GB1575374A

GB1575374A - Turbines driven by the exhaust gas from a blast furnace

Info

Publication number: GB1575374A
Application number: GB4006477A
Authority: GB
Original assignee: Mitsui Engineering and Shipbuilding Co Ltd; Nippon Steel Corp
Current assignee: Mitsui Engineering and Shipbuilding Co Ltd; Nippon Steel Corp
Priority date: 1977-09-26
Filing date: 1977-09-26
Publication date: 1980-09-24

Description

(54) IMPROVEMENTS IN OR RELATING TO TURBINES DRIVEN BY THE EXHAUST GAS FROM A BLAST FURNACE (71) We, MITSUI ENGINEERING & BR< SHIPBUILDING COMPANY LIMITED, of 6-4 Tsukiji 5-chome, Chuo-ku, Tokyo, Japan, and NIPPON STEEL CORPORATION, of 6-3, temachi 2-chome, Chiyoda-ku, Tokyo, Japan, both Japanese companies, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to turbines driven by the exhaust gas from a blast furnace.

An exhaust gas discharged in a large quantity from a blast furnace has a high temperature and a high pressure. When the blast furnace exhaust gas is washed with water in a dust precipitator or the like disposed downstream, its temperature is lowered to a level approximating to embient temperature but it still retains a pressure energy. In iron manufacturing plants, it is one of important problems for attaining the energy-saving effect how to effectively recover such pressure energy possessed by a blast furnace exhaust gas.

As a most conveniently workable method for recovery of such pressure energy, there can be mentioned a method in which a turbine is driven by utilizing the blast furnace exhaust gas and a power generator is driven by this turbine, and hence the pressure energy is converted to electric energy.

This energy recovery method, however, still involves problems to be solved. In the first place, the pressure of the blast furnace exhaust gas is not constant, but in general, it is readily changed depending on the resistance in the blast furnace, which depends on the molten state of ore or the flow state of blast furnace slag. During the operation in the blast furnace, a part of the -packed - material is molten and coagulated and is often suspended in the blast furnace. When this suspended state becomes untenable, the coagulated mass falls down and a large quantity of a high temperature gas is blows out at the same time. This is the so-called "blow-out" phenomenon.

In the normal operation of the blast furnace, the temperature of the gas at the outlet of the blast furnace is 200 to 250"C.

Since this high temperature is cooled by water sprayed from a venturi scrubber or the like of a dust precipitator disposed between the outlet of the blast furnace and the turbine, the temperature of the gas at the inlet of the turbine is lowered to 60 to 80 C. However, when the blow-out phenomenon takes place, the temperature of the gas at the inlet of the turbine is elevated to 250"C. or higher. Accordingly, because of elongation of the turbine rotor or moving blades, or uneven distortion of a casing, such undesirable phenomenon as abnormal contact of the outer ends of the moving blades with the casing can occur or the power generator is overloaded.

Secondly, dust contained in the exhaust gas adhere to the transportation passage or the turbine, especially a stationary blade thereof, and this dust disturbs the gas flow and reduces the efficiency of the turbine.

As means for preventing adhesion and accumulation of dust to the casing inlet and stationary blade of the turbine, there is adopted a method in which parts to which dust is likely to adhere are coated with a material having a good parting property, such as a fluorine resin, a phenolic resin or crystalline metal oxide ceramics.

When the interior of the turbine is coated with such material having a good parting property, it is possible to prevent'adherence of dust and the resulting reduction of the efficiency of the turbine; but because such coating material lacks heat resistance or readily undergoes thermal degredation, if the above-mentioned "blow-out" phenomenon takes place in the blastfurnace, high temperature gas is instantaneously introduced into the transportation passage and the turbine, and thermally degrades the coating material.

In the blast furnace, packed materials such as ore change their shapes moment by moment, and therefore, it is impossible to prevent occurrence of the "blow-out" phenomenon. Accordingly, the turbine system must be designed and arranged so as to cope with this unavoidable "blow-out" phenomenon.

According to the present invention there is provided, in an apparatus which, in operation, feeds an exhaust gas from a blast furnace to a turbine, a protective device for the turbine which protective device comprises means for feeding water into a gas transportation passage between the blast furnace and the turbine and/or into the interior of the turbine and/or emergency shut off valve means, said protective device further comprising means capable of detecting the occurrence of a blow-out phenomenon in the blast furnace, operation of said means for feeding water and/or said emergency shut off valve means being initiated by a signal emitted from said detecting means.

In general, the temperature of the blast furnace exhaust gas at an inlet portion of the turbine is 60 to 80 C. but when the blow-out phenomenon takes place, it rises to about 250"C. and simultaneously, the gas pressure is elevated. Accordingly, in the present invention, this increase of the exhaust gas temperature elevation of the exhaust gas pressure and/or other changes in the exhaust gas are detected, and in response to the detection signal, a cooling water spraying device is operated, or a shutoff valve means is operated.

The position for detecting rising of the exhaust gas temperature or elevation of the exhaust gas pressure is selected in view of the velocity of the exhaust gas so that the cooling water spraying device can be operated without any substantial time lag from the point of occurrence of the blow-out phenomenon. Namely, means for detecting rising of the exhaust gas temperature or elevation of the exhaust gas pressure is disposed at the top of the blast furnace or in a piping in the vicinity thereof. Electric sensing means and electric signal-transmitting means are preferably used as means for detecting the temperature or pressure and means for transmitting a detection signal, respectively.

Most conspicuous changes caused by the blow-out phenomenon are those of the temperature and pressure. In addition, the composition of the exhaust gas and the combustion state are considerably influenced by the blow-out phenomenon. In the present invention, means for detecting the change of the temperature and/or pressure is/are the most appropriate means for detecting occurrence of the blow-out phenomenon, but means for detecting changes of such factors as the composition of the exhaust gas or the combustion state could be used.

A water spraying device is most preferred as means for cooling the high temperature exhaust gas. More specifically, water requires a large quantity of latent heat for evaporation, and since the exhaust gas has passed through the dust-removing step including a dust collector and a venturi scrubber and is then fed to the turbine, a considerable amount of water is contained in the exhaust gas fed to the turbine and hence if water is applied to the exhaust gas for lowering the temperature, no particular problem or disadvantage is brought about.

In the present invention, water may be fed in the form of a mixture with an agent for protecting the interior of the turbine or with other additives according to need.

In general, water spraying means is preferably disposed at an inlet of the turbine, but it may be located in part of the pipe passage.

It is preferred that water is sprayed in the atomized state under a high pressure so that it is instantaneously dispersed and gasified in the exhaust gas. The amount of water sprayed can be controlled so that the temperature of the exhaust gas fed to the turbine is maintained within the range of 60 to 800C. However, this temperature range differs to some extent according to the characteristics of the turbine and the material from which it is made. Accordingly, the amount of water sprayed is dependent on the turbine actually employed.

When the turbine or the exhaust gas transportation pipe passage is formed of a material which is not sufficiently heat resistance, water is directly sprayed to a part of such material in order to prevent the temperature of said part rising and also to prevent thermal degradation of the material.

In the present invention, since occurrence of the blow-out phenomenon in the blast furnace is detected and water is sprayed into the exhaust gas in response to a detection signal, the temperature of the exhaust gas can be effectively maintained at a predetermined level and hence, uneven distortion by thermal expansion of the interior of the turbine can be prevented. Therefore, a material which readily undergoes thermal degradation disposed in the exhaust gas transportation pipe passage or turbine, can be effectively protected and the turbine can be stably operated at high efficiency and the energy of the exhaust gas can be effectively recovered.

Further, if water is directly sprayed to a part where thermal degradation is likely to occur, the piping system can be protected efficiently.

Still in addition, in the present invention, if continuous operation of the turbine becomes impractical due to the blow-out phenomenon, the flow of the exhaust gas into the turbine can be stopped by closing a shut off valve.

For a better understanding of the invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a diagram illustrating an exhaust gas system of a blast furnace with means for actuating an emergency shut off valve on receipt of a signal indicating occurrence of the blow-out phenomenon; Figure 2 is a diagram illustrating an exhaust gas system similar to that of Figure 1 with means for spraying cooling water into a turbine on receipt of a signal indicating occurrence of the blow-out phenomenon; Figure 3 is a sectional side view of the gas inlet portion of a turbine; and Figure 4 is a diagram illustrating an exhaust gas system similar to that of Figure 1 or 2 with means for spraying cooling water to a gas flow passage leading to a turbine.

Figures 1, 2 and 4 are diagrams illustrating embodiments of the protective device of the present invention for protecting a turbine driven by a blast furnace exhaust gas from the blow-out phenomenon caused in a blast furnace In these Figures, a double line indicates the flow system of an exhaust gas from a blast furnace or the drive between turbine and generator, a solid line indicates the flow system of cooling water, and a dot line represents an electric control circuit.

Referring to Figure 1, an exhaust gas passes through an exhaust gas pipe 2a, connected to the top of a blast furnace 1, to a dust collector 3 where most of the dust contained in the exhaust gas is removed therefrom. Then, the exhaust gas is fed to a venturi scrubber 4 through an exhaust gas pipe 2b. In this venturi scrubber 4, the exhaust gas is treated with water or, with a solution of suitable chemicals, so that it will not cause any trouble, e.g. corrosion, at subsequent stages in the process. A main exhaust gas pipe passage 2c branches into a gas flow passage 2e leading to the turbine and into a gas flow control passage 2d. The gas flow control pasage 2d extends to a second venturi scrubber 6 through a top pressure control valve 5 for controlling the top pressure in the furnace 1. The second venturi scrubber 6 may be disposed just after the first venturi scrubber 4.The gas flow passage 2e is connected to a turbine 7 and the exhaust gas, after passing through the turbine 7, is fed to the second venturi scrubber 6 through an exhaust gas flow passage 2f. A power generator 8 or other load is connected to the turbine 7, and the energy possessed by the exhaust gas is recovered through the power generator 8.

Means for detecting the temperature or pressure, namely a temperature or pressure relay 21, is disposed in the exhaust gas pipe 2a at a position close to the blast furnace 1. A signal generated by the relay 21 is transmitted through an electric control circuit 22 to control an emergency shut off valve 41. Gas flow passage 2e includes a governor valve 42 for controlling the gas flow to the turbine, and gas flow passage 2f includes a shut off valve 44.

An exhaust gas discharged from the blast furnace 1 is first introduced in the dust collector 3 where coarse dust particles are precipitated and separated. Then, the gas flow is introduced into the venturi scrubber 4 where a considerable proportion of fine dust particles is removed by spraying the gas with water or a chemical solution, the temperature of the gas thereby being lowered to such a level, namely 60 to 800 C., that the gas can be used in the turbine.

The flow rate of the gas passing through the gas flow control passage 2d is controlled by the valve 5 so that the pressure of the blast furnace gas is maintained at a certain level irrespectively of the load on the turbine 7. The exhaust gas from the turbine 7 joins the gas flow from the passage 2d, and the combined gas is fed to a subsequent gas-utilizing plant through the second venturi scrubber 6 and an exhaust gas flow passage 2g.

The temperature or pressure relay 21 is disposed to detect an abrupt change in the temperature or pressure of the exhaust gas caused by the blow-out phenomenon in the blast furnace 1. It is preferred that the sensing part of the relay 21 be composed of a material which is not degraded even when exposed to dust-containing exhaust gas, and that the surface of the sensing part of the relay 21 be covered with a crystalline metal oxide ceramic coating and the coating surface be polished so as to prevent adherence and deposition of dust.

The temperature or pressure relay 21 may be disposed in any part of the passageway between the blast furnace 1 and the turbine 7. However, in order to-assure a sufficient time from the point of detection of a temperature or pressure change by the blow-out phenomenon to the point of arrival of an abnormally high temperature gas at the turbine 7 and provide sufficient time for actuation of the turbine-protective device, it is preferred that the relay 21 be disposed at a position as close to the blast furnace 1 as possible.

In the foregoing embodiment, when the blow-out phenomenon takes place in the blast furnace 1, abnormal elevation of the temperature or pressure is detected by the relay 21 and closes the emergency shut off valve 41 and opens the valve 5, whereby introduction of the gas into the turbine 7 is intercepted. Since the operation time of the emergency shut off valve is much shorter than that of the septum valve, there may arise a fear of elevation of the pressure in the entire system. However, since the volume of the entire system is large, in general, this elevation of the pressure is not significant.

In the embodiment of the invention described above, the turbine 7 does not operate when the blow-out phenomenon takes place and the above protective means is actuated.

In contrast, in the embodiment of the elevation illustrated by Figures 2 and 3 cooling water is sprayed in the interior of the turbine and the turbine can be operated continuously even if the blow-out phenomenon takes place.

Figure 2 is a systematic diagram similar to Figure 1. In Figure 2, the turbine is provided with a water spraying device comprising a water pouring valve 23 and a cooling water pipe 24. When the blow-out phenome non occurs and it detected by the pressure or temperature relay 21, the water pouring valve 23 is opened on receipt of a signal from relay 21 and sprinkles cooling water in the interior of the turbine, thereby lowering the gas temperature.

Figure 3 is a sectional view of part of turbine 7 showing where cooling water is sprayed into the turbine 7. A rotor shaft 34 is rotatably supported at the centre of a casing 31 and a moving blade 33 is fixed to the periphery of the rotor shaft 34. Further, a stationary blade 32 is mounted in the casing 31. A cooling water-spraying nozzle 25 is mounted in the vicinity of a gas supply opening 35 so that cooling water is sprayed onto a first stage stationary blade 36 fixed to the casing 31. Cooling water sprayed from the nozzle 25 is dispersed in the gas flowing in the casing 31 and receives heat therefrom and evaporates, whereby the temperature of the gas is lowered.

It is preferred that the cooling water spraying nozzle 25 is disposed at a location where the exhaust gas is fed into the tur bine as shown in Figure 3. If the temperature of the gas is lowered by spraying of cooling water, elevation of the temperature of parts of the turbine is greatly reduced, and degradation of a material having poor heat resistance, for example a coating layer formed on the stationary blade to prevent adhesion of dust, can be effectively prevented. Moreover, dust adhering to the stationary blades and the inlet portion of the casing can be removed.

If it is not necessary to lower the temperature of the gas fed to the turbine so much, the cooling water spraying nozzle may be disposed at a position other than that mentioned above. For example, it may be disposed in any part of the exhaust gas passageway between the blast furnace and the turbine.

In one embodiment of the invention, the temperature of a part which readily undergoes thermal degradation is locally lowered.

For example, when the first stage stationary blade is coated with a material which is likely to undergo thermal degradation, cooling water is sprayed on to it so as to protect only the area of the coating. In this embodiment, the amount of water to be sprayed can be reduced, but in many cases the temperature of the gas passing through the turbine is not so lowered.

However, thermal degradation of the part that is likely to undergo thermal degradation can be effectively prevented.

When the blow-out phenomenon takes place in the blast furnace, because of elevation of the temperature and pressure, the output of the turbine is increased. Accordingly, when the capacity of the power generator is limited, it is necessary to adopt means coping with this increase of the output of the turbine. It is possible to cope with the elevation of the pressure by opening and closing the top pressure control valve and governor valve according to a customary control, but special arrangements should be made to cope with the increase of the output of the turbine caused by the rising of the temperature. A temperature relay 21 is disposed as shown in Figure 4, and a control circuit 22 is arranged so that when the temperature detected by the relay 21 exceeds a predetermined level, the governor valve is closed to a degree corresponding to the excess of the temperature over the predetermined level. By this arrangement, it is possible to prevent an excessive load from being imposed on the power generator.

In another embodiment of the invention, the water spraying means is located in the passageway upstream of the turbine. Such an arrangement facilitates disposition of water spraying means. Thus, a plurality of water spraying nozzles may be mounted and maintenance of the water spraying means can be done with ease. At any rate, in the embodiments described above which employ water for lowering of the gas temperature, it is necessary to atomize the water.

WHAT WE CLAIM IS: 1. In an apparatus which, in operation, feeds an exhaust gas from a blast furnace to a turbine, a protective device for the turbine which protective device comprises means for feeding water into a gas transportation passage between the blast furnace and the turbine and/or into the interior of the turbine and/or an emergency shut off valve means, said protective device further comprising means capable of detecting the occurrence of a blow-out phenomenon in the blast furnace, operation of said means for feeding water and/or said emergency shut off valve means being initiated by a signal emitted from said detecting means.

2. A protective device as claimed in claim 1, wherein said means for feeding water into a gas transportation passage comprises a spraying means.

3. A protective device as claimed in claim 1, wherein the means for feeding cooling water is disposed in the gas inlet portion of the turbine.

4. A protective device as claimed in claim 1 or 2, wherein said means capable of detecting the occurrence of the blow-out phenomenon in the blast furnace is means sensing a change in the temperature and/or pressure of the exhaust gas.

5. A protective device as claimed in claim 1, 2 or 3, wherein part of the stator of the turbine is coated with a material to which dust hardly adheres and said means for spraying water is disposed in the vicinity of said coated part of the stator.

6. A protective device as claimed in claim 1, 2 or 4,. wherein a passageway for the exhaust gas from the blast furnace branches into a part for feeding the exhaust gas to the turbine and a part for controlling the flow of the exhaust gas so that a predetermined amount of the exhaust gas can be supplied to the turbine.

7. In an apparatus which, in operation, feeds an exhaust gas from a blast furnace to a turbine and drives the turbine by the action of the exhaust gas, a protective device for the turbine to be driven by the blast furnace exhaust gas, which comprises means for feeding water to a material readily undergoing thermal distortion or thermal degradation, which is disposed in the turbine, and means for sensing and detecting occurrence of the blow-out phenomenon in the blast furnace, wherein said feeding means is operated by said detecting means on detection of occurrence of the blow-out phenomenon in the blast furnace.

8. In an apparatus which, in operation, feeds an exhaust gas from a blast furnace to a turbine driven by the exhaust gas, a protective device for the turbine to be driven by the blast furnace exhaust gas, which comprises a control valve disposed at an exhaust gas inlet of the turbine and means for sensing and detecting occurrence of the blow-out phenomenon in the blast furnace, wherein on receipt of a detection signal from said detecting means, said control valve is operated to control the flow amount of the gas so that an overload owing to increase of the output of the turbine by the temperature rising caused by the blow-out phenomenon is not imposed on a power generator connected to the turbine.

9. A protective device substantially as hereinbefore described with reference to and as shown in Figure 1, Figures 2 and 3 or Figure 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. water. WHAT WE CLAIM IS:

1. In an apparatus which, in operation, feeds an exhaust gas from a blast furnace to a turbine, a protective device for the turbine which protective device comprises means for feeding water into a gas transportation passage between the blast furnace and the turbine and/or into the interior of the turbine and/or an emergency shut off valve means, said protective device further comprising means capable of detecting the occurrence of a blow-out phenomenon in the blast furnace, operation of said means for feeding water and/or said emergency shut off valve means being initiated by a signal emitted from said detecting means.