WO2012076707A1

WO2012076707A1 - Method for feeding hot gas to a shaft furnace

Info

Publication number: WO2012076707A1
Application number: PCT/EP2011/072373
Authority: WO
Inventors: Guy Thillen; Lionel Hausemer; Christian De Gruiter
Original assignee: Paul Wurth SA
Current assignee: Paul Wurth SA
Priority date: 2010-12-10
Filing date: 2011-12-09
Publication date: 2012-06-14
Anticipated expiration: 2013-06-10
Also published as: RU2013131400A; KR20140043309A; LU91764B1; BR112013014354A2; EP2649207A1

Abstract

The present invention proposes a method for feeding hot gas to a shaft furnace, in particular into a blast furnace. The method comprises providing a tuyere stock arrangement comprising a bustle pipe (56) arranged for receiving hot gas form a gas main (58) and a plurality of tuyere stocks (18) for feeding hot gas from said bustle pipe (56) into said shaft furnace, said tuyere stocks (18) being arranged around the circumference of said shaft furnace, each tuyere stock (18)comprising a downleg section (39) for connection to a bustle pipe; a blowpipe (34) for feeding the hot gas to the shaft furnace through a tuyere arranged in an opening in a shell (12) of the shaft furnace; and an elbow (37) arranged between the downleg section (39) and the blowpipe (34). According to an aspect of the invention, a Laval type restriction (40, 40', 40'') is arranged in the tuyere stock (18).

Description

METHOD FOR FEEDING HOT GAS TO A SHAFT FURNACE

Technical Field

[0001 ] The present invention generally relates to a novel method for feeding hot gas, generally blast air, to a shaft furnace, in particular through a plurality of tuyere stocks.

Background Art

[0002] In shaft furnaces, particularly in blast furnaces, pressurized hot gas, typically pressurized hot air and generally referred to as "hot blast air", is blown into the furnace for the combustion of coke, resulting in CO gas necessary for the reduction of ore in the shaft furnace.

[0003] Conventionally, a circumferential bustle pipe is arranged in the tuyere band around the outer shell of the shaft furnace, at a certain distance therefrom. The hot gas is fed from the bustle pipe through a plurality of tuyere stocks that blow the hot gas into the shaft furnace. A tuyere stock is generally provided with bellows for compensating for relative movements, which are mainly due to thermal expansions, between the bustle pipe and the shaft furnace. Such a conventional bustle pipe arrangement is e.g. known from WO 86/05520.

[0004] Currently, the flow rate of hot gas through the tuyere stocks into the shaft furnace is regulated by a blower arranged upstream of the bustle pipe. A hot blast main feeds the hot gas from the blower to the bustle pipe. In order to guarantee high efficiency, smooth operation and good burden descent, it is important that all internal processes in the shaft furnace are symmetrical. Thus, an equal distribution of hot gas into the shaft furnace is mandatory.

[0005] It is state of the art to attempt to reach equal distribution by providing tuyeres with small enough diameter and high enough pressure loss. However, if the flow rate of hot gas is lower than the nominal flow rate of the hot blast system, equal distribution is no longer guaranteed because the pressure loss in the tuyere stock is too small compared to other pressure losses in the circuit. As a consequence, tuyere stocks placed in proximity to the hot blast main tend to have higher flow rates than tuyere stocks placed diametrically opposite the hot blast main. Furthermore, it may occur that a tuyere becomes blocked or partially blocked by unreduced burden. Such material blocks in front of the tuyeres reduce the flow rate through that tuyere. Also, dissymmetrical pressure losses at the tuyeres, resp. at the blowpipes, may be caused by improper adjustment of auxiliary fuel lances, which may lead to an early pre-combustion of the fuel in the tuyere.

[0006] An uneven feed of hot gas into the shaft furnace may lead to an uneven, possibly even uncontrolled, gas distribution in the shaft furnace. The most dramatic and uncontrolled phenomena are the so-called channeling and fluidization wherein gas from a limited region in the shaft furnace goes directly from the tuyeres to the top, without reducing ores, thus leading to high gas temperatures at the top with potential damages to equipment arranged in the top of the shaft furnace.

[0007] In JP 09095720 A and JP 2002241818 A, equal distribution of hot gas may be achieved by providing butterfly valves in the individual tuyere stocks. Such butterfly valves can be individually operated to regulate the flow of hot gas through the respective tuyere stocks. The butterfly valve comprises a disc-shaped control member mounted on a rotation axis centrally arranged in the path of the hot blast. In the closed position, the disc-shaped control member is perpendicular to the flow of hot blast and essentially blocks the path of the hot blast. The control member may then be rotated by 90° into its open position, wherein the control member is essentially parallel to the flow of hot blast, thereby allowing the hot blast to flow through the valve. In intermediate positions, the flow through the valve can be more or less restricted, thereby achieving a regulation of the flow through the respective tuyere stock. A disadvantage of this method is that the reliability and durability of such butterfly valves is compromised by the exposure to the extreme conditions reigning in the tuyere stocks.

[0008] Furthermore, the regulation method using butterfly valves mounted in the tuyere stocks implicates a rather cumbersome control system, as each butterfly valve has to be individually controlled to increase or decrease the flow of hot gas through the respective tuyere stock. [0009] There is thus a need for an improved method wherein a good and equal flow rate through all the tuyeres can be guaranteed, thereby also improving overall gas efficiency, hence fuel consumption, in the shaft furnace.

Technical Problem

[0010] It is an object of the present invention to provide a method for feeding hot gas to a shaft furnace. This object is achieved by a method as claimed in claim 1 .

General Description of the Invention

[001 1 ] The present invention proposes a method for feeding hot gas to a shaft furnace, in particular into a blast furnace. The method comprises providing a tuyere stock arrangement comprising a bustle pipe arranged for receiving hot gas form a gas main and a plurality of tuyere stocks for feeding hot gas from said bustle pipe into said shaft furnace, said tuyere stocks being arranged around the circumference of said shaft furnace, each tuyere stock comprising a downleg section for connection to said bustle pipe, a blowpipe for feeding the hot gas to the shaft furnace through a tuyere arranged in an opening in a shell of the shaft furnace and an elbow arranged between the downleg section and the blowpipe. According to an aspect of the invention, the method further comprises the step of providing a Laval type restriction in each of the tuyere stocks.

[0012] Through the use of Laval type restrictions in the tuyere stocks the uniform distribution of hot gas into a shaft furnace can be more easily achieved. Indeed, there is no need for providing each tuyere stock with a regulation device that has to be individually controlled and that is liable to mechanical failure due to its many, generally complicated, mechanical parts. The Laval type restriction is a durable regulation device that is installed in the tuyere stock and does not need individual control.

[0013] The Laval type restriction is a nozzle having an asymmetric hourglass-shape with a convergent nozzle entry section and a divergent nozzle exit section and is carefully balanced so as to accelerate the incoming hot gas in the nozzle entry section to reach sonic speed at the nozzle throat and supersonic speed in the nozzle exit section. [0014] Across the Laval type restriction, the pressure drop increases as the square of the mass flow until sound velocity is reached (choked condition). For higher mass flows, the pressure drop increases drastically.

[0015] The diameter of the tuyere exit is in the same size range as the velocity must be kept in the same range such as to provide a kinetic energy of the stream similar to what it is in the normal configuration. Indeed, the flow rate through the tuyere stock is no longer influenced by what happens in front of the tuyere. Flow conditions in a balanced Laval nozzle only depend on pressure conditions upstream of the Laval nozzle.

[0016] The flow rate of hot gas into the furnace is adjusted by only varying the pressure conditions at the blower.

[0017] The Laval type restriction further allows for some of the pressure to be regained, through which, in some cases, the total energy consumption of the blower can be reduced compared to a classic tuyere stock arrangement in which smaller tuyeres may have been arranged in an attempt to reach equal distribution.

[0018] Preferably, at least some of the Laval type restrictions are operated in sonic behaviour. Indeed, when some of the Laval type restrictions are operated in sonic behaviour, the repartition of the flow through the different tuyeres is improved. For those tuyeres where the mass flow would have been higher if there were no Laval type restriction, the mass flow is chocked by the Laval type restriction and thus redistributed to the other tuyeres. A more uniform flow through the tuyeres is thus achieved.

[0019] Most preferably, all of the Laval type restrictions are operated in sonic behaviour. If all the tuyeres are chocked by the Laval type restriction, the flow is identical in each tuyere.

[0020] The method advantageously comprises the step of regulating the mass flow of hot gas through the tuyere stocks by means of a blower arranged upstream of said bustle pipe.

[0021 ] The Laval type restriction may, according to an embodiment of the invention, be arranged in the downleg section. Preferably however, the Laval type restriction is arranged in the blowpipe. [0022] According to one embodiment, the Laval type restriction is arranged in a rear end of the blowpipe, in the vicinity of the elbow. According to another embodiment, the Laval type restriction is arranged in a front end of the blowpipe, in the vicinity of the connection to the opening arranged in the shell of the shaft furnace.

[0023] A tuyere may be arranged in the opening arranged in the shell of the shaft furnace, the blowpipe connecting to the tuyere for blowing hot gas through the tuyere into the shaft furnace.

[0024] Alternatively, by introducing a Laval type restriction in the tuyere stock, a diffuser may be arranged in the opening arranged in the shell of the shaft furnace, the blowpipe connecting to the diffuser for blowing hot gas through the tuyere into the shaft furnace.

[0025] Such a diffuser is preferably formed and arranged so as to be an extension of an exit section of the Laval type restriction. Also, downstream of the Laval type restriction, the blowpipe preferably has its inner diameter gradually increasing in such a way as to form an extension of an exit section of the Laval type restriction.

Brief Description of the Drawing

[0026] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic cut through a tuyere stock arrangement with a tuyere stock according to one embodiment of the present invention;

Figure 2 is a schematic cut through a Laval type restriction as arranged in the tuyere stock of Figure 1 ;

Figure 3 is a schematic cut through a tuyere stock arrangement with a tuyere stock according to another embodiment of the present invention;

Figure 4 is a schematic cut through a tuyere stock arrangement with a tuyere stock according to a further embodiment of the present invention;

Figure 5 is a schematic top view of a hot gas distribution system for feeding hot gas to a shaft furnace; and

Figure 6 is a graph showing the results of mass flow through individual tuyeres with and without Laval type restriction arranged in the tuyere stock. Description of Preferred Embodiment

[0027] Figure 1 shows a tuyere stock arrangement for feeding hot gas, generally hot blast air, through a furnace shell 12. The tuyere stock arrangement comprises a tuyere 14 arranged in the furnace shell 12. The tuyere 14 is maintained in position by a tuyere cooler 16. The tuyere stock arrangement further comprises a tuyere stock 18 for feeding hot gas from a bustle main (not shown) to the tuyere 14.

[0028] The tuyere 14 has a tuyere body 20 with a front face 24 and an opposite rear face 26. A tuyere channel 28 is centrally arranged through the tuyere body 20 and extends from the rear face 26 to the front face 24. The rear face 26 of the tuyere 14 is configured to receive a front portion 32 of a blowpipe 34, which is connected, with an opposite rear portion 36, generally in the form of an elbow 37, to a downleg section 39, which is, in turn connected to by a bustle pipe 38 (not shown). The blowpipe 34, elbow 37 and downleg section 39 are generally referred to collectively as tuyere stock 18.

[0029] Furthermore, an auxiliary fuel injection lance (not shown) may be provided for feeding an auxiliary fuel, generally pulverized coal or natural gas, into the shaft furnace at the tuyere level. Due to the injection of the fuel into the shaft furnace the amount of coke fed into the furnace can be reduced. As fuel, such as e.g. coal, is generally cheaper than coke, this leads to a reduction in running costs of the shaft furnace. Generally, such auxiliary fuel is fed into the stream of hot gas within the tuyere 14 or the blowpipe 34. Further, in order to promote the combustion of the auxiliary fuel, gas injection lances (not shown) may be provided for feeding oxidizing gas, such as oxygen, to the fuel. Combined lances may be used to feed auxiliary fuel and oxidizing gas into the tuyere 14 or blowpipe 34 may be used. Such combined lances, generally referred to as oxycoal lances, use two concentric pipes for separately feeding auxiliary fuel and oxidizing gas to the tip of the combined lance.

[0030] According to an important aspect of the present invention, a Laval type restriction 40, 40', 40" is arranged in the tuyere stock 18.

[0031 ] Figure 1 shows one embodiment of the present invention, wherein a Laval type restriction 40 is arranged in the downleg section 39 of the tuyere stock 18. Such a Laval type restriction 40 is, as is more clearly shown in Figure 2, a nozzle having an asymmetric hourglass-shape with a convergent nozzle entry section 42, a nozzle throat 44 and a divergent nozzle exit section 46. The nozzle is carefully balanced so as to accelerate the incoming hot gas in the nozzle entry section 42, to reach sonic speed at the nozzle throat 44 and supersonic speed in the nozzle exit section 46.

[0032] By placing a Laval type restriction 40 in the downleg section 39 of the tuyere stock 18, the portion of the tuyere stock 18 downstream of the Laval type restriction 40 may have flow channels with a diameter larger than those generally used today. The front diameter of the tuyere need however not be changed. The pressure drop for equal distribution happens in the Laval type restriction 40 and the flow rates of hot gas through the tuyere stock 18 is not influenced by conditions downstream of the Laval type restriction 40.

[0033] Figure 3 shows another embodiment of the present invention, with an alternative arrangement for a Laval type restriction 40'. Most of the features of this embodiment are identical to the embodiment shown in Figure 1 and will therefore not be explained in further detail herebelow. Identical references signs refer to identical features.

[0034] In this embodiment, a Laval type restriction 40' is arranged in a rear portion 36 of the blowpipe 34, in the vicinity of the elbow 37. The Laval type restriction 40' itself is very similar to the Laval type restriction 40 of Figure 1 or 2. Its divergent nozzle exit section 46' however is arranged and configured so as to diverge in such a way as to create a continuously diverging channel leading into the shaft furnace. The blowpipe 34 has its central channel 48 therein formed so as to conform to the continuously diverging channel. The front portion 32 of the blowpipe 34 contacts a rear face of a diffuser 50 arranged in the shell 12 the shaft furnace. Such a diffuser 50 has a central channel 52 formed so as to conform to the continuously diverging channel. This configuration has the advantage of further reducing pressure losses in the hot blast distribution system.

[0035] Figure 4 shows a further embodiment of the present invention, with an alternative arrangement for Laval type restriction 40". Most of the features of this embodiment are identical to the embodiment shown in Figure 3 and will therefore not be explained in further detail herebelow. Identical references signs refer to identical features.

[0036] In this embodiment, a Laval type restriction 40" is arranged in a front portion 32 of the blowpipe 34, in the vicinity of the connection to the opening arranged in the shell 12 of the shaft furnace. The Laval type restriction 40" itself is again very similar to the Laval type restriction 40 of Figure 1 or 2. Its divergent nozzle exit section 46" however is arranged and configured so as to diverge in such a way as to create a continuously diverging channel leading into the shaft furnace. The blowpipe 34 has its central channel 48 therein formed so as to conform to the continuously diverging channel. The front portion 32 of the blowpipe 34 contacts a rear face of a diffuser 50 arranged in the shell 12 the shaft furnace. Such a diffuser 50 has a central channel 52 formed so as to conform to the continuously diverging channel.

[0037] Figure 5 shows a hot gas distribution system 54 for feeding hot gas to a shaft furnace. The hot gas distribution system 54 comprises a circumferential bustle pipe 56 arranged around the outer shell of the shaft furnace, at a certain distance therefrom. The bustle pipe 56 receives hot gas from a gas main 58 and redistributes it around the shaft furnace. The hot gas is then fed from the bustle pipe 56 through a plurality of tuyere stocks 18 into the shaft furnace. From the Figure, it appears that the tuyere stocks 18 in proximity to the gas main 58 tend to receive more hot gas than the tuyere stocks 18 that are located further away from the gas main 58.

[0038] Example

[0039] In order to show the efficiency of the proposed method, a pressure loss model has been used to show the difference between the mass flow through individual tuyeres, once in a system with Laval type restrictions and once in a system without Laval type restrictions. From the results, which are shown in Figure 6, it can be seen that the mass flow is considerably more uniform when Laval type restrictions are used. The standard deviation in the system without Laval type restrictions has been found to be 0.304, whereas the standard deviation in the system with Laval type restrictions has been found to be 0.086, which is considerably lower. Thus the Laval type restrictions allow achieving a considerably more uniform distribution of hot gas in the shaft furnace.

[0040] It should finally be noted that the length and position of the Laval type restriction shown in the figures are not limitative and that the length and position of the Laval type restriction within the tuyere stock may vary.

Legend of Reference Numbers:

12 furnace shell 39 downleg section

14 tuyere 40 Laval type restriction

16 tuyere cooler 42 nozzle entry section

18 tuyere stock 44 nozzle throat

20 tuyere body 46 nozzle exit section

24 front face 48 central channel

26 rear face 50 d iff user

28 tuyere channel 52 central channel

32 front portion 54 hot gas distribution system

34 blowpipe 56 bustle pipe

36 rear portion 58 gas main

37 elbow

Claims

1 . Method for feeding hot gas to a shaft furnace, in particular a blast furnace, said method comprising:

providing a tuyere stock arrangement comprising a bustle pipe arranged for receiving hot gas form a gas main and a plurality of tuyere stocks for feeding hot gas from said bustle pipe into said shaft furnace, said tuyere stocks being arranged around the circumference of said shaft furnace, each tuyere stock comprising a downleg section for connection to said bustle pipe, a blowpipe for feeding said hot gas to said shaft furnace through a tuyere arranged in an opening of a shell of said shaft furnace and an elbow arranged between said downleg section and said blowpipe

characterized in that said method further comprises the further step of providing a Laval type restriction in each of said tuyere stocks.

2. The method according to claim 1 , comprising the step of operating at least some of the Laval type restrictions in sonic behaviour.

3. The method according to claim 1 or 2, comprising the step of operating all of the Laval type restrictions in sonic behaviour.

4. The method according to any of claims 1 to 3, comprising the step of regulating the mass flow of hot gas through the tuyere stocks by means of a blower arranged upstream of said bustle pipe.

5. The method according to any of claims 1 to 4, comprising

arranging said Laval type restriction in said downleg section of said tuyere stocks.

6. The method according to any of claims 1 to 4, comprising

arranging said Laval type restriction is arranged in said blowpipe of said tuyere stocks.

7. The method according to claim 6, comprising

arranging said Laval type restriction in a rear end of said blowpipe, in the vicinity of said elbow.

8. The method according to claim 6, comprising

arranging said Laval type restriction in a front end of said blowpipe, in the vicinity of the connection to said opening arranged in said shell of said shaft furnace.

9. The method according to any of claims 1 to 8, comprising

providing a tuyere in said opening arranged in said shell of said shaft furnace, said blowpipe connecting to said tuyere for blowing hot gas through said tuyere into said shaft furnace.

10. The method according to any of claims 1 to 8, comprising

providing a diffuser in said opening arranged in said shell of said shaft furnace, said blowpipe connecting to said diffuser for blowing hot gas through said tuyere into said shaft furnace.

1 1 . The method according to claim 10, comprising

providing a diffuser that is formed and arranged so as to be an extension of an exit section of said Laval type restriction.

12. The method according to claim 10, comprising

providing a blowpipe that has, downstream of said Laval type restriction, its inner diameter gradually increasing in such a way as to form an extension of an exit section of said Laval type restriction.