GB2490990A - A tie bar for a hot blast stove - Google Patents

Abstract

A tie bar 14 comprising a metal beam 11 and a temperature control device 12, 13. The temperature control device may comprise a heating element, and may additionally comprise a temperature sensor, a switch, and a controller to control switching the heating element between a first and second temperature. The tie bar may further comprise an insulating layer. Alternatively the temperature control device may comprise an insulating layer. The insulating layer may comprise an elastic material. The insulating layer may comprise mastic. The metal beam may comprise a steel beam. Also claimed is an external combustion hot stove comprising a combustion chamber, a chequer chamber, and one or more of the tie bars connecting the combustion chamber to the chequer chamber.

Description

TIE BARS

This invention relates to tie bars, in particular for a combustion chamber of a blast furnace external combustion stove.

Conventionally, differential thermal expansion associated with tie bars on an S external combustion chambcr hot blast stove may give rise to issues with the integrity of the crossover refractory design and thermal hot spot problems.

Hot blast stoves are regenerative heat exchangers and are most commonly used to provide high temperature air (hot blast) required for the production of iron in blast furnaces. For stoves with an external combustion chamber a crossover is required to connect the external combustion chamber to the chequer chamber. Due to the large amount of thermal expansion during warm up, it is necessary to have an expansion joint high up on the crossover. Tie beams are required to restrain cyclic pressure force across this expansion joint.

in order for the internal refractory insulation layer to remain effective, it is desirable to minimise any movement in the crossover by keeping the tie bars at a fixed length during changing ambient temperatures (such as between summer and winter or in severe weather conditions, such as rainstorms). To date, this problem has not been addressed. Various designs of tie bars exist, but they do not address the problem of differential thermal expansion.

in accordance with a first aspect of the present invention a tie bar comprises a metal beam and a temperature control device.

The tie bar provides support for the expansion joint in the stove crossover.

Preferably, the temperature control device comprises a heating element.

The heating element reduces the effects of thermal expansion in the tie bar, helping to maintain the integrity of the refractory lining inside the crossover.

Preferably, the tie bar further comprises a temperature sensor, a switch and a controller to control switching the heating element between a first and a second temperature.

This allows the temperature and therefore the expansion of the tie bar to be set to an appropriate point for various modes of operation of the hot blast stove.

Preferably, the tie bar further comprises an insulating layer.

To further reduce the effects of thermal expansion in the tie bar, helping to maintain the integrity of the refractory lining inside the crossover.

Alternatively, the temperature control device comprises an only an insulating layer, without the heating element, Preferably, the insulating layer comprises an elastic material.

To allow some movement without breaking the integrity of the insulating layer.

Preferably, the insulating layer comprises mastic.

Preferably, the metal beam comprises a steel beam.

in accordance with a second aspect of the present invention, an external combustion hot blast stove comprises a combustion chamber, a chequer chamber and one or more tic bars according to the first aspect connecting the combustion chamber to the chequer chamber.

An example of tie bars according to the present invention will now be described with reference to the accompanying drawings in which: Figure l illustrates conventional tic bars on a hot blast stove; Figure 2 shows an alternative tie bar arrangement; Figure 3 illustrates the forces in the example of Fig.l; Figure 4 shows sonic examples of a tic bar according to the present invention; and, Figure 5 illustrates a hot blast stove incorporating tie bars according to the present invention An example of a standard design for a hot blast stove is shown in Fig. 1. Tie bars I are connected between an external combustion chamber 2 and a chequer chamber 3 of the stove. The tie bars 1 are constructed from steel and have pins on either side to allow articulation during growth, or contraction, of the two chambers 2, 3.

Fig. 2 shows an example of a stove of the type in Fig. 1 for usc in a blast furnace. The tie bars 1 are clearly visible between the chequer chamber 3 and the combustion chamber 2. Fig.3 illustrates the forces involved 4, 5, requiring the tie bars between the two chambers 2, 3. The tie bars 1 may change in length dLp due to pressure, or may change in length dLt due to temperature. The overall change in length dL = dLp + dLt.

For this example, with a typical length of tie bar of 9m, the change in length dL 6 may be as much as 10.4mm, which can result in effects such as cracking or parting of refractory bricks within the crossover, potentially leading to tracking of hot gas towards the shell which could in turn lead to the generation of hot spots and a reduction in the integrity of the shell itself.

The design illustrated in Fig. 1 has tended to suffer from hotspots for a number of reasons most particularly due to the unfavourable, but unavoidable, location of the high temperature and pressure expansion joint. In the past, various methods have been tried to eradicate the overheating problem. These have focussed on stopping the flow S of hot gas into the void within the expansion joint by applying pressure, as well as improving refractory design. Fig.2 illustrates an example in which the problem has been addressed by changing the position and quantity of tie bars to have many small tie bars located directly around the expansion joint, rather than t\vo large tie bars attached to the outer edges of the domes.

An alternative design (not shown) uses a large fixed one piece dome and accommodates the movement by having a vertical expansion joint located on the combustion chamber shaft. This design also requires tie bars to restrain the pressure force and likevise experiences varying movement due to changing ambient conditions.

This results in the need to use a complex hydraulic foot that allows the combustion chamber to grow downwards.

it is not possible to simply ignore the problem, as the beams of the tie bars will grow in length as the ambient temperature increases, causing the refractory bricks to part or crack which may result in hot gas getting in towards the steel shell of the crossover.

One alternative to the prior art approaches to the problem is to provide a block of some sort, such as mastic and inject this into the void within the expansion joint.

Due to the shorter length of metal of the tie bars, the effects of varying temperature are reduced. If the bars do extend then they will become loose and can be tightened to maintain tight refractories.

However, there are still practical issues with changing an existing tie bar design to deal with the problem and this may result in a large amount of on-site welding being required.

Thus, examples of the present invention are illustrated in Fig.4. A tie bar 14 is provided with a metal tie bar beam ii and at least one temperature control device. This may be in the form of a heating element 12 or an insulation layer 13. The temperature control device provided in the tie bars 14 of the present invention allows control of the temperature of the tie bar beams 11 and therefore control of their thermal expansion. In the example of Fig.4a, a first temperature control device on a beam 11 of the tie bar 14 is a trace heating clement 12 to provide active control to maintain the tie bar at a more constant temperature and reduce or eliminate thermal expansion and contraction. An advantage of using trace heating is that the system can be retrofitted onto a tie beam design. In addition, in this example, a second temperature control device in the form of S a suitable thermally insulating layer 13 is provided outside the tie bar beam 11 and trace heating element 12. This helps to maintain the temperature produced by the trace heating and reduce the effect of ambient conditions. Fig.4b shows an example, in which the temperature control device comprises an insulation layer 13, directly in contact with the metal beam 11. The use of insulation, or lagging, with or without the trace heating, reduces the effects of temperature variation without adding to the running costs. This insulating layer may include mastic, or an equivalent material and is a relatively inexpensive solution, by comparison with prior art methods. Fig.4c shows an example of the tie bar of the present invention in which a trace heating element 12 is provided on the tie beam ii, without the insulation layer. The invention minimises the effect of differential thermal expansion, giving a more robust mechanical design and aids the integrity of the crossover refractory lining.

Without this solution, the tie beams extend and contract as a result of changes in ambient conditions which cause the expansion joint and the refractory insulation bricks to open up. This may result in hot gas getting through towards the steel shell and causing damage.

The tie bars may further comprise, temperature sensoi; a switch and a controller to switch between start up and operating temperatures. A first temperature during start up is used to prc-load the tie bars in a controlled way by choosing the first temperature to be an elevated installation or erection temperature generated using the trace heating.

Having achieved the installation temperature, the switch causes a lower level of heating to be applied and the controller maintains the temperature of the tic bars at this second reduced, operating temperature. Conventionally, pre-loading of the bars has been addressed by controlling the tension by torquing of the tie bars. The tie beams, due to their design, cannot be adjusted in length. The tie bolts can be to an extent, but because of their large size this can prove difficult in practice. However, the use of a temperature control device or devices in the tie bars of the present invention enables this problem to be addressed.

Claims (9)

1. CLAIMS1. A tie bar, the tie bar comprising a metal beam and a temperature control device.
2. 2. A tie bar according to claim 1, wherein the temperature control device comprises a heating element.
3. 3. A tie bar according to claim 2, wherein the tie bar fttrther comprises a temperature sensor, a switch and a controller to control switching the heating element between a first and a second temperature.
4. 4. A tie bar according to claim 2 or claim3, wherein the tie bar further comprises an insulating layer.
5. 5. A tie bar according to claim 1, wherein the temperature control device comprises an insulating layer.
6. 6. A tie bar according to claim 4 or claim 5, wherein the insulating layer comprises an elastic material.
7. 7. A tie bar according to any of claims 4 to 6, wherein the insulating layer comprises mastic.
8. 8. A tie bar according to any preceding claim, wherein the metal beam comprises a steel beam.
9. 9. An external combustion hot blast stove comprising a combustion chamber, a chequer chamber and one or more tie bars according to any preceding claim connecting the combustion chamber to the chequer chamber.