GB2155603A - Regulating flame temperature within shaft furnaces - Google Patents

Abstract

The flame temperature in a blast furnace 5 is regulated by adjusting the water content of the fresh air introduced into a cowper 1 providing the blast. The flame temperature can be monitored by a sensor 16 linked to a device 9 which controls valve 14 for admitting water from container 13. Alternatively the required water content can be determined empirically. Water is preferably added via atomizer 15 after compression of the air by compressor 4. The water may be introduced as steam generated by the energy of the system. <IMAGE>

Description

SPECIFICATION Regulating flame temperature within shaft furnaces The invention concerns a method of regulating flame temperature within a shaft furnace in the course of raw metal production.

One may in principle regulate flame temperature within shaft furnaces through regulation of hot air temperature: one empirically determines the flame temperature that is suited to the composition of the charge and one then endeavours to set such temperature accordingly by any suitable means.

It is known that one may decrease flame temperature in shaft furnaces and in parallel thereto decrease the consumption of expensive reducing substances, by introducing cheaper reducing matter into the shaft furnace, together with the hot air, through the furnace tuyeres. In blast furnaces e.g., one may thus replace a part of the coke by solid fuels such as coal or lignite, or by liquid fuels, or by gaseous fuels; the thermal capacity of the blast furnace gas will remain constant or may even rise.

It is also known that introduction of steam into the blast furnace, through the tuyeres, will result on the one hand in a substantial decrease in flame temperature, since water molecules are split and resulting oxygen combines with carbon to yield carbon monoxide and where there is generated hydrogen on the other hand, which hydrogen is a reducing agent just as well as carbon monoxide and which raises the thermal capacity of the blast furnace gas.

Regardless of whether one introduces solid, liquid, or gaseous additives into the blast furnace, one will have to accordingly adapt the hot air tuyeres and one will have to seek a reliable supply of such additives. Thus it is no surprise that equipment costs and additive costs correspond to a part or even to the total of the achieved savings.

What is desired is a process which allows one to regulate flame temperature within a shaft furnace, while using an additive that is universally accessible and cheap, which method entails minimal apparatus and minimal energy requirements and which also yields an increase in thermal capacity of the blast furnace gas.

The present invention provides a method which comprises regulating flame temperature through the water content of the fresh air that is introduced in the cowper and where an increase in water content leads to a decrease in flame temperature as well as to an increase in hydrogen content of the furnace gas. The water contained in the fresh air ultimately reaches the furnace as superheated steam; thus a further development of the method comprises using steam that is generated exclusively with the help of energy from the furnace-cowper system. This may be achieved by using the sensible heat of the fresh air that is introduced into the cowper and that is heated to more than 1 00 C through the mechanical work of a compressor.

The method according to the invention can be used so as to yield several advantages, as follows.

Modern shaft furnaces operate under pressure so that the fresh air has to be compressed beyond operating pressure, with the result of creating heat. A first advantage consists in that it is surprisingly not disadvantageous, but outright advantageous to cool the heated fresh air prior to introducing it in the cowper. The reason is that any heat provided to the cowper via the fresh air, will act in the lower part of the cowper, meaning that the structure bearing the refractory material will be heated. Once the cowper operation is switched from blowing phase to heating phase, this heat would be discarded through the flue.

A further advantage consists in that it is sufficient to inject calculated amounts of water into the fresh air supply line, downstream of the compressor, to assure that it is split into oxygen and hydrogen within the furnace flame zone. This means that one may do without a costly steam generator, since the equipment necessary to practise the method consists of merely an atomizer with a pump whose flow rate is adjustable.

Still a further advantage consists in the possibility of operating the cowper at a temperature suited to the nature of its refractory filling. Thus it is known that cowpers filled with silica refractories should be operated at a relatively high temperature, which obviously results in a correspondingly high hot air temperature. However, should the blast furnace operation require a decrease in flame temperature, for instance in view of an unavoidable alteration in charge composition, one may easily achieve such decrease, at no particular costs, by increasing the moisture content of the fresh air according to the invention.

The rise in furnace gas hydrogen content is a further advantage. We have observed an approx. 0.6% hydrogen content in blast furnace gas corresponding to a 10 g/Nm3 moisture content in fresh air; raising this to 20 g/Nm3 results in a hydrogen content of approx. 1.2%.

We have further observed that the feeding of water into the fresh air supply line leads to an improvement in furnace operation regularity, indicated by a drop in pressure which decreases the load on the compressor drive.

It seems worthwhile to mention that one should preferably feed demineralized water only. Indeed mineral deposits on the refractory fillings of the cowper may lead to problems, in that there may occur local zones where the material would show lowered melting points.

The invention will be described further, by way of example, with reference to the accompanying drawing, whose sole Figure is a schematic view of a blast furnace plant.

Blast furnace 5 is connected to cowper 1 via line 6, which has a valve V3. Cowper 1 has a structure 11 that bears refractory filling 10. Cowper 1 is further connected with flue 3 via line 8, which has a valve V1, and with compressor 4 via line 7, which has a valve V2. While the cowper runs in heating phase, valves V2 and V3 are shut, valve V2 is open, and burner 2 is fed gas (G) and air (A).

While cowper 1 runs in blowing phase, burner 2 is not in operation, valve V1 is shut, and valves V2 and V3 are open. Compressor 4 blows fresh air into cowper 1, when this air is heated before reaching furnace 5. Measuring device 1 6 monitors flame temperature in furnace 5; it is connected, via a transformer, with calculator 9. This calculator compares measurement results with preselected data and activates regulatory valve 1 4 in correspondence thereto, so that the amount of water that is necessary in order to set the desired flame temperature is fed from container 13, which is filled with demineralized water, into atomizer 1 5 which is installed in line 7.

Instead of feeding water into the compressed fresh air, one may obviously resort to increasing the moisture content of fresh air prior to compressing. One may furthermore feed steam in the fresh air instead of water, in which case one will evidently make use of the advantages offered by generating the steam with energy from the furnace-cowper system, for instance by operating a heat-exchanger within line 7. It is essential, according to the invention, that the water content of the fresh air be set to selected values before being fed into the cowper.

As explained in the example given above, flame temperature regulation may be performed continuously with the help of a calculator and by monitoring the actual temperature on a continuous basis. One may, however, also monitor the natural moisture content of fresh air and adjust such to values corresponding to the desired flame temperature, in accordance with logging tables or curves which have to be established for each individual furnace.

Claims (7)

1. A method of regulating flame temperature within a shaft furnace into which there is fed hot air from a cowper, in which such regulation comprises regulating the water content of the fresh air that is introduced into the cowper.

2. A method as claimed in claim 1, comprising monitoring the flame temperature in the furnace, comparing the measurement results with preselected data, and, in accordance therewith, feeding-larger or smaller quantities of water to the fresh air.

3. A method as claimed in claim 1, comprising monitoring the water content of the fresh air and adjusting it to empirically established values leading to the desired flame temperatures, by adding controlled amounts of water.

4. A method as claimed in claim 2 or 3, in which water is added to the fresh air following compression of the fresh air.

5. A method as claimed in any of claims 1 to 3, in which with a view to decreasing flame temperature and concurrently therewith increasing the hydrogen content of the furnace gas, atomized water is added to the fresh air.

6. A method as claimed in any of claims 1 to 3, in which steam generated with the help of energy from the furnace-cowper system is added to the fresh air.

7. A method of regulating flame temperature within a shaft furnace, substantially as described with reference to the accompanying drawing.