KR820000851B1 - Method for the direct reduction of clron using gas from coal - Google Patents

Abstract

In the direct redn. of iron oxide with hot reducing gas to produce iron and a CO2 contg. spent reducing gas, the improvement comprises(a) removing a large portion of the CO2 from the gas; (b) forming a hot gasifier gas from fossil fuel; (c) tempering the gas (b) with a first stream of the reductant -rich gas produced in (a) to produce a hot gas mixt.; (d) reacting the gas mixt. (c) with a S acceptor to form a hot desulphurized gas; (e) heating a second stream of the gas produced in (a); and (f) mixing the gas (e) with gas (d) to form a reducing gas having a quality of >=8 and a temp. of 760-900≰C for introduction to the furnace.

Description

Direct reduction method of iron using coal gas

Process diagram showing an embodiment of the present invention.

Direct reduction of iron oxides, such as pellets or lump ores, into solid metal iron has recently been carried out in many plants around the world. The annual output of the plant in operation or under construction, produced by direct reduction, exceeds 150 million metric tons.

These plants are mainly used in sl ectric arc steelmaking furnaces to make feedstock.

The annual output of the plant in operation or under construction, produced by direct reduction, exceeds 150 million metric tons. These plants are mainly used in electrified arc steelmaking furnaces to make feedstock.

Directly-reduced iron was planned to be increased to meet global demand, such as the feedstock, as the electric arc steel mill was built.

Most plants that manufacture iron by direct reduction use natural gas as the reducing agent.

The natural gas is converted to produce CO and H ₂ as reducing agents.

Some plants use the kiln process in a rotary kiln process, such as the SL-RL process, in which the coal is separated into CO and H ₂ and reacted directly with coal in-situ without gasification. This is because coal is used as the reducing agent.

This is in contrast to the need for natural gas of 3,0 to 3.5 G.cals per metric ton for direct reduction of iron in more efficient natural gas processes such as the Midren, Profer or Amco processes. In contrast.

Gasification of coal with oxygen and steam by partial oxidation to produce a gas that can be used in various methods of directly reducing iron is available in various ways such as US Patent No. 3,853,538, which has not been put to practical use.

The above methods have not been put to practical use because the process is too complicated, uneconomical and the coal demand is too high. The biggest reason for the uneconomical and high coal demand is that hot gas from coal gasifiers has a reducing agent (CO + H ₂ ) compared to the oxidizing agent (CO ₂ H ₂ O steam), which is used directly for the direct reduction of iron. Because too little.

In the present invention, the hot gas from the coal gasifier is reduced by the reaction with a sulfur acceptor, in particular lime, in order to produce a hot desulfurized gas which is reduced together with the reducing gas used up from the reduction furnace.

The second stream of reduced gas used to be raised is heated by combustion of the consumed reducing gas and mixed with the hot desulfurized gas to produce a hot reducing gas for use in the reduction furnace.

The method according to the invention can achieve high thermal efficiency and make practical use of iron reduction directly using coal gasification as a reducing agent source of the improved coal gasification technology currently under development.

The method according to the present invention requires approximately 3.1 Gcals of coal to gasify and 0.4 Gcals of coal to generate 30% efficiency for producing oxygen necessary for gasification, so the total coal requirement is metric. About 3.5 Gcals per ton.

An object of the present invention is to reduce the coal consumption to a minimum by increasing the thermal efficiency in the direct reduction of iron using coal gas. In addition, the present invention provides a method of directly reducing iron by directly using hot gas from a coal gas machine by mixing the reduced gas consumed by the rising furnace.

In addition, desulfurization of hot gas from coal gas by reaction with sulfur-actuate such as lime, and hot reducing gas is made by mixing recycled reducing gas and desulfurized gas with a lot of hot reducing agent. .

It is also to provide a more efficient method than known methods that can reuse the gas used in the reduction furnace.

When described in detail with reference to the drawings as follows.

The direct reduction of the refractorylined counterflow shaft typer is 10 in the figure.

Iron oxide (12), a raw material, usually 5-30 mm in size and present in the form of oxide pellets or natural ore masses, is fed to the fuel inlet 14 and enters the furnace through the raw material pipe 16. The reduced iron, pellets and / or lumped product are discharged through the discharge pipe 18 at the bottom of the furnace by the discharge conveyor 20, the speed being able to control the lowering of the charges in the furnace 10. have.

The new hot reducing gas enters through the hot reducing gas inlet pipe 21 and passes through several gas inlets 22 provided in the fire wall in the middle of the furnace 10.

The hot reducing gas enters the interior and flows back upward against the descending ash.

The used reducing gas with high CO ₂ discharges the charge near the stock line 24 at the top of the furnace, replacing oxidation with the feed from the feed pipe 16.

The CO ₂ -rich used reducing gas will hereinafter be referred to as top gas and is discharged from the furnace through an offtake pipe 26.

In the lower area below the furnace 10, the reduced iron is cooled before it is discharged. The hot reducing gas enters the interior and flows upwards against the descending ash.

The reduced gas used with high CO ₂ discharges the charges near the stock line 24 at the top of the furnace as a substitute for the feed from the oxide feed pipe 16.

The CO ₂ -rich used reducing gas will hereinafter be referred to as top gas and is discharged from the furnace through an off take pipe 26.

The lower area below the furnace 10 is equipped with a cooling gas circuit for cooling the reduced iron prior to discharge.

The cooling circuit has a cooling gas inlet 30 connected to the cooling gas distribution unit 31 in the furnace, and has a cooling gas resin portion 32 above the cooling gas distribution unit 31, and has a cooling gas outlet ( 34) and an external gas recirculation system with a cooler-scrubber 39 and a recirculation fan 38.

Oxygen or oxygen coming through the injector 42 and H ₂ O are exhausted from the system through the exhaust pipe 52 for use as a gas.

The other part of the top gas is exhausted through the pipe 54 for use as combustion fuel. The other part of the top gas is compressed in the gas compressor 56 and fed through a pipe 60 to a general regenerative type CO ₂ removal device 58.

In the CO ₂ removal unit 58, most of the CO ₂ is that the reducing agent leaving the CO ₂ removal unit 58 through pipe 64 is removed from the top gas to produce a rich gas. A portion of the reducing agent rich gas is supplied to the conditioning pipe 66 to regulate the hot gas in the pipe 46 to a temperature below the resolidification point.

The regulating gas that can be converted is fed to the gas discharge zone of the gaseous machine 40 which is not affected by the adverse effect of the gasification temperature.

After mixing by the regulating gas of the pipe 66, the hot gas in the partially cooled pipe 46 is supplied to the gas desulfurizer 70 through the gas inlet pipe 68.

The desulfurizer 70 is followed by a lifter-line counter, in which a special limestone is fed through a feed hopper 72 and fuel pipe 74 to form a charge in the desulfurizer 70. Is mounted on the upper part of the shaft type furnace.

The regulated hot gas fed through the gas inlet pipe 68 enters the desulfurizer through the gas inlet 76 in the fire wall located in the center of the furnace.

The gas rises in the reverse direction for the descending charge. The hot desulphurized gas exits the charge at the stock line 78 and is fed to the offlake pipe 80. The specially reacted lime containing residual lime which has not reacted with sulfur is discharged from the desulfurizer via the discharge pipe 82 by the discharge conveyor 84. Removal of the special material reacted by the conveyor 84 through the pipe 82 may cause the charge to move by gravity and control the descent of the charge through the desulfurizer 70.

Some of the reducing agent-rich gas from the CO ₂ remover (58) passes the pipe (86) to a cooling gas distributor (88) with a desulfurizer (70) at the bottom as a cooling gas to cool the charge before being discharged. Supplied through.

The cooling gas rises upwards through the desulfurizer and is preheated by a hot charge that descends before reaching the middle portion. The gas heater 90 is equipped to heat the gas rich in the reducing agent of the pipe 99 to a suitable temperature for use as a reducing gas in the reduction furnace 10.

A burner 94, which has several heating tubes 92 and exhaust gas chimneys 96 for heating, and which is one of the heating tubes, is shown in the drawing. The hot exhaust gas from the chimney 96 is used to heat the combustion air of the source 98 used for the burner 94 in a heat exchanger (not shown). The fuel used for burner 94 is a top gas supplied to pipe 54.

The heated reducing agent-rich gas leaving the heater 90 through the pipe 100 is mixed with the hot desulfurized gas exiting the desulfurizer 70 and passed through the pipe 102 to obtain the gas temperature of the desired furnace inlet. Regulates a gas rich in cold reducing agents.

The final gas mixture is a hot reducing gas supplied to the reduction furnace 10 through the gas inlet 21.

The type of reduction furnace with the highest efficiency in direct reduction of iron is a counterflow type shaft furnace in which the reducing gas and the reduced solids flow back to each other.

By this relationship, the hot reducing gas not only reduces the iron oxide of the metal iron but also heats the incoming cold iron oxide to maintain the reduction temperature.

The counterflow type shaft fakees also have a higher chemical efficiency than the other types of reduction furnaces because the hot reducing gas supplied to the furnace is sufficiently hot.

The quality of the reducing gas is usually expressed by the ratio of the reducing agent (CO ₂ + H ₂ ) to the oxidizing agent (CO ₂ + H ₂ O) of the gas mixture.

In a typical plant using natural gas, the quality of the hot reducing gas should be at least about 8 in order to achieve the maximum chemical efficiency of the counter blow shaft reduction furnace. Good gaseous quality in the gasification of pulverized solid fossil fuels such as coal or lignite in a partial oxidation type gaseous gas such as gaseous gas 40, which produces mainly hot gases containing CO, H ₂ , CO ₂ and H ₂ O. Gases are practically produced at around 3-4.

However, development plants and experimental coal gasifiers currently use improved gasifiers to produce at least six hot gases.

The present invention can produce a good hot gas that is fed to the reduction furnace without cooling the gas below the temperature. The operation described below is carried out with oxygen, H ₂ 0 and pulverized coal, in an entrained-bed type gaseous machine which produces a hot gas containing mainly CO, H ₂ , CO ₂ and H ₂ O. Is based on gasification of a typical American western bituminous coal.

The temperature to gasify in the gas is usually 1400 ° C. At this temperature the coal ash becomes a liquid and the chilled water is removed as slag at the bottom of the gas.

Referring to the drawings as a special example of the present invention, the reducing gas is about 10 ℃ 815 ℃ and is supplied to the reduction furnace 10 through the gas inlet (21).

The hot gas is distributed between the charges in the furnace and rises upward against the charge of the descending iron oxide. CO and H ₂ in the gas react with iron oxide by a known reduction reaction to produce CO ₂ , H ₂ O and metal iron.

When iron oxide is reduced to metal iron, due to chemical thermodynamic laws, only a portion of the internal reducing agent (CO + H ₂ ) can be reacted prior to the oxidants (CO ₂ and H ₂ 0) produced to stop the reduction reaction. The thermodynamic form is due to about 1.5 used reducing gas leaving the furnace to offtake pipe 26. In the gas cooler-scuba rubber 50, much water vapor is condensed and cooled in the gas by top gas cooling of 2.0. Removed.

The gas of about 2.0 is a good fuel for combustion, and is a neutral gas having no reducing ability to directly reduce iron. A small amount of top gas of about 2,0 is used as fuel for the burner 94 of the gas heater 90.

Another portion of the gas is exhausted from the system through exhaust pipe 52.

The exhausted gas is supplied to fuel in a boiler, not shown, to produce the steam needed to operate the CO ₂ removal device 58.

Most of the top gas is recycled as it passes through the CO ₂ removal device 58 where most of the CO ₂ is removed due to the reducing agent rich gas leaving the CO ₂ removal device through the pipe 64. The reducing agent-rich gas, as high as 23, serves four purposes.

The hot gaseous gas leaving the coal gaseous 40 through the pipe 46 is 1370 ° C. and is about 6.5.

The gas, which contains H ₂ S and COS from sulfur from coal and water droplets from unreacted coal charcoal and ash carryover, solidifies the material room so that it can be transported through a pipe in hot gas gas. To this end, the control stream 66 of the gas, which is also rich in reducing agent, is mixed with the hot gas to maintain the mixture temperature at 950 ° C. in the desulfurizer 70 of the gas inlet pipe 68. The mixing gas is adjusted to about 9.0 in the gas inlet pipe 68 by controlling by mixing with the cold gas rich in the reducing agent. Special limestone is supplied to the desulfurizer 70.

The particle size is on the order of 3 to 20 mm in order for the charge to have a good gas transmission. The rate of passage of the hot gas supplied to the desulfurizer 70 is much higher than that of the cold limestone supplied to the desulfurizer. The cause is due to the sudden rise in the gas temperature of the limestone under the stoke line 78. The above also allows the limestone to be quickly baked into quicklime to burn lime (CaO) to react with the removal of the constituents from H ₂ S and COS and gaseous gas. Therefore, burned limestone dashes will be supplied, which is uneconomical.

The hot gaseous gas is adjusted to 950 ° C. by a cold gas rich in reducing agent prior to feeding to the desulfurizer 70 in order to react H ₂ S and COS with lime in a known manner.

H ₂ S + CaO = CaS + H ₂ O COS + CaO = CaS + CO ₂

Lowering the oxidant (CO ₂ + H ₂ O) capacity in hot gases by controlling the gas rich in good reducing agent also helps to remove H ₂ S and COS. The capacity of hot gaseous sulfur to select special coal is about 3900 parts per million (ppmv) of H ₂ S plus COS.

By adjusting the reaction temperature of 950 ° C. and lowering the CO ₂ + H ₂ O capacity after the adjustment, the sulfur capacity of the gas leaving the desulfurizer is about 120 ppmv.

This level of sulfur is below the maximum that can be obtained in the direct reduction of iron and is further reduced by the mixing of hot or cold reducing gas with sulfur liberated in pipes 100 and 102. The amount of limestone is determined by the amount of sulfur contained in the coal. The amount of CO ₂ + H ₂ O formed in the desulfurizer by the reaction of lime and sulfur is an extremely small part of the total gas amount and has little effect on the quality of the gas leaving the desulfurizer to the outlet 80. In addition, CO ₂ from the desulfurizer has little effect on the quality of the gas because limestone is calcined to burn lime. The microaddition of CO ₂ + H ₂ O gas is shown in the table below. The hot charge leaving the reaction zone in the desulfurizer 70 is cooled before being discharged by the supply of a relatively small stream of reducing agent-rich gas through the pipe 86 to cool the gas in the distribution 88.

The high quality cooling gas flows upward and is preheated by the hot charge descending in the cooling zone and then flows towards the center of the reaction zone by the gas coming from the inlet 76. A portion of the reducing agent rich gas that leaves the CO ₂ removal device 58 through the pipe 64 is fed to the gas heater 90 through the pipe 99. In a heater including several heat resistant alloy heationg tubes 92, the gas is heated to around 815 ° C, a temperature suitable for direct reduction of most iron oxide feed material.

The temperature can be about 760-900 degreeC. In the embodiment, the gas leaving the desulfurizer 70 through the gas outlet 80 becomes limestone to burn lime, and is about 915 ° C. after the incoming cold limestone is heated.

The gas at about 915 ° C. is cooled to about 815 ° C. by mixing with a portion of the reducing gas rich in reducing agent supplied through pipe 102.

The addition of the reducing agent rich gas through the pipe 102 causes the reducing agent rich gas to be heated in the heater 80 to a temperature lower than 815 ° C. in order to maintain the temperature of the reducing gas mixture at about 815 ° C. at the reducing gas inlet 21. The above process may be omitted by heating. The addition of the regulating gas through the pipe 102 facilitates the temperature control of the hot reducing gas supplied through the reducing gas inlet 21. The accompanying chart shows the results of the comparative experiment according to the present invention.

All plots are based on metric tons of iron produced by direct reduction based on metallization of 92% and carbon capacity of 1.5%. Table 1 displays the gas passage rate and gas quality (reducing agent for oxidant) at the locations indicated in the figure.

[Figure 1]

The used gas stream at outlet 26 is lower than the stream of reducing gas at inlet 21 because 1.5% carbon is added to iron which is directly reduced by the reaction of reducing gas and CO.

Table 2 shows the fuel required for coal gas 40.

[Table 2]

Table 3 displays the fuel and outgoing quantities required for the desulfurizer 70.

[Chart 3]

Table 4 displays the energy required for the present invention.

[Table 4]

Table 5 displays the gas temperatures at the indicated locations.

[Table 5]

Table 6 displays the gas analysis table at the locations indicated.

[Table 6]

The stream of gaseous gas passing through pipe 46 shown in the examples is 931 nm ³ per metric ton for iron produced by direct reduction. The gas contains 85.5% of reducing agent CO + H ₂ and 796 nm ³ .

In the inlet pipe 21 the stream of hot reducing gas is 1744 nm ³ , 88.6% of the CO + H ₂ reducing agent 1969 nm ³ . Therefore, only 46% of CO + H ₂ required for direct reduction in the furnace 10 is supplied by the gas group 40.

The remaining 54% of the reducing gas required is supplied by recycling the used gas from the direct reduction reactor.

Although counter-flow type shaft disulfides are used to degas the gas, the gas desulfurization does not depart from the basic concepts of the present invention, but in a manufacturing apparatus other than a shaft, such as a fluidized bed of lime particles. It may also be prepared. Furthermore, to convert lime, desulfurization agents can use other suitable sulfur liquid filters such as manganese oxide.

As described above, it can be seen that the method of directly using iron as a reducing agent to directly reduce iron in order to directly reduce the thermal efficiency is good, useful, and practical. The following is a summary of the present invention. The present invention is a method for directly reducing iron in a shaft reduction furnace.

The spent gas from the furnace is raised to the reducing agent by removal of CO ₂ and water to form a rising gas.

Fossil fuels are gasified to produce hot gas that regulates the first stream of rising gas.

The mixture is desulfurized by reaction with lime to produce hot degassed gas.

The second stream of rising gas is heated and mixed with the hot desulfurized gas to produce a hot reducing gas.

Claims (1)

Remove a certain amount of CO ₂ from the reducing gas used to make the reducing agent-rich gas, fossil fuel to make the hot gas gas, and the hot gas mixture to reduce the reducing agent-rich gas of the first stream. To control the hot gaseous gas, to produce a hot reaction mixture with a sulfur acceptor to make hot desulphurized gas, to heat a second stream rich in reducing agent, and to at least gas at a temperature of 760-900 ° C. to feed the furnace. Mixing with a second stream of said heated reducing agent-rich gas with hot desulfurized gas to form a reducing gas having a ratio of reducing agent to oxidant of the mixture of 8, the hot reducing gas used CO ₂ containing reduced gas Is fed to the furnace to reduce iron oxides in the metalized iron product. Emergency how you want the iron in a direct reduction with features.

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