Method for producing gas mixture and method for supplying gas mixture

Abstract

Provided is a method for producing a gas mixture that is produced in an iron mill and consumed as a fuel, and that, even when the generated amount of coke oven gas has become low, can be used continuously without upgrading an existing facility suitable for a conventional gas mixture. In the present invention, a first gas that is a secondary gas generated in an iron mill, a second gas that is a gas of which an index A indicating a discharge heat quantity is higher than that of a coke oven gas, and a third gas that is a gas of which an index B indicating a combustion speed is higher than that of the coke oven gas are mixed. Preferably, the coke oven gas is further mixed at a concentration of more than 0 vol% but less than 50 vol%.

Description

Method for producing mixed gas and method for supplying mixed gas

[0001] The present invention relates to a method for producing a mixed gas produced in a steelworks and consumed as fuel, and a method for supplying the mixed gas.

[0002] Coke is the main fuel used in the production of pig iron using a blast furnace. Coke is produced by carbonizing coal in a coke oven. Coke ovens are often installed alongside steelworks. Coke oven gas, which is generated when producing coke in a coke oven, contains flammable gases such as hydrogen, methane, and carbon monoxide. Therefore, steelworks recover coke oven gas and use it as fuel for heating furnaces, etc.

[0003] The calorific value when coke oven gas is burned is approximately 18,000 kJ / Nm ３ Therefore, the calorific value is adjusted by mixing a gas with a lower calorific value with the coke oven gas. For example, Patent Document 1 describes an invention of a method for supplying a mixed gas having a target calorific value by mixing a blast furnace gas and a converter gas, which have low calorific values, with coke oven gas stored separately in a gas holder.

[0004] When using a mixed gas as fuel, known indices are used to represent the combustibility of the mixed gas. For example, Patent Document 2 describes that the quality of the mixed gas is controlled using the Wobbe index, which is an index indicating the calorific value of discharge, and the speed factor, which is an index indicating the combustion speed, as indices representing the combustibility of the mixed gas. By adjusting the mixing ratio of the mixed gas so that these indices match target values, the mixed gas can be burned stably.

[0005] JP 2017-187209 A JP 51-56804 A

[0006] As mentioned above, conventional mixed gases containing coke oven gas are highly useful as fuel in steelworks. However, in recent years, efforts to achieve carbon neutrality have been made to reduce the amount of coke used in blast furnaces or molten iron production facilities, and development of coke-free molten iron production methods has been progressing. Due to these technological trends, it is expected that it will become increasingly difficult to use coke oven gas as fuel in steelworks in the future. Therefore, it is possible to produce mixed gases by mixing natural gas or petroleum gas with blast furnace gas instead of coke oven gas, and use the resulting mixed gas as a new fuel.

[0007] However, the inventors' investigations revealed that when attempting to produce a new mixed gas by blending natural gas or petroleum gas with blast furnace gas, it is not possible to simultaneously achieve both the index indicating the calorific value of the new mixed gas that matches the index indicating the calorific value of the conventional mixed gas and the index indicating the combustion rate of the new mixed gas that matches the index indicating the combustion rate of the conventional mixed gas. Specifically, when attempting to match the index indicating the calorific value of the new mixed gas with the index indicating the calorific value of the conventional mixed gas, the index indicating the combustion rate of the new mixed gas becomes smaller than the index indicating the combustion rate of the conventional mixed gas. If it is not possible to match both the index indicating the calorific value and the index indicating the combustion rate of the new mixed gas with the index indicating the calorific value of the conventional mixed gas, in order to maintain the performance of the heating furnace using the mixed gas, it will be necessary to significantly change the specifications of existing equipment, such as the piping that supplies the mixed gas to the heating furnace and the burners equipped in the heating furnace. Such equipment upgrades are extremely costly.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to produce a mixed gas having an index indicating the discharge heat quantity and an index indicating the combustion rate equivalent to those of conventional mixed gases, even when the amount of coke oven gas generated is reduced.

[0009] The gist and configuration of the present invention are as follows.

[0010] [1] A method for producing a mixed gas, comprising a mixing step of producing a mixed gas by mixing a first gas, which is a by-gas generated in a steelworks; a second gas, which is a gas having an index A indicating a discharged heat quantity higher than that of coke oven gas; and a third gas, which is a gas having an index B indicating a combustion speed higher than that of the coke oven gas.

[0011] [2] The method for producing a mixed gas according to [1] above, wherein the mixing ratio of the first gas is 50 vol% or more and less than 100 vol%, the mixing ratio of the second gas is more than 0 vol% and 15 vol% or less, and the mixing ratio of the third gas is more than 0 vol% and 30 vol% or less.

[0012] [3] The method for producing a mixed gas according to the above [1] or [2], wherein the first gas contains at least one of blast furnace gas and converter gas, the second gas is natural gas or petroleum gas, and the third gas is hydrogen gas.

[0013] [4] The method for producing a mixed gas according to any one of [1] to [3] above, wherein the contents of the first to third gases are adjusted so that the index A of the mixed gas falls within a target range of the index A of a conventional mixed gas produced by mixing the subsidiary gas and the coke oven gas, and the index B of the mixed gas falls within a target range of the index B of the conventional mixed gas.

[0014] [5] The method for producing a mixed gas according to the above [4], wherein the conventional mixed gas contains 60 vol % of the blast furnace gas and 40 vol % of the coke oven gas.

[0015] [6] The method for producing a mixed gas according to any one of the above [1] to [5], wherein the index A is a Wobbe index and the index B is a speed factor.

[0016] [7] The method for producing a mixed gas according to any one of [1] to [6] above, wherein in the mixing step, more than 0 vol % and less than 50 vol % of the coke oven gas is further mixed.

[0017] [8] The method for producing a mixed gas according to the above [7], wherein a mixing ratio of the second gas and the third gas is adjusted depending on a content of the coke oven gas in the mixed gas.

[0018] [9] A method for supplying a mixed gas, comprising: a mixing step of producing a mixed gas by mixing a first gas which is a by-gas generated in a steelworks; a second gas which is a gas having an index A indicating a discharged heat quantity higher than that of coke oven gas; and a third gas which is a gas having an index B indicating a combustion speed higher than that of the coke oven gas; and supplying the mixed gas.

[0019]

[10] The method for supplying a mixed gas according to the above [9], wherein the mixing ratio of the first gas is 50 vol% or more and less than 100 vol%, the mixing ratio of the second gas is more than 0 vol% and 15 vol% or less, and the mixing ratio of the third gas is more than 0 vol% and 30 vol% or less.

[0020]

[11] The method for supplying a mixed gas according to the above [9] or

[10] , wherein the first gas contains at least one of blast furnace gas and converter gas, the second gas is natural gas or petroleum gas, and the third gas is hydrogen gas.

[0021]

[12] The method for supplying a mixed gas described in any one of [9] to

[11] above, wherein the contents of the first to third gases are adjusted so that the index A of the mixed gas falls within a target range of the index A of a conventional mixed gas produced by mixing the subsidiary gas and the coke oven gas, and the index B of the mixed gas falls within a target range of the index B of the conventional mixed gas.

[0022]

[13] The method for supplying a mixed gas according to the above

[12] , wherein the conventional mixed gas contains 60 vol % of the blast furnace gas and 40 vol % of the coke oven gas.

[0023]

[14] The method for supplying a mixed gas according to any one of the above [9] to

[13] , wherein the index A is a Wobbe index and the index B is a speed factor.

[0024]

[15] The method for supplying a mixed gas according to any one of [9] to

[14] above, wherein in the mixing step, more than 0 vol % and less than 50 vol % of the coke oven gas is further mixed.

[0025]

[16] The method for supplying a mixed gas according to the above

[15] , wherein a mixing ratio of the second gas and the third gas is adjusted depending on a content of the coke oven gas in the mixed gas.

[0026] According to the present invention, even if the amount of coke oven gas generated decreases, a mixed gas can be produced that can continue to be used as is without updating existing equipment that is compatible with conventional mixed gases.

[0027] FIG. 1 is a piping diagram showing an example of a mixed gas supply system in a steelworks.

[0028] In this specification, the mixing ratio of a mixed gas, i.e., the proportion of each gas in the mixed gas, is expressed as a volume percentage (vol%). For precision, the mixing ratio of a mixed gas may be expressed as the volume percentage of each gas under standard conditions. Standard conditions refer to a state in which the gas temperature is 0°C and the gas pressure is 1 atmosphere.

[0029] <Conventional mixed gas> First, to facilitate understanding of the present invention, the utilization of by-gases generated in steelworks will be described. In steelworks, iron ore is reduced using a blast furnace or molten iron production facility to produce molten pig iron. The gas generated from a blast furnace is called blast furnace gas, and is a type of by-gas generated in steelworks. Blast furnace gas is composed mainly of nitrogen and carbon monoxide, with small amounts of carbon dioxide and hydrogen. The calorific value of blast furnace gas is approximately 3,000 kJ / Nm ３ Therefore, the calorific value is insufficient for use as fuel in steelworks. For this reason, in the prior art, the calorific value is supplemented by mixing the blast furnace gas with the coke oven gas, which has a high calorific value as described above. The mixing ratio in this conventional mixed gas can be, for example, 60 vol% (volume percentage) of blast furnace gas and 40 vol% of coke oven gas. However, the mixing ratio of the blast furnace gas and coke oven gas in the conventional mixed gas is not limited to the above mixing ratio.

[0030] In integrated steelworks where molten iron production and steelmaking are carried out on the same site, converter gas can be used in addition to blast furnace gas as a component of the mixed gas. Converter gas is a by-gas generated during the molten iron refining process using an LD converter. Converter gas is primarily composed of carbon monoxide, and also contains trace amounts of carbon dioxide, oxygen, nitrogen, and hydrogen. The calorific value of converter gas is approximately 7,500 kJ / Nm ３ However, since its calorific value is still insufficient as a fuel, it is preferable to use it mixed with coke oven gas. Table 1 shows the calorific value, Wobbe index, and speed factor for blast furnace gas, converter gas, coke oven gas, and a conventional mixed gas containing 60 vol% blast furnace gas and 40 vol% coke oven gas. The values ​​for the conventional mixed gas are values ​​obtained by proportional calculation based on the values ​​for blast furnace gas and coke oven gas and the results of component analysis of these gases.

[0031]

[0032] FIG. 1 is a piping diagram showing an example of a mixed gas supply system in a steelworks. As shown in FIG. 1, in a steelworks, a mixed gas is produced by mixing blast furnace gas and / or converter gas, which are secondary gases, with high-calorie coke oven gas. The mixing ratio of the mixed gas is adjusted by controlling the volumetric flow rate of the gas using a valve or the like. The mixed gas is increased in pressure using a blower (booster) indicated by the symbol "BL" and sent to the destination. It is preferable to install multiple blowers to accommodate large flow rates and for ease of maintenance. The destination of the mixed gas is not particularly limited, and the mixed gas is supplied to various plants within the steelworks, such as a hot rolling mill, a plate mill, and a cold rolling mill, and used as fuel for heating furnaces. The piping used in the mixed gas supply system shown in FIG. 1 and the burners of the heating furnaces installed in each plant are designed to conform to conventional mixed gas specifications.

[0033] The amounts and component ratios of blast furnace gas, converter gas, and coke oven gas generated are not always constant, but change from moment to moment depending on the operational status, changes in the raw materials used, etc. For this reason, the calorific values, Wobbe indexes, and speed factors of these gases also change over time, and in reality, they fluctuate within a range of approximately ±10% from the representative values ​​shown in Table 1. In conventional mixed gas production, target ranges for the Wobbe index and speed factor of the mixed gas shown in Table 1 are set, and the mixing ratio of the mixed gas is adjusted so that these indices fall within the target ranges.

[0034] Next, an embodiment of the present invention will be described in detail.

[0035] 1. Method for Producing Mixed Gas In one embodiment, the present invention is a method for producing a mixed gas, comprising a mixing step of producing a mixed gas by mixing a first gas, which is a by-gas generated in a steelworks, a second gas, which is a gas having an index A indicating a discharged calorific value higher than that of coke oven gas, and a third gas, which is a gas having an index B indicating a combustion rate higher than that of coke oven gas.

[0036] Among the gases contained in the mixed gas according to this embodiment, the first gas, which is a secondary gas, and the second gas, which is a gas having a higher index A indicating the discharged calorific value than the coke oven gas, are both mixtures and contain components in common. This also applies to the coke oven gas in the preferred embodiment described below. However, when expressing the mixing ratio of a mixed gas in this specification, the first gas, the second gas, and the coke oven gas, which are the basis of the mixing operation, are always treated as a single mixture, and the ratio is expressed using the mixture as a unit. The order in which the gases are mixed is not particularly limited, and they may be mixed in any order.

[0037] <First Gas> In the method for producing a mixed gas according to the present invention, a first gas, which is a by-gas generated in a steelworks, is mixed with another gas. In this specification, "by-gas" refers to a low-calorie gas that is generated by-production during the production of molten pig iron or steelmaking in a steelworks, and includes a combustible gas. Since by-gas is inevitably generated in conjunction with production activities in a steelworks, its effective utilization is desired. Coke oven gas is not included in the first gas.

[0038] In a preferred embodiment, the mixing ratio of the first gas in the mixed gas is 50 vol% or more. In this case, the first gas, which is a secondary gas, can be consumed as fuel without waste. The ratio of the first gas in the mixed gas is more preferably 60 vol% or more. In a preferred embodiment, the ratio of the first gas in the mixed gas is less than 100 vol%. In this case, the mixing ratios of the second gas, which is a gas having a higher index A indicating a discharge calorific value than coke oven gas described below, and the third gas, which has a higher index B indicating a combustion speed than coke oven gas, are set to more than 0 vol%, thereby increasing the calorific value of the mixed gas. The mixing ratio of the first gas in the mixed gas is more preferably 90 vol% or less, even more preferably 80 vol% or less, and even more preferably 70 vol% or less.

[0039] In a preferred embodiment, the first gas includes at least one of blast furnace gas and converter gas. As shown in Table 1, blast furnace gas and converter gas have lower calorific values ​​than coke oven gas, and therefore their calorific values ​​are insufficient for use as fuel in steelworks. Furthermore, their Wobbe index and speed factor are also smaller than those of conventional mixed gases.

[0040] <Second Gas> In the method for producing a mixed gas according to the present invention, a second gas having an index A indicating a discharged calorific value higher than that of coke oven gas is mixed with another gas. The discharged calorific value of a gas refers to the amount of heat generated when the gas is burned in a burner provided in a heating furnace. The discharged calorific value is an indicator of the heating furnace's ability to heat the material to be treated. In a preferred embodiment, the mixing ratio of the second gas in the mixed gas is greater than 0 vol%. In this case, the calorific value of the mixed gas can be increased. The mixing ratio of the second gas in the mixed gas is more preferably 5 vol% or more. In a preferred embodiment, the mixing ratio of the second gas in the mixed gas is 15 vol% or less. In this case, an excessive increase in production costs can be prevented. As described below, when coke oven gas is mixed with the second gas, the mixing ratio of the second gas can be reduced depending on the mixing ratio of the coke oven gas.

[0041] In a preferred embodiment, the second gas is natural gas or petroleum gas. These gases are not generated at the steelworks but are supplied from a supplier. Natural gas generally contains approximately 90 vol% methane, with small amounts of ethane, propane, and butane. Petroleum gas generally contains 70-80 vol% butane and 20-30 vol% propane, although the composition varies depending on the specifications. Table 1 shows the calorific values, Wobbe indexes, and speed factors of natural gas and petroleum gas. As shown in Table 1, both natural gas and petroleum gas have higher calorific values ​​and Wobbe indexes than coke oven gas, so the addition of these gases can increase the calorific value and Wobbe index of the mixed gas. In a preferred embodiment, the mixed gas may contain either natural gas or petroleum gas, or both. When natural gas and petroleum gas are simultaneously contained, the total content of the natural gas and petroleum gas in the mixed gas is greater than 0 vol% and less than or equal to 15 vol%.

[0042] As will be described later, hydrogen gas corresponds to a third gas, which is a gas having a higher index B indicating a combustion rate than coke oven gas in a preferred embodiment of the present invention. Hydrogen gas is not included in the second gas.

[0043] In the present invention, the index A indicating the calorific value of the discharged gas may be the calorific value of the gas, or preferably the Wobbe index of the gas. The Wobbe index is the value obtained by dividing the calorific value of the gas by the square root of the density of the gas. The Wobbe index is a measure of the amount of heat generated by a burner. By setting the Wobbe index of the mixed gas to a constant value, a constant calorific value can be obtained regardless of the type of gas, without changing the diameter of the pipe supplying the mixed gas. It is preferable that the Wobbe index of the mixed gas is 2,000 or more in order to obtain a sufficient calorific value.

[0044] <Third Gas> In the method for producing a mixed gas according to the present invention, a third gas having a higher index B, which indicates a combustion rate, than coke oven gas is mixed with another gas. The combustion rate of a gas refers to the speed at which a flame spreads when the gas is burned. The lighter the gas molecules, the higher the combustion rate, and this serves as a measure of the stability and continuity of the flame. In a preferred embodiment, the mixing ratio of the third gas in the mixed gas is greater than 0 vol%. In this case, the index A, which indicates the discharge heat quantity of the mixed gas, and the index B, which indicates the combustion rate, can be increased. The mixing ratio of the third gas in the mixed gas is more preferably 6.0 vol% or more. In a preferred embodiment, the mixing ratio of the third gas in the mixed gas is 30 vol% or less. In this case, an excessive increase in production costs can be prevented. The mixing ratio of the third gas in the mixed gas is more preferably 25 vol% or less. As described below, when coke oven gas is mixed with the third gas, the mixing ratio of the third gas can be adjusted depending on the mixing ratio of the coke oven gas.

[0045] In a preferred embodiment, the third gas is hydrogen gas. In this specification, "hydrogen gas" refers to a gas that is mixed into a mixed gas as a separate component from mixtures of by-gases, natural gas, petroleum gas, coke oven gas, and the like. The hydrogen contained in coke oven gas, the hydrogen contained in general blast furnace gas, and the trace amounts of hydrogen contained in general converter gas are not considered hydrogen gas in this specification. Hydrogen gas may be supplied by a supplier or produced at a steelworks. Table 1 shows the calorific value, Wobbe index, and speed factor of hydrogen gas. The speed factor of hydrogen gas is 100.0, as defined below. As shown in Table 1, hydrogen gas has a higher speed factor than coke oven gas. Therefore, by including hydrogen gas, the speed factor of the mixed gas can be made closer to that of conventional mixed gases.

[0046] In the present invention, the index B indicating the burning speed of a gas may be the burning speed coefficient of the gas, or preferably the speed factor of the gas. The speed factor is an index proposed by Weaver, and is calculated as a relative value based on the flame speed coefficient measured for each gas species constituting the mixed gas, with the speed factor of hydrogen being set at 100. The calculation formula for the speed factor S is shown below.

[0047]

[0048] where i is a parameter representing the type of flammable gas contained in the mixed gas, and X ｉ is the volume fraction of combustible gas i, F ｉ is the flame speed coefficient of combustible gas i, A is the theoretical air volume of the mixed gas, Z is the volume fraction of the inert gas, and Q is the volume fraction of oxygen. A speed factor of 12 or more is preferable in order to stabilize the flame in a burner burning the mixed gas and prevent the flame from going out.

[0049] <Mixed Gas> The mixed gas production method of the present invention includes a production step of producing a mixed gas by mixing the above-described first gas, second gas, and third gas. As described above, by mixing the first gas and the second gas, it is possible to compensate for the calorific value that is insufficient in the first gas. Furthermore, by further mixing the third gas, it is possible to increase the combustion rate that is insufficient in the mixed gas of the first gas and the second gas. Due to these effects, the mixed gas production method of the present invention can produce a mixed gas in which index A indicating the discharged calorific value and index B indicating the combustion rate are not significantly different from those in conventional mixed gases containing coke oven gas.

[0050] In a preferred embodiment, in the method for producing a mixed gas according to the present invention, the mixing ratio of the first gas is 50 vol% or more and less than 100 vol%, the mixing ratio of the second gas is more than 0 vol% and 15 vol% or less, and the mixing ratio of the third gas is more than 0 vol% and 30 vol% or less. By setting the mixing ratios of the mixed gas within the preferred ranges, it is possible to consume the secondary gas as fuel without waste and to prevent an excessive increase in production costs.

[0051] In a preferred embodiment, in the method for producing a mixed gas according to the present invention, the contents of the first to third gases are adjusted so that the index A of the mixed gas falls within the target range of index A of a conventional mixed gas produced by mixing by-gas and coke oven gas, and the index B of the mixed gas falls within the target range of index B of the conventional mixed gas. This makes it possible to produce a mixed gas whose indices are not significantly different from those of the conventional mixed gas.

[0052] As described above, in conventional mixed gas production, target values ​​for the Wobbe index, which indicates the calorific value of the discharged mixed gas, and the speed factor, which indicates the combustion rate, are set, and the mixing ratio of the mixed gas is adjusted so that these indices fall within the target ranges. In the preferred method for producing a mixed gas according to the present invention, the target ranges for the index indicating the calorific value of the discharged mixed gas and the index indicating the combustion rate are also followed, and the gas contents are adjusted so that indexes A and B fall within the target ranges. This allows time fluctuations in indexes A and B within the limits of the target ranges, enabling stable operation.

[0053] The target ranges for index A, which indicates the amount of heat discharged, and index B, which indicates the combustion rate, may be set at any range as long as existing equipment compatible with conventional mixed gases can continue to be used as is without updating it. For example, the target range for the Wobbe index is preferably set to a range of ±15% of the target value, i.e., a range of 85% to 115% of the target value. More preferably, the target range is set to a range of ±10% of the target value. On the other hand, as described above, the speed factor is calculated as a relative value when the speed factor of hydrogen is set to 100. The larger the value, the more stable the flame and the more likely it is to prevent the flame from going out. Therefore, it is preferable to set the target range for the speed factor to 11 or more without setting a target value or upper limit. A more preferable target range for the speed factor is 12 or more.

[0054] Examples of mixed gases obtained by carrying out the method for producing a mixed gas according to this preferred embodiment and comparative examples are shown in Table 2. The values ​​of the calorific value (Index A), Wobbe Index (Index A), and speed factor (Index B) of the examples and comparative examples shown in Table 2 are not values ​​measured after actually producing the mixed gas, but are values ​​calculated by proportional calculation based on the values ​​of the calorific value, Wobbe Index, and speed factor of the examples and comparative examples shown in Table 1 and the mixing ratio of the mixed gas.

[0055]

[0056] Among the examples shown in Table 2, Example 1 contains natural gas (second gas) as the second gas, while Example 2 contains petroleum gas as the second gas. According to the present invention, as shown in Examples 1 and 2, the mixing ratio of the mixed gas can be adjusted to show values ​​for the Wobbe Index and Speed ​​Factor equal to those of the conventional mixed gas shown in Table 1. This is because, as shown in Table 1, hydrogen gas as the third gas has a higher speed factor than coke oven gas, and the Wobbe Index (Index A) and Speed ​​Factor (Index B) can be individually adjusted by adjusting the mixing ratio of the mixed gas. As a result, the mixed gases of Examples 1 and 2 can be used in place of conventional mixed gases without upgrading the equipment. Note that, as shown in Table 1, petroleum gas has a higher calorific value, Wobbe Index, and Speed ​​Factor than natural gas. Therefore, in Example 2 shown in Table 2, in which petroleum gas is selected as the second gas, the mixing ratio of the second gas can be reduced compared to Example 1, in which natural gas is selected as the second gas.

[0057] On the other hand, even in Comparative Examples 1 to 3, which do not include hydrogen gas as the third gas, it is possible to adjust the mixing ratio of the mixed gas so that the Wobbe index (index A) is equal to that of a conventional mixed gas, as in Comparative Examples 1 and 2, or to adjust the mixing ratio of the mixed gas so that the calorific value (index A) is equal to that of a conventional mixed gas, as in Comparative Example 3. However, the speed factor (index B) of these comparative examples is lower than that of a conventional mixed gas. Therefore, if the mixed gases of Comparative Examples 1 to 3 are supplied to a conventional heating furnace, the flame may become unstable and may go out. Therefore, the mixed gases of Comparative Examples 1 to 3 cannot be used in place of conventional mixed gases.

[0058] The mixed gases shown in Examples 1 and 2 in Table 2 were prepared by adjusting the mixing ratio of the mixed gases so that both the Wobbe index (index A) and the speed factor (index B) were equal to those of the conventional mixed gases shown in Table 1. However, in the method for producing a mixed gas according to the present invention, it is practically impossible, or at least extremely difficult, to constantly adjust the indexes A and B of the mixed gas so that they are exactly equal to those of the conventional mixed gases. This is because, as mentioned above, various error factors are involved in actual operation, such as fluctuations over time in the components of secondary gases and the like that are used as raw materials for the mixed gas, temperature, pressure, and the like, measurement errors of various sensors, and errors in the means for controlling the gas flow rate, such as valves.

[0059] In view of the above circumstances, in a preferred embodiment, the gas contents in the mixed gas are adjusted so that index A falls within the target range of index A for a conventional mixed gas produced by mixing a by-gas and coke oven gas, but the index A does not need to be strictly equal to the target value at all times, and the adjustment may include temporary or steady-state errors. Similarly, the gas contents in the mixed gas are adjusted so that index B falls within the target range of index B for a conventional mixed gas produced by mixing a by-gas and coke oven gas.

[0060] In the above embodiment, the first gas, which is a secondary gas generated in a steelworks, is blast furnace gas. However, the first gas according to the present invention is not limited to blast furnace gas. Furthermore, the first gas and the second gas do not necessarily have to be a single type of gas, but may be a mixture of multiple types of gases. In the method for producing a mixed gas according to the present invention, a gas that does not belong to any of the first gas, second gas, and third gas may be mixed in a ratio that does not impair the effects of the present invention.

[0061] <Mixed gas containing coke oven gas> In a preferred embodiment, the present invention is a method for producing a mixed gas, in which, in addition to the first gas, the second gas, and the third gas, more than 0 vol % and less than 50 vol % of coke oven gas is further mixed in the mixing step.

[0062] In a more preferred embodiment, the present invention is a method for producing a mixed gas, which, in addition to the above configuration, adjusts a mixing ratio of the second gas and the third gas depending on a content of the coke oven gas in the mixed gas.

[0063] As mentioned above, in recent years, the amount of coke used in blast furnaces or hot metal production processes has been reduced, and coke-free hot metal production methods have been developed. Therefore, it is expected that the amount of coke oven gas generated in steelworks will decrease in the future. However, because coke oven gas has a high calorific value, it is preferable to effectively utilize it while it is still being generated. Therefore, in a preferred embodiment, coke oven gas is contained as a component of the mixed gas. By mixing coke oven gas, it can be effectively used as fuel regardless of the amount generated. Furthermore, the mixing ratios of the second gas and the third gas in the mixed gas can be reduced, thereby reducing the production cost of the mixed gas.

[0064] If the proportion of coke oven gas in the mixed gas is more than 0 vol%, the mixing ratios of the second gas and the third gas can be reduced, thereby reducing the production cost of the mixed gas. The proportion of coke oven gas in the mixed gas is more preferably 10 vol% or more. If the proportion of coke oven gas in the mixed gas is less than 50 vol%, the amount of coke oven gas required will not exceed the mixing ratio of coke oven gas in conventional mixed gases. The proportion of coke oven gas in the mixed gas is more preferably less than 40 vol%.

[0065] Among the mixed gases containing coke oven gas obtained by carrying out the mixed gas production method according to the preferred embodiment, Table 3 shows an example of the invention in which natural gas was used as the second gas.

[0066]

[0067] Table 4 shows an example of the invention in which petroleum gas is used as the second gas in a mixed gas containing coke oven gas.

[0068]

[0069] As can be seen from Tables 3 and 4, according to the preferred embodiment described above, even if the amount of coke oven gas generated decreases, the coke oven gas ratio in the mixed gas can be adjusted arbitrarily between the current 40 vol% and 0 vol%. This makes it possible to flexibly respond to fluctuations in the amount of coke oven gas generated without replacing existing heating furnaces. On the other hand, even when coke oven gas is mixed, as shown in Comparative Example 4 in Table 3, if hydrogen gas is not mixed as the third gas, it is not possible to make both the Wobbe index (index A) and the speed factor (index B) match those of the conventional mixed gas.

[0070] The blending ratios of natural gas or petroleum gas as the second gas and hydrogen gas as the third gas shown in Table 2 can be determined by solving an equation for two variables in which indexes A and B are equal to those of conventional blended gases. As described above, these indices for the blended gas can be calculated by proportional calculation using the blending ratios of each gas. Similarly, the blending ratios of natural gas or petroleum gas as the second gas and hydrogen gas as the third gas shown in Tables 3 and 4 can be determined by first selecting an arbitrary value for the blending ratio of coke oven gas and then solving an equation based on the selected blending ratio of coke oven gas. This allows the blending ratios of other gases to be appropriately adjusted depending on the content of coke oven gas in the blended gas. These calculations can be performed, for example, using the regression function of a spreadsheet program.

[0071] Referring again to FIG. 1 , in the method for producing a mixed gas according to the present invention, it is preferable to increase the pressure of a first gas containing at least one of blast furnace gas and converter gas using a blower, and then mix the first gas with natural gas or petroleum gas as a second gas and hydrogen gas as a third gas. By increasing the pressure of the first gas before mixing with the second and third gases, it is possible to prevent the second and third gases from flowing back upstream into the mixed gas supply system shown in FIG. 1 . The second and third gases are delivered via piping from a storage container such as a gas cylinder or a vaporizer, and their pressures are adjusted as necessary using a pressure reducing valve before being mixed with the first gas. As described above, the mixing ratio can be adjusted by adjusting the volumetric flow rate of the gases to be mixed using a valve or the like. The volumetric flow rate of each gas can be measured, for example, using a flow meter.

[0072] 1 illustrates an example in which one piping system is used for mixing the second gas and the third gas, but separate piping systems may be provided for the second gas and the third gas. Regarding the order in which the second gas and the third gas are mixed with the first gas, the second gas may be mixed first, or the third gas may be mixed first. Alternatively, as illustrated in FIG. 1, a premix of the second gas and the third gas may be mixed with the first gas.

[0073] When producing a mixed gas containing coke oven gas, it is preferable to mix the coke oven gas with the first gas upstream of the blower, as illustrated in Fig. 1. Since both the first gas and the coke oven gas are low-pressure gases recovered at atmospheric pressure, they can be mixed by the above-mentioned method. However, in the method for producing a mixed gas according to the present invention, the order in which the gases are mixed is not limited to the order illustrated in Fig. 1.

[0074] 2. Method for Supplying Mixed Gas In another embodiment, the present invention is a method for supplying a mixed gas, the method comprising a mixing step of producing a mixed gas by mixing a first gas, which is a by-gas generated in a steelworks, a second gas, which is a gas having an index A indicating a discharge calorific value higher than that of coke oven gas, and a third gas, which is a gas having an index B indicating a combustion rate higher than that of coke oven gas, and supplying the mixed gas. In this embodiment, the mixed gas is supplied in place of a conventional mixed gas that is produced and supplied by mixing a by-gas and coke oven gas. The supplied mixed gas is used in the operation of the steelworks.

[0075] As described above, the piping used in the mixed gas supply system shown in Figure 1 and the burners of the heating furnaces installed in each factory are designed to conform to the specifications of the conventional mixed gas that is produced and supplied by mixing by-gas and coke oven gas. According to the mixed gas supply method of the present invention, even when the mixed gas of the present invention is supplied instead of such a conventional mixed gas, the existing equipment can be used as is.

[0076] As described above, according to the present invention, by mixing a first gas, which is a secondary gas, a second gas having a higher index A indicating the amount of heat discharged than coke oven gas, and a third gas having a higher index B indicating the combustion speed than coke oven gas, it is possible to produce a mixed gas that has properties equivalent to those of a conventional mixed gas that contains a large amount of coke oven gas and that can be used as a substitute for the conventional mixed gas.

Claims

1. The first gas is a by-product gas generated in a steel mill, The second gas is a gas with a higher output heat index A than coke oven gas, A third gas, which has a higher combustion rate index B than the aforementioned coke oven gas, A method for producing a mixed gas, comprising a mixing step of mixing to produce a mixed gas.

2. The mixing ratio of the first gas is 50 vol% or more and less than 100 vol%, The mixing ratio of the second gas is greater than 0 vol% and less than or equal to 15 vol%, The mixing ratio of the three gases is greater than 0 vol% and less than or equal to 30 vol%. A method for producing a mixed gas according to claim 1.

3. The first gas includes at least one of blast furnace gas and converter gas. The second gas is natural gas or petroleum gas. The third gas is hydrogen gas. A method for producing a mixed gas according to claim 1 or 2.

4. The content of the first to third gases is adjusted so that the index A of the mixed gas falls within the target range of the index A of a conventional mixed gas produced by mixing the by-product gas and the coke oven gas, and the index B of the mixed gas falls within the target range of the index B of the conventional mixed gas. A method for producing a mixed gas according to claim 1 or 2.

5. The conventional mixed gas is a mixed gas containing 60 vol% blast furnace gas and 40 vol% coke oven gas as the secondary gas. A method for producing a mixed gas according to claim 4.

6. The aforementioned index A is the Wobbe index, and the aforementioned index B is the speed factor. A method for producing a mixed gas according to claim 1 or 2.

7. In the mixing step, the coke oven gas is further mixed in an amount greater than 0 vol% and less than 50 vol%. A method for producing a mixed gas according to claim 1 or 2.

8. The mixing ratio of the second gas and the third gas is adjusted according to the content of the coke oven gas in the mixed gas. A method for producing a mixed gas according to claim 7.

9. The first gas is a by-product gas generated in a steel mill, The second gas is a gas with a higher output heat index A than coke oven gas, A third gas, which has a higher combustion rate index B than the aforementioned coke oven gas, The process includes a mixing step to produce a mixed gas by mixing the following: A method for supplying the aforementioned mixed gas.

10. The mixing ratio of the first gas is 50 vol% or more and less than 100 vol%, The mixing ratio of the second gas is greater than 0 vol% and less than or equal to 15 vol%, The mixing ratio of the three gases is greater than 0 vol% and less than or equal to 30 vol%. The method for supplying a mixed gas according to claim 9.

11. The first gas includes at least one of blast furnace gas and converter gas. The second gas is natural gas or petroleum gas. The third gas is hydrogen gas. A method for supplying a mixed gas according to claim 9 or 10.

12. The content of the first to third gases is adjusted so that the index A of the mixed gas falls within the target range of the index A of a conventional mixed gas produced by mixing the by-product gas and the coke oven gas, and the index B of the mixed gas falls within the target range of the index B of the conventional mixed gas. A method for supplying a mixed gas according to claim 9 or 10.

13. The conventional mixed gas is a mixed gas containing 60 vol% blast furnace gas and 40 vol% coke oven gas as the secondary gas. The method for supplying a mixed gas according to claim 12.

14. The aforementioned index A is the Wobbe index, and the aforementioned index B is the speed factor. A method for supplying a mixed gas according to claim 9 or 10.

15. In the mixing step, the coke oven gas is further mixed in an amount greater than 0 vol% and less than 50 vol%. A method for supplying a mixed gas according to claim 9 or 10.

16. The mixing ratio of the second gas and the third gas is adjusted according to the content of the coke oven gas in the mixed gas. The method for supplying a mixed gas according to claim 15.