CN1479791A - Cooling system for metallurgical melting furnace - Google Patents

Abstract

The invention relates to a cooling system for a metallurgical smelting furnace, containing a cooling element (16i; i=1, 2, 3, 4) which is integrated into a wall in the metallurgical smelting furnace and which contains at least one internal cooling refrigerating channel (18i; i=1, 2, 3, 4). A predetermined cool water volume flow (Qi; i=1, 2, 3, 4) passes through said channel, guaranteeing the required cooling performance. The cooling system is embodied in such a way that a static absolute pressure which is less than the atmospheric pressure at the place of installation of the metallurgical smelting furnace is produced in the greater part of the at least one internal cooling channel (18i; i=;1, 2, 3, 4) of said predetermined cooling water flow (Qi; i=1, 2, 3, 4). A preliminarily container (24) for cooling water is arranged at a higher position than the cooling element(s) (16i; i=;1, 2, 3, 4) so that the geodesic superrelevation thereof determines the rest pressure in the cooling circuit.

Description

Cooling system for metallurgical melting furnace

technical field

The invention relates to a cooling system for a metallurgical smelting furnace.

Background technique

At present, most of the cooling systems used in crucible or vertical metallurgical melting furnaces are designed as closed cooling water systems. The system consists of a cooling unit integrated into the furnace wall and equipped with cooling ducts. The cooling water is pumped through the cooling pipes of the cooling unit. Air cushions are used to maintain the static pressure in the device such as the box to ensure that the static pressure at each point of the cooling pipeline is within the range of several bars. This type of cooling system is referred to below as a "pressure circulation system". On the one hand, the evaporation temperature of the cooling water increases due to the overpressure in the cooling pipes, which has a positive impact on the safety of the cooling system, since the formation of steam can greatly reduce the cooling capacity and thus lead to local overheating of the cooling unit. On the other hand, however, it has long been known that the use of such pressure circulation systems in metallurgical furnaces is not without danger. Because even a small leak will cause a large amount of cooling water to enter the melting furnace, causing damage to the refractory lining, and in some cases, even violent explosions, for example, when cooling water accumulates in the melting furnace and This is followed by liquid metal cover.

To prevent these dangers, the well-known spray cooling system has been used in metallurgical melting furnaces for more than one hundred years. However, such cooling systems are by no means able to provide the same cooling capacity as cooling units incorporated in the furnace walls, and are also particularly problematic with regard to their maintenance.

The cooling system of spraying water has been developed as a "new" cooling system that can replace the pressure circulation system. This system comprises a cooling box, which is integrated in the furnace wall, and a number of nozzles in an inner chamber for spraying cooling water on the inner wall of the chamber facing the furnace interior. Most of the overpressure in the nozzle is reduced so that only a small overpressure is kept in the cooling box. However, such water spray cooling systems are relatively expensive to manufacture and also take up a lot of space in the furnace wall.

It is worth noting that some parts of the metallurgical melting furnace are still not cooled for safety reasons. This is the case, for example, in the bottom of electric arc furnaces used in electric steelworks.

It has long been proposed to negatively pressurize the cooling systems of metallurgical smelting furnaces. The intent is to prevent cooling water from entering the melting furnace in the event of a small leak in the cooling unit. For example, a solution of this nature for wall cooling of an electric arc furnace was disclosed as early as 1984 in US Patent 4,603,423. This cooling system consists of a feed water pump, a storage tank for cooling water, a pressure reducing valve, cooling units connected in parallel, an air extraction pump and a gas separator. The feed water pump sends the cooling water from the storage tank to the cooling unit through the pressure reducing valve, and the pressure of the pressure reducing valve is lower than the atmospheric pressure downstream. The suction pump is used to suck the cooling water through the cooling unit and then reversely press it into the storage tank through the gas separator. A similar negative pressure cooling system is described in JP09287733.

The most likely reason why this type of negative pressure cooling system has not been widely accepted by metallurgical smelting furnaces is that there are many doubts about its safety. In fact, even slight pressure fluctuations can cause overheating of the cooling unit.

purpose of invention

It is an object of the present invention to provide a reliable cooling system for metallurgical smelting furnaces, which is safer than known pressure circulation systems, which guarantees a higher cooling capacity than conventional spray cooling systems, allows the use of more cooling water than known spray cooling systems The cooling system is a more compact, simpler cooling unit, and is safer than the negative pressure cooling systems that have been proposed so far. The object of the invention is achieved by means of a cooling system as claimed in claim 1 .

description of the invention

The cooling system used in the metallurgical smelting furnace of the present invention comprises at least one cooling unit integrated into the furnace wall of the metallurgical smelting furnace. The designation "furnace walls" includes the side walls of the melting furnace and the bottom or roof of the melting furnace. A minimal cooling unit has at least one internal cooling pipe through which a predetermined cooling water flow ensuring the necessary cooling capacity flows. The cooling system additionally comprises at least one storage tank for cooling water and at least one cooling water pump for drawing the cooling water heated in the cooling unit and pumping it back to the storage tank. In this case, the cooling system is hydraulically designed in such a way that, with a predetermined flow of cooling water, in the largest part of said at least one internal cooling tube, there is a lower static pressure than in the area where the metallurgical smelting furnace is installed environmental pressure. In other words, in the at least one cooling unit no overpressure of the cooling water occurs compared to the ambient pressure. This means that even if there is a slight leak in the cooling unit, the cooling water will not enter the melting furnace. Instead, ambient air or furnace gases are drawn into the internal cooling ducts of the cooling unit as a result of the leakage. Leakage can be directly monitored by gas detection devices due to the inhalation of furnace gases. Thus, there is a marked improvement in the general safety of people and equipment. The disadvantages of the known spray cooling systems are eliminated by controlling the flow of cooling water through the internal cooling pipes of the cooling unit. The cooling unit necessary for the cooling system of the invention is more compact and cheaper to manufacture than a water sprayed cooling box. It is worth noting that the cooling system of the present invention is suitable for use in both crucible and vertical metallurgical melting furnaces. In this case, it is possible to design only part of the furnace cooling system as a negative pressure system. For example, furnace cooling in particularly hazardous areas of a metallurgical smelting furnace can be designed as an underpressure system according to the invention, but the rest of the smelting furnace remains a conventional overpressure system. The cooling system according to the invention advantageously has a feedwater tank for cooling water which is installed above the at least one cooling unit and in which atmospheric pressure is maintained. The water supply tank supplies cooling water to the at least one cooling unit, and its geodesic height can determine the maximum static pressure or inlet pressure in the cooling circulation system. This forms an enlarged vessel for cooling water. Since the inlet pressure is statically fixed, dangerous pressure fluctuations in the cooling system can be virtually eliminated. This significantly improves the safety of the cooling system according to the invention compared to known negative pressure cooling systems.

Using the cooling system of the invention it is possible to create a safe bottom cooling system for metallurgical electric arc furnaces, for example. Advantageously, the cooling system according to the invention can also be used as a roof cooling system in such metallurgical arc furnaces. The cooling system according to the invention is particularly advantageously suitable for bottom cooling of blast furnaces. In all these cases, the high airtightness of the cooling system according to the invention is of particular importance.

The cooling system is usually designed as a closed circuit system, that is to say it has a recooling system and at least one cooling water pump. The cooling water pump removes the cooling water heated in the cooling unit and sends it back to the water tank through at least one recooling system. However, it is equally possible to operate the cooling system as an open cooling system, that is to say supply fresh water to the feed tank and exclude hot water return.

Advantageously, the degassing box is installed between the cooling water pump(s) and the cooling unit(s). The gas detection device can detect the furnace gas separated from the cooling water in the degassing box and indicate the leakage of the cooling system in the furnace area.

In a preferred embodiment, the degassing box comprises a gas space above the cooling water and a vacuum pump for creating a vacuum in this gas space.

In the cooling system of the invention, solid copper or cast iron cooling plates can advantageously be used as the cooling unit. However, in certain areas of the melting furnace, calandria and coils are not excluded and are also less expensive.

Description of drawings

A specific embodiment of the invention will be described below with the aid of the drawings.

Fig. 1 shows the connection diagram of the cooling system of the present invention.

FIG. 2 is a schematic view of a modification of the degassing box of the cooling system shown in FIG. 1 .

Preferred embodiments of the invention are described with the aid of the drawings

Figure 1 shows a simplified connection diagram of a cooling system for a metallurgical smelting furnace. The cooling circulation system of the melting furnace is set at 10. The cooling circulation system 10 includes a cooling water feed collector 12 and a cooling water return collector 14 . Several cooling units 16i (i=1, 2, 3, 4) are connected between the cooling water feed collector 12 and the cooling water return collector 14 . The cooling units 16i (i=1, 2, 3, 4) shown are cooling plates made, for example, of copper or cast iron, which are connected with cooling pipes 18i (i=1, 2, 3, 4) for cooling water. become a whole. These cooling plates 16i (i=1, 2, 3, 4) are installed inside the outer shell and are usually covered by a refractory lining. It is worth noting that these cooling units 16i (i=1, 2, 3, 4 ) can also be called "cooling wall" professionally.

Each cooling unit 16i (i=1,2,3,4) has a valve 20i (i=1,2,3,4) in its feed water connection and a valve 22i (i= 1, 2, 3, 4). These valves 20i and 22i make it possible to isolate the respective cooling unit 16i (i=1, 2, 3, 4) from the cooling circuit 10 . Likewise, it can also be designed such that at least one of the two valves 20i and 22i can fine-tune the pressure loss in the corresponding cooling unit 16i (i=1, 2, 3, 4). All cooling units 16i (i=1, 2, 3, 4) are connected in parallel in FIG. 1 . However, it is not excluded that the cooling circuit system 10 may also comprise cooling units connected in series.

Reference numeral 24 is designated as a cooling water feed water tank, which is installed above the cooling water feed water collector 12. The feed water tank 24 communicates with the atmosphere through the discharge pipe 25, so that the cooling water in the feed water tank 24 maintains atmospheric pressure. Cooling water can also flow into the cooling water feed collector 12 in a lower amount from the feed water tank 24 via the feed water pipe 26 . Drain pipe 27 may empty feed tank 24 into drain 28 if desired. Furthermore, the overflow device 29 likewise terminates in said drain pipe 27 .

Reference numeral 30 in FIG. 1 is designated as a closed degassing box into which cooling water flows from the reflux collector 14 . A vacuum pump 32 is connected to the degassing box 30 . The vacuum pump generates a negative pressure in the gas space 33 above the cooling water. It is worth emphasizing that the degassing box 30 is divided by a partition 34 into an injection box 36 and a suction box 38 . The cooling water flows into the injection box 36 through the return pipe 40, and most of the solid particles brought in by the cooling water are deposited in the injection box 36. When the cooling water level in the degassing box 30 is slightly above the partition 34 , the cooling water flows into the suction box 38 and also into the suction pipe 42 . The vacuum pump 32 can be, for example, a jet pump operated by means of compressed air. Reference numeral 44 designates a compressed air source (ie, a compressor for compressed air or a distribution system for compressed air), to which the jet pump 32 is connected to generate the suction jet. The suction jet creates a vacuum in the degassing box 30 . As shown in FIG. 1 , the outlet pipe of the jet pump 32 is connected to a water trap 48 through a waste air pipe 46 , where the cooling water sucked by the degassing box 30 is separated from the waste air. The water trap 48 can be installed above the feed water tank 24, for example, so that the separated cooling water can return to the feed water tank 24 through the pipe 50 by gravity.

The suction line 42 is connected to a low-pressure booster station 52 comprising, for example, two pumps 54 and 56 connected in parallel, one of which is always in operation and the other in standby. If the pumps 54 and 56 are centrifugal pumps, the NPSH (net pressure head) value present in the equipment must of course be higher than the NPSH value required for the centrifugal pump. Therefore, the centrifugal pump must be installed at a certain height below the degassing box 30, if necessary. However, to avoid the use of deep pump shafts, cavitation-insensitive pumps can also be used.

The pumps 54 , 56 are thus connected on the suction side to the degassing tank 30 via the suction line 42 . On the pressure side, it is connected to the feedwater tank 24 via a pressure line 58 . A subcooling system 60 for cooling water is installed in the pressure line 58 . Thus, the pumps 54 , 56 pump cooling water from the deaeration tank 30 , through the recooling system 60 , and back into the feedwater tank 24 . Reference numeral 62 is designated as a fresh water pipe, whereby water loss can be replenished or changed.

According to an important feature of the present invention, the cooling system is hydraulically designed in such a way that the largest part of the cooling duct 18i maintains a static pressure under a predetermined flow of cooling water, which is lower than the atmospheric pressure in the installation area of the metallurgical smelting furnace . In Fig. 1, Qi (i=1, 2, 3, 4) specifies the necessary predetermined cooling water flow in the corresponding cooling unit 16i (i=1, 2, 3, 4), which must be removed under the predetermined feed water heat and restore the temperature of the cooling water. The feed water piping to each cooling unit 16i is designed such that the inlet of the cooling piping 18i is under a slight vacuum. Cooling water flows through the cooling water pipe 18i from top to bottom. In the cooling water pipe 18i, the static pressure is affected by local and linear pressure loss (loss energy), the cross section of the pipe (velocity energy and gradient (potential energy)). It is worth noting that the loss of pressure and the reduction of the cross-section of the pipe can increase the vacuum (ie, the static absolute pressure decreases), while the gradient can reduce the vacuum (ie, the static absolute pressure increases). In order to slowly increase the vacuum from the feed connection to the return connection with a uniform pipe cross-section, the energy lost must increase somewhat faster than the decrease in potential energy.

Accurate calculation of the static pressure existing at various points in the cooling circulation system 10 is important to control the void problem. However, with modern computer programs for calculating pipe flow, this is no problem for professionals. In order to achieve sufficient safety in order to prevent voids in the cooling pipes, the static absolute pressure at any point in the cooling circulation system 10 should not be lower than kP _{D, where k} is a safety factor greater than 1 and P _D is the cooling water at the highest Evaporation pressure at cooling water temperature. It is conceivable that, for example at a maximum cooling water return temperature of 40°C, the static absolute pressure at any point in the cooling cycle should not drop below 0.4 bar.

The degree of vacuum in the cooling unit 16i (i=1, 2, 3, 4) ensures that no cooling water will enter the melting furnace even if there is a small leakage in the cooling circulation system 10 . In contrast, air or furnace gas is sucked into the cooling circuit 10 by leakage. In FIG. 1, reference numeral 70 is designated a gas monitoring device, which responds to the furnace gas collected in the gas space 33 of the degassing box 30 when a leak occurs in the cooling circulation system 10 . The operator of the melting furnace can quickly receive a reliable indication of leakage in the cooling circulation system 10 through the gas detection device 70 .

If the degassing box 30 is installed significantly below the return collector 14, the vacuum pump 32 can be omitted if necessary. Figure 2 shows a degassing box 130 of this type. The degassing tank is placed at a certain geodetic height H below the return collector 14 and is connected to it by means of a return line 40 with very little pressure loss, causing the static absolute pressure of the cooling water in the return line 40 to rise sharply. High so that the static absolute pressure in the reflux collector 14 is slightly above atmospheric pressure. Thus, degassing in the degassing box 30 can be achieved by means of a simple ventilation fan 132 to the atmosphere. In Fig. 2, reference numeral 134 is defined as a gas monitoring device capable of responding to the gas in the furnace. When the cooling circulation system 10 leaks, the gas in the furnace gathers at the front of the gas exchange valve 132 of the degassing box 130 until the gas is replaced. The valve opens. With the aid of this monitoring device 132, the furnace operator can receive very quickly a reliable indication that a leak has formed in the cooling circuit 10.

Claims (7)

1. A cooling system for a metallurgical smelting furnace, comprising: At least one cooling unit (16i; i=1, 2, 3, 4) integrated in the furnace wall of the metallurgical smelting furnace and having at least one internal cooling duct (18i; i=1, 2, 3, 4 ), the predetermined cooling water flow (Qi; i=1, 2, 3, 4,) flows through this pipeline, thereby ensuring the necessary cooling capacity; at least one storage tank for cooling water; and at least one cooling water pump (54, 56) that sucks the cooling water heated in the cooling unit (16i; i=1, 2, 3, 4) and pumps it back to the storage tank; The cooling system is hydraulically designed such that the maximum portion of said at least one internal cooling duct (18i; i=1, 2, 3, 4) is at a predetermined cooling water flow (Qi; i=1, 2, 3, 4 ), maintain a static absolute pressure, which is less than the atmospheric pressure at the place where the metallurgical smelting furnace is installed; It is characterized in that, The storage tank for cooling water is made of a feed water tank (24) for cooling water, which is installed above said at least one cooling unit (16i; i=1, 2, 3, 4). 2. The cooling system as claimed in claim 1, characterized in that a hydraulic recooling system (60) is arranged between at least one cooling water pump (54, 56) and the feedwater tank (24). 3. The cooling system according to claim 1 or 2, characterized in that it is installed on the cooling water pump (54, 56) and the at least one cooling unit (16i; i=1,2,3,4) according to the hydraulic principle ) between the degassing box (30,130); and a gas monitoring device (70,134) for detecting the gas in the furnace separated from the cooling water in the degassing box (30,130). 4. The cooling system according to claim 2, characterized in that the gas space (33) above the cooling water in the degassing box (30); and for the gas space (33) above the cooling water to generate vacuum Vacuum pump (32). 5. Cooling system according to any one of claims 1-4, characterized in that said at least one cooling unit (16i, i=1, 2, 3, 4) is a solid body made of copper or cast iron cooling plate. 6. A metallurgical melting furnace comprising at least one cooling system according to any one of the preceding claims. 7. Metallurgical smelting furnace according to claim 6, comprising at least one cooling system according to any one of the preceding claims as furnace bottom cooling of the smelting furnace.

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