JP2012082791A - Gas mixing apparatus used for electric power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas mixing apparatus used in an electric power generation system capable of properly controlling a mixing ratio of mixed fuel gas to fuel air even if auxiliary-fuel gas varies, and preventing misfire and an increase in NOx concentration.SOLUTION: A gas mixing controller 8 of the gas mixing apparatus 6 includes a reading device 81, a calculation device 82, and an adjustment device 83. The reading device 81 reads power generation output W by a watt meter 31, exhaust pressure P by a pressure gauge 72, and exhaust temperature T by a thermometer 73 at predetermined time interval. The calculation device 82 determines a target exhaust resistance Rr when the measured power generation output W is output from a relation map M, determines chimney effect Z using a structure of an exhaust pipe 22 and the measured exhaust temperature T, and determines the exhaust resistance R determined by adding the chimney effect Z to the exhaust pressure P. The adjusting device 83 adjusts an opening of a mixed gas control valve 71 so that the exhaust resistance R becomes the target exhaust resistance Rr.

Description

  The present invention relates to a gas mixing apparatus configured to supply a mixed fuel gas of a main fuel gas and a sub fuel gas to a power generation system.

  A power generation system configured to operate a gas engine using two types of fuel gas, which is a main fuel gas such as city gas and a secondary fuel gas such as biogas, and to operate a generator based on the output of the gas engine. In the generation system), various system methods are employed. For example, a method of adjusting the supply flow rate of an air-fuel mixture of main fuel gas and combustion air according to the calorific value of the auxiliary fuel gas, mixing two types of fuel gas, and burning, main fuel gas and auxiliary fuel gas And a method of performing combustion while controlling the air ratio.

  For example, Patent Document 1 discloses a gas engine configured to operate by supplying an air-fuel mixture of an auxiliary fuel gas such as biogas and combustion air and a main fuel gas such as city gas to the gas engine. Has been. In Patent Document 1, the oxygen concentration or nitrogen oxide (NOx) concentration in the exhaust gas of the gas engine is measured, and the valve opening for changing the supply flow rate of the main fuel gas to the gas engine based on this concentration is measured. By adjusting the degree, the air ratio is controlled and the gas engine is operated stably.

  Further, in the air-fuel ratio control device for a gas engine of Patent Document 2, one or more input signals (for example, exhaust gas pressure, temperature, or volume flow rate) that change according to a change in mass flow rate of exhaust gas are received and adjusted output. It is disclosed to control the air-fuel ratio in the intake air amount of the engine by generating a signal. According to this, NOx can be reduced in the gas engine in which the fuel component may greatly fluctuate.

JP 2005-30302 A Japanese Patent Application Laid-Open No. 2000-220481

  However, biogas generally contains a large amount of incombustible components such as carbon dioxide and nitrogen. In Patent Document 1, when the opening degree of the valve is adjusted so that the oxygen concentration in the exhaust gas becomes constant, the ratio of biogas in the fuel gas, the content of hydrogen, carbon dioxide, etc. in the biogas changes Further, the exhaust amount of the exhaust gas changes, and the combustion temperature in the gas engine changes.

Specifically, when the incombustible component in the mixed fuel gas increases due to the increase in the incombustible component in the auxiliary fuel gas, the exhaust amount of the exhaust gas increases and the oxygen concentration in the exhaust gas decreases. Therefore, when the oxygen concentration constant control is performed, the supply amount of combustion air is increased in order to increase the oxygen concentration in the exhaust gas (in Patent Document 1, the opening degree of the valve of the main fuel gas) This causes a decrease in combustion in the gas engine and a cause of misfire and the like.
On the other hand, when the incombustible component in the mixed fuel gas decreases due to the decrease in the incombustible component in the auxiliary fuel gas, the exhaust amount of the exhaust gas decreases and the oxygen concentration in the exhaust gas increases. Therefore, when the oxygen concentration constant control is performed, the supply amount of combustion air is decreased in order to reduce the oxygen concentration in the exhaust gas (in Patent Document 1, the opening degree of the valve of the main fuel gas) This increases the combustion temperature in the gas engine and increases the amount of NOx generated.

  Moreover, in patent document 2, when constructing | generating the cogeneration system which uses the exhaust gas from a gas engine for an exhaust heat recovery apparatus etc., it cannot employ | adopt as it is. That is, in this case, the exhaust gas temperature in the exhaust pipe is reduced in a case where a large amount of exhaust gas exhaust heat is recovered to the exhaust heat recovery device or the like, and a case where a small amount of exhaust gas exhaust heat is recovered to the exhaust heat recovery device or the like. The exhaust pressure may fluctuate greatly due to the difference. Therefore, in this case, it is impossible to suppress the amount of NOx generated and prevent misfire.

  The present invention has been made in view of such conventional problems, and there is a case where there is a change in the calorific value of the auxiliary fuel gas, and a case where a large amount of exhaust heat of the exhaust gas is recovered and a case where there is little recovery. However, it is an object of the present invention to provide a gas mixing device for use in a power generation system that can appropriately control the mixing ratio of the mixed fuel gas to the combustion air to prevent misfire and increase in NOx concentration.

The present invention is equipped with a power generation system configured to operate a generator by operating a gas engine, and a main fuel gas such as city gas and a sub fuel gas such as biogas are mixed in the power generation system. A gas mixing device configured to supply the mixed fuel gas,
The power generation system includes a power meter that measures the power generation output of the power generator, a mixture supply that creates a mixture by mixing combustion air sucked from an air pipe and the mixed fuel gas supplied to the fuel pipe A throttle valve for adjusting a flow rate of the air-fuel mixture supplied to the gas engine, and an opening of the throttle valve to adjust the opening of the throttle valve. And a main controller for controlling the output to a predetermined target power generation output,
The gas mixing device includes a mixed gas control valve for adjusting a flow rate of the mixed fuel gas supplied to the fuel pipe, a pressure gauge for measuring an exhaust pressure in the exhaust pipe of the gas engine, and an exhaust gas in the exhaust pipe. A thermometer that measures the temperature, and a gas mixing controller that controls the mixing ratio of the mixed fuel gas to the combustion air by adjusting the opening of the mixed gas control valve,
The gas mixing controller has an exhaust resistance obtained by adding a chimney effect Zm to a power generation output Wm measured by the power meter and an exhaust pressure Pm measured by the pressure gauge when the power generation output Wm is output. The relationship with Rm is preset as a relationship map,
The gas mixing controller includes a reading unit that reads a power generation output W measured by the wattmeter, an exhaust pressure P measured by the pressure gauge, and an exhaust temperature T measured by the thermometer;
The target exhaust resistance Rr when the measured power generation output W is output is obtained from the relationship map, the chimney effect Z is obtained using the exhaust pipe structure and the measured exhaust temperature T, and the exhaust pressure P is determined. Calculating means for obtaining the exhaust resistance R by adding the chimney effect Z;
The gas mixing device used in the power generation system further comprises an adjusting means for adjusting the opening of the mixed gas control valve so that the exhaust resistance R becomes the target exhaust resistance Rr. .

In the gas mixing device used in the power generation system of the present invention, when the calorific value of the auxiliary fuel gas varies, the mixing ratio of the mixed fuel gas and the combustion air according to the calorific value of the mixed fuel gas is set appropriately. Thus, a device for preventing misfire from occurring in the gas engine and preventing an increase in the NOx concentration in the exhaust gas of the gas engine is performed.
In the present invention, focusing on the fact that the power generation output of the generator and the exhaust amount of the exhaust gas have a predetermined correlation, the exhaust pipe of the exhaust pipe that is substantially proportional to the exhaust amount of the exhaust gas at the predetermined power generation output. The mixed gas control valve is controlled so that the exhaust resistance becomes constant, and the mixing ratio of the mixed fuel gas to the combustion air is changed. In particular, when recovering exhaust heat of exhaust gas exhausted from a gas engine, a case where a large amount of exhaust gas exhaust heat is recovered to an exhaust heat recovery device, etc., and an exhaust heat recovery device with less exhaust gas exhaust heat The temperature of the exhaust gas is greatly different from the case where the gas is recovered. The gas mixing controller takes into account that the actually measured exhaust pressure is lower due to the chimney effect that occurs when the exhaust gas rises in the exhaust pipe, and corrects this chimney effect to correct the mixed gas control valve. Take control.

The gas mixing apparatus of the present invention includes a mixed gas control valve, a pressure gauge, a thermometer, and a gas mixing controller, and is attached to an existing power generation system when using a mixed fuel gas of a main fuel gas and a sub fuel gas. Can be used.
Before operating the power generation system, supply fuel gas (main fuel gas etc.) with almost no fluctuation in calorific value to the power generation system. The mixing ratio of the mixed fuel gas and the combustion air at which the NOx concentration becomes the target NOx concentration is set. When setting each mixing ratio, the power generation output W, the exhaust pressure P, and the exhaust temperature T are actually measured and the chimney effect Z is calculated. The exhaust resistance R, which is the sum of the exhaust pressure P and the chimney effect Z, is calculated. Ask. Thus, a relationship map between the power generation output Wm and the exhaust resistance Rm is created, and this relationship map is set in the gas mixing controller.

The gas mixing controller of the gas mixing apparatus includes a reading unit, a calculating unit, and an adjusting unit, and the mixed gas control valve is controlled by these units.
The gas mixing controller reads the power generation output W, the exhaust pressure P, and the exhaust temperature T by the reading means. At this time, these values can be read a plurality of times at predetermined time intervals. The gas mixing controller obtains the target exhaust resistance Rr when the measured power generation output W is output from the relation map by the calculating means, and obtains the chimney effect Z using the structure of the exhaust pipe and the measured exhaust temperature T.

Then, the gas mixing controller adjusts the opening degree of the mixed gas control valve by the adjusting means so that the exhaust resistance R obtained by adding the chimney effect Z to the exhaust pressure P becomes the target exhaust resistance Rr.
Here, when the calorific value of the auxiliary fuel gas decreases, the power generation output W of the generator decreases, and the opening of the throttle valve increases to compensate for the decrease in the power generation output W. It is considered that the exhaust pressure P in the pipe is high. When the opening degree of the throttle valve increases, the supply amount of the mixed fuel gas to the gas engine increases and the supply amount of the combustion air also increases.

At this time, it is considered that the exhaust resistance R including the exhaust pressure P when the generator outputs a predetermined target power generation output is higher than the target exhaust resistance Rr. Therefore, the adjusting means of the gas mixing controller is adjusted so that the opening of the mixed gas control valve is increased, and the exhaust resistance R is brought close to the target exhaust resistance Rr.
As a result, the calorific value of the auxiliary fuel gas is reduced, the mixing ratio of the mixed fuel gas to the combustion air is low, and the combustion state of the gas engine in the gas lean state (the lean state of the mixed fuel gas) is returned to the optimum combustion state. be able to. Therefore, a gas lean state can be avoided and misfire can be prevented from occurring in the gas engine.

On the other hand, when the calorific value of the auxiliary fuel gas increases, the power generation output W of the generator increases, and the opening of the throttle valve decreases to suppress the increase in power generation output W. As a result, the exhaust pipe It is thought that the exhaust pressure P at the time is low. When the opening of the throttle valve is reduced, the supply amount of the mixed fuel gas to the gas engine is reduced and the supply amount of the combustion air is also reduced. At this time, it is considered that the exhaust resistance R including the exhaust pressure P when the generator outputs a predetermined target power generation output is lower than the target exhaust resistance Rr. Therefore, the adjustment means of the gas mixing controller is adjusted so that the opening of the mixed gas control valve is reduced, and the exhaust resistance R is brought close to the target exhaust resistance Rr.
As a result, the calorific value of the auxiliary fuel gas increases, the mixing ratio of the mixed fuel gas to the combustion air is high, and the combustion state of the gas engine in the gas rich state (the rich state of the mixed fuel gas) is returned to the optimal combustion state. be able to. Therefore, a gas rich state can be avoided and an increase in the NOx concentration in the exhaust gas of the gas engine can be prevented.

By the way, when the power generation system recovers a large amount of exhaust gas exhaust heat, the temperature of the exhaust gas is significantly lowered. On the other hand, when the exhaust heat is hardly recovered, the temperature of the exhaust gas is significantly increased. In these cases, a large difference occurs in the value of the chimney effect Z.
On the other hand, in the present invention, the exhaust resistance R is obtained in consideration of the chimney effect Z. Therefore, the exhaust resistance R can be calculated accurately, and the accuracy of controlling the mixed gas control valve by the adjusting means of the gas mixing controller can be improved. As a result, the mixing ratio of the mixed fuel gas and the combustion air can be appropriately controlled, and the occurrence of misfire and the NOx concentration both in the case where a large amount of exhaust gas exhaust heat is recovered and in the case where the exhaust gas hardly recovers. Can be prevented and stable combustion of the gas engine can be performed.

  Therefore, according to the gas mixing device of the present invention, combustion occurs in the case where there is a change in the calorific value of the auxiliary fuel gas, and in the case where a large amount of exhaust heat of the exhaust gas is recovered and in the case where the exhaust heat is hardly recovered. It is possible to prevent misfire and increase in NOx concentration by appropriately controlling the mixing ratio of the mixed fuel gas to the working air.

Explanatory drawing which shows the structure of the electric power generation system and gas mixing apparatus concerning an Example. The graph which shows these relationship by taking the power generation output W on a horizontal axis | shaft and taking the exhaust resistance R on a vertical axis | shaft concerning an Example. The graph which shows these relationship, taking the exhaust temperature T on a horizontal axis and taking the chimney effect Z of a chimney on a vertical axis | shaft concerning an Example. The flowchart which shows the method of controlling an electric power generation system concerning an Example. The graph which shows these relationship, taking the exhaust resistance R of an exhaust pipe on a horizontal axis | shaft concerning an Example, and taking NOx density | concentration in exhaust gas on a vertical axis | shaft. Explanatory drawing which shows the composition and volume change at the time of exhaust gas being made from mixed fuel gas about the case where mixed fuel gas consists only of methane concerning the simulation of a control method. Explanatory drawing which shows the composition and volume change at the time of exhaust gas being made from mixed fuel gas about the case where mixed fuel gas consists only of hydrogen concerning the simulation of a control method. Explanatory drawing which shows the composition and volume change at the time of exhaust gas being made from mixed fuel gas about the case where mixed fuel gas consists of methane and a carbon dioxide concerning the simulation of a control method. The graph which shows these relations, taking the mixed combustion rate of the auxiliary fuel gas with respect to the whole mixed fuel gas, and taking the NOx density | concentration and exhaust resistance R in exhaust gas on a vertical axis | shaft concerning an Example.

A preferred embodiment of the gas mixing apparatus used in the above-described power generation system of the present invention will be described.
In the present invention, the reading means is configured to sequentially read the power generation output W, the exhaust pressure P, and the exhaust temperature T at predetermined time intervals, and the adjusting means is configured such that the exhaust resistance R is When the target exhaust resistance Rr is larger than a value obtained by adding a predetermined dead zone pressure width X, the opening of the mixed gas control valve is increased by a predetermined amount, while the exhaust resistance R is increased from the target exhaust resistance Rr by a predetermined amount. When the dead zone pressure width X is smaller than the subtracted value, the opening degree of the mixed gas control valve is preferably configured to be reduced by a predetermined amount.
In this case, the calculation accuracy of the exhaust resistance R can be increased by using the average value Wav of the power generation output W, the average value Tav of the exhaust temperature T, and the average value Pav of the exhaust pressure P. The adjusting means can easily control the mixed gas control valve.

Preferably, the calculating means is configured to obtain the exhaust resistance R as a converted exhaust resistance obtained by converting the exhaust temperature T into a reference exhaust gas temperature Ts (Claim 3).
In this case, the exhaust resistance R is corrected and used as the converted exhaust resistance in consideration of changes in the density and volume of the exhaust gas depending on the exhaust temperature T. Thereby, the exhaust resistance R can be calculated more accurately in consideration of the fluctuation of the exhaust temperature T.

Further, the power generation system includes an exhaust heat recovery unit of the exhaust heat recovery device and a bypass valve that bypasses the exhaust heat recovery unit with respect to the exhaust pipe, and an opening degree of the bypass valve is adjusted. Thus, it can be used in a state where the amount of heat recovered from the exhaust heat recovery section is changed (claim 4).
Even when the exhaust heat recovery amount of the exhaust gas greatly fluctuates, by obtaining the exhaust resistance R in consideration of the chimney effect Z in the gas mixing device, stable combustion of the gas engine can be performed.

Hereinafter, embodiments of a gas mixing apparatus used in a power generation system of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the gas mixing device 6 used in the power generation system 1 of the present example is equipped with the power generation system 1 configured to operate the generator 3 by operating the gas engine 2, and to the power generation system 1. A mixed fuel gas F3 obtained by mixing a main fuel gas F1 such as city gas (13A) and a sub fuel gas F2 such as biogas is supplied.
The power generation system 1 mixes a wattmeter 31 that measures the power generation output W of the generator 3, the combustion air A sucked from the air pipe 41 and the mixed fuel gas F <b> 3 supplied to the fuel pipe 42. A mixture supply pipe 43 for generating G, a throttle valve 21 for adjusting the flow rate of the mixture G to be supplied to the gas engine 2 and adjusting the opening of the throttle valve 21. And a main controller 5 for controlling the power generation output W of the power generator 3 to a predetermined target power generation output.

The gas mixing device 6 includes a mixed gas control valve 71 for adjusting the flow rate of the mixed fuel gas F3 supplied to the fuel pipe 42, a pressure gauge 72 for measuring the exhaust pressure P in the exhaust pipe 22 of the gas engine 2, and an exhaust gas. A thermometer 73 that measures the exhaust gas temperature T in the pipe 22 and a gas mixing controller 8 that controls the mixing ratio of the mixed fuel gas F3 to the combustion air A by adjusting the opening of the mixed gas control valve 71 are provided. .
As shown in FIG. 2, the gas mixing controller 8 adds the chimney effect Zm to the power generation output Wm measured by the wattmeter 31 and the exhaust pressure Pm measured by the pressure gauge 72 when the power generation output Wm is output. The relationship with the exhaust resistance Rm determined in advance is set in advance as a relationship map M.

  As shown in FIG. 1, the gas mixing controller 8 includes the following reading means 81, calculation means 82, and adjustment means 83. The reading means 81 is configured to read the power generation output W measured by the wattmeter 31, the exhaust pressure P measured by the pressure gauge 72, and the exhaust temperature T measured by the thermometer 73 at a predetermined time interval (sampling interval) t1. Has been. The calculating means 82 obtains the target exhaust resistance Rr when outputting the measured power generation output W from the relationship map M, obtains the chimney effect Z using the structure of the exhaust pipe 22 and the measured exhaust temperature T, and the exhaust pressure. An exhaust resistance R obtained by adding the chimney effect Z to P is obtained. The adjusting means 83 is configured to adjust the opening degree of the mixed gas control valve 71 so that the exhaust resistance R becomes the target exhaust resistance Rr.

Hereinafter, the gas mixing device 6 of this example will be described in detail with reference to FIGS.
The gas mixing device 6 used in the power generation system 1 of the present example supplies the mixed fuel gas F3 of the main fuel gas F1 and the auxiliary fuel gas F2 to the power generation system 1, and the amount of heat generated by the auxiliary fuel gas F2 varies. If this occurs, the mixing ratio of the mixed fuel gas F3 and the combustion air A according to the calorific value of the mixed fuel gas F3 is made appropriate to prevent the misfire of the gas engine 2 and This is to prevent an increase in the NOx concentration in the exhaust gas H.

In this example, paying attention to the fact that the power generation output W of the generator 3 and the exhaust amount of the exhaust gas H have a predetermined correlation, the exhaust amount of the exhaust gas H is substantially equal to the predetermined power output W. The mixed gas control valve 71 is controlled so that the exhaust resistance R of the proportional exhaust pipe becomes constant, and the mixing ratio of the mixed fuel gas F3 to the combustion air A is changed. The exhaust resistance R is approximately proportional to ρ × Q ² where Q is the flow rate of the exhaust gas H and ρ is the density of the exhaust gas H. Therefore, if the exhaust resistance R is controlled to be constant, the flow rate of the exhaust gas H Can be made almost constant. As a result, the gas mixing device 6 of the present example can control the combustion temperature of the gas engine 2 that affects the NOx concentration in the exhaust gas H to be substantially constant, and the NOx concentration can be appropriately reduced to a predetermined target value or less. Can be kept within range. Further, since the exhaust resistance R is almost proportional to the square of the flow rate of the exhaust gas H, it can be said that the detection sensitivity is high.

  In particular, when recovering the exhaust heat of the exhaust gas H exhausted from the gas engine 2, a large amount of exhaust heat of the exhaust gas H is recovered to an exhaust heat recovery device or the like, and the exhaust heat of the exhaust gas H is reduced. The temperature of the exhaust gas H is greatly different from the case of recovery to an exhaust heat recovery device or the like. The gas mixing controller 8 considers that the actually measured exhaust pressure P is lower due to the chimney effect Z generated when the exhaust gas H rises in the exhaust pipe 22, and corrects the chimney effect Z by this correction. Then, the mixed gas control valve 71 is controlled.

The exhaust resistance R refers to the ease with which the exhaust gas H flows in the exhaust pipe 22.
The longer the exhaust pipe 22 is, the higher the exhaust pressure P by the pressure gauge 72 disposed at the outlet of the gas engine 2 (inlet of the exhaust pipe 22). That is, the longer the exhaust pipe 22, the higher the exhaust resistance R. On the other hand, when the height of the exhaust pipe 22 is large, the higher the exhaust temperature T of the exhaust gas H, the higher the exhaust gas H rises (due to the temperature difference between the exhaust gas H and the atmosphere at the outlet of the exhaust pipe 22). The chimney effect Z as a force generated from the difference in specific gravity acts greatly. Thereby, the exhaust pressure P measured by the pressure gauge 72 is lowered by the chimney effect Z.
Therefore, in the gas mixing controller 8, the exhaust resistance R is obtained by the calculating means 82 by the sum of the exhaust pressure P and the chimney effect Z.

The main fuel gas F1 in this example is a city gas (13A) having a constant calorific value, and the sub fuel gas F2 in this example is a biogas that may cause fluctuations in the calorific value.
As shown in FIG. 1, in the power generation system 1 of this example, the gas engine 2 is configured to have a plurality of cylinders, and the throttle valve 21 in the air-fuel mixture supply pipe 43 adjusts the opening degree of the gas engine 2. The flow rate of the air-fuel mixture G supplied to the engine 2 is adjusted. The generator 3 is configured to supply electric power to various loads, and can operate in cooperation with a commercial power source or the like.
Both the main controller 5 and the gas mixing controller 8 are configured using a computer. The main controller 5 can be configured to receive data on the power generation output W from the wattmeter 31 and adjust the opening of the throttle valve 21 to control the power generation output W of the generator 3 to a predetermined target power generation output. . Note that, instead of the data of the power generation output W, data on the rotational speed by a rotational speed meter provided in the generator 3 can also be used.

  An intake filter 411 for preventing foreign matter from entering the gas engine 2 is provided at the inlet of the air pipe 41 opened to the outside air. In addition, a mixer 44 that mixes the mixed fuel gas F3 and the combustion air A is provided at the junction of the fuel pipe 42 through which the mixed fuel gas F3 flows and the air pipe 41 through which the combustion air A flows. When the combustion air A flows through the venturi 441 using the suction action of the venturi 441, the mixer 44 has a negative pressure in the throat portion 442 of the venturi 441, and the combustion air A is generated by the suction force of the negative pressure. On the other hand, the mixed fuel gas F3 is drawn in to produce a mixture G of the two.

As shown in FIG. 1, the gas mixing device 6 includes a main fuel pipe 61 to which the main fuel gas F1 is supplied from its supply source, and a sub fuel gas F2 to which a sub fuel gas F2 is supplied from a tank of the sub fuel gas F2 such as biogas. The mixed fuel gas F <b> 3 is supplied to the fuel pipe 42 by joining the fuel pipe 62.
The mixed gas control valve 71 of this example is provided in the mixed fuel pipe 63 where the main fuel pipe 61 and the sub fuel pipe 62 merge, and receives a command from the gas mixing controller 8 to adjust the flow rate of the mixed fuel gas F3. It is configured to The gas mixing device 6 of this example includes an outside air thermometer 74 that measures the temperature of outside air. When the chimney effect Z is obtained when creating the relationship map M and during operation, correction is performed using the temperature of the outside air.

  As shown in FIG. 1, the gas mixing device 6 of the present example is a power generation system 1 that has already been installed as a unit in which the components 71, 72, 73, 74, 8, pipes 61, 62, 63, etc. are integrated. It is configured so that it can be easily equipped. Specifically, the gas mixing device 6 joins the main fuel pipe 61 through which the main fuel gas F1 passes, the sub fuel pipe 62 through which the sub fuel gas F2 passes, the sub fuel pipe 62, and the main fuel pipe 61. A mixed fuel pipe 63 through which the mixed fuel gas F3 passes, a mixed gas control valve 71 disposed in the mixed fuel pipe 63, a pressure gauge 72 for measuring the exhaust pressure P in the exhaust pipe 22, and an exhaust temperature in the exhaust pipe 22 A thermometer 73 for measuring T, an outside air thermometer 74 for measuring the temperature of the outside air, and the gas mixing controller 8 are configured as a unit. In addition, the pressure gauge 72, the thermometer 73, and the outside air thermometer 74 used for the gas mixing apparatus 6 can use what was equipped previously, when equipped in the power generation system 1 previously.

  The gas mixing device 6 is configured to connect the mixed fuel pipe 63 to the fuel pipe 42 in the power generation system 1 and read the power generation output W of the wattmeter 31 provided in the generator 3 into the gas mixing controller 8. Thus, the power generation system 1 that has already been installed can be easily equipped. Thereby, the modification in the power generation system 1 can be minimized.

FIG. 2 shows an example of the relationship map M set in the gas mixing controller 8 in advance. In the figure, the horizontal axis represents the power generation output W, and the vertical axis represents the exhaust resistance R, showing these relationships.
This relationship map M shows the power generation output W of the generator 3 and the exhaust pipe 22 when combustion is performed at a mixture ratio of a predetermined mixed fuel gas F3 and combustion air A that achieves a target predetermined NOx concentration. Is represented by the correlation with the exhaust resistance R.

In creating the relationship map M of the present example, when the main fuel gas F1 with little variation in the calorific value is supplied to the gas engine 2 of the power generation system 1 and the generator 3 is operated, for each predetermined power generation output W In addition, the mixing ratio of the mixed fuel gas F3 and the combustion air A is set while manually adjusting the NOx concentration in the exhaust gas H to be measured becomes the target NOx concentration. When setting each mixing ratio, the power generation output W, the exhaust pressure P, and the exhaust temperature T are actually measured and the chimney effect Z is calculated. The exhaust resistance R, which is the sum of the exhaust pressure P and the chimney effect Z, is calculated. Ask. Thus, the relationship map M between the power generation output Wm and the exhaust resistance Rm is created, and this relationship map M is set in the gas mixing controller 8.
When a predetermined power generation output W of the generator 3 is measured by the wattmeter 31, the target exhaust resistance Rr when the power generation output W is output can be read from the relationship map M.

The power generation system 1 of this example is often installed in a building or the like, and the exhaust pipe 22 for exhausting the exhaust gas H from the gas engine 2 is formed long upward.
The chimney effect Z by the structure of the exhaust pipe 22 can be obtained by the following equation, for example. That is, when the chimney height of the exhaust pipe 22 is H (m), the outside air temperature is TG (° C.), and the average inlet / outlet temperature of the exhaust gas H in the exhaust pipe 22 is TH (° C.), the chimney effect Z ( Pa) can be obtained from Z = H × 9.8 × {353 / (273 + TG) -342 / (273 + TH)}. The exhaust resistance R (Pa) can be obtained from the sum of the exhaust pressure P (Pa) in the exhaust pipe 22 and the chimney effect Z (R = P + Z).
Here, the inlet / outlet average temperature TH is an average value of the exhaust temperature at the inlet of the exhaust pipe 22 (exhaust temperature at the outlet of the gas engine 2) T measured by the thermometer 73 and the exhaust temperature at the outlet of the exhaust pipe 22. Indicated. The exhaust temperature at the outlet of the exhaust pipe 22 is estimated and determined based on the exhaust temperature at the inlet of the exhaust pipe 22. Note that the exhaust temperature at the outlet of the exhaust pipe 22 can also be measured.

  Further, in this example, the chimney effect Z is defined as the average value TGav of a plurality of measured values within the predetermined average value calculation time of the outside air temperature TG, the inlet / outlet average temperature TH, and the predetermined average of the inlet / outlet average temperature TH. The chimney effect Z is obtained by using the average value THav of a plurality of measurement values within the value calculation time t3, and the exhaust resistance R is calculated as the average value Pav of the plurality of measurement values within the predetermined average value calculation time of the exhaust pressure P. It is configured to obtain by addition.

Further, since the exhaust resistance R is obtained instead of measuring the exhaust amount of the exhaust gas H, the exhaust gas having a high temperature of 100 to 500 ° C. is considered in consideration of the influence of the difference in the exhaust temperature T on the exhaust resistance R. As the converted exhaust resistance Rs when converted to the reference exhaust gas temperature (for example, 120 ° C.) based on the H temperature, it can be used for calculation in the calculation means 82.
The converted exhaust resistance Rs can be obtained from Rs = R × (273 + Ts) / (273 + T) where the temperature of the reference exhaust gas is Ts (° C.).
If the exhaust pipe 22 is short, the resistance during exhaust becomes low, and a sufficient exhaust pressure P cannot be measured. Therefore, in this case, an exhaust resistance within the allowable range of the gas engine 2 can be applied by providing a throttle or the like in the exhaust pipe 22.

The calculation means 82 of this example is configured to obtain the target exhaust resistance Rr by checking the average value Wav of a plurality of measured values within a predetermined average value calculation time of the power generation output W against the relationship map M.
Further, when the exhaust resistance R is larger than the value obtained by adding the predetermined dead zone pressure width X to the target exhaust resistance Rr, the adjusting means 83 of this example increases the opening of the mixed gas control valve 71 by a predetermined amount, When the exhaust resistance R is smaller than a value obtained by subtracting a predetermined dead zone pressure width X from the target exhaust resistance Rr, the opening degree of the mixed gas control valve 71 is configured to be decreased by a predetermined amount.

  Further, as shown in FIG. 1, the power generation system 1 of this example is configured so that the exhaust heat of the exhaust gas H exhausted from the exhaust pipe 22 of the gas engine 2 can be recovered by the exhaust heat recovery device. The power generation system 1 is provided with an exhaust heat recovery unit 23 of the exhaust heat recovery device and a bypass valve 24 that bypasses the exhaust heat recovery unit 23 with respect to the exhaust pipe 22. The gas mixing device 6 is configured to be used in a state where the amount of heat recovered from the exhaust heat recovery unit 23 is changed by adjusting the opening degree of the bypass valve 24.

The exhaust heat recovery unit 23 and the bypass valve 24 of this example are disposed in the vicinity of the inlet of the exhaust pipe 22 of the gas engine 2, and the pressure gauge 72 and the thermometer 73 are disposed in the exhaust pipe 22. And on the downstream side of the bypass valve 24. The pressure gauge 72 or the thermometer 73 measures the exhaust pressure P or the exhaust temperature T near the inlet of the exhaust pipe 22.
The exhaust heat recovered by the exhaust heat recovery device can be used for various exhaust heat utilization devices. The exhaust heat recovery device can adjust the amount of exhaust heat recovered from the exhaust gas H in response to a request from the exhaust heat utilization device.

A sub fuel pressure gauge for measuring the pressure of the sub fuel gas F <b> 2 in the sub fuel pipe 62 can be disposed in the sub fuel pipe 62. The gas mixing controller 8 reads the pressure of the auxiliary fuel gas F2 measured by the auxiliary fuel pressure gauge, and stops the supply of the auxiliary fuel gas F2 when the pressure of the auxiliary fuel gas F2 is lower than a predetermined set pressure. Only the main fuel gas F <b> 1 can be supplied to the gas engine 2.
The main fuel pipe 61 can be provided with a manual valve 75 as necessary. In this case, a trial operation is performed in advance before the main operation of the power generation system 1, and the initial mixing ratio of the main fuel gas F 1 and the auxiliary fuel gas F 2 is adjusted by adjusting the opening degree of the manual valve 75. Can be determined.

  The manual valve 75 can be a control valve 75 that can be controlled by the gas mixing controller 8. In this case, the gas mixing controller 8 is configured to adjust the opening degree of the control valve 75 according to the opening degree of the mixed gas control valve 71 and to change the mixing ratio of the main fuel gas F1 and the auxiliary fuel gas F2. can do. For example, when the heat amount of the auxiliary fuel gas (biogas) F2 becomes too low and the exhaust gas resistance R is too high even when the mixed gas control valve 71 is fully open, the gas mixing controller 8 opens the opening of the control valve 75. Can be increased to increase the proportion of the main fuel gas (city gas) F1. As a result, a gas lean state that may cause misfire in the gas engine 2 can be avoided, the amount of heat of the mixed fuel gas F3 can be increased, and the exhaust resistance R can be set to the target exhaust resistance Rr. Therefore, the range of the calorific value of the auxiliary fuel gas (biogas) F2 that can be used for the power generation system 1 can be increased.

  FIG. 3 shows an example of the relationship between the exhaust temperature T on the horizontal axis and the chimney effect Z of the chimney (exhaust pipe 22) on the vertical axis. In the figure, the chimney effect increases as the exhaust temperature T (the temperature of the exhaust gas H) increases. When a large amount of exhaust heat from the exhaust gas H is recovered by the exhaust heat recovery device, the exhaust temperature T is in the vicinity of 120 to 200 ° C. on the left side, and the exhaust heat recovery device recovers the exhaust heat from the exhaust gas H. In the case of hardly collecting or not collecting B, the exhaust temperature T in the exhaust pipe 22 is in the vicinity of 400 to 500 ° C. on the right side.

Next, a method for controlling the power generation system 1 by attaching the gas mixing device 6 of this example to the power generation system 1 will be described with reference to the flowchart of FIG.
First, the reading means 81 of the gas mixing controller 8 reads the power generation output W by the wattmeter 31, the exhaust pressure P by the pressure gauge 72, the exhaust temperature T by the thermometer 73, every predetermined measurement time interval t 1 (for example, 1 second) The outside temperature TG is measured by the outside temperature thermometer 74 (step S1 in the figure), and this measurement is repeated until a predetermined control time t2 (for example, 10 seconds) is reached (S2).
Next, when the predetermined control time t2 has elapsed, the calculation means 82 of the gas mixing controller 8 determines the power generation output W, the exhaust pressure P, the exhaust gas at a predetermined average value calculation time t3 (for example, 1 minute) retroactive from the current measurement time point. Average values Wav, Pav, Tav, and TGav for the temperature T and the outside air temperature TG are obtained (S3).

Next, the calculating means 82 calculates the chimney effect Z (Pa), the chimney height of the exhaust pipe 22 as H (m), the average value THav (° C.) within the predetermined average value calculation time t3 of the inlet / outlet average temperature TH, Using the average value TGav (° C.) of the outside air temperature TG, it is obtained from Z = H × 9.8 × {353 / (273 + TGav) -342 / (273 + THav)} (S4).
Next, the calculation means 82 calculates the exhaust resistance R (Pa) from R = Pav + Z using the average value Pav (Pa) of the exhaust pressure P and the chimney effect Z (Pa) (S5).
Next, the calculation means 82 considers the influence of the difference in the exhaust gas temperature T on the exhaust gas resistance R, and uses the converted exhaust gas resistance Rs corrected for the exhaust gas resistance R as the reference exhaust gas H temperature as Ts (° C.). = R × (273 + Ts) / (273 + Tav) (S6).

Next, the calculating means 82 collates the average value Wav of the power generation output W with the relationship map M, and reads the target exhaust resistance Rr corresponding to this value Wav from the relationship map M (S7).
Next, the adjusting means 83 determines whether or not the converted exhaust resistance Rs is larger than a value obtained by adding a predetermined dead zone pressure width X to the target exhaust resistance Rr (S8). If Rs> Rr + X, The opening degree of the mixed gas control valve 71 is increased by a predetermined amount (S9).
On the other hand, when Rs> Rr + X is not satisfied, the adjusting unit 83 determines whether or not the converted exhaust resistance Rs is smaller than a value obtained by subtracting a predetermined dead zone pressure width X from the target exhaust resistance Rr (S10). If <Rr-X, the opening degree of the mixed gas control valve 71 is decreased by a predetermined amount (S11). The adjusting means 83 maintains the opening of the mixed gas control valve 71 when Rs <Rr−X is not satisfied.
Thus, the power generation system 1 can be stably operated by the gas mixing device 6.

By the way, the auxiliary fuel gas F2 is a biogas, and the biogas contains hydrogen, carbon monoxide, carbon dioxide and the like in addition to methane, and its calorific value is likely to change due to the change in its composition. .
When the calorific value of the auxiliary fuel gas F2 decreases, the power generation output W of the generator 3 decreases, and the opening of the throttle valve 21 increases to compensate for this decrease in power generation output W. As a result, The exhaust resistance R in the exhaust pipe 22 is considered to be high. When the opening degree of the throttle valve 21 increases, the supply amount of the mixed fuel gas F3 to the gas engine 2 increases and the supply amount of the combustion air A also increases.

At this time, it is considered that the exhaust resistance R including the exhaust pressure P when the generator 3 outputs a predetermined target power generation output is higher than the target exhaust resistance Rr. Therefore, the adjustment unit 83 of the gas mixing controller 8 adjusts the opening of the mixed gas control valve 71 so that the exhaust resistance R approaches the target exhaust resistance Rr.
Thereby, the calorific value of the auxiliary fuel gas F2 is reduced, the mixing ratio of the mixed fuel gas F3 to the combustion air A is low, and the combustion state of the gas engine 2 in the gas lean state (the lean state of the mixed fuel gas F3) is optimized. It is possible to return to a proper combustion state. Therefore, the gas lean state can be avoided and the misfire can be prevented from occurring in the gas engine 2.

On the other hand, when the calorific value of the auxiliary fuel gas F2 is increased, the power generation output W of the generator 3 is increased, and the opening of the throttle valve 21 is reduced in order to suppress the increase of the power generation output W, and as a result. It is considered that the exhaust resistance R in the exhaust pipe 22 is low. When the opening degree of the throttle valve 21 decreases, the supply amount of the mixed fuel gas F3 to the gas engine 2 decreases and the supply amount of the combustion air A also decreases. At this time, it is considered that the exhaust resistance R including the exhaust pressure P when the generator 3 outputs a predetermined target power generation output is lower than the target exhaust resistance Rr. Therefore, the adjustment unit 83 of the gas mixing controller 8 adjusts the opening of the mixed gas control valve 71 so that the exhaust resistance R approaches the target exhaust resistance Rr.
As a result, the calorific value of the auxiliary fuel gas F2 increases, the mixing ratio of the mixed fuel gas F3 to the combustion air A is high, and the combustion state of the gas engine 2 in the gas rich state (the rich state of the mixed fuel gas F3) is optimized. It is possible to return to a proper combustion state. Therefore, a gas rich state can be avoided and an increase in the NOx concentration in the exhaust gas H of the gas engine 2 can be prevented.

By the way, when the power generation system 1 recovers a large amount of exhaust heat of the exhaust gas H, the temperature of the exhaust gas H is significantly lowered (around 120 ° C.), whereas when the exhaust heat is not recovered, the exhaust gas H is exhausted. The temperature of the gas H is significantly increased (around 400 to 500 ° C.). In these cases, a large difference occurs in the value of the chimney effect Z.
On the other hand, in the gas mixing controller 8 of this example, the exhaust resistance R is obtained in consideration of the chimney effect Z. Therefore, the exhaust resistance R can be accurately calculated, and the accuracy of controlling the mixed gas control valve 71 by the adjusting means 83 of the gas mixing controller 8 can be improved. Thereby, it is possible to appropriately control the mixing ratio of the mixed fuel gas F3 and the combustion air A, and the occurrence of misfire and the occurrence of misfiring both in the case where a large amount of exhaust heat of the exhaust gas H is recovered and in the case where it is not recovered An increase in the NOx concentration can be prevented and stable combustion of the gas engine 2 can be performed.

FIG. 5 shows an example of the relationship between the horizontal axis representing the exhaust resistance R of the exhaust pipe 22 and the vertical axis representing the NOx concentration (ratio) in the exhaust gas H.
In this figure, when obtaining the relationship line when the chimney effect Z is taken into consideration, when the power generation output W in the generator 3 is operated so as to become a predetermined value, the mixed fuel gas F3 and the combustion air A While varying the mixing ratio, measuring the exhaust pressure P, the exhaust temperature T, etc. at each mixing ratio to obtain the exhaust resistance R in consideration of the chimney effect Z, the NOx in the exhaust gas H at each mixing ratio The concentration was measured. In the figure, the plotted points of circles, triangles, and diamonds indicate the NOx concentrations when the mixing ratios are different. A relation line C is drawn by regression analysis of each plot point.

  Further, when operating the generator 3 so that the power generation output W becomes a predetermined value, when the exhaust resistance R is obtained ignoring the chimney effect Z, the exhaust temperature T of the exhaust gas H is constant at 450 ° C. , The relationship between the exhaust resistance R and the NOx concentration in the exhaust gas H is an estimated line D. When the chimney effect Z is ignored, the amount of offset of the relationship line D to the left from the relationship line C increases as the exhaust temperature T increases.

The chimney effect Z of the exhaust pipe 22 increases as the exhaust temperature T of the exhaust gas H increases, and the former increases by 0.03 to 0.04 (kPa) when the exhaust temperature T is between 400 ° C. and 120 ° C. ( (See FIG. 3). Even with such a difference in the chimney effect Z, as can be seen from FIG. 5, the NOx concentration may change greatly depending on the setting of the target value of the NOx concentration.
When the chimney effect Z is ignored, the exhaust resistance decreases as the exhaust temperature T increases, and the gas mixing controller 8 controls the exhaust resistance to be the target exhaust resistance. Although the ratio is increased and the NOx concentration is lowered, there is a risk that the efficiency of the gas engine 2 is reduced and a problem of misfire occurs.
Therefore, by correcting the exhaust resistance R using the chimney effect Z, it is possible to suppress the reduction in efficiency of the gas engine 2 and the occurrence of misfire.

(Control method simulation)
In this simulation, a control method for supplying the gas mixture G to the gas engine 2 and operating the gas engine 2 with the pressure of the intake manifold (the pressure of the gas mixture G) provided on the downstream side of the throttle valve 21 being constant ( In the case of performing the intake manifold pressure constant control), the change in the volume and composition of the exhaust gas H with respect to the volume and composition of the mixture G will be described. Then, with respect to the change in volume and composition, the effect when the exhaust resistance constant control (exhaust gas amount constant control) shown in the first embodiment is performed, the problem when the intake manifold pressure constant control is performed, and the exhaust The problem in the case of performing the control method (constant oxygen concentration control) for operating the gas engine 2 with the oxygen concentration in the exhaust gas H in the pipe 22 constant will be verified.

  Here, in this simulation, it is considered that most of the main fuel gas F1 and the auxiliary fuel gas F2 are composed of methane, while the biogas as the auxiliary fuel gas F2 includes hydrogen, carbon dioxide, and the like. In the case where the mixed fuel gas F3 is made of only methane, the case of being made of only hydrogen, or the case of being made of methane and carbon dioxide, the change in volume and composition when complete combustion is performed is shown. Examine the validity.

Hereinafter, the composition and volume of the exhaust gas H after combustion when the total volume of the mixture G of the mixed fuel gas F3 and the combustion air A supplied to the gas engine 2 is 5 (Nm ³ ) ( Nm ³ ) will be described.
Here, the calorific value of hydrogen is 10.76 (MJ / Nm ³ ), and the calorific value of methane is 35.85 (MJ / Nm ³ ). The volume of 1 (Nm ³ ) methane was 0.3 (Nm ³ ) (35.85 × 0.3 = 10.76).

As shown in FIG. 6, when the mixed fuel gas F3 is composed only of methane, the volume ratio (Nm ³ ) of CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O is 1 for CH ₄ and ₂ for O 2. On the other hand, CO ₂ is 1 and H ₂ O is 2. In this case, the mixture G supplied to the gas engine 2 has an overall volume of 5 (Nm ³ ), methane is 0.3 (Nm ³ ), and combustion air A is the remaining 4.7 (Nm ³ ). When included, oxygen used for combustion of methane is 0.6 (Nm ³ ) out of 4.7 (Nm ³ ). When complete combustion of methane is performed, the entire volume remains 5 (Nm ³ ), oxygen 0.6 (Nm ³ ) in the combustion air A is consumed, and carbon dioxide is 0.3 (Nm ³ ), 0.6 (Nm ³ ) of water is generated, and the remainder remains 4.1 (Nm ³ ) as residual air (remaining gas other than oxygen consumed for combustion in the combustion air A). become.

As shown in FIG. 7, when the mixed fuel gas F3 is composed of only hydrogen, the volume ratio (Nm ³ ) of H ₂ + 0.5O ₂ → H ₂ O is 1 for H _{2 and} 0 for O _2. .5, H ₂ O is 1. In this case, the mixture G supplied to the gas engine 2 has a total volume of 5 (Nm ³ ), hydrogen 1 (Nm ³ ), and combustion air A 4 remaining (Nm ³ ). Oxygen used for combustion is 0.5 (Nm ³ ) out of 4 (Nm ³ ). When the complete combustion of hydrogen is performed, the entire volume is reduced to 4.5 (Nm ³ ), oxygen 0.5 (Nm ³ ) in the combustion air A is consumed, and water is 1 ( Nm ³ ) and 3.5 (Nm ³ ) remains as the remaining air.

As shown in FIG. 8, when the mixed fuel gas F3 is made of methane and carbon dioxide, the mixture G supplied to the gas engine 2 has an overall volume of 5 (Nm ³ ) and methane of 0.3 (Nm ^3). ), 0.3 (Nm ³ ) of carbon dioxide and the remaining 4.4 (Nm ³ ) of combustion air A, oxygen used for combustion of methane is 0. of 4.4 (Nm ³ ). 6 (Nm ³ ). When complete combustion of methane is performed, the entire volume remains 5 (Nm ³ ), oxygen 0.6 (Nm ³ ) in the combustion air A is consumed, and carbon dioxide is 0.3 (Nm ³ ) and 0.6 (Nm ³ ) of water are generated, the total amount of carbon dioxide is 0.6 (Nm ³ ), and the remainder remains as 3.8 (Nm ³ ) as residual air.

  When the mixed fuel gas F3 is made only of hydrogen and the combustion operation of the gas engine 2 is performed by the constant control of the intake manifold pressure, the temperature of the exhaust gas H increases as the volume decreases, and the NOx concentration in the exhaust gas H increases. Will increase. That is, according to the intake manifold pressure constant control, hydrogen is contained in the auxiliary fuel gas F2, and as the amount of hydrogen increases, the NOx concentration increases.

When the mixed fuel gas F3 consists only of methane (see FIG. 6), the oxygen amount before combustion is 4.7 × 0.21 (oxygen concentration in the air) = 0.987 (Nm ³ ), The amount of oxygen after combustion is 0.987−0.6 = 0.387 (Nm ³ ), whereas when the mixed fuel gas F3 is composed of methane and carbon dioxide (see FIG. 8), before combustion Of oxygen is 4.4 × 0.21 (oxygen concentration in the air) = 0.924 (Nm ³ ), and the amount of oxygen after combustion is 0.924−0.6 = 0.324 (Nm ³ ).

Consider a case in which carbon dioxide is included when the gas engine 2 is burned by oxygen concentration constant control.
When carbon dioxide is not included in the gas mixture G (when the mixed fuel gas F3 in FIG. 6 includes only methane), the oxygen concentration in the exhaust gas H is 0.387 / 5 × 100% = 7. 74%. Therefore, assuming that the target oxygen concentration in the exhaust gas H is 7%, the mixing ratio of the combustion air A is reduced so that the oxygen concentration becomes 7%, the gas becomes rich, and the NOx concentration increases. Will do.
On the other hand, when the gas mixture G contains carbon dioxide (when the mixed fuel gas F3 in FIG. 8 contains methane and carbon dioxide), the oxygen concentration in the exhaust gas H is 0.324 / 5 × 100% = 6.48%. Therefore, assuming that the target oxygen concentration in the exhaust gas H is 7%, the mixing ratio of the combustion air A is increased so that the oxygen concentration becomes 7%, gas leaning occurs, and misfire occurs. There is a fear.

As described above, in the case where the exhaust resistance constant control shown in the first embodiment is performed in contrast to the case where the intake manifold pressure constant control or the oxygen concentration constant control is performed, the possibility of the increase in the NOx concentration and the occurrence of misfire is eliminated. Can do. That is, in the case of performing exhaust resistance constant control, when hydrogen is contained in the mixed fuel gas F3, when the mixed fuel gas F3 having a certain amount of heat is burned regardless of the composition (constant power generation output) By controlling the exhaust amount of the exhaust gas H to be constant (when W is output), the combustion temperature in the gas engine 2 is stabilized and the increase in the NOx concentration is prevented. This state is represented in FIG. 7 as a state in which the volume of the air-fuel mixture G is increased so that the volume of the exhaust gas becomes 5 (Nm ³ ), as indicated by a two-dot chain line.

In addition, in the case where the exhaust resistance constant control is performed, when carbon dioxide is contained in the mixed fuel gas F3, the supply amount of the combustion air A is maintained, and the volume of the mixed fuel gas F3 and the exhaust gas H before and after combustion is maintained. Is controlled so that it hardly changes, and misfire is prevented.
Therefore, it can be seen that by performing the exhaust resistance constant control shown in the first embodiment, an increase in the NOx concentration can be prevented and the occurrence of misfire can be prevented.

In FIG. 9, the horizontal axis represents the mixed combustion rate (mixing rate) of the auxiliary fuel gas F2 with respect to the entire mixed fuel gas F3, and the vertical axis represents the NOx concentration and the exhaust resistance R in the exhaust gas H. The results of measuring the NOx concentration in the exhaust gas H and calculating the change in the exhaust resistance R for the case of performing the exhaust resistance constant control of Example 1 and the case of performing the conventional oxygen concentration constant control are shown. The composition of the auxiliary fuel gas F2 was 60% vol for methane and 40% vol for carbon dioxide.
When the oxygen concentration constant control is performed, the exhaust resistance R changes with the change in the mixed combustion rate of the auxiliary fuel gas F2. In particular, it can be seen that the NOx concentration in the exhaust gas H exhausted from the gas engine 2 increases when the co-firing rate of the auxiliary fuel gas F2 is low. This is probably because when the co-firing rate of the auxiliary fuel gas F2 is lowered, the exhaust amount of the exhaust gas H is decreased and the combustion temperature of the gas engine 2 is increased, so that the NOx concentration is increased.

  On the other hand, when the exhaust resistance constant control is performed, the exhaust resistance R becomes substantially constant with respect to the change in the mixed combustion rate of the auxiliary fuel gas F2. It can be seen that the exhaust resistance R is substantially constant, the exhaust amount of the exhaust gas H becomes substantially constant, and the NOx concentration in the exhaust gas H can be kept substantially constant.

DESCRIPTION OF SYMBOLS 1 Power generation system 2 Gas engine 21 Throttle valve 22 Exhaust pipe 3 Generator 31 Wattmeter 41 Air piping 42 Fuel piping 43 Mixture supply piping 5 Main controller 6 Gas mixing device 71 Mixed gas control valve 72 Pressure gauge 73 Thermometer 74 Outside temperature Total 8 Gas mixing controller 81 Reading means 82 Calculation means 83 Adjustment means F1 Main fuel gas F2 Sub fuel gas F3 Mixed fuel gas A Combustion air G Mixture H Exhaust gas M Relation map W Power generation output P Exhaust pressure T Exhaust temperature TG Outside air Temperature Z Chimney effect R Exhaust resistance Rr Target exhaust resistance

Claims (4)

A mixed fuel gas equipped with a power generation system configured to operate a generator by operating a gas engine and mixed with a main fuel gas such as city gas and a sub fuel gas such as biogas in the power generation system A gas mixing device configured to supply
The power generation system includes a power meter that measures the power generation output of the power generator, a mixture supply that creates a mixture by mixing combustion air sucked from an air pipe and the mixed fuel gas supplied to the fuel pipe A throttle valve for adjusting a flow rate of the air-fuel mixture supplied to the gas engine, and an opening of the throttle valve to adjust the opening of the throttle valve. And a main controller for controlling the output to a predetermined target power generation output,
The gas mixing device includes a mixed gas control valve for adjusting a flow rate of the mixed fuel gas supplied to the fuel pipe, a pressure gauge for measuring an exhaust pressure in the exhaust pipe of the gas engine, and an exhaust gas in the exhaust pipe. A thermometer that measures the temperature, and a gas mixing controller that controls the mixing ratio of the mixed fuel gas to the combustion air by adjusting the opening of the mixed gas control valve,
The gas mixing controller has an exhaust resistance obtained by adding a chimney effect Zm to a power generation output Wm measured by the power meter and an exhaust pressure Pm measured by the pressure gauge when the power generation output Wm is output. The relationship with Rm is preset as a relationship map,
The gas mixing controller includes a reading unit that reads a power generation output W measured by the wattmeter, an exhaust pressure P measured by the pressure gauge, and an exhaust temperature T measured by the thermometer;
The target exhaust resistance Rr when the measured power generation output W is output is obtained from the relationship map, the chimney effect Z is obtained using the exhaust pipe structure and the measured exhaust temperature T, and the exhaust pressure P is determined. Calculating means for obtaining the exhaust resistance R by adding the chimney effect Z;
A gas mixing apparatus for use in a power generation system, comprising: an adjusting means for adjusting an opening of the mixed gas control valve so that the exhaust resistance R becomes the target exhaust resistance Rr. In the gas mixing device used in the power generation system according to claim 1, the reading means is configured to sequentially read the power generation output W, the exhaust pressure P, and the exhaust temperature T at predetermined time intervals.
When the exhaust resistance R is greater than a value obtained by adding a predetermined dead zone pressure width X to the target exhaust resistance Rr, the adjusting means increases the opening of the mixed gas control valve by a predetermined amount, while the exhaust resistance R When the resistance R is smaller than a value obtained by subtracting a predetermined dead zone pressure width X from the target exhaust resistance Rr, the power generation system is configured to decrease the opening of the mixed gas control valve by a predetermined amount. Gas mixing device used for   3. The gas mixing device used in the power generation system according to claim 1, wherein the calculation unit is configured to obtain the exhaust resistance R as a converted exhaust resistance obtained by converting the exhaust temperature T to a reference exhaust gas temperature Ts. A gas mixing device for use in a power generation system. The gas mixing device used for the power generation system according to any one of claims 1 to 3, wherein the power generation system includes an exhaust heat recovery unit of the exhaust heat recovery device and the exhaust heat recovery unit with respect to the exhaust pipe. With a bypass valve to bypass,
A gas mixing device used in a power generation system, wherein the heat generation amount recovered from the exhaust heat recovery unit is changed by adjusting an opening degree of the bypass valve.

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