CN109297045B - System and method for online correction of low-level heating value of coal quality of thermal power plant - Google Patents
System and method for online correction of low-level heating value of coal quality of thermal power plant Download PDFInfo
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- CN109297045B CN109297045B CN201811279273.9A CN201811279273A CN109297045B CN 109297045 B CN109297045 B CN 109297045B CN 201811279273 A CN201811279273 A CN 201811279273A CN 109297045 B CN109297045 B CN 109297045B
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- 239000003245 coal Substances 0.000 title claims abstract description 152
- 238000010438 heat treatment Methods 0.000 title claims abstract description 81
- 238000012937 correction Methods 0.000 title claims abstract description 30
- 238000000034 method Methods 0.000 title claims abstract description 19
- 238000004364 calculation method Methods 0.000 claims description 15
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 230000000087 stabilizing effect Effects 0.000 claims description 3
- 239000000779 smoke Substances 0.000 description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 14
- 238000010521 absorption reaction Methods 0.000 description 9
- 230000009286 beneficial effect Effects 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 238000013461 design Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 1
- 230000017525 heat dissipation Effects 0.000 description 1
- 238000012886 linear function Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000010977 unit operation Methods 0.000 description 1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N5/00—Systems for controlling combustion
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23M—CASINGS, LININGS, WALLS OR DOORS SPECIALLY ADAPTED FOR COMBUSTION CHAMBERS, e.g. FIREBRIDGES; DEVICES FOR DEFLECTING AIR, FLAMES OR COMBUSTION PRODUCTS IN COMBUSTION CHAMBERS; SAFETY ARRANGEMENTS SPECIALLY ADAPTED FOR COMBUSTION APPARATUS; DETAILS OF COMBUSTION CHAMBERS, NOT OTHERWISE PROVIDED FOR
- F23M11/00—Safety arrangements
- F23M11/04—Means for supervising combustion, e.g. windows
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
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Abstract
The invention provides a system and a method for online correction of low-level heating value of coal quality of a thermal power plant, comprising a unit steady-state operation condition judging unit, a low-level heating value online updating unit of coal quality and a DCS (distributed control system) boiler main control system, wherein the DCS boiler main control system is electrically connected with the unit steady-state operation condition judging unit and the low-level heating value online updating unit of coal quality; the unit steady-state operation condition judging unit is used for outputting a unit steady-state operation condition judging signal, outputting the unit steady-state operation condition judging signal to a DCS boiler main control system of the DCS boiler main control system, acquiring coal quality low-level heating value according to the received unit steady-state operation condition judging signal, transmitting the acquired coal quality low-level heating value to the coal quality low-level heating value on-line updating unit, and outputting a corrected coal feeding baseline by the coal quality low-level heating value on-line updating unit; can effectively overcome the strong influence of the coal quality and coal variety variability of the large delay and hysteresis coal-fired boiler on the running stability and economy of the unit.
Description
Technical Field
The invention belongs to the field of thermal parameter measurement of boilers of thermal power plants, and particularly relates to a system and a method for online correction of low-level heating value of coal quality of a thermal power plant.
Background
The rich coal, lean oil and low gas resource endowment in China determines that the thermal power takes the dominant position of the power supply structure for a long time. With the continuous development of new energy power, the utilization hours of thermal power are reduced year by year, but the annual energy generation of 2017 thermal power still accounts for more than 70%, and the main reason is that the thermal power has strong controllability, and compared with the large randomness and fluctuation of the new energy power, the thermal power is more beneficial to the safe and stable operation of a power grid. Along with the continuous development of new energy power, the scheduling mode of the power grid at the current stage is faced, the flexibility of thermal power is improved, the flexibility of thermal power unit operation refers to the rapidness and the depth of unit variable load, and the high-flexibility operation brings higher requirements to a machine furnace coordination control system of the unit, so that on one hand, the coordination control is required to meet the requirements of AGC and primary frequency modulation assessment of the power grid, and on the other hand, the coordination system is required to adapt to the large-range variable load working condition of the unit, so that the robustness of the coordination system becomes vital.
Coal quality variation is one of the important factors affecting the robustness of the unit coordination system. At present, most of power plants in China adopt mixed coal blending combustion to reduce the power generation cost and improve the economic benefit, which undoubtedly increases the variation range of coal quality. The principle of the method is that a correction coefficient is generated according to the deviation between the designed coal low-level heating value and the actual coal low-level heating value, and then long integral processing is carried out by multiplying the deviation between the coal supply quantity and the designed coal quantity, wherein the actual coal low-level heating value is generally manually input by an operator and given, and the method has serious hysteresis for a delay-delay coal-fired boiler and is generally only suitable for a unit with little change of the coal low-level heating value.
Disclosure of Invention
The invention aims to provide a system and a method for on-line correction of low-grade heating value of coal quality in a thermal power plant, which solve the problem that a fuel low-grade heating value correction loop arranged in a traditional thermal power unit fuel control system is not suitable for the frequent change of the coal quality low-grade heating value of a delay coal-fired boiler.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides a coal quality low-grade heating value online correction system of a thermal power plant, which comprises a unit steady-state operation condition judging unit, a coal quality low-grade heating value online updating unit and a DCS boiler main control system, wherein the DCS boiler main control system is electrically connected with the unit steady-state operation condition judging unit and the coal quality low-grade heating value online updating unit;
the unit steady-state operation condition judging unit is used for outputting a unit steady-state operation condition judging signal and outputting the unit steady-state operation condition judging signal to the DCS boiler main control system;
the DCS boiler main control system is used for acquiring the low-grade heating value of the coal according to the received unit stable working condition judging signal, transmitting the acquired low-grade heating value of the coal to the on-line updating unit of the low-grade heating value of the coal, and the on-line updating unit of the low-grade heating value of the coal is used for outputting a corrected coal feeding baseline.
Preferably, the input end of the unit steady-state operation condition judging unit is connected with the unit target load, the unit actual power, the pre-unit pressure set value and the main steam pressure feedback value; and the output end DCS boiler main control system of the unit steady-state operation condition judging unit.
Preferably, the unit for judging the steady-state operation condition of the unit comprises a first judging block, a first NOT block, a first delay triggering block, a second judging block, a second NOT block, a second delay triggering block and an AND gate block,
the unit target load and the unit actual power are connected with the input end of a first difference block, the output end of the first difference block is connected with the input end of a first judgment block, the output end of the first judgment block is connected with the input end of a first NOT gate block, the output end of the first NOT gate block is connected with the input end of a first delay trigger block, and the output end of the first delay trigger block is connected with the input end of an AND gate block;
the set value of the pressure before the engine and the feedback value of the main steam pressure are connected with the input end of a second difference block, the output end of the second difference block is connected with the input end of a second judgment block, the output end of the second judgment block is connected with the input end of a second NOT gate block, the output end of the second NOT gate block is connected with the input end of a second delay trigger block, and the output end of the second delay trigger block is connected with the input end of an AND gate block; and the output end of the AND gate block is a DCS boiler main control system.
Preferably, the input end of the coal quality low-grade heating value online updating unit is connected with the coal quality low-grade heating value and the unit load setting after speed limiting, and the output end of the coal quality low-grade heating value online updating unit is a DCS boiler main control system.
Preferably, the coal low-order heating value online updating unit comprises a logic switching block, a division block, an amplitude limiting block, a load coal amount function module and a multiplication block, wherein the coal low-order heating value is connected with the YES end of the input end of the logic switching block, the output end of the input end of the logic switching block is connected with the input end of the division block, the input end of the division block is also connected with a coal low-order heating value set value, the output end of the division block is connected with the input end of the amplitude limiting block, and the output end of the amplitude limiting block is connected with the input end of the multiplication block;
the set load value of the unit after speed limiting is connected with the input end of the load coal quantity function module, the output end of the load coal quantity function module is connected with the input end of the multiplication block, and the output end of the multiplication block is connected with the DCS boiler main control system.
An online correction method for low-level heating value of coal in a thermal power plant is based on an online correction system for low-level heating value of coal in a thermal power plant, and comprises the following steps:
firstly, outputting a unit stable working condition judging signal according to a unit stable working condition judging unit, and outputting the unit stable working condition judging signal to a DCS boiler main control system;
secondly, the DCS boiler main control system acquires the low-grade heating value of the coal according to the received unit stable working condition judging signal, and transmits the acquired low-grade heating value of the coal to the on-line updating unit of the low-grade heating value of the coal;
and finally, outputting a corrected coal feeding baseline by the coal quality low-grade heating value on-line updating unit according to the coal quality low-grade heating value.
Preferably, the specific method for outputting the unit stable working condition judging signal by the unit stable working condition judging unit is as follows:
first, upper and lower limit values of a target load of a unit and a set value of a pressure before the unit are set, wherein,
if the real power value of the unit is smaller than or equal to the set target load upper limit value of the unit and larger than the set target load lower limit value of the unit, the logic signal output by the first judging block is 0;
if the real power value of the unit is larger than the set target load upper limit value of the unit or smaller than the set target load lower limit value of the unit, the logic signal output by the first judging block is 1;
if the main steam pressure feedback value is smaller than or equal to the set upper limit value of the set front pressure set value and larger than the set lower limit value of the set front pressure set value, the logic signal output by the second judging block is 0;
if the main steam pressure feedback value is larger than the set upper limit value of the set front pressure set value or smaller than the set lower limit value of the set front pressure set value, the logic signal output by the second judging block is 1;
then, the NOT gate block inverts the accessed switching value signal and accesses the output switching value signal to the delay trigger block;
then, the delay triggering module performs delay triggering on the input switching value signal, wherein when the input switching value signal is changed from the switching value 1 to 0, the switching value 0 is directly output without delay; when the input switching value signal is changed from the switching value 0 to 1, outputting the switching value 1 after the set delay time T;
finally, when the light quantity signals output by the first delay trigger block and the second delay trigger block received by the AND gate block are 1, the light quantity signal output by the AND gate block is 1, so that the running condition of the unit is illustrated to be in a steady state; otherwise, the ON-light quantity signal output by the AND gate block is 0.
Preferably, the specific method for outputting the corrected coal feeding baseline by the coal quality low-rank heating value on-line updating unit is as follows:
firstly, when an EN end of a logic switching block receives a unit working condition stabilizing signal, taking an analog input signal of a YES end as an output logic signal a of the logic switching block; when the EN end of the editing switching block receives the unstable signal of the working condition of the unit, taking the analog input signal of the NO end as an output logic signal a of the logic switching block;
secondly, inputting the logic signal a and the coal low-order heating value set value into a division block to calculate a quotient, and outputting a logic signal b by the division block;
then, inputting the logic signal b into a limiting block, wherein when the value of the logic signal b is between an upper limit value and a lower limit value, the limiting block outputs the logic signal b; when the value of the logic signal b is larger than the upper limit value, the amplitude limiting block outputs the upper limit value; when the value of the logic signal b is smaller than the lower limit value, the amplitude limiting block outputs the lower limit value;
then, inputting the load set value of the limited unit into a load coal quantity function module for instruction conversion, and outputting a required coal quantity instruction by the load coal quantity function module;
and then, outputting and inputting the output of the limiting block and the output of the load coal quantity function module into the multiplication block to perform product calculation, and finally outputting and correcting the multiplication block and feeding the corrected multiplication block to the coal baseline.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides an online correction for low-grade heating value of coal quality in a thermal power plant, which divides the total heat of a boiler by the coal supply amount to form a real-time calculated value of the low-grade heating value of the coal quality; then judging whether the unit is in a steady-state operation condition according to the real-time operation values of the unit load and the main steam pressure, and updating and forming steady-state coal low-level heating value when the unit is in the steady-state operation condition; and finally, dividing the designed low-grade heating value of the coal quality by the steady-state low-grade heating value of the coal quality to obtain a coal quality correction coefficient, and directly multiplying the coal quality correction coefficient on a main control of the boiler to adjust the total coal feeding amount of the unit, thereby effectively overcoming the strong influence of the coal quality and coal variety change of the delayed and lagged coal-fired boiler on the running stability and economy of the unit.
Drawings
FIG. 1 is a steady state operating condition judgment logic of a unit;
FIG. 2 steady-state coal low-order heating value online updating correction logic.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The invention provides an online correction system for low-level heating value of coal quality of a thermal power plant, which comprises the following components: a unit steady-state operation condition judging unit and a coal quality low-level heating value online updating unit, wherein,
and judging the steady-state operation condition of the unit, wherein the change condition of the load and the pressure in front of the unit can show whether the unit is in the steady-state operation condition or not, so that the unit load and the pressure in front of the unit are used for judging whether the unit is in the steady-state operation condition or not.
For the unit load, when the deviation between the unit actual power and the target load is smaller than a certain range and the deviation between the unit actual power and the target load is still smaller than a certain range after a certain time, the unit load is considered to be in a steady-state working condition;
for the front pressure, when the deviation between the front pressure feedback value and the set value thereof is smaller than a certain range and the deviation between the front pressure feedback value and the set value is still smaller than a certain range after a certain time, the front pressure is considered to be in a steady-state working condition;
when the load and the pressure in front of the machine set are simultaneously in a steady-state working condition, the machine set is considered to enter the steady-state working condition, and the steady-state running state of the machine set is set to be 1.
As shown in fig. 1, the unit for judging the steady-state operation condition of the unit comprises a first difference block, a first judgment block, a first NOT block, a first delay trigger block, a second difference block, a second judgment block, a second NOT block, a second delay trigger block and an AND gate block, wherein the target load of the unit and the real power of the unit are connected to the input end of the first difference block, the output end of the first difference block is connected to the first judgment block, the output end of the first judgment block is connected to the first NOT block, the output end of the first NOT block is connected to the first delay trigger block, and the first delay output end is connected to the input end of the AND gate block;
the set value of the pressure before the engine and the feedback value of the main steam pressure are connected to the input end of a second difference block, the output end of the second difference block is connected to a second judgment block, the output end of the second judgment block is connected to a second NOT gate block, the output end of the second NOT gate block is connected to a second delay trigger block, and the second delay output end is connected to the input end of the AND gate block; and the AND gate block outputs a unit stable working condition judging signal.
As shown in fig. 2, the online updating unit of the low-rank calorific value of coal is mainly used for determining how to update the calculated low-rank calorific value of coal. The low-grade calorific value of the coal is calculated under a steady-state working condition, and all operation parameters of the unit are not matched in time sequence in a dynamic process, so that the calculated low-grade calorific value of the coal cannot reflect the actual operation condition of the current unit, and the low-grade calorific value of the coal can only be updated under the steady-state working condition.
The coal low-order heating value online updating unit comprises a logic switching block, a division block, a limiting block, a load coal amount function module and a multiplication block, wherein the input end YES of the logic switching block is connected with the real-time calculated value of the coal low-order heating value, the NO is connected with the output of the logic switching block, the EN enabling end is connected with the steady-state working condition judgment, and the output end of the logic switching block is simultaneously connected with the input end of the division block; the input end of the division block is connected with the design value of the low-grade calorific value of the coal and the output end of the logic switching block to obtain the correction coefficient of the low-grade calorific value of the coal, and the correction coefficient is sent into the amplitude limiting block through the output end; in the amplitude limiting block, the correction coefficient and the upper and lower limit values of the correction coefficient are subjected to amplitude limiting treatment, and then the correction coefficient and the upper and lower limit values are sent to the multiplication block through an output end;
after speed limiting, the unit load is set to be connected with a load coal quantity function module to obtain a required coal quantity instruction; the correction coefficient and the required coal quantity instruction are subjected to product calculation in the multiplication block, the corrected coal-feeding base line is output and sent to a DCS boiler main control system for optimization control, and specifically:
firstly, when an EN end of a logic switching block receives a unit working condition stabilizing signal, taking an analog input signal of a YES end as an output logic signal a of the logic switching block; when the EN end of the editing switching block receives the unstable signal of the working condition of the unit, taking the analog input signal of the NO end as an output logic signal a of the logic switching block;
secondly, inputting the logic signal a and the coal low-order heating value set value into a division block to calculate a quotient, and outputting a logic signal b by the division block;
then, inputting the logic signal b into a limiting block, wherein when the value of the logic signal b is between an upper limit value and a lower limit value, the limiting block outputs the logic signal b; when the value of the logic signal b is larger than the upper limit value, the amplitude limiting block outputs the upper limit value; when the value of the logic signal b is smaller than the lower limit value, the amplitude limiting block outputs the lower limit value;
then, inputting the load set value of the limited unit into a load coal quantity function module for instruction conversion, and outputting a required coal quantity instruction by the load coal quantity function module;
and then, outputting and inputting the output of the limiting block and the output of the load coal quantity function module into the multiplication block to perform product calculation, and finally outputting and correcting the multiplication block and feeding the corrected multiplication block to the coal baseline.
The description of each functional module is as follows:
the output of the difference block is the difference between the value of the input end In1 and the value of the input end In 2;
judging the received signal value, outputting 0 if the received signal value is smaller than or equal to the set upper limit value and larger than the set lower limit value, and outputting 1 if the received signal value is larger than the set upper limit value or smaller than the set lower limit value;
the NOT gate block inverts the access signal, outputs an open light quantity 0 when the input is the open light quantity 1, and outputs a switch quantity 1 when the input is the open light quantity 0;
the delay triggering module performs delay triggering on the input switching value signal, when the input signal is that the switching value 1 is changed to 0, the input signal is output to be the switching value 0 without delay, and when the input signal is that the switching value 0 is changed to 1, the input signal is output to be the switching value 1 after the set delay time T.
The AND gate block outputs 1 when all the access input ends are 1, and outputs 0 when any one of the access input ends is 0;
when the enable end EN is a switching value signal 1, the logic switching block selects an analog value input signal of the YES end as output; when the enable end EN is an open light quantity signal 0, selecting an analog quantity input signal of the NO end as output;
the output of the division block is the quotient of the value of the input end In1 and the input end In 2;
the output of the multiplication block is the product of the value of the input end In1 and the input end In 2;
setting upper and lower limit values of a logic signal output by the division block in the amplitude limiting block, carrying out amplitude limiting processing on an input signal according to the set upper limit value High and lower limit value Low, and outputting the same value as the input signal when the input signal is between the upper limit value and the lower limit value; when the input signal is greater than the upper limit value, outputting as the upper limit value; when the input signal is smaller than the lower limit value, outputting the input signal as the lower limit value;
the load coal quantity function block is in a multi-point broken line function form, and the load instruction after the input signal speed limiting is converted into a required coal quantity instruction.
1) On-line calculation of low-level heating value of coal
The heat burned and utilized by the coal in the boiler is the effective heat absorption of the boiler, and the heat loss mainly comprises smoke exhaust heat loss, chemical incomplete combustion heat loss, mechanical incomplete combustion heat loss, heat dissipation loss and ash physical heat loss. Among the losses, the smoke exhaust loss is the largest in proportion, and other losses are smaller and negligible, so the patent considers that the heat generated by burning the coal in the boiler is mainly the effective heat absorption capacity and the smoke exhaust heat loss of the boiler, establishes the total heat of the boiler mainly the effective heat absorption capacity and the smoke exhaust heat loss of the boiler, and then divides the total heat by the coal supply amount to obtain the low-level heat productivity of the coal in and out of the boiler, and the specific calculation formula is as follows
Wherein: q (Q) net,ar The low-position heating value of coal is kJ/kg; q (Q) b The total heat MW of the boiler is mainly the effective heat absorption capacity of the boiler and the heat loss of the discharged smoke; b (B) v Kg/s for coal feed; k is a coefficient related to efficiency.
a) On-line calculation of effective heat absorption capacity of boiler
The effective heat absorbed by the working medium in the boiler can be expressed as the sum of the heat absorbed by the main steam and the reheat steam, and the heat consumed by heating the feedwater and the heat consumed by superheating and the desuperheater part desuperheater water is subtracted. The specific calculation formula is as follows:
Q 1 ＝D gr i gr -D gs i gs +D jws (i zr -i jws )+D zr (i zr -i gp ) (2)
wherein: dgr is the main steam flow, kg/s; igr is the main vapor enthalpy, MJ/kg; i.e gs Is the enthalpy of water supply, MJ/kg; d (D) gs Is the water supply flow rate, kg/s; d (D) jws Kg/s for reducing the flow of warm water; i.e jws MJ/kg for heat reduction of water enthalpy; d (D) zr Kg/s for reheat steam flow; i.e zr For reheat steam enthalpy, MJ/kg; i.e gp Is the enthalpy of high cylinder exhaust steam, MJ/kg.
b) Online calculation of smoke exhaust heat loss
The heat loss of the exhausted smoke can be calculated according to the temperature of the cold air and the temperature of the exhausted smoke and the total air quantity. The specific calculation formula is as follows:
Q 2 ＝1.071*(1.3593+0.000188t 1 )*(t 1 -t 0 )*Q a (3)
wherein: q (Q) a The total air quantity is kg/s; t is t 0 Cold air temperature, DEG C; t is t 1 Is the temperature of the discharged smoke, and the temperature is DEG C.
The method has the beneficial effects that the low-level calorific value of the coal quality of the coal-fired unit is calculated in real time, the coal feeding baseline of the unit is calibrated in real time, and the influence of variable coal quality on the running stability and economy of the unit is overcome.
The invention provides an online correction method for low-grade heat productivity of coal quality of a thermal power plant, which comprises judging steady-state operation conditions of a unit, online calculation of low-grade heat of the coal quality, and online updating correction of the low-grade heat productivity of the steady-state coal quality. The online correction method for the low-level heating value of the coal quality of the thermal power plant comprises the following steps:
the configuration is built in the control system according to the configuration shown in fig. 1 and 2.
According to the method for calculating the effective heat absorption capacity on line in the specification, the effective heat absorption capacity of the boiler is calculated according to real-time information such as main steam flow, main steam pressure, main steam temperature, water supply flow, water supply pressure, water supply temperature, reheat steam flow, reheat heat section steam pressure, reheat heat section steam temperature, reheat cold section steam pressure, reheat cold section steam temperature, superheat desuperheating water flow, reheat desuperheating water flow and the like, and the specific calculation formula is as follows:
Q 1 ＝D gr i gr -D gs i gs +D jws (i zr -i jws )+D zr (i zr -i gp )
(1)
wherein: dgr is the main steam flow, kg/s; igr is the main vapor enthalpy, MJ/kg; i.e gs Is the enthalpy of water supply, MJ/kg; d (D) gs Is the water supply flow rate, kg/s; d (D) jws Kg/s for reducing the flow of warm water; i.e jws MJ/kg for heat reduction of water enthalpy; d (D) zr Kg/s for reheat steam flow; i.e zr For reheat steam enthalpy, MJ/kg; i.e gp Is the enthalpy of high cylinder exhaust steam, MJ/kg.
Secondly, according to the online calculation method of the smoke exhaust heat loss shown in the specification, the smoke exhaust loss is calculated by real-time information such as total air quantity, cold air temperature, hot air temperature and the like, and the specific calculation formula is as follows:
Q 2 ＝1.071*(1.3593+0.000188t 1 )*(t 1 -t 0 )*Q a
(2)
wherein: q (Q) a The total air quantity is kg/s; t is t 0 Cold air temperature, DEG C; t is t 1 Is the temperature of the discharged smoke, and the temperature is DEG C.
And thirdly, according to the on-line calculation method of the low-level calorific value of the coal quality shown in the description, superposing the effective heat absorption capacity and the smoke exhaust heat loss of the boiler to form the total heat of the boiler mainly comprising the effective heat absorption capacity and the smoke exhaust heat loss, and dividing the total heat by the coal feeding capacity to obtain the low-level calorific value of the coal quality entering the boiler.
And fourthly, judging whether the unit is in a steady-state working condition or not in real time according to real-time information of the load and the main steam pressure of the unit according to the steady-state working condition judgment logic of the unit shown in fig. 1, and outputting 1 by the steady-state working condition judgment logic of the unit when the unit is in the steady-state working condition. Wherein the upper limit value of the third judgment block is set to 6MW and the lower limit value is set to-6 MW; the delay time of the seventh delay trigger block is set to 300 seconds; the upper limit value of the fourth judgment block is set to be 0.3Mpa, and the lower limit value is set to be-0.3 Mpa; the delay time of the seventh delay trigger block is set to 300 seconds.
And fifthly, performing steady-state updating on the coal low-level heating value calculated in real time according to the steady-state coal low-level heating value updating correction logic shown in fig. 2. When the steady-state operation condition judgment logic output of the unit is 1, the coal quality low-level heating value calculated in real time acts on the division module, and the current coal quality curve is corrected after passing through the amplitude limiting module; however, when the unit steady-state operation condition judgment logic output is 0, the output of the first logic switching block keeps the last moment of result and does not correct the coal quantity curve. The upper limit value of the third limiter block is set to 1.1 and the lower limit value is set to 0.9. The load coal quantity function is set according to the actual running condition of the unit and the low-level heating value under the design working condition, namely, a relation curve of the load and the coal quantity instruction is generally a linear function relation.
Claims (5)
1. The system is characterized by comprising a unit steady state operation condition judging unit, a unit for updating the low-level heating value of the coal and a DCS boiler main control system, wherein the DCS boiler main control system is electrically connected with the unit steady state operation condition judging unit and the unit for updating the low-level heating value of the coal;
the unit steady-state operation condition judging unit is used for outputting a unit steady-state operation condition judging signal and outputting the unit steady-state operation condition judging signal to the DCS boiler main control system;
the DCS boiler main control system is used for acquiring the low-grade heating value of the coal according to the received unit stable working condition judging signal, transmitting the acquired low-grade heating value of the coal to the on-line updating unit of the low-grade heating value of the coal, and the on-line updating unit of the low-grade heating value of the coal is used for outputting a corrected coal feeding baseline;
the input end of the coal quality low-grade heating value online updating unit is connected with the coal quality low-grade heating value and the set load after speed limiting, and the output end of the coal quality low-grade heating value online updating unit is connected with the DCS boiler main control system;
the on-line updating unit of the coal low-order heating value comprises a logic switching block, a division block, an amplitude limiting block, a load coal amount function module and a multiplication block, wherein the coal low-order heating value is connected with the YES end of the input end of the logic switching block, the output end of the input end of the logic switching block is connected with the input end of the division block, the input end of the division block is also connected with a coal low-order heating value set value, the output end of the division block is connected with the input end of the amplitude limiting block, and the output end of the amplitude limiting block is connected with the input end of the multiplication block;
the set load value of the unit after speed limiting is connected with the input end of the load coal quantity function module, the output end of the load coal quantity function module is connected with the input end of the multiplication block, and the output end of the multiplication block is connected with the DCS boiler main control system.
2. The online correction system for low-level heating value of coal quality of thermal power plant according to claim 1, wherein the input end of the unit steady-state operation condition judging unit is connected with the unit target load, the unit actual power, the pre-unit pressure set value and the main steam pressure feedback value; and the output end DCS boiler main control system of the unit steady-state operation condition judging unit.
3. The on-line correction system for low-grade heating value of coal quality of thermal power plant according to claim 2, wherein the unit steady-state operation condition judging unit comprises a first judging block, a first NOT block, a first delay triggering block, a second judging block, a second NOT block, a second delay triggering block and an AND gate block,
the output end of the first NOT gate block is connected with the input end of the first delay trigger block, and the output end of the first delay trigger block is connected with the input end of the AND gate block;
the difference between the set value of the pressure before the engine and the feedback value of the main steam pressure is connected with the input end of a second judging block, the output end of the second judging block is connected with the input end of a second NOT gate block, the output end of the second NOT gate block is connected with the input end of a second delay triggering block, and the output end of the second delay triggering block is connected with the input end of an AND gate block; and the output end of the AND gate block is a DCS boiler main control system.
4. An online correction method for low-grade heating value of coal quality in a thermal power plant, which is characterized by comprising the following steps based on the online correction system for low-grade heating value of coal quality in a thermal power plant as claimed in any one of claims 1-3:
firstly, outputting a unit stable working condition judging signal according to a unit stable working condition judging unit, and outputting the unit stable working condition judging signal to a DCS boiler main control system;
secondly, the DCS boiler main control system acquires the low-grade heating value of the coal according to the received unit stable working condition judging signal, and transmits the acquired low-grade heating value of the coal to the on-line updating unit of the low-grade heating value of the coal;
finally, the coal quality low-level heating value online updating unit outputs a corrected coal feeding baseline according to the coal quality low-level heating value;
the specific method for the coal quality low-level heating value on-line updating unit to output the corrected coal feeding baseline comprises the following steps:
firstly, when an EN end of a logic switching block receives a unit working condition stabilizing signal, taking an analog input signal of a YES end as an output logic signal a of the logic switching block; when the EN end of the editing switching block receives the unstable signal of the working condition of the unit, taking the analog input signal of the NO end as an output logic signal a of the logic switching block;
secondly, inputting the logic signal a and the coal low-level heating value set value into a division block to calculate a quotient, and outputting the logic signal b by the division block;
then, inputting the logic signal b into a limiting block, wherein when the value of the logic signal b is between an upper limit value and a lower limit value, the limiting block outputs the logic signal b; when the value of the logic signal b is larger than the upper limit value, the amplitude limiting block outputs the upper limit value; when the value of the logic signal b is smaller than the lower limit value, the amplitude limiting block outputs the lower limit value;
then, inputting the load set value of the limited unit into a load coal quantity function module for instruction conversion, and outputting a required coal quantity instruction by the load coal quantity function module;
and then, outputting and inputting the output of the limiting block and the output of the load coal quantity function module into the multiplication block to perform product calculation, and finally outputting and correcting the multiplication block and feeding the corrected multiplication block to the coal baseline.
5. The method for online correction of low-rank calorific value of coal quality in a thermal power plant according to claim 4, wherein the specific method for outputting a unit steady state operation condition judgment signal by the unit steady state operation condition judgment unit is as follows:
first, upper and lower limit values of a target load of a unit and a set value of a pressure before the unit are set, wherein,
if the real power value of the unit is smaller than or equal to the set target load upper limit value of the unit and larger than the set target load lower limit value of the unit, the logic signal output by the first judging block is 0;
if the real power value of the unit is larger than the set target load upper limit value of the unit or smaller than the set target load lower limit value of the unit, the logic signal output by the first judging block is 1;
if the main steam pressure feedback value is smaller than or equal to the set upper limit value of the set front pressure set value and larger than the set lower limit value of the set front pressure set value, the logic signal output by the second judging block is 0;
if the main steam pressure feedback value is larger than the set upper limit value of the set front pressure set value or smaller than the set lower limit value of the set front pressure set value, the logic signal output by the second judging block is 1;
then, the NOT gate block inverts the accessed switching value signal and accesses the output switching value signal to the delay trigger block;
then, the delay triggering module performs delay triggering on the input switching value signal, wherein when the input switching value signal is changed from the switching value 1 to 0, the switching value 0 is directly output without delay; when the input switching value signal is changed from the switching value 0 to 1, outputting the switching value 1 after the set delay time T;
finally, when the light quantity signals output by the first delay trigger block and the second delay trigger block received by the AND gate block are 1, the light quantity signal output by the AND gate block is 1, so that the running condition of the unit is illustrated to be in a steady state; otherwise, the ON-light quantity signal output by the AND gate block is 0.
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