Positive pressure dense phase pneumatic ash conveying method and system for energy-saving coal-fired power plant

Abstract

A method for positive pressure dense phase pneumatic ash conveying in an energy-saving coal-fired power plant: an analog material level measurement device is installed on the silo pump; when the material level measured by the material level sensor is greater than the material level high setting value or the ash loading time exceeds the theoretical ash loading time, the ash loading ends and enters the ash conveying queue; when the ash conveying queue ends, the ash conveying is timed at the same time; if the ash conveying time T2 exceeds the ash conveying timeout setting, the program stops and reports a timeout alarm; when the ash conveying gas pressure measured by the ash conveying pressure sensor is less than the pressure setting and the material level measured by the material level sensor is greater than the material level low setting, the ash conveying ends and the next round of ash loading and conveying begins. The present invention improves the control strategy of the ash conveying system and perfects the fault judgment configuration, greatly improves the accuracy of the fly ash material level measurement of the ash conveying system, ensures the stable, efficient and economical operation of the ash conveying system, effectively reduces the ash conveying frequency, improves the ash-to-gas ratio, and reduces the power consumption rate of the ash conveying air compressor.

Description

Technical Field

[0001] The invention relates to a positive pressure dense phase pneumatic ash conveying method for an energy-saving coal-fired power plant, and also relates to a positive pressure dense phase pneumatic ash conveying system for an energy-saving coal-fired power plant corresponding to the method. Background Art

[0002] The ash conveying pneumatic system of a thermal power plant is the main peripheral auxiliary equipment of a thermal power plant, used to convey the fly ash produced by the combustion of coal in the boiler. The specific work flow is as follows: Figure 1 As shown. The fly ash generated by the combustion of coal in the boiler enters the flue 1 at the tail end of the boiler along with the flue gas, and is collected by the multiple rows of high-voltage electrostatic precipitators 2 on both sides of A and B, and then enters the ash hopper 3. Under the control of the ash loading program, the feed valve 4 is opened, and the fly ash falls into the silo pump 5. When the ash loading time reaches the ash loading time T1 or the fly ash level value measured by the switch-type level sensor 6 in the silo pump 5 reaches the high alarm setting value, the feed valve 4 is closed, the ash loading is completed, and the ash conveying queue sequence is entered. If no other ash conveying unit is conveying ash or the queue sequence of this ash conveying unit is the first, and the ash conveying main pipe pressure 14 meets the set requirements, the ash conveying program is entered. Under the control of the ash conveying program, the silo pump outlet valve 7 is opened, and the ash enters the ash conveying pipeline 8. A plurality of ash conveying air compressors 9 operating in parallel produce conveying gas which enters the air inlet valve 11 of the ash conveying unit that needs to convey fly ash through the ash conveying main pipe 10, and conveys the ash in the ash conveying pipeline 8 of the unit. The positive pressure dense phase gas flow carrying the ash flows out of the discharge valve 12 of the ash conveying unit and is finally delivered to the ash bin 13. When the conveying time reaches the ash conveying time T2 and the ash conveying pipeline pressure 15 is less than the set pressure, the silo pump outlet valve 7 and the air inlet valve 11 and the discharge valve 12 of the conveying unit are closed, the ash conveying process ends, and a new round of ash loading and conveying begins. The ash conveying air compressor is operated in an n+m mode, that is, n air compressors are always running to ensure the basic conveying gas volume and pressure requirements under normal conditions, and m compressors are standby to meet the additional gas volume requirements under overload and abnormal conditions.

[0003] Under the traditional ash conveying control strategy, since it is operated according to the time sequence, there are the following problems that lead to poor ash conveying effect or poor economic benefits:

[0004] 1. Inaccurate fly ash level measurement. The original fly ash level measurement equipment is a radio frequency admittance type level switch, which can only simply determine whether the level is higher or lower than a certain value, and cannot accurately measure the specific level value, so it is impossible to determine whether the fly ash in the silo pump is loaded in place or transported cleanly.

[0005] Second, the amount of fly ash collected by the ash hoppers of different ash conveying units during the specified ash loading waiting interval is inconsistent. Some ash conveying units have collected enough ash and started normal ash conveying, while some ash conveying units have not collected enough ash but will still load and convey ash after the specified time. This will increase the frequency of ash conveying and increase the output of the air compressor.

[0006] 3. The amount of fly ash loaded by the silo pumps of different ash conveying units within the specified ash loading time is inconsistent. The ash conveying unit loaded with more fly ash can make full use of the ash conveying time. When the pipeline pressure is lower than the set value, the conveying is considered completed. However, for the ash conveying unit loaded with less fly ash, if the minimum ash conveying time is not reached, the ash conveying process will continue even if the pipeline pressure is lower than the set value, wasting time and increasing the output of the air compressor.

[0007] In order to improve the economy and stability of the pneumatic ash conveying system, it is necessary to change its existing control strategy and add the equipment required for new control strategy measurement and the logic configuration required for control to control the safe and economical operation of the ash conveying system. Summary of the invention

[0008] The first technical problem to be solved by the present invention is to provide an energy-saving coal-fired power plant positive pressure dense phase pneumatic ash conveying method.

[0009] The second technical problem to be solved by the present invention is to provide a system dedicated to the method.

[0010] The method and system of the present invention can improve the accuracy of fly ash level measurement and optimize the control strategy and logical configuration of the fly ash conveying program, while ensuring the normal operation of the ash conveying system, reducing the ash conveying frequency, improving the ash-to-gas ratio, and reducing the power consumption of the ash conveying air compressor.

[0011] To solve the above-mentioned first technical problem, the technical solution adopted by the present invention is as follows:

[0012] An energy-saving coal-fired power plant positive pressure dense phase pneumatic ash conveying method, which is characterized by comprising the following steps:

[0013] S1. Ash loading (refers only to fly ash entering the silo pump, excluding electrostatic precipitator 2 entering the ash hopper 3)

[0014] When you click on the program to start running, the program first enters the ash loading, the silo pump feed valve 4 automatically opens, the fly ash falls into the silo pump 5, and the ash loading step starts timing T1;

[0015] When one of the following conditions is met, the loading is completed and the ash delivery queue state is entered, otherwise the loading continues:

[0016] 1) The analog material level L measured by the silo pump material level sensor 305 is higher than the material level high setting value LH ;

[0017] 2) Exceeds the theoretical loading time T calculated by load, ash content, heat, and correction coefficient using function formula 311 opt ;

[0018]

[0019] In addition, when the loading time T1 exceeds the loading timeout setting value T max1 The whole program stops and alarms when the timeout occurs;

[0020] S2. Ash transport

[0021] The conveying order of different electric fields is carried out according to the order of the ash loading completion time of the ash loading unit. The first waiting is the first conveying. When the waiting is over, the ash conveying step is entered and the ash conveying step starts timing T2.

[0022] When one of the following conditions is met, the ash feeding ends and the next round of ash loading and feeding begins, otherwise the ash feeding continues:

[0023] 1) The analog material level height L measured by the silo pump material level sensor 305 is lower than the material level low setting value L L ;

[0024] 2) The ash conveying gas pressure 308 measured by the ash conveying pressure sensor 310 is less than the pressure setting value 307;

[0025] In addition, when the ash delivery time T2 exceeds the ash delivery timeout setting value T max2 The entire program stops and a timeout alarm is sounded.

[0026] To solve the above second technical problem, the technical solution adopted by the present invention is as follows:

[0027] An energy-saving coal-fired power plant positive pressure dense phase pneumatic ash conveying system, characterized by comprising:

[0028] A tail flue 1 providing a flow channel for boiler flue gas of the coal-fired power plant;

[0029] A high-voltage electric precipitator 2 for removing fly ash from flue gas in a tail flue 1, the inlet of which is connected to the tail flue 1;

[0030] An ash hopper 3 for collecting fly ash ionized by the high-voltage electric precipitator 2, the inlet of which is connected to the outlet of the high-voltage electric precipitator 2;

[0031] A valve feed valve 4 for controlling the ash hopper 3 to load ash into the silo pump 5, the inlet of which is connected to the outlet of the ash hopper 3;

[0032] A silo pump 5 for loading the ash collected in the ash hopper 3, the inlet of which is connected to the outlet of the valve feed valve 4;

[0033] A material level sensor 6 for measuring the height of the fly ash material level in the silo pump 5 is installed in the silo pump 5;

[0034] A silo pump outlet valve 7 for controlling the silo pump 5 to feed ash into the ash conveying pipeline 8, the inlet of which is connected to the outlet of the silo pump 5;

[0035] An ash conveying pipeline 8 for conveying fly ash, the inlet of which is connected to the outlet of the silo pump outlet valve 7;

[0036] An ash storage 13 for loading fly ash transported by the ash transport system, the inlet of which is connected to the outlet of the ash transport pipeline 8;

[0037] The ash conveying air compressor 9 is used to produce the air required for fly ash conveying, and its output reaches the ash conveying pipeline 8 through the ash conveying main pipe 10 for ash conveying air circulation equipped with an air intake valve 11 for controlling the air intake of the ash conveying pipeline 8 of the ash conveying unit.

[0038] The ash conveying pipeline 8 is also equipped with a discharge valve 12 for controlling the gas outlet of the ash conveying pipeline 8 of the ash conveying unit and a pressure transmitter 15 for measuring the pressure of the ash conveying pipeline 8 of the ash conveying unit.

[0039] The ash conveying main pipe 10 is also provided with a pressure transmitter 14 for measuring the pressure of the ash conveying main pipe 10.

[0040] The circuit elements include a 220V AC power supply 201 for providing power to the silo pump level sensor 202, a Schneider ACI03000 analog input card 203 for converting the 4-20mA DC power signal sent by the level sensor 202 into a digital signal, a Schneider XBP00600 backplane 204 for sending the digital signal to the controller via a bus, and a Schneider CPU67160 controller 205 for processing and calculating the digital signal.

[0041] The material level measurement sensor 305 is a non-contact integrated material level meter based on ray collection monitoring, external power supply, four-wire system, 220V AC power supply 201, and the output signal is a 4-20mA analog signal. It is converted into a digital signal through the Schneider ACI03000 analog input card 203 and then transmitted to the CPU67160 controller 205 through the XBP00600 backplane 204 local bus to participate in the logic configuration control. The wiring scheme after the transformation is shown in the figure Figure 2 .

[0042] The ash conveying air compressor is of screw type, and the rated exhaust volume of each air compressor is not less than 46.2Nm 3 / min, the rated exhaust pressure is not less than 0.75MPa, the pressure transmitter has a range of 0-1MPa, and is respectively installed on the ash conveying mother pipe 10 in front of the air inlet valve of each unit ash conveying pipeline 8 and in front of the discharge valve 12 of each unit ash conveying pipeline 8, and the distance from the valve is not less than 3 times the pipeline diameter.

[0043] The power supply of the material level sensor 202 is a 220V AC power supply, the output signal is a 4-20mA DC signal powered by the sensor itself, the measuring range is 0-6m, the measuring dead zone is 0.3m, and the installation position is located next to the silo pump inlet, at least 0.3m away from the dust falling position of the silo pump inlet and the edge of the silo pump, and the probe rod is directed vertically downward.

[0044] Beneficial effects: The present invention designs a new energy-saving control strategy and logic configuration for the ash conveying system, and adds the equipment required for the corresponding control. Its main advantages are:

[0045] 1) It can greatly improve the accuracy of ash level measurement, allowing operators to clearly observe the ash loading and transportation conditions during the entire ash conveying process.

[0046] 2) It can accurately control the ash loading time and ash conveying time, avoid wasting time and air compressor output, effectively reduce the ash conveying frequency, reduce the power consumption of the ash conveying air compressor, and improve the ash-gas ratio, thereby improving the economic benefits of the power plant.

[0047] 3) In order to prevent the ash conveying system from being abnormal due to failure of the measuring device, an intelligent judgment alarm for program running time timeout is added, which reduces the monitoring intensity of the operating personnel while ensuring the stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0049] Figure 1 It is a schematic diagram of the composition and connection relationship of the positive pressure dense phase pneumatic ash conveying system of a coal-fired power plant of the present invention;

[0050] Figure 2 It is a schematic diagram of the circuit composition and connection relationship of the material level sensor of the positive pressure dense phase pneumatic ash conveying system of a coal-fired power plant after the modification of the present invention;

[0051] Figure 3 It is a control flow diagram of a positive pressure dense phase pneumatic ash conveying system for a coal-fired power plant according to the present invention.

[0052] Description of reference numerals:

[0053] 1- tail flue, 2- high-voltage electric precipitator, 3- ash hopper, 4- feed valve, 5- bin pump, 6- material level sensor, 7- bin pump outlet valve, 8- ash conveying pipeline, 9- ash conveying air compressor, 10- ash conveying main pipe, 11- air inlet valve, 12- discharge valve, 13- ash storage, 14- ash conveying main pipe pressure transmitter, 15- ash conveying pipeline pressure transmitter;

[0054] 201-220V AC power supply, 202-level sensor, 203-Schneider ACI03000 analog input card, 204-Schneider XBP00600 backplane, 205-Schneider CPU67160 controller.

[0055] 301- Ash loading timeout setting value, 302- Theoretical ash loading time calculated by load, ash content, heat and correction coefficient, 303- Silo pump material level high setting value, 304- Material level measured by material level sensor, 305- Material level sensor, 306- Ash delivery timeout setting value, 307- Ash delivery end pressure setting value, 308- Delivery gas pressure measured by ash delivery unit pipeline pressure transmitter, 309- Silo pump material level low setting value, 310- Ash delivery unit pipeline pressure transmitter, 311- Ash loading theoretical time calculation formula.

[0056] The following parameters are used in the calculation formula for the theoretical ash loading time in the present invention: theoretical ash loading time, ash loading time under 75% load condition of the unit, unit s, coal consumption under 75% load condition of the unit, unit t / h, ash content of coal entering the furnace when the unit is 75% load rate, unit %, low calorific value of coal entering the furnace when the unit is 75% load rate, unit MJ / kg, coal amount of coal feeder under actual situation, unit t / h, ash content of coal entering the furnace under actual situation, unit %, low calorific value of coal entering the furnace under actual situation, unit MJ / kg, manual correction coefficient. DETAILED DESCRIPTION

[0057] The embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and specific implementation examples.

[0058] like Figures 1 to 3The system embodiment of the present invention shown comprises: a tail flue 1 providing a circulation channel for the flue gas of the boiler of the coal-fired power plant; a high-voltage electric precipitator 2 for removing fly ash in the flue gas of the tail flue 1, the inlet of which is connected to the tail flue 1; an ash hopper 3 for collecting fly ash ionized by the high-voltage electric precipitator 2, the inlet of which is connected to the outlet of the high-voltage electric precipitator 2; a valve feed valve 4 for controlling the ash hopper 3 to load ash into a silo pump 5, the inlet of which is connected to the outlet of the ash hopper 3; a silo pump 5 for loading the ash collected in the ash hopper 3, the inlet of which is connected to the outlet of the valve feed valve 4; a valve for measuring the fly ash material in the silo pump 5 A material level sensor 6 for measuring the material level is installed in the silo pump 5; a silo pump outlet valve 7 for controlling the silo pump 5 to feed ash into the ash conveying pipeline 8, the inlet of which is connected to the outlet of the silo pump 5; the ash conveying pipeline 8 for conveying fly ash, the inlet of which is connected to the outlet of the silo pump outlet valve 7; an ash storage 13 for loading the ash conveying system to convey fly ash, the inlet of which is connected to the outlet of the ash conveying pipeline 8; an ash conveying air compressor 9 for producing the air required for fly ash conveying, the output of which reaches the ash conveying pipeline 8 through an ash conveying main pipe 10 for ash conveying air circulation equipped with an air intake valve 11 for controlling the air intake of the ash conveying pipeline 8 of the ash conveying unit.

[0059] The ash conveying pipeline 8 is also equipped with a discharge valve 12 for controlling the gas outlet of the ash conveying pipeline 8 of the ash conveying unit and a pressure transmitter 15 for measuring the pressure of the ash conveying pipeline 8 of the ash conveying unit. The ash conveying mother pipe 10 is also equipped with a pressure transmitter 14 for measuring the pressure of the ash conveying mother pipe 10. The material level measurement sensor 305 is a non-contact integrated material level meter based on ray collection monitoring, externally powered, four-wire system, the power supply is 220V AC power supply 201, the output signal is 4~20mA analog signal, which is converted into a digital signal through Schneider ACI03000 analog input card 203 and then transmitted to the CPU67160 controller 205 through the XBP00600 backplane 204 local bus to participate in logic configuration control. The wiring scheme after transformation is shown in the figure below. Figure 2 .

[0060] Working process

[0061] After the coal is burned in the boiler, the incombustible ash enters the flue 1 at the tail of the boiler on both sides along with the flue gas generated by the combustion in the furnace. The ash entrained in the flue gas is electrically separated when passing through the high-voltage electrostatic precipitator 2. After the dust particles combine with negative ions and carry negative voltage, they tend to discharge and deposit on the anode surface, and fall into the ash hopper 3 under the action of vibration.

[0062] When the program is clicked to start running, the program first enters the ash loading process, the silo pump feed valve 4 automatically opens, and the fly ash falls into the silo pump 5. At the same time, the ash loading step starts timing T1. When the ash loading time reaches the theoretical setting value 302 of the ash loading time calculated according to the load, coal ash content, low calorific value of coal, etc., or the fly ash level 304 measured by the level sensor 6 in the silo pump 5 reaches the high setting value 303, the silo pump feed valve 4 automatically closes, and the ash loading process ends.

[0063] When other ash conveying units are conveying ash, this unit needs to queue up and wait for ash conveying according to the order of the ash loading unit end time. The principle of ash conveying sequence is to wait first and convey first. When the waiting is over, the ash conveying step is entered and the ash conveying step starts timing T2. After the ash conveying step starts, the silo pump outlet valve 7 opens automatically, and the fly ash in the silo pump 5 falls into the ash conveying pipeline 8 where the unit is located. Multiple ash conveying air compressors 9 running in parallel generate enough compressed air to ensure the air pressure measured by the ash conveying main pipe pressure transmitter 14 in the ash conveying main pipe 10. When the ash conveying unit starts to convey ash, the air inlet valve 11 and the discharge valve 12 of the unit are automatically opened, and the compressed air in the ash conveying main pipe 10 enters the ash conveying pipeline 8 of the unit through the air inlet valve 11, and the fly ash entering the ash conveying pipeline 8 is pneumatically conveyed. The compressed air carrying the fly ash flows out of the ash conveying pipeline 8 through the discharge valve 12 and finally enters the ash bin 13. When the fly ash level 304 in the silo pump 5 is lower than the set value 309 and the ash conveying pipeline pressure 308 measured by the ash conveying pipeline pressure transmitter 15 is lower than the ash conveying end pressure set value 307, the silo pump outlet valve 7, the air inlet valve 11, and the discharge valve 12 are automatically closed, the ash conveying process ends, and a new round of ash loading and ash conveying begins, and the cycle is repeated until the ash conveying program control is stopped. If the ash loading time or ash conveying time exceeds the time during the ash loading and conveying process, the program ends and a timeout alarm is issued.

[0064] See also Figure 2 The material level sensor 2 is changed from the original material level switch to a non-contact integrated material level meter, powered by a 220V AC power supply 1, and the measured output signal is changed from the original switch dry contact signal to a 4-20mA analog signal. The analog signal enters the Schneider ACI03000 analog input card 203 for analog-to-digital conversion, and then is transmitted to the Schneider CPU67160 controller 205 via the Schneider XBP00600 backplane 204 local bus.

[0065] As the calculation formula for the theoretical ash loading time in the present invention, the theoretical ash loading time is the actual ash loading time measured under 75% load of the unit multiplied by the ratio of the product of the coal feed amount under the operating condition and the ash content of the coal under the operating condition to the low calorific value of the coal under the operating condition, and then divided by the ratio of the product of the coal feed amount under the actual load and the ash content of the coal under the operating condition to the low calorific value of the coal under the operating condition, and finally multiplied by the manual correction coefficient, and the result is the theoretical ash loading time.

Claims

1. A positive pressure dense phase pneumatic ash conveying method for energy-saving coal-fired power plants, characterized by: The following steps are involved: S1. Ash loading Click the program to start running. The program will first start the ash loading step. The valve feed valve (4) will automatically open, and the fly ash will fall into the silo pump (5). At the same time, the ash loading step will start timing T1; When one of the following conditions is met, the ash loading is completed and the ash delivery queue is entered, otherwise the ash loading continues: 1) The analog material level L measured by the silo pump material level sensor (305) is higher than the material level high setting value L H ; 2) Exceeding the theoretical loading time calculated by the load, ash content, heat, and correction factor through the function formula (311) ---------------311； In addition, when the loading time T1 exceeds the loading timeout setting value T max1 When the timer is reached, the entire program stops and an alarm is sounded; S2. Ash transport The order of ash conveying in different electric fields is based on the order of the ash loading completion time of the ash loading unit. The first waiting step is followed by the conveying step. When the waiting step is over, the ash conveying step enters and the timing T2 of the ash conveying step is started. When one of the following conditions is met, the ash conveying ends and the next round of ash loading and conveying begins, otherwise the ash conveying continues: 1) The analog material level height L measured by the silo pump material level sensor (305) is lower than the material level low setting value L L ; 2) The ash conveying gas pressure (308) measured by the ash conveying pressure sensor (310) is less than the pressure setting value (307); In addition, when the ash delivery time T2 exceeds the ash delivery timeout setting value T max2 The entire program stops and issues a timeout alarm.

2. An energy-saving coal-fired power plant positive pressure dense phase pneumatic ash conveying system specially used for the method as claimed in claim 1, characterized in that include: A tail flue (1) providing a flow channel for boiler flue gas of the coal-fired power plant; A high-voltage electric precipitator (2) for removing fly ash from flue gas in a tail flue, the inlet of which is connected to the tail flue; An ash hopper (3) for collecting fly ash ionized by a high-voltage electric precipitator, the inlet of which is connected to the outlet of the high-voltage electric precipitator; A valve feed valve (4) for controlling the ash hopper to load ash into the silo pump (5), the inlet of which is connected to the outlet of the ash hopper; A silo pump (5) for loading the ash collected in the ash hopper, the inlet of which is connected to the outlet of the valve feed valve; A material level sensor (6) for measuring the height of the fly ash material level in the silo pump, installed in the silo pump; A silo pump outlet valve (7) for controlling the silo pump to feed ash into the ash conveying pipeline (8), the inlet of which is connected to the outlet of the silo pump; An ash conveying pipeline (8) for conveying fly ash, the inlet of which is connected to the outlet of the silo pump outlet valve (7); An ash storage device (13) for loading fly ash transported by the ash transport system, the inlet of which is connected to the outlet of the ash transport pipeline; The ash conveying air compressor (9) is used to produce the air required for fly ash conveying, and its output is transmitted to the ash conveying pipeline through an ash conveying main pipe (10) for ash conveying air circulation equipped with an air intake valve (11) for controlling the air intake of the ash conveying pipeline of the ash conveying unit.

3. The energy-saving coal-fired power plant positive pressure dense phase pneumatic ash conveying system according to claim 2 is characterized by: The ash conveying pipeline is also provided with a valve discharge valve (12) for controlling the gas outlet of the ash conveying pipeline of the ash conveying unit and an ash conveying pipeline pressure transmitter (15) for measuring the pressure of the ash conveying pipeline of the ash conveying unit.

4. The energy-saving coal-fired power plant positive pressure dense phase pneumatic ash conveying system according to claim 3 is characterized by: The ash conveying main pipe is also provided with an ash conveying main pipe pressure transmitter (14) for measuring the ash conveying main pipe pressure. The ash conveying main pipe pressure transmitter is respectively installed on the ash conveying main pipe (10) in front of the air inlet valve of each unit ash conveying pipeline and in front of the valve discharge valve (12) of each unit ash conveying pipeline, and the distance from the valve is not less than 3 times the pipeline diameter.

5. The energy-saving coal-fired power plant positive pressure dense phase pneumatic ash conveying system according to claim 4 is characterized in that: The pump level sensor (305) is a non-contact integrated level meter based on ray collection monitoring, with an external four-wire power supply, a 220V AC power supply (201), and an output signal of 4-20mA analog signal, which is converted into a digital signal through the Schneider ACI03000 analog input card (203) and then transmitted to the CPU67160 controller (205) through the XBP00600 backplane (204) local bus to participate in the logic configuration control; the ash conveying air compressor is a screw type, and the rated exhaust volume of each ash conveying air compressor is not less than 46.2Nm 3 / min, the rated exhaust pressure is not less than 0.75MPa.

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