METHOD FOR MANUFACTURING MOLTEN IRONS BY INJECTING A HYDROCARBON GAS AND APPARATUS FOR MANUFACTURING MOLTEN IRONS USING THE SAME

Technical Field
The present invention relates to a method for manufacturing molten iron by injecting gas containing hydrocarbons and an apparatus for manufacturing molten iron using the same. More particularly, the present invention relates to a method for manufacturing molten iron and an apparatus for manufacturing molten iron for generating a reducing gas of good quality which is necessary to melt the reduced iron by injecting the gas containing hydrocarbons into a melter-gasifier.
Background Art
The iron and steel industry is a core industry that supplies the basic materials needed in construction and in the manufacture of automobiles, ships, home appliances, and many other products we use. It is also an industry with one of the longest histories that has progressed together with humanity. In an iron foundry, which plays a pivotal roll in the iron and steel industry, after molten iron, which is pig iron in a molten state, is produced by using iron ore and coal as raw materials, steel is produced from the molten iron and then supplied to customers.
At present, approximately 60% of the world’s iron production is realized by using the blast furnace process developed from the 14th century. In the blast furnace process, coke produced by using bituminous coal and iron ore that have undergone a sintering process are charged into a blast furnace, and hot gas is supplied to the blast furnace to reduce the iron ore to iron, thereby manufacturing molten iron. However, in the blast furnace method, it is necessary to provide accessory equipment for manufacturing coke and sintered ore. Furthermore, there is a problem that environmental pollution due to the accessory equipments is severe.
In order to solve these problems of the blast furnace method, much research is being conducted into a smelting reduction process for manufacturing molten iron in many countries. In the reduction smelting process, molten iron is manufactured in a melter-gasifier by directly using general coal as a fuel and a reducing agent and iron ore as an iron source. Here, oxygen is injected into the melter-gasifier through a plurality of tuyeres installed in an outer wall, thereby combusting a coal-packed bed in the melter-gasifier. The oxygen is converted into a hot reducing gas and is transferred to the reduction reactor. Then, the hot reducing gas reduces iron ore and is discharged to the outside.
Coal such as lumped coal or coal briquettes is charged into the melter-gasifier as a heat source. The manufacturing costs depend on a charging amount of coal. Therefore, iron ore with a high reduction ratio should be charged into the melter-gasifier in order to minimize the charging amount of the coal. For this, a reducing gas of good quality should be supplied to the reduction reactor and then the reduction ratio of the iron ore should be raised as high as possible.
The iron ore can be reduced by using hydrogen (H2) and carbon monoxide (CO) contained in the reducing gas. Therefore, a large amount of hydrogen and carbon monoxide must be generated in the melter-gasifier in which the reducing gas is generated. There is a problem in that a larger amount of coal fuels than necessary should be combusted in the melter-gasifier in order to generate such a large amount of reducing gas.
In addition, since pure oxygen is injected into the melter-gasifier, the temperature of the raceway in which coal char or coke are combusted is high at about 4000?. Since the temperature of the raceway is so high, a severe thermal load is applied to a lower portion of the melter-gasifier. Therefore, a tuyere through which pure oxygen is injected is often melted and therefore damaged. Furthermore, a refractory of the lower portion of the blast furnace is damaged, and thereby there is a problem in that longevity of the melter-gasifier is shortened.
DISCLOSURE
Technical Problem
The present invention is contrived to solve the above problem, and provides a method for manufacturing molten iron by injecting a gas containing hydrocarbons and then to not only increase an amount of the reducing gas but also to improve the quality thereof.
In addition, the present invention is contrived to provide an apparatus for manufacturing molten iron using the above method for manufacturing molten iron.
Technical Solution
In a method for manufacturing molten iron according to the present invention, the method includes reducing iron ore in a reduction reactor to convert the iron ore into reduced materials, charging lumped carbonaceous materials into a melter-gasifier connected to the reduction reactor and forming a coal-packed bed, injecting a gas containing oxygen into the coal-packed bed and forming a raceway, combusting the lumped carbonaceous materials in the raceway and generating a reducing gas, directly injecting a gas containing hydrocarbons into the raceway after forming the raceway and then further generating the reducing gas, and charging the reduced materials into the melter-gasifier, contacting the reduced materials with the reducing gas, and melting the reduced materials.
Preferably, an injecting velocity of the gas containing hydrocarbons is less than an injecting velocity of the gas containing oxygen in the further generating the reducing gas.
A ratio of the injecting velocity of the gas containing oxygen to the injecting velocity of the gas containing hydrocarbons is preferably in a range from 1.5 to 3.0.
Preferably, the gas containing hydrocarbons is injected into the melter-gasifier while being spaced apart from the gas containing oxygen in the further generating the reducing gas.
The gas containing oxygen is preferably injected into the melter-gasifier through a tuyere installed in the melter-gasifier, and a diameter F of the tuyere through which the gas containing oxygen is injected and a horizontal distance F from an injecting position of the gas containing hydrocarbons in the melter-gasifier to an ignition starting position of the gas containing hydrocarbons satisfies the below formula.
7.0 = F/F = 14.0
The gas containing hydrocarbons is preferably injected into the raceway through a lance installed in the melter-gasifier, and a velocity of the gas containing hydrocarbons at an outlet of the lance is greater than a velocity of the gas containing hydrocarbons at an inlet of the lance in the further generating the reducing gas.
Steam is preferably mixed with the gas containing oxygen to be supplied in the forming the raceway.
The steam is preferably injected with the gas containing oxygen together through the tuyere installed in the melter-gasifier, and an angle between the steam and the gas containing oxygen at a mixing starting position is in a range from 18 degrees to 26 degrees.
The steam is preferably mixed with the gas containing oxygen before being injected into the melter-gasifier, and a diameter F of the tuyere through which the gas containing oxygen is injected, a diameter d of the lance through which the gas containing hydrocarbons is injected such that it is spaced apart from the gas containing oxygen, and a horizontal distance L from an injecting position of the gas containing oxygen in the melter-gasifier to a mixing starting position of the gas containing oxygen satisfy the below formula.
10.0 = L/(F+d) = 20.0
The gas containing hydrocarbons preferably includes at least one gas from a group consisting of liquid natural gas (LNG), liquid petroleum gas (LPG), blast furnace gas (BFG), and coke oven gas (COG) in the further generating the reducing gas.
A method for manufacturing molten iron according to the present invention may further include supplying the reducing gas generated in the melter-gasifier to the reduction reactor.
An apparatus for manufacturing molten iron according to the present invention includes a reduction reactor that reduces iron ore and converts the iron ore into reduced materials, and a melter-gasifier into which the reduced materials and lumped carbonaceous materials are charged, wherein the melter-gasifier is connected to the reduction reactor, and the melter-gasifier forms a coal-packed bed and manufactures the molten iron. A gas containing oxygen is injected into the coal-packed bed, a raceway is formed, and then a reducing gas is generated. A gas containing hydrocarbons is directly injected to the raceway after the raceway is formed, and thereby the reducing gas is further generated. The molten iron is manufactured by contacting the reducing gas with the reduced materials.
An injecting velocity of the gas containing hydrocarbons is preferably less than an injecting velocity of the gas containing oxygen.
A ratio of the injecting velocity of the gas containing oxygen to the injecting velocity of the gas containing hydrocarbons is preferably in a range from 1.5 to 3.0.
Preferably, the melter-gasifier further includes a tuyere installed in a side thereof. The tuyere includes a penetrated opening that injects the gas containing oxygen into the melter-gasifier, and a lance that is spaced apart from the penetrated opening and injects the gas containing hydrocarbons into the melter-gasifier.
An inner diameter of an outlet of the lance through which the gas containing hydrocarbons exits is preferably less than an inner diameter of an inlet of the lance through which the gas containing hydrocarbons flows in.
Preferably, an inner diameter of the lance is gradually reduced along a direction in which the gas containing hydrocarbons flows to near the outlet of the lance, and is then maintained at the same diameter close to the outlet of the lance.
A diameter F of the tuyere through which the gas containing oxygen is preferably injected into the melter-gasifier and a horizontal distance F from an injecting position of the gas containing hydrocarbons in the melter-gasifier to an ignition starting position of the gas containing hydrocarbons satisfy the below formula.
7.0 = F/F = 14.0
The tuyere is preferably connected to a steam injection line for injecting steam.
The steam is preferably mixed with the gas containing oxygen before being injected into the melter-gasifier, and an angle between the steam and the gas containing oxygen during mixing is preferably in a range from 18 degrees to 26 degrees.
The steam is preferably mixed with the gas containing oxygen before being injected into the melter-gasifier, and a diameter F of the tuyere through which the gas containing oxygen is injected, a diameter d of the lance through which the gas containing hydrocarbons is injected such that it is spaced apart from the gas containing oxygen, and a horizontal distance L from an injecting position of the gas containing oxygen in the melter-gasifier to a mixing starting position of the gas containing oxygen satisfy the below formula.
10.0 = L/(F+d) = 20.0
The apparatus for manufacturing molten iron according to the present invention further includes a reducing gas supply line that supplies the reducing gas generated in the melter-gasifier to the reduction reactor.
Preferably, the reduction reactor is a fluidized-bed reduction reactor.
Preferably, the reduction reactor is a packed-bed reduction reactor.
Advantageous Effects
In a method for manufacturing the molten iron according to the present invention, a reducing gas with high reducing power can be produced by injecting a gas containing hydrocarbons. Therefore, a reduction ratio of the iron ore is improved, and thereby manufacturing cost of the molten iron is greatly reduced.
It is possible to prevent the temperature in a lower portion of the melter-gasifier from being excessively raised by using heat of decomposition of the gas containing hydrocarbons. In addition, a large amount of the gases are discharged when the gas containing hydrocarbons is decomposed, and thereby heat in the lower portion of the melter-gasifier can be efficiently transferred to an upper space of a coal-packed bed.
DESCRIPTION OF DRAWINGS
FIG. 1 is a schematic view of an apparatus for manufacturing molten iron according to the first exemplary embodiment of the present invention.
FIG. 2 is detailed view of the tuyere of FIG. 1.
FIG. 3 is a schematic view that shows a forming state of a raceway in the apparatus for manufacturing molten iron of FIG. 1.
FIG. 4 is a schematic view of the tuyere included in the apparatus for manufacturing molten iron according to the second exemplary embodiment of the present invention.
FIG. 5 is a schematic view of the apparatus for manufacturing molten iron according to the third exemplary embodiment of the present invention
FIG. 6 is a graph showing changes of production amounts of the molten iron according to an experimental example of the present invention and a comparative example of a prior art.
FIG. 7 is a graph showing changes of a reducing agent ratio according to an experimental example of the present invention and a comparative example of the prior art.
FIG. 8 is a graph showing changes of production amounts of the molten iron and reducing agent ratio according to an experimental example of the present invention and a comparative example of the prior art.
FIG. 9 is a graph showing a temperature change of the raceway according to an experimental example of the present invention and a comparative example of the prior art.
FIG. 10 is a graph showing a temperature change of molten iron according to an experimental example of the present invention and a comparative example of the prior art.
FIG. 11 is a graph showing a change of Si content in the molten iron according to an experimental example of the present invention and a comparative example of the prior art.
BEST MODE
Exemplary embodiments of the present invention will be explained below with reference to FIGs. 1 to 5. The exemplary embodiments are merely to illustrate the present invention and the present invention is not limited thereto.
FIG. 1 schematically illustrates an apparatus for manufacturing molten iron 100 according to the first exemplary embodiment of the present invention. The apparatus for manufacturing molten iron 100 illustrated in FIG. 1 is merely to illustrate the present invention and the present invention is not limited thereto. Therefore, the apparatus for manufacturing molten iron 100 can be modified to other forms.
The apparatus for manufacturing molten iron 100 illustrated in FIG. 1 includes a reduction reactor 30 and a melter-gasifier 60. In addition, it can include other devices if necessary. The iron ore is charged into the reduction reactor 30 and are then reduced therein. Additives can also be used if necessary. The iron ore, which will be charged into the reduction reactor 30, is pre-dried in a lumped state. The iron ore is converted into the reduced materials while passing through the reduction reactor 30. The reduction reactor 30 is a packed-bed reduction reactor into which a reducing gas is supplied from the melter-gasifier 60, forming a packed bed therein.
The iron ore is converted into the reduced materials while passing through the packed bed. Lumped carbonaceous materials are charged into an upper portion of the melter-gasifier 60, and then a coal-packed bed is formed therein. For example, lumped coal or coal briquettes can be the lumped carbonaceous materials. Fine coal is manufactured by pressing and molding coal briquettes. In addition, coke can be charged into the melter-gasifier 60 if necessary. A plurality of tuyeres 80 are installed on an outer wall of the melter-gasifier 60, and a gas containing oxygen and a gas containing hydrocarbons are injected therethrough. The gas containing oxygen is a gas that contains oxygen, and pure oxygen at room temperature can also be used. The gas containing oxygen is injected into the coal-packed bed and then forms a raceway. The lumped carbonaceous materials are combusted in the raceway, thereby generating the reducing gas. The gas containing hydrocarbons can be any gas that contains hydrocarbons.
For example, liquid natural gas (LNG), liquid petroleum gas (LPG), blast furnace gas (BFG), coke oven gas (COG), and so on can be used. Therefore, at least one gas selected from a group consisting of the above-mentioned gases containing hydrocarbons can be used.
If the gas containing hydrocarbons is injected into the melter-gasifier, the generating amount of the reducing gas, which is necessary to reduce the iron ore, is increased. For example, the LNG can be one of the gases containing hydrocarbons. If LNG and coal of the same amounts are charged into the melter-gasifier, the generating amounts of the gases are as described in the following Table 1.
Table 1
Item Generating amount of gases (Nm3/kg)
CO H2 total
LNG 1.42 (35%) 2.67 (65%) 4.09 (100%)
Coal 1.46 (79%) 0.38 (21%) 1.84 (100%)

As shown in Table 1, LNG generates reducing gas at an amount of 2.2 times more than that of the coal. In particular, hydrogen of the reducing gas is greatly increased. The reducing power of hydrogen is three times or greater than that of carbon monoxide. Therefore, if the gas containing hydrocarbons is injected into the melter-gasifier, a large amount of reducing gas of good quality can be obtained.
If a large amount of reducing gas of good quality is supplied into the reduction reactor, a burden of the reduced iron in the melter-gasifier is reduced since a reduction ratio of the reduced iron in the reduction reactor is increased. Therefore, the reducing agent ratio may be reduced. In addition, a production amount of reduced iron under a constant reduction ratio condition is increased. Therefore, a heat loss amount through a furnace body of the melter-gasifier is increased, and thereby a reducing agent cost accrued by manufacturing molten iron is reduced.
The reduced materials, which are reduced in the reduction reactor 30, are charged into the upper portion of the melter-gasifier 60 and are then melted while passing through the coal-packed bed. The reduced materials directly contact the reducing gas and are then melted. The molten iron can be manufactured by using the above method. A tap is installed at a lower portion of the melter-gasifier 60 to discharge molten iron and slag to the outside therethrough.
The reducing gas containing hydrogen and carbon monoxide is generated from the coal-packed bed formed in the melter-gasifier 60. Since the upper portion of the melter-gasifier 60 is dome-shaped, the melter-gasifier 60 is advantageous for the generation of the reducing gas. The reducing gas discharged from the melter-gasifier 60 is supplied to the reduction reactor 30 via a reducing gas supply line 70. Therefore, iron ore can be reduced and plasticized by the reducing gas. Although the reducing gas is illustrated to be directly supplied to the reduction reactor 30 in FIG. 1, it can be supplied to the reduction reactor 30 from other devices.
As illustrated in FIG. 2, the gas containing oxygen and the gas containing hydrocarbons can be injected through the tuyere 80 installed in the above-described melter-gasifier 60. FIG. 2 illustrates a sectional structure of the tuyere 80. A lance 603 illustrated in FIG. 2 has a predetermined thickness. A structure of the tuyere 80 illustrated in FIG. 2 is merely to exemplify the present invention and the present invention is not limited thereto. Therefore, the structure thereof can be variously modified into other forms.
A plurality of cooling pipes 605 are formed in the tuyere 80 to cool the tuyere 80. Therefore, the tuyere 80, which is exposed to high temperatures in the melter-gasifier, is prevented from being damaged.
The gas containing oxygen is injected into the melter-gasifier through a penetrated opening 601 of the tuyere 80. Meanwhile, the gas containing hydrocarbons is injected into the melter-gasifier through the lance 603 of the tuyere 80. The gas containing hydrocarbons is injected into the melter-gasifier separately from the gas containing oxygen. When the gas containing hydrocarbons and the gas containing oxygen are pre-mixed to be charged, the gas containing hydrocarbons is ignited by the gas containing oxygen and then high heat is generated.
That is, since the oxidization rate of oxygen is high, the temperature of the raceway is high at about 4000?. The gas containing hydrocarbons is combusted in the tuyere by radiation heat caused by the high temperature, and thereby the tuyere can be melted and damaged. In order to prevent the above phenomenon, the gas containing hydrocarbons is injected into the melter-gasifier separately from the gas containing oxygen. Since the gas containing hydrocarbons is injected through the lance 603, the gas containing hydrocarbons and the oxygen do not meet each other in the tuyere. Since a thermal load applied to a front end 6011 of the tuyere 80 due to the above structure is greatly reduced, the gas containing hydrocarbons can be stably injected into the raceway.
As shown in FIG. 2, the gas containing hydrocarbons flows through the lance 603. The gas containing hydrocarbons inflows through an inlet of the lance 603 and then exits through an outlet thereof. Here, an inner diameter of the outlet of the lance 603 is less than that of the inlet thereof. Since the lance 603 has the above structure, a final velocity of the gas containing hydrocarbons becomes greater than the initial velocity thereof when the gas containing hydrocarbons passes through the lance 603. Therefore, a pressure loss due to the gas containing hydrocarbons at a high speed is minimized while the injecting velocity of the gas containing hydrocarbons in the outlet of the lance 603 can be further increased. Since the final velocity of the gas containing hydrocarbons becomes greater than the initial velocity thereof, the gas containing hydrocarbons can be easily injected into the melter-gasifier.
The lance 603 preferably has a shape as illustrated in FIG. 2 in order to make the flow of the gas containing hydrocarbons smoother. That is, the inner diameter of the lance 603 is gradually reduced in a direction along which the gas containing hydrocarbons flows near the outlet of the lance 603. Then, the inner diameter of the lance 603 is maintained at an area close to the outlet of the lance 603.
In addition, as shown in FIG. 2, the gas containing hydrocarbons is directly injected into the raceway that is formed by the gas containing oxygen. That is, the gas containing hydrocarbons is not mixed with the gas containing oxygen in the tuyere 80 but rather is directly injected into the raceway. The gas containing hydrocarbons, which is directly injected into the raceway, is directly combusted and reformed in the raceway. Therefore, a reducing gas containing a large amount of hydrogen for reducing and heat for melting reduced materials can be further generated.
Firstly, the gas containing oxygen is injected into the melter-gasifier in order to combust the coal char forming the coal-packed bed. Since the velocity of the gas containing oxygen is about 170m/s to 230m/s, kinetic energy of the gas containing oxygen pushes away the coal char that falls in front of the tuyere. Therefore, the raceway is formed in front of the tuyere. The raceway is a hollow space and the coal char is mainly combusted near the raceway. The oxygen in the gas containing oxygen generates heat by the reaction described in the below Formula 1 in the raceway formed in front of the tuyere 80.
?Formula 1?
C + O2 ? CO2 7,840 kcal/kg-C
CO2 + C ? 2CO -3,440 kcal/kg-C
--------------------------------------------------------------
2CO + O2 ? 2CO 4,400 kcal/kg-C

That is, 1kg of carbon is reacted with oxygen of the same amount and then heat of 2,200 kcal is generated. The temperature of the raceway in the melter-gasifier is high at about 4,000? due to the carbon combustion heat. Since the temperature of the raceway is high as stated above, the front end of the tuyere can be damaged by being melted and a refractory installed in the melter-gasifier can be damaged. In addition, the high temperature may cause an increase in the amount of silicon as an impurity in the molten iron.
However, since the gas containing hydrocarbons is directly injected into the raceway in the first exemplary embodiment of the present invention and then the temperature of the raceway is lowered, the above-described problem can be prevented. The hydrocarbons contained in the gas containing hydrocarbons, which is injected into the raceway, is decomposed as in the following Formula 2.
?Formula 2?
CH4 ? C + 2H2 -1,370 kcal/kg-C
The gas containing hydrocarbons, which is injected into the melter-gasifier, is decomposed into carbon and hydrogen by the process of Formula 2. In this case, a large amount of heat of about 1,380 kcal is absorbed per 1kg of CH4. Therefore, the temperature of the raceway can be lowered to a temperature of equal to or below 3000?. Thus, the tuyere and the refractory can be protected and the quality of the molten iron can be improved.
The gas containing oxygen is injected at a speed that is faster than that of the gas containing hydrocarbons in order to form a raceway. That is, the injecting velocity of the gas containing hydrocarbons is less than that of the gas containing oxygen. Therefore, after reducing gas is generated by using the gas containing oxygen, the reducing gas is further generated by the gas containing hydrocarbons.
A ratio of injecting velocity of the gas containing oxygen with respect to that of the gas containing hydrocarbons is maintained at a range from 1.5 to 3.0. If the ratio is less than 1.5, since the gas containing hydrocarbons and the gas containing oxygen are injected together, a front end 6011 of the tuyere 80 is ignited and then damaged by melting. On the contrary, if the ratio is over 3.0, combustion is not perfectly performed due to an influence on the formation of the raceway.
FIG. 3 schematically illustrates a state in which the tuyere 80 illustrated in FIG. 2 is operated. The operating state of the tuyere 80 illustrated in FIG. 3 is merely to illustrate the present invention and the present invention is not limited thereto.
As shown in FIG. 3, the reducing gas is generated in the coal char bed by forming a raceway by the gas containing oxygen that is supplied through the tuyere 80. In addition, the gas containing hydrocarbons, which is supplied through the tuyere 80, is directly injected into the raceway, thereby further generating the reducing gas.
An angle ? and a combustion focusing distance F should be suitably controlled in order to efficiently reform the gas containing hydrocarbons in the raceway. The angle ? is an angle between the gas containing oxygen and the gas containing hydrocarbons that are injected. The combustion focusing distance F is a horizontal distance from the injecting position of the gas containing hydrocarbons in the melter-gasifier to the ignition starting position b of the gas containing hydrocarbons. That is, it is a horizontal distance from where the gas containing hydrocarbons is combusted to the end of the tuyere. Here, the horizontal distance does not mean a distance that is actually measured between the injecting position a and the ignition starting position b, but is a distance that makes a right angle with a gravitational direction.
The angle ? can be suitably controlled by adjusting the lance 603. If the angle ? is too great, a thermal load applied to the tuyere is increased since the combustion focusing distance (F) becomes too short. In addition, if the angle ? is too small, ignition of the gas containing hydrocarbons is delayed since the combustion focusing distance (F) becomes too long. The angle ? depends on a diameter of the tuyere. The diameter F illustrated in FIG. 3 is that of the penetrated opening 601 where the gas containing oxygen is injected into the melter-gasifier through the tuyere 80.
Here, F/F is preferably equal to or more than 7.0 and equal to or less than 14.0. The reforming efficiency can be optimized in the above range. The units of F and F are mm. If F/F is less than 7.0, the tuyere can be damaged because heat is applied to the tuyere. In addition, if F/F is greater than 14.0, the gas containing hydrocarbons is not completely reformed in the raceway and then exits the raceway.
FIG. 4 schematically illustrates a structure of a gas injecting device 90 included in the apparatus for manufacturing molten iron according to the second exemplary embodiment of the present invention. The structure of the gas injecting device 90 illustrated in FIG. 4 is merely to illustrate the present invention and the present invention is not limited thereto. In addition, since the tuyere 80 included in the gas injecting device 90 is the same as that included in the apparatus for manufacturing molten iron according to the above-described first exemplary embodiment of the present invention, the same reference numerals are used.
The gas injecting device 90 illustrated in FIG. 4 includes a steam injection line 701. The steam is mixed with the gas containing oxygen before being injected into the melter-gasifier. Since the steam is injected to be mixed with the gas containing oxygen, it is not necessary to install another steam injection line to inject steam into the tuyere 80. Therefore, the structure of the tuyere 80 can be simplified. Since the gas containing oxygen is supplied into the melter-gasifier through a blowpipe 703, it is easily mixed with the steam.
The steam directly contacts the gas containing hydrocarbons in the raceway, thereby promoting a reforming reaction of the gas containing hydrocarbons. The reforming reaction is described in the following Formula 3. Here, CH4 is a main component of the gas containing hydrocarbons.
?Formula 3?
CH4 + H2O ? CO + 3H2 ?H = +228,000kJ/kg-mol
As described in Formula 3, the steam contacts the gas containing hydrocarbons, and then is decomposed into carbon monoxide and hydrogen. This also generates an endothermic reaction by absorbing heat from the surroundings. Heat of 228,000kJ per 1mol of CH4 is consumed during the endothermic reaction. The temperature of the raceway can be reduced by the endothermic reaction. Therefore, a thermal load that is applied to the tuyere 80 and inner walls of the melter-gasifier is reduced, and thereby the tuyere 80 and the inner walls of the melter-gasifier are prevented from being overheated or being melted and damaged.
A detailed explanation of the above contacting phenomenon between the steam and the gas containing hydrocarbons is sequentially described in the following Formula 4.
?Formula 4?
CH4 + H2O ? CO + 3H2
CO + 1/2O2 ? CO2
3H2 + 3/2O2 ? 3H2O
CO2 + C (char) ? 2CO
3H2O + 3C (char) ? 3CO + 3H2
CH4 + H2O + 2O2 + 4C (char) ? 5CO + 3H2
As described in the above Formula 4, the steam functions as a starting material of the gas containing hydrocarbons. That is, the steam converts carbon contained in the gas containing hydrocarbons into carbon monoxide. The carbon monoxide and hydrogen generated by reacting the gas containing hydrocarbons and the steam are combusted in the raceway, thereby becoming carbon dioxide and water. The carbon dioxide and water exit the raceway and then pass through the coal char bed layer while reacting with the coal char, thereby being converted into carbon monoxide and hydrogen again.
The reducing gas containing carbon monoxide and hydrogen rises in the melter-gasifier and oxygen remains in the reduced materials, and thereby the reduced materials are completely reduced. Particularly, the reducing gas rises while passing through the char bed in the melter-gasifier. In this case, the reduction ratio of the iron ore can be further increased by transferring a large amount of heat form the lower portion of the melter-gasifier to the upper portion thereof and transferring the reducing gas into the reduction reactor. Therefore, as an example, the reduction ratio of the iron ore can be controlled to be about 70% to 80%. Particularly, since steam generates hydrogen with a reducing power of three times that of carbon monoxide, it is advantageous in reduction of the iron ore.
As shown in FIG. 4, steam is mixed with the gas containing oxygen before being injected into the melter-gasifier. Since the gas containing oxygen may be at room temperature, water should be injected in a steam state in order to prevent components from being damaged due to condensation of the water. Furthermore, the steam can be condensed in the blowpipe 703 or the tuyere 80. In this case, the water deteriorates the high-speed flow of the gas containing oxygen. Therefore, a pressure loss of the entire gas injecting device 90 is generated, and thereby the tuyere 80 is damaged by melting near the raceway. Accordingly, the installation position of the blowpipe 703 or the tuyere 80 must be suitably controlled in order for the steam to not be condensed.
As shown in FIG. 4, the angle a, which is made between the steam and the gas containing oxygen, is preferably in a range from 18 degrees to 26 degrees when the steam and the gas containing oxygen are mixed together. When the steam injection line 701 is installed in the blowpipe 703, it is impossible to make the angle a less than 18 degrees considering design factors. In addition, if the angle a is more than 26 degrees, the flow of the gas containing oxygen can be blocked and then steam can be condensed. Therefore, it is preferable that the angle a is maintained within the above range.
In FIG. 4, it is preferable that F, d, and L have a suitable relationship. Here, F is a diameter of the tuyere, d is a diameter of the lance, and L is a horizontal distance from an injection position c in the melter-gasifier to an initial starting position e for mixing the steam and the gas containing oxygen. Namely, L/(F+d) is preferably equal to or greater than 10.0 and equal to or less than 20.0.
If L/(F+d) is less than 10.0, the steam and the gas containing oxygen are not mixed well. In addition, if L/(F+d) is over 20.0, the steam is condensed during mixing of the injected steam and oxygen. Therefore, it is necessary to control the installing position of the steam injection line 701 in order to satisfy the above range.
FIG. 5 illustrates an apparatus for manufacturing molten iron 300 according to the third exemplary embodiment of the present invention. Since a melter-gasifier 60 illustrated in FIG. 5 is the same as the melter-gasifier illustrated in FIG. 1, the same reference numerals are used and a detailed description thereof is omitted.
The apparatus for manufacturing molten iron 300 includes at least one fluidized-bed reduction reactor 20, melter-gasifier 60, a reducing gas supply line 70, and an apparatus for manufacturing compacted iron 40. In addition, a hot pressure equalizing device 50 can be further included to transfer compacted iron manufactured in the apparatus for manufacturing compacted iron 40 to the melter-gasifier 60. The hot pressure equalizing device 50 transfers compacted iron manufactured in the apparatus for manufacturing compacted iron 40 to the melter-gasifier 60. The apparatus for manufacturing compacted iron 40 and the hot pressure equalizing device 50 can be omitted.
The apparatus for manufacturing molten iron 300 can use fine iron ore. Additives can also be used if necessary. A fluidized bed is formed in the fluidized-bed reduction reactor 20 to reduce the iron ore. The fluidized-bed reduction reactor 20 includes a first fluidized-bed reduction reactor 201, a second fluidized-bed reduction reactor 203, a third fluidized-bed reduction reactor 205, and a fourth fluidized-bed reduction reactor 207. Although four fluidized-bed reduction reactors are illustrated in FIG. 5, this is merely to illustrate the present invention and the present invention is not limited thereto. Therefore, three fluidized-bed reduction reactors can also be used.
The first fluidized-bed reduction reactor 201 preheats iron ore by using a reducing gas discharged from the second fluidized-bed reduction reactor 203. The second and third fluidized-bed reduction reactors 203 and 205 pre-reduce preheated iron ore. In addition, the fourth fluidized-bed reduction reactor 207 finally reduces pre-reduced iron ore and then converts it into reduced materials.
The iron ore is reduced and heated while passing through the fluidized-bed reduction reactor 20. For this, the reducing gas generated in the melter-gasifier 60 is supplied to the fluidized-bed reduction reactor 20 through the reducing gas supply line 70. The reduced iron ore is manufactured into the compacted iron by the apparatus for manufacturing compacted iron 40.
The apparatus for manufacturing compacted iron 40 includes a charging hopper 401, a pair of rollers 403, a crusher 405, and a storage bin 407. In addition, other devices are further included if necessary. The charging hopper 401 restores iron ore that is reduced while passing through the fluidized-bed reduction reactor 20. The iron ore is charged from the charging hopper 401 into the pair of rollers 403 and is then formed to be pressed in a form of a strip. The pressed iron ore is crushed in the crusher 405 and then stored as compacted iron ore in the storage bin 407.
The present invention will be explained in detail with reference to the experimental example below. The experimental example of the present invention is merely to illustrate the present invention, and the present invention is not limited thereto.
In the experimental example of the present invention, molten iron was manufactured by using an apparatus for manufacturing molten iron illustrated in FIG. 5. Twenty-six tuyeres were installed in a sidewall of the apparatus for manufacturing molten iron, and the diameter of each tuyere was 23mm. The production amount of the molten iron was 2500 t-p/d, and the amount of blown oxygen was 36,000m3/hr. The temperature of the raceway in the melter-gasifier was 3,850? before injecting liquid natural gas. 25-50 kg/thm of the liquid natural gas was injected into the melter-gasifier and then molten iron was manufactured.
Experimental conditions of the comparative example of the prior art were the same as those of the present invention except for the injection of the liquid natural gas.
Since other detailed methods for manufacturing molten iron can be understood by those skilled in the art, detailed descriptions thereof are omitted. Experimental results according to the experimental example and the comparative example are as follows.
Production amount of the molten iron and reducing agent ratio
As shown in FIG. 6, the production amount of the molten iron was 2250 tons per day in the experimental example, while that of the comparative example was 2100 tons per day. Therefore, the production amount of the molten iron in the experimental example was increased by 150 tons per day relative to the comparative example. That is, the generating amount of hydrogen in the melter-gasifier caused by injecting LNG in the experimental example was increased, and thereby the production amount of the reduced iron with a suitable reduction ratio was increased.
Meanwhile, as shown in FIG. 7, 790kg of a reducing agent was consumed in order to produce 1 ton of molten iron in the experimental example. On the contrary, 850kg of a reducing agent was consumed in order to produce 1 ton of the molten iron in the comparative example. Therefore, 60kg less of the reducing agent was used in the experimental example than was used in the comparative example. This is because the amount of heat discharging through the furnace body of the melter-gasifier is reduced as the production amount of molten iron is increased.
FIG. 8 is a graph that illustrates both the above-described production amount of the molten iron and the reducing agent ratio. In FIG. 8, data of the experimental examples are represented as ¦, and data of the comparative examples are represented as ?. As shown in FIG. 8, the data of the experimental examples are mainly located in the right lower side of FIG. 8. Therefore, it is known that the reducing agent ratio is low and the production amount of molten iron is large. On the contrary, the data of the comparative examples are mainly located in the left upper portion of FIG. 8. Therefore, it is known that the reducing agent ratio is high and the production amount of molten iron is small. Accordingly, according to the experimental examples, the molten iron was manufactured with a minimized cost relative to the comparative examples.
FIGs. 9 and 10 respectively illustrate temperature of the molten iron and temperature of the raceway for the experimental example and the comparative example. As shown in FIG. 9, the temperature of the molten iron of the experimental example was 1495?, while that of the comparative example was 1515?. Therefore, it is known that the temperature of the molten iron in the experimental example is lower by 20? relative to the comparative example.
In addition, as shown in FIG. 10, the temperature for the raceway in the experimental example was 3850? while that for the comparative example was 3570?, which is much lower than that for the experimental example. That is, the temperature of the raceway in the experimental example was 280? lower than that in the comparative example. When the temperature of the raceway is lowered as such, the tuyere receives less damage. That is, as the temperature of the raceway becomes low, a thermal load of a front end of the tuyere is reduced. Therefore, since a phenomenon in which the tuyere is melted and damaged does not occur, the operation of the melter-gasifier is stabilized while injecting LNG. In addition, it is known that an amount of silicon in the molten iron is reduced as the temperature of the raceway is lowered. This will be explained in detail below with reference to FIG. 11.
As shown in FIG. 11, Si content in the molten iron is small at about 0.9% in the experimental example. On the contrary, Si content in the molten iron is about 1.3% in the comparative example, which is 0.4% more than that of the experimental example. When the LNG is injected as in the experimental example, temperatures of the molten iron and the raceway are lowered and stabilized (see FIGs. 9 and 10). When the temperature of the raceway is lowered, the velocity and amount of silicon dioxide (SiO2) among an ash component in the coal char that is converted into SiO gas are reduced. Therefore, as described in the below Formula 5, less SiO gas is added to the molten iron.
[Formula 5]
SiO + [C] in the molten iron ? CO + [Si] in the molten iron
If the content of the silicon in the molten iron is high, the silicon in the molten iron should be removed since quality of the molten iron is deteriorated. Therefore, the manufacturing cost of the molten iron is increased. Accordingly, as described in the experimental example, the quality of the molten iron is improved by injecting LNG and therefore the manufacturing cost of the molten iron can be reduced.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.