Multi-variable control boiler on-line automatic pollution discharge method

Abstract

The invention relates to a multivariable control boiler on-line automatic blowdown method. The method comprises the following steps that 1, boiler blowdown automatic starting conditions are confirmed; 2, calculating a continuous pollution discharge amount according to an established multiple linear regression equation; 3, periodically discharging pollution according to a calculation result coupling effect; and 4, continuously collecting water quality data to judge the progress of an automatic pollution discharge process. And step 5, ending the automatic blowdown process of the boiler. According to the scheme, by means of the boiler on-line automatic pollution discharge method, coupling automatic control over continuous pollution discharge and regular pollution discharge of the boiler can be achieved, and the potential safety hazards that due to excessive pollution discharge, a large amount of high-temperature saturated water is lost, heat energy and demineralized water resources are wasted, and the salinity of boiler water is higher and higher due to insufficient pollution discharge are eliminated; and the quality of superheated steam can meet the national standard requirement, and salt deposition or corrosion of a thermodynamic system is reduced.

Description

Technical Field

[0001] The invention relates to a sewage discharge method, in particular to an online automatic sewage discharge method for a boiler with multivariable control, and belongs to the technical field of boiler water control of steam boilers. Background Art

[0002] During the operation of the steam boiler, as the steam is produced, the boiler water is concentrated. When the salt concentration rises to a certain level, the boiler water will produce foam, steam and water will co-boil, and the steam will carry a large amount of water, causing serious false water levels and making the furnace condition unstable. Therefore, the salt concentration of the boiler water must be controlled to ensure the steam quality and the safety of the boiler operation. The main method to control the salt concentration of the boiler water is to discharge the boiler water at the part with higher salt concentration below the evaporation surface of the boiler water, and add low-concentration feed water to dilute the salt concentration of the boiler water. Boiler discharge is divided into continuous discharge and periodic discharge: Periodic discharge is also called intermittent discharge or bottom discharge. When the boiler is under low load and high water level, the discharge valve is opened to discharge the sediments and dirt residues such as clay, sludge, precipitation and corrosion products at the bottom of the drum. Most domestic industrial boilers adopt a specified time and date, and the blowdown valve is fully opened manually for 30 seconds and then immediately closed. Each blowdown valve is operated in turn. This traditional regular blowdown method cannot achieve on-demand control of the blowdown volume. In the face of changes in steam flow, either excessive discharge causes energy waste, or it is difficult to ensure that the boiler water is qualified when the load changes greatly. Continuous blowdown is also called surface blowdown. This blowdown method continuously discharges the boiler water with the highest concentration from the surface layer of the drum boiler water to reduce the alkalinity, chloride ions and suspended solids on the surface of the boiler water, prevent the occurrence of steam-water co-evaporation and the corrosion of the boiler water to the drum wall. At present, most domestic industrial boilers adjust the time and opening of continuous blowdown according to the quality of the boiler water. If the blowdown volume is insufficient, the salt concentration of the boiler water will become higher and higher; on the contrary, if the blowdown volume is too large, the boiler water containing a large amount of heat energy is discharged, which will cause energy loss and waste of high-quality desalted water.

[0003] Through the applicant's search, there are currently no relevant documents and patent technologies involving a multivariable controlled online automatic blowdown method for boilers. The relevant announcement of automatic blowdown is the "Steam Boiler System with Automatic Correction of Blowdown Benchmark Data" with application number "201810818816.3", but it mainly automatically controls regular blowdown based on the amount of steam generated by the boiler and the amount of water input into the boiler. Other automatic controls for continuous discharge based on boiler water quality, such as the "A Boiler Automatic Blowdown Device and Method" published with application number "201911060031.5", control the opening and stopping of the continuous discharge valve by enabling the conductivity monitoring device to detect the boiler water conductivity in real time.

[0004] In view of the current manual control of periodic and continuous blowdown and single variable control of boiler automatic blowdown, which are prone to excessive blowdown and untimely blowdown, resulting in heat energy waste or deterioration of boiler water quality, as well as the need for vigorous development of intelligent manufacturing in power plants and the widespread use of boiler water level automatic control technology, the present invention provides a multivariable controlled boiler online automatic blowdown method. The method starts the boiler automatic blowdown process according to the logic of feed water hydrogen conductivity, boiler water conductivity, and boiler water phosphate content, establishes a regression equation through multivariate linear regression analysis, associates the continuous blowdown actuator to control the opening of the continuous blowdown valve, and at the same time establishes a coupling relationship based on the calculated continuous blowdown volume and periodic blowdown, associates the periodic blowdown actuator to control the opening and time of the periodic blowdown valve, and realizes the boiler online automatic blowdown function, thereby replacing manual operation and eliminating the unstable state caused by manual operation. Summary of the invention

[0005] The present invention is aimed at the problems existing in the prior art and provides a method for online automatic blowdown of boilers with multivariable control. The automatic blowdown process of the boiler is started according to the logic of feed water hydrogen conductivity, boiler water conductivity and boiler water phosphate content. A multivariate linear regression equation is established through regression analysis, and a continuous blowdown actuator is associated to control the opening of the continuous blowdown valve. At the same time, a coupling relationship is established based on the calculated continuous blowdown volume and periodic blowdown, and a periodic blowdown actuator is associated to control the opening and time of the periodic blowdown valve, so as to avoid safety hazards caused by insufficient blowdown and increasing boiler water salinity and excessive blowdown leading to the loss of a large amount of high-temperature saturated water, resulting in waste of heat energy and desalted water resources, thereby ensuring that the quality of boiler water is within the prescribed allowable range, truly realizing the online automatic blowdown function of the boiler, and improving the automation level of the boiler blowdown process.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: a multivariable controlled boiler online automatic blowdown method, the method comprising the following steps:

[0007] Step 1: Confirm the conditions for automatic start of boiler blowdown;

[0008] 1.1 During the normal operation of the boiler, the analog input value of the drum water level is used to perform a two-out-of-three voting process to confirm that the boiler water level is within the normal range of -100 to +250mm;

[0009] 1.2 Make quality judgment through the analog input value of the continuous blowdown valve opening to confirm that the continuous blowdown valve actuator is normal; 1.3 Through the on-site online analysis of the conductivity meter and phosphorus meter signal transfer, access the DCS to collect the real-time hydrogen conductivity of the feed water, the conductivity of the boiler water and the phosphate content, and make quality judgment;

[0010] 1.4 Compare the boiler water conductivity with 100 times the feed water hydrogen conductivity. When the ratio is greater than 1 and the phosphate content is greater than 15 mg / L, the trigger command automatically opens the continuous sewage discharge valve actuator, and the continuous sewage discharge automatically opens and enters the automatic sewage discharge stage. The default value of the continuous sewage discharge valve opening command is 50%. When the control command and the valve opening feedback deviation are within plus or minus 5%, it is judged that the automatic opening process is triggered correctly.

[0011] Step 2: Calculate the continuous discharge volume based on the established multivariate linear regression equation

[0012] 2.1 Comprehensively analyze the boiler operation data, and explore the factors related to the boiler discharge volume and boiler water quality, mainly including: feed water hydrogen conductivity, boiler water conductivity, and phosphate content. The opening of the continuous valve has a great influence on the boiler discharge volume. If the opening of the continuous valve is too large, it will waste boiler water. If the opening of the continuous valve is too small, it will cause boiler pollution. The boiler operation procedures and standardized operations stipulate that the opening of the continuous valve is controlled at 50%. The requirements for feed water hydrogen conductivity are already high and must be lower than 0.3uS / cm. Only when the feed water hydrogen conductivity is lower than the specified value range can the water quality be guaranteed. The value of boiler water conductivity is mainly determined by the degree of corrosion and combustion in the boiler pipeline. Reasonable adjustment of the phosphate content and control of the boiler water quality indicators within the standard range can protect the inner wall of the boiler. If the phosphate content is too high, the alkalinity of the boiler water will increase, which is easy to form foam and affect the combustion of the boiler. If the phosphate content is too low, the boiler and the inner wall of the pipeline cannot be guaranteed. From these parameters, find the blowdown opening time, opening duration and opening size factors, and control the blowdown device in a timely and accurate manner;

[0013] 2.2 Through multivariate linear regression analysis, the multivariate linear regression equation of the valve opening size, feed water hydrogen conductivity, boiler water conductivity, and phosphate content is:

[0014] K=-11.2-0.09C+1.55D+0.89S

[0015] Where K: opening of the continuous valve; C: hydrogen conductivity of feed water, unit is uS / cm; D: electrical conductivity of boiler water, unit is uS / cm; S: phosphate content, unit is mg / L;

[0016] 2.4 The DCS system automatically adjusts the valve opening according to the real-time data of the regression equation. As the continuous blowdown time increases, the boiler water conductivity and phosphate content continue to decrease, and the continuous blowdown valve opening will continue to decrease to reduce steam loss. If the boiler water conductivity and phosphate content increase, the continuous blowdown valve opening will also be automatically increased to meet the water quality requirements; 2.5 Calculate the continuous blowdown volume according to the regression equation

[0017] Q = 0.2*K*T;

[0018] Step 3: Regularly discharge sewage according to the coupling effect of calculation results,

[0019] 3.1 According to the calculation results, when the continuous sewage discharge volume accumulates to 6 tons, the regular sewage discharge valve is automatically started through coupling. The No. 1 regular sewage discharge valve is fully opened for 30 seconds and then immediately closed. The No. 2 regular sewage discharge valve is opened and closed in turn. When all 16 regular sewage discharge valves are opened and closed, the regular sewage discharge ends and the continuous sewage discharge volume returns to zero;

[0020] 3.2 When the cumulative value of continuous sewage discharge reaches 6 tons again, the regular sewage discharge valve is automatically started again through coupling to carry out the next round of regular sewage discharge, that is, the No. 1 regular sewage discharge valve is fully opened for 30 seconds and then immediately closed, and the No. 2 regular sewage discharge valve is opened. The 16 sewage discharge valves are carried out in sequence. When all 16 regular sewage discharge valves are opened and closed, the regular sewage discharge is completed and the continuous sewage discharge volume returns to zero; 3.3 Regular sewage discharge is automatically opened through coupling in sequence until the continuous sewage discharge process is completed;

[0021] Step 4: Continuously collect water quality data to determine the progress of the automatic sewage discharge process;

[0022] 4.1 Continuously collect feed water hydrogen conductivity, boiler water conductivity and phosphate content in real time;

[0023] 4.2 Compare the boiler water conductivity with 100 times the feed water hydrogen conductivity. When the ratio is ≤0.5 and the phosphate content is ≤5mg / L, the continuous blowdown valve actuator signal is triggered to close. If the automatic periodic blowdown process ends at this time, the entire boiler automatic blowdown process ends. If the continuous blowdown valve actuator signal is triggered to close while the automatic periodic blowdown is in progress, the entire boiler automatic blowdown process ends when the periodic blowdown process ends.

[0024] Step 5: The boiler automatic blowdown process ends.

[0025] Compared with the prior art, the present invention has the following advantages: 1) The scheme utilizes the provided boiler online automatic blowdown method to realize the coupled automatic control of the boiler's continuous blowdown and periodic blowdown, eliminating the waste of heat energy and desalted water resources caused by excessive blowdown resulting in the loss of a large amount of high-temperature saturated water and the safety hazard of increasingly high boiler water salinity due to insufficient blowdown, and can also ensure that the quality of superheated steam meets national standards and reduce salt accumulation or corrosion in the thermal system; 2) The realization of the boiler's automatic online blowdown function can also reduce the labor intensity of workers during continuous and periodic blowdown, which is of great significance to improving labor efficiency and realizing intelligent manufacturing of power plants. 3) The present invention proposes for the first time a multivariable control method for automatic boiler blowdown, and realizes the idea of ​​full-function online automation of blowdown through the coupling effect of continuous blowdown and periodic blowdown. The automatic blowdown process is started by the logical relationship between feed water hydrogen conductivity, boiler water conductivity and phosphate content. The relationship between multiple parameters and continuous blowdown is used to establish a multivariate linear regression equation, and the continuous blowdown amount is calculated for coupling control with the periodic blowdown, so as to accurately control the boiler's blowdown amount within a safe and economical range, effectively reduce steam loss during blowdown, and achieve energy-saving operation of the steam system. DETAILED DESCRIPTION

[0026] In order to deepen the understanding of the present invention, a detailed description is given below in conjunction with embodiments.

[0027] Example 1: A multivariable controlled on-line automatic blowdown method for a boiler (the following steps are all implemented in a DCS system), the control method is as follows:

[0028] Step 1) Confirmation of the conditions for automatic start of boiler blowdown;

[0029] 1.1 During the normal operation of the boiler, the analog input value of the drum water level is used to perform a two-out-of-three voting process to confirm that the boiler water level is within the normal range of -100 to +250mm;

[0030] 1.2 Make quality judgment through the analog input value of the continuous blowdown valve opening to confirm that the continuous blowdown valve actuator is normal; 1.3 Through the on-site online analysis of the conductivity meter and phosphorus meter signal transfer, access the DCS to collect the real-time hydrogen conductivity of the feed water, the conductivity of the boiler water and the phosphate content, and make quality judgment;

[0031] 1.4 Compare the boiler water conductivity with 100 times the feed water hydrogen conductivity. When the ratio is greater than 1 and the phosphate content is greater than 15 mg / L, the trigger command automatically opens the continuous sewage discharge valve actuator, and the continuous sewage discharge automatically opens and enters the automatic sewage discharge stage. The default value of the continuous sewage discharge valve opening command is 50%. When the control command and the valve opening feedback deviation are within plus or minus 5%, it is judged that the automatic opening process is triggered correctly.

[0032] Step 2) Calculate the continuous discharge volume based on the established multivariate linear regression equation

[0033] 2.1 Comprehensively analyze the boiler operation data, and explore the factors related to the boiler discharge volume and boiler water quality, mainly including: feed water hydrogen conductivity, boiler water conductivity, and phosphate content. The opening of the continuous valve has a great influence on the boiler discharge volume. If the opening of the continuous valve is too large, it will waste boiler water. If the opening of the continuous valve is too small, it will cause boiler pollution. The boiler operation procedures and standardized operations stipulate that the opening of the continuous valve is controlled at 50%. The requirements for feed water hydrogen conductivity are already high and must be lower than 0.3uS / cm. Only when the feed water hydrogen conductivity is lower than the specified value range can the water quality be guaranteed. The value of boiler water conductivity is mainly determined by the degree of corrosion and combustion in the boiler pipeline. Reasonable adjustment of the phosphate content and control of the boiler water quality indicators within the standard range can protect the inner wall of the boiler. If the phosphate content is too high, the alkalinity of the boiler water will increase, which is easy to form foam and affect the combustion of the boiler. If the phosphate content is too low, the boiler and the inner wall of the pipeline cannot be guaranteed. From these parameters, find the blowdown opening time, opening duration and opening size factors, and control the blowdown device in a timely and accurate manner;

[0034] 2.2 Through multivariate linear regression analysis, the multivariate linear regression equation of the valve opening size, feed water hydrogen conductivity, boiler water conductivity, and phosphate content is:

[0035] K=-11.2-0.09C+1.55D+0.89S

[0036] Where K: opening of the continuous valve; C: hydrogen conductivity of feed water, unit is uS / cm; D: electrical conductivity of boiler water, unit is uS / cm; S: phosphate content, unit is mg / L;

[0037] That is, when the hydrogen conductivity of the feed water decreases by 0.01uS / cm, the opening of the continuous sewage valve needs to be increased by 0.9%

[0038] When the conductivity of boiler water decreases by 1uS / cm, the opening of the continuous sewage valve can be reduced by 1.55%

[0039] When the phosphate content decreases by 1 mg / L, the continuous sewage valve opening can be reduced by 0.89%

[0040] And from the multivariate linear regression analysis, it can be seen that the conductivity of boiler water has the strongest correlation, followed by the phosphate content.

[0041]

[0042]

[0043] 2.4 The DCS system automatically adjusts the valve opening according to the real-time data of the regression equation. As the continuous blowdown time increases, the boiler water conductivity and phosphate content continue to decrease, and the continuous blowdown valve opening will continue to decrease to reduce steam loss. If the boiler water conductivity and phosphate content increase, the continuous blowdown valve opening will also be automatically increased to meet the water quality requirements;

[0044] 2.5 Calculate the continuous discharge volume based on the regression equation

[0045] Q=0.2*K*T

[0046] If the continuous sewage valve opening is 50%, the sewage discharge volume of opening 10uS / cm is 0.2*50%*10=1 ton;

[0047] Step 3) Regularly discharge sewage according to the coupling effect of calculation results

[0048] 3.1 According to the calculation results, if the average opening of the continuous sewage valve is 50%, the sewage discharge volume after opening for 60 minutes is 0.2*50%*60=6 tons. When the continuous sewage discharge volume accumulates to 6 tons, the regular sewage discharge valve is automatically started through coupling. The No. 1 regular sewage discharge valve is fully opened for 30 seconds and then immediately closed. The No. 2 regular sewage discharge valve is opened and closed, and the 16 sewage discharge valves are opened and closed in turn. When all the 16 regular sewage discharge valves are opened and closed, the regular sewage discharge ends and the continuous sewage discharge volume returns to zero.

[0049] 3.2 When the cumulative value of continuous sewage discharge reaches 6 tons again, the regular sewage discharge valve is automatically started again through coupling to carry out the next round of regular sewage discharge, that is, the No. 1 regular sewage discharge valve is fully opened for 30 seconds and then immediately closed, and the No. 2 regular sewage discharge valve is opened. The 16 sewage discharge valves are carried out in sequence. When all 16 regular sewage discharge valves are opened and closed, the regular sewage discharge is completed and the continuous sewage discharge volume returns to zero; 3.3 Regular sewage discharge is automatically opened through coupling in sequence until the continuous sewage discharge process is completed;

[0050] Step 4) Continuously collect water quality data to determine the progress of the automatic sewage discharge process;

[0051] 4.1 Continuously collect feed water hydrogen conductivity, boiler water conductivity and phosphate content in real time;

[0052] 4.2 Compare the boiler water conductivity with 100 times the feed water hydrogen conductivity. When the ratio is ≤0.5 and the phosphate content is ≤5mg / L, the continuous blowdown valve actuator signal is triggered to close. If the automatic periodic blowdown process ends at this time, the entire boiler automatic blowdown process ends. If the continuous blowdown valve actuator signal is triggered to close while the automatic periodic blowdown is in progress, the entire boiler automatic blowdown process ends when the periodic blowdown process ends.

[0053] Step 5) The boiler automatic blowdown process ends.

[0054] It should be noted that the above embodiments are not intended to limit the protection scope of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions all fall within the protection scope of the claims of the present invention.

Claims

1. A multivariable controlled on-line automatic blowdown method for a boiler, characterized in that: The method comprises the following steps: Step 1: Confirm the conditions for automatic start of boiler blowdown; Step 2: Calculate the continuous discharge volume based on the established multivariate linear regression equation Step 3: Regularly discharge sewage according to the coupling effect of calculation results, Step 4: Continuously collect water quality data to determine the progress of the automatic sewage discharge process; Step 5: The boiler automatic blowdown process ends.

2. The method for online automatic blowdown of a boiler with multivariable control according to claim 1, characterized in that: Step 1: Confirm the conditions for automatic start of boiler blowdown, as follows: 1.1 During the normal operation of the boiler, the analog input value of the drum water level is used to perform a two-out-of-three voting process to confirm that the boiler water level is within the normal range of -100 to +250mm; 1.2 Make quality judgment through the analog input value of the continuous sewage valve opening to confirm that the continuous sewage valve actuator is normal; 1.3 Through on-site online analysis of conductivity meter and phosphorus meter signal transfer, the DCS is connected to collect feed water hydrogen conductivity, boiler water conductivity and phosphate content in real time, and quality judgment is made; 1.4 Compare the boiler water conductivity with 100 times the feed water hydrogen conductivity. When the ratio is greater than 1 and the phosphate content is greater than 15 mg / L, the trigger command automatically opens the continuous sewage discharge valve actuator, and the continuous sewage discharge automatically opens and enters the automatic sewage discharge stage. The default value of the continuous sewage discharge valve opening command is 50%. When the control command and the valve opening feedback deviation are within plus or minus 5%, it is judged that the automatic opening process is triggered correctly.

3. The method for online automatic blowdown of a boiler with multivariable control according to claim 2, characterized in that: Step 2: Calculate the continuous discharge volume based on the established multiple linear regression equation, as follows: 2.1 Comprehensively analyze the boiler operation data and explore the factors related to boiler discharge and boiler water quality: feed water hydrogen conductivity, boiler water conductivity, phosphate content, 2.2 Through multivariate linear regression analysis, the multivariate linear regression equation of the valve opening size, feed water hydrogen conductivity, boiler water conductivity, and phosphate content is: K=-11.2-0.09C+1.55D+0.89S, Where K: opening of the continuous valve; C: hydrogen conductivity of feed water, unit is uS / cm; D: electrical conductivity of boiler water, unit is uS / cm; S: phosphate content, unit is mg / L; 2.4 The DCS system automatically adjusts the valve opening according to the real-time data of the regression equation. As the continuous blowdown time increases, the boiler water conductivity and phosphate content continue to decrease, and the continuous blowdown valve opening will be continuously reduced to reduce steam loss. If the boiler water conductivity and phosphate content increase, the continuous blowdown valve opening will be automatically increased to meet the water quality requirements. 2.5 Calculate the continuous discharge volume according to the regression equation. Q = 0.2*K*T.

4. The method for online automatic blowdown of a boiler with multivariable control according to claim 3 is characterized in that: Step 3: Discharge sewage regularly according to the coupling effect of calculation results, as follows: 3.1 According to the calculation results, when the continuous sewage discharge volume accumulates to 6 tons, the regular sewage discharge valve is automatically started through coupling. The No. 1 regular sewage discharge valve is fully opened for 30 seconds and then immediately closed. The No. 2 regular sewage discharge valve is opened and closed in turn. When all 16 regular sewage discharge valves are opened and closed, the regular sewage discharge ends and the continuous sewage discharge volume returns to zero; 3.2 When the cumulative value of continuous sewage discharge reaches 6 tons again, the regular sewage discharge valve will be automatically started again through coupling to carry out the next round of regular sewage discharge, that is, the No. 1 regular sewage discharge valve will be fully opened for 30 seconds and then immediately closed, and the No. 2 regular sewage discharge valve will be opened. The 16 sewage discharge valves will be carried out in turn. When all 16 regular sewage discharge valves are opened and closed, the regular sewage discharge is completed and the continuous sewage discharge volume returns to zero; 3.3 Automatically start regular sewage discharge through coupling action in sequence until the continuous sewage discharge process is completed.

5. The multivariable controlled on-line automatic blowdown method for boilers according to claim 3 or 4, characterized in that: Step 4: Continuously collect water quality data to determine the progress of the automatic sewage discharge process; the details are as follows: 4.1 Continuously collect feed water hydrogen conductivity, boiler water conductivity and phosphate content in real time; 4.2 Compare the boiler water conductivity with 100 times the feed water hydrogen conductivity. When the ratio is ≤0.5 and the phosphate content is ≤5mg / L, the continuous blowdown valve actuator signal is triggered to close. If the automatic periodic blowdown process ends at this time, the entire boiler automatic blowdown process ends. If the continuous blowdown valve actuator signal is triggered to close while automatic periodic blowdown is in progress, the entire boiler automatic blowdown process ends after the periodic blowdown process ends.

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