JP7579751B2 - Composition estimation device and fluid mixing system - Google Patents

Description

The present invention relates to a composition estimation device and a fluid mixing system.

Various combustion appliances such as gas burners used in industrial furnaces are configured to burn fuel gas and combustion air at a specified mixture ratio. In addition to city gas, propane, hydrogen, etc. may be used as fuel gas. In such cases, the composition of the fuel gas will be different, and in order to perform proper combustion, it is necessary to appropriately change the mixture ratio of fuel gas and combustion air.

For example, the fuel supply system described in Patent Document 1 uses a thermal flow meter and a composition-independent flow meter that can measure the flow rate independent of the composition of the gas fuel in order to provide an appropriate fuel supply even when the properties of the gas fuel change. If the degree of deviation between the measurement value of the thermal flow meter and the measurement value of the composition-independent flow meter is large enough to indicate an abnormal state, the fuel supply device is configured to adjust the amount of gas fuel supplied to the supply target.

WO2013/111776 publication

In the fuel supply system of Patent Document 1, for example, when the composition (type) of the fuel gas is intentionally varied, no effort is made to appropriately change the mixture ratio of the fuel gas and the combustion air by utilizing the difference in the characteristic coefficient of the thermal flow meter according to the fluid composition. Furthermore, in the fuel supply system of Patent Document 1, when the composition (type) of the fuel gas is intentionally varied, no effort is made to estimate the composition of the fuel gas. Therefore, further effort is needed to more appropriately generate a mixed fluid of the required composition.

The present invention was made in consideration of these problems, and aims to provide a composition estimation device and a fluid mixing system that can more appropriately generate a fluid with the required composition.

One aspect of the present invention is
a thermal flow meter that is set to measure a mass flow rate of a reference fluid having a specific composition and that measures a mass flow rate of a measurement fluid different from the reference fluid flowing through a pipe;
a volumetric flowmeter that is arranged in series with the thermal flowmeter in the pipe and measures a volumetric flow rate of the measurement fluid flowing through the pipe;
a calculation device that calculates a characteristic coefficient b of the measured fluid by the equation b = a × Qa/Qb, where a is a characteristic coefficient of the reference fluid set in the thermal flow meter, Qa is a mass flow rate of the measured fluid measured by the thermal flow meter, and Qb is a volumetric flow rate of the measured fluid measured by the volumetric flow meter, and estimates the composition of the measured fluid based on the characteristic coefficient b of the measured fluid.

Another aspect of the present invention is
1. A fluid mixing system that generates a mixed fluid by mixing a first fluid and a second fluid, and sets a mixing ratio of the first fluid to the second fluid in the mixed fluid to a target mixing ratio,
a first pipe to which the first fluid is supplied;
A second pipe to which the second fluid is supplied;
a junction pipe where the first pipe and the second pipe join together;
a thermal flow meter that is disposed in the junction pipe and configured to measure a mass flow rate of a reference fluid having a specific composition, and that measures a mass flow rate of the mixed fluid flowing through the junction pipe;
a volumetric flowmeter that is arranged in series with the thermal flowmeter in the junction pipe and measures a volumetric flow rate of the mixed fluid flowing through the junction pipe;
an adjusting valve for adjusting a mixing ratio of the first fluid and the second fluid;
a control device for controlling the thermal flow meter, the volumetric flow meter, and the regulating valve;
The control device includes:
an information acquiring unit that acquires information on a composition of the first fluid, a composition of the second fluid, and the target mixing ratio;
a relationship setting unit that sets a target flow rate relationship or a target characteristic coefficient based on a relationship between a mass flow rate measured by the thermal flow meter and a volumetric flow rate measured by the volumetric flow meter for the mixed fluid having the target mixing ratio when a composition of the first fluid, a composition of the second fluid, and the target mixing ratio are determined;
an opening adjustment unit that adjusts the opening of the regulating valve so that a measured flow rate relationship between a measured mass flow rate measured by the thermal flow meter and a measured volumetric flow rate measured by the volumetric flow meter coincides with the target flow rate relationship, or so that a measured characteristic coefficient based on the measured mass flow rate, the measured volumetric flow rate, and a characteristic coefficient of the reference fluid coincides with the target characteristic coefficient.

(One aspect of the composition estimation device)
In the composition estimation device of the one aspect, a thermal flowmeter and a volumetric flowmeter are arranged in series in a pipe, and the composition of the measurement fluid, the mass flow rate of which is measured by the thermal flowmeter, is estimated using a characteristic coefficient a of a reference fluid set in the thermal flowmeter, a mass flow rate Qa of the measurement fluid measured by the thermal flowmeter, and a volumetric flow rate Qb of the measurement fluid measured by the volumetric flowmeter. The characteristic coefficient in the thermal flowmeter indicates a value that is specific to the composition of the fluid whose mass flow rate is measured by the thermal flowmeter, and is determined according to the composition of the fluid.

In the composition estimation device of the above embodiment, the composition of the measurement fluid, whose mass flow rate is measured by the thermal flow meter, is estimated by utilizing the difference in the characteristic coefficient of the thermal flow meter according to the composition of the fluid. Specifically, focusing on the fact that the product of the characteristic coefficient a of the reference fluid and the mass flow rate Qa of the measurement fluid is equivalent to the product of the characteristic coefficient b of the measurement fluid and the volumetric flow rate Qb of the measurement fluid, the calculation device calculates the characteristic coefficient b of the measurement fluid by b = a x Qa / Qb, and estimates the composition of the measurement fluid based on the characteristic coefficient b of the measurement fluid. The relationship between the characteristic coefficient b of the measurement fluid and the composition of the measurement fluid may be determined in advance by testing, theoretical calculation, etc.

With this configuration, by using a pipe in which a thermal flow meter and a volumetric flow meter are arranged in series, it is possible to estimate the composition of the measurement fluid when the composition of the measurement fluid, the flow rate of which is measured, differs from the composition of the reference fluid. Therefore, for example, when the measurement fluid is fuel gas or a mixture of a known fuel gas and combustion air, it becomes possible to estimate the composition of the fuel gas or mixture, and the mixing ratio of the fuel gas and the combustion air can be adjusted appropriately.

Therefore, according to the composition estimation device of the above embodiment, it is possible to more appropriately generate a fluid with the required composition by estimating the composition of the measured fluid.

(Another aspect of the fluid mixing system)
In the fluid mixing system of the other aspect, a thermal flowmeter and a volumetric flowmeter are arranged in series in a junction pipe through which a mixed fluid obtained by mixing a first fluid and a second fluid flows, and when a mixed fluid having a composition different from the composition of a reference fluid set in the thermal flowmeter is used, the mixing ratio of the first fluid and the second fluid is set to a target mixing ratio. In the fluid mixing system of the other aspect, the control device adjusts the opening of the adjustment valve to set the mixing ratio of the first fluid and the second fluid to the target mixing ratio when information on the composition of the first fluid and the composition of the second fluid is obtained by utilizing the difference in the characteristic coefficient of the thermal flowmeter depending on the fluid composition.

Specifically, the control device has an information acquisition unit, a relationship setting unit, and an opening adjustment unit. The information acquisition unit acquires information on the composition of the first fluid, the composition of the second fluid, and the target mixing ratio, and the relationship setting unit sets a target flow rate relationship or a target characteristic coefficient based on the relationship between the mass flow rate by the thermal flow meter and the volumetric flow rate by the volumetric flow meter for the mixed fluid of the target mixing ratio when the composition of the first fluid, the composition of the second fluid, and the target mixing ratio are determined. The target flow rate relationship reflects the relationship between the characteristic coefficient of the reference fluid in the thermal flow meter and the target characteristic coefficient of the mixed fluid of the target mixing ratio in the thermal flow meter.

The opening adjustment unit adjusts the opening of the regulating valve so that the measured flow rate relationship between the measured mass flow rate measured by the thermal flow meter and the measured volumetric flow rate measured by the volumetric flow meter matches the target flow rate relationship, or so that the measured characteristic coefficient based on the measured mass flow rate, the measured volumetric flow rate, and the characteristic coefficient of the reference fluid matches the target characteristic coefficient. When the measured flow rate relationship matches the target flow rate relationship within an acceptable range, or when the measured characteristic coefficient matches the target characteristic coefficient within an acceptable range, it can be determined that a mixed fluid of the target composition has been generated. Therefore, for example, when the first fluid is fuel gas and the second fluid is combustion air, the mixture ratio of the fuel gas and the combustion air can be set to the target mixture ratio.

Therefore, according to the fluid mixing system of the other aspect, a mixed fluid with a required composition can be more appropriately generated by generating a mixed fluid with a target mixing ratio.

FIG. 1 is an explanatory diagram showing a composition estimation device according to a first embodiment. FIG. 2 is an explanatory diagram showing a fluid mixing system according to the second embodiment. FIG. 3 is a graph showing a target flow rate relationship between a volumetric flow rate and a mass flow rate, and a relationship between a characteristic coefficient of a reference fluid and a characteristic coefficient of a mixed fluid according to the second embodiment. FIG. 4 is a graph showing the relationship between the volumetric flow rate and the mass flow rate in terms of actual measured values and theoretical values according to the second embodiment. FIG. 5 is a flowchart showing a main routine of a control method for a fluid mixing system according to the second embodiment. FIG. 6 is a flowchart showing a first adjustment routine of the control method for the fluid mixing system according to the second embodiment. FIG. 7 is a flowchart showing a second adjustment routine of the control method for the fluid mixing system according to the second embodiment.

Preferred embodiments of the composition estimation device and fluid mixing system described above will be described with reference to the drawings.
<Embodiment 1>
1 , the composition estimation device 1A of this embodiment includes a thermal flow meter 2, a volumetric flow meter 3, and a calculation device 4A. The thermal flow meter 2 is set to measure the mass flow rate Qa of a reference fluid having a specific composition, and is configured to measure the mass flow rate Qa of a measurement fluid M different from the reference fluid, which flows through a pipe 5. The volumetric flow meter 3 is disposed in series with the thermal flow meter 2 in the pipe 5, and is configured to measure the volumetric flow rate Qb of the measurement fluid M flowing through the pipe 5.

The calculation device 4A is configured to calculate the characteristic coefficient b of the measured fluid M by b = a x Qa/Qb, where a is the characteristic coefficient of the reference fluid set in the thermal flowmeter 2, Qa is the mass flow rate of the measured fluid M measured by the thermal flowmeter 2, and Qb is the volumetric flow rate of the measured fluid M measured by the volumetric flowmeter 3, and to estimate the composition of the measured fluid M based on the characteristic coefficient b of the measured fluid M.

The composition estimation device 1A of this embodiment will be described in detail below.
1, the composition estimation device 1A enables the supply of a mixture as a fluid having a required composition to a combustion appliance 6 that combusts a mixture of fuel gas and combustion air. A pipe 5 constituting the composition estimation device 1A is connected to the combustion appliance 6 and is for supplying the mixture as a measurement fluid M to the combustion appliance 6.

The measurement fluid M and the reference fluid in this embodiment are a mixture of fuel gas and combustion air as gases (gases). Fuel gases include city gas, propane, hydrogen, etc. Combustion air includes air (fresh air), a mixture of air and exhaust gas, etc. The pipe 5 is connected to a supply source 50 of the measurement fluid M.

(Thermal Flow Meter 2)
As shown in Fig. 1, the thermal flow meter 2 measures the mass flow rate Qa [g/s] of a gas. The thermal flow meter 2 detects the mass flow rate Qa based on the change in heat quantity accompanying the movement of the measurement fluid M per unit time. The thermal flow meter 2 has a heater, a temperature sensor arranged upstream of the heater, and a temperature sensor arranged downstream of the heater. The thermal flow meter 2 includes a temperature difference measurement method that measures the flow rate based on the difference between the temperature of the fluid upstream of the heater and the temperature of the fluid downstream of the heater, and a power consumption measurement method that controls the heater so that the difference between the temperature of the fluid upstream of the heater and the temperature of the fluid downstream of the heater is constant.

The thermal flow meter 2 generates an error in the measurement result of the mass flow rate Qa when the composition of the measured fluid M changes. In the thermal flow meter 2, a specific coefficient according to the composition of the fluid is set in order to correctly measure the mass flow rate Qa. The amount of heat H [J] taken by the measurement unit of the thermal flow meter 2 is expressed by H∝Qa·ρ·c/λ using the mass flow rate Qa [g/s], density ρ [g/m ³ ], low pressure specific heat c [J/(g·K)], and thermal conductivity λ [W/(m·K)] of the thermal flow meter 2. In other words, H is proportional to Qa·ρ·c/λ. And while the mass flow rate Qa and the amount of heat H change appropriately, ρ·c/λ, which is determined by the density ρ, low pressure specific heat c, and thermal conductivity λ, has a specific value according to various mixtures of gases.

In this embodiment, the composition estimation device 1A makes the measured fluid M different from the reference fluid set in the thermal flow meter 2, intentionally creates an error in the mass flow rate Qa measured by the thermal flow meter 2, and uses this error to estimate the composition of the measured fluid M. This error occurs due to differences in the eigenvalue of ρ·c/λ, which is the coefficient of measurement by the thermal flow meter 2, depending on the composition of the measured fluid M.

(Volumetric flow meter 3)
As shown in Fig. 1, the volumetric flowmeter 3 measures the volumetric flow rate Qb [ ^m3 /s] of a gas. The volumetric flowmeter 3 detects the volumetric flow rate Qb of the measurement fluid M flowing through a pipe 5 based on the volume change per unit time of the measurement fluid M. The volumetric flowmeter 3 includes a positive displacement flowmeter that measures the flow rate using the rotation of two meshing elliptical gears, a vortex flowmeter that measures the flow rate using the frequency (flow velocity) of Karman vortices generated in the pipe 5, and a turbine flowmeter that measures the flow rate using the rotation of an impeller. The volumetric flowmeter 3 can appropriately measure the flow rate of the measurement fluid M regardless of differences in the composition of the measurement fluid M.

(Calculation device 4A)
1, the calculation device 4A is configured by a computer such as a sequencer (programmable computer). The calculation device 4A is configured to receive information on the mass flow rate Qa of the measurement fluid M from the thermal flow meter 2, and to receive information on the volumetric flow rate Qb of the measurement fluid M from the volumetric flow meter 3. The calculation device 4A is also configured to receive information on the characteristic coefficient a of the reference fluid set in the thermal flow meter 2.

The characteristic coefficient a of the reference fluid is represented by the characteristic value of ρ1·c1/λ1, which is the coefficient of measurement by the thermal flowmeter 2, using the density ρ1, low pressure specific heat c1, and thermal conductivity λ1 of the reference fluid. The characteristic coefficient b of the measurement fluid M is represented by the characteristic value of ρ2·c2/λ2, which is the coefficient of measurement by the thermal flowmeter 2, using the density ρ2, low pressure specific heat c2, and thermal conductivity λ2 of the measurement fluid M. The calculation device 4A utilizes the fact that the characteristic coefficient a, which is the characteristic value of ρ1·c1/λ1 of the reference fluid, differs from the characteristic coefficient b, which is the characteristic value of ρ2·c2/λ2 of the measurement fluid M, because the composition of the measurement fluid M differs from the composition of the reference fluid.

While the composition of the reference fluid is known, the composition of the measurement fluid M is unknown. In the calculation device 4A, characteristic coefficients, which are characteristic values of ρ·c/λ, are calculated for mixtures of various gases. The characteristic coefficients may be calculated by actually measuring the mass heat quantity Qa when gas flows through the pipe 5 in which the thermal flowmeter 2 is arranged, or by calculation using the known values of density ρ, low-pressure specific heat c, and thermal conductivity λ for the various gases. The calculation device 4A then estimates the composition of the measurement fluid M, which is the various gases, based on the characteristic coefficients.

If the composition of the measurement fluid M is different from that of the reference fluid, the value of the mass flow rate Qa measured by the thermal flowmeter 2 will be different from the value of the volumetric flow rate Qb measured by the volumetric flowmeter 3. Then, the calculation device 4A uses the characteristic coefficient a, mass flow rate Qa, and volumetric flow rate Qb of the reference fluid to determine the characteristic coefficient b of the measurement fluid M by b = a x Qa/Qb, making it possible to estimate the composition of the measurement fluid M based on the characteristic coefficient b of the measurement fluid M.

(Action and Effect)
In the composition estimation device 1A of this embodiment, the composition of the measurement fluid M is estimated using a characteristic coefficient a of the reference fluid, the mass flow rate Qa of the measurement fluid M, and the volumetric flow rate Qb of the measurement fluid M. The characteristic coefficient in the thermal flow meter 2 indicates a value that is specific to the composition of the fluid whose mass flow rate Qa is measured by the thermal flow meter 2, and is determined according to the composition of the fluid.

In the composition estimation device 1A of this embodiment, the characteristic coefficient b of the measured fluid M is calculated by b = a x Qa / Qb, utilizing the difference in the characteristic coefficient in the thermal flowmeter 2 according to the composition of the fluid, in other words, the product of the characteristic coefficient a of the reference fluid and the mass flow rate Qa of the measured fluid M is equivalent to the product of the characteristic coefficient b of the measured fluid M and the volumetric flow rate Qb of the measured fluid M, and the composition of the measured fluid M is estimated based on the characteristic coefficient b of the measured fluid M. With this configuration, when the composition of the measured fluid M whose flow rate is measured differs from the composition of the reference fluid, the composition of the measured fluid M can be estimated. Therefore, for example, when the measured fluid M is a fuel gas or a mixture of a known fuel gas and combustion air, the composition of the fuel gas or mixture can be estimated, and the mixture ratio of the fuel gas and the combustion air can be appropriately adjusted.

Therefore, the composition estimation device 1A of this embodiment can more appropriately generate a fluid with the required composition by estimating the composition of the measurement fluid M.

<Embodiment 2>
This embodiment shows a fluid mixing system 1B that obtains a mixed fluid M1 with a target mixing ratio by utilizing a pipe 5 in which a thermal flow meter 2 and a volumetric flow meter 3 are arranged in series. The fluid mixing system 1B of this embodiment generates a mixed fluid M1 in which a first fluid R1 and a second fluid R2 are mixed, and sets the mixing ratio of the first fluid R1 and the second fluid R2 in the mixed fluid M1 to the target mixing ratio.

As shown in FIG. 2, the fluid mixing system 1B includes a first pipe 5A, a second pipe 5B, a junction pipe 5C, a thermal flowmeter 2, a volumetric flowmeter 3, adjustment valves 51 and 52, and a control device 4B. The first pipe 5A is supplied with a first fluid R1. The second pipe 5B is supplied with a second fluid R2. The junction pipe 5C is a combination of the first pipe 5A and the second pipe 5B. The thermal flowmeter 2 is disposed in the junction pipe 5C and is set to measure the mass flow rate Qa of a reference fluid of a specific composition, and is configured to measure the mass flow rate Qa of the mixed fluid M1 (measurement fluid M) flowing through the junction pipe 5C.

The volumetric flowmeter 3 is arranged in series with the thermal flowmeter 2 in the junction pipe 5C, and is configured to measure the volumetric flow rate Qb of the mixed fluid M1 (measurement fluid M) flowing through the junction pipe 5C. The adjustment valves 51 and 52 are for adjusting the mixing ratio of the first fluid R1 and the second fluid R2. The control device 4B is configured to control the thermal flowmeter 2, the volumetric flowmeter 3, and the adjustment valves 51 and 52.

The control device 4B has an information acquisition unit 41, a relationship setting unit 42, and an opening adjustment unit 43. The information acquisition unit 41 is configured to acquire information on the composition of the first fluid R1, the composition of the second fluid R2, and the target mixing ratio. The relationship setting unit 42 is configured to set a target flow rate relationship based on the relationship between the mass flow rate Qa by the thermal flow meter 2 and the volume flow rate Qb by the volumetric flow meter 3 for the mixed fluid M1 having a target mixing ratio when the composition of the first fluid R1, the composition of the second fluid R2, and the target mixing ratio are determined. The relationship setting unit 42 may be configured to set a target characteristic coefficient b _r based on the relationship between the mass flow rate Qa and the volume flow rate Qb for the mixed fluid M1 having the target mixing ratio.

The opening adjustment unit 43 is configured to adjust the openings of the adjustment valves 51, 52 so that the measured flow rate relationship between the measured mass flow rate Qa measured by the thermal flowmeter 2 and the measured volumetric flow rate Qb measured by the volumetric flowmeter 3 coincides with the target flow rate relationship. Note that the opening adjustment unit 43 may adjust the openings of the adjustment valves 51, 52 so that a measured characteristic coefficient b _m based on the measured mass flow rate Qa, the measured volumetric flow rate Qb, and the characteristic coefficient a of the reference fluid coincides with a target characteristic coefficient b _r .

The fluid mixing system 1B of this embodiment will be described in detail below.
2, the fluid mixing system 1B supplies a mixture of fuel gas and combustion air as a mixed fluid M1 having a target mixture ratio to a combustion appliance 6 that burns the mixture of the fuel gas and the combustion air. The junction pipe 5C is connected to the combustion appliance 6 and is for supplying the mixture as the mixed fluid M1 to the combustion appliance 6. The first pipe 5A is connected to a fuel gas supply source 53A, and the second pipe 5B is connected to a combustion air supply source 53B such as a fan.

The adjustment valves 51, 52 include a first adjustment valve 51 arranged in the first pipe 5A and a second adjustment valve 52 arranged in the second pipe 5B. The thermal flow meter 2 and the volumetric flow meter 3 are the same as those shown in the first embodiment.

The thermal flow meter 2 of this embodiment is set to measure the mass flow rate Qa of a mixture of city gas and combustion air (fresh air) as a reference fluid of a specific composition. In other words, a specific coefficient is set for the mixture of city gas and combustion air in the thermal flow meter 2. In this embodiment, the first fluid R1 is a gas (gas) such as propane or hydrogen that has a different composition from city gas, and the second fluid R2 is combustion air. Note that both the first fluid R1 and the second fluid R2 may be fuel gas. For example, the first fluid R1 and the second fluid R2 may be city gas and hydrogen, or propane and hydrogen.

(Information Acquisition Unit 41)
As shown in FIG. 2, the information acquisition unit 41 of the control device 4B is configured to acquire information on the composition of propane as the first fluid R1, the composition of combustion air as the second fluid R2, and the target mixture ratio of the first fluid R1 and the second fluid R2. The target mixture ratio is set as an air ratio (excess air ratio) or an air-fuel ratio at which propane and combustion air can be stably combusted without misfire. The information acquisition unit 41 receives information on the type of the first fluid R1, the type of the second fluid R2, and the target mixture ratio through an input operation by the manager of the fluid mixing system 1B. In addition, the information acquisition unit 41 acquires a characteristic coefficient b1 of the first fluid R1 and a characteristic coefficient b2 of the second fluid R2. These characteristic coefficients b1 and b2 are used to determine whether to increase or decrease the opening degree of the first adjustment valve 51 or the second adjustment valve 52.

(Relationship Setting Unit 42)
As shown in Fig. 2, in the relationship setting unit 42 of the control device 4B, various types of the first fluid R1 and the second fluid R2 are set, and a target flow rate relationship between the mass flow rate Qa by the thermal flow meter 2 and the volume flow rate Qb by the volume flow meter 3 is set when the mixing ratio of the first fluid R1 and the second fluid R2 changes appropriately. In addition, in the relationship setting unit 42 of this embodiment, when the composition of the first fluid R1 and the composition of the second fluid R2 are fixed, a target flow rate relationship is set when the mixing ratio of the first fluid R1 and the second fluid R2 changes. When the composition of the mixed fluid M1 flowing in the junction pipe 5C changes, the volume flow rate Qb by the volume flow meter 3 does not change, while the mass flow rate Qa by the thermal flow meter 2 changes. Then, the ratio of the mass flow rate Qa by the thermal flow meter 2 to the volume flow rate Qb by the volume flow meter 3 changes according to the change in the composition of the mixed fluid M1.

As shown in FIG. 3, the target flow rate relationship is shown as the relationship between the volumetric flow rate Qb and the mass flow rate Qa, or the relationship between the characteristic coefficient a of the reference fluid and the characteristic coefficient b of the mixed fluid M1 (measured fluid M) when the ratio of the flow rate of the second fluid R2 to the flow rate of the first fluid R1 is changed when the composition of the first fluid R1, in other words the type of fuel gas, is determined. The relationship between the volumetric flow rate Qb and the mass flow rate Qa is a linear proportional relationship, and is also shown as the ratio between the characteristic coefficient a of the reference fluid and the characteristic coefficient b of the mixed fluid M1 (measured fluid M).

In this embodiment, as in the first embodiment, the relationship is utilized in which the product of the characteristic coefficient a of the reference fluid and the mass flow rate Qa is equivalent to the product of the characteristic coefficient b of the measurement fluid M and the volumetric flow rate Qb. This relationship is expressed as a·Qa=b·Qb, or in other words, Qb=(a/b)·Qa. The relationship between the volumetric flow rate Qb and the mass flow rate Qa is expressed by a straight line with a gradient of a/b.

The target flow rate relationship Qa _r /Qb _r between the mass flow rate Qa _r and the volumetric flow rate Qb _r for the mixed fluid M1 with the target mixing ratio is also expressed as the characteristic coefficient b _r of the mixed fluid M1 with the target mixing ratio based on the equation b _r =a·(Qa _r /Qb _r ) and the characteristic coefficient a of the reference fluid being known. This characteristic coefficient b _r is expressed by the characteristic value of b _r =ρ·c/λ using the density ρ, low pressure specific heat c, and thermal conductivity λ for the mixed fluid M1 with the target mixing ratio.

In this case, the measured flow rate relationship Qa/Qb between the measured mass flow rate Qa and the measured volumetric flow rate Qb is also expressed as a measured characteristic coefficient _bm of the measured mixed fluid M1 based on the equation _bm = a·(Qa/Qb) and the characteristic coefficient a of the reference fluid being known. This measured characteristic coefficient _bm is calculated using the characteristic coefficient a of the reference fluid, the measured mass flow rate Qa, and the measured volumetric flow rate Qb.

In Fig. 4, the thermal flowmeter 2 is set to a mixture of city gas and combustion air as the reference fluid, and the mixture of propane and combustion air is set to a mixed fluid M1. The thermal flowmeter 2 measures the mass flow rate Qa and the volumetric flow rate Qb is measured by the volumetric flowmeter 3. The relationship between the volumetric flow rate Qb and the mass flow rate Qa is shown as a first straight line L1. In Fig. 4, the relationship between the calculated volumetric flow rate Qb and the mass flow rate Qa, which is calculated from the ratio of the characteristic coefficient a of the reference fluid to the characteristic coefficient b of the mixed fluid M1 (measurement fluid M), is shown as a second straight line L2. There is a slight difference between the first straight line L1 and the second straight line L2. The target flow rate relationship and the target characteristic coefficient b _r may be determined by performing calibration between the actual measurement value and the theoretical value.

When setting the target flow rate relationship, a correction coefficient is calculated so that the second line L2, which is the theoretical value relationship, approaches the first line L1, which is the actual measurement value relationship. The target flow rate relationship is then the corrected target flow rate relationship obtained by correcting the second line L2 using the correction coefficient.

On the other hand, a correction coefficient may be calculated so that the first line L1, which is the relationship between the actual measured values, approaches the second line L2, which is the relationship between the theoretical values. In this case, the opening adjustment unit 43 adjusts the adjustment valves 51 and 52 so that the measured flow rate relationship after correction, in which the measured flow rate relationship between the measured mass flow rate Qa and the measured volumetric flow rate Qb is corrected by the correction coefficient, coincides with the target flow rate relationship.

(Opening degree adjustment unit 43)
As shown in the figure, the opening adjustment unit 43 is configured to adjust the opening of the first adjustment valve 51 to determine the supply amount of fuel gas as the first fluid R1 used for combustion, and then adjust the opening of the second adjustment valve 52 to determine the supply amount of combustion air as the second fluid R2 used for combustion. The opening adjustment unit 43 is configured to adjust the second adjustment valve 52 so that the measured flow rate relationship coincides with the target flow rate relationship, and to determine the air ratio of the mixture to be supplied to the combustion appliance 6 as the mixed fluid M1 of the target mixture ratio.

(Method of Controlling Fluid Mixing System 1B)
A control method for the fluid mixing system 1B will be described below with reference to the flowcharts of Figures 5 to 7. Each flowchart illustrates a case in which the relationship setting unit 42 uses a target characteristic coefficient b _r instead of the target flow rate relationship.

In the main routine of Fig. 5, the control device 4B acquires information on the type of fuel gas used for the first fluid R1, the use of combustion air for the second fluid R2, and the target mixture ratio of the first fluid R1 and the second fluid R2 by the information acquisition unit 41 (step S101 in Fig. 5). At this time, the characteristic coefficient b1 of the first fluid R1 and the characteristic coefficient b2 of the second fluid R2 are acquired. These characteristic coefficients b1 and b2 are calculated based on the database in the information acquisition unit 41 (step S102). In addition, the control device 4B calculates the target characteristic coefficient b _r of the mixture of fuel gas and combustion air (mixed fluid M1) having the target mixture ratio in the relationship setting unit 42 and sets it (step S103).

Next, the control device 4B adjusts the opening of the first adjustment valve 51 by the opening adjustment unit 43 to determine the flow rate of the fuel gas as the first fluid R1 flowing from the first pipe 5A to the junction pipe 5C (step S104). Next, the control device 4B adjusts the opening of the second adjustment valve 52 by the opening adjustment unit 43 to change the flow rate of the combustion air as the second fluid R2 flowing from the second pipe 5B to the junction pipe 5C (step S105).

Next, the control device 4B measures the mass flow rate Qa of the mixture by the thermal flowmeter 2, and measures the volumetric flow rate Qb of the mixture by the volumetric flowmeter 3 (step S106).Then, the control device 4B uses the characteristic coefficient a of the reference fluid, the measured measured mass flow rate Qa, and the measured measured volumetric flow rate Qb to determine the measured characteristic coefficient _bm of the measured mixture (step S107).

Next, the control device 4B judges whether the measured characteristic coefficient b _m of the mixture is within the allowable range of the target characteristic coefficient b _r of the mixture having the target mixture ratio (step S108). The allowable range of the target characteristic coefficient b _r is expressed as b _r ±α. If the measured characteristic coefficient b _m is within the allowable range of the target characteristic coefficient b _r , it is determined that the mixture ratio of the first fluid R1 and the second fluid R2 in the mixture is within the allowable range of the target mixture ratio, and the opening degree of the second adjustment valve 52 is fixed (step S109).

On the other hand, if the measured characteristic coefficient _bm is not within the allowable range of the target characteristic coefficient _br , the control device 4B determines whether the characteristic coefficient b1 of the first fluid R1 is greater than the characteristic coefficient b2 of the second fluid R2 (step S110). If the characteristic coefficient b1 of the first fluid R1 is greater than the characteristic coefficient b2 of the second fluid R2, the control device 4B executes a first adjustment routine (step S111).

In the first adjustment routine in FIG. 6, it is determined whether the measured characteristic coefficient b _m exceeds the allowable range of the target characteristic coefficient b _r (step S201 in FIG. 6). If the measured characteristic coefficient b _m exceeds the allowable range of the target characteristic coefficient b _r , the opening degree of the second adjustment valve 52 is increased by a predetermined amount (step S202). On the other hand, if the measured characteristic coefficient b _m does not exceed the allowable range of the target characteristic coefficient b _r , it is determined that the measured characteristic coefficient b _m is below the allowable range of the target characteristic coefficient b _r , and the opening degree of the second adjustment valve 52 is decreased by a predetermined amount (step S203).

For example, when the first fluid R1 is propane, the characteristic coefficient b1 calculated by ρ·c/λ using the density ρ, low pressure specific heat c, and thermal conductivity λ is 0.2042. The characteristic coefficient b2 calculated by ρ·c/λ for the combustion air (fresh air) as the second fluid R2 is 0.0538. When the characteristic coefficient b1 of the first fluid R1 is larger than the characteristic coefficient b2 of the second fluid R2 and the measured characteristic coefficient b _m is outside the allowable range of the target characteristic coefficient b _r , it is determined that the combustion air as the second fluid R2 is insufficient, and the opening degree of the second adjustment valve is increased by a predetermined amount. On the other hand, when the characteristic coefficient b1 of the first fluid R1 is larger than the characteristic coefficient b2 of the second fluid R2 and the measured characteristic coefficient b _m is not outside the allowable range of the target characteristic coefficient b _r , it is determined that the combustion air as the second fluid R2 is excessive, and the opening degree of the second adjustment valve is decreased by a predetermined amount.

Next, returning from the first adjustment routine to the main routine, the control device 4B again measures the mass flow rate Qa of the mixture by the thermal flowmeter 2 and again measures the volumetric flow rate Qb of the mixture by the volumetric flowmeter 3 (step S106 in FIG. 5).Then, the control device 4B again determines the measured characteristic coefficient bm of the measured mixture using the characteristic _coefficient a of the reference fluid, the measured measured mass flow rate Qa, and the measured measured volumetric flow rate Qb (step S107).

In step S110, if the characteristic coefficient b1 of the first fluid R1 is not greater (smaller) than the characteristic coefficient b2 of the second fluid R2, the control device 4B executes a second adjustment routine (step S112). In the second adjustment routine of FIG. 7, it is determined whether the measured characteristic coefficient b _m exceeds the allowable range of the target characteristic coefficient b _r (step S301 in FIG. 7). If the measured characteristic coefficient b _m exceeds the allowable range of the target characteristic coefficient b _r , the opening degree of the second adjustment valve 52 is decreased by a predetermined amount (step S302). On the other hand, if the measured characteristic coefficient b _m does not exceed the allowable range of the target characteristic coefficient b _r , it is determined that the measured characteristic coefficient b _m is less than the allowable range of the target characteristic coefficient b _r , and the opening degree of the second adjustment valve 52 is increased by a predetermined amount (step S303).

For example, when the first fluid R1 is hydrogen, the characteristic coefficient b1 is 0.0076. The characteristic coefficient b2 for the combustion air (fresh air) as the second fluid R2 is 0.0538. When the characteristic coefficient b1 of the first fluid R1 is smaller than the characteristic coefficient b2 of the second fluid R2 and the measured characteristic coefficient b _m is outside the allowable range of the target characteristic coefficient b _r , it is determined that the combustion air as the second fluid R2 is excessive, and the opening degree of the second adjustment valve is decreased by a predetermined amount. On the other hand, when the characteristic coefficient b1 of the first fluid R1 is smaller than the characteristic coefficient b2 of the second fluid R2 and the measured characteristic coefficient b _m is not outside the allowable range of the target characteristic coefficient b _r , it is determined that the combustion air as the second fluid R2 is insufficient, and the opening degree of the second adjustment valve is increased by a predetermined amount.

Next, returning from the second adjustment routine to the main routine, the control device 4B again measures the mass flow rate Qa of the mixture by the thermal flowmeter 2 and again measures the volumetric flow rate Qb of the mixture by the volumetric flowmeter 3 (step S106 in FIG. 5).Then, the control device 4B again determines the measured characteristic coefficient bm of the measured mixture using the characteristic _coefficient a of the reference fluid, the measured measured mass flow rate Qa, and the measured measured volumetric flow rate Qb (step S107).

Thereafter, steps S106 to S112 are repeated until the measured characteristic coefficient b _m falls within the allowable range of the target characteristic coefficient b _r . Then, when the mixture ratio of the air-fuel mixture falls within the allowable range of the target mixture ratio, the opening degree of the second adjustment valve 52 is fixed (step S109). In this way, the mixture ratio (air ratio) of the air-fuel mixture supplied to the combustion appliance 6 is set within the allowable range of the target mixture ratio.

In the control method of the fluid mixing system 1B of this embodiment, the first fluid R1 is a fuel gas and the second fluid R2 is combustion air. In addition, the first fluid R1 and the second fluid R2 may be various fuel gases having different compositions.

(Action and Effect)
In the fluid mixing system 1B of this embodiment, the control device 4B utilizes the difference in the characteristic coefficient in the thermal flow meter 2 depending on the fluid composition, and when information on the composition of the first fluid R1 and the composition of the second fluid R2 is acquired, adjusts the opening of the adjustment valves 51, 52 to bring the mixing ratio of the first fluid R1 and the second fluid R2 to a target mixing ratio.

Specifically, the control device 4B has an information acquisition unit 41, a relationship setting unit 42, and an opening adjustment unit 43. The information acquisition unit 41 acquires information on the composition of the first fluid R1, the composition of the second fluid R2, and the target mixing ratio, and the relationship setting unit 42 sets a target flow rate relationship or a target characteristic coefficient b r based on the relationship between the mass flow rate Qa by the thermal flow meter 2 and the volumetric flow rate Qb by the volumetric flow meter 3 for the mixed fluid M1 of the target mixing ratio when the composition of the first fluid R1, the composition of the second fluid R2, and the target mixing ratio are determined. The target flow rate relationship reflects the relationship between the characteristic coefficient a of the reference fluid in the thermal flow meter 2 and the target characteristic coefficient b _r of the mixed fluid M1 of the target mixing ratio in the thermal flow meter ₂ .

The opening degree adjustment unit 43 adjusts the opening degree of the adjustment valves 51, 52 so that the measured flow rate relationship between the measured mass flow rate Qa measured by the thermal flow meter 2 and the measured volume flow rate Qb measured by the volumetric flow meter 3 matches the target flow rate relationship, or so that the measured characteristic coefficient b _m based on the measured mass flow rate Qa, the measured volume flow rate Qb, and the characteristic coefficient a of the reference fluid matches the target characteristic coefficient b _r . When the measured flow rate relationship matches the target flow rate relationship within an allowable range, or when the measured characteristic coefficient b _m matches the target characteristic coefficient b _r within an allowable range, it can be determined that the mixed fluid M1 of the target composition has been generated. Therefore, when the first fluid R1 is the fuel gas and the second fluid R2 is the combustion air, the mixture ratio of the fuel gas and the combustion air can be set to the target mixture ratio.

Therefore, according to the fluid mixing system 1B of this embodiment, by generating a mixed fluid M1 with a target mixing ratio, it is possible to more appropriately generate a mixed fluid M1 with the required composition.

Other configurations, actions, and effects of the fluid mixing system 1B of this embodiment are the same as those of the composition estimation device 1A of embodiment 1. In this embodiment, components designated by the same reference numerals as those in embodiment 1 are the same as those in embodiment 1.

<Other embodiments>
The first fluid R1 and the second fluid R2 may be fuel gases having different compositions, and the mixed fluid M may be a mixture of a plurality of types of fuel gases. The fluid mixing system 1B may be configured in two stages and used to generate a mixed fluid having a target mixing ratio in which three types of fluids, the first fluid R1, the second fluid R2, and the third fluid, are mixed. In this case, the first stage fluid mixing system 1B generates a mixed fluid M in which the first fluid R1 and the second fluid R2 are mixed at a target mixing ratio, and the second stage fluid mixing system 1B generates a final mixed fluid in which the mixed fluid M and the third fluid are mixed at the target mixing ratio.

The present invention is not limited to the embodiments, and further different embodiments can be constructed without departing from the gist of the present invention. The present invention also includes various modified examples, modifications within the scope of equivalents, etc. Furthermore, the combinations and forms of the various components envisioned from the present invention are also included in the technical concept of the present invention.

REFERENCE SIGNS LIST 1A Composition estimation device 1B Fluid mixing system 2 Thermal flow meter 3 Volumetric flow meter 4A Calculation device 4B Control device 41 Information acquisition unit 42 Relationship setting unit 43 Opening adjustment unit 5 Piping 5A First pipe 5B Second pipe 5C Junction pipe 51 First adjustment valve 52 Second adjustment valve 6 Combustion equipment Qa Mass flow rate Qb Volumetric flow rate M Measured fluid R1 First fluid R2 Second fluid M1 Mixed fluid

Claims (3)

a thermal flow meter that is set to measure a mass flow rate of a reference fluid having a specific composition and that measures a mass flow rate of a measurement fluid different from the reference fluid flowing through a pipe;
a volumetric flowmeter that is arranged in series with the thermal flowmeter in the pipe and measures a volumetric flow rate of the measurement fluid flowing through the pipe;
a calculation device that calculates a characteristic coefficient b of the measurement fluid by the equation b = a × Qa/Qb, where a is a characteristic coefficient of the reference fluid set in the thermal flow meter, Qa is a mass flow rate of the measurement fluid measured by the thermal flow meter, and Qb is a volumetric flow rate of the measurement fluid measured by the volumetric flow meter, and estimates a composition of the measurement fluid based on the characteristic coefficient b of the measurement fluid. 1. A fluid mixing system that generates a mixed fluid by mixing a first fluid and a second fluid, and sets a mixing ratio of the first fluid to the second fluid in the mixed fluid to a target mixing ratio,
a first pipe to which the first fluid is supplied;
A second pipe to which the second fluid is supplied;
a junction pipe where the first pipe and the second pipe join together;
a thermal flow meter that is disposed in the junction pipe and configured to measure a mass flow rate of a reference fluid having a specific composition, and that measures a mass flow rate of the mixed fluid flowing through the junction pipe;
a volumetric flowmeter that is arranged in series with the thermal flowmeter in the junction pipe and measures a volumetric flow rate of the mixed fluid flowing through the junction pipe;
an adjusting valve for adjusting a mixing ratio of the first fluid and the second fluid;
a control device for controlling the thermal flow meter, the volumetric flow meter, and the regulating valve;
The control device includes:
an information acquiring unit that acquires information on a composition of the first fluid, a composition of the second fluid, and the target mixing ratio;
a relationship setting unit that sets a target flow rate relationship or a target characteristic coefficient based on a relationship between a mass flow rate measured by the thermal flow meter and a volumetric flow rate measured by the volumetric flow meter for the mixed fluid having the target mixing ratio when a composition of the first fluid, a composition of the second fluid, and the target mixing ratio are determined;
an opening adjustment unit that adjusts the opening of the regulating valve so that a measured flow rate relationship between a measured mass flow rate measured by the thermal flow meter and a measured volumetric flow rate measured by the volumetric flow meter matches the target flow rate relationship, or so that a measured characteristic coefficient based on the measured mass flow rate, the measured volumetric flow rate, and a characteristic coefficient of the reference fluid matches the target characteristic coefficient. 3. The fluid mixing system according to claim 2, wherein the relationship setting unit sets the target flow rate relationship or the target characteristic coefficient when a mixing ratio of the first fluid to the second fluid changes when a composition of the first fluid and a composition of the second fluid are determined.

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