WO2014146867A1

WO2014146867A1 - Hot blast stove

Info

Publication number: WO2014146867A1
Application number: PCT/EP2014/053559
Authority: WO
Inventors: Alex Michael SMITH
Original assignee: Siemens PLC
Current assignee: Siemens PLC
Priority date: 2013-03-22
Filing date: 2014-02-24
Publication date: 2014-09-25
Anticipated expiration: 2015-09-22
Also published as: GB2512139A; GB201305304D0; GB2512139B

Abstract

An internal combustion chamber hot blast stove comprises a chequer chamber (3), a combustion chamber (2) and a dividing wall (6). The dividing wall further comprises a cavity (23). The stove further comprises a cavity inlet (22) and a cavity outlet (26) and a supply of extraction gas connected to the cavity inlet (22). The cavity outlet (26) is connected to a feedback line to an air inlet of the combustion chamber (2).

Description

HOT BLAST STOVE

This invention relates to a hot blast stove, in particular an internal combustion chamber hot blast stove.

Internal combustion chamber hot blast stoves comprise a chequer chamber and a combustion chamber, separated by a dividing wall. Fuel gas enters the combustion chamber and the products of combustion of the fuel gas pass out of the top of the combustion chamber and down the chequer chamber to heat up the chequer bricks. However, internal combustion chamber hot blast stoves generate relatively high emissions when compared with an equivalent external combustion chamber design. This may be due to uncombusted gas passing through cracks in the bricks of the dividing wall, or through joints between the bricks, into the base of the chequer chamber. If the pressure on the chequer chamber side of the dividing wall is lower than the pressure on the combustion chamber side, then there is a driving force for gas to find its way through the wall, either through cracks, between bricks, or through permeability o f the refractory itself.

Reductions in emissions from internal combustion chamber hot blast stoves have been achieved by various design improvements, including refinement of the burner design to improve combustion efficiency and also the use of large refractory blocks or panels in the dividing wall, rather than larger numbers of smaller bricks. These methods have the effect of reducing the passage of uncombusted gas through the wall into the chequer chamber, but further improvement is required to address increasingly stringent emissions targets.

In accordance with a first aspect of the present invention an internal combustion chamber hot blast stove comprises a chequer chamber, a combustion chamber and a dividing wall; wherein the dividing wall further comprises a cavity; wherein the stove further comprises a cavity inlet and a cavity outlet and a supply of extraction gas connected to the cavity inlet; and wherein the cavity outlet is connected to a feedback line to an air inlet of the combustion chamber.

Preferably, the extraction gas comprises one of nitrogen or air.

Preferably, the cavity is formed between a combustion chamber wall and a chequer chamber wall of the dividing wall.

Preferably, the cavity extends in height to at least the base of a burner in the combustion chamber. Preferably, the cavity extends along the full length of the dividing wall.

Preferably, the stove further comprises one or more metal plates mounted to at least part of the dividing wall.

Preferably, the plates extend along the same length of the dividing wall as the cavity.

In accordance with a second aspect of the present invention, a method of operating a hot blast stove comprising a chequer chamber, a combustion chamber and a dividing wall comprising a cavity comprises supplying extraction gas to the cavity; supplying fuel gas to the combustion chamber; burning the fuel gas to generate combustion products to heat the chequer chamber; and extracting uncombusted fuel gas from the cavity by flowing the extraction gas along the length of the cavity.

Preferably, the method further comprises feeding extracted gas back to an air inlet.

Preferably, the method further comprises determining that fuel gas supply has ceased and terminating the flow of extraction gas before starting to heat cold blast in the chequer chamber.

Using a cavity wall in at least part of the dividing wall between the combustion chamber and chequer chamber with a flow of gas, typically of air or non pollutant gas, through it changes the pressure relationship and carries uncombusted gas out of the stove for reuse or other processing.

An example of a hot blast stove and a method of operation according to the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 illustrates a conventional internal combustion chamber hot blast stove;

Figure 2 illustrates an example of an internal combustion chamber hot blast stove according to the present invention;

Figures 3a and 3b illustrates the dividing wall of Fig.2 in more detail; and, Figure 4 is a flow diagram of a method of operating the stove of Figs.2 and 3

A conventional internal combustion chamber hot blast stove 1 is illustrated in Fig.1. The stove comprises a combustion chamber 2 and a chequer chamber 3 which are separated by a dividing wall 6. A burner 10 at the base of the combustion chamber 2 is supplied with a fuel gas 4, which may be blast furnace gas or a mixture of blast furnace gas and a high calorific value enrichment gas. The combustion products pass up to the top of the stove as indicated by arrow 5 and down through the chequer chamber 3 as indicated by arrow 8. The chequer bricks are heated up by the passing combustion products, which then exit through outlet 9 at the bottom of the chequer chamber. However, the dividing wall is typically made of refractory bricks and their natural porosity, as well as cracks formed or joints between the bricks, or where the dividing wall joins the side walls of the stove, mean that some uncombusted fuel gas 7 may pass through the dividing wall into the bottom of the chequer chamber 3 and exit through the outlet 9, increasing the carbon monoxide content of the waste gas exiting the chequer chamber. Although an internal combustion chamber hot blast stove results in a lower capital cost than an equivalent external combustion chamber stove, the higher emissions levels may lead to customers preferring to opt for an external stove design.

As shown in Fig.2 and Figs.3a and 3b, the present invention addresses the problems of the prior art by constructing the dividing wall 21 with a cavity 23 formed by walls 24 and 25 and providing a gas supply that flows through the cavity from an inlet 22 on the stove shell to an outlet 26 on the stove shell and is collected and fed back to the fuel supply. The narrow cavity 23 inside the dividing wall between the combustion and chequer chambers runs for the full length of the dividing wall and part way up the height of the wall. For optimum results, the cavity 23 runs at least up to the height of the base of the burner. During operation of the combustion phase, a substantially constant supply of gas, typically air or nitrogen, is passed through the cavity 23 from the inlet 22 to the outlet 26. This supply of air gives the void a slight positive pressure, which acts to reduce, or eliminate the driving force which otherwise encourages uncombusted fuel gas to pass through the wall 25 from the combustion chamber 2 to the chequer chamber 3. However, even if there is some passage of fuel gas through the wall 25, the extraction gas carries the penetrating fuel gas out through the outlet branch 26 along with the gas, rather than allowing it to pass through the cavity and the wall 24 into the chequer chamber. The extracted gas is mostly air with only a very small concentration of fuel gas and this extracted gas is fed back to the air inlet and mixed with the combustion air to be sent into the combustion chamber. Any combustible gas components carried in the extraction gas are of such a low

concentration that their effect on the air is negligible.

The cavity alone provides an improvement on conventional dividing walls, but better results are achieved by also having a supply of gas passing through this cavity to intercept any uncombusted gas which has managed to get through the first part 25 of the dividing wall into the cavity 23. The invention results in a reduction in emissions compared to conventional internal combustion chamber stove designs, allowing users to benefit from the lower capital cost of internal combustion chamber stove, without a negative effect on emissions.

Another feature which could be used to address the problem of the present invention is the use of alloy plates installed as part of the dividing wall to reduce the passage of gas through the wall. This is illustrated in Fig.3b. Although, these plates may provide a good degree of prevention initially, they are unlikely to last the full life of the stove. After an initial period of operation with the plates in place, emissions would eventually rise back to the previous levels once the plates reach the end of their useful life. However, used in combination with the cavity of the present invention, the metal plates may improve emission control for at least a part of the lifetime of the stove. The plates may extend along the full length of the partition wall, or only along that part of the partition wall provided with the cavity. In some cases, it may be desirable for the metal plate to extend a little beyond the end of the cavity, still on the partition wall.

Fig.4 is a flow diagram showing a method of operation of the internal combustion hot blast stove of the present invention. Conventionally, at the start of the gas cycle, fuel gas enters 32 the combustion chamber and is burnt by the burner to generate 33 combustion products which provide heat to the chequer chamber 3. In the hot blast stove of the present invention, before the fuel gas enters the combustion chamber 2, the extraction gas supply is activated 31 and starts to flow through the cavity 23 of the dividing wall 21. This ensures that any uncombusted gas which penetrates the wall 25 between the combustion chamber 2 and the cavity 23 is carried away 34 before it can enter the chequer chamber. This continues 37 for as long as there is a supply of fuel gas entering the combustion chamber. When the gas cycle has finished 35, 36 and the fuel gas supply has ceased, then the extraction gas is no longer required and is terminated 38. The stove is now ready to start the blast cycle 39 and heat up the cold blast by passing it through the heated chequer chamber 3.

Claims

1. An internal combustion chamber hot blast stove comprising a chequer chamber, a combustion chamber and a dividing wall; wherein the dividing wall further comprises a cavity; wherein the stove further comprises a cavity inlet and a cavity outlet and a supply of extraction gas connected to the cavity inlet; and wherein the cavity outlet is connected to a feedback line to an air inlet of the combustion chamber.

2. A stove according to claim 1, wherein the extraction gas comprises one of nitrogen or air.

3. A stove according to claim 1 or claim 2, wherein the cavity is formed between a combustion chamber wall and a chequer chamber wall of the dividing wall..

4. A stove according to any preceding claim, wherein the cavity extends in height to the base of a burner in the combustion chamber.

5. A stove according to any preceding claim, wherein the cavity extends along the full length of the dividing wall.

6. A stove according to any preceding claim, further comprising one or more metal plates mounted to at least part of the dividing wall.

7. A stove according to claim 6, wherein the plates extend along the same length of the dividing wall as the cavity.

8. A method of operating a hot blast stove comprising a chequer chamber, a combustion chamber and a dividing wall comprising a cavity; the method comprising supplying extraction gas to the cavity; supplying fuel gas to the combustion chamber; burning the fuel gas to generate combustion products to heat the chequer chamber; and extracting uncombusted fuel gas from the cavity by flowing the extraction gas along the length of the cavity.

9. A method according to claim 8, further comprising feeding extracted gas back to an air inlet.

10. A method according to claim 8 or claim 9, further comprising determining that fuel gas supply has ceased and terminating the flow of extraction gas before starting to heat cold blast in the chequer chamber.