out a gas cleaning operation on the cooled gas; and (d) discharging the cleaned gas to the atmosphere.

The invention also provides a gas when cleaned by a method according to the invention.

The invention also provides cupola furnace apparatus comprising (a) a cupola furnace comprising an upright furnace shaft leading to a duct which, adjacent its junction with the shaft, extends transversely of the shaft, the duct being arranged to collect hot dirty gas from the shaft; (b) means for cooling the gas by diluting the gas with a cooler gas introduced into the duct downstream of where in the operation of the apparatus the gas to be cleaned becomes clear of the shaft cross-section and in a direction unopposed to the general direction of gas flow along the duct; and (c) means for cleaning the cooled gas and discharging the cleaned gas to the atmosphere.

There now follows a description, to be read with reference to the accompanying drawings, of cupola furnace apparatus embodying the invention. This description, which is also illustrative of method and product aspects of the invention, is given by way of example only, and not by way of limitation of the invention.

In the accompanying drawings: Figure I shows a simple flow diagram of first cupola furnace apparatus embodying the invention; Figure 2 shows a diagrammatic side view of the first cupola furnace apparatus embodying the invention; Figure 3 shows a section on the line III-III of Figure 2; Figure 4 shows a side view of parts of second cupola furnace apparatus embodying the invention; Figure 5 shows a section on the line V-V of Figure 4; Figure 6 shows an end view of a damper plate of the second apparatus; and Figure 7 shows a modification of the second apparatus.

The first apparatus embodying the invention comprises a cupola furnace 10 comprising a refractory lined upright vertical furnace shaft 12 (Figure 2) in which is provided a charging opening and door 14. In the operation of the furnace, the shaft 12 is charged through the door with, for example, pig iron, iron and steel scrap, coke and flux; the charging material 16 is melted in the shaft 12 by combustion of the coke. This combustion generates a hot dirty particleladen gas which requires to be cleaned before discharge to the atmosphere. The hot gas at the top of the shaft is at a temperature up to 1000"C with occasional peaks up to 1500"C.

The shaft 12 leads to a duct 22 of circular cross-section which extends horizontally from its junction with an upper end portion of the shaft 12 above the level of the door 14. The duct 22 leads towards gas cleaning means 23 (Figure 1), for example a cyclone or bag filter. The hot gas is drawn through the duct 22 and the gas cleaning means, by an induced draught fan 25 which is located downstream (as shown in Figure 1) or upstream of the gas cleaning means.

Cleaned gas from the gas cleaning means is discharged to the atmosphere.

The shaft 12 extends upwardly above the duct 22, and an upper opening 18 thereof is normally closed by a pivoted cap 20. Means (not shown) is provided to open the cap 20 to discharge the gas rising in the shaft 12 directly to atmosphere in the event of temperature conditions which would be liable to damage the gas cleaning means; the means for opening the cap 20 is thermostatically controlled.

A vertical duct 26 leads into the duct 22, and the hot gas flowing along the duct 22 is cooled by dilution with cold ambient air induced by the action of the fan 25 into the duct 22 direct from the atmosphere through the duct 26. It will be realised that since the duct 26 is at right angles to the duct 22, the cooler gas is introduced into the duct 22 in a direction unopposed to the general direction of gas flow along the duct 22.

The duct 22 comprises an initial refractory lined upstream portion 24 leading directly from the shaft 12, but the remainder of the duct 22 is unlined. It will be realised that the gas to be cleaned becomes clear of the shaft cross-section when it enters the portion 24 from the shaft 12. The length (L) of the refractory lined portion 24 is sufficient to allow flow conditions to stabilise before the duct 26 is reached, and is equal to between 0.5 and 5 times the initial internal diameter (D) of the duct portion 24, e.g. about one diameter.

The duct 26 is of rectangular cross-section and leads into the duct 22 via an orifice 27 in the duct 22, where the refractory lined portion 24 terminates downstream of the shaft 12. The duct 26 extends downward for some distance below the duct 22, and its internal width (B) (Figure 3) is not greater than and preferably approximately equal to the thickness (T) (Figures 2 and 3) of the refractory lining of the portion 24.

The duct 26 is tangential to the duct 22, and thus the cold air is introduced transversely into the duct 22 to follow initially a rotary path (Figure 3) extending peripherally around the duct. The gas is introduced at the duct 22 at a given flow velocity; and this and the rotary path are believed to result initially in the cold air providing a cool outer gas layer protecting the unlined portions of the duct 22 from the hot gas, and gradually mixing into the hot gas as the gases flow downstream along the duct. Thus, the temperature of the hot gas decreases in a downstream direction, and the unlined portions of the duct 22 are at all times protected from excessively high temperatures.

The lower end portion of the duct 26 is fitted with a control damper 30, which is arranged to control the flow rate of cold air entering the duct 22. The damper 30 could be profiled to give a rough venturi or streamlined shape to minimise undesirable turbulence from the discharge side. The damper 30 may be fixed to give an average condition, and this should be satisfactory if the gas cleaning means is a cyclone. Alternatively, the damper 30 may be variable in response to conditions at the gas cleaning means to maintain a substantially constant temperature there; this should be suitable for bag filters as well as cyclones.

The gases entering the duct 22 from the shaft 12 are normally fully combusted, and it is intended that there should be no combustion where the duct 26 enters the duct 22.

When the gas cleaning means is a bag filter it incorporates fibrous filter material which is for example glass fibre or synthetic resinous fibre; and when normal constructional materials are used, the temperature of the gas entering the bag filter is not greater than 200"C for glass fiber and not greater than 1200C for synthetic resinous fibre.

When the gas cleaning means is a cyclone of normal constructional materials, the temperature of the gas entering the cyclone is not greater than 450"C.

The flow rate of cold air induced though the duct 26 is from 0.1 to 10 volumes (S.T.P.) (e.g. 1.5 to 9 volumes) of air per volume (S.T.P.) of hot gas leaving the shaft 12.

The second apparatus embodying the invention (Figures 4, 5 and 6) resembles in many respects the first apparatus described with reference to Figures 1, 2 and 3, and is described herein in so far as it differs therefrom, similar reference characters being used to indicate similar parts.

A duct 22 of circular cross-section leads horizontally out of a cupola furnace shaft 12. The duct 22 comprises an initial upstream portion 24 of uniform internal diameter, which is refractory lined, but the remainder of the duct 22 is not refractory line.

The duct 22 comprises a frusto-conical portion 26 which converges in a downstream direction and overlaps the portion 24. At the overlap the portion 26 is wider than the portion 24, so that annular orifice means 28 is provided between the duct portions 24, 26 in a vertical plane. The duct portion 26 is followed by a portion 30 of a diameter dependent upon the relevant gas flow rate, and which may be of the same internal diameter as the portion 24 as shown in Figure 4.

The angle a of the frusto-conical portion 26 is preferably between 20 and 40 , e.g.

300.

The duct portion 24 comprises a converging frusto-conical downstream end face 24a, the angle ss of which is at least 20"; e.g. the angle ss is 45". Alternatively, the end face 24a may be radial, i.e. angle ss is 90".

The length of the refractory lined duct portion 24 is sufficient to allow flow conditions to stabilise before the cold air introduced into the duct 22 through the orifice means 28 is encountered; the length (L) of the portion 24 is again equal to between 0.5 and 5 times the initial internal diameter (D) of the portion 24 approximately equal to said diameter.

The cold air is introduced into the duct 22 at a given flow velocity, so that the cold air entering through the annular orifice means 28 initially provides a cool outer gas layer protecting the unlined portions of the duct 22 from the hot gas, and gradually mixes into the hot gas as the gases flow downstream along the duct 22.

The frusto-conical duct portion 26 comprises an annular upstream flange 32 to which are secured a plurality of L-shaped (Figure 4) centralising ribs 34, which are arranged to secure the duct portion 24 and the duct portion 26 in coaxial relationship to each other. A horizontal portion of each rib 34 is secured to the duct portion 24. The ribs 34 define a plurality of orifice portions 35, (Figure 5), which together constitute the annular orifice means 28.

An annular plate 36 is secured over vertical portions of the ribs 34, and the plate 36 comprises (Figure 6) a plurality of orifice portions 38 which alternate with blanked-off portions 40. During installation of the apparatus, the degree of registration between the orifice portions 38 and the orifice portions 35 is adjusted to give a required flow rate of cold air entering the duct 22 in the subsequent operation of the apparatus.

The plate 36 is then welded to the ribs 34 to fix a required degree of registration. Alternatively, a rotary damper (not shown) may be provided in place of the fixed plate 36, being permanently adjustable in response to conditions at the gas cleaning means to maintain a substantially constant temperature there; this adjustable arrangement should be suitable whether the gas cleaning means is a bag filter or a cyclone, but may be more necessary where a bag filter is employed.

The flow rate of cold air induced through the annular orifice means 28 is again from 0.1 to 10 volumes (S.T.P.) (e.g. 1.5 to 9 volumes) of air per volume (S.T.P.) of hot gas leaving the shaft 12.

It will be realised that the longitudinal position of the duct portion 24 relative to the frusto-conical duct portion 26, is readily variable during installation to obtain a required setting which is then fixed by the ribs 34. It will further be realised that the geometry of the assembly of duct portion 24 and duct portion 26 is such that it acts as a thermal expansion joint; expansion is allowed for by the arrangement of the ribs 34 and damper plate 36. However, a separate expansion joint may be included downstream of the duct portion 26.

In the modification shown in Figure 7, the duct portion 24 comprises a converging downstream end portion 46 which is frustoconical internally as well as externally and has a similar angle of conicity to the duct portion 26, so that an annular flow passage 48 is provided between the duct portion 46 and the duct portion 26, the passage 48 being of uniform cross-sectional area. The duct portion 24 as shown in Figure 7 starts to converge approximately at the upstream end of the duct portion 26.

WHAT WE CLAIM IS: 1. A method of cleaning, for discharge to the atmosphere, a hot dirty gas emanating from a cupola furnace comprising an upright furnace shaft leading to a duct which, adjacent its junction with the shaft, extends transversely of the shaft, which method comprises (a) Passing the gas from the shaft into the duct; (b) cooling the gas by diluting the gas with a cooler gas introduced into the duct downstream of where the gas to be cleaned becomes clear of the shaft cross-section the cooler gas being introduced in a direction unopposed to the general direction of gas flow along the duct; (c) carrying out a gas cleaning operation on the cooled gas; and (d) discharging the cleaned gas to the atmosphere.

2. A method of cleaning, for discharge to the atmophere, a hot dirty gas emanating from a cupola furnace comprising an upright furnace shaft leading to a duct which, adjacent its junction with the shaft, extends transversely of the shaft, which method comprises (a) passing the gas from the shaft into the duct; (b) cooling the gas by diluting the gas with a cooler gas introduced into the duct downstream of where the gas to be cleaned becomes clear of the shaft crosssection the coller gas being introduced in a direction unopposed to the general direction of gas flow along the duct and so that it initially provides a cool outer gas layer protecting the duct from the hot gas and mixes into the hot gas as the gases flow downstream along the duct; (c) carrying out a gas cleaning operation on the cooled gas; and (d) discharging the cleaned gas to the atmosphere.

3. A method according to claim 1 or claim 2, wherein the cooler gas is induced into the duct by suction means downstream of where the cooler gas is introduced.

4. A method according to any one of claims 1, 2 and 3, wherein the hot gas is substantially non-combustible where the cooler gas is introduced.

5. A method according to any one of the preceding claims, wherein the cooler gas is ambient air direct from the atmosphere.

6. A method according to any one of the preceding claims, wherein the flow rate of cooler gas introduced into the duct is from 0.1 to 10 volumes (S.T.P.) of cooler gas per volume (S.T.P.) of hot gas emanating from the furnace.

7. A method according to any one of the preceding claims, wherein the hot gas prior to dilution is at a temperature up to 15000C.

8. A method according to any one of claims 1 to 6, wherein the hot gas prior to dilution is at a temperature up to 1000"C.

9. A method according to any one of the preceding claims, wherein the gas cleaning operation is carried out by means of a bag filter.

10. A method according to any one of claims 1 to 8, wherein the gas cleaning operation is carried out by means of a cyclone.

11. A method according to claim 9, wherein the gas entering the bag filter is at a temperature not greater than 200"C.

12. A method according to claim 10, wherein the temperature of the gas entering the cyclone is not greater than 450"C.

13. A method according to any one of the preceding claims, wherein the duct comprises an initial refractory lined upstream portion leading directly from the furnace shaft and having a length equal to between 0.5 and 5 times the initial internal diameter of the duct, the cooler gas being introduced at a downstream end of said duct portion.

14. A method according to any one of the preceding Claims, wherein the cooler gas is introduced transversely into the duct to follow initially a rotary path extending peripherally around the duct.

15. A method according to any one of Claims 1 to 13, wherein the cooler gas is introduced tangentially into the duct via a second duct of rectangular cross-section.

16. A method according to any one of Claims 1 to 12, wherein the cooler gas is introduced tangentially into the duct via a second duct of rectangular cross-section; the first mentioned duct comprises an initial refractory lined upstream portion leading directly from the furnace shaft; and the second duct has an internal width not greater than the thickness of the refractory lining of said upstream duct portion.

17. A method according to Claim 13, wherein the cooler gas is introduced into the duct generally annularly with respect to the gas flow along the duct.

18. A method according to any one of Claims 1 to 13, wherein the cooler gas is introduced into the duct generally annularly with respect to the gas flow along the duct via annular orifice means, the axis of which extends transversely of the furnace shaft.

19. A method of cleaning a hot dirty gas substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

20. A method of cleaning a hot dirty gas substantially as hereinbefore described with reference to Figures 4, 5 and 6; or Figure 7 of the accompanying drawings.

21. A gas when cleaned by a method according to any one of claims 1, 2, 19 and 20.

22. Cupola furnace apparatus compris

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. being of uniform cross-sectional area. The duct portion 24 as shown in Figure 7 starts to converge approximately at the upstream end of the duct portion 26. WHAT WE CLAIM IS:

1. A method of cleaning, for discharge to the atmosphere, a hot dirty gas emanating from a cupola furnace comprising an upright furnace shaft leading to a duct which, adjacent its junction with the shaft, extends transversely of the shaft, which method comprises (a) Passing the gas from the shaft into the duct; (b) cooling the gas by diluting the gas with a cooler gas introduced into the duct downstream of where the gas to be cleaned becomes clear of the shaft cross-section the cooler gas being introduced in a direction unopposed to the general direction of gas flow along the duct; (c) carrying out a gas cleaning operation on the cooled gas; and (d) discharging the cleaned gas to the atmosphere.

22. Cupola furnace apparatus compris

ing (a) a cupola furnace comprising an upright furnace shaft leading to a duct which, adjacent its junction with the shaft, extends transversely of the shaft, the duct being arranged to collect hot dirty gas from the shaft; (b) means for cooling the gas by diluting the gas with a cooler gas introduced into the duct downstream of where in the operation of the apparatus the gas to be cleaned becomes clear of the shaft crosssection and in a direction unopposed to the general direction of gas flow along the duct; and (c) means for cleaning the cooled gas and discharging the cleaned gas to the atmosphere.

23. Apparatus according to claim 22 comprising, downstream of where the cooler gas is introduced, suction means for inducing the cooler gas into the duct.

24. Apparatus according to claim 22 or claim 23, wherein the duct communicates with the atmosphere so that the cooler gas is ambient air direct from the atmosphere.

25. Apparatus according to any one of Claims 22, 23 and 24 wherein the gas cleaning means comprises a bag filter.

26. Apparatus according to any one of Claims 22, 23 and 24, wherein the gas cleaning means comprises a cyclone.

27. Apparatus according to any one of Claims 22 to 26, wherein the duct comprises an initial refractory lined upstream portion leading directly from the furnace shaft and having a length equal to between 0.5 and 5 times the initial internal diameter of the duct, the arrangement being such that the cooler gas is introduced adjacent a downstream end of said duct portion.

28. Apparatus according to any one of Claims 22 to 27, wherein the cooling means is arranged to introduce the cooler gas into the duct to follow initially a rotary path extending peripherally around the duct.

29. Apparatus according to any one of Claims 22 to 27, wherein the cooling means comprises a second duct of rectangular cross-section through which the cooler gas is introduced tangentially into the duct.

30. Apparatus according to any one of Claims 22 to 27, wherein the cooling means comprises a second duct of rectangular cross-section, through which the cooler gas is introduced tangentially into the duct; the first mentioned duct comprises an initial refractory lined upstream portion leading directly from the furnace shaft; and the second duct has a width not greater than the thickness of the refractory lining of said upstream duct portion.

31. Apparatus according to Claim 27, wherein the cooling means is arranged to introduce the cooler gas into the duct generally annularly with respect to the gas flow along the duct.

32. Apparatus according to any one of Claims 22 to 27, wherein the cooling means comprises annular orifice means for introducing the cooler gas into the duct generally annularly with respect to the gas flow along the duct, the axis of the orifice means extending transversely of the furnace shaft.

33. Cupola furnace apparatus constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the accompanying drawings.

34. Cupola furnace apparatus constructed, arranged and adapted to operate substantially as hereinbefore described with reference to Figure 4, 5 and 6; or Figure 7 of the accompanying drawings.