JP2013130375A - Method of manufacturing combustible gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a combustible gas of high combustibility, from a blast furnace gas.SOLUTION: A hydrogen-containing gas b as a gas composed of hydrogen and/or a compound including hydrogen, is introduced to a blast furnace 3 with the air heated by a hot-blast stove 1 or oxygen-enriched air a, then an incombustible gas g is separated and removed from the blast furnace gas c discharged from the blast furnace 3, by an incombustible gas separating/removing section 4, and a gas e of high calory is added to the obtained gas d after the separation according to the necessity to obtain the combustible gas f.

Description

  The present invention relates to a method for producing a combustible gas, and more particularly to a method for producing a combustible gas having high combustibility from a by-product gas discharged from the top of a blast furnace.

In general, steelworks produce gas called by-product gas from equipment such as coke ovens, blast furnaces, and converters, and this by-product gas has combustibility that can be used as fuel, such as hydrogen, carbon monoxide, and methane. In addition to gas, nonflammable gases such as nitrogen and carbon dioxide are contained. Most of these by-product gases are used in applications that use heat generated by combustion in power plants, heating furnaces, etc., but as mentioned above, these by-product gases include nitrogen and carbon dioxide. Since an inert component such as carbon is contained, the heat per volume is about 700 to 4500 kcal / Nm ³ , which is lower than propane gas and natural gas, which are general fuel gases.

In particular, since the blast furnace gas, which is a by-product gas discharged from the blast furnace, contains about 50 to 55% by volume of nitrogen and about 20 to 23% by volume of carbon dioxide, the amount of heat per unit volume is 700 kcal / Nm. ^{While being} about ³ , the concentration of hydrogen contained is around 3% by volume. For this reason, blast furnace gas alone has a shortage of heat and low hydrogen concentration and low combustibility, so by purchasing and mixing other by-product gas or natural gas containing high heat and containing hydrogen, It is often used by increasing the amount of heat and hydrogen concentration per unit volume.

  In addition, since the amount of by-product gas generated at steelworks is the largest, blast furnace gas is inevitably in the amount of other by-product gas or natural gas used to improve the flammability of this blast furnace gas. This increases the consumption of valuable high calorific gas or increases the purchase of expensive fuel.

  On the other hand, efforts are being made to reduce the use of coal-based raw materials in the steelmaking process from the viewpoint of energy security, which is the departure from the recent dependence on fossil fuels, or in response to various environmental problems. As a result, the calorific value of the exhaust gas from each process in the steel works is reduced, the proportion of the coke oven gas with a higher calorie per unit volume is reduced, and the proportion of the blast furnace gas with a lower calorie is reduced. There was a tendency to increase, and it was necessary to develop a method for effectively using this blast furnace gas.

  For this reason, some proposals have been made regarding methods for removing inert components from these by-product gases in advance, and particularly regarding methods for separating and recovering carbon dioxide from these by-product gases in response to recent requests for reduction of carbon dioxide emissions. ing.

For example, Patent Document 1 proposes a method of reducing separation and recovery costs by utilizing waste heat discharged from a steelworks when carbon dioxide is separated and recovered from a by-product gas of the steelworks by a chemical recovery method. Has been.
Patent Document 2 proposes a method in which factory steam is used together with waste heat for the separation of carbon dioxide from by-product gas.

  Further, Patent Document 3 describes that when carbon dioxide and / or nitrogen is separated and removed from the blast furnace gas to increase the amount of heat of the blast furnace gas, the mist in the blast furnace gas is separated prior to the separation and removal of carbon dioxide and / or nitrogen. A technique for separating carbon dioxide or nitrogen from blast furnace gas efficiently and with low input energy by preliminarily performing a pretreatment process for removing dust and sulfur is described.

JP 2004-237167 A JP 2004-292298 A JP 2009-108241 A

However, development of the manufacturing method of the gas which has still higher combustibility than the gas obtained by the method described in patent documents 1-3 was calculated | required.
Therefore, an object of the present invention is to provide a method for producing a combustible gas having a high combustibility from a blast furnace gas having a large amount of emissions.

  As a result of intensive investigations on how to solve the above problems, the inventors of the present invention discharged hydrogen and / or a compound containing hydrogen (hereinafter referred to as “hydrogen-containing gas”) into the blast furnace and discharged from the blast furnace. It has been found that it is effective to increase the concentration of hydrogen and carbon dioxide contained in the blast furnace gas, and then to separate and remove the nonflammable gas from the blast furnace gas, thereby completing the present invention.

That is, the gist of the present invention is as follows.
(1) Combustibility characterized by obtaining a combustible gas by introducing a gas comprising hydrogen and / or a compound containing hydrogen into a blast furnace, and then separating and removing the non-combustible gas from the exhaust gas discharged from the blast furnace. Gas production method.

(2) The method for producing a combustible gas according to (1), wherein the amount of hydrogen contained in the gas introduced into the blast furnace is 1 to 18 kg per ton of molten iron.

(3) The method for producing a combustible gas according to (1) or (2), wherein the separation and removal of the incombustible gas is performed by a pressure swing type physical adsorption method.

(4) The hydrogen-containing gas is any one of hydrogen gas, liquefied natural gas, and methane gas, or a mixed gas of two or more of them, (1) to (3), Method for producing combustible gas.

  According to the present invention, hydrogen and / or carbon dioxide-containing gas contained in the blast furnace gas discharged from the top of the furnace can be increased by introducing hydrogen-containing gas comprising hydrogen and / or a compound containing hydrogen into the blast furnace. The increased hydrogen content in the blast furnace gas increases the flammability of the blast furnace gas itself, and the increased carbon dioxide content effectively removes carbon dioxide from the blast furnace gas by the physical adsorption method. Therefore, combustible gas having high combustibility can be produced.

It is a figure which shows the apparatus used for the manufacturing method of the combustion gas by this invention. It is a figure which shows the relationship between the supply amount of the hydrogen containing gas introduce | transduced into a blast furnace, and the composition of a blast furnace gas. It is a figure which shows the relationship between the supply amount of the hydrogen containing gas introduced into a blast furnace, and the calorie | heat amount of blast furnace gas. It is a figure which shows the relationship between the supply amount of the hydrogen-containing gas introduced into a blast furnace, and the composition of the gas after isolate | separating a carbon dioxide from blast furnace gas. It is a figure which shows the relationship between the supply amount of the hydrogen-containing gas introduced into a blast furnace, and the calorie | heat amount per unit volume of the gas after isolate | separating carbon dioxide from blast furnace gas and blast furnace gas. The supply amount of the hydrogen-containing gas introduced into the blast furnace, the amount of hydrogen gas to be newly added necessary for the hydrogen concentration of the gas after separating carbon dioxide from the blast furnace gas and the blast furnace gas to be 6% by volume, It is a figure which shows the relationship. The supply amount of the hydrogen-containing gas to be introduced into the blast furnace and the amount of heat per unit volume of the gas after separating the blast furnace gas and carbon dioxide from the blast furnace gas should be newly added, which is necessary for 1050 kcal / Nm ³ It is a figure which shows the relationship with the quantity of methane gas.

Before describing the method for producing a combustible gas according to the present invention, a method for producing a combustible gas according to the prior art will be described first.
A conventional method for producing a combustible gas is as follows. That is, first, air heated to 1,050 to 1,250 ° C. by a hot air furnace or air having an oxygen concentration increased to about 30% by volume (hereinafter referred to as “oxygen-enriched air”) is used at 900 to 1100 Nm ³ blast furnace per ton of hot metal. Blow into the bottom of the. This blown air or oxygen-enriched air reacts with the carbon material inside the blast furnace to generate heat necessary for the reduction of iron ore, and by-product gas generated in the blast furnace is used as blast furnace gas from the top of the furnace. Discharge. As described above, since the concentration and heat quantity of hydrogen contained in the discharged blast furnace gas are low, nonflammable gases such as carbon dioxide and nitrogen are then separated and removed by the nonflammable gas separation and removal unit.

Usually, in blast furnace operation using only coal-based materials such as coke and pulverized coal as the reducing material, the component composition of the blast furnace gas is carbon monoxide: 21-26% by volume, hydrogen: 3-5% by volume, carbon dioxide: 19 -23% by volume and nitrogen: 53-59% by volume. When this blast furnace gas is used as fuel in a power plant, in order to increase the amount of heat per unit volume, for example, coke oven gas (about 4500 kcal / Nm ³ ) and liquefied natural gas (about 9500 kcal / Nm ³ ) and other gases having a high calorific value (hereinafter referred to as “high calorific gas”) are added to adjust the calorie to about 1050 kcal / Nm ³ , For example, coke oven gas or hydrogen separated from coke oven gas must be added and adjusted so that the concentration of hydrogen contained in the gas is 6% by volume. Combustion gas is obtained through such adjustment.

Next, a method for producing a combustible gas according to the present invention will be described.
FIG. 1 is a diagram showing an apparatus used in a method for producing a combustible gas according to the present invention. This combustible gas production apparatus 10 includes a hot stove 1 for heating air or oxygen-enriched air used for reaction of a raw material in a blast furnace 3, and a high calorific gas supply unit 2 for supplying a hydrogen-containing gas b or a high calorific gas e. A blast furnace 3 for producing pig iron by reacting the supplied air with iron ore and coke, and a non-flammable gas separation and removal for separating and removing the non-flammable gas g from the blast furnace gas c discharged from the blast furnace 3 Power generation using the part 4 and the post-separation gas d from which the non-combustible gas g is separated and removed by the non-combustible gas separation and removal part 4 or the combustible gas f in which the high-calorie gas e is mixed with the post-separation gas d And a nonflammable gas liquefying section 6 for liquefying the nonflammable gas g.

  A method for producing a combustible gas using the combustible gas production apparatus 10 is as follows. That is, first, the air a heated by the hot stove 1 is mixed with the hydrogen-containing gas b sent from the high calorific gas supply unit 2 and blown into the lower part of the blast furnace 3. Is used for heat generation, the hydrogen-containing gas b is used for heat generation and iron ore reduction, and the gas after the reaction is discharged from the top of the furnace as a blast furnace gas c.

A major feature of the method for producing a combustible gas according to the present invention is that the hydrogen-containing gas b is introduced into the blast furnace 3 from the high calorific gas supply unit 2. That is, the hydrogen-containing gas b is mixed with the air a heated by the hot stove 1 and introduced into the blast furnace 3. Thereby, the concentration of hydrogen and carbon dioxide contained in the blast furnace gas c discharged from the blast furnace 3 can be increased as will be described later. Here, an increase in the hydrogen concentration in the blast furnace gas c leads to an increase in the amount of heat of the blast furnace gas c, and an increase in the carbon dioxide concentration separates and removes carbon dioxide from the blast furnace gas c by the nonflammable gas separation and removal unit 4. Leading to improved efficiency. As a result, the concentration of hydrogen and carbon dioxide contained in the blast furnace gas c is improved by separating and removing nonflammable gases g such as carbon dioxide and nitrogen from the blast furnace gas c (hereinafter referred to as “post-separation gas”). ) The amount of heat of d, and hence the amount of heat of the finally obtained combustible gas f can be increased. Hereinafter, each process in the manufacturing method of the combustible gas by this invention is demonstrated.
In addition, by supplying the hydrogen-containing gas b to the blast furnace 3, an increase in the hydrogen concentration contained in the blast furnace gas c discharged from the blast furnace 3 is supplied to the inside of the blast furnace 3 as described later. Note that this is a result of the equilibrium reaction in the blast furnace 3 after that, and is not an increase due to the addition of the hydrogen-containing gas b itself.

  The amount of hydrogen-containing gas b introduced into the blast furnace 3 is expressed as 1 to 18 kg in terms of hydrogen weight per ton of hot metal. Here, the lower limit is set to 1 kg because introduction of the hydrogen-containing gas b has a low effect of increasing the hydrogen concentration and the heat quantity of the blast furnace gas c. On the other hand, the upper limit is set to 18 kg mass% because the hydrogen concentration and heat quantity of the blast furnace gas c increase due to the addition of the hydrogen-containing gas b itself, which is outside the scope of the process proposed in the present invention, and the reduction reaction by hydrogen. This is because the temperature in the blast furnace is lowered due to the endothermic reaction that is characteristic of the above.

  FIG. 2 shows the relationship between the supply amount of the hydrogen-containing gas b to the blast furnace 3 and the composition of the blast furnace gas c. FIG. 3 shows the relationship between the supply amount of the hydrogen-containing gas b to the blast furnace 3 and the heat amount per unit volume of the blast furnace gas c discharged from the blast furnace 3. From FIG. 2, it can be seen that as the supply amount of the hydrogen-containing gas b to the blast furnace 3 increases, the ratio of carbon monoxide, carbon dioxide and hydrogen in the blast furnace gas c increases while the ratio of nitrogen decreases. 3 that the amount of heat of the blast furnace gas c increases as the supply amount of the hydrogen-containing gas b increases.

In order to use the blast furnace gas c discharged from the blast furnace 3 as a fuel in a power plant, for example, the amount of heat per unit volume of the gas is adjusted to about 1050 kcal / Nm ³ as described above, and the hydrogen concentration is 6 volumes. However, as can be seen from FIG. 2, the hydrogen concentration contained in the blast furnace gas c is 6% by volume when the supply amount of the hydrogen-containing gas b is 8 kg-H / tonn of hot metal or more. However, as can be seen from FIG. 3, the heat amount of the blast furnace gas c does not exceed 1050 kcal / Nm ³ unless the supply amount of the hydrogen-containing gas b is 22 kg-H / tonn of hot metal. For this reason, it is necessary to add some high heat quantity gas e to the blast furnace gas c to increase the heat quantity.

  Here, in the present invention, the nonflammable gas separation and removal unit 4 separates and removes the nonflammable gas g contained in the blast furnace gas c. That is, by introducing the nonflammable gas g such as carbon dioxide and nitrogen from the blast furnace gas c into the nonflammable gas separation and removal unit 4, carbon dioxide and nitrogen can be removed, and the nonflammable gas g is removed. Since the hydrogen concentration and the heat quantity of the separated gas d are increased, it is possible to reduce the amount of the hydrogen-containing gas b and the high calorie gas e added to the separated gas d.

  As a method for separating nonflammable gas g such as carbon dioxide and nitrogen by the nonflammable gas separation and removal unit 4, generally known chemical absorption method, physical absorption method, hydrate method, membrane separation method, physical adsorption method Etc., and combinations of these are available. In particular, physical adsorption methods (PSA method, TSA method, PTSA method, etc.) are preferable because the power required for separation is relatively small.

The blast furnace gas c discharged from the top of the blast furnace furnace is introduced into the incombustible gas separation / removal section 4, where most of the carbon dioxide component contained in the blast furnace gas c is removed by the adsorbent. The configuration and operating conditions of the nonflammable gas separation / removal unit 4 are not particularly limited, and any configuration and method may be used as long as carbon dioxide can be separated from the gas having the above composition by a pressure swing.
Also, the carbon dioxide adsorbent is not particularly limited, but a material similar to activated carbon or zeolite is suitable.
The method for removing nitrogen from the blast furnace gas c is not particularly limited, and an adsorption separation method or a membrane separation method using an adsorbent capable of adsorbing nitrogen can be used. Of the incombustible gas components separated from the blast furnace gas c, carbon dioxide is sent to the incombustible gas liquefying unit 6 and liquefied.

  As an example, the composition and the amount of heat of the separated gas d after carbon dioxide is separated from the blast furnace gas c by the nonflammable gas separation and removal unit 4 are shown in FIGS. 4 and 5, respectively. From FIG. 4, as in the case of the blast furnace gas c, as the supply amount of the hydrogen-containing gas b to the blast furnace 3 increases, the proportion of carbon monoxide, carbon dioxide and hydrogen in the post-separation gas d increases. It can be seen that the rate decreases. Further, from FIG. 5, by separating and removing carbon dioxide from the blast furnace gas c by the nonflammable gas separation and removal unit 4, the concentration and heat quantity of hydrogen contained in the separated gas d are greatly increased compared to the blast furnace gas c. I understand that.

The separated gas d from which the incombustible gas has been separated and removed and the high calorific gas e supplied by the high calorific gas supply unit 2 are mixed, and the calorie per unit volume of the mixed gas is 1050 kcal / Nm. ^3. Combustible gas f is obtained by adjusting the hydrogen concentration to 6% by volume. The combustible gas f thus obtained is sent to the power plant 5, for example, and used as fuel.

  As the high calorie gas e added to the separated gas d, hydrogen, liquefied natural gas, methane gas, or the like can be used.

  FIG. 6 shows the relationship between the supply amount of the hydrogen-containing gas b supplied to the blast furnace 3 and the amount of hydrogen to be added to make the hydrogen concentration of the combustible gas f 6% or more. Here, carbon dioxide is separated and removed from the blast furnace gas c by the incombustible gas separation and removal unit 4. As is apparent from this figure, when the supply amount of the hydrogen-containing gas b is 9 kg-H / tonn of molten iron or more, the blast furnace gas c itself exceeds the hydrogen concentration of 6%, so that adjustment regarding the hydrogen concentration is not necessary. On the other hand, when the supply amount of the hydrogen-containing gas b is 9 kg-H / molten ton or less, it is necessary to add hydrogen to the blast furnace gas c, but the separation is performed by separating and removing carbon dioxide by the nonflammable gas separation and removal unit 4. As for the post gas d, it can be seen that the amount of hydrogen added to make the hydrogen concentration 6% can be reduced.

FIG. 7 shows the amount of methane gas that needs to be added so that the heat per unit volume of the separated gas d is 1050 kcal / Nm ³ or more. When the supply amount of the hydrogen-containing gas b supplied to the blast furnace 3 is 18 kg-H / molten ton or more, since the blast furnace gas c itself exceeds 1050 kcal / Nm ³ , adjustment regarding the amount of heat becomes unnecessary. It is understood that methane gas needs to be added to the blast furnace gas c below 18 kg-H / tonn of hot metal, but the added amount of methane gas can be reduced with respect to the separated gas d from which carbon dioxide has been removed by the incombustible gas separation and removal unit 4. .

  Thus, by introducing the hydrogen-containing gas containing hydrogen into the blast furnace, the hydrogen and carbon dioxide-containing gas contained in the blast furnace gas discharged from the top of the furnace can be increased, and the hydrogen contained in the blast furnace gas can be increased. The flammability of the blast furnace gas itself is increased by increasing the content ratio, and since the carbon dioxide content ratio is increased, carbon dioxide can be efficiently removed from the blast furnace gas by the physical adsorption method. Combustible gas can be produced.

(Comparative Example 1)
The average blast furnace gas composition in a state where the gas injected into the blast furnace does not contain a hydrogen-containing gas is as follows: carbon dioxide 22%, carbon monoxide 22%, nitrogen 53%, hydrogen 3% (heat per volume = 750 kcal / Nm ³ The hydrogen and methane gas addition amounts were calculated such that when hydrogen and methane gas were added thereto, the total hydrogen concentration was 6% and the heat per volume was 1050 kcal / Nm ³ or more. As a result, it was calculated that the required amount of hydrogen was 45 Nm ³ / tona and the amount of methane was 50 Nm ³ / tona.

(Comparative Example 2)
In the blast furnace operation in which the average blast furnace gas composition in the state in which no gas containing hydrogen is contained in the gas blown into the blast furnace is the same as in Comparative Example 1, hydrogen is used as the hydrogen-containing gas blown into the blast furnace, and the amount is 9 kg- When H / molten iron was used, how the blast furnace gas composition changed was calculated according to the equilibrium condition. As a result, the blast furnace gas composition was 22% carbon dioxide, 23% carbon monoxide, 48% nitrogen, and 7% hydrogen (heat per volume = 870 kcal / Nm ³ ). Similar to Comparative Example 1, when hydrogen and methane gas were added thereto, the hydrogen and methane gas addition amounts were calculated such that the total hydrogen concentration was 6% and the heat per volume was 1050 kcal / Nm ³ or more. As a result, the amount of hydrogen required 0 Nm 3 ^/ hot metal ton, the amount of methane is calculated to be 30 Nm 3 ^/ hot metal ton, the added amount of hydrogen is not required, it can be seen that the addition of methane is still required .

(Comparative Example 3)
The blast furnace gas composition was calculated in the same manner as in Comparative Example 2 except that the amount of hydrogen blown into the blast furnace was 18 kg-H / tonn of molten iron. As a result, the blast furnace gas composition was 23% carbon dioxide, 25% carbon monoxide, and 41% nitrogen. Hydrogen was 11% (amount of heat per volume = 1030 kcal / Nm ³ ). Similar to Comparative Example 2, when hydrogen and methane gas were added thereto, the hydrogen and methane gas addition amounts were calculated such that the total hydrogen concentration was 6% and the heat per volume was 1050 kcal / Nm ³ or more. As a result, it is calculated that the required amount of hydrogen is 0 Nm ³ / molten metal ton, and the amount of methane is 2 Nm ³ / molten metal ton, and it is understood that the addition of methane is still necessary, although the addition of hydrogen is unnecessary.

(Comparative Example 4)
In Comparative Example 1, it was assumed that a part of carbon dioxide was separated and removed from the blast furnace gas. Here, a PSA device is used as the separation device, and the carbon dioxide concentration of the gas separated and removed from the blast furnace gas is 99% (the balance is carbon monoxide), and the proportion of carbon dioxide is 80% (the balance remains in the blast furnace gas). It was. As a result, the blast furnace gas composition from which a part of carbon dioxide was separated was 5% carbon dioxide, 26% carbon monoxide, 64% nitrogen, and 4% hydrogen (heat per volume = 900 kcal / Nm ³ ). Similar to Comparative Example 1, when hydrogen and methane gas were added thereto, the hydrogen and methane gas addition amounts were calculated such that the total hydrogen concentration was 6% and the heat per volume was 1050 kcal / Nm ³ or more. As a result, the amount of hydrogen required 28 Nm 3 ^/ hot metal ton, the amount of methane is calculated to be 18 Nm 3 ^/ hot metal ton, it can be seen the addition of hydrogen and methane is still needed.

(Invention Example 1)
In Comparative Example 2, it was assumed that a part of carbon dioxide was separated and removed from the blast furnace gas having the composition of Comparative Example 2. Here, a PSA device was used as a separation device, and the carbon dioxide concentration of the gas separated and removed from the blast furnace gas was 99% (the balance was carbon monoxide), and the carbon dioxide ratio was 80% (the balance remained in the blast furnace gas). As a result, the blast furnace gas composition from which a part of carbon dioxide was separated was 5% carbon dioxide, 28% carbon monoxide, 58% nitrogen, and 8% hydrogen (heat per volume = 1050 kcal / Nm ³ ). That is, the hydrogen concentration was 6% or more and the heat per volume was 1050 kcal / Nm ³ or more only by the separation operation by PSA, and the addition of new hydrogen and methane gas was unnecessary.

(Invention Example 2)
The blast furnace gas composition in which a part of carbon dioxide was separated as a result of calculating the blast furnace gas composition after performing the same carbon dioxide separation operation as in Invention Example 1 except that the blast furnace gas composition was the same as in Comparative Example 3. Was 6% carbon dioxide, 31% carbon monoxide, 50% nitrogen, and 13% hydrogen (heat per volume = 1270 kcal / Nm ³ ). That is, the hydrogen concentration was 6% or more and the heat per volume was 1050 kcal / Nm ³ or more only by the separation operation by PSA, and the addition of new hydrogen and methane gas was unnecessary.

  According to the present invention, the concentration of hydrogen and carbon dioxide contained in a large amount of blast furnace gas discharged at a steel works is increased, and a noncombustible gas is separated and removed from the blast furnace gas to produce a combustible gas having high combustibility. Therefore, it is useful as a way to obtain an energy source in steelworks.

DESCRIPTION OF SYMBOLS 1 Hot blast furnace 2 High calorific gas supply part 3 Blast furnace 4 Incombustible gas separation removal part 5 Power station 6 Incombustible gas liquefaction part 10 Combustible gas production apparatus a Air or oxygen enriched air b Hydrogen containing gas c Blast furnace gas d After separation Gas e High calorific gas f Combustible gas g Nonflammable gas

Claims (4)

  Production of a combustible gas characterized by obtaining a combustible gas by introducing a gas comprising hydrogen and / or a compound containing hydrogen into a blast furnace and then separating and removing the non-combustible gas from the exhaust gas discharged from the blast furnace Method.   The method for producing a combustible gas according to claim 1, wherein the amount of hydrogen contained in the gas introduced into the blast furnace is 1 to 18 kg per ton of molten iron.   The method for producing a combustible gas according to claim 1, wherein the separation and removal of the incombustible gas is performed by a pressure swing type physical adsorption method.   The combustible gas according to any one of claims 1 to 3, wherein the hydrogen-containing gas is any one of hydrogen gas, liquefied natural gas, and methane gas, or a mixed gas of two or more of these. Manufacturing method.

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