WO2018095577A1

WO2018095577A1 - A method for heating a blast furnace stove and blast furnace stove

Info

Publication number: WO2018095577A1
Application number: PCT/EP2017/025342
Authority: WO
Inventors: Cameron ANDREW
Original assignee: Linde Aktiengesellschaft
Priority date: 2016-11-24
Filing date: 2017-11-23
Publication date: 2018-05-31
Also published as: GB201619843D0

Abstract

The invention relates to a method for heating a blast furnace stove wherein fuel is combusted in a burner in a combustion chamber in the stove. Combustion gases from the combustion chamber are provided to heat the refractory material in the stove. The exhausted flue gases from the stove and an oxidant rich stream are supplied to a precombustion chamber upstream of the burner. Gas from the blast furnace is supplied to the burner and a portion of the gas from the blast furnace is supplied to the pre-combustion chamber such that the recycled flue gases, oxidant rich stream and portion of the blast furnace gases are partially combusted upstream of the burner and are subsequently fed to the burner.

Description

A METHOD FOR HEATING A BLAST FURNACE STOVE

AND BLAST FURNACE STOVE

The present invention relates to a method for heating a blast furnace stove. Such a stove is known in the art, for example, from EP 2492358. The stove comprises a combustion chamber and a region filled with refractory material. The burner is fed both with a fuel and with an oxidant rich stream. These are combusted in a combustion chamber by the burner and the hot gases are used to heat the refractory material before the flue gases exit the stove to a flue gas treatment plant. The fuel supplied to the burners is typically a low grade fuel such as "top gas" which is supplied from the furnace. Once the refractory material has reached its target temperature, the stove is then operated in blast air heating mode in which air passes through the refractory material in which it is rapidly heated before being fed to the blast furnace. The improvement disclosed in EP 2492358 is the provision of flue gas recycling. This takes a portion of the hot flue gas which has passed through the refractory material and, rather than disposing of this or sending it to a flue gas treatment plant such as a heat exchanger, it recycles a portion of the flue gas back to the burner to combine with the oxidant stream upstream of the burner. A higher-oxygen content oxidant to be used to combust the low-grade fuel such as the top gas. However, because this has a greater oxygen content, the combusted gas will reach a higher temperature. This is undesirable when used in existing stoves as the stove can overheat. By diluting the high-oxygen oxidant with a proportion of the recycled flue gas, the maximum temperature is brought down to an acceptable level.

The present invention provides an improvement to such a method.

Whilst flue gas recycling is effective at significantly reducing the overall flow rate, it does increase the fuel gas volumetric flow rate while reducing the flow of the oxidant rich stream. This will change the jet momentum fluxes from the burner nozzles and could lead to the flame instability. This could be dealt with by redesigning the burner nozzle geometry.

However, this is not an option if flue gas recycling is to be applied to existing stove designs.

According to the present invention, there is provided a method for heating a blast furnace stove according to claim 1 . The present invention introduces a pre-combustion chamber which receives a portion of the blast furnace gas together with the recycled flue gas and oxidant rich stream. The blast furnace gas in the pre-combustion chamber is used to heat and expand the combined oxidant and flue gas recycle stream to match the volumetric flow of air for the conventional burner design whilst reducing the amount of blast furnace gas fed to the fuel nozzles of the burner.

The use of such a pre-combustion chamber allows for a successful retro-fit of flue gas recycling to existing stoves.

The invention is in particular useful for shaftless stoves, top combustion stoves or so-called Kalugin shaftless stoves. An example of the present invention also extends to a blast furnace stove according to claim 2.

An example of a method and stove in accordance with the present invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of the gas supplied to a stove in accordance with the prior art; and

Fig. 2 is a similar view according to the present invention. Fig. 1 shows a typical layout of a gas supply to a stove which employs a flue gas recycle such as that disclosed in EP 2492358.

The burner 1 in the stove is provided with a first gas stream comprising an oxidant rich stream 2 which is a gas stream with enriched oxygen content. This is combined in a mixing chamber 3 with a flue gas recycle 4 which comprises a proportion of the gas which has heated the refractory material in the stove. This stream is supplied to the nozzles of the burner which previously received just the air stream. A second fuel stream 5 is provided by the blast furnace gas which is fed to the fuel nozzles of the burner. The improvement provided by the present invention is the addition of a splitter valve 10 which leads a proportion of the blast furnace gas to a pre-combustion chamber 12

(replacing the mixing chamber 3) which received the flue gas recycle 4 and oxidant rich streams. Pre-combustion in this chamber heats and expands the combined stream to approximately match the volumetric flow rate of air for a conventional burner such that the relative volumetric proportions of the streams being fed to the two sets of burner orifices matches more closely the proportions of a conventional stream without a flue gas recycle. This is demonstrated in the table below (Figures in m³):

In the above table, first row of figures are for a conventional air/fuel burner. The second row are for a burner employing flue gas recycle, the third row show the figures for a combined flue gas recycle and pre-combustion chamber according to the present invention; and using synthetic air as the only oxygen source; and the fourth row shows a second example according to the invention, where a portion of the synthetic air is replaced by air.

In a conventional air/fuel burner, the combined fuel flow is 63380m³, and the air flow is 92400m³. For the fuel gas recycle system, the combined fuel flow is higher at 78176m³. However, the flow of combined oxidants (which is the flow fed to the air nozzles of the burner) is 48216m³ which is significantly lower than the air flow rate of the conventional burner (92400m³). By contrast, in the first example of the present invention, whilst the total combined fuel flow remains the same as the previous example, the volumetric flow rate (9231 1 m³) of the combined oxidant is much closer to the original air flow rate. This is achieved using the same flow rate of flue gas recycle and oxygen as in the previous example and is caused by the expansion effect of the combustion in the pre-combustion chamber. As can be seen from the table, the temperature of this gas is now 422⁵C as compared to 149⁵C without the pre-combustion chamber. In a second example of the present invention, some of the synthetic air (with an oxygen content of 27%) has been replaced by air thereby reducing the overall oxygen content to 24.2%. As can be seen, the ratio of the combined fuel flow to the combined oxidants is broadly in line with the traditional air/fuel burner.

An example of a stove which can receive the gases from the pre-combustion chamber as described above is shown in Fig. 3.

The stoves 100 are operated cyclically, so that at any point in time at least one stove is operated on blast and the rest of the stoves are operated on gas.

Fig. 3 is a section view through a conventional stove 100 of a modern type. The stove 100 comprises an external combustion chamber 101 , refractory material 102 and a dome 103. When operated on gas, it is critical that the temperature in the dome 103 does not become too high, since there is then a risk of damage to the stove 100. It is to be understood that there are also stoves with internal combustion chambers, and that the present invention is equally applicable to the operation of such stoves.

The gases from the pre-combustion chamber 12 are fed into a combustion zone of the combustion chamber 101 , in which combustion takes place, via an air burner 108. The burner 108 comprises a fuel inlet 105 which receives the gases from the pre-combustion chamber 12 and an air inlet 104. The hot combustion gases then stream up through the chamber 101 , past the dome 103 and down through the refractory material 102, thereby heating the latter. When existing through the port 106, the temperature of the combustion gases is conventionally about 200⁵C to 350⁵C.

When the refractory material has reached a predetermined temperature, the operation is switched to on blast operation. Then, air is introduced through the port 106, streams through the hot refractory material 102, via the dome 103 and the combustion chamber 101 , and out through an outlet port 107. At this point the blast air has a typical temperature of 1 100⁵C to 1200⁵C.

Further details of this stove are disclosed in EP 2492358.

Claims

CLAIMS:

1 . A method for heating a blast furnace stove comprising:

combusting fuel in a burner in a combustion chamber in the stove;

providing combustion gases from the combustion chamber to heat the refractory material in the stove;

recycling exhausted flue gases from the stove;

providing the recycled flue gases with an oxidant rich stream for supplying to a pre- combustion chamber upstream of the burner;

supplying gas from the blast furnace to the burner; and

supplying a portion of the gas from the blast furnace to the pre-combustion chamber such that the recycled flue gases, oxidant rich stream and portion of the blast furnace gases are partially combusted upstream of the burner and are subsequently fed to the burner.

2. A method according to claim 1 , wherein the oxidant rich stream includes synthetic air.

3. A method according to claim 1 , wherein the oxidant rich stream has from 21 % to 32% oxygen by volume.

4. A method according to any one of the preceding claims, wherein the oxidant rich stream has from 24% to 29% oxygen by volume.

5. A method according to any one of the preceding claims, wherein the oxidant rich stream includes air.

6. A method according to any one of the preceding claims for heating a shaftless stove or a top combustion stove.

7. A blast furnace stove comprising a burner to combust gases in a combustion chamber to heat a refractory material in the stove, the stove comprising a blast furnace gas supply line directed to fuel nozzles within the burner; a splitter valve in the blast furnace gas supply line to split the blast furnace gas into a first stream to a first set of nozzles in the burner and a second stream to a pre- combustion chamber;

a flue gas recycle stream leading to the pre-combustion chamber;

an oxidant rich stream leading to the pre-combustion chamber; and

a line leading from the pre-combustion chamber to supply the pre-combusted blast furnace gas, flue gas recycle and oxidant rich stream to a second set of nozzles in the burner.

8. A stove according to claim 7, wherein the oxidant rich stream contains synthetic air.

9. A stove according to claim 7 or claim 8, wherein the oxidant rich stream has an oxygen content of 21 % to 32% by volume.

10. A stove according to claim 9, wherein the oxidant rich stream has an oxygen content of 24% to 29% by volume.

1 1 . A stove according to any one of claims 7 to 10, wherein the oxidant rich stream includes air.