JPH05263613A - Energy recovering device in molten reducing iron manufacturing - Google Patents

Abstract

PURPOSE:To easily recover carbon dioxide and prevent nitrogen oxide or carbon dioxide from being dumped to the atmosphere by subjecting exhaust gas in a reducing furnace to combustion by not air but oxygen, and using the resultant combustion gas as gas for dilution for a temperature. CONSTITUTION:Reducing furnace exhaust gas, which is cooled in a first cooler 3 and pressurized in an exhaust gas compressor 4, is introduced into an oxygen combustor 9, to be utilized as fuel. A part of oxygen to be used in a reducing furnace 1 is branched and supplied into the oxygen combustor 9, thus generating combustion gas of a high temperature. Accordingly, the exhaust gas in the reducing furnace is burnt with oxygen so that nitrogen cannot be included into the main component of the combustion gas. The combustion gas is adapted to drive an expansion turbine 10. Most of the gas exhausted from the expansion turbine 10 is supplied into the oxygen combustor 9 through a circulating path 17, thus cooling high temperature gas after combustion. A part of the gas recovers carbon dioxide in a carbon dioxide recovering device 20, where the recovery can be easily carried out because the gas is consisted of carbon dioxide and steam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an energy recovery system for a smelting reduction iron reduction furnace and an iron blast furnace.

[0002]

2. Description of the Related Art FIG. 4 is a system diagram showing an example of a conventional energy recovery device for a reduction furnace. In this figure, iron ore is supplied from the upper part to the reduction furnace (1), and coal and limestone are supplied in the form of fine powder from the side wall. Further, oxygen is supplied from the lower part, and the iron ore is melted and reduced by the combustion of coal to produce iron. In the reduction furnace (1), hydrogen gas,
A mixed gas of carbon monoxide and carbon dioxide gas is continuously generated to be in a pressurized state, and is discharged to the outside of the furnace as exhaust gas.
The discharged exhaust gas is separated in the separator (2) into a solid content accompanying the gas, and the solid content returns to the reducing furnace (1) again. The exhaust gas is then cooled to a predetermined temperature (normal temperature) by the cooler (3) and pressurized by the exhaust gas compressor (4).

The pressurized exhaust gas reaches the combustor (8) and is used as fuel. That is, the gas discharged from the reduction furnace (1) is a combustible gas because the main components are hydrogen, carbon monoxide, and carbon dioxide gas. Then, this is burned to obtain high-temperature gas and recover it as energy. At this time, oxygen in the air and the exhaust gas from the reducing furnace are oxidatively burned to a high temperature, and therefore, in order to dilute this gas to a predetermined temperature, excess air is pressurized and supplied by the air compressor (17). The combustion gas that has left the combustor (8) is expanded in the expansion turbine (10) to obtain rotational power and drive the generator (11) and the compressors (4) and (7). The gas discharged from the expansion turbine (10) is further heat-recovered by the exhaust heat recovery boiler (12) and released to the atmosphere. Exhaust heat recovery boiler (1
The steam generated in 2) expands in the steam turbine (13) and drives it to rotate.

As described above, the air compressor (7) for pressurizing air, the expansion turbine (10), and the generator (11) are arranged on one axis. Further, the exhaust gas compressor (4) for pressurizing the exhaust gas is also arranged on the same axis, but it is a different axis depending on the convenience of operation.

[0005]

It is an ideal connection method that the rotating devices necessary for energy recovery are arranged on one axis as described above, although it is an ideal connection method. However, the following restrictions apply. This could be a problem in some cases, which was a problem.

One is the problem of shaft vibration. Vibration caused by the connection of a large number of rotating devices tends to have a hypersensitive vibration response due to the connection method and misalignment.
Further, torsional vibration is likely to occur in the long shaft, which may lead to an accident. Even if the stability is evaluated for the lateral axial vibration that occurs in each device, it is difficult to predict the vibration due to misalignment between the connection and the device because it changes depending on the installation method, the ground, and the like.

The second is the problem of starting torque. A device called a compressor continuously requires torque, and the torque is negative even at the time of starting. In addition, the expansion turbine, if the flow rate of the working gas is secured and the temperature does not exceed the predetermined temperature,
No positive torque is produced. Therefore, this type of energy recovery requires a starting device that compensates for the negative torque at the time of starting. If the number of devices connected to the expansion turbine on one axis increases, the negative torque at the time of starting increases and the required capacity of the starting device also increases.

Further, there is a problem of surging. The compressor is
The passage area through which the gas passes is gradually reduced in accordance with the compression characteristics of the handled gas. When handling a high-molecular-weight gas, the volume reduction rate due to compression is particularly large, so the passage area is significantly reduced. Further, this compressor originally requires a negative torque, and when the speed is increased from the stationary state, the torque increases in proportion to almost the square of the rotation speed. When the number of revolutions is low, the pressure also rises in proportion to the square of the number of revolutions, so even if the total amount of sucked gas is pushed to the high pressure stage side, the passage with a relatively narrow area can be sufficiently used. It cannot flow, and some gas flows backwards and plunges into surging. Since this surging is accompanied by a torque fluctuation, the rotational speed also fluctuates and becomes unstable. This phenomenon is particularly remarkable in a gas having a large molecular weight.

[0009]

In order to solve the above-mentioned conventional problems, the present invention provides a first cooler for cooling exhaust gas of an ironmaking furnace containing hydrogen and carbon monoxide, and the first cooler. Driven by combustion gas generated in the oxygen generator, a first compressor for compressing the exhaust gas discharged from the first compressor, an oxygen combustor that burns the exhaust gas discharged from the first compressor with oxygen, and a combustion gas generated in the oxygen generator. An expansion turbine coaxially connected to the rotary shaft of the first compressor, a generator coaxially connected to the rotary shaft of the expansion turbine, and a second turbine for cooling the combustion gas exiting the expansion turbine. A cooler, a second compressor that is coaxially connected to the rotary shaft of the expansion turbine, and that compresses the combustion gas that exits the second cooler, and the combustion gas that exits the second compressor. Third cooler that cools the rotating shaft of the expansion turbine A third compressor for compressing the combustion gases, which is connected coaxially exit said third cooler, the third
Carbon dioxide recovery device for separating carbon dioxide gas from the combustion gas discharged from the compressor, and a circulation line for branching a part of the combustion gas discharged from the third compressor to the oxycombustor And a bleed line for communicating at least a part of the compression process of the first, second and third compressors with an inlet of a cooler provided immediately upstream of the compressor. The present invention proposes an energy recovery device for smelting reduction iron making characterized by the above.

[0010]

In the present invention, the exhaust gas of the reducing furnace is compressed and burned, and when the combustion gas drives the expansion turbine to recover energy, the exhaust gas of the reducing furnace is burned with oxygen instead of air, and Since the combustion gas, that is, a mixed gas of carbon dioxide gas and steam is used as a gas for temperature dilution, nitrogen does not enter the combustion gas. Therefore, carbon dioxide can be easily recovered, and nitrogen oxide and carbon dioxide need not be discarded into the atmosphere.

Further, in the present invention, since the extraction line which communicates with the inlet of the cooler provided immediately upstream of the compressor in the middle of the compression process of the compressor is provided, in the low rotational speed range, If the bleeding mechanism is opened to bleed off a part of the absorbed gas and then the bleeding mechanism is closed as the rotation speed increases, the rotation speed can be increased without surging.

On the other hand, extracting a part of the gas in the low rotation speed range lowers the discharge pressure of the compressor and the flow rate of the gas passing through the compressor. Get smaller. Further, since the pressure on the suction side of the compressor can be lowered by the bypass line extending from the discharge side to the suction side of the compressor, the suction flow rate (weight flow rate) of the compressor can be reduced and the torque can be reduced. .. The expansion turbine also has a negative torque at the time of starting, but when the fuel is injected and ignited, a positive torque is generated. Since this increases as the number of revolutions increases, it can be self-sustaining if the starter covers the torque until immediately after fuel ignition, and thereafter, it can be accelerated by adding fuel. As described above, reducing the starting torque of the compressor is effective for reducing the capacity of the starting device.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, 2 and 3 are system diagrams showing first, second and third embodiments of the present invention, respectively. In these figures, the portions similar to the conventional one described with reference to FIG.
The same symbols are attached and detailed explanations are omitted.

In this embodiment, the reducing furnace exhaust gas cooled by the first cooler (3) and pressurized by the exhaust gas compressor (first compressor) (4) is converted into the oxygen combustor (9). Will be used as fuel. In this oxycombustor (9), oxygen used in the reduction furnace (1) is partially branched and supplied, and the exhaust gas is oxidized to generate high-temperature combustion gas. As described above, in the present embodiment, since the exhaust gas of the reduction furnace is burned using oxygen, the main components of the combustion gas are carbon dioxide gas and water vapor, and nitrogen is not included.

Thereafter, the combustion gas is expanded in the expansion turbine (10) in the same manner as in the conventional case to obtain the rotational power and the generator (11).
And driving the exhaust gas compressor (4) and others. The gas exiting the expansion turbine (10) is further fed to the second cooler (1
After being cooled to room temperature in 5), it is pressurized by the circulating gas compressor (second compressor) (16), and most of it is circulated to the oxycombustor (9) through the circulation pipe (17). It is used for cooling (temperature dilution) the high temperature gas supplied and burned to a predetermined temperature. The temperature is governed by the heat resistant temperature of the expansion turbine (10).

A part of the gas discharged from the circulating gas compressor (16) is cooled again to room temperature by the third cooler (18), and is further cooled by the carbon dioxide gas compressor (third compressor) (19). It is pressurized and reaches the carbon dioxide recovery device (20). The main components of this gas are only carbon dioxide and water vapor as described above. Since water vapor is easily condensed by cooling to be condensed water, carbon dioxide can be easily recovered by cooling and pressurizing this gas.
In this case, water vapor exists as a partial pressure at the lowest temperature of the circulation system, and if it exceeds this, it becomes water and is discharged out of the system. Then, since a gas having the same molecular weight as the exhaust gas becomes a surplus in the circulation system, this gas is taken out from the system by the carbon dioxide gas compressor (19) and pressurized in the carbon dioxide gas recovery device (20) to be recovered.

In this embodiment, in the oxygen combustor (9), the exhaust gas of the reduction furnace (1) is burned by using oxygen instead of air, and a mixed gas such as carbon dioxide and steam is used as a gas for temperature dilution. Since it is used, there is no nitrogen in the combustion gas. Therefore, carbon dioxide can be recovered without requiring a special separation device, and nitrogen oxides and carbon dioxide need not be discarded into the atmosphere. And since the oxygen production process is attached to the smelting reduction iron making equipment and this oxygen can be used,
No new oxygen production equipment is required.

The exhaust gas compressor (4), the expansion turbine (10), the circulating gas compressor (16) and the carbon dioxide gas compressor (19) of this embodiment are arranged uniaxially and coaxially with the generator (11). It is connected. Each compressor (4), (16), (1
9) produces a negative torque and the expansion turbine (10) produces a positive torque, and this difference is the power generation amount of the generator (11). The devices arranged on these one axis all have a negative torque at the start. Therefore, in order to obtain the torque required for the start, a starter (21) is provided at the shaft end to accelerate the start-up. To carry.

Since the exhaust gas of the reduction furnace (1) may not be obtained at the time of starting, a separate starting fuel (natural gas, etc.)
A line (22) is provided. That is, when the shaft system started by the starter (21) gradually increases in speed and the circulating gas begins to recycle, the starting fuel is ignited and burned by oxygen in the oxycombustor (9). When this amount of fuel increases, the torque of the expansion turbine (10) increases and the shaft system is accelerated so that it can rotate independently without a starter. At this time, the activation device (21) is disconnected from this shaft system. When the fuel and oxygen are further increased, the rotation speed further increases, the rated speed is reached, and the start-up is completed.

The negative torque of each of the compressors (4), (16) and (19) increases in proportion to the square of the increase in the rotation speed. Therefore, in this embodiment, the compressor is provided with an extraction mechanism and an extraction line to reduce the starting torque. Since the compressor that handles high-molecular-weight gas has a large reduction ratio of the passage area in the compression stroke, the gas sucked on the low-pressure side may pass through without increasing the passage pressure on the high-pressure side under conditions where the rotation speed is excessive. There is a possibility that some of them may flow backward and cause a surging phenomenon, but in the present embodiment, this can also be prevented by installing a bleeding mechanism and a bleeding line.

The bleeding mechanism and the bleeding line are attached in the middle of the impeller of the compressor, and are kept open at the time of startup. Then, the sucked gas is boosted by the impeller in the compressor, and a part of the gas is extracted in the extraction mechanism, so that the amount of gas flowing into the impeller after that is decreased and the torque required for starting is reduced. .. The gas extracted here is returned to the suction side of the compressor, cooled by the cooler on the suction side, and sucked into the compressor again. The bleed line is closed as the number of revolutions increases, and the gas is boosted without bleed at full speed at the rated speed.

In FIG. 1, when the circulating gas compressor (16) is provided with a bleeding mechanism and a bleeding line (16a), in FIG. 2, the circulating gas compressor (16) and the carbon dioxide gas compressor (19) are bleeding mechanism and bleeding. When lines (16a) and (19a) are provided, and FIG. 3 shows all compressors (4), (16) and (19)
Bleeding mechanism, bleeding lines (4a), (16a), (19
The case where a) is provided is shown. Whether or not the bleeding mechanism and the bleeding line as described above are provided depends on the individual case. The torque ratio of each device differs depending on the design conditions, but the outline is as follows: exhaust gas compressor (4) is -1.0, expansion turbine (10) is +9.5, circulating gas compressor (16) is -4.6, carbon dioxide. Gas compressor (19)
Is −1.5. Therefore, the circulating gas compressor (16) must always be provided with an extraction mechanism and an extraction line, but the presence or absence of the other compressors (4) and (19) can be determined depending on the plant scale.

[0023]

According to the present invention, the following effects can be obtained.

1) Since the exhaust gas of the reduction furnace is burned by using oxygen instead of air, and the mixed gas of carbon dioxide gas and steam is used as the gas for temperature dilution, nitrogen is not present in the combustion gas. Therefore, carbon dioxide can be recovered without requiring a special separation device, and nitrogen oxides and carbon dioxide need not be discarded into the atmosphere. An oxygen production process is attached to the smelting reduction ironmaking equipment, and the oxygen can be used, so that no new oxygen production equipment is required.

2) By providing the pipe line for extracting air from the middle of the compression process of the compressor, the torque at the time of starting can be reduced and the starting device can be miniaturized. As a result, it is possible to arrange the rotating devices on the same axis, omit the electric motor required in the case of separate placement, and improve the power transmission efficiency between the devices. In addition, this uniaxial operation simplifies the operation including starting and stopping, and reduces the area required for installation.

3) The bleeding prevents the surging of the compressor.

[Brief description of drawings]

FIG. 1 is a system diagram showing a first embodiment of the present invention.

FIG. 2 is a system diagram showing a second embodiment of the present invention.

FIG. 3 is a system diagram showing a third embodiment of the present invention.

FIG. 4 is a system diagram showing an example of a conventional energy recovery device for a reduction furnace.

[Explanation of symbols]

(1) Reduction furnace (2) Separator (3) (First) cooler (4) Exhaust gas compressor (first compressor) (7) Air compressor (8) Combustor (9) Oxygen combustion Unit (10) Expansion turbine (11) Generator (12) Exhaust heat recovery boiler (13) Steam turbine (15) Second cooler (16) Circulating gas compressor (second compressor) (17) Circulating pipe Line (18) Third cooler (19) Carbon dioxide gas compressor (third compressor) (20) Carbon dioxide gas recovery device (21) Starter device (22) Fuel line for starting (4a), (16a), (19a) Extraction line

Claims (1)

[Claims] 1. A first cooler for cooling the exhaust gas of an iron-making furnace containing hydrogen and carbon monoxide, a first compressor for compressing the exhaust gas leaving the first cooler, and the first compressor. An oxygen combustor that burns the exhaust gas from the compressor using oxygen, and an expansion turbine that is driven by the combustion gas generated in the oxygen generator and that is coaxially connected to the rotation shaft of the first compressor. A generator that is coaxially connected to the expansion shaft of the expansion turbine, a second cooler that cools the combustion gas that exits the expansion turbine, and a coaxial connection to the rotation shaft of the expansion turbine. A second compressor that compresses the combustion gas that exits the second cooler, a third cooler that cools the combustion gas that exits the second compressor, and a coaxial shaft of the expansion turbine. And compresses the combustion gas from the third cooler connected to A third compressor, a carbon dioxide recovery device for separating carbon dioxide from the combustion gas discharged from the third compressor, and a part of the combustion gas discharged from the third compressor. And a circulation line for supplying the oxy-fuel combustor to the oxy-fuel combustor, and a cooler provided immediately upstream of the compressor in the middle of the compression process of at least a part of the first, second and third compressors. An energy recovery apparatus for smelting and reducing ironmaking, comprising: an extraction line communicating with an inlet.