JP5464376B2 - Combustor, gas turbine, and fuel control method for combustor - Google Patents

Description

  The present invention relates to a combustor, a gas turbine, and a fuel control method for the combustor.

  For example, when using a low nitrogen-containing fuel with a low nitrogen content such as natural gas, kerosene, or light oil, most of the NOx generated in the combustor is thermal NOx generated by oxidizing nitrogen in the air. Since the generation of thermal NOx is highly temperature dependent, gas turbines that use low nitrogen-containing fuel generally attempt to reduce NOx by reducing the flame temperature. As a measure for reducing the flame temperature, premixed combustion is known in which fuel and air are mixed in advance and then burned. However, in the conventional premixed combustion system, when the temperature of the combustion air is high, or when the self-ignition temperature of the fuel is low, “backfire” in which the fuel burns inside the premixer can occur. Therefore, in order to reduce the NOx by appropriately controlling the flame temperature while preventing backfire, fuel is injected into a large number of small-diameter holes, and the fuel is injected into the combustion chamber as coaxial jets with air. Yes (see Patent Document 1).

  On the other hand, considering the ratio of fuel to air supplied to the combustor, that is, the fuel-air ratio, in the operation of a gas turbine, the fuel-air ratio is usually small when the gas turbine load is low, and the fuel-air ratio is high when the gas turbine load is high. Increase the ratio. In a combustor that aims at low NOx combustion including the combustors that form a large number of coaxial jets as described above, if the fuel-air ratio is reduced, the amount of NOx generated is suppressed, but the combustion stability is lowered. Conversely, increasing the fuel-air ratio tends to increase the amount of NOx generated. On the other hand, in order to realize low NOx stable combustion in a wide load range of the gas turbine, the local fuel-air ratio of the burning burner is kept constant by increasing the number of burners to be burned as the fuel-air ratio increases. It is known to keep within the range (see Patent Document 2 etc.).

JP 2003-148734 A JP 2005-30667 A

  In order to reduce NOx by increasing the number of burners to be burned as the fuel / air ratio increases, the local fuel / air ratio of the burning burner should not be close to the stoichiometric ratio. is necessary. On the other hand, in order to maintain stable combustion even when the fuel-air ratio is the smallest, it is necessary to set the fuel-air ratio of the burning burner group (pilot burners) to be sufficiently larger than the stable lower-limit local fuel-air ratio. .

  When the gas turbine load is increased by burning the pilot burner set in this way, the fuel-air ratio of the pilot burner is increased across the stoichiometric ratio. Therefore, the amount of NOx generated increases while the local fuel-air ratio is in the vicinity of the stoichiometric ratio in the process of increasing the gas turbine load.

  An object of the present invention is to provide a combustor, a gas turbine, and a fuel control method for the combustor that can reduce the amount of NOx generated when the local fuel-air ratio of the burner rises across the stoichiometric ratio. It is in.

  In order to achieve the above object, the present invention comprises a pilot burner composed of a plurality of burners connected to individual fuel systems, and when the fuel-air ratio of the pilot burner passes the stoichiometric ratio, By setting the fuel-air ratio to the fuel lean side and the fuel rich side with respect to the stoichiometric ratio, each burner passes through the vicinity of the stoichiometric ratio in a short time.

  According to the present invention, the amount of NOx generated when the local fuel-air ratio of the burner rises across the stoichiometric ratio can be reduced.

It is a schematic structure figure showing the side sectional view of the important section of the combustor concerning a 1st embodiment of the present invention combined with the schematic diagram of the whole gas turbine plant. It is a sectional side view which expands and represents the principal part of the burner with which the combustor which concerns on the 1st Embodiment of this invention was equipped. FIG. 3 is an enlarged view of a part III in FIG. 2. It is the figure which looked at the air hole plate with which the combustor which concerns on the 1st Embodiment of this invention was equipped was seen from the combustion chamber side. It is sectional drawing by the VV line in FIG. It is the graph which illustrated transition of the fuel flow rate of the pilot burner accompanying execution of the stoichiometric ratio avoidance procedure in the combustor concerning a 1st embodiment of the present invention. It is the graph which illustrated transition of the fuel air ratio of the pilot burner accompanying execution of the stoichiometric ratio avoidance procedure in the combustor concerning a 1st embodiment of the present invention. It is a flowchart showing the control procedure of the pilot burner including the stoichiometric ratio avoidance procedure by the control apparatus with which the combustor which concerns on the 1st Embodiment of this invention was equipped. It is the graph which illustrated transition of the fuel flow rate of the pilot burner accompanying execution of the stoichiometric ratio avoidance procedure in the combustor concerning a 2nd embodiment of the present invention. It is the graph which illustrated transition of the fuel air ratio of a pilot burner accompanying execution of the stoichiometric ratio avoidance procedure in the combustor concerning a 2nd embodiment of the present invention. It is a flowchart showing the control procedure of the pilot burner including the stoichiometric ratio avoidance procedure by the control apparatus with which the combustor which concerns on the 2nd Embodiment of this invention was equipped. It is a schematic block diagram of the pilot burner with which the combustor which concerns on the 3rd Embodiment of this invention was equipped. It is the schematic block diagram which represented the sectional side view of the principal part of the combustor which concerns on the 4th Embodiment of this invention with the schematic diagram of the whole gas turbine plant.

  Embodiments of the present invention will be described below with reference to the drawings.

(1) 1st Embodiment FIG. 1: is the schematic block diagram which represented the side sectional drawing of the principal part of the combustor which concerns on the 1st Embodiment of this invention with the schematic diagram of the whole gas turbine plant. .

  The gas turbine plant shown in FIG. 1 mainly mixes a compressor 1 that compresses air 101 to generate high-pressure compressed air 102, and compressed air 102 introduced from the compressor 1 and fuel 201-203. The combustor 2 generates the combustion gas 105 by burning and then the turbine 3 driven by the combustion gas 105 introduced from the combustor 2. The compressor 1 is coaxially connected to the turbine 3 and the generator 4. The compressor 1 is driven by the rotational power of the turbine 3, and the generator 4 connected to the compressor 1 is driven to generate power. It is like that.

  The combustor 2 includes a cylindrical combustor liner 10 that forms a combustion chamber 8 that combusts an air-fuel mixture of fuel 201-203 and combustion air 104, and a flow of combustion gas 105 at the inner periphery of the combustor liner 10. Burner 9 disposed at the end of the upstream side in the direction (hereinafter simply referred to as “upstream side” and the opposite side as “downstream side”) and the cylindrical combustion surrounding the outer periphery of the combustor liner 10 The outer cylinder 7 is provided. The burner 9 includes a plurality of fuel nozzles 31 for injecting fuel 201-203, a disk-like air hole plate 33 disposed at the upstream end of the combustor liner 10, and the upstream end of the combustor outer cylinder 7. And a disc-shaped combustor cover 8. The air hole plate 33 is provided with a plurality of air holes 32 that face the downstream side of each fuel nozzle 31 and through which the combustion air 104 from the compressor 1 passes.

  The compressed air 102 compressed by the compressor 1 flows into the combustor 2 and flows through an annular flow path between the combustor outer cylinder 7 and the combustor liner 10. A part of the compressed air 102 flows into the combustion chamber 8 through an air hole (not shown) provided in the outer peripheral portion of the combustor liner 10 as the cooling air 103 of the combustor liner 10. Further, the remaining air 102 flows into the combustion chamber 8 through the air holes 32 provided in the air hole plate 33 as combustion air 104.

  In the present embodiment, the supply system of the fuel 201-203 is provided with a shut-off valve 211-213 and a flow control valve 221-223, respectively, and the control device 300 uses the shut-off valve 211-213 and the flow control valve 221-223. By controlling this, the flow rate of the fuel 201-203 can be individually controlled. As shown in FIG. 2 later, the supply system of the fuel 201-203 in the present embodiment is a system branched from a discharge system 200 of a pump (not shown) connected to a fuel tank (not shown). The discharge system 200 is provided with a shutoff valve 210 (see FIG. 2 below). The shut-off valve 210 also operates according to a command from the control device 300.

  Each fuel nozzle 31 protrudes downstream from the combustor cover 8 and is connected to the fuel header 231-233. The fuel headers 231-233 distribute the fuel 201-203 to the fuel nozzles 31 and are provided within the thickness of the combustor cover 8. In the present embodiment, the fuel header 231 is a disk-shaped space provided at the center of the combustor shaft. The fuel header 232 is an annular space located on the outer peripheral side of the fuel header 231. The fuel header 233 is an annular space located further on the outer peripheral side than the fuel header 232.

  As described above, the plurality of fuel nozzles 31 are divided into three fuel systems: a first group connected to the fuel header 231, a second group connected to the fuel header 232, and a third group connected to the fuel header 233. The fuel can be controlled on a system-by-system basis by controlling the opening / closing of the shut-off valves 211-213 and the opening degree of the flow control valves 221-223.

  FIG. 2 is an enlarged side sectional view showing a main part of the burner 9 used in the combustor of the present embodiment, and FIG. 3 is an enlarged view of a portion III in FIG.

  A plurality of fuel nozzles 31 are attached to each fuel nozzle header 231-233 of the combustor cover 8, and a plurality of air holes 32 corresponding to each one of the fuel nozzles 31 are provided in the air hole plate 33. It has been. The air hole plate 33 is supported by the combustor cover 8 via a support 34.

  As shown in FIG. 3, the air holes 32 provided in the air plate 33 and the corresponding fuel nozzles 31 are provided so as to be substantially coaxial (the axial center lines substantially coincide), and the fuel in the center A coaxial jet of fuel and air in which the periphery of the jet 35 is covered with air 36 can be formed. According to this coaxial jet structure, since fuel and air are not mixed in the air holes 32, the self-ignition of the fuel is suppressed, and a highly reliable combustor is formed without melting the air hole plate 33. can do. Further, by forming a large number of such small coaxial jets, the interface between the fuel and air is increased and mixing is promoted, so that the amount of NOx generated can be suppressed. In this way, both NOx reduction and stable combustion can be achieved.

  4 is a view of the air hole plate 33 as viewed from the combustion chamber 8 side, and FIG. 5 is a cross-sectional view taken along line VV in FIG.

  In the present embodiment, the air holes 32 and the corresponding fuel nozzles 31 (see FIG. 2 and the like) are arranged in a plurality of rows (eight rows in this embodiment) concentrically. Further, the first column, the second column,..., The eighth column in this order from the inside. In this embodiment, the first column to the fourth column are the first burner 91, the fifth column is the second burner 92, the sixth column. The eighth column is divided from the third burner 93. In the present embodiment, the burners 91 and 92 constitute a pilot burner for maintaining the combustion stability of the combustor 2 when the gas turbine is started and when the load is low, and the pilot burner includes a plurality of burners (this embodiment In this embodiment, two burners are provided. The burner 93 constitutes a main burner for achieving the low NOx performance of the combustor 2 from the low load to the high load of the gas turbine.

  The fuel nozzles 31 of the burners 91-93 are connected to headers 231-233 (see FIG. 2). By controlling the shut-off valves 211-213 and the flow rate control valves 221-223 by the control device 300 by such a divided structure of the fuel nozzle 31, the flow rate of the fuel 201-203 of the burner 91-93 is individually set for each burner. Can be controlled. Further, the air holes 32 of the first burner 91 are inclined in the circumferential direction as shown in FIGS. Specifically, the first row of air holes 32 are tangential to the pitch circle of the first row in the direction of flow of the combustion gas 105 of the combustor liner 10 (from the back to the front in the direction orthogonal to the plane of FIG. 4). Is inclined by a set angle α on one side (counterclockwise in FIG. 4). The same applies to the second to fourth columns. Thereby, a swirl component is imparted to the entire air flow ejected from the first burner 91, and the flame is stabilized by the circulating flow generated thereby. The flames of the outer burners 92 and 93 are stabilized by the combustion heat generated by the first burner 91.

  Here, the control device 300 stores a storage unit 301 (see FIG. 2) that stores a high NOx local fuel / air ratio range (local fuel / air ratio range to be avoided) that includes a stoichiometric ratio, and fuels 201 to 203. And an arithmetic unit 302 that outputs a command to the shutoff valves 210 and 211 to 213 and the flow rate control valves 221 to 223 of the fuel system. The storage unit 301 also stores a fuel supply control program for the pilot burners (burners 91 and 92). The calculation unit 301 reads this program, and when increasing the fuel / air ratio of the pilot burner across the stoichiometric ratio from the start of the gas turbine to the low load, the local fuel / air ratio of the burners 91 and 92 is calculated. The local fuel-air ratio region (hereinafter referred to as the low-NOx local fuel-air ratio region on the fuel lean side) lower than the high NOx local fuel-air ratio range and the local fuel-air ratio region (hereinafter referred to as “high NOx local fuel-air ratio range”). , A stoichiometric ratio avoidance procedure is performed that distributes to the low-NOx local fuel-air ratio region on the fuel-rich side.

  Next, the operation of the combustor according to the present embodiment will be described.

  FIG. 6 is a graph illustrating the transition of the fuel flow rate of the pilot burner accompanying the execution of the stoichiometric ratio avoidance procedure, and FIG. 7 is a graph illustrating the transition of the fuel-air ratio of the pilot burner accompanying the execution of the stoichiometric ratio avoidance procedure. It is.

  6 and 7 is the fuel-air ratio of the pilot burner, and the flow rate (mass flow rate) of the fuel supplied to the pilot burner, that is, the fuels 201 and 202 supplied to the fuel nozzles 31 of the burners 91 and 92, respectively. , Unit kg / s) is divided by the sum of the flow rate (mass flow rate, unit kg / s) of the combustion air 104 supplied to the pilot burner. Hereinafter, the flow rate of the combustion air 104 supplied to the air holes 32 of the first burner 91 is A1, and the flow rate of the combustion air 104 supplied to the air holes 32 of the second burner 92 is A2.

  The vertical axis of the graph in FIG. 6 indicates the sum of fuel flow rates supplied to the fuel nozzles 31 of the burners 91 and 92 and the ratio thereof. In the present embodiment, the combustion air amount (A1 + A2) of the pilot burner is set to 1 kg / s in order to simplify the numerical value. Therefore, the fuel flow rate on the vertical axis with respect to the pilot fuel-air ratio on the horizontal axis is indicated by a thick line (straight line) in FIG. Transition as shown. The breakdown of the fuel flow rates F1 and F2 supplied to the burners 91 and 92 changes as shown by thin lines (folded lines) in FIG. On the other hand, the vertical axis of the graph in FIG. 7 represents the local fuel-air ratio of each of the burners 91 and 92 when the fuel flow rate changes as shown in FIG.

  In this embodiment, when the combustion air (A1 + A2) of the pilot burner is 100%, A1 = 40% and A2 = 60%. Also, assuming natural gas mainly composed of methane as fuel, the fuel / air ratio, which is the stoichiometric ratio, is 0.058, and the high NOx local fuel / air ratio range (hatching region) is increased in order to increase NOx emissions. 0.04-0.07. This high NOx local fuel-air ratio range is exemplified as 0.04-0.07 in the present embodiment, but is a set range including the stoichiometric ratio, and how much is above and below the stoichiometric ratio. The range depends on the operating conditions.

  FIG. 8 is a flowchart showing a pilot burner control procedure including a stoichiometric ratio avoidance procedure by the controller 300. Hereinafter, the stoichiometric ratio avoidance procedure will be described with reference to FIG. 8 together with FIGS.

(1) Steps 101 and 102
In steps 101 and 102, the local fuel-air ratio of the burners 91 and 92 is increased in the low NOx local fuel-air ratio region on the lean side of the fuel that is lower than the high NOx local fuel-air ratio range.

  Specifically, the arithmetic unit 302 of the control device 300 starts the control of FIG. 8 with the start of the gas turbine, and calculates the fuel flow rate command value S1 of the first burner 91 and the fuel flow rate command value S2 of the second burner 92. Both are increased (step 101). The procedure of this step 101 is such that the fuel-air ratio of the pilot burner is set to a first target value a (0.034 (both burners 91 and 92 in this embodiment) set to be less than the lower limit 0.04 of the local fuel-air ratio range. 0.034) is executed in a range up to reaching. The fuel distribution of the burners 91 and 92 during this period is a value (here 4: 6) that matches the distribution of the combustion air flow rates A1 and A2 (see FIG. 6), and the local fuel-air ratio (F1 / A1) of the first burner 91. ) And the local fuel-air ratio (F2 / A2) of the second burner 92 are equal (see FIG. 7). At this stage, as shown in FIG. 7, since the local fuel-air ratio is smaller than the high NOx local fuel-air ratio range, low NOx can be achieved.

  During this time, the calculation unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S11 and S21, respectively (step 102). If the target values S11 and S21 have not been reached, the burner 91 is determined. , 92 is determined to have not yet reached the first target value a, and the procedure of step 101 is continued.

(2) Step 103-108
In subsequent steps 103-108, the fuel with the local fuel-air ratio of the burner 91 higher than the high NOx local fuel-air ratio range while the local fuel-air ratio of the burner 92 is left in the low NOx local fuel-air ratio region on the fuel lean side. Increase to the low NOx local fuel-air ratio region on the rich side. Specifically, it is as follows.

(2-1) Steps 103 and 104
When the fuel flow rate command values S1 and S2 reach S11 and S21, respectively, the calculation unit 302 determines that the fuel-air ratio of the burners 91 and 92 has reached the first target value a in the previous step 102, and the process proceeds to step 103. The procedure is shifted to decrease the fuel flow rate command value S2, increase the increase rate of the fuel flow rate command value S1, increase the ratio of the fuel flow rate F1 of the first burner 91, and decrease the ratio of the fuel flow rate F2 of the second burner 92. (See FIG. 6). The procedure of this step 103 is that the fuel / air ratio of the burners 91 and 92 is set to the second target value b (in this embodiment, 0.036 (the breakdown is 0.075 for the burner 91 and 0.01 for the burner 92). It is executed in the range until it reaches (Yes). In order to linearly increase the fuel-air ratio of the pilot burner, the local fuel-air ratio (F2 / A2) of the second burner 92 is thus set to a predetermined value (here, 0.01) within the low NOx region on the fuel lean side. ) To the value of the low NOx local fuel-air ratio region on the fuel rich side exceeding the high NOx local fuel-air ratio range (here 0.075), the local fuel-air ratio (F1 / A1) is raised at once (see FIG. 7), and the fuel-air ratio of the pilot burner is increased (two-dotted line in FIG. 7, see FIG. 6).

  During this time, the calculation unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S12 and S22, respectively (step 104). If the target values S12 and S22 have not been reached, the burner 91 is determined. , 92 are determined to have not yet reached the second target value b, and the procedure of step 103 is continued.

(2-2) Steps 105 and 106
When the fuel flow command values S1 and S2 reach S12 and S22, respectively, the calculation unit 302 determines in step 104 that the fuel-air ratio of the burners 91 and 92 has reached the second target value b, and proceeds to step 105. Then, the fuel flow rate command value S2 is increased while keeping the fuel flow rate command value S1 constant, and the ratio of the fuel flow rate F2 of the second burner 92 is increased (see FIG. 6). The procedure of this step 105 is that the fuel / air ratio of the burners 91 and 92 is set to the third target value c (in this embodiment, 0.05 (the breakdown is 0.075 for the burner 91 and 0.03 for the burner 92). It is executed in the range until it reaches (Yes). That is, only the local fuel-air ratio (F2 / A2) of the second burner 92 is within a range that does not deviate from the low NOx region on the lean side of the fuel (here, the local fuel-air ratio (F1 / A1) of the first burner 91 is constant). Then, it is increased (to 0.03) (see FIG. 7), and the fuel-air ratio of the pilot burner is increased to a predetermined value (here, 0.05) (two-dotted line in FIG. 7, see FIG. 6).

  During this time, the calculation unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S13 and S23, respectively (step 106). If the target values S13 and S23 have not been reached, the burner is determined. It is determined that the fuel-air ratio of 91 and 92 has not yet reached the third target value c, and the procedure of step 105 is continued.

(2-3) Steps 107 and 108
When the fuel flow command values S1 and S2 reach S13 and S23, respectively, the calculation unit 302 determines in step 106 that the fuel-air ratio of the burners 91 and 92 has reached the third target value c, and proceeds to step 107. The fuel flow rate command value S1 is increased while keeping the fuel flow rate command value S2 constant, and the ratio of the fuel flow rate F1 of the first burner 91 is increased (see FIG. 6). The procedure of step 107 is the fourth target value d (the burner 91 is 0.095 and the burner 92 is 0.03 in this embodiment) in which the fuel-air ratio of the burners 91 and 92 is set. It is executed in the range until it reaches (Yes). That is, when the third target value c is reached and there is no room for raising the local fuel-air ratio (F2 / A2) of the second burner 92 in the low NOx region on the lean side of the fuel, the local fuel-air of the second burner 92 is reached. Only the local fuel-air ratio (F1 / A1) of the first burner 91 is increased in the low-NOx region on the fuel rich side (up to 0.095 here) while keeping the ratio (F2 / A2) constant (see FIG. 7). Then, the fuel-air ratio of the pilot burner is increased (see the two-dot chain line in FIG. 7 and FIG. 6).

  During this time, the arithmetic unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S14 and S24, respectively (step 108). If the target values S14 and S24 have not been reached, the burner 91 is determined. , 92 is determined to have not yet reached the fourth target value d, and the procedure of step 107 is continued.

(3) Steps 109-112
In subsequent steps 109-112, the local fuel-air ratio of the burner 92 is increased from the low NOx local fuel-air ratio region on the lean fuel side to the low NOx local fuel-air ratio region on the fuel rich side, and the local fuel-air ratio of the burner 91 is increased. The ratio is decreased from the low NOx local fuel-air ratio region on the fuel rich side to the low NOx local fuel-air ratio region on the fuel lean side. Specifically, it is as follows.

(3-1) Steps 109 and 110
When the fuel flow command values S1 and S2 reach S14 and S24, respectively, the calculation unit 302 determines in step 108 that the fuel-air ratio of the burners 91 and 92 has reached the fourth target value d, and proceeds to step 109. Then, the fuel flow rate command value S1 is decreased and the fuel flow rate command value S2 is increased to increase the ratio of the fuel flow rate F2 (see FIG. 6). The procedure of this step 109 is that the fuel / air ratio of the burners 91 and 92 is set to the fifth target value e (in this embodiment, 0.0602 (the breakdown is 0.035 for the burner 91 and 0.077 for the burner 92). It is executed in the range until it reaches (Yes). That is, the local fuel-air ratio (F1 / A1) of the first burner 91 is rapidly decreased from the low-NOx region on the fuel rich side to the value (here 0.035) on the low-NOx region on the fuel lean side. The local fuel-air ratio (F2 / A2) of the burner 92 is rapidly increased from the low NOx region on the lean fuel side to the value of the low NOx region on the rich fuel side (here, 0.077) (see FIG. 7). The fuel-air ratio is increased (see the two-dotted line in FIG. 7 and FIG. 6).

  During this time, the calculation unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S15 and S25, respectively (step 110). If the target values S15 and S25 have not been reached, the burner is determined. It is determined that the fuel-air ratio of 91 and 92 has not yet reached the fifth target value e, and the procedure of step 109 is continued.

(3-2) Steps 111 and 112
When the fuel flow command values S1 and S2 reach S15 and S25, respectively, the calculation unit 302 determines that the fuel-air ratio of the burners 91 and 92 has reached the fifth target value e, and moves the procedure to step 111. While maintaining the fuel flow rate command value S1 constant, the rate of increase of the fuel flow rate command value S2 is decreased, and the rate of the fuel flow rate F2 of the second burner 92 is gradually increased (see FIG. 6). The procedure of this step 111 is the sixth target value f in which the fuel-air ratio of the burners 91 and 92 is set (0.074 in the present embodiment (the burner 91 is 0.035 and the burner 92 is 0.1)). It is executed in the range until it reaches.

  During this time, the arithmetic unit 302 determines whether or not the fuel flow rate command values S1 and S2 have reached the target values S16 and S26, respectively (step 112). If the target values S16 and S26 have not been reached, the burner is determined. It is determined that the fuel-air ratio of 91 and 92 has not yet reached the sixth target value f, and the procedure of step 111 is continued. That is, while the local fuel-air ratio (F1 / A1) of the first burner 91 is kept constant, only the local fuel-air ratio (F2 / A2) of the second burner 92 is set in the low-NOx region on the fuel-rich side (in this case, 0. 1) (see FIG. 7), and the fuel-air ratio of the pilot burner is increased (two-dotted line in FIG. 7, see FIG. 6).

(4) Step 113
In step 113, the local fuel-air ratio of the burner 91 is increased from the low NOx local fuel-air ratio region on the fuel lean side to the low NOx local fuel-air ratio region on the fuel rich side.

  Specifically, when the fuel flow rate command values S1 and S2 reach S16 and S26, respectively, the calculation unit 302 sets the fuel of the entire pilot burner to the sixth target value f exceeding the high NOx local fuel-air ratio range in step 112. It is determined that the air ratio has been reached, the procedure of step 113 is executed, and the stoichiometric ratio avoidance procedure is terminated. In this step 113, the fuel flow rate command value S1 is increased and the fuel flow rate command value S2 is decreased, and the ratio of the fuel flow rate F1 of the first burner 91 is increased until the local fuel-air ratios of the burners 91 and 92 become equal. (See FIG. 6). That is, in step 112, it is determined that the fuel / air ratio of the entire pilot burner has exceeded the upper limit (here, 0.07) of the high NOx local fuel / air ratio range. In this step 113, the fuel flow rate of the burners 91 and 92 is determined. The distribution of F1 and F2 is returned to the distribution of airflow rates A1 and A2 (4: 6). Thereafter, during the low load operation, the fuel / air ratio of the pilot burner is set to a predetermined value under the condition of F1 / A1 = F2 / A2. Increase to the value. Since the local fuel-air ratio is sufficiently larger (away from the stoichiometric ratio) than the high NOx local fuel-air ratio range, the low NOx can be achieved by the amount that the local fuel-air ratio increases from the sixth target value f. .

  Next, the function and effect of this embodiment will be described.

  If the stoichiometric ratio avoidance procedure is not executed, if the fuel / air ratio of the pilot burner exceeds the first target value a and the local fuel / air ratio of the burners 91 and 92 is kept equal, the actual local fuel / fuel ratio is maintained. The air ratio (individual local fuel / air ratio of burners 91 and 92) both exceeds 0.04 and enters the high NOx local fuel / air ratio range. Thereafter, the fuel / air ratio of the pilot burner exceeds 0.07. The actual local fuel-air ratio will shift within the high NOx local fuel-air ratio range for an appropriate period of time.

  On the other hand, in the present embodiment, the burners 91 and 92 are in a process in which the fuel / air ratio of the pilot burner shifts from the low NOx local fuel / air ratio region on the lean fuel side to the low NOx local fuel / air ratio region on the fuel rich side. Skillfully adjust the ratio of the fuel flow rate F1, F2 (see Fig. 6), and the high-NOx locality is largely over the period during which the fuel-air ratio (two-dotted line) of the pilot burner changes the high-NOx local fuel-air ratio range. The actual local fuel-air ratio (individual local fuel-air ratios of the burners 91 and 92) can be shifted while avoiding the fuel-air ratio range (see FIG. 7).

  Therefore, according to the present embodiment, since the burners 91 and 92 can be individually suppressed in the NOx generation amount by quickly passing through the high NOx local fuel / air ratio range, the local fuel / air ratio of the burner is The amount of NOx generated by rising across the stoichiometric ratio can be reduced (FIG. 7 also shows the state of increase / decrease in the amount of NOx generated accompanying the execution of the stoichiometric ratio avoidance procedure).

  In order to avoid combustion in the vicinity of the stoichiometric ratio, it is conceivable to increase the number of burners capable of individually controlling the fuel flow rate and increase the number of burners burned many times. In this case, however, the structure of the fuel header is complicated, and the number of fuel control systems is increased, which increases the cost and complicates the operation. On the other hand, in the present embodiment, the high NOx local fuel-air ratio range can be skillfully avoided by controlling the ratio of the fuel flow rates F1, F2 of the burners 91, 92, so the number of fuel systems is increased more than necessary. This is unnecessary, and it is possible to suppress the complexity of the structure and the increase in the fuel control system.

  In the present embodiment, the air flow rates A1 and A2 are differentiated by 40% and 60%. Therefore, the fuel flow rates F1 and F2 are differentiated in order to make the local fuel-air ratios of the burners 91 and 92 equal. Can do. Therefore, the burner 92 that can inject more fuel is used in the low NOx local fuel-air ratio region on the fuel rich side until the local fuel-air ratio reaches the sixth target value f from the fifth target value e. Can do. As a result, the fuel flow rate F2 is increased on the fuel rich side until the local fuel / air ratio reaches the sixth target value f from the fifth target value e to the low NOx local fuel / air ratio region on the fuel lean side. Therefore, the local fuel-air ratio of the burner 91 can be suppressed to a value with a margin (0.035 in the present embodiment) up to the high NOx local fuel-air ratio range, which is advantageous for lowering NOx.

(2) Second Embodiment The present embodiment is different from the first embodiment in that the first embodiment sets the local fuel-air ratio of the burners 91 and 92 to the fuel rich side and In this embodiment, the procedure for avoiding the stoichiometric ratio is performed without replacement, while the fuel lean side and the fuel rich side are replaced after the fuel lean side is allocated. Details will be described below.

  FIG. 9 is a graph illustrating the transition of the fuel flow rate of the pilot burner accompanying the execution of the stoichiometric ratio avoidance procedure in the combustor according to the second embodiment of the present invention, and FIG. 10 is the execution of the stoichiometric ratio avoidance procedure. It is the graph which illustrated transition of the fuel air ratio of a pilot burner accompanying with. 9 and 10 correspond to FIGS. 6 and 7 of the first embodiment.

  In the present embodiment, with respect to the flow rates A1 and A2 of the combustion air 104 supplied to the air holes 32 of the burners 91 and 92, when the combustion air (A1 + A2) of the pilot burner is 100%, A1 = A2 = 50% It is designed to be. The combustor configuration is the same as that of the first embodiment.

  FIG. 11 is a flowchart showing a pilot burner control procedure including a stoichiometric ratio avoidance procedure by the controller 300. The stoichiometric ratio avoidance procedure will be described below with reference to FIG. 11 together with FIGS.

(1) Steps 201 and 202
Steps 201 and 202 correspond to steps 101 and 102 in the stoichiometric ratio avoidance procedure of the first embodiment.

  Specifically, the arithmetic unit 302 of the control device 300 starts the control of FIG. 11 with the start of the gas turbine, and increases both the fuel flow rate command values S1 and S2 of the burners 91 and 92 (step 201). The procedure of this step 201 is such that the fuel-air ratio of the pilot burner is set to the first target value a (0.038 (both burners 91 and 92 in this embodiment) set to be less than the lower limit 0.04 of the local fuel-air ratio range. 0.038) is executed in the range up to reaching. During this period, the fuel distribution of the burners 91 and 92 is set to a value (5: 5) that matches the distribution of the combustion air flow rates A1 and A2 (see FIG. 9), and the local fuel-air ratio (F1 / A1) of the first burner 91 is The local fuel-air ratio (F2 / A2) of the second burner 92 is made equal (see FIG. 10). At this stage, since the local fuel-air ratio is smaller than the high NOx local fuel-air ratio range as shown in FIG. 10, low NOx can be achieved.

  During this time, the calculation unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S11 and S21, respectively (step 202). If the target values S11 and S21 have not been reached, the burner 91 is determined. , 92 are determined to have not yet reached the first target value a, and the procedure of step 201 is continued.

(2) Step 203-208
The subsequent steps 203-208 correspond to steps 103-108 in the stoichiometric ratio avoidance procedure of the first embodiment. Specifically, it is as follows.

(2-1) Steps 203 and 204
When the fuel flow rate command values S1 and S2 reach S11 and S21, respectively, the calculation unit 302 determines that the fuel-air ratio of the burners 91 and 92 has reached the first target value a in the previous step 202, and the process proceeds to step 203. The procedure is shifted to decrease the fuel flow rate command value S2 and increase the increase rate of the fuel flow rate command value S1 (see FIG. 9). The procedure of this step 203 is that the fuel / air ratio of the burners 91 and 92 is set to the second target value b (in this embodiment, 0.04 (the breakdown is 0.07 for the burner 91 and 0.01 for the burner 92)). It is executed in the range until it reaches (Yes). In order to linearly increase the fuel / air ratio of the pilot burner, the local fuel / air ratio (F2 / A2) of the second burner 92 is reduced to a predetermined value in the low NOx region on the lean side of the fuel in this way. The local fuel-air ratio (F1 / A1) of the first burner 91 is rapidly increased to the value of the low-NOx local fuel-air ratio region on the rich side (see FIG. 10), and the fuel-air ratio of the pilot burner is increased (see FIG. 10). FIG. 9 shows a two-dot difference line in FIG.

  During this time, the arithmetic unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S12 and S22, respectively (step 204). If the target values S12 and S22 have not been reached, the burner 91 is determined. , 92 are determined to have not yet reached the second target value b, and the procedure of step 203 is continued.

(2-2) Steps 205 and 206
When the fuel flow command values S1 and S2 reach S12 and S22, respectively, the calculation unit 302 determines in step 204 that the fuel-air ratio of the burners 91 and 92 has reached the second target value b, and proceeds to step 205. The fuel flow rate command value S2 is increased while keeping the fuel flow rate command value S1 constant, and the ratio of the fuel flow rate F2 of the second burner 92 is increased (see FIG. 9). The procedure of this step 205 is that the fuel / air ratio of the burners 91 and 92 is set to the third target value c (in this embodiment, 0.054 (the breakdown is 0.07 for the burner 91 and 0.038 for the burner 92). It is executed in the range until it reaches (Yes). That is, only the local fuel-air ratio (F2 / A2) of the second burner 92 is increased within a range that does not deviate from the low-NOx region on the fuel lean side, while keeping the local fuel-air ratio (F1 / A1) of the first burner 91 constant. (Refer to FIG. 10) The fuel-air ratio of the pilot burner is increased to a predetermined value (two-dot chain line in FIG. 10, see FIG. 9).

  During this time, the calculation unit 302 determines whether or not the fuel flow command values S1 and S2 have reached the target values S13 and S23, respectively (step 206). If the target values S13 and S23 have not been reached, the burner is determined. It is determined that the fuel-air ratio of 91 and 92 has not yet reached the third target value c, and the procedure of step 205 is continued.

(2-3) Steps 207 and 208
When the fuel flow rate command values S1 and S2 reach S13 and S23, respectively, the calculation unit 302 determines in step 206 that the fuel-air ratio of the burners 91 and 92 has reached the third target value c, and the procedure proceeds to step 207. The fuel flow rate command value S1 is increased while keeping the fuel flow rate command value S2 constant, and the ratio of the fuel flow rate F1 of the first burner 91 is increased (see FIG. 9). The procedure of this step 207 is the fourth target value d (the burner 91 is 0.098 and the burner 92 is 0.038 in this embodiment) in which the fuel-air ratio of the burners 91 and 92 is set. It is executed in the range until it reaches (Yes). That is, when the third target value c is reached and there is no room for raising the local fuel-air ratio (F2 / A2) of the second burner 92 in the low NOx region on the lean side of the fuel, the local fuel-air of the second burner 92 is reached. While keeping the ratio (F2 / A2) constant, only the local fuel-air ratio (F1 / A1) of the first burner 91 is increased in the low NOx region on the fuel rich side (see FIG. 10), and the fuel-air ratio of the pilot burner is increased. It is increased (see the two-dot chain line in FIG. 10, see FIG. 9).

  During this time, the arithmetic unit 302 determines whether or not the fuel flow rate command values S1 and S2 have reached the target values S14 and S24, respectively (step 208). If the target values S14 and S24 have not been reached, the burner 91 is determined. , 92 is determined to have not yet reached the fourth target value d, and the procedure of step 207 is continued.

(4) Step 209
In step 209, the local fuel-air ratio of the burner 92 is increased from the low NOx local fuel-air ratio region on the lean fuel side to the low NOx local fuel-air ratio region on the fuel rich side.

  Specifically, when the fuel flow rate command values S1 and S2 reach S14 and S24, respectively, the calculation unit 302 sets the fuel of the entire pilot burner to the fourth target value d exceeding the high NOx local fuel-air ratio range in step 208. It is determined that the air ratio has been reached, the procedure of step 209 is executed, and the stoichiometric ratio avoidance procedure is terminated. In this step 209, the fuel flow rate command value S1 is decreased and the fuel flow rate command value S2 is increased, and the ratio of the fuel flow rate F2 of the second burner 92 is increased until the local fuel-air ratio of the burners 91 and 92 becomes equal. (See FIG. 9). That is, in step 208, it is determined that the fuel / air ratio of the entire pilot burner has exceeded the upper limit (here, 0.07) of the high NOx local fuel / air ratio range. In this step 209, the fuel flow rate of the burners 91 and 92 is determined. The distribution of F1 and F2 is returned to the distribution of air flow rates A1 and A2 (5: 5). Thereafter, during the low load operation, the fuel / air ratio of the pilot burner is set to a predetermined value under the condition of F1 / A1 = F2 / A2. Increase to the value. Since the local fuel-air ratio is sufficiently larger (away from the stoichiometric ratio) than the high NOx local fuel-air ratio range, the low NOx can be achieved by the amount that the local fuel-air ratio increases from the fourth target value d. .

  Also in the present embodiment, since the NOx generation amount can be individually suppressed by passing the high NOx local fuel-air ratio range quickly for each of the burners 91 and 92, the local fuel-air ratio of the burner is the stoichiometry. The amount of NOx generated by rising across the ratio can be reduced. Further, it is not necessary to add more fuel systems than necessary, and it is possible to suppress the complexity of the structure and the increase in the fuel control system.

  Further, this embodiment has an advantage in that the control procedure is simpler than that of the first embodiment.

(3) Third Embodiment In the first and second embodiments, a burner that promotes the mixing of fuel and air by forming a large number of coaxial jets of fuel and air to reduce NOx is applied. In this embodiment, a burner having a different type from that of the first embodiment is exemplified as an application example.

  FIG. 12 is a schematic configuration diagram of a pilot burner provided in a combustor according to a third embodiment of the present invention. Parts similar to those of the above-described embodiment are denoted by the same reference numerals as those of the above-described drawings, and description thereof is omitted.

  The pilot burner shown in FIG. 12 includes a double cylindrical main nozzle 401 having an inner peripheral flow path and an outer peripheral flow path therein. A plurality of sub-nozzles 431 extending in the radial direction are provided on the outer peripheral portion of the main nozzle 401. The inner peripheral flow path of the main nozzle 401 is connected to a fuel injection hole at the downstream end of the main nozzle 401, and the fuel 201 is directed from the fuel injection hole of the main nozzle 401 toward the combustion chamber as a fuel jet 35a in the vicinity of the combustor shaft. Be injected. On the other hand, the outer peripheral flow path of the main nozzle 401 is connected to the sub nozzle 431, and the fuel 202 is injected toward the combustion chamber as a fuel jet 35 b from the injection hole of the sub nozzle 431 on the outer peripheral side of the main nozzle 401. In the present embodiment, the main nozzle 401 and the sub nozzle 431 function as a first burner 491 and a second burner 492 (corresponding to the burners 91 and 92 in the first embodiment), respectively. Two rows of swirl vanes 37 and 38 are provided concentrically around the main nozzle 401, and fuel jets 35a and 104b are respectively formed by combustion air 104a and 104b ejected to the combustion chamber via the swirl vanes 37 and 38, respectively. A turning component is imparted to 35b to stabilize the flame.

  The present invention is also applicable to such a pilot burner, and when the fuel-air ratio of the pilot burner rises across the vicinity of the stoichiometric ratio, the burner 491, as in the first and second embodiments, is used. By setting the local fuel-air ratio of 492 separately for the fuel lean side and the fuel rich side, the NOx generation amount can be suppressed in both the burners 491 and 492, and the pilot burner can be reduced in NOx. it can.

(4) Fourth Embodiment In the above description, the case where the pilot burner is divided into two systems has been described as an example. However, the present invention can also be applied when the pilot burner is divided into three or more systems.

  Further, the case where the fuel flow rates F1, F2 are controlled according to the command values (S11, S21, etc.) previously determined for each fuel system has been described by way of example, but some state quantity that changes according to the operation of the gas turbine The fuel system may be controlled according to the detected value.

  For example, normally, power generation amount = fuel flow rate × heat generation amount × efficiency, and since the power generation amount changes according to the fuel-air ratio, the detector 501 detects the power generation amount (load) as shown in FIG. It is also conceivable to control the fuel system based on the detection value of the detector 501 so that the behavior of the fuel flow rate and the fuel-air ratio as shown in FIG. 6 and FIG. 7 or FIG. 9 and FIG.

  Further, since it is each fuel-air ratio represented on the vertical axis of the graphs of FIGS. 7 and 10 that actually affects the NOx emission amount, a detector 502 (shown together with FIG. 13) for detecting the air flow rate is provided. Thus, it is conceivable to control the fuel system based on the detection value of the detector 502. However, since the air flow meter is expensive and causes pressure loss when it is installed in the flow path, the air flow rate is calculated from the turbine rotation speed based on the inlet valve opening of the compressor 1, and this is used as the detected value of the air flow rate. You can also Further, a detector 503 (shown together with FIG. 13) for detecting the NOx concentration is provided in the exhaust passage of the turbine 3, and the timing for switching the ratio of the fuel flow rates F1, F2 can be determined directly from the NOx concentration in the exhaust gas. Can be considered.

DESCRIPTION OF SYMBOLS 1 Compressor 2 Combustor 3 Turbine 31 Fuel nozzle 32 Air hole 91 1st burner (burner, pilot burner)
92 2nd burner (burner, pilot burner)
93 3rd burner (main burner)
102 Compressed air 105 Combustion gas 201, 202 Fuel 300 Control device 301 Storage unit 302 Calculation unit

Claims (10)

With the main burner,
A pilot burner having a plurality of burners;
A control device for controlling the fuel flow rate of the plurality of burners,
The control device includes:
A storage unit for storing a set high NOx local fuel-air ratio range including a stoichiometric ratio;
A calculation unit that outputs a command to the fuel system of the plurality of burners,
The arithmetic unit, when increasing the fuel-air ratio of the pilot burner across the stoichiometric ratio, each local fuel-air ratio of the plurality of burners, local lower than the high NOx local fuel-air ratio range A low-NOx local fuel-air ratio region on the fuel lean side that is a fuel-air ratio region, and a low-NOx local fuel-air ratio region on the fuel-rich side that is a local fuel-air ratio region that is higher than the high NOx local fuel-air ratio range A combustor that performs a stoichiometric avoidance procedure. The combustor of claim 1.
The stoichiometric ratio avoidance procedure is:
Increasing the local fuel-air ratio of the plurality of burners in the low-NOx local fuel-air ratio region on the fuel lean side lower than the high NOx local fuel-air ratio range;
While the local fuel-air ratio of one burner is left in the low NOx local fuel-air ratio region on the lean side of the fuel, the local fuel-air ratio of the other burner is higher on the fuel rich side than the high NOx local fuel-air ratio range. Procedure to raise to low NOx local fuel-air ratio region,
The local fuel-air ratio of the one burner is increased from the low NOx local fuel-air ratio region on the lean fuel side to the low NOx local fuel-air ratio region on the fuel rich side, and the local fuel-air ratio of the other burner From the low-NOx local fuel-air ratio region on the fuel rich side to the low-NOx local fuel-air ratio region on the fuel lean side, and the local fuel-air ratio of the other burner on the low-NOx side on the fuel lean side A combustor comprising a procedure of raising from a local fuel / air ratio region to a low NOx local fuel / air ratio region on the fuel-rich side. The combustor of claim 2.
The air flow rate supplied to the one burner is larger than the air flow rate supplied to the other burner, and before and after the execution of the stoichiometric ratio avoidance procedure, the first burner and the other burner The distribution of the supplied fuel flow rate is set equal to the distribution of the air flow rate supplied to the first burner and the other burner. The combustor of claim 1.
The stoichiometric ratio avoidance procedure is:
Increasing the local fuel-air ratio of the plurality of burners in the low-NOx local fuel-air ratio region on the fuel lean side lower than the high NOx local fuel-air ratio range;
While the local fuel-air ratio of one burner is left in the low NOx local fuel-air ratio region on the lean side of the fuel, the local fuel-air ratio of the other burner is higher on the fuel rich side than the high NOx local fuel-air ratio range. A procedure for raising the local fuel / air ratio of the one burner from the low NOx local fuel / air ratio region on the lean fuel side to the low NOx local fuel / air ratio region on the rich fuel side A combustor comprising a lifting procedure. The combustor of claim 4.
The air flow rate supplied to the one burner is equal to the air flow rate supplied to the other burner, and supplied to the first burner and the other burner before and after the execution of the stoichiometric ratio avoidance procedure. The combustor is characterized in that the distribution of the fuel flow rate is set equal to the distribution of the air flow rate supplied to the first burner and the other burners. The combustor according to claim 1,
The plurality of burners each include an air hole located at an upstream end of the combustion chamber and a fuel nozzle arranged coaxially with the air hole, and are arranged in a plurality of concentric rows around the combustor axis. A combustor characterized by comprising: A compressor for compressing air;
A combustor that mixes and burns compressed air and fuel from the compressor to generate combustion gas;
A turbine driven by the combustion gas generated by the combustor,
The combustor,
With the main burner,
A pilot burner having a plurality of burners;
A control device for controlling the fuel flow rate of the plurality of burners,
The control device includes:
A storage unit for storing a set high NOx local fuel-air ratio range including a stoichiometric ratio;
A calculation unit that outputs a command to the fuel system of the plurality of burners,
The arithmetic unit, when increasing the fuel-air ratio of the pilot burner across the stoichiometric ratio, each local fuel-air ratio of the plurality of burners, local lower than the high NOx local fuel-air ratio range A low-NOx local fuel-air ratio region on the fuel lean side that is a fuel-air ratio region, and a low-NOx local fuel-air ratio region on the fuel-rich side that is a local fuel-air ratio region that is higher than the high NOx local fuel-air ratio range A gas turbine characterized by executing a distribution stoichiometric ratio avoidance procedure. A fuel control method for a combustor including a main burner and a pilot burner having a plurality of burners,
Set high NOx local fuel-air ratio range including stoichiometric ratio,
When increasing the fuel / air ratio of the pilot burner across the stoichiometric ratio, each local fuel / air ratio of the plurality of burners is reduced in a local fuel / air ratio region lower than the high NOx local fuel / air ratio range. A stoichiometric ratio that is allocated to a low NOx local fuel-air ratio region on a fuel lean side and a low NOx local fuel-air ratio region on a fuel rich side that is a local fuel-air ratio region that is higher than the high NOx local fuel-air ratio range A fuel control method for a combustor, wherein an avoidance procedure is executed. The fuel control method for a combustor according to claim 8, wherein
The stoichiometric ratio avoidance procedure is:
Increasing the local fuel-air ratio of the plurality of burners in the low-NOx local fuel-air ratio region on the fuel lean side lower than the high NOx local fuel-air ratio range;
While the local fuel-air ratio of one burner is left in the low NOx local fuel-air ratio region on the lean side of the fuel, the local fuel-air ratio of the other burner is higher on the fuel rich side than the high NOx local fuel-air ratio range. Procedure to raise to low NOx local fuel-air ratio region,
The local fuel-air ratio of the one burner is increased from the low NOx local fuel-air ratio region on the lean fuel side to the low NOx local fuel-air ratio region on the fuel rich side, and the local fuel-air ratio of the other burner From the low-NOx local fuel-air ratio region on the fuel rich side to the low-NOx local fuel-air ratio region on the fuel lean side, and the local fuel-air ratio of the other burner on the low-NOx side on the fuel lean side A fuel control method for a combustor, comprising a step of increasing from a local fuel-air ratio region to a low-NOx local fuel-air ratio region on the fuel rich side. The fuel control method for a combustor according to claim 8, wherein
The stoichiometric ratio avoidance procedure is:
Increasing the local fuel-air ratio of the plurality of burners in the low-NOx local fuel-air ratio region on the fuel lean side lower than the high NOx local fuel-air ratio range;
While the local fuel-air ratio of one burner is left in the low NOx local fuel-air ratio region on the lean side of the fuel, the local fuel-air ratio of the other burner is higher on the fuel rich side than the high NOx local fuel-air ratio range. A procedure for raising the local fuel / air ratio of the one burner from the low NOx local fuel / air ratio region on the lean fuel side to the low NOx local fuel / air ratio region on the rich fuel side A method for controlling a fuel in a combustor, comprising a step of raising the combustor.

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