JP4830636B2 - Fuel control device for power plant - Google Patents

Description

  The present invention relates to a fuel control device for a power plant that enables stable control of fuel during low-load operation in a steam power plant or a gas turbine power plant.

  In power plants such as thermal power plants and gas turbine power plants, liquefied fuels such as LNG (liquefied natural gas) and LPG (liquefied petroleum gas) are temporarily stored in a tank, gasified while being taken out, and used as fuel. . In general, LNG is transferred to each power plant through a pipeline, and LPG is stored in a tank in each power plant and used. When such liquefied fuel is stored in a tank, BOG (boil-off gas: natural vaporized gas) is generated in the tank. Conventionally, as such BOG processing, there has been a method in which a reliquefaction apparatus is used to return to the output line in the tank or from the tank (see, for example, Patent Document 1).

  However, in such a configuration for re-liquefying BOG, a large-scale facility is required, for example, a configuration for re-liquefaction is required, so that BOG is also used as fuel.

FIG. 2 is a block diagram showing a conventional fuel control device for a power plant.
In the LNG supply path 1, LNG from the LNG tank 2 is vaporized by the heat exchanger 3 and supplied as LNG vaporized gas (NG). The LPG / BOG supply path 4 is supplied with a mixture of LPG vaporized gas (PG) obtained by vaporizing LPG from the LPG tank 5 by the heat exchanger 6 and BOG generated in the tank. Here, it is assumed that the LNG tank 2 and the heat exchanger 3 are arranged at a place different from the power plant, and the LNG vaporized gas is supplied to the LNG supply path 1 via a pipeline or the like. On the other hand, it is assumed that the LPG tank 5 and the heat exchanger 6 are provided in the power plant.

  The first pressure control valve 7 and the second pressure control valve 8 are provided in the LNG supply path 1 and the LPG / BOG supply path 4, respectively, and are pressure control valves that control the pressures of the respective flow paths. The LNG supply path 1 and the LPG / BOG supply path 4 are provided with flow rate measuring units (FX) 9 and 10, respectively. The flow rate measuring units 9 and 10 allow the LNG supply path 1 and the LPG / BOG supply path 4 to be provided. The flow rate is measured. The co-firing rate calculation unit 11 calculates the co-firing rate based on the measurement values of the flow rate measuring units 9 and 10 and outputs the result to the co-firing control unit 12. Further, the pressure value of the LPG / BOG supply path 4 is measured by a pressure measuring unit (PX) 13, and the LPG / BOG pressure setting unit 14 receives the given LPG / BOG set value. Based on the measured value of the pressure measuring unit 13, the opening setting value is output to the LPG / BOG opening setting unit 15.

  The mixed firing adjusting unit 12 opens the first pressure regulating valve 7 and the second pressure regulating valve 8 based on the given mixed firing rate set value and the mixed firing rate value calculated by the mixed firing rate calculating unit 11. It is a control unit that calculates degree command values and outputs the respective opening command values to the first opening setting unit 16 and the second opening setting unit 17. The pressure adjusting unit 18 is provided in the fuel supply path 19 on the downstream side of the junction of the LNG supply path 1 and the LPG / BOG supply path 4 with the pressure setting value corresponding to the mixed combustion rate calculated by the mixed combustion rate calculation unit 11. The controller is configured to output an opening command value to the first opening setting unit 16 and the second opening setting unit 17 based on the pressure measurement value from the pressure measurement unit (PX) 20.

  The flow rate command unit 21 outputs the opening command value to the fuel control valve 23 based on the given flow rate command value and the flow rate measurement value of the flow rate measurement unit (FX) 22 provided in the fuel supply path 19. Is. The fuel adjustment valve 23 is a control valve for controlling fuel supply to a burner (not shown) of the boiler unit 24.

Next, operation | movement of the fuel control apparatus of the power plant comprised in this way is demonstrated.
First, an opening degree command is given to the fuel control valve 23 based on the flow rate command value given to the flow rate command unit 21, and the flow rate of the fuel supply path 19 is controlled to a predetermined value. Further, the pressure value of the fuel supply path 19 is measured by the pressure measuring unit 20, and this measured value is input to the pressure adjusting unit 18.

  On the other hand, when a desired LPG / BOG set value is given to the LPG / BOG pressure setting unit 14, the LPG / BOG pressure setting unit 14 opens based on the difference from the pressure value of the LPG / BOG supply path 4 measured by the pressure measurement unit 13. The degree command value is output to the LPG / BOG opening setting unit 15. Further, the flow rate measurement units 9 and 10 measure the flow rates of the LNG supply path 1 and the LPG / BOG supply path 4, and the mixed firing rate calculation unit 11 calculates the mixed firing rate RG based on these values. The mixed firing rate RG is calculated by, for example, LNG flow rate / (LNG flow rate + LPG / BOG flow rate).

  Based on the difference value between the given mixed-burning rate set value and the actual mixed-burning rate RG obtained by the mixed-burning rate calculation unit 11, the mixed-burning adjustment unit 12 performs the first opening setting unit 16 and the second opening. Each opening command value is output to the setting unit 17. That is, when the ratio of LPG / BOG is large in the value of the actual mixture ratio RG with respect to the set value of the mixture ratio, the opening degree command value on the closing side with respect to the second pressure control valve 8, When the ratio of LPG / BOG is small, the opening degree of the opening side with respect to the second pressure regulation valve 8 is output. For the command value and the first pressure regulating valve 7, the opening command value on the closing side is output. The first pressure control valve 7 and the second pressure control valve 8 are controlled by such an opening command value.

  Further, the pressure adjusting unit 18 holds information on the pressure value corresponding to the mixed firing rate, which has a relationship as shown in FIG. 3, for example. FIG. 3 is an explanatory diagram showing the relationship between the mixed firing rate and the pressure value, where the horizontal axis represents the mixed firing rate (LNG / (LNG + LPG)), and the vertical axis represents the pressure value. That is, when the ratio of LNG is 100%, the pressure value is A, and when the ratio of LNG is 0%, the pressure value is B (A> B).

  In the pressure adjusting unit 18, a pressure value corresponding to the mixed combustion rate is obtained from the relationship between the mixed combustion rate and the pressure value as shown in FIG. 3, and this pressure value and the fuel supply path 19 measured by the pressure measuring unit 20 are obtained. An opening command value is output based on the difference from the pressure value. Then, the opening command value is given to the first opening setting unit 16 and the second opening setting unit 17, and the first pressure regulating valve 7 and the second pressure regulating valve 8 are controlled. That is, when the actual pressure value measured by the pressure measuring unit 20 is higher than the pressure value obtained from the mixed firing rate, the first pressure regulating valve 7 and the second pressure regulating valve 8 are closed. The opening degree command value on the side is output, and in the reverse case, the opening degree command value on the open side is output.

JP-A-10-252996

  Today, power plants are starting to perform transformer operation to cope with load fluctuations. And control from which the operation | movement in the further low load zone is attained from a viewpoint of the efficiency improvement at the time of performing such a transformation operation is calculated | required. However, when considering operation in such a low load zone in a power plant, there are the following problems in the fuel control.

  For example, in low load operation, less fuel is required than in rated operation. However, since the generation of BOG is independent of the load, the ratio of LPG / BOG in the fuel is relatively high during low load operation. Further, BOG is supplied spontaneously, and the supply amount thereof also changes depending on the temperature condition, the amount of LPG stored in the LPG tank 5, and the like. As the LPG / BOG ratio increases, the LPG / BOG variation greatly affects the mixed firing rate RG. Further, as shown in FIG. 3 described above, as the LPG / BOG ratio increases, pressure control is performed in a low pressure region.

  Due to such factors, the first pressure control valve 7 and the second pressure control valve 8 are controlled by the opening command value of the co-firing control unit 12, and the pressure control unit 18 also controls the first pressure control valve 7 and the second pressure control valve 8 based on the co-firing rate RG. In order to control the first pressure control valve 7 and the second pressure control valve 8, during the low load operation, the mixed combustion control unit 12 and the pressure control unit 18 depend on the pressure fluctuation in the fuel supply path 19 and the fluctuation of the mixed combustion rate RG. There was a problem that both controls would interfere with each other and diverge.

  Such a problem is that the flow rate of LNG is large during rated operation, so the relative ratio of LPG / BOG in the mixed firing rate RG is small, the fluctuation of LPG / BOG can be absorbed, and the pressure adjustment Since the control in the region where the pressure setting is high is also performed in the part 18, it hardly occurs. However, as described above, in the low load operation, the ratio of LPG / BOG is increased, so that stable flow rate control becomes difficult. And the factor that the stable control of such flow control is difficult had the problem that it will become a restriction | limiting in implement | achieving the low load operation | movement as a power plant.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain a fuel control device for a power plant that contributes to the realization of low-load operation of the power plant.

  A fuel control device for a power plant according to the present invention includes a first pressure control valve that controls a pressure of a first fuel that flows through a first fuel supply path, a first fuel that flows through a second fuel supply path, Includes a second pressure regulating valve for controlling the pressure of the second fuel / BOG, which is a gas in which a second type of second fuel and a boil-off gas of the second fuel are mixed, and a first fuel supply path. A mixed combustion rate for calculating a mixed combustion rate of the first fuel and the second fuel / BOG based on the flow rate of the first fuel flowing and the flow rate of the second fuel / BOG flowing in the second fuel supply path. The calculation unit, the first-order lag element that outputs the mixed combustion rate calculated by the mixed combustion rate calculation unit with a predetermined delay, the first fuel, and the second fuel / BOG have a predetermined mixed combustion rate. Thus, the first pressure regulating valve and the second pressure are based on the mixed combustion rate value output from the first-order lag element. A co-firing control unit that issues an opening degree command to the control valve, a value that gives a predetermined delay to the pressure value corresponding to the co-firing rate calculated by the co-firing rate calculation unit, a first fuel supply path, and a second And a pressure control unit that issues an opening degree command to the first pressure control valve and the second pressure control valve based on the pressure value of the mixed gas in the fuel supply path joined with the fuel supply path. .

  Further, in the fuel control device for a power plant according to the present invention, the pressure adjusting unit includes a value obtained by giving a predetermined delay to the pressure value corresponding to the mixed combustion rate calculated by the mixed combustion rate calculating unit, and the first fuel. There is a dead zone setting unit that does not change the output within a predetermined range of the difference value between the pressure value of the mixed gas in the fuel supply channel where the supply channel and the second fuel supply channel merge, and based on the output of the dead zone setting unit An opening degree command is sent out.

According to the fuel control device for a power plant of the present invention, stable fuel supply control can be performed even when a small amount of fuel is supplied. As a result, it is possible to contribute to the realization of low-load operation of the power plant. .
Further, according to the fuel control device for a power plant of the present invention, since the pressure adjustment unit includes the dead zone setting unit, it is possible to absorb fluctuations in the opening command value due to the control accuracy of the pressure adjustment valve, and Stable fuel supply control can be realized.

Embodiment 1 FIG.
1 is a configuration diagram showing a fuel control device for a power plant according to Embodiment 1 of the present invention.
In the figure, the configurations of the LNG supply path 1 to the second opening setting section 17 and the fuel supply path 19 to the boiler section 24 are the same as those shown in FIG. The description is omitted. The basic function of the pressure adjusting unit 18a is the same as that of the pressure adjusting unit 18 of FIG. 2, but is different from the configuration of FIG. 2 in that a change rate limiting unit 182 and a dead zone setting unit 184 are provided. That is, the pressure adjusting unit 18 a includes a pressure setting unit 181, a change rate limiting unit 182, a differentiator 183, a dead zone setting unit 184, and a PI control unit 185. The pressure setting unit 181 is a functional unit that calculates a pressure setting value based on the mixed firing rate RG calculated by the mixed firing rate calculating unit 11. The change rate limiting unit 182 is a functional unit that limits the change rate with respect to the pressure set value output from the pressure setting unit 181. The difference unit 183 is an arithmetic unit that calculates a difference value between the pressure set value output via the change rate limiting unit 182 and the pressure measurement value of the fuel supply path 19 measured by the pressure measurement unit 20. The dead zone setting unit 184 is a functional unit that sets a dead zone in which the output value does not change within a predetermined range with respect to the output value from the differentiator 183. The PI control unit 185 is a control unit that performs PI control based on the value output via the dead zone setting unit 184.

  Further, in the present embodiment, a first-order lag element 25 is provided in the output line from the mixed firing rate calculating unit 11 to the mixed firing adjusting unit 12. That is, it is configured such that a change in the value of the mixed combustion rate calculated by the mixed combustion rate calculating unit 11 is notified to the mixed combustion adjusting unit 12 via the first-order lag element 25.

  In the present embodiment, the LNG supply path 1 is the first fuel supply path, LNG is the first fuel, LPG / BOG supply path 4 is the second fuel supply path, and LPG / BOG is the second fuel / passage. It corresponds to BOG.

  In the fuel control device of the power plant configured as described above, when the mixed combustion rate changes due to a change in the supply amount of BOG in the LPG / BOG supply path 4, the mixed combustion rate calculation unit 11 calculates the mixed combustion rate RG indicating this. Output. The mixed firing rate RG is notified to the mixed firing rate calculation unit 11 via the first-order lag element 25. That is, the change in the mixed firing rate is input to the mixed firing adjusting unit 12 as a value with a predetermined delay amount. For this reason, the co-firing control unit 12 gradually changes the opening command values to the first pressure control valve 7 and the second pressure control valve 8 with a predetermined delay amount with respect to the change of the co-firing rate.

  Further, when there is a change in the co-firing rate output from the co-firing rate calculation unit 11, in the pressure adjustment unit 18 a, the rate-of-change limiting unit 182 determines a predetermined value for the change in the pressure setting value output from the pressure setting unit 181. Is output to the differentiator 183 with a delay amount of. Thereby, the difference value with the pressure measurement value of the fuel supply path 19 output from the differentiator 183 also changes gently, and as a result, the change of the opening degree command value output from the pressure adjustment part 18a also becomes gentle. Therefore, when the mixed combustion rate changes, the opening command value output from the pressure adjusting unit 18a also changes slowly, and the opening control of the first pressure adjusting valve 7 and the second pressure adjusting valve 8 is also performed slowly. It will be. Further, in the pressure adjusting unit 18a, the output to the PI control unit 185 does not occur when the output from the differentiator 183 is within the range of the dead zone value of the dead zone setting unit 184. The opening command value to the valve 7 and the second pressure regulating valve 8 is not output. That is, even if a slight fluctuation of the mixed combustion rate or the pressure value of the fuel supply path 19 occurs, the first pressure control valve 7 and the second pressure control valve 8 are controlled by the pressure control unit 18a. Absent.

  Even when the ratio of LPG / BOG in the fuel is relatively increased by the control of the first pressure regulating valve 7 and the second pressure regulating valve 8 by the mixed combustion regulating unit 12 and the pressure regulating unit 18a, As a result, stable fuel supply to the boiler unit 24 can be realized even when the fuel supply amount is low during low-load operation. .

  In the above embodiment, the case where the first fuel is LNG and the second fuel is LPG has been described. However, the present invention is not limited to these fuels, and the second fuel is the first fuel. Any type of fuel can be used as long as it is a different type of fuel and is configured to co-fire the gas mixed with the BOG with the first fuel.

It is a block diagram which shows the fuel control apparatus of the power plant by Embodiment 1 of this invention. It is a block diagram which shows the fuel control apparatus of the conventional power plant. It is explanatory drawing which shows the relationship between a co-firing rate and a pressure setting value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 LNG supply path 4 LPG / BOG supply path 7 1st pressure regulating valve 8 2nd pressure regulating valve 11 Mixed combustion rate calculating part 12 Mixed combustion regulating part 18a Pressure regulating part 19 Fuel supply path 25 Primary delay element 181 Pressure setting part 182 Change rate limiting unit 183 Differentiator 184 Dead band setting unit 185 PI control unit

Claims (2)

A first pressure control valve for controlling the pressure of the first fuel flowing through the first fuel supply path;
Controlling the pressure of the second fuel / BOG, which is a gas obtained by mixing a second type of fuel different from the first fuel flowing through the second fuel supply path and the boil-off gas of the second fuel. A second pressure regulating valve;
Based on the flow rate of the first fuel flowing through the first fuel supply channel and the flow rate of the second fuel / BOG flowing through the second fuel supply channel, the first fuel and the second fuel A co-firing rate calculation unit for calculating a co-firing rate with / BOG;
A first-order lag element that outputs a predetermined delay to the mixed-burning rate calculated by the mixed-burning rate calculation unit;
The first pressure control valve and the first pressure control valve and the second fuel / BOG based on the value of the mixed combustion rate output from the first-order lag element so that the second fuel / BOG has a predetermined mixed combustion rate. A co-firing control unit that issues an opening degree command to the second pressure control valve;
A fuel supply path in which a value obtained by giving a predetermined delay to the pressure value corresponding to the mixed combustion rate calculated by the mixed combustion rate calculation unit and the first fuel supply path and the second fuel supply path are merged A fuel control device for a power plant, comprising: a pressure control unit that issues an opening degree command to the first pressure control valve and the second pressure control valve on the basis of the pressure value of the mixed gas.   The pressure adjusting unit is a fuel in which a value obtained by giving a predetermined delay to the pressure value corresponding to the mixed combustion rate calculated by the mixed combustion rate calculating unit, and the first fuel supply channel and the second fuel supply channel merged. 2. A dead zone setting unit that does not change the output within a predetermined range of a difference value from the pressure value of the mixed gas in the supply path, and sends an opening degree command based on the output of the dead zone setting unit. The fuel control device for a power plant according to 1.

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