Support system for smelting-furnace exhaust-gas stack

Abstract

A furnace has a top from which very hot gases are exhausted. An exhaust system has a vent stack connected to the top of the furnace. The stack is cooled with a heat-transfer medium to a predetermined temperature. A plurality of support elements hold the stack off a floor, and the support elements are heated with a heat-transfer medium generally to the predetermined temperature.

Description

FIELD OF THE INVENTION

The present invention relates to a smelting-furnace exhaust-gas stack. More particularly this invention concerns a support system for such a stack.

BACKGROUND OF THE INVENTION

A typical reduction furnace for smelting pig iron produces very hot exhaust gas that collects at the top of the furnace and then passes into an exhaust-gas stack, a tubular construction through which the gases move for cooling, cleaning, recycling, and exhausting to the atmosphere. In the furnace of the system according to the invention in particular exhaust gases with fairly high gas pressures are produced that arrive in the exhaust gas stack at superatmospheric pressure. In this stack, for example, a pressure of about 0.8 bar above atmospheric pressure is present. In the gas-tight exhaust gas stack, the exhaust gases are cooled to a temperature that is appropriate, for example, for preheating ore. The exhaust gas entering the exhaust-gas stack has a high temperature of, for example, about 1450° C. and cooling of the exhaust-gas stack is carried out with a cooling medium, particularly with boiling water at a temperature of 260° C., for example.

Systems of the kind described above are known where the exhaust-gas stack is supported on a surface, e.g. the floor, by support struts or elements that are in fact massive steel beams. These support elements are generally in turn supported on different surfaces by means of springs. Due to the high temperature of the exhaust-gas stack with the cooling medium (water vapor), start-up of the system is associated with thermal expansion of the exhaust-gas stack sections, which expansion occurs relative to other components of the system, particularly relative to a duct connecting the stack to the furnace. Normally expansion occurs in the vertical direction as well as in the horizontal direction. To compensate for differential expansion, appropriate complex components disposed between the system components are required.

A further problem arises when working with excess gas pressure in the exhaust-gas stack. As a result, the system elements are effectively pushed apart. The compensators and/or components of them have to be designed accordingly. A compensator of this type generally has to be able to compensate out relative movements in various spatial directions. These measures known from the related art are relatively complex and expensive.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved system for supporting an exhaust-gas stack that is simple and effective.

Another object is the provision of such an improved system for supporting an exhaust-gas stack that is simple and effective.

SUMMARY OF THE INVENTION

In combination with a furnace having a top from which very hot gases are exhausted, a vent system has according to the invention an exhaust stack connected to the top of the furnace. The stack is cooled with a heat-transfer medium to a predetermined temperature. A plurality of support elements hold the stack off a floor, and the support elements are heated with a heat-transfer medium generally to the predetermined temperature.

The predetermined temperature of the cooling medium fed to the exhaust-gas stack is greater than or substantially greater than room temperature. Consequently, corresponding thermal expansions occur during start-up of the system. So as to cool the exhaust-gas stack, the cooling medium is pumped through cooling pipes in or on the wall of the exhaust-gas stack. According to one embodiment of the invention, the cooling pipes form the wall of the exhaust-gas stack. This wall may be provided with an outer insulating layer.

The support elements are straight or substantially straight struts or posts. According to the invention the support elements are oriented vertically or substantially vertically. According to one embodiment, the vertical orientation relates to the rest position of the system, meaning when the system is not in operation. As will be explained in more detail below, the vertical support elements or vertical supports can be deflected from their vertical orientation into an inclined position during operation of the system. However, it is also part of the invention that the support elements or the vertical supports in the rest position of the system assume an inclined position and that these support elements or these vertical supports are then deflected into a more vertical orientation during operation of the system.

An essential embodiment of the invention is characterized in that the exhaust gas reaching the exhaust-gas stack is under superatmospheric pressure. The internal gas pressure of the exhaust-gas stack is suitably 0.6 to 1.0 bar above atmospheric pressure, preferably 0.7 to 0.9 bar above atmospheric pressure, and particularly preferred about 0.8 bar above atmospheric pressure. The exhaust gas penetrating into the exhaust-gas stack generally has a gas temperature of 1200 to 1600° C., preferably 1300 to 1500° C., and particularly preferred a gas temperature of about 1450° C. The system according to the invention is advantageously suited for operation at excess exhaust gas pressure in the exhaust-gas stack.

It is part of the invention that the support elements are supported at their lower ends on the same surface or at the same level. In other words, the lower ends of the support elements are located in one and the same horizontal load-transfer plane. The lower ends of the support elements may be supported by a steel frame or structure whose elements form or define the load-transfer plane. It is part of the invention that the load-transfer plane according to the invention is horizontal. It is also part of the invention that the furnace is supported with its dead weight on or at the load transfer surface. According to another embodiment, the furnace can be supported on a suitable foundation.

The cooling medium for the exhaust-gas stack has a temperature of more than 150° C. and preferably of more than 200° C. According to a very preferred embodiment of the invention, the cooling medium for the exhaust-gas stack has a temperature of 220 to 280° C., and particularly a temperature of 240 to 280° C. One embodiment of the invention is characterized in that the predetermined temperature of the cooling medium is 250 to 270° C. and particularly about 260° C.

It is part of the invention that the cooling medium is pumped through cooling pipes forming the casing of the exhaust-gas stack. According to a particularly preferred embodiment of the invention, the cooling medium is boiling water with a predetermined temperature of more than 150° C., preferably of more than 200° C. and particularly preferred of more than 240° C. According to this embodiment of the invention, the exhaust-gas stack is cooled by evaporative cooling.

According to the invention, the medium used to heat the support element likewise has the predetermined temperature or substantially has the predetermined temperature (the same as the cooling medium for the exhaust-gas stack). Within the framework of the invention, in a particularly preferred embodiment the cooling medium that is used for cooling the exhaust-gas stack, and that preferably is boiling water, is also used as the medium for heating the support elements. This means that the medium used to heat the support elements corresponds to the cooling medium used to cool the exhaust-gas stack. Of course the stack and the supports have generally the same coefficient of thermal expansion, topically all being made of the same material, normally steel.

According to a particularly preferred embodiment of the invention, the support elements are tubes through which the medium flows. The support elements can be pipes through which the medium having the predetermined temperature flows. Boiling water with a temperature of about 260° C. flows through these tubes when the cooling medium for the exhaust-gas stack has a predetermined temperature of 260° C. The predetermined temperature of the medium for the support element also refers to the temperature of the medium fed to the support elements.

In accordance with the invention the support elements are configured as vertical articulated columns. Each support element is connected at one end to the exhaust-gas stack via a pivot and is connected at the other to a load-transfer surface via another pivot. This configuration according to the invention of the support elements as articulated columns allows the absorption of horizontal thermal expansion of the system elements or of the exhaust-gas stack sections. In doing so, an articulated column that is connected to the exhaust-gas stack may deflect laterally with a corresponding horizontal expansion. This way, resistance to movement in the horizontal direction is effectively avoided. According to a particularly preferred embodiment, the invention therefore operates with support elements that are configured as cooled articulated columns and through which the medium is pumped at the predetermined temperature.

According to one embodiment of the invention, the support elements can each be supported on the load-transfer surface by means of a spring. Such a spring is suitably a disk spring.

It is part of the invention that the vertical height of the load-transfer surface is determined as a function of the temperature difference between the furnace and the exhaust-gas stack. This temperature difference is more particularly the difference between the predetermined temperature of the cooling medium for the exhaust-gas stack and/or for the support elements and the temperature of the cooling medium for cooling the furnace walls and/or the inside furnace walls. The furnace walls, particularly in the upper furnace part connected to the exhaust-gas stack, are cooled with a cooling medium that has a temperature that is typically lower or substantially lower than the predetermined temperature of the cooling medium for the exhaust-gas stack. The cooling medium with the furnace temperature is suitably likewise pumped through cooling pipes provided on the furnace walls.

The furnace temperature is the temperature of the cooling medium fed to the furnace and/or the cooling pipes for the furnace. Cooling of the walls and/or inside walls of the furnace is achieved, for example, with a cooling medium having a furnace temperature of 80° C., while cooling of the exhaust-gas stack and of the support elements is achieved, for example, with a cooling medium or medium having a temperature of 260° C. This results in different vertical thermal expansions on the furnace on the one hand and on the exhaust-gas stack and/or on the support elements on the other hand. In other words, the vertical longitudinal expansions (in mm) of the aforementioned system components at 80° C. and at 260° C. are different.

The furnace and/or the top of the furnace are typically made of the same material or substantially of the same material as the exhaust-gas stack section connected to the furnace and as the support elements. These system components are preferably made of steel or are substantially made of steel. So as to compensate out the above-mentioned difference, according to the invention the load-transfer surface for the cooled support elements is raised, in particular as a function of the temperature difference and/or the difference of the expansion coefficients. The support elements or vertical supports are therefore shortened. This measure has proven particularly effective, and the different vertical expansions of the furnace and the exhaust-gas stack and/or of the support elements can thus be reliably neutralized. The load-transfer surface defines the ideal reference point in the vertical direction, while the horizontal reference point can be selected freely and according to the invention is preferably placed on the centerline of the furnace vessel.

The exhaust-gas stack according to the invention is suitably configured such that the upper region of the furnace is first connected to a horizontal exhaust-gas stack section and/or a slightly inclined and substantially horizontal exhaust-gas connecting duct. A vertical exhaust-gas stack section is connected to this horizontal and/or inclined exhaust-gas stack section or duct so that the exhaust gas may be directed vertically upward therein. At the upper end of this first vertical exhaust-gas stack section, the exhaust gas is fed into a second vertical exhaust gas section via a deflection section, through which second section the exhaust gas is directed downward again. According to a preferred embodiment of the invention, the exhaust-gas stack section thus has a downwardly open or upside-down U-shape with a connected horizontal and/or inclined exhaust-gas stack section that establishes the connection to the upper part of the furnace.

The invention is based on the realization that due to the configuration of the system according to the invention differing relative thermal expansions of system components may be effectively and reliably avoided. This also applies to excess exhaust-gas pressure in the exhaust-gas stack, which are generally present in the system according to the invention. In the systems known from the related art, these higher gas pressures are very problematic, however this problem is effectively resolved with the system according to the invention. The invention is therefore based on the realization that heating of the vertical support elements of the exhaust-gas stack, particularly heating to the same temperature as that used for cooling the exhaust-gas stack, results in a surprisingly reliable and effective solution to the technical problem of the invention.

It is part of the invention that the support elements of the exhaust-gas stack are supported on the same load transfer surface. The invention is furthermore based on the realization that differing interfering thermal expansions can be avoided particularly effectively when the vertical height of the load-transfer surface is defined as a function of the temperature difference between furnace cooling and exhaust-gas stack cooling and/or support element cooling. The invention is furthermore based on the realization that additional horizontal thermal expansions can be effectively absorbed and/or compensated out when the support elements are configured as articulated columns. Due to the configuration of the system according to the invention, complex compensators and/or a complex design of transitional regions between the system components can be eliminated. Intricate compensation solutions that are complex and complicated above all at higher gas pressures in the exhaust-gas stack can be avoided. Insofar, the system according to the invention is characterized by a simpler and less complex design compared to the systems known from the related art. A system according to the invention is therefore also less expensive to produce than systems of this type known so far from the related art.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. is a partly schematic small-scale view of a furnace and exhaust stack according to the invention; and

FIG. 2 is a larger-scale view of one of the support struts for the exhaust stack.

SPECIFIC DESCRIPTION

As seen in FIG. 1 a system for cooling exhaust gases, particularly for cooling exhaust gases from a smelting reduction furnace for pig iron production a furnace 1 from which exhaust gases are emitted. In an upper region 2 of the furnace 1 is connected to an exhaust-gas stack 3 for discharging and cooling the exhaust gases. The exhaust gases are cooled in the gas-tight and cooled exhaust-gas stack 3 to a temperature that is suited, for example, for preheating ore. Further discharge of the cooled exhaust gases from the exhaust-gas stack 3 is not shown in detail in the drawing.

In the embodiment according to FIG. 1, the upper region 2 of the furnace 1 is first connected to a horizontal and/or slightly inclined exhaust-gas stack section or connecting duct 4. This exhaust-gas stack section 4 transitions into a first vertical exhaust-gas stack section 5. The exhaust gas then flows via a downwardly U-shaped deflection section 6 into a second vertical exhaust-gas stack section 7 in which the gases move downward. The exhaust-gas stack 3 thus has a reverse U-shape with a horizontal exhaust-gas stack section 4 connected to it to establish a connection to the upper region 2 of the furnace 1. The exhaust gases flowing from the upper region 2 of the furnace 1 into the exhaust-gas stack section 4 may have a temperature of about 1450° C. as well as a superatmospheric pressure of about 0.8 bar above atmospheric pressure.

The walls of the exhaust-gas stack 3 are cooled by a medium that is pumped from a supply 11 through cooling pipes forming the walls of the exhaust-gas stack 3, which walls are not shown. The supplied cooling medium has a temperature T1 that is 260° C. in the illustrated embodiment. This relatively high temperature T1 results in heat-related expansion of the exhaust-gas stack during start-up of the systems. The cooling medium is suitably boiling water. The exhaust-gas stack 3 is supported on a surface by support elements or vertical supports. The lower ends of the vertical supports 8 are supported at one and the same horizontal load-transfer surface or level L that is supported above the floor or ground 12 by a steel structure that is not shown in detail. In the illustrated embodiment, the furnace 1 is likewise supported on the ground 12 or on a suitable foundation.

It is part of the invention that the vertical supports 8 are heated by a medium that in the example has the same temperature T1 as the cooling medium for the exhaust-gas stack 3. In other words, the vertical supports 8 are heated by means of a medium that can be pumped from the same supply 11 to a temperature T1 of 260° C. This medium is preferably also boiling water. The vertical supports 8 are preferably configured as tubes, and in the example they are configured as pipes through which the medium is conducted with the temperature T1. Since the vertical supports 8 are heated according to the invention and since the vertical supports 8 are supported on the same load-transfer surface L, interfering relative expansions of exhaust-gas stack sections can be effectively avoided. For this reason, the complex compensator elements known from the prior art can be advantageously avoided.

In the illustrated example according to the figures, only one side of the structure with vertical supports 8 is shown. Such supports 8, however, are provided on both sides of the exhaust-gas stack 3. According to a particularly preferred embodiment of the invention, the vertical supports 8 are configured as articulated columns. For this purpose, the vertical supports 8 are pivoted with the upper ends thereof to the exhaust-gas stack 3 and with the lower ends thereof to the load-transfer surface L and/or to a steel construction defining the load-transfer surface L. This way, interfering horizontal thermal expansions can be effectively compensated, This is indicated in FIGS. 1 and 2.

It is also part of the invention that the vertical height h of the load-transfer surface L is defined as a function of the difference between the temperature T1 on the exhaust-gas stack and the temperature T2 on the furnace. The upper region 2 of the furnace 1 is also cooled by a cooling medium that is pumped through cooling pipes that are not shown in detail and that are provided on the inside walls of the furnace 1. The supplied cooling medium for cooling this upper region 2 has a temperature T2 that is lower than the temperature T1 of the cooling medium for the exhaust-gas stack 3. The temperature T2 of the cooling medium for cooling the upper region 2 is 80° C. in the illustrated embodiment. The load-transfer surface L is therefore raised as a function of the temperature difference between the furnace 1 and the exhaust-gas stack 3 or the vertical supports 8, specifically by the vertical height h. This shortens the length of the vertical supports 8. Consequently, interfering vertical relative expansions between the furnace 1 and the exhaust-gas stack 3 can be compensated for. In other words, the load-transfer surface L is raised to compensate for the furnace expanding vertically in accordance with a temperature of 260° C. Washer springs 14 in the lower ends of the struts 8 (see FIG. 2) also provide a measure of movement compensation.

In FIG. 1 guide rockers 9 are shown that are pivoted on fixed supports 13 and the exhaust-gas stack 3 and that extend at a small acute angle to the horizontal so that they can follow the vertical and horizontal expansions of the exhaust-gas stack 3 (in relation to the reference point of the overall system). This has been indicated in FIG. 1. Additionally, braces or spacers 10 are provided between the vertical exhaust-gas stack sections 5 and 7, through which spacers preferably also the cooling medium flows at the temperature T1 (260° C.). This also effectively prevents interfering relative expansions and ensures particularly a parallel configuration of the vertical exhaust-gas stack sections 5 and 7.

Claims

1. In combination with a furnace having a top from which very hot gases are exhausted,. a system comprising: an exhaust stack connected to the top of the furnace; means for cooling the stack with a heat-transfer medium to a predetermined temperature; a plurality of support elements holding the stack off a floor; and means for heating the support elements with a heat-transfer medium generally to the predetermined temperature.

2. The exhaust-gas vent system defined in claim 1 wherein the support elements have lower ends all at generally the same level.

3. The exhaust-gas vent system defined in claim 1 wherein the predetermined temperature is at least 150° C.

4. The exhaust-gas vent system defined in claim 3 wherein both of the cooling mediums are boiling water.

5. The exhaust-gas vent system defined in claim 1 wherein the supports are tubular and the respective cooling medium is a fluid circulated through the supports.

6. The exhaust-gas vent system defined in claim 1 wherein the supports have upper ends pivoted on the stack and lower ends pivoted on the floor.

7. The exhaust-gas vent system defined in claim 6 wherein each lower end is provided with a spring supporting it resiliently on the floor.

8. The exhaust-gas vent system defined in claim 1 wherein the supports have lower ends all supported above the floor at the same level, a height between the level and the floor being determined by the temperature differential between the stack and the furnace.

9. The exhaust-gas vent system defined in claim 1 wherein the stack has vertical and horizontal sections.

10. The exhaust-gas vent system defined in claim 9 wherein the stack is downwardly U-shaped, has two horizontally spaced vertical sections, and is provided with a brace extending horizontally from one of the vertical sections and bearing horizontally on the other of the vertical sections.