CN109681909B - Combustion control method of lean coal for combustion of boiler in W-shaped flame combustion mode - Google Patents

Combustion control method of lean coal for combustion of boiler in W-shaped flame combustion mode Download PDF

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CN109681909B
CN109681909B CN201811561617.5A CN201811561617A CN109681909B CN 109681909 B CN109681909 B CN 109681909B CN 201811561617 A CN201811561617 A CN 201811561617A CN 109681909 B CN109681909 B CN 109681909B
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mill
coal
inlet
grinding
outlet
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CN109681909A (en
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陈辉
杨希刚
蔡培
戴维葆
王爱英
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Guoneng Nanjing Electric Power Test Research Co.,Ltd.
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Guodian Nanjing Electric Power Test Research Co Ltd
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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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N1/00—Regulating fuel supply
    • F23N1/02—Regulating fuel supply conjointly with air supply
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N2223/00—Signal processing; Details thereof
    • F23N2223/40—Simulation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N2239/00—Fuels
    • F23N2239/02—Solid fuels
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23N—REGULATING OR CONTROLLING COMBUSTION
    • F23N2900/00—Special features of, or arrangements for controlling combustion
    • F23N2900/05003—Measuring NOx content in flue gas

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Abstract

The invention discloses a combustion control method of lean coal for a boiler in a W-shaped flame combustion mode, which controls the fineness R90 of coal powder to be 2.9-6.1% by adjusting the operation method of a coal mill. The control method of the invention is adopted to control the fineness of the pulverized coal of the lean coal for the W-shaped flame combustion boiler, which can effectively reduce the fineness of the pulverized coal, reduce the carbon content of the fly ash of the boiler and the concentration of NOX at the outlet of the economizer, and improve the boiler efficiency and the unit economy.

Description

Combustion control method of lean coal for combustion of boiler in W-shaped flame combustion mode
Technical Field
The invention relates to a control method for lean coal used for a W-shaped flame combustion boiler.
Background
The utility boiler actually operates in a state where low-nitrogen combustion, economical coal for combustion, and medium-low load operation are mutually superimposed, which causes a number of rather serious problems: the carbon content of fly ash and large slag is increased, the temperature reduction water amount is increased and the like; coking on a heating surface, high-temperature corrosion of a hearth, low-load stable combustion and other safety problems; NOXThe generated amount exceeds the standard, the ammonia injection is excessive, the preheater is blocked and the like. The technical key to solving or relieving the problems is the fineness of the pulverized coal. The specific surface area of solid particles is increased by the finer pulverized coal, each process of precipitation, ignition, stable combustion and burnout is strengthened, and the pulverized coal is beneficial to reducing carbon content of the fly ash and low-nitrogen combustion; the coke in the main combustion area is contacted with oxygen more quickly, and the generation of NO by nitrogen-oxygen reaction is reducedXAnd enhance NO conversionXConversion to N2The oxygen-deficient combustion under the condition of constant excess air coefficient is further realized, and the reduction of NO is realizedXIs favorable; the pulverized coal particles have smaller inertia, the intensity of pyrolysis and combustion of the rotary flue gas thrown to the boundary is weakened, the reductive atmosphere of the wall surface of the hearth is improved, and the high-temperature corrosion is favorably reduced. The research on the reasonable selection of the fineness of the pulverized coal has practical value for solving the problems of combustion.
Disclosure of Invention
The invention aims to solve the defects in the prior art and provide a method for reasonably selecting and adjusting the fineness of coal powder when burning lean coal so as to reduce the fly ash content of a boilerCarbon amount, economizer outlet NOXConcentration, and improves boiler efficiency and unit economy.
In order to achieve the aim, the invention provides a combustion control method of lean coal for a boiler adopting a W-shaped flame combustion mode, which controls the fineness R90 of coal powder to be 2.9-6.1% and preferably controls the fineness R90 of coal powder to be 3.0-6.0% by adjusting the operation method of a coal mill.
Most preferably, the fineness of the pulverized coal R90 is controlled to be 3.0-3.2%.
The combustion control method comprises the following specific steps:
(1) under the low-nitrogen combustion state of the boiler, the load of the unit is kept unchanged, and the proportion of over-fire air, the running oxygen and the running number of coal mills are kept unchanged;
(2) when the load of the unit is 330MW, controlling four ABCD coal mills as follows:
the grinding output of A is 40t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 294 ℃, the opening of hot air is 100%, the opening of cold air door is 0%, the frequency of dynamic separator is 40Hz-50Hz, the differential pressure of inlet and outlet of coal grinding mill is 3.3kPa-4.4kPa, the ventilation quantity of A grinding is 45.8t/h-46t/h, and the temperature of outlet of A grinding is 100-102 ℃;
the grinding output of the B mill is 27t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 292 ℃, the opening of hot air is 100 percent, the opening of cold air door is 0 percent, the frequency of a dynamic separator is 40Hz to 50Hz, the differential pressure of an inlet and an outlet of a coal mill is 4.0kPa to 4.6kPa, the ventilation quantity of the B mill is 40.5t/h to 41.1t/h, and the temperature of the outlet of the B mill is 101 to 102 ℃;
c mill outlet force is 37t/h, mill inlet primary air pressure is 5.3kPa, mill inlet air temperature is 295 ℃, hot air opening degree is 100%, cold air opening degree is 0%, dynamic separator frequency is 40Hz-50Hz, coal mill inlet and outlet differential pressure is 3.7kPa-4.6kPa, C mill ventilation amount is 35.8t/h-36t/h, and C mill outlet temperature is 105 ℃ -106 ℃;
the D mill output is 33t/h, the primary air pressure of the mill inlet is 5.3kPa, the air temperature of the mill inlet is 295 ℃, the opening degree of the hot air is 100%, the opening degree of the cold air door is 0%, the frequency of the dynamic separator is 40Hz to 50Hz, the differential pressure of the inlet and the outlet of the coal mill is 3.7kPa to 4.3kPa, the ventilation quantity of the D mill is 37.8t/h to 39t/h, and the temperature of the outlet of the D mill is 99 to 100 ℃;
when the load of the unit is 260MW, the four ABCD coal mills are controlled as follows:
the grinding output of A is 30t/h, the primary air pressure of a grinding inlet is 5.0kPa, the air temperature of the grinding inlet is 270 ℃, the opening of hot air is 100 percent, the opening of cold air door is 40 percent, the frequency of a dynamic separator is 40Hz-50Hz, the differential pressure of an inlet and an outlet of a coal grinding machine is 2.8kPa-3.3kPa, the ventilation quantity of A grinding is 32.9t/h-33t/h, and the temperature of an outlet of A grinding is 112 ℃ -115 ℃;
the grinding output of the B mill is 22t/h, the primary air pressure of a grinding inlet is 5.0kPa, the air temperature of the grinding inlet is 293 ℃, the opening of hot air is 100%, the opening of cold air door is 40%, the frequency of a dynamic separator is 40Hz-50Hz, the differential pressure of an inlet and an outlet of a coal mill is 2.8kPa-3.5kPa, the ventilation quantity of the B mill is 29.1t/h-29.8t/h, and the temperature of the outlet of the B mill is 111-112 ℃;
c mill outlet 31t/h, mill inlet primary air pressure 5.3kPa, mill inlet air temperature 305 ℃, hot air opening 100%, cold air opening 0%, dynamic separator frequency 40Hz-50Hz, coal mill inlet and outlet differential pressure 3.2kPa-3.8kPa, C mill ventilation 31.9t/h-33t/h, C mill outlet temperature 105 ℃ -106 ℃;
the D mill output is 33t/h, the primary air pressure of the mill inlet is 5.3kPa, the air temperature of the mill inlet is 305 ℃, the opening of the hot air is 100%, the opening of the cold air door is 0%, the frequency of the dynamic separator is 40Hz-50Hz, the differential pressure of the inlet and the outlet of the coal mill is 3.4kPa-4.0kPa, the ventilation quantity of the D mill is 32.8t/h-34t/h, and the temperature of the outlet of the D mill is 100-102 ℃.
In the step (1), under the low-nitrogen combustion state of the boiler, the load of the unit is maintained to be 330MW or 260MW, the proportion of the over-fire air is maintained to be 25%, the operation oxygen is maintained to be 3.85% -4.06% when the load of the unit is 330MW, and the operation oxygen is maintained to be 4.38% -4.46% when the load of the unit is 260 MW.
The specific control method for the four ABCD coal mills in the step (2) is as follows:
at 330MW load, the A mill output is 40t/h, the mill inlet primary air pressure is 5.3kPa, the mill inlet air temperature is 294 ℃, the hot air opening is 100%, the cold air opening is 0%, the dynamic separator frequency (40Hz, 45Hz, 50Hz), the coal mill inlet and outlet differential pressure (3.3kPa, 4.0kPa, 4.4kPa), the A mill ventilation (45.8t/h, 46t/h, 45.9t/h), the A mill outlet temperature (100 ℃, 101 ℃, 102 ℃), and the coal powder fineness R90 are respectively (6%, 4.5%, 3.2%). The grinding output of B is 27t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 292 ℃, the opening degree of hot air is 100%, the opening degree of cold air is 0%, the frequency of a dynamic separator (40Hz, 45Hz and 50Hz), the differential pressure of an inlet and an outlet of a coal mill (3.7kPa, 4.0kPa and 4.6kPa), the ventilation quantity of B grinding (40.5t/h, 41t/h and 41.1t/h), the outlet temperature of B grinding (102 ℃, 101 ℃ and 102 ℃), and the fineness of coal powder R90 are respectively (5.8%, 4.3% and 3.0%). C mill outlet force of 37t/h, mill inlet primary air pressure of 5.3kPa, mill inlet air temperature of 295 ℃, hot air opening degree of 100%, cold air opening degree of 0%, dynamic separator frequency (40Hz, 45Hz, 50Hz), coal mill inlet and outlet differential pressure (3.7kPa, 4.0kPa, 4.6kPa), C mill ventilation amount (35.8t/h, 36t/h, 35.9t/h), C mill outlet temperature (106 ℃, 105 ℃, 106 ℃), and coal dust fineness R90 of 6.1%, 4.3%, 3.1% respectively. The D mill output is 33t/h, the mill inlet primary air pressure is 5.3kPa, the mill inlet air temperature is 295 ℃, the hot air opening is 100%, the cold air opening is 0%, the dynamic separator frequency (40Hz, 45Hz and 50Hz), the coal mill inlet and outlet differential pressure (3.7kPa, 4.0kPa and 4.3kPa), the D mill ventilation amount (37.8t/h, 38t/h and 39t/h), the D mill outlet temperature (100 ℃, 99 ℃ and 99 ℃) and the coal powder fineness R90 are respectively (5.8%, 4.0% and 3.1%).
Under the load of 260MW, the A mill output is 30t/h, the mill inlet primary air pressure is 5.0kPa, the mill inlet air temperature is 270 ℃, the hot air opening is 100 percent, the cold air opening is 40 percent, the dynamic separator frequency (40Hz, 45Hz and 50Hz), the inlet and outlet differential pressure of a coal mill (2.8kPa, 3.2kPa and 3.3kPa), the A mill ventilation amount (33t/h, 33t/h and 32.9t/h), the A mill outlet temperature (115 ℃, 114 ℃ and 112 ℃) and the coal powder fineness R90 are respectively (6.2%, 4.1% and 3.0%). The grinding output of B22 t/h, the primary air pressure of grinding inlet 5.0kPa, the air temperature of grinding inlet 293 ℃, the opening of hot air 100%, the opening of cold air door 40%, the frequency of dynamic separator (40Hz, 45Hz, 50Hz), the differential pressure of inlet and outlet of coal grinding mill (2.8kPa, 3.2kPa, 3.5kPa), the ventilation of B grinding (29.6t/h, 29.8t/h, 29.1t/h), the outlet temperature of B grinding (112 ℃, 111 ℃, 112 ℃), the fineness of coal powder R90 are respectively (5.6%, 4.0%, 3.1%). 31t/h of C mill outlet, 5.3kPa of primary air pressure at the mill inlet, 305 ℃ of air temperature at the mill inlet, 100% of opening of hot air, 0% of opening of cold air door, frequencies of dynamic separators (40Hz, 45Hz and 50Hz), differential pressure at the inlet and outlet of the coal mill (3.2kPa, 3.5kPa and 3.8kPa), ventilation of C mill (32.8t/h, 33t/h and 31.9t/h), temperature at the outlet of C mill (106 ℃, 105 ℃ and 106 ℃), and fineness R90 of coal powder (6.0%, 3.9% and 2.9%) respectively. D mill output of 33t/h, mill inlet primary air pressure of 5.3kPa, mill inlet air temperature of 305 ℃, hot air opening of 100%, cold air opening of 0%, dynamic separator frequency (40Hz, 45Hz, 50Hz), coal mill inlet and outlet differential pressure (3.4kPa3.7kPa, 4.0kPa), D mill ventilation (32.8t/h, 33t/h, 34t/h), D mill outlet temperature (100 ℃, 102 ℃), and coal dust fineness R90 of (5.9%, 3.9%, 3.1%) respectively.
Preferably, the control method for the ABCD four coal mills in the step (2) is as follows:
when the load of the unit is 330MW,
the grinding output of A is 40t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 294 ℃, the opening of hot air is 100%, the opening of cold air is 0%, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal grinding machine is 4.4kPa, the ventilation quantity of A grinding is 45.9t/h, and the temperature of an outlet of A grinding is 102 ℃;
the grinding output of the B mill is 27t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 292 ℃, the opening of hot air is 100 percent, the opening of cold air is 0 percent, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal mill is 4.6kPa, the ventilation quantity of the B mill is 41.1t/h, and the temperature of the outlet of the B mill is 102 ℃;
c, grinding outlet force of 37t/h, primary air pressure of a grinding inlet of 5.3kPa, air temperature of a grinding inlet of 295 ℃, opening degree of hot air of 100%, opening degree of cold air door of 0%, frequency of a dynamic separator of 50Hz, differential pressure of an inlet and an outlet of a coal grinding machine of 4.6kPa, ventilation quantity of the C grinding of 35.9t/h and outlet temperature of the C grinding of 106 ℃;
the D mill output is 33t/h, the primary air pressure of the mill inlet is 5.3kPa, the air temperature of the mill inlet is 295 ℃, the opening degree of the hot air door is 100%, the opening degree of the cold air door is 0%, the frequency of the dynamic separator is 50Hz, the differential pressure of the inlet and the outlet of the coal mill is 4.3kPa, the ventilation quantity of the D mill is 39t/h, and the temperature of the outlet of the D mill is 99 ℃;
when the load of the unit is 260MW,
the grinding output of the A mill is 30t/h, the primary air pressure of a grinding inlet is 5.0kPa, the air temperature of the grinding inlet is 270 ℃, the opening of hot air is 100 percent, the opening of cold air is 40 percent, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal mill is 3.3kPa, the ventilation quantity of the A mill is 32.9t/h, and the temperature of the outlet of the A mill is 112 ℃;
the grinding output of the B mill is 22t/h, the primary air pressure of a grinding inlet is 5.0kPa, the air temperature of the grinding inlet is 293 ℃, the opening of hot air is 100%, the opening of cold air is 40%, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal mill is 3.5kPa, the ventilation quantity of the B mill is 29.1t/h, and the temperature of the outlet of the B mill is 112 ℃;
c mill outlet 31t/h, mill inlet primary air pressure 5.3kPa, mill inlet air temperature 305 ℃, hot air opening 100%, cold air opening 0%, dynamic separator frequency 50Hz, coal mill inlet and outlet differential pressure 3.8kPa, C mill ventilation 31.9, C mill outlet temperature 106 ℃;
the D mill output is 33t/h, the primary air pressure of the mill inlet is 5.3kPa, the mill inlet air temperature is 305 ℃, the hot air opening is 100%, the cold air opening is 0%, the dynamic separator frequency is 50Hz, the inlet and outlet differential pressure of the coal mill is 4.0kPa, the D mill ventilation is 34t/h, and the D mill outlet temperature is 102 ℃.
Compared with the prior art, the invention has the following advantages:
the control method of the invention is adopted to control the fineness of the coal dust of the lean coal for the W-shaped flame combustion boiler, which can effectively reduce the fineness of the coal dust, reduce the carbon content of the boiler fly ash and reduce NO at the outlet of the economizerXConcentration, and improves boiler efficiency and unit economy.
Drawings
FIG. 1 is a three-dimensional and grid diagram of numerical simulation of a No. 1 furnace of a Country electric and Security power plant according to the present invention;
FIG. 2 is a comparison graph of hearth temperature field distribution under different pulverized coal fineness of 330MW load;
FIG. 3 is a comparison graph of the distribution of the volatile components at the nozzle of the burner under different coal powder fineness of 330MW load;
FIG. 4 is a comparison graph of the CO concentration distribution in a hearth under different coal powder fineness of 330MW load;
FIG. 5 shows NO in a hearth under different 330MW loads and different coal powder finenessxA concentration distribution comparison graph (also shown as an abstract figure);
FIG. 6 is a comparison graph of the residence time of coal dust in a hearth under different coal dust fineness of 330MW load;
FIG. 7 is a comparison graph of hearth temperature field distribution under different coal powder fineness of 260MW load;
FIG. 8 is a comparison graph of burner nozzle volatile component distribution under different coal powder fineness of 260MW load;
FIG. 9 is a comparison graph of CO concentration distribution in a hearth under different coal powder fineness under 260MW load;
FIG. 10 shows NO in a hearth under different coal powder fineness under 260MW loadxA concentration profile comparison plot;
FIG. 11 is a graph comparing the residence time of coal powder in a hearth under different coal powder fineness under 260MW load.
Detailed Description
The present invention will be described in detail with reference to specific examples.
The embodiment of the invention adopts a W-shaped flame boiler with the model number DG1025/18/2-II10 of the No. 1 boiler of the national Electrical and Amphibian Power Generation Co., Ltd, and is a subcritical intermediate single reheating natural circulation boiler which is introduced into the technology of the Foster-Whiler company of America by the eastern boiler corporation. The double-arch single-hearth combustor is characterized in that the combustors are arranged on the front arch and the rear arch of the lower hearth and are W-shaped flames, a double-flue structure at the tail part is adopted, a baffle plate is adopted to adjust the temperature of reheated steam, solid slag is discharged, an all-steel framework is adopted, a full-suspension structure is adopted, balanced ventilation is realized, and the boiler is arranged in the open air. The pulverizing system adopts a positive pressure direct-blowing system of a double-inlet double-outlet ball mill, and 4 coal mills are BBD4060 type coal produced by Shenyang heavy machinery Limited liability company and use lean coal for combustion.
The combustion equipment adopts a double-arch heat-insulating hearth, burners are arranged on front and rear arches of a lower hearth, double-channel shade separation low-NOx pulverized coal burners, a graded air distribution and a W flame combustion mode, the hearth is divided into an upper part and a lower part, the total height is 48153mm, the size of the upper hearth is 24765 × 7620mm, the size of the lower hearth is 24765 × 13725mm, and the main design parameters of the boiler are shown in a table 1.
The main design parameters of the boiler are shown in table 1 below.
TABLE 1 boiler main parameter table (design coal type)
Name (R) Unit of MCR 75％ECR
Flow of superheated steam t/h 935 701.3
Superheater outlet steam pressure MPa 17.42 17.14
Superheater outlet steam temperature ℃ 540 540
Pressure of steam drum MPa 18.54 17.77
Reheat steam flow t/h 780.66 595
Reheat steam inlet/outlet pressure MPa 3.60/3.44 2.76/2.63
Reheat steam inlet/outlet temperature ℃ 316/540 299/540
Temperature of feed water ℃ 267 250
Smoke exhaust temperature (after correction) ℃ 140 133
First-stage desuperheating water quantity t/h 14.6 7.1
Two-stage desuperheating water quantity t/h 7.3 3.5
Coal consumption t/h 119.3 92.94
Efficiency of boiler ％ 90.59 90.88
In the numerical simulation and experimental research of the method for controlling the fineness of the lean pulverized coal for the W-shaped flame combustion boiler, the coal type is close to the designed coal type of a power plant, and the coal type is shown in a table 2.
TABLE 2 boiler design coal data
Item Unit of Design coal type Test coal species
Carbon of oxo group ％ 59.95 56.19
Radical hydrogen generation ％ 2.25 2.03
Oxygen radical take-up ％ 0.57 0.95
Radical nitrogen recovery ％ 0.94 0.94
Radical sulfur ％ 2.29 3.14
Receiving base water ％ 7 7.90
Ash of the received base ％ 27 28.85
Low heating value of received base kJ/kg 21443 21100
Dry ash-free base volatiles ％ 12.5 13.2
Coefficient of grindability / 69 65
As can be seen from Table 2, the test coal types and the design coal types were poor ones with little difference.
Example 1(330MW load)
The coal mill specifically put into operation in this example was an ABCD4 coal mill.
The method for controlling the fineness of the high-ash bituminous coal powder for the boiler in the front-wall and rear-wall combustion mode comprises the following specific steps:
(1) under the low-nitrogen combustion state of the boiler, the load of a unit is kept unchanged at 330MW, the proportion of over-fire air (25%), the running oxygen amount (3.85% -4.06%), the number of running coal mills (ABCD mill) and the like are kept unchanged, and the influence of different coal powder fineness on the combustion of the boiler is analyzed through numerical simulation;
(2) according to the numerical simulation result of the first step, field test research is carried out, the proportion of over-fire air (25%), the running oxygen (3.85% -4.06% under 330MW load), the running number of coal mills (ABCD grinding under 330MW load) and the like are kept unchanged under the low-nitrogen combustion state of the boiler, and the influence of different coal powder fineness on the boiler combustion is analyzed through tests.
At 330MW load, the A mill output is 40t/h, the mill inlet primary air pressure is 5.3kPa, the mill inlet air temperature is 294 ℃, the hot air opening is 100%, the cold air opening is 0%, the dynamic separator frequency (40Hz, 45Hz, 50Hz), the coal mill inlet and outlet differential pressure (3.3kPa, 4.0kPa, 4.4kPa), the A mill ventilation (45.8t/h, 46t/h, 45.9t/h), the A mill outlet temperature (100 ℃, 101 ℃, 102 ℃), and the coal powder fineness R90 are respectively (6%, 4.5%, 3.2%). The grinding output of B is 27t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 292 ℃, the opening degree of hot air is 100%, the opening degree of cold air is 0%, the frequency of a dynamic separator (40Hz, 45Hz and 50Hz), the differential pressure of an inlet and an outlet of a coal mill (3.0kPa, 3.4kPa and 3.6kPa), the ventilation quantity of B grinding (40.5t/h, 41t/h and 41.1t/h), the outlet temperature of B grinding (102 ℃, 101 ℃ and 102 ℃), and the fineness of coal powder R90 are respectively (5.8%, 4.3% and 3.0%). C mill outlet force of 37t/h, mill inlet primary air pressure of 5.3kPa, mill inlet air temperature of 295 ℃, hot air opening degree of 100%, cold air opening degree of 0%, dynamic separator frequency (40Hz, 45Hz, 50Hz), coal mill inlet and outlet differential pressure (3.7kPa, 4.0kPa, 4.6kPa), C mill ventilation amount (35.8t/h, 36t/h, 35.9t/h), C mill outlet temperature (106 ℃, 105 ℃, 106 ℃), and coal dust fineness R90 of 6.1%, 4.3%, 3.1% respectively. The D mill output is 33t/h, the mill inlet primary air pressure is 5.3kPa, the mill inlet air temperature is 295 ℃, the hot air opening is 100%, the cold air opening is 0%, the dynamic separator frequency (40Hz, 45Hz and 50Hz), the coal mill inlet and outlet differential pressure (3.7kPa, 4.0kPa and 4.3kPa), the D mill ventilation amount (37.8t/h, 38t/h and 39t/h), the D mill outlet temperature (100 ℃, 99 ℃ and 99 ℃) and the coal powder fineness R90 are respectively (5.8%, 4.0% and 3.1%).
(3) By combining numerical simulation and experimental research, the optimal control value of the fineness (R90) of the burning lean coal powder in the low-nitrogen combustion state of the W-shaped flame combustion mode boiler is about 3%.
1. Numerical simulation analysis process and results
The simulation is carried out by modeling and simulating the whole furnace. FIG. 1 shows the gridding of a boiler model, wherein the gridding of each burner position in the main combustion area is encrypted in order to reflect the combustion condition of the main combustion area more accurately.
The simulation mainly researches the center of combustion flame and the temperature change of the hearth before and after the transformation, so that the heat absorption condition of the heating surface is not studied in detail in the simulation.
Under the condition of 330MW load, considering the deep nitrogen combustion state of the boiler, the coal powder fineness (R) is changed by keeping the over-fire air proportion to be about 25 percent, the secondary air distribution mode, the operation oxygen quantity, the number of coal mills in operation and the like unchanged906 percent, 4.5 percent and 3 percent respectively), wherein the fineness of the coal dust is 6 percent calculated according to recommended calculation formula of powder process system design and calculation guide rules, 2012 edition. And analyzing the influence of the change of the fineness of the coal powder on combustion. The numerical simulation conditions are shown in Table 3. The simulation results are shown in table 4, fig. 2-6.
Numerical simulation working condition of different coal powder fineness under table 3330 MW
Working conditions Working condition 1 Working condition 2 Working condition 3
Description of the working conditions α＝1.24 α＝1.24 α＝1.24
Description of the working conditions Fine powder 6 Fine powder 4.5 Fine powder 3
R90＝6.00％ R90＝4.50％ R90＝3.00％
SOFA wind ratio 25％ 25％ 25％
Numerical simulation results of different coal powder fineness under table 4330 MW
Figure BDA0001913393420000081
Figure BDA0001913393420000091
As can be seen from tables 3-4 and FIGS. 2-6, the influence of changing the fineness of the pulverized coal on combustion is obvious under the conditions of 330MW load, over-fire air ratio of about 25 percent and deep low-nitrogen combustion of the unit.
(1) Along with the reduction of the thinning of the coal powder, the specific surface area of the coal powder in unit mass in contact with oxygen and hot smoke in the furnace is increased, the ignition is earlier, the burnout is more thorough, the heat release is more under the condition of the same coal powder amount, and therefore the water average of the overall temperature of the hearth is slightly higher than that of the original working condition.
(2) Reducing the granularity of the coal powder is beneficial to burn out, and the carbon content of the fly ash is gradually reduced from the working condition 1 to the working condition 3. When the fineness of the coal dust is reduced from 6.0% to 3.0%, the carbon content of the fly ash is reduced from 13.19% to 8.32%, and the carbon content is reduced by about 4.87%.
(3) Along with the reduction of the particle size of the pulverized coal, the concentration of NOx at the outlet of the hearth is gradually reduced. The NOx concentration at the outlet of the hearth under the working conditions 2 and 3 is reduced by about 2.9 percent and 13.7 percent respectively compared with that under the working condition 1.
2. Test procedure and results
The total coal quantity, the running oxygen quantity, the SOFA air proportion, the coal mill output, the coal mill ventilation quantity, the inlet primary air pressure and the like are kept unchanged, and 3 working conditions of the frequency of the variable-state separator are developed.
Under the deep low-nitrogen combustion state of the boiler, the proportion of over-fire air (25%), the running oxygen (3.85% -4.06), the running number of coal mills (ABCD mill) and the like are kept unchanged, and the influence of different coal powder fineness on the boiler combustion is analyzed through tests.
And testing the heat efficiency of the boiler and the power consumption of the auxiliary machine under different working conditions. The unit operation is shown in table 5. The furnace efficiency calculation parameters under various working conditions are shown in Table 6. The comparison of the economics at different coal fines is shown in Table 7.
Running mode of rotating speed unit of separator in 5330 MW load variation state
Figure BDA0001913393420000092
Figure BDA0001913393420000101
Figure BDA0001913393420000111
Test result table for thermal efficiency of boiler with different load of 6330 MW and different working conditions of rotating speed of separator
Item Unit of Working condition 1 Working condition 2 Working condition 3
Fineness of coal dust R90 ％ 6.0 4.5 3.2
Test coal quality (carbon) ％ 56.19 56.19 56.19
Test coal quality (Hydrogen) ％ 2.03 2.03 2.03
Test coal quality (oxygen) ％ 0.95 0.95 0.95
Test coal quality (nitrogen) ％ 0.94 0.94 0.94
Test coal quality (Sulfur) ％ 3.14 3.14 3.14
Test coal quality (Ash) ％ 28.85 28.85 28.85
Test coal quality (moisture) ％ 7.90 7.90 7.90
Volatile matter (air drying base) ％ 11.24 11.24 11.24
Test coal quality (Low calorific value) kJ/kg coal 21100 21100 21100
Smoke exhaust temperature (after correction) ℃ 116.30 116.22 115.73
Carbon content of fly ash ％ 11.70 7.80 6.51
Carbon content of slag ％ 1.63 1.50 1.03
Thermal efficiency of boiler ％ 85.96 88.85 89.54
TABLE 7330 MW comparison of economic efficiency under various working conditions of load-to-fineness of pulverized coal
Figure BDA0001913393420000112
Figure BDA0001913393420000121
3. Determining the optimum coal fines fineness
As can be seen from tables 5 to 7, the fineness of the pulverized coal is changed in a 330MW load, the proportion of the over-fire air is about 25%, and the influence on combustion is obvious through tests in a deep low-nitrogen combustion mode of a unit.
(a) The carbon content of the fly ash is reduced from 11.7 percent to 6.51 percent, the change is obvious, and the carbon content is reduced by about 5.21 percent points. The change of the temperature of the discharged smoke is not obvious, the boiler efficiency is improved by 3.58 percentage points, and the coal consumption is reduced by about 12.17 g/(KW.h).
(b) The amount of the reduced temperature water is in a decreasing trend. The amount of the superheated cooling water is reduced by 18 t/h.
(c) After the fineness of the coal dust is reduced by 2.8 percentage points, the power consumption of a coal mill and the electric quantity of a fan are increased from 14517kW.h to 14625kW.h, 108kW.h is increased, and the amplification is 0.75%.
(d) After the fineness of the coal dust is reduced by 2.8 percentage points, the concentration of nitrogen oxide at the outlet of the economizer is reduced by about 175mg/Nm3The amplitude reduction reaches 18.6 percent.
Tests show that the carbon content of the numerical simulation fly ash and the carbon content of the large slag at the outlet of the economizer are different from the actual field test result under the working conditions of different coal powder fineness under the load of 330MW, which indicates that the numerical simulation is more accurate. When the fineness R90 of the coal powder is reduced from 6% to 3.2%, the carbon content of fly ash and large slag is reduced more, the boiler efficiency is improved by 3.58%, the nitrogen oxides are reduced, the amount of overheated desuperheating water is reduced, and the unit economy and environmental protection are obviously improved.
When the fineness of the coal powder R90 is reduced to 3.2%, the more the fineness of the coal powder is reduced, the larger the differential pressure of the coal mill is found in the test process, the risk also exists in the safe and stable operation of the coal mill, when the fineness of the coal powder is reduced to 3.2%, the coal powder is combusted more in advance, and the risk of burning a nozzle of a combustor is caused. Comprehensive analysis shows that when the lean coal is combusted, the selection of the fineness R90 of the coal powder is about 3 percent more reasonable.
Example 2(260MW load)
The coal mill specifically put into operation in this example was an ABCD4 coal mill.
The invention relates to a method for controlling the fineness of lean coal powder for a boiler in a W-shaped flame combustion mode, which comprises the following specific steps:
(1) under the low-nitrogen combustion state of the boiler, the load of a unit is kept unchanged at 265MW, the proportion of over-fire air (25%), the running oxygen amount (4.38% -4.46%), the running number of coal mills (ABCD mill) and the like are kept unchanged, and the influence of different coal powder fineness on the combustion of the boiler is analyzed through numerical simulation;
(2) and (3) carrying out field test research according to the numerical simulation result of the first step, keeping the proportion of over-fired air (25%), the running oxygen (4.38% -4.46%), the running number of coal mills (ABCD mill) and the like unchanged in the deep low-nitrogen combustion state of the boiler, and analyzing the influence of different coal powder fineness on the combustion of the boiler through tests.
Under the load of 260MW, the A mill output is 30t/h, the mill inlet primary air pressure is 5.0kPa, the mill inlet air temperature is 270 ℃, the hot air opening is 100 percent, the cold air opening is 40 percent, the dynamic separator frequency (40Hz, 45Hz and 50Hz), the inlet and outlet differential pressure of a coal mill (3.0kPa, 3.3kPa and 3.7kPa), the A mill ventilation amount (33t/h, 33t/h and 32.9t/h), the A mill outlet temperature (115 ℃, 114 ℃ and 112 ℃) and the coal powder fineness R90 are respectively (6.2%, 4.1% and 3.0%). The grinding output of B22 t/h, the primary air pressure of grinding inlet 5.0kPa, the air temperature of grinding inlet 293 ℃, the opening of hot air 100%, the opening of cold air door 40%, the frequency of dynamic separator (40Hz, 45Hz, 50Hz), the differential pressure of inlet and outlet of coal grinding mill (2.8kPa, 3.2kPa, 3.5kPa), the ventilation of B grinding (29.6t/h, 29.8t/h, 29.1t/h), the outlet temperature of B grinding (112 ℃, 111 ℃, 112 ℃), the fineness of coal powder R90 are respectively (5.6%, 4.0%, 3.1%). 31t/h of C mill outlet, 5.3kPa of primary air pressure at the mill inlet, 305 ℃ of air temperature at the mill inlet, 100% of opening of hot air, 0% of opening of cold air door, frequencies of dynamic separators (40Hz, 45Hz and 50Hz), differential pressure at the inlet and outlet of the coal mill (3.2kPa, 3.5kPa and 3.8kPa), ventilation of C mill (32.8t/h, 33t/h and 31.9t/h), temperature at the outlet of C mill (106 ℃, 105 ℃ and 106 ℃), and fineness R90 of coal powder (6.0%, 3.9% and 2.9%) respectively. D mill output of 33t/h, mill inlet primary air pressure of 5.3kPa, mill inlet air temperature of 305 ℃, hot air opening of 100%, cold air opening of 0%, dynamic separator frequency (40Hz, 45Hz, 50Hz), coal mill inlet and outlet differential pressure (3.4kPa3.7kPa, 4.0kPa), D mill ventilation (32.8t/h, 33t/h, 34t/h), D mill outlet temperature (100 ℃, 102 ℃), and coal dust fineness R90 of (5.9%, 3.9%, 3.1%) respectively.
(3) By combining numerical simulation and experimental research, the optimal control value of the fineness (R90) of the burning lean coal powder in the low-nitrogen combustion state of the W-shaped flame combustion mode boiler is about 3%.
1. Numerical simulation analysis process and results
Under the load of 260MW, considering the deep nitrogen combustion state of the boiler, the fineness of the pulverized coal (R) is changed while keeping the proportion of the over-fire air to be about 25 percent, the secondary air distribution mode, the operation oxygen amount, the number of the coal mills in operation and the like unchanged906 percent, 4.5 percent and 3 percent respectively), wherein the fineness of the coal dust is 6 percent calculated according to recommended calculation formula of powder process system design and calculation guide rules, 2012 edition. And analyzing the influence of the change of the fineness of the coal powder on combustion. The numerical simulation conditions are shown in Table 8. The simulation results are shown in table 9, fig. 7-11.
Simulation working condition of different coal powder fineness numerical values under table 8260 MW
Working conditions Working condition 4 Working condition 5 Working condition 6
Description of the working conditions α＝1.27 α＝1.27 α＝1.27
Description of the working conditions Fine powder 6 Fine powder 4.5 Fine powder 3
R90＝6.00％ R90＝4.50％ R90＝3.00％
SOFA wind ratio 25％ 25％ 25％
Table 9260 MW simulation results of different coal powder fineness numbers
Figure BDA0001913393420000141
As can be seen from tables 8-9 and FIGS. 7-11, the influence of changing the fineness of the pulverized coal on combustion is obvious under the conditions of 260MW load, about 25% of over-fire air proportion and deep low-nitrogen combustion of the unit.
(1) Along with the reduction of the thinning of the coal powder, the specific surface area of the coal powder in unit mass in contact with oxygen and hot smoke in the furnace is increased, the ignition is earlier, the burnout is more thorough, the heat release is more under the condition of the same coal powder amount, and therefore the water average of the overall temperature of the hearth is slightly higher than that of the original working condition.
(2) Reducing the granularity of the coal powder is beneficial to burn out, and the carbon content of the fly ash is gradually reduced from the working condition 4 to the working condition 6. When the fineness of the coal dust is reduced from 5.9% to 3.0%, the carbon content of fly ash is reduced from 10.17% to 6.14%, the carbon content is reduced by about 4 percentage points, and the coal consumption is reduced by about 8 g/kW.h.
(3) Along with the reduction of the particle size of the pulverized coal, the concentration of NOx at the outlet of the hearth is gradually reduced. The NOx concentration at the outlet of the hearth under the working conditions 5 and 6 is reduced by about 2.4 percent and 14.5 percent respectively compared with that under the working condition 4.
Fineness of coal powder when power station boiler is in deep low-nitrogen combustion state and burning lean coalChange the carbon content of the fly ash of the boiler and the NO at the outlet of the economizerXThe concentration, the temperature field of the hearth and the CO concentration of the hearth have obvious influence. When the fineness of the coal powder is reduced from 6% to 3%, the carbon content of fly ash is reduced by 4%, and NO is discharged from an economizerXThe concentration drops by about 14.5%. When the power station boiler is in a deep low-nitrogen combustion state and is used for burning lean coal, the operation of the fineness of the pulverized coal is reduced as much as possible on the premise that a pulverized coal preparation system is safe and allowable in operation in order to achieve the best economy and environmental protection of a unit. In order to ensure the long-term safety of a pulverizing system and the safety of a burner nozzle, the fineness R90 of the pulverized coal is controlled to be about 3 percent better when the lean coal for the W-shaped flame combustion boiler is burnt through numerical simulation
2. Experimental study procedure and results
The total coal quantity, the running oxygen quantity, the SOFA air proportion, the coal mill output, the coal mill ventilation quantity, the inlet primary air pressure and the like are kept unchanged, and 3 working conditions of the frequency of the variable-state separator are developed.
And testing the heat efficiency of the boiler and the power consumption of the auxiliary machine under different working conditions. The unit operation is shown in table 10. The furnace efficiency calculation parameters under various working conditions are shown in a table 11. The economic analysis is shown in Table 11.
Operating mode of rotating speed unit of table 10260 MW load change state separator
Figure BDA0001913393420000151
Figure BDA0001913393420000161
Figure BDA0001913393420000171
Experimental result table for thermal efficiency of boiler with 11260 MW load different separator rotating speed working conditions
Item Unit of Working condition 4 Working condition 5 Working condition 6
Fineness of coal dust R90 ％ 6.1 4.8 2.9
Test coal quality (carbon) ％ 56.19 56.19 56.19
Test coal quality (Hydrogen) ％ 2.03 2.03 2.03
Test coal quality (oxygen) ％ 0.95 0.95 0.95
Test coal quality (nitrogen) ％ 0.94 0.94 0.94
Test coal quality (Sulfur) ％ 3.14 3.14 3.14
Test coal quality (Ash) ％ 28.85 28.85 28.85
Test coal quality (moisture) ％ 7.90 7.90 7.90
Volatile matter (air drying base) ％ 11.24 11.24 11.24
Test coal quality (Low calorific value) kJ/kg coal 21100 21100 21100
Smoke exhaust temperature (after correction) ℃ 115.60 115.07 115.93
Carbon content of fly ash ％ 11.30 7.51 6.33
Carbon content of slag ％ 2.13 2.10 1.53
Thermal efficiency of boiler ％ 85.73 88.62 89.24
TABLE 12260 MW comparison of economical efficiency under various working conditions of load-variable coal powder fineness
Figure BDA0001913393420000172
Figure BDA0001913393420000181
3. Determining the optimum coal fines fineness
As can be seen from tables 10 to 12, the fineness of the pulverized coal is changed under the conditions of 260MW load, over-fire air proportion of about 25 percent and deep low-nitrogen combustion of the unit, and tests show that the influence on combustion is obvious.
(a) When the fineness of the coal dust is reduced from 6.1% to 2.9%, the carbon content of the fly ash is reduced from 11.3% to 6.33%, the change is obvious, and the carbon content is reduced by about 5 percentage points. The change of the exhaust gas temperature is not obvious, the boiler efficiency is improved by 3.51 percentage points, and the coal consumption is reduced by about 11.94g/(KW h).
(b) The amount of the reduced temperature water is in a decreasing trend. The amount of the superheated cooling water is reduced by 14 t/h.
(c) After the fineness of the coal powder is reduced by 2.2 percent, the power consumption of a coal mill and the electric quantity of a fan are increased from 13811kW.h to 13811kW.h, 100kW.h is increased, and the amplitude is increased by 0.72 percent.
(d) After the fineness of the coal dust is reduced by 2.2 percentage points, the concentration of nitrogen oxide at the outlet of the economizer is reduced by about 117mg/Nm3The amplitude reduction reaches 13.9 percent.
Tests show that under the load of 260MW, the carbon content of the numerical simulation fly ash and the carbon content of the large slag at the outlet of the economizer are different from the actual field test result under the working conditions of different coal powder fineness, and the numerical simulation is more accurate. When the fineness R90 of the coal powder is reduced from 6% to 3%, the carbon content of fly ash and large slag is reduced more, the boiler efficiency is improved by 3.63%, the nitrogen oxides are reduced, the amount of overheat desuperheating water is reduced, and the unit economy and environmental protection are obviously improved.
The more the fineness of the pulverized coal is reduced, the larger the differential pressure of the coal mill is found in the test process, the risk also exists in the safe and stable operation of the coal mill, when the fineness of the pulverized coal is reduced to 3%, the pulverized coal is combusted more in advance, and the risk of burning a nozzle of a combustor is caused. Comprehensive analysis shows that when the lean coal is combusted, the selection of the fineness R90 of the coal powder is about 3 percent more reasonable.

Claims (1)

1. A combustion control method of lean coal for a boiler adopting a W-shaped flame combustion mode is characterized in that the combustion control method controls the fineness R90 of coal powder to be 3.0-3.2% by adjusting the operation method of a coal mill; the combustion control method includes the steps of:
(1) in a low-nitrogen combustion state of a boiler, maintaining the load of a unit to be 330MW or 260MW unchanged, maintaining the over-fire air proportion to be 25% unchanged, the operation oxygen amount unchanged and the number of 4 coal mills in operation unchanged; when the load of the unit is 330MW, the running oxygen amount is maintained at 3.85% -4.06%, and when the load of the unit is 260MW, the running oxygen amount is maintained at 4.38% -4.46%;
(2) when the load of the unit is 330MW, controlling four ABCD coal mills as follows:
the grinding output of A is 40t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 294 ℃, the opening of hot air is 100%, the opening of cold air is 0%, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal grinding machine is 4.4kPa, the ventilation quantity of A grinding is 45.9t/h, and the temperature of an outlet of A grinding is 102 ℃;
the grinding output of the B mill is 27t/h, the primary air pressure of a grinding inlet is 5.3kPa, the air temperature of the grinding inlet is 292 ℃, the opening of hot air is 100 percent, the opening of cold air is 0 percent, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal mill is 4.6kPa, the ventilation quantity of the B mill is 41.1t/h, and the temperature of the outlet of the B mill is 102 ℃;
c, grinding outlet force of 37t/h, primary air pressure of a grinding inlet of 5.3kPa, air temperature of a grinding inlet of 295 ℃, opening degree of hot air of 100%, opening degree of cold air door of 0%, frequency of a dynamic separator of 50Hz, differential pressure of an inlet and an outlet of a coal grinding machine of 4.6kPa, ventilation quantity of the C grinding of 35.9t/h and outlet temperature of the C grinding of 106 ℃;
the D mill output is 33t/h, the primary air pressure of the mill inlet is 5.3kPa, the air temperature of the mill inlet is 295 ℃, the opening degree of the hot air door is 100%, the opening degree of the cold air door is 0%, the frequency of the dynamic separator is 50Hz, the differential pressure of the inlet and the outlet of the coal mill is 4.3kPa, the ventilation quantity of the D mill is 39t/h, and the temperature of the outlet of the D mill is 99 ℃;
when the load of the unit is 260MW, the four ABCD coal mills are controlled as follows:
the grinding output of the A mill is 30t/h, the primary air pressure of a grinding inlet is 5.0kPa, the air temperature of the grinding inlet is 270 ℃, the opening of hot air is 100 percent, the opening of cold air is 40 percent, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal mill is 3.3kPa, the ventilation quantity of the A mill is 32.9t/h, and the temperature of the outlet of the A mill is 112 ℃;
the grinding output of the B mill is 22t/h, the primary air pressure of a grinding inlet is 5.0kPa, the air temperature of the grinding inlet is 293 ℃, the opening of hot air is 100%, the opening of cold air is 40%, the frequency of a dynamic separator is 50Hz, the differential pressure of an inlet and an outlet of a coal mill is 3.5kPa, the ventilation quantity of the B mill is 29.1t/h, and the temperature of the outlet of the B mill is 112 ℃;
c, grinding output of 31t/h, primary air pressure of a grinding inlet of 5.3kPa, air temperature of the grinding inlet of 305 ℃, opening of hot air of 100 percent, opening of cold air door of 0 percent, frequency of a dynamic separator of 50Hz, differential pressure of an inlet and an outlet of a coal grinding mill of 3.8kPa, ventilation quantity of the C grinding of 31.9t/h and outlet temperature of the C grinding of 106 ℃;
the D mill output is 33t/h, the primary air pressure of the mill inlet is 5.3kPa, the mill inlet air temperature is 305 ℃, the hot air opening is 100%, the cold air opening is 0%, the dynamic separator frequency is 50Hz, the inlet and outlet differential pressure of the coal mill is 4.0kPa, the D mill ventilation is 34t/h, and the D mill outlet temperature is 102 ℃.
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