Patent Application
20110197831
The present invention relates to a pulverized coal burning boiler such as a power generation boiler apparatus and particularly to a pulverized coal burning boiler in which a plurality of coal feeding pipes are connected to a single milling means such as a roller mill so that pulverized coal generated by the milling means is distributed to the plurality of coal feeding pipes, fed to individual pulverized coal burners and burned.
Conventionally, a pulverized coal burning boiler uses a two-stage burning method in which air with a smaller ratio than a theoretical air ratio is imported by a burner and low NOx combustion is performed in a reducing atmosphere in order to reduce the amount of emergence of NOx and then additional air is imported from an after airport (hereinafter abbreviated as AAP) as a post-stage in order to burn unburned contents such as CO.
To achieve complete burning at a furnace outlet finally, the amount of air imported into a combustion device as a whole is imported so excessively as to be about 1.2 which is more than the theoretical air ratio of 1.0.
In recent years, there has been an increasing demand for combustion at a ratio as close to the theoretical air ratio of 1.0 as possible, i.e. at a low excess air ratio for the purpose of reducing the amount of combustion gas to thereby attain reduction in size of a furnace and an exhaust gas processing device, etc. following the furnace, reduction in various kinds of fan motive utilities, etc.
With respect to the background art 1, for example, Patent Documents 1 to 3 can be listed.
The amount of this additional air is supplied so that the total amount of air containing the amount of air supplied from the pulverized coal burners 702 exceeds the theoretical air amount. This is for the purpose of compensating for local shortage of air caused by uneven supply of pulverized coal to the pulverized coal burners 702 or the purpose of compensating for imperfect mixing of exhaust gas from the pulverized coal burners 702 and air imported from the AAPs 703 as will be described later.
Accordingly, as the excess ratio of the total air amount to the theoretical air amount, that is, the excess air ratio increases, the concentration of CO in exhaust gas decreases but thermal loss due to exhaust gas increases to cause lowering of boiler efficiency. For this reason, the excess air ratio is generally set to be about 20-30%. Incidentally, there may be a pulverized coal burning boiler using a so-called single-stage combustion method in which all air is supplied from pulverized coal burners without provision of any AAP.
Raw coal is milled by milling means so that pulverized coal is generated and supplied to the respective pulverized coal burners 702. Although the amounts of pulverized coal supplied to the respective pulverized coal burners 702 are adjusted to be equal at the time of trial operation, a deviation may be generated between the supply amounts of pulverized coal in vessel left and right because it is difficult to adjust the amounts of pulverized coal uniformly based on all loads and the supply amounts of pulverized coal may be unbalanced in accordance with aging. The deviation between the supply amounts of pulverized coal in vessel left and right causes a deviation between combustion gas temperatures in the furnace. As a result, a deviation is generated between steam temperatures in the vessel left and right.
As shown in
In Japan, the reheating steam temperature generally must not be increased by 8° C. or higher from a designated steam condition. Accordingly, in the state in which the higher one is 5° C. higher and the lower one is −5° C. lower than the steam condition, tolerance on control is only 3° C., as shown in
JP-A-6-101806 (Patent Document 4) has described that a deviation between reheating steam temperatures is reduced when the apertures of gas distributing dampers disposed in the rear of a furnace are adjusted to apply biases to the vessel left and right.
As shown in
JP-A-9-21505 (Patent Document 5) has described that a connection pipe 902 connecting the inlet and outlet of a primary reheater 901 is provided and a steam flow rate adjusting valve 903 inserted in an intermediate portion of the connection pipe 902 is operated based on a temperature difference between the vessel left and right systems to adjust the flow rates of steam in the vessel left and right to thereby reduce the deviation between reheating steam temperatures, as shown in
In
As shown in
Alternatively, the amounts of spray water in superheater inlet sprays 723 and 724 shown in
In
As described in (Background Art 1), combustion at a low excess air ratio has a demerit that the supply amount of combustion air decreases greatly and production of an unburned component such as CO increases in comparison with the related art.
A pulverized coal burning method for reducing the amount of produced NOx has been disclosed in the Patent Document 1. Specifically, combustion of pulverized coal by an in-flame denitration type pulverized coal burner which forms a reducing flame region short of oxygen takes a point of view that the concentration of NOx in exhaust gas is largely affected by the temperature of the reducing flame region or the air ratio of the reducing flame region.
Configuration is made so that a light extractor is attached to the pulverized coal burner, light of flame in the reducing flame region formed by the burner is detected by the light extractor, the detection signal is led to an emission spectrometer, the intensity of emitted light is detected, the temperature of the reducing flame region or the air ratio of the reducing flame region is calculated, and the amount of pulverized coal or the amount of air supplied to the burner is controlled based on a result of the calculation.
This pulverized coal burning method is effective in reducing NOx but brings a state short of oxygen as a whole. As a result, there is a problem that production of an unburned component such as CO increases.
In a structure (see
In the method in which the deviation between the reheating steam temperatures in the vessel left and right is eliminated by the gas distributing dampers described in (Background Art 3), the gas distributing dampers 718 to 721 are disposed in the respective space portions partitioned as shown in
Because the gas distributing dampers 718 to 721 are mechanically slow in operating velocity and a metal thermal capacity is interposed in each of the gas distributing dampers 718 to 721, for example, gas distributing damper reheating steam temperature characteristic exhibits a wasteful time of 1-5 minutes and a time constant of about 3-10 minutes. Finally, because of the interference and the response delay of the gas distributing dampers 718 to 721, response of the gas distributing dampers 718 to 721 to the reheating steam temperature and the main steam temperature is further worsened so that there is a possibility that the deviation between the vessel left and right steam temperatures cannot be eliminated by the gas distributing dampers 718 to 721. In this case, a superheater spray which has a wasteful time of 30 seconds to 2 minutes and a time constant of 2-5 minutes, that is, has rapider response than the gas distributing dampers 718 to 721 is started to keep the steam temperature condition.
To use the reheater spray is to cool superheated steam with spray water. This causes lowering of efficiency of the combustion device. Moreover, when the number of times of importing compressed water into a connection pipe in which superheated steam circulates increases, the spray is damaged by thermal shock so that the lifetime of the spay is shortened.
In the method (see
In the structure (see
In the method in which the amounts of spray water put into the secondary superheater inlet spray 723 and the tertiary superheater inlet spray 724 are biased in the vessel left and right as shown in
A first object of the invention is to provide a pulverized coal burning boiler in which production of an unburned component such as CO is reduced in a pulverized coal burning boiler having a reduced excess air ratio.
A second object of the invention is to provide a pulverized coal burning boiler which is so highly efficient that a deviation between steam temperatures in the vessel left and right can be reduced.
A first means of the invention to achieve the first object is a pulverized coal burning boiler including:
milling means such as vertical roller mills which generate pulverized coal by milling supplied coal;
coal feeding pipes which are arranged in such a manner that a plurality of coal feeding pipes are connected to one milling means and through which the pulverized coal is airflow-conveyed by primary air;
pulverized coal burners which are connected to front end sides of the coal feeding pipes respectively and which have pulverized coal nozzles disposed so as to face into a furnace;
combustion air supply means which supply combustion air other than the primary air to the pulverized coal burners individually;
combustion air supply amount measuring means which measure the supply amounts of the combustion air supplied by the combustion air supply means individually;
combustion air supply amount adjusting means which adjust the supply amounts of the combustion air; and
burner air ratio setting means which set burner air ratios;
wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air;
the pulverized coal burning boiler characterized in that there are provided:
pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively; and
air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept.
According to a second means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal supply amount measuring means are attached to the coal feeding pipes of pulverized coal burners or pulverized coal burner groups high in unburned component reducing effect in the pulverized coal burners so that the supply amounts of combustion air are adjusted individually.
According to a third means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal burners are disposed as several stages for the furnace and the pulverized coal supply amount measuring means are attached to the coal feeding pipes of the pulverized coal burners except the pulverized coal burners disposed on the lower stage so that the supply amounts of combustion air are adjusted individually.
According to a fourth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal burners are disposed as several stages for the furnace and the pulverized coal supply amount measuring means are attached to the coal feeding pipes of the pulverized coal burners disposed on at least the uppermost stage so that the supply amounts of combustion air are adjusted individually.
According to a fifth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that a plurality of the pulverized coal burners are disposed side by side to form a burner stage, a plurality of after air ports are disposed side by side on a downstream side of the burner stage in an exhaust gas flow direction,
the amount of combustion air supplied to at least one of the pulverized coal burners is adjusted, and
the amount of combustion air supplied to an after air port near to flame formed by the pulverized coal burner is adjusted.
According to a sixth means of the invention, the pulverized coal burning boiler defined in the fifth means is characterized in that the plurality of pulverized coal burners and the plurality of after air ports are disposed so as to be separated into a vessel front and a vessel back of a furnace,
when the amount of combustion air supplied to the pulverized coal burners disposed in the vessel front is adjusted, the amount of combustion air supplied to the after air ports disposed in the vessel back is adjusted, and
when the amount of combustion air supplied to the pulverized coal burners disposed in the vessel back is adjusted, the amount of combustion air supplied to the after air ports disposed in the vessel front is adjusted.
According to a seventh means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that a plurality of after air ports are dispersively disposed on a downstream side of the pulverized coal burners in an exhaust gas flow direction, concentration distribution detection means such as a concentration measuring meter for detecting a distribution of oxygen concentrations or CO concentrations in exhaust gas is provided in a flue on a downstream side of the after air ports in an exhaust gas flow direction, and
while the amount of combustion air supplied to the pulverized coal burners is adjusted, the amount of combustion air supplied to the after air ports corresponding to a low oxygen concentration or high CO concentration region detected by the concentration distribution detection means is increased.
According to an eighth means of the invention, the pulverized coal burning boiler defined in any one of the fifth to seventh means is characterized in that the pulverized coal burners are disposed as a plurality of stages for a furnace, the pulverized coal burners to adjust the supply amount of combustion air are pulverized coal burners disposed on the uppermost stage.
According to a ninth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that each of the pulverized coal supply amount measuring means has a microwave resonance pipe through which a mixed fluid of the pulverized coal and primary air circulates, and a microwave transmitter and a microwave receiver which are disposed in the microwave resonance pipe so as to be at a predetermined distance from each other along a direction of a flow of the mixed fluid, and
the microwave transmitter transmits microwaves to the microwave receiver to measure a resonance frequency of the microwave resonance pipe to thereby measure the supply amount of the pulverized coal based on the resonance frequency.
According to a tenth means of the invention, the pulverized coal burning boiler defined in the ninth means is characterized in that a part of each of the coal feeding pipes is used as the microwave resonance pipe.
According to an eleventh means of the invention, the pulverized coal burning boiler defined in the ninth or tenth means is characterized in that the microwave transmitter and the microwave receiver protrude into the microwave resonance pipe, and a knocking member such as fluid guiding means which will be described later is disposed on an upstream side of the microwave transmitter in the microwave resonance pipe to unravel a flow of the pulverized coal condensed like a string in the microwave resonance pipe.
According to a twelfth means of the invention, the pulverized coal burning boiler defined in the first means is characterized in that the pulverized coal supply amount measuring means has a first charge sensor and a second charge sensor which are disposed in each of the coal feeding pipes so as to be at a predetermined distance from each other along an axial direction of the coal feeding pipe, and
movement of electrostatic charges resulting from passage of pulverized coal in the coal feeding pipe is measured by the two charge sensors so that the supply amount of pulverized coal is measured based on the movement of electrostatic charges measured by the two charge sensors.
According to a thirteenth means of the invention, the pulverized coal burning boiler defined in the twelfth means is characterized in that the first charge sensor and the second charge sensor are circular and fluid guiding means is provided on an upstream side of the charge sensors to collect pulverized coal and pour the collected pulverized coal into a central portion side of the coal feeding pipe to thereby reduce the amount of pulverized coal passing through an inner circumferential side of the charge sensors.
A fourteenth means of the invention to achieve the second object is a pulverized coal burning boiler provided with a first reheater system and a second reheater system disposed side by side so that supplied steam circulates while forked into the first and second reheater systems, characterized in that there are provided:
reheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second reheater systems;
reheater outlet steam temperature measuring means which measure reheater outlet steam temperatures of the first and second reheater systems; and
reheating steam distributing amount control means which send control command signals to the reheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means.
A fifteenth means of the invention to achieve the second object is a pulverized coal burning boiler including:
milling means which generate pulverized coal by milling supplied coal;
coal feeding pipes which are arranged in such a manner that a plurality of coal feeding pipes are connected to one milling means and through which the pulverized coal is airflow-conveyed by primary air;
pulverized coal burners which are connected to front end sides of the coal feeding pipes respectively and which have pulverized coal nozzles disposed so as to face into a furnace;
combustion air supply means which supply combustion air other than the primary air to the pulverized coal burners individually;
combustion air supply amount measuring means which measure the supply amounts of the combustion air supplied by the combustion air supply means individually;
combustion air supply amount adjusting means which adjust the supply amounts of the combustion air;
burner air ratio setting means which set burner air ratios; and
a reheater which has a first reheater system and a second reheater system disposed side by side;
wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air; and
steam from a high-pressure turbine is heated by the reheater and supplied to middle-pressure and low-pressure turbines;
the pulverized coal burning boiler characterized in that there are provided:
pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively;
air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept;
reheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second reheater systems;
reheater outlet steam temperature measuring means which measure reheater outlet steam temperatures of the first and second reheater systems; and
reheating steam distributing amount control means which send control command signals to the reheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means.
According to a sixteenth means of the invention, the pulverized coal burning boiler defined in the fourteenth or fifteenth means is characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first reheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second reheater system, and
control command signals are output from the reheating steam distributing amount control means to the reheating steam distributing amount adjusting means based on the deviation between the reheater outlet steam temperatures measured by the reheater outlet steam temperature measuring means and the deviation between the supply amounts of pulverized coal calculated by the pulverized coal supply amount deviation calculating means.
According to a seventeenth means of the invention, the pulverized coal burning boiler defined in the fourteenth or fifteenth means is characterized in that there are provided:
reheating steam temperature deviation prediction means which has reheating steam temperature deviation prediction models and which predicts a reheating steam temperature deviation based on information exerting influence on the reheating steam temperatures; and
correction means which obtain correction signals for correcting control command signals output from the reheating steam distributing amount control means based on the reheating steam temperature deviation value predicted by the reheating steam temperature deviation prediction means.
According to an eighteenth means of the invention, the pulverized coal burning boiler defined in the seventeenth means is characterized in that the information exerting influence on the reheating steam temperatures contains at least one piece of information selected from the group consisting of the supply amount of pulverized coal, the supply amount of water, the flow rate of spray, and the power generator output.
A nineteenth means of the invention to achieve the second object is a pulverized coal burning boiler provided with a first superheater system and a second superheater system disposed side by side so that supplied steam circulates while forked into the first and second superheater systems, characterized in that there are provided:
superheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second superheater systems;
superheater outlet steam temperature measuring means which measure superheater outlet steam temperatures of the first and second superheater systems; and
superheating steam distributing amount control means which send control command signals to the superheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the superheater outlet steam temperatures measured by the superheater outlet steam temperature measuring means.
A twentieth means of the invention to achieve the second object is a pulverized coal burning boiler including:
milling means which generate pulverized coal by milling supplied coal;
coal feeding pipes which are arranged in such a manner that a plurality of coal feeding pipes are connected to one milling means and through which the pulverized coal is airflow-conveyed by primary air;
pulverized coal burners which are connected to front end sides of the coal feeding pipes respectively and which have pulverized coal nozzles disposed so as to face into a furnace;
combustion air supply means which supply combustion air other than the primary air to the pulverized coal burners individually;
combustion air supply amount measuring means which measure the supply amounts of the combustion air supplied by the combustion air supply means individually;
combustion air supply amount adjusting means which adjust the supply amounts of the combustion air;
burner air ratio setting means which set burner air ratios; and
a superheater which has a first superheater system and a second superheater system disposed side by side;
wherein pulverized coal milled and generated by the milling means is distributed to the coal feeding pipes, jetted from the pulverized coal nozzles into the furnace and burned under supply of the combustion air; and
steam is superheated by the superheater and supplied to a high-pressure turbine;
the pulverized coal burning boiler characterized in that there are provided:
pulverized coal supply amount measuring means which individually measure the supply amounts of pulverized coal conveyed through the coal feeding pipes respectively; air supply amount control means which calculate the supply amounts of combustion air corresponding to the supply amounts of pulverized coal based on the supply amounts of pulverized coal measured by the pulverized coal supply amount measuring means and the supply amounts of combustion air supplied to the pulverized coal burners connected to the coal feeding pipes and measured by the combustion air supply amount measuring means and send control command signals to the combustion air supply amount adjusting means so that burner air ratios set by the burner air ratio setting means can be kept;
superheating steam distributing amount adjusting means which adjust the amounts of steam distributed to the first and second superheater systems;
superheater outlet steam temperature measuring means which measure superheater outlet steam temperatures of the first and second superheater systems; and
superheating steam distributing amount control means which send control command signals to the superheating steam distributing amount adjusting means to eliminate the temperature difference based on a deviation between the superheater outlet steam temperatures measured by the superheater outlet steam temperature measuring means.
According to a twenty-first means of the invention, the pulverized coal burning boiler defined in the nineteenth or twentieth means is characterized in that there is provided pulverized coal supply amount deviation calculating means which calculates a deviation between the amount of pulverized coal supplied to pulverized coal burners of a group heating the first superheater system and the amount of pulverized coal supplied to pulverized coal burners of a group heating the second superheater system, and
control command signals are output from the superheating steam distributing amount control means to the superheating steam distributing amount adjusting means based on the deviation between the superheater output steam temperatures measured by the superheater outlet steam temperature measuring means and the deviation between the supply amounts of pulverized coal calculated by the pulverized coal supply amount deviation calculating means.
According to a twenty-second means of the invention, the pulverized coal burning boiler defined in the nineteenth or twentieth means is characterized in that there are provided:
superheating steam temperature deviation prediction means which has superheating steam temperature deviation prediction models and which predicts a superheating steam temperature deviation based on information exerting influence on the superheating steam temperatures; and
correction means which obtain correction signals for correcting control command signals output from the superheating steam distributing amount control means based on the superheating steam temperature deviation value predicted by the superheating steam temperature deviation prediction means.
According to a twenty-third means of the invention, the pulverized coal burning boiler defined in the twenty-second means is characterized in that the information exerting influence on the superheating steam temperatures contains at least one piece of information selected from the group consisting of the supply amount of pulverized coal, the supply amount of water, the flow rate of spray, and the power generator output.
The first means of the invention is configured as described above. Because the flow rates of pulverized coal conveyed through the coal feeding pipes are measured individually so that the supply amounts of combustion air corresponding to the supply amounts of pulverized coal can be calculated and supplied so that burner air ratios set in advance can be kept, production of an unburned component such as CO can be reduced effectively even in the pulverized coal burning boiler in which the excess air ratio is reduced, for example, to 1.1.
The fourteenth, fifteenth, nineteenth and twentieth means of the invention are configured as described above. Because the steam temperature deviation is detected to adjust the flow rates of steam, the steam temperature deviation can be reduced to zero to attain improvement in efficiency.
Specific contents of the invention will be described below with reference to the drawings.
As shown in
After raw coal 5 is put into a coal banker 6, the raw coal 5 is supplied to the vertical roller mill 3 by a coal supply 7 and milled. Pulverized coal milled and generated while dried with the primary air A1 is conveyed by the primary air A1, jetted from pulverized coal nozzles 8 into a pulverized coal burning boiler 9 and ignited/burned. The secondary air A2 is heated by a steam type air preheater 10 and the exhaust gas type air preheater 4, fed to a wind box 11 and after air ports (AAP) 65 and subjected to combustion in the pulverized coal burning boiler 9.
A system for exhaust gas generated by the combustion of the pulverized coal is formed so that dust is removed by a dust collector 12, NOx is reduced by a denitrator 13, the exhaust gas is sucked by an induced blower 14 via the exhaust gas type air preheater 4, a sulfur content is removed by a desulfurizer 15, and the exhaust gas is released from a chimney 16 into the atmospheric air.
Although this example shows the case where the dust collector 12, the denitrator 13 and the exhaust gas type air preheater 4 are disposed in this order from an upstream side in a direction of a flow of the exhaust gas, there may be, for example, the case where the denitrator 13, the exhaust gas type air preheater 4 and the dust collector 12 are disposed in this order.
As shown in
The milling portion 21 includes a housing 26, a milling table 27, milling rollers 28 rolled on the milling table 27, and a throat 29 which is a primary air inlet provided in an outer circumference of the milling table 27.
The classifying portion 22 includes the housing 26, a cyclone type stationary classifier 30 disposed in the inside of the housing 26, and a rotary classifier 31 disposed in the inside of the stationary classifier 30. The stationary classifier 30 has a fixed fin 32, and a recovery cone 33 provided so as to be connected to a lower end of the fixed fin 32. The rotary classifier 31 has a rotary shaft 34, and a rotary vane 35 supported to the rotary shaft 34.
The milling portion driving portion 23 includes a milling portion motor 36 for driving the milling table 27 to rotate, a pedestal 37 on which the milling table 27 is mounted rotatably, pressure frames 38 and brackets 39 for supporting the milling rollers 28, a rod 40, a pressure cylinder 41 for adjusting pressurizing force of each milling roller 28 acting on the milling table 27, etc.
The classifying portion driving portion 24 has a classifier motor 42, an output of which is transmitted to the rotary shaft 34 of the classifying portion 22 through gears. The distributing portion 25 is provided in an upper portion of the vertical roller mill 3 and has one distributing chamber 47 to which coal feeding pipes 43 are connected. In this embodiment, about 4-6 coal feeding pipes 43 are connected. However, only one coal feeding pipe 43 is drawn in
Raw coal 5 supplied by a coal supply pipe 44 drops down into a central portion of the milling table 27 rotating, moves to an outer circumferential side by centrifugal force generated with rotation of the milling table 27 and is clamped between the milling table 27 and each milling roller 28 so as to be milled.
The milled coal grains further move to the outer circumference, become confluent with primary air 45 heated to 150° C.-300° C. led into a milling chamber from the throat 29 provided in the outer circumference of the milling table 27, and are blown up while dried. The blown-up grains are primary-classified according to weight, so that rough coal grains drop down and return to the milling portion 21.
Small coal grains which have reached the classifying portion 22 are classified (secondary-classified) into pulverized coal not larger than a predetermined grain size and roughly-powdered coal larger than the predetermined grain size by the stationary classifier 30 and the rotary classifier 31. The roughly-powdered coal drops along the inner wall of the recovery cone 33 so that the roughly-powdered coal will be milled again. On the other hand, a mixed fluid 46 of pulverized coal not larger than the predetermined grain size and primary air is fed into the distributing chamber 47. In the distributing chamber 47, the mixed fluid 46 is distributed into the coal feeding pipes 43 and conveyed to the pulverized coal nozzles 8 through the coal feeding pipes 43 respectively.
Incidentally, a small number of coal feeding pipes (e.g. about 1-4 pipes) may be connected to the mill so that each of the coal feeding pipes branches halfway and leads to two or more burners. The description “coal feeding pipes connected for one milling means” in Claim 1 includes such a form.
Fine-powdered coal flowmeters 51 are attached to intermediate portions of the coal feeding pipes 43 respectively. The configuration and measuring theory of each pulverized coal flowmeter 51 will be described below.
The pulverized coal flowmeter 51 used in this embodiment is classified into a microwave type flowmeter and an electrostatic charge type flowmeter.
Although the transmitter 52 transmits microwaves to the receiver 53, the resonance frequency of the coal feeding pipe 43 (microwave resonance pipe) varies according to dielectric constant ∈r in the inside of the pipe. The dielectric constant ∈r of air is 1 whereas the dielectric constant ∈r of coal is about 4. Frequency characteristic in the case where the coal feeding pipe 43 is empty and frequency characteristic in the case where the mixed fluid 46 of pulverized coal and primary air flows in the coal feeding pipe 43 can be measured based on the difference between the dielectric constants, so that the flow rate of pulverized coal flowing in the coal feeding pipe 43 can be calculated based on the difference between resonance frequencies.
As shown in
First, a concentration ρ of pulverized coal passing through the coal feeding pipe 43 is obtained by the charge sensors 54a and 54b. Then, a passage time τ of pulverized coal from the first charge sensor 54a to the second charge sensor 54b is obtained. The passage time τ can be measured based on a time difference between a fluctuating phenomenon (specific waveform portion) detected when pulverized coal passes through the first charge sensor 54a and a fluctuating phenomenon (the same specific waveform portion) detected when pulverized coal passes through the second charge sensor 54b. Then, the flow velocity V of pulverized coal is calculated based on the relational expression V=L/τ. Then, the flow rate Q of pulverized coal can be calculated based on the relational expression Q=ρ×V×S in which ρ is the concentration of pulverized coal, V is the flow velocity of pulverized coal, and S is the flow sectional area of the coal feeding pipe 43.
Incidentally, as shown in
The flow rate of pulverized coal distributed from the mill to each burner always varies according to the amount of coal supplied to the mill, the deviation on distribution, etc. Incidentally, in the background art, the amount of air supplied to each burner and each downstream-side AAP could not be controlled in real time because there was no means for measuring the flow rate of pulverized coal directly. Therefore, it was necessary to supply excessive air to the furnace combustion region as a whole for complete combustion of unburned parts such as CO, so that it was impossible to obtain combustion at a low excess air ratio as described above.
When the pulverized coal flowmeter 51 is used, the flow rate of pulverized coal distributed from the mill to each burner can be measured accurately. Accordingly, the amount of air supplied to each burner and each AAP can be adjusted/controlled precisely in accordance with the measured flow rate of pulverized coal, so that combustion can be made at an air ratio as close to the theoretical air ratio of 1.0 as possible, that is, at a low excess air ratio.
In this embodiment, for example, four pulverized coal burners 61a to 61d are disposed in vessel front of the pulverized coal burning boiler 9 while four pulverized coal burners 61e to 61h are disposed in vessel back thereof so as to be opposite to the four pulverized coal burners 61a and 61d respectively. Two mills 3 are disposed in vessel front and in vessel back, respectively. Four coal feeding pipes 43a to 43d extended from the vessel front mill 3a are connected to the pulverized coal burners 61a to 61d respectively while four coal feeding pipes 43e to 43h extended from the vessel back mill 3b are connected to the pulverized coal burners 61e to 61h respectively.
Pulverized coal flowmeters 51a to 51h are attached to the coal feeding pipes 43a to 43h respectively so that the flow rates of pulverized coal passing through the coal feeding pipes 43 can be measured individually.
Although this embodiment has been described in the case where the combustion air 62 is supplied to the outer circumference of the pulverized coal nozzle 8, the invention is not limited thereto as long as the combustion air 62 can be supplied so that pulverized coal jetted from the pulverized coal nozzle 8 into the furnace can be burned.
In this graph, 0% deviation means detection of pulverized coal at the average flow rate (X/4 in this example). This example shows that pulverized coal at flow rates lower than the average flow rate is conveyed to the coal feeding pipes 43a and 43b while pulverized coal at flow rates higher than the average flow rate is conveyed to the coal feeding pipes 43c and 43d. For example, the deviation of the measured value is caused by a pressure loss difference based on the pipe length difference between the coal feeding pipes 43, the structure of the mill, etc. It is confirmed that the deviation varies according to the operating condition of the mill such as the rotational velocity of the rotary classifier.
In this embodiment, a deviation state of the flow rate of pulverized coal conveyed by each coal feeding pipe 43 is detected, the amount of supplied combustion air corresponding to the amount of supplied pulverized coal is calculated based on the deviation individually for each burner so that the air ratio set by the burner air ratio setting means can be kept, and a control signal is transmitted to each combustion air supply amount adjusting means 64 to thereby adjust the amount of combustion air supplied to each burner 61 individually.
A left half of
On the other hand, combustion air supply amount adjusting means 64a and 64b and air flowmeters 67a and 67b are attached individually to intermediate portions of combustion air supply paths 63a and 63b provided correspondingly to the burners 61a and 61b respectively. Measured values of the amounts of air supplied to the burners 61a and 61b and measured individually by the air flowmeters 67a and 67b are also input to the control circuit 66. There is a mechanism that the control circuit 66 outputs combustion air supply amount control signals 68a and 68b to the combustion air supply amount adjusting means 64a and 64b individually.
A supplied coal amount 71, a burner air ratio 72, a theoretical air amount 73, combustion air amounts 74a and 74b for the respective burners, etc. are input to the control circuit 66 in advance. In this embodiment, the burner air ratio 72 is set at 0.8 and the AAP air ratio is set at 0.3. Accordingly, the air ratio of the whole boiler is a low excess air ratio of 1.1.
Combustion air supply amounts corresponding to the pulverized coal supply amounts are calculated and output as combustion air amount command values 68a and 68b based on the various set values and the deviation values of the pulverized coal amounts in the respective coal feeding pipes 43a and 43b so that the aforementioned burner air ratio can be kept. Various multipliers 76, subtracters 77, etc. in the control circuit 66 are used as means for calculating the command values 68a and 68b. Limiting items of correction amount limiters 75a and 75b provided on the output end side of the control circuit 66 are upper and lower limits of absolute values, change widths, and change ratios.
When the combustion air supply amounts corresponding to the pulverized coal supply amounts in the respective coal feeding pipes are controlled individually as described above, a CO reducing effect is large in combustion at a low excess air ratio.
As shown in
The amount of CO produced when pulverized coal (fuel) was equally distributed to burners in each burner stage was measured and regarded as a reference value (1.00) (see left columns in
Then, the pulverized coal flowmeters 51 were attached to the coal feeding pipes 43 connected to the burners 61 respectively and the combustion air amount was adjusted as described in the first embodiment. Results thereof were shown in right columns in
Therefore, this embodiment is configured so that the pulverized coal flowmeters 51, the control circuit 66, etc. are not attached to the lower stage but the pulverized coal flowmeters 51, the control circuit 66, etc. are attached to the upper and middle stages having a CO reducing effect, especially, to at least the upper stage to adjust the combustion air amount.
Although this embodiment has been described in the case where whether the pulverized coal flowmeters 51 and the control circuit 66 are attached or not is determined in accordance with each burner stage, the magnitudes of the CO reducing effect in all burners may be grasped in advance by an experiment or the like so that the pulverized coal flowmeters 51 and the control circuit 66 can be selectively attached to burners having a CO reducing effect.
Therefore, this embodiment is configured so that the flow rate of primary air is calculated and the amount of supplied combustion air 62 is adjusted in consideration of the flow rate of primary air, for example, by means of reducing the amount of supplied combustion air 62 when the flow rate of primary air is high. Incidentally, calculation of the flow rate of primary air and adjustment of the amount of supplied combustion air 62 based on the calculation result are performed by the control circuit 66.
This embodiment is particularly effective for a coal type such as subbituminous coal low in theoretical air amount because the rate of the amount of primary air in the coal type is higher than that in another coal type such as bituminous coal. The theoretical air amount of bituminous coal is 7.0 m3N/kg whereas the theoretical air amount of subbituminous coal is 5.5 m3N/kg which is small.
In this embodiment, as shown in
A burner combustion air amount adjustable range in each of the pulverized coal burners 61a to 61h is limited in advance from view of burner design. In this embodiment, the adjustable range is limited to 10% of the rating burner combustion air amount.
For example, when the air amount needs to increase by 13% of the rating air amount as a result of calculation based on the output of the pulverized coal flowmeter 51c shown in
The amount of AAP air needs to cover the remaining 10%. The CO reducing effect in the case where the amount of air supplied to the vessel-front AAP 65c just above the pulverized coal burner 61c was increased by 10% and the CO reducing effect in the case where the amount of air supplied to the vessel-back AAP 65g on the side opposite to the pulverized coal burner 61c was increased by 10% were examined. When the amount of air supplied to the vessel-front AAP 65c was increased, there was little effect (see the left of the lower stage in
In this embodiment, the number of AAPs 65 is larger than the number of pulverized coal burners 61, so that each pulverized coal burner 61 is disposed just below a midpoint between two AAPs 65. For example, when the amount of air supplied to the vessel-front pulverized coal burner 61b is increased, the amount of air supplied to the vessel-back AAPs 65g and 65h substantially opposite to the pulverized coal burner 61b, that is, nearest to flame formed by the pulverized coal burner 61b is increased while divided into two equal parts for the vessel-back AAPs 65g and 65h. Configuration is made so that when the amount of air supplied to the vessel-front pulverized coal burner 61c is increased, air is increased while divided into two equal parts for the vessel-back AAPs 65h and 65i substantially opposite to the pulverized coal burner 61c.
A plurality of detection ends 81 (four in this embodiment) of the oxygen densitometer 80 are disposed in a widthwise direction X (see
In this embodiment, the total amount of AAP air supplied to all the AAPs 65 is determined to be constant. For example, when the concentration of oxygen measured at the measuring point ⊚ is lower than that measured at any other measuring point or when the concentration of CO measured at the measuring point ⊚ is higher than that measured at any other measuring point, a command signal is output from the control portion to increase the amount of AAP air on the vessel front and vessel left side.
Although this embodiment has been described in the case where the total amount of AAP air supplied to all the AAPs 65 is determined to be constant and then the amounts of AAP air supplied to the AAPs 65 respectively are determined, the total amount of AAP air may be not determined to be constant so that the amount of air supplied to an AAP corresponding to the region where a low oxygen concentration or a high CO concentration is detected can be increased simply. Accordingly, in this case, the total amount of AAP air is increased by the amount.
According to these embodiments, the amount of AAP air can be accurately distributed to a region high in unburned gas concentration.
Incidentally, also in the fifth and sixth embodiments, the amount of burner combustion air is adjusted in accordance with the flow rate of pulverized coal but the amount of air not covered is supplemented as AAP air.
Therefore, this embodiment is configured so that the coal supply amount data 85 is multiplied by a correction coefficient in consideration of the staying time in the mill so that the corrected coal supply amount data 85 is output to the pulverized coal flowmeter 51 (control circuit 66).
According to this embodiment, the detection accuracy of the pulverized coal flowmeter 51 can be improved. This embodiment is suitable for a system in which the absolute amounts of pulverized coal passing through the respective coal feeding pipes 43 are measured by the pulverized coal flowmeters 51 so that deviations between the respective coal feeding pipes 43 are calculated based on the absolute amounts.
Therefore, in this embodiment, as shown in
The percentage C of moisture contained in raw coal varies according to the coal type. The percentage C of moisture according to the coal type can be stored in a storage portion (not shown) of the control circuit 66 in advance by analysis or the like. The amount Q of coal supplied to the mill 3 can be obtained based on the rotational speed of the coal supply 7. The flow rate A of primary air A1 supplied to the mill 3 can be obtained based on the rotational speed of the forcing blower 1.
The estimated value of the amount of evaporation of moisture in coal milled in the mill 3 is calculated based on these data in accordance with the following relational expression:
Moisture Evaporation Amount Estimated Value=f(C,Q,A,ΔT)
in which f is a correction coefficient.
The percentage of moisture contained in pulverized coal passing through the pulverized coal flowmeter 51 is estimated based on the thus calculated estimated value of the moisture evaporation amount to thereby correct the output of the pulverized coal flowmeter 51 so that detection accuracy can be improved.
In this embodiment, fluid guiding means 88 made of an abrasion-resistant material or coated with an abrasion-resistant material is disposed on an upstream side of the pulverized coal flowmeter 51 in order to improve accuracy of the pulverized coal flowmeter 51 and prevent abrasion due to pulverized coal. Specifically as shown in
When the group of pulverized coal flows in the coal feeding pipe 43, pulverized coal is not distributed substantially equally in the pipe but becomes in most cases a flow condensed like an irregularly bent string. The uneven flow has a bad influence on detection accuracy of the pulverized coal flowmeter 51.
In this embodiment, a microwave type pulverized coal flowmeter 51a having a transmitter 52 and a receiver 53 is disposed in an intermediate portion of the coal feeding pipe 43. Because the transmitter 52 and the receiver 53 are inserted into the coal feeding pipe 43, the transmitter 52 and the receiver 53 are worn out by collision with pulverized coal.
Therefore, in this embodiment, the turning plate 90 is raised as shown in
Moreover, the concentration of pulverized coal flowing on the transmitter 52 side and on the receiver 53 side is reduced by the turning plate 90 so as not to hinder measurement to thereby suppress abrasion of the transmitter 52 and the receiver 53.
As shown in
Pulverized coal in the mixed fluid 46 conveyed by the coal feeding pipe 43 is collected to the central portion side of the coal feeding pipe 43 by the reduced diameter portion 92 or the trumpet-shaped member 94. Accordingly, the amount of pulverized coal passing through the inner circumferential surface side of the charge sensors 54a and 54b is reduced so that abrasion of the charge sensors 54a and 54b due to pulverized coal can be suppressed.
In this embodiment, the first reheater system 103 has a primary reheater inlet header 105a, a primary reheater 106a, a primary reheater outlet header 107a, a secondary reheater inlet header 108a, a secondary reheater 109a, and a secondary reheater outlet header 110a. The second reheater system 104 has a primary reheater inlet header 105b, a primary reheater 106b, a primary reheater outlet header 107b, a secondary reheater inlet header 108b, a secondary reheater 109b, and a secondary reheater outlet header 110b.
In this embodiment, a first reheating steam distributing valve 111 and a second reheating steam distributing valve 112 are disposed on the inlet side of the first reheater system 103 and the second reheater system 104. A first reheater steam thermometer 113 and a second reheater steam thermometer 114 are disposed on the outlet side of the first reheater system 103 and the second reheater system 104.
Steam supplied from a high-pressure turbine (not shown) is forked into two flow paths via one reheater spray 115. The forked steam is heated while passing through the first and second reheater systems 103 and 104 from the first and second reheating steam distributing valves 111 and 112 respectively, so that the reheated steam is fed from the secondary reheater outlet headers 110a and 110b to middle/low-pressure turbines.
Although this embodiment is configured so that the distributing valves 111 and 112 are provided in the first and second reheater systems 103 and 104 respectively to thereby adjust the flow rates of distributed steam, a distributing valve may be provided in one reheater system so that the flow rates of steam distributed to the first and second reheater systems can be adjusted by operation of the distributing valves.
A method of adjusting apertures of the distributing valves 111 and 112 will be described below. First, the reheater outlet steam temperatures 116 and 117 of vessel left and right, that is, of the first and second reheater systems 103 and 104 are measured by the reheater steam thermometers 113 and 114, so that the measured signals are input to a subtracter 118 to obtain a deviation value 119. The signal of the deviation value 119 is input to a PI controller 120, so that aperture adjusting signals 121 and 122 for eliminating the deviation value 119 are output from the PI controller 120 to the distributing valves 111 and 112 respectively. On this occasion, an operation reverse in phase to the distributing valve 111 is performed on the distributing valve 112 through an inverter (“−1”) 123.
As shown in
Although the example has been described in the case where both the apertures of the distributing valves 111 and 112 are adjusted, the same effect can be expected in the case where only the aperture of the distributing valve (e.g. distributing valve 112) on an ROT reduced side, that is, on a side required to reduce the flow rate of distributed steam is throttled.
Although the embodiment has been described in the case where the distributing valves 111 and 112 are disposed on the inlet side of the first and second reheater systems 103 and 104 respectively, a resistor such as an orifice may be provided in place of one distributing valve (e.g. distributing valve 111) so that the flow rates of steam distributed to the first and second reheater systems 103 and 104 can be adjusted when only the aperture of the other distributing valve (e.g. distributing valve 112) is adjusted.
Because ROTs of the first and second reheater systems 103 and 104 are averaged when the maximum temperature limit of ROT is a reference steam condition plus 8° C. or lower, there is a function of keeping tolerance at 8° C. Accordingly, the number of times for starting the reheater spray 115 can be reduced against disturbance due to the load change in the combustion device, stopping of the mill, the start of a soot blower, etc., so that improvement in boiler efficiency and improvement in life of the reheater spray 115 can be attained.
An attempt to reduce the excess air ratio to about 10% has been made in order to attain further reduction of NOx and improvement of boiler efficiency in recent years. In the excess air ratio of 10%, there is a possibility that CO will be produced because of local shortage of air even when the amounts of pulverized coal supplied to the burners are slightly uneven. To cope with this, a method of individually measuring the amounts of pulverized coal supplied to the respective burners to thereby dynamically adjust combustion air supplied to the respective burners, that is, individual burner air ratio control has been proposed in the first to tenth embodiments, etc.
In a pulverized coal burning boiler using the individual burner air ratio control, there is a possibility that the deviation between combustion gas temperatures in vessel left and right may become large compared with a pulverized coal burning boiler in which combustion air is equally supplied to the respective burners. In the background art, because air was equally supplied to the vessel left and right, imperfect combustion due to shortage of air occurred in a place where much pulverized coal was supplied so that the deviation between thermal loads in the vessel left and right was suppressed compared with the deviation between the amounts of pulverized coal. However, when just enough air is given to pulverized coal supplied to the vessel left and right with a deviation as in the individual burner air ratio control, the deviation between the amounts of supplied pulverized coal appears directly as a deviation between thermal loads in the vessel left and right.
For example, assume that pulverized coal 15% larger than the average value of the supply amounts is supplied to the vessel right side, that is, pulverized coal 15% smaller than the average value is supplied to the vessel left side in a pulverized coal burning boiler operated at an excess air ratio of 10%. On the other hand, because air is equally supplied to all after air ports, the deviation between the amounts of pulverized coal supplied to the vessel left and right exceeds supplied air tolerance to cause imperfect combustion. For this reason, though fuel (pulverized coal) 15% larger is supplied to the vessel right side, increase in thermal load is reduced to 10%. However, in the pulverized coal burning boiler using the individual burner air ratio control, because air just fit to the deviation between the amounts of supplied pulverized coal is supplied, 15% increase in thermal load equal to the deviation between the amounts of supplied pulverized coal appears in the aforementioned example. The increase in thermal load has a direct influence on the amount of heat exchange in a heat exchanger to bring a deviation between steam temperatures. This embodiment aims at this respect.
In the pulverized coal burning boiler, the deviation between the amounts of pulverized coal supplied to the respective burners appears as a deviation between ROTs with a time lag as described above. This is because a heat exchanger having a large number of heat-transfer pipes has a response delay corresponding to change in gas temperature caused by its metal heat capacity. The time constant sometimes reaches tens of seconds to several minutes.
In this embodiment, like the first embodiment etc., the supply amounts of combustion air corresponding to the supply amounts of pulverized coal are calculated based on the flow rates of pulverized coal measured by the pulverized coal flowmeters 51a to 51h and the supply amounts of combustion air measured by the air flowmeters 67a to 67h and control command signals are sent to combustion air supply amount adjusting means 64a to 64h so that the burner air ratio set by the burner air ratio setting means can be kept.
As shown in
The flows of exhaust gas produced by combustion in the respective pulverized coal burners 61a to 61h are substantially directly poured into flues without large disorder and give heat to the repeater 100.
Accordingly, in this embodiment, from the relation between
In this embodiment, in addition to the aforementioned combustion air supply amount individual control, measured values of the flow rates of pulverized coal from the pulverized coal flowmeters 51a to 51h are input to a vessel left/right fuel supply amount calculator 124 as shown in
A vessel left/right fuel supply amount calculated value 125 calculated thus is input to a bias calculator 126. The bias calculator 126 obtains a deviation between the flow rate of pulverized coal supplied to the vessel left side pulverized coal burners 61c, 61d, 61g and 61h and the flow rate of pulverized coal supplied to the vessel right side pulverized coal burners 61a, 61b, 61e and 61f and calculates bias values 127 and 128 for the aperture adjusting signals 121 and 122 as the PI feedback control signals based on the pulverized coal flow rate deviation value. Incidentally, optimum patterns for the size of the bias (the shape of the feed-forward component) are obtained by dynamic characteristic calculation in advance and the patterns are adjusted at the time of trial operation.
The calculated bias values 127 and 128 are added to the aperture adjusting signals 121 and 122 by adders 129 and 130 respectively to obtain aperture adjusting signals 131 and 131 in consideration of deviations of the flow rate of pulverized coal to thereby adjust the apertures of the distributing valves 111 and 112.
As shown in
According to the twelfth embodiment, there is a possibility that the feed-forward component may be so intensive that the temperature reduction is too large or too small in accordance with the occasion because the feed-forward component has a substantially fixed shape.
For example, as shown in
This embodiment is accomplished in consideration of this respect.
In this embodiment, various kinds of reheating steam temperature deviation prediction models 133 for predicting reheating steam temperature deviations based on pieces of information exerting influence on the reheating steam temperature, such as the amount of supplied fuel, the flow rate of boiler supplied water, the amount of superheater inlet spray, the output of a power generator, etc. are prepared so that the reheating steam temperature deviation prediction models 133 are stored in a storage portion (not shown) of reheating steam temperature deviation prediction means 134.
The amount of supplied fuel 135, the flow rate of boiler supplied water 136, the amount of superheater inlet spray 137 and the power generator output 138 in the pulverized coal burning boiler currently operating are input to the reheating steam temperature deviation prediction means 134, so that a predicted reheating steam temperature deviation value 139 is obtained by referring to these input values and the reheating steam temperature deviation prediction models 133.
The predicted reheating steam temperature deviation value 139 is input to reheating steam distributing valve aperture correction means 140. The reheating steam distributing valve aperture correction means 140 generates distributing valve aperture correction signals 141 and 142 based on the predicted reheating steam temperature deviation value 139. The distributing valve aperture correction signals 141 and 142 are added to the aperture adjusting signals 121 and 122 by adders 143 and 144 respectively, so that the apertures of the reheating steam distributing valves 111 and 112 are adjusted based on the corrected aperture adjusting signals 145 and 146 respectively.
In this embodiment, the apertures of the distributing valves 104a and 104b are adjusted at time D (as represented by the hatched portion in
In a superheater, when a bias between the vessel left and right is applied to the input amount of superheater spray, the deviation between the vessel left and right superheating steam temperatures can be reduced. However, when the deviation between the vessel left and right superheating steam temperatures is high, it is necessary to increase the flow rate of spray because tolerance of steam temperature control as the original purpose of the superheater spray is reduced, and control follow-up characteristic is worsened because spray control is complicated. As a result, increase in the flow rate of spray means increase in the amount of bypassing the heat-transfer surface halfway, so that boiler efficiency is lowered.
In this embodiment, the flow rates of steam in the vessel left and right of the superheater are adjusted to eliminate the deviation between the vessel left and right main steam temperatures.
A superheater 200 disposed from an upper portion of a furnace into a flue on a downstream side in an exhaust gas flow direction thereof includes a primary superheater portion 201 and a secondary superheater portion 202 from view of arrangement and configuration of members. The superheater 200 includes a first superheater system 204 on the vessel left side and a second superheater system 205 on the vessel right side from view of steam flow path systems. The first superheater system 204 and the second superheater system 205 are arranged side by side.
In this embodiment, the first superheater system 204 has a primary superheater inlet header 206a, a primary superheater 207a, a primary superheater outlet header 208a, a secondary superheater inlet header 209a, a secondary superheater 210a, a secondary superheater outlet header 211a, a tertiary superheater inlet header 212a, a tertiary superheater 213a, and a tertiary superheater outlet header 214a. The second superheater system 205 has a primary superheater inlet header 206b, a primary superheater 207b, a primary superheater outlet header 208b, a secondary superheater inlet header 209b, a secondary superheater 210b, a secondary superheater outlet header 211b, a tertiary superheater inlet header 212b, a tertiary superheater 213b, and a tertiary superheater outlet header 214b.
In this embodiment, a first superheating steam distributing valve 215 and a second superheating steam distributing valve 216 are disposed on the inlet side of the first superheater system 204 and the second superheater system 205. A first superheater steam thermometer 217 and a second superheater steam thermometer 218 are disposed on the outlet side of the first superheater system 204 and the second superheater system 205.
In the first superheater system 204, a secondary superheater inlet spray 219a is attached to a connection pipe which connects the primary superheater outlet header 208a and the secondary superheater inlet header 209a. A tertiary superheater inlet spray 220a is attached to a connection pipe which connects the secondary superheater outlet header 211a and the tertiary superheater inlet header 212a. In the second superheater system 205, a secondary superheater inlet spray 219b is attached to a connection pipe which connects the primary superheater outlet header 208b and the secondary superheater inlet header 209b. A tertiary superheater inlet spray 220b is attached to a connection pipe which connects the secondary superheater outlet header 211b and the tertiary superheater inlet header 212b.
Steam supplied from a cage (not shown) is forked into two flow paths via outlet headers 221a and 221b. The forked steam is superheated while passing through the first and second superheater systems 204 and 205 from the first and second superheating steam distributing valves 215 and 216 respectively, so that the superheated steam is fed from the tertiary superheater outlet headers 214a and 214b to high-pressure turbines.
A method of adjusting the apertures of the distributing valves 215 and 216 will be described below. First, superheater outlet steam temperatures 222 and 223 of vessel left and right, that is, of the first and second superheater systems 204 and 205 are measured by the superheater steam thermometers 217 and 218, so that the measured signals are input to a subtracter 224 to obtain a deviation value 225. The signal of the deviation value 225 is input to a PI controller 226, so that aperture adjusting signals 227 and 228 for eliminating the deviation value 225 are output from the PI controller 226 to the distributing valves 215 and 216 respectively. On this occasion, an operation reverse in phase to the distributing valve 215 is performed on the distributing valve 216 through an inverter (“−1”) 229.
When a deviation is generated between the amounts of fuel supplied to the burners for a certain reason, a deviation is lately generated between superheater outlet steam temperatures (SOTs) 222 and 223 of the first and second superheater systems 204 and 205. This deviation is detected by the superheater steam thermometers 217 and 218 to perform an operation of opening the aperture of the distributing valve (e.g. distributing valve 215) of a system high in SOT based on the aperture adjusting signal 227 and contrariwise throttling the aperture of the distributing valve (e.g. distributing valve 216) of a system low in SOT based on the aperture adjusting signal 228. Accordingly, the flow rate of steam distributed to the system high in SOT, that is, having an increased thermal load increases and the flow rate of steam distributed to the system low in SOT, that is, having a decreased thermal load decreases, so that the deviation between SOTs of the first and second superheater systems 204 and 205 is eliminated.
Although
As shown in
A vessel left/right fuel supply amount calculated value 231 calculated thus is input to a bias calculator 232. The bias calculator 232 obtains a deviation between the flow rate of pulverized coal supplied to the vessel left side pulverized coal burners 61c, 61d, 61g and 61h and the flow rate of pulverized coal supplied to the vessel right side pulverized coal burners 61a, 61b, 61e and 61f and calculates bias values 233 and 234 for the aperture adjusting signals 227 and 228 as the PI feedback control signals based on the pulverized coal flow rate deviation value. Incidentally, optimum patterns for the size of the bias (the shape of the feed-forward component) are obtained by dynamic characteristic calculation in advance and the patterns are adjusted at the time of trial operation.
The calculated bias values 233 and 234 are added to the aperture adjusting signals 227 and 228 by adders 235 and 236 respectively to obtain aperture adjusting signals 237 and 238 in consideration of deviations of the flow rate of pulverized coal to thereby adjust the apertures of the distributing valves 215 and 216.
Although
In this embodiment, various kinds of superheating steam temperature deviation prediction models 240 for predicting superheating steam temperature deviations based on pieces of information exerting influence on the superheating steam temperature, such as the amount of supplied fuel, the flow rate of boiler supplied water, the amount of superheater inlet spray, the power generator output, etc. are prepared so that the superheating steam temperature deviation prediction models 240 are stored in a storage portion (not shown) of superheating steam temperature deviation prediction means 241.
The amount of supplied fuel 242, the flow rate of boiler supplied water 243, the amount of superheater inlet spray 244 and the power generator output 245 in the pulverized coal burning boiler currently operating are input to the superheating steam temperature deviation prediction means 241, so that a predicted superheating steam temperature deviation value 246 is obtained by referring to these input values and the superheating steam temperature deviation prediction models 240.
The predicted superheating steam temperature deviation value 246 is input to superheating steam distributing valve aperture correction means 247. The superheating steam distributing valve aperture correction means 247 generates distributing valve aperture correction signals 248 and 249 based on the predicted superheating steam temperature deviation value 246. The distributing valve aperture correction signals 248 and 249 are added to the aperture adjusting signals 227 and 228 by adders 250 and 251 respectively, so that the apertures of the superheating steam distributing valves 215 and 216 are adjusted based on corrected aperture adjusting signals 252 and 253 respectively.
Although
Although the embodiment has been described in the case where steam distributing valve control for reheater systems and steam distributing valve control for superheater systems are performed separately, steam distributing valve control for reheater systems and superheater systems can be performed in only one pulverized coal burning boiler.
Specific effects of the invention are as follows.
(1) With respect to the problem that the deviation between reheater vessel left and right steam temperatures cannot be eliminated thoroughly by the background-art method of exchanging reheater vessel left and right systems, the effect of reducing the steam temperature deviation to zero is obtained according to this invention because the flow rates of steam are adjusted while the deviation between the reheater vessel left and right steam temperatures is viewed.
(2) With respect to the problem that response is delayed due to the influence of interference and the operating velocity of a gas damper in the background-art method using the gas damper for adjusting the deviation between reheater vessel left and right steam temperatures, the effect of quickening the response characteristic is obtained according to this invention because adjustment of the flow rates of steam supplied to the reheater vessel left and right does not interfere with the superheater and the flow rates of steam supplied to the superheater vessel left and right does not likewise interfere with the reheater.
(3) With respect to the problem that lowering of efficiency due to bypassing, increase in the heat-transfer surface and sudden increase in temperature in the bypassed heat-transfer surface occur in the background-art method in which a connection pipe for connecting the inlet and outlet of the primary reheater is provided to adjust the flow rates of steam in the vessel left and right systems, the problem of lowering of efficiency, increase in the heat-transfer surface and sudden increase in temperature of the bypassed heat-transfer surface does not occur in this invention because bypassing can be avoided when the balance between the flow rates of steam supplied to the repeater vessel left and right is changed.
(4) With respect to the problem that the deviation between superheater vessel left and right steam temperatures cannot be eliminated thoroughly by the background-art method of exchanging superheater vessel left and right systems, the effect of reducing the steam temperature deviation to zero is obtained according to this invention because the flow rates of steam are adjusted while the deviation between the superheater vessel left and right steam temperatures is viewed.
With respect to the problem that the flow rate of spray increases in the background-art method of applying a bias to the flow rate of superheating spray between the vessel left and right, the effect of reducing the flow rate of spray is obtained according to this invention because the deviation between the superheater vessel left and right steam temperatures is adjusted only based on the flow rate of steam led into the superheater so that the spray is used only for adjusting the temperature of superheating steam.
1: forcing blower, 2: primary air forcing blower, 3: vertical roller mill, 4: exhaust gas type air preheater, 5: raw coal, 6: coal banker, 7: coal supply, 8: pulverized coal nozzle, 9: pulverized coal burning boiler, 10: steam type air preheater, 11: wind box, 12: dust collector, 13: denitrater, 14: induced blower, 15: desulfurizer, 21: milling portion, 22: classifying portion, 23: milling portion driving portion, 24: classifying portion driving portion, 25: distributing portion, 43: coal feeding pipe, 44: coal supply pipe, 45: primary air, 46: mixed fluid, 47: distributing chamber, 51: pulverized coal flowmeter, 51a: microwave type pulverized coal flowmeter, 51b: electrostatic charge type pulverized coal flowmeter, 52: microwave transmitter, 53: microwave receiver, 54a: first charge sensor, 54b: second charge sensor, 61: pulverized coal burner, 62: combustion air, 63: combustion air supply path, 64: combustion air supply amount adjusting means, 65: AAP, 66: control circuit, 67: air flowmeter, 68: combustion air amount control command value, 69: adder, 70: divider, 71: coal supply amount, 72: burner air ratio, 73: theoretical air amount, 74: combustion air amount, 75: correction amount limiter, 76: multiplier, 77: subtracter, 78: furnace, 79: economizer, 80: oxygen concentration measuring meter, 81: detection end, 82: flue, 83: AAP air, 84: supply amount adjuster, 85: coal supply amount data, 86: mill inlet thermometer, 87: mill outlet thermometer, 88: fluid guiding means, 89: separation plate, 90: turning plate, 91: turning shaft, 92: reduced-diameter portion, 93: taper face, 94: trumpet-shaped member, A: air, A1: primary air, A2: secondary air.
100: reheater, 101: primary reheater portion, 102: secondary reheater portion, 103: first reheater system, 104: second reheater system, 105: primary reheater inlet header, 106: primary reheater, 107: primary reheater outlet header, 108: secondary reheater inlet header, 109: secondary reheater, 110: secondary reheater outlet header, 111: first reheating steam distributing valve, 112: second reheating steam distributing valve, 113: first reheating steam thermometer, 114: second reheating steam thermometer, 115: reheater spray, 116: first reheater outlet steam temperature, 117: second reheater outlet steam temperature, 118: subtracter, 119: deviation value, 120: PI controller, 121, 122: aperture adjusting signal, 123: inverter, 124: vessel left/right fuel supply amount calculator, 125: vessel left/right fuel supply amount calculated value, 126: bias calculator, 127, 128: bias calculated value, 129, 130: adder, 131, 132: aperture adjusting signal, 133: reheating steam temperature deviation prediction model, 134: reheating steam temperature deviation prediction means, 135: fuel supply amount, 136, boiler water supply amount, 137: superheater inlet spray amount, 138: power generator output, 139: predictive reheating steam deviation value, 140: reheating steam distributing valve aperture correction means, 141, 142: distributing valve aperture correction signal, 143, 144: adder, 200: superheater, 201: primary superheater portion, 202: secondary superheater portion, 203: tertiary superheater portion, 204: first superheater system, 205: second superheater system, 206: primary superheater inlet header, 207: primary superheater, 208: primary superheater outlet header, 209: secondary superheader inlet header, 210: secondary superheater, 211: secondary superheater outlet header, 212: tertiary superheater inlet header, 213: tertiary superheater, 214: tertiary superheater outlet header, 215: first superheating steam distributing valve, 216: second superheating steam distributing valve, 217: first superheating steam thermometer, 218: second superheating steam thermometer, 219: secondary superheater inlet spray, 220: tertiary superheater inlet spray, 221: outlet header, 222, 223: superheater outlet steam temperature, 224: subtracter, 225: deviation value, 226: PI controller, 227, 228: aperture adjusting signal, 229: inverter, 230: vessel left/right fuel supply amount calculator, 231: vessel left/right fuel supply amount calculated value, 232: bias calculator, 233, 234: bias calculated value, 235, 236: adder, 237, 238: aperture adjusting signal, 240: superheating steam temperature deviation prediction model, 241: superheating steam temperature deviation prediction means, 242: fuel supply amount, 243: boiler water supply amount, 244: superheater inlet spray amount, 245: power generator output, 246: predictive superheating steam deviation value, 247: superheating steam distributing valve aperture correction means, 248, 249: distributing valve aperture correction signal, 250, 251: adder, 252, 253: aperture adjusting signal.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-105973 | Apr 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/057184 | 4/11/2008 | WO | 00 | 3/25/2010 |
