Cooling system for a metallurgical furnace

Details Cooling system for a metallurgical furnace Cooling system for a metallurgical furnace

2002-10-22

2004-09-21

Kastler, Scott (Department: 1742)

Metallurgical apparatus

Means for melting or vaporizing metal or treating liquefied...

With means to cool treating means

C266S193000, C122S00100C

Reexamination Certificate

active

06793874

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a cooling system for a metallurgical furnace, in particular a blast furnace.
BACKGROUND OF THE INVENTION
Known blast furnace cooling systems are cooling water circuits, in which cooling water is circulated in a closed circuit by electric circulation pumps. The elements of the blast furnace to be cooled (i.e. the cooling staves and cooling boxes of the furnace walls, the tuyeres and hot blast equipment) are regrouped in several parallel branches or sub-circuits, which are hydraulically balanced so that a predetermined flow of cooling water circulates through each sub-circuit. A common return line, comprising one or more heat exchangers, closes the cooling circuit.
In case of an electric power failure the cooling is interrupted because the electric circulation pumps do not work. To protect cooled elements against damages in such a case, it is known to provide an emergency cooling system. Such an emergency cooling circuit comprises a gravity tank that is mounted on a support structure that is higher than the blast furnace. An emergency feed line, which is designed for a very low pressure drop, connects this gravity tank to the cooling water circuit of the blast furnace and is provided with an emergency feed valve. An emergency cooling water overflow with an emergency overflow valve is provided at the highest point of the closed cooling circuit. In case of an electric power failure, the emergency feed valve and the emergency overflow valve open. Gravity pushes the water reserve contained in the gravity tank into the cooling circuit of the blast furnace. At the highest point of this cooling circuit, the cooling water is discharged of the cooling circuit through the open emergency overflow valve into a receiving tank. In summary, emergency cooling takes place by gravity in an open circuit until the gravity tank is empty. A high pressure pump station is required to refill the gravity tank. As this high pressure pump station is generally equipped with electrical pumps, the refilling operation can only start after the end of the power failure. It will be noted that the cooling system is without effective emergency cooling function until the gravity tank is refilled.
In order to reduce the storage capacity of the emergency gravity tank, it is known to provide an emergency pump with an internal combustion engine in the closed cooling circuit. In this case it is theoretically sufficient to dimension the storage capacity of the gravity tank to bridge the time needed for starting the emergency pump. Once the emergency pump has started, the emergency feed valve and the emergency discharge valve are closed so that the cooling system works again as a closed circuit.
It will be noted that such an emergency cooling system is quite expensive. Important cost factors are not only the gravity tank and its support structure, but also the big diameter emergency water pipe, which may be several hundred meters long. In this context it will be noted that the emergency pump may help to reduce the costs of the gravity tank itself, but has of course no influence on the costs of the big diameter emergency water pipe.
It is also well known that frost protection for the gravity tank and the feed line up to the emergency feed valve often causes serious problems. Furthermore, as the emergency water is often charged with solid corrosion particles and algae, the cooling circuits of the blast furnace are contaminated after an emergency water discharge. It follows that the cooling circuits must be rinsed thoroughly after each emergency water discharge. This is in particular troublesome, if short electric power failures triggering a discharge of the emergency cooling system are quite frequent.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a cooling system for a that is less expensive but nevertheless more reliable than existing cooling systems on metallurgical furnaces.
SUMMARY OF THE INVENTION
A metallurgical furnace cooling system in accordance with the present invention includes a cooling circuit comprising an inlet and an outlet for cooling water. A return line connects the outlet to the inlet so as to form a closed cooling circuit with at least one circulation pump for circulating cooling water through this closed circuit. An emergency feed line with an emergency feed valve is connected to the inlet of the cooling circuit. This emergency feed valve opens in case of a power failure. At its highest point, the closed cooling circuit is equipped with an emergency overflow valve, which opens in case of a power failure, so that the closed cooling circuit becomes an open cooling circuit with an atmospheric pressure discharge at its highest point. In accordance with an important aspect of the present invention, the emergency water gravity tank is replaced by a pressure vessel means connected to the emergency feed line. This pressure vessel means contains a certain volume of emergency water that is pressurised by a pressurised gas. The gas pressure in the pressure vessel means warrants that an emergency water flow establishes through the open cooling circuit, in the direction of the emergency overflow valve, when the emergency feed valve and the emergency overflow valve open in case of a power failure. It will be appreciated that such a cooling circuit is a solution to a long-felt need for a cooling system for metallurgical furnaces, in particular blast furnaces, with an emergency cooling function, which is less expensive than the gravity tank solution, but nevertheless more reliable. As the pressure vessel means need not be mounted on a support tower that is higher than the blast furnace, it can be located much closer to the blast furnace, so that the emergency feed line gets shorter. Furthermore, the diameter of the emergency feed line can be reduced, because: (1) this line is shorter; and (2) a higher pressure drop in this line can be easily compensated by a higher gas pressure in the pressure vessel means. It follows that important savings can be made with regard to the costs of the emergency feed line. Further cost savings are due to the fact that an high pressure pump station, which is needed for refilling a gravity tank, becomes superfluous. Indeed, the pressure vessel means of a cooling system in accordance with the present invention can be easily refilled when the tank is depressurised, so that no high pressure pump station is necessary. After refilling with water, the pressure vessel means can be repressurised by injection of a pressurised gas. It will be appreciated that in blast furnace or steel making plants, pressurised nitrogen is normally available in the required quantities and at the required pressure for rapidly pressurising the pressure vessel means. With the system in accordance of the invention it is consequently possible to have two or more successive emergency water discharges to bridge the time laps until the end of the power failure or until the start of an emergency pump or an emergency power unit. Accordingly, the water reserve in the pressure vessel means can be much smaller than in a gravity tank. It will further be appreciated that freezing protection is easier with pressure vessel means that are located close to ground level and close to the cooling circuit, than with a high gravity tank located further away from the blast furnace. Another advantage is found in the fact that the pressurised gas in the pressure vessel means, which is generally nitrogen, avoids that the emergency water comes into contact with the atmosphere, which is of course of advantage with respect to water quality and corrosion problems. It follows that it can be expected that the emergency water from the pressure vessel means will be normally free of solid corrosion particles and algae and that contaminate of cooling circuits after an emergency water discharge will be the exception.
In accordance with another important aspect of the present invention, the pressure vessel means is not only used as pressurised emergency water reserve,

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