Mixing ratio calculation device

Abstract

To provide a mixing ratio calculation device for inexpensively and simply detecting a mixing ratio and its fluctuation.SOLUTION: A mixing ratio of at least one of a first composition fuel and a second composition fuel contained in a mixed fuel is calculated on the basis of concentrations of two components in an exhaust gas generated in a combustion device for burning the mixed fuel composed of the first composition fuel and the second composition fuel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a mixing ratio calculation device. [Background technology]

[0002] Boiler systems that generate steam by burning a mixture of fuel gas and combustion air in a predetermined ratio to heat water have been known. In this type of boiler system, the flow rate of the fuel gas is adjusted by a flow control valve or the like in accordance with the amount of combustion air supplied so that the air ratio, which is the ratio of the theoretical air volume to the amount of air supplied to the boiler, is constant.

[0003] The air ratio is a value set by the boiler equipment, and if the air ratio fluctuates, for example, there is a possibility that combustion efficiency will decrease due to heat loss caused by excess air, or that energy loss will increase due to incomplete combustion, so it is desirable to maintain it within the set range (or constant) as much as possible.

[0004] When the mass flow rate of fuel gas fluctuates due to temperature or pressure fluctuations, even if the volumetric flow rate of the fuel gas is constant, the theoretical amount of combustion air required to combust the fuel gas changes, causing the air ratio to fluctuate. For this reason, in order to deal with fluctuations in the air ratio, constant O2 control has been put into practical use, in which combustion is performed at a predetermined air ratio by feedback-controlling the fuel gas flow rate based on the oxygen concentration in the exhaust gas from the boiler equipment, and various technologies have been disclosed that accurately reflect the combustion state of the boiler in the air ratio (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-008803 Summary of the Invention [Problem to be solved by the invention]

[0006] Recently, increasing environmental awareness has led to efforts to reduce carbon dioxide emissions associated with combustion by burning hydrogen fuel in boilers and other equipment. Therefore, it is desirable to reduce carbon dioxide emissions associated with combustion in boilers by burning a mixture of city gas and hydrogen, for example. When burning a mixture of gases, the calorific value and theoretical air volume per unit volume of fuel vary depending on the ratio of each fuel component in the mixture. Furthermore, the air ratio required to maintain a favorable combustion state also varies. Therefore, without any adjustment or control, the risk of boiler puncture due to reduced thermal output and the risk of incomplete combustion or misfire due to variations in the air ratio increase. Therefore, it is necessary to control the fuel flow rate, combustion air flow rate, and air ratio according to the fuel composition. To obtain information on the fuel composition required for control according to the fuel composition, a measuring instrument (e.g., a gas analyzer or density meter) capable of identifying the hydrogen mixture ratio (composition) can be installed. However, such measuring instruments are expensive, increasing costs and complicating the fuel supply route. Furthermore, when mixing fuels inside a boiler, it is possible to adopt an alternative method of determining the mixing ratio from the opening of a flow control valve that adjusts the flow rate of each fuel or from a flow meter. However, when fuels are mixed and supplied outside a boiler, the above-mentioned alternative method cannot be adopted.

[0007] The present invention has been devised in view of the above circumstances, and its object is to provide a mixture ratio calculation device that detects the mixture ratio and its fluctuations inexpensively and simply. [Means for solving the problem]

[0008] In order to achieve the above object, the mixing ratio calculation device of the present invention calculates the mixing ratio of at least one of the fuel of a first composition and the fuel of a second composition contained in a mixed fuel based on two components of exhaust gas generated in a combustion device that combusts a mixed fuel consisting of a fuel of a first composition and a fuel of a second composition.

[0009] Preferably, a predetermined mathematical formula derived from a chemical reaction formula for combustion of the first composition and a chemical reaction formula for combustion of the second composition is used to calculate the mixing ratio of at least one of the fuel of the first composition and the fuel of the second composition contained in the mixed fuel based on the concentrations of two components of the exhaust gas.

[0010] According to the above configuration, it is possible to inexpensively and simply detect the mixture ratio of at least one of the fuel with the first composition and the fuel with the second composition contained in the mixed fuel, and the fluctuation thereof. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 10 is a diagram for explaining the process of deriving a formula for calculating the mixing ratio of hydrogen in a mixed gas. [Figure 2] 1 is a table for specifying the calorific value according to the mixing ratio of hydrogen (H2). [Figure 3] 10A and 10B are diagrams for explaining a process for deriving a formula for calculating the mixing ratio of ammonia in a mixed gas according to a modified example. [Figure 4] 10A and 10B are diagrams for explaining a process for deriving a formula for calculating the mixing ratio of hydrogen in a mixed gas according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0012] A mixing ratio calculation device according to an embodiment of the present invention will be described below. An example of the mixing ratio calculation device according to this embodiment will be described, in which the device is used to calculate the mixing ratio of each component constituting a mixed gas used as fuel in a combustion device such as a boiler. An example of the mixed gas is a gas containing methane (CH4), which is a hydrocarbon, and hydrogen (H2). The combustion device is not limited to a boiler, and may be any combustion device that burns a mixed gas as fuel, such as a combustion device used in ships, airplanes, automobiles, industrial furnaces, etc.

[0013] The mixing ratio calculation device of this embodiment calculates the mixing ratio of at least one of hydrogen and hydrocarbons based on the concentrations of at least two components (e.g., oxygen concentration and carbon dioxide concentration) in the exhaust gas generated in the combustion device, based on a calculation program stored in a memory unit of the mixing ratio calculation device (described below). For example, an O2 sensor (oxygen concentration detector) that detects the oxygen concentration of the exhaust gas and a CO2 sensor (carbon dioxide concentration detector) that detects the carbon dioxide concentration of the exhaust gas are installed in an exhaust gas discharge path from the combustion device, and the mixing ratio calculation device identifies the oxygen concentration and carbon dioxide concentration of the exhaust gas based on information from the O2 sensor and the CO2 sensor, and calculates the mixing ratio of at least one of hydrogen and hydrocarbons based on the calculation program. While the O2 sensor and the CO2 sensor are configured to be included in the combustion device, they may also be configured to be included in the mixing ratio calculation device. Furthermore, the mixing ratio calculation device may be a separate component from the combustion device, or may be included in a control unit that controls the combustion state of the combustion device.

[0014] The calculation program in this embodiment is a program that calculates the mixing ratio of hydrogen in a mixed gas by performing the calculation process exemplified by Equation 9 in Fig. 1. Equation 9 in Fig. 1 is a mathematical formula derived from the chemical reaction formula for hydrogen combustion and the chemical reaction formula for hydrocarbon combustion. The process of deriving Equation 9 will be explained using Equations 1 to 8 shown in Fig. 1.

[0015] Equation 1 shows the general chemical reaction formula for methane (CH4), a hydrocarbon. The formula on the left side of the arrow in Equation 1 is the chemical formula before an excess of air (mmoles of air) is supplied to methane and a chemical reaction occurs, and the formula on the right side of the arrow in Equation 1 is the chemical formula after combustion. When methane is burned, carbon dioxide (CO2), water (H20), and nitrogen (N2) are produced. Note that the term beginning with (m-1) represents excess air.

[0016] Equation 2 shows the general chemical reaction formula for hydrogen (H2). The formula shown on the left side of the arrow in Equation 2 is the chemical formula before an excess of air (mmoles of air) is supplied to hydrogen and a chemical reaction occurs, and the formula shown on the right side of the arrow in Equation 2 is the chemical formula after combustion. When hydrogen is burned, water (H20) and nitrogen (N2) are produced. Note that the term beginning with (m-1) represents the excess air.

[0017] Equations 3 and 4 show the chemical reaction equations for methane (CH4) and hydrogen (H2) when the mixing ratio of hydrogen (H2) in the mixed gas is x and the mixing ratio of methane (CH4) is (1-x). Specifically, Equation 3 is an equation obtained by multiplying Equation 1 by the mixing ratio of methane (CH4), which is (1-x), and Equation 4 is an equation obtained by multiplying Equation 2 by the mixing ratio of hydrogen (H2), which is x.

[0018] Equation 5 shows the percentage (concentration) of O2 in the post-combustion exhaust gas, which is expressed as the sum of the right-hand sides of Equation 3 and Equation 4. Equation 6 shows the percentage (concentration) of CO2 in the post-combustion exhaust gas, which is expressed as the sum of the right-hand sides of Equation 3 and Equation 4. The O2 and CO2 concentrations indicate the percentage of each gas contained in all the exhaust gas components, and correspond to the number of moles of O2 and CO2, respectively, out of the total amount (total moles) of exhaust gas. Therefore, Equation 5 and Equation 6 do not need to take into account differences in the composition of oxygen (O2), carbon dioxide (CO2), water (H2O), nitrogen (N2), etc., and therefore show quantitative relationships (each converted to 1 (1 mole)).

[0019] In Equation 5, the denominator shows the sum of the right-hand sides of Equation 3 and Equation 4 (with each component converted to 1), and the numerator shows the sum of the terms on the right-hand sides of Equation 3 and Equation 4 that contain oxygen (O2) (with the O2 component converted to 1), which shows the concentration of oxygen (O2) contained in the exhaust gas.

[0020] In Equation 6, the denominator shows the sum of the right-hand sides of Equation 3 and Equation 4 (with each component converted to 1), and the numerator shows the sum of the terms containing carbon dioxide (CO2) on the right-hand sides of Equation 3 and Equation 4 (effectively only Equation 3) (with the CO2 component converted to 1), which shows the concentration of carbon dioxide (CO2) contained in the exhaust gas.

[0021] Equation 7 is obtained by dividing equation 5 by equation 6, so that the left side takes the form O2 / CO2 = ···, and then transforming this form by moving m-1 to the left side.

[0022] Next, by substituting equation 7 for (m-1) in equation 6 and rearranging it, we obtain equation 8. For example, by dividing the denominator on the right side of equation 6 into terms that include (m-1) and terms that do not, and then substituting equation 7 for (m-1) in the resulting equation, we can simplify the fraction in the denominator by 2(1-x) + 0.5x, simplify the right side by (1-x), multiply both sides by the denominator on the right side, multiply both sides by 1 / CO2, move the terms that include x to the left side and the terms that do not include x to the right side, and divide both sides by {1 + 0.5 79 / 21}, thereby obtaining equation 8. Note that x is the mixture ratio of hydrogen (H2) and (1-x) is the mixture ratio of methane (CH4), so it is obvious that H2 / CH4 = x / (1-x).

[0023] Equation 9 is obtained by multiplying both sides of Equation 8 by (1-x), moving the x term to the left side, and rearranging it so that x is equal to (=). In this way, x, the hydrogen (H2) mixture ratio, can be calculated from the oxygen concentration and carbon dioxide concentration of the exhaust gas. A calculation program for calculating Equation 9 is stored in the memory of the mixture ratio calculation device. Therefore, the mixture ratio calculation device can calculate the hydrogen (H2) mixture ratio in the mixed gas from the oxygen concentration and carbon dioxide concentration in the exhaust gas. O2 sensors and CO2 sensors are often installed in combustion devices to measure the oxygen concentration and carbon dioxide concentration that control the combustion state, and are relatively inexpensive compared to measuring instruments (such as gas analyzers and density meters) that can determine the hydrogen mixture ratio (composition). Therefore, the mixture ratio calculation device can inexpensively and simply detect the hydrogen mixture ratio and its fluctuations in the mixed gas.

[0024] The mixing ratio calculation device transmits to the combustion device mixing ratio information capable of identifying the mixing ratio of hydrogen (H2) in the mixed gas calculated from the oxygen concentration and carbon dioxide concentration in the exhaust gas. The mixing ratio calculation device may transmit the mixing ratio information at predetermined time intervals (e.g., every 10 seconds), or may transmit the mixing ratio information when the mixing ratio of hydrogen (H2) changes. The combustion device, for example, controls at least one of the supply amount of the mixed gas and the supply amount of combustion air according to the mixing ratio identified from the received mixing ratio information. FIG. 2 is a table for identifying the calorific value according to the mixing ratio of hydrogen (H2). In FIG. 2, the horizontal axis represents the mixing ratio of hydrogen (H2) and the vertical axis represents the calorific value. The combustion device, for example, identifies the calorific value according to the mixing ratio identified from the received mixing ratio information based on the relationship shown in FIG. 2, calculates an appropriate air ratio according to the calorific value, and controls at least one of the supply amount of the mixed gas and the supply amount of combustion air to achieve the air ratio. The mixing ratio calculation device may calculate the mixing ratio, identify the heat generation amount according to the mixing ratio, and transmit information that can identify the heat generation amount to the combustion device, or may further calculate an appropriate air ratio according to the identified heat generation amount and transmit information that can identify the air ratio to the combustion device.

[0025] In the above embodiment, an example was shown in which the mixing ratio of hydrogen in a mixed gas is calculated based on the oxygen concentration and carbon dioxide concentration of the exhaust gas generated in the combustion device, but the invention is not limited to this and may also be applied to calculating the mixing ratio of hydrocarbons (methane) in a mixed gas. In this case, a calculation program that obtains (1-x) equal to (=), which corresponds to CH4 from Equation 8, is stored in a storage unit, and the mixing ratio of hydrocarbons (methane) is calculated using the calculation program.

[0026] In the above embodiment, a fuel in which hydrogen and hydrocarbon are mixed is exemplified as the mixed gas (mixed fuel), but it is not limited to this, and it may be a fuel in which ammonia and hydrocarbon are mixed, or a fuel in which ammonia and hydrogen are mixed. Also, in calculating the mixing ratio, oxygen and carbon dioxide are exemplified as two components of the exhaust gas, but it is not limited to this, and any combination of components that are independent compositions contained in the exhaust gas may be used, for example, oxygen and water. Such examples will be described below.

[0027] Figure 3 shows an example of calculating the ammonia mixing ratio from the oxygen and carbon dioxide in exhaust gas when the mixed gas (mixed fuel) is a fuel that is a mixture of ammonia and hydrocarbons. In Figure 3, a formula (see Formula 15) showing the proportion (concentration) of O2 in the exhaust gas after combustion and a formula (see Formula 16) showing the proportion (concentration) of CO2 are derived from the general chemical reaction formula (see Formulas 11 and 13) for methane (CH4), a hydrocarbon, and the general chemical reaction formula (see Formulas 12 and 14) for ammonia (NH3). Equation 15 is then divided by Equation 16 to move m-1 to the left side (see Formula 17), and Equation 18 is derived by substituting Equation 17 for (m-1) in Equation 16 and rearranging it. Both sides are then multiplied by (1-x), and the x term is moved to the left side to make x equal (=), resulting in Equation 19 (see Formula 19). In this way, the mixing ratio x of ammonia (NH3) can be calculated from the oxygen concentration and carbon dioxide concentration of the exhaust gas. A calculation program for calculating Equation 19 is stored in the memory of the mixing ratio calculation device, and it becomes possible to calculate the mixing ratio of ammonia (NH3) in the mixed gas from the oxygen concentration and carbon dioxide concentration in the exhaust gas.

[0028] Figure 4 shows an example of calculating the hydrogen mixing ratio from the oxygen and water in the exhaust gas when the mixed gas (mixed fuel) is a fuel mixture of ammonia and hydrogen. In Figure 4, a formula (see Formula 25) showing the ratio (concentration) of O in the exhaust gas after combustion and a formula (see Formula 26) showing the ratio (concentration) of HO are derived from the general chemical reaction formulas for hydrogen (H) (see Formulas 21 and 23) and ammonia (NH) (see Formulas 22 and 24). Formula 25 is then divided by Formula 26 to move m-1 to the left side (see Formula 27). Formula 27 is then substituted for (m-1) in Formula 25, and the x term is moved to the left side to derive a formula (see Formula 28) where x is equal to (=). In this way, x, the hydrogen (H) mixing ratio, can be calculated from the oxygen concentration and water in the exhaust gas. A calculation program for calculating Equation 28 is stored in the storage unit of the mixture ratio calculation device, and it is possible to calculate the mixture ratio of hydrogen (H2) in the mixed gas from the oxygen concentration and water in the exhaust gas.

[0029] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

Claims

1. A mixing ratio calculation device that calculates a mixing ratio of at least one of a fuel having a first composition and a fuel having a second composition contained in a mixed fuel based on concentrations of two components in exhaust gas generated in a combustion device that combusts a mixed fuel consisting of a fuel having a first composition and a fuel having a second composition.

2. 2. The mixing ratio calculation device according to claim 1, wherein a mixing ratio of at least one of the fuel of the first composition and the fuel of the second composition contained in the mixed fuel is calculated based on concentrations of two components of the exhaust gas by using a predetermined mathematical formula derived from a chemical reaction formula related to combustion of the first composition and a chemical reaction formula related to combustion of the second composition.

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