CN112206645A - Thermal power plant desulfurization efficiency control method and system - Google Patents
Thermal power plant desulfurization efficiency control method and system Download PDFInfo
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Abstract
The invention provides a thermal power plant desulfurization efficiency control method and system. The desulfurization efficiency control method comprises the following steps: measuring the pH value of the absorption liquid in the absorption tower to obtain a pH measured value; collecting desulfurization feedforward parameters including SO2Mass flow rate signal, SO2The mass flow is the air supply volume and the flue gas SO of the boiler2The value of the concentration product; collecting desulfurization feedback parameters, wherein the desulfurization feedback parameters are pH difference signals, and the pH difference is the difference between a pH measured value and a given pH value; adding SO2And superposing the mass flow signal and the pH difference signal to obtain a desulfurization adjustment signal, and controlling the input amount of limestone slurry according to the desulfurization adjustment signal to maintain the fluctuation of the pH measurement value within a given pH control value. The invention controls the desulfurization efficiency of the thermal power plant to reduce the addition of the desulfurizer as much as possibleThereby reducing the operation cost of the power plant as much as possible and reducing the secondary pollution.
Description
Technical Field
The invention belongs to the technical field of thermal power plant desulfurization, and particularly relates to a thermal power plant desulfurization efficiency control method and system.
Background
With the rapid development of industry in China, pollution caused by industrial waste gas is not visible in all parts. The construction and development of the electric power industry in China are mainly coal-fired thermal power plants, and with the development of the electric power industry, pollutants generated in the electric power production process of the thermal power plants are greatly increased, wherein sulfur dioxide is a main pollutant generated by the thermal power plants and is a main pollution source facing China.
Under the pressure of environmental protection, thermal power plants are provided with desulfurization systems, the measures effectively reduce the emission of sulfur dioxide in flue gas, but greatly increase the power generation cost of the thermal power plants, so that how to reduce the addition of a desulfurizing agent as much as possible on the premise of ensuring the flue gas desulfurization effect of the thermal power plants is an important means for improving the economy of the thermal power plants.
At present, each power generation enterprise puts emphasis on how to achieve discharge after reaching standards, and research on how to reduce the running cost per se on the premise of ensuring discharge after reaching standards is less. If the addition amount of the desulfurizer cannot be accurately controlled, the operation cost of a power plant is increased, and extra pollution is caused.
Disclosure of Invention
The first purpose of the invention is to provide a thermal power plant desulfurization efficiency control method. The desulfurization efficiency control method comprises the following steps:
measuring the pH value of the absorption liquid in the absorption tower to obtain a pH measured value;
collecting desulfurization feedforward parameters including SO2Mass flow rate signal, SO2The mass flow is the air supply volume and the flue gas SO of the boiler2The value of the concentration product;
collecting desulfurization feedback parameters, wherein the desulfurization feedback parameters comprise pH difference signals, and the pH difference is the absolute value of the pH measured value and a given pH value difference;
subjecting the SO to2And superposing the mass flow signal and the pH difference signal to obtain a desulfurization adjustment signal, and controlling the input amount of limestone slurry according to the desulfurization adjustment signal to maintain the fluctuation of the pH measured value within a given pH fluctuation value.
In some embodiments of the invention, the step of determining the pH of the absorption liquid in the absorption column creates a time lag, and the time lag is compensated for.
In some embodiments of the invention, t ═ s \ v + t according to the formula1+t2Compensating for the lag time; wherein t is the compensation time, s is the distance from the absorption tower to the pH measurement point, v is the flow rate of the limestone slurry, t1The time required for treating the sample of absorption liquid in the absorption column, t2The absorption liquid sample and SO in the absorption tower2The reaction time of (2).
In some embodiments of the invention, the t is1Is 3-5 min.
In some embodiments of the invention, the t is2Is 2-4 h.
In some embodiments of the invention, controlling the limestone slurry input based on the de-sulfurization adjustment signal comprises:
according to the SO2Calculating the required limestone slurry flow rate by using the mass flow signal so as to determine the required limestone slurry input amount of the absorption tower;
and correcting and calculating the input amount of the limestone slurry according to the pH difference signal.
In some embodiments of the present invention, the desulfurization efficiency control method further comprises the steps of: and when the fluctuation of the pH measured value exceeds a given pH control value, alarming to remind an operator to check reasons, and manually adjusting to maintain the fluctuation of the pH measured value within the given pH control value.
In some embodiments of the invention, the given pH control value is 5.4 ± 0.2, and when the pH measurement value is below 5.2, the limestone slurry input is increased by manual adjustment; when the pH measurement is above 5.6, manual adjustment reduces the limestone slurry input.
In some embodiments of the invention, when the SO fails to pass2When the fluctuation of the pH measured value is maintained within the given fluctuation value by the mass flow signal and the pH difference signal, establishing a mathematical model library, adding experience values and detection values of operators, and measuring by using a mathematical fuzzy algorithmAnd calculating the desulfurization feedforward parameter, superposing the desulfurization feedforward parameter and the pH difference signal to obtain a desulfurization adjusting signal, and controlling the input amount of limestone slurry according to the desulfurization adjusting signal to maintain the fluctuation of the pH measured value within the given pH fluctuation value.
It is another object of the present invention to provide a desulfurization efficiency control system for a thermal power plant, which includes:
the pH detector is used for measuring the pH value of the absorption liquid in the absorption tower to obtain a pH measured value;
a limestone slurry regulating valve for regulating the input amount of limestone slurry fed into the absorption tower;
the first desulfurization signal processor is used for comparing the pH measured value with a given pH value to obtain a pH difference value and outputting a pH difference value signal;
the desulfurization feedback controller is used for acquiring a pH difference value signal, wherein the pH difference value is the difference value between the pH measured value and a given pH value;
a desulfurization feedforward controller for collecting desulfurization feedforward parameters including SO2Mass flow rate signal, SO2The mass flow is the air supply volume and the flue gas SO of the boiler2The value of the concentration product;
a desulfurization signal processor for converting the SO2Superposing the mass flow signal and the pH difference signal to obtain a desulfurization adjustment signal, and outputting the desulfurization adjustment signal;
the desulfurization feedback controller and the desulfurization feedforward controller are also used for controlling the opening degree of the limestone slurry regulating valve according to the desulfurization regulating signal so as to maintain the fluctuation of the pH measured value within a given pH fluctuation value.
The invention controls the desulfurization efficiency of the thermal power plant to reduce the addition of the desulfurizer as much as possible, thereby reducing the operation cost of the power plant as much as possible and reducing secondary pollution.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
Fig. 1 is a process flow diagram of desulfurization efficiency control of a thermal power plant according to an embodiment of the present invention.
Fig. 2 is a process flow diagram of desulfurization efficiency control of a thermal power plant according to another embodiment of the present invention.
Fig. 3 is a process flow diagram of desulfurization efficiency control of a thermal power plant according to another embodiment of the present invention.
Fig. 4 is a schematic structural diagram of a desulfurization efficiency control system of a thermal power plant according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The terms "comprising" and "having," and any variations thereof, in the description and claims of this application and the drawings described herein are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.
The desulfurization efficiency control system provided by the present invention will be described in detail below.
1 relationship between pH value and Process in desulfurization System
In the Wet Flue Gas Desulfurization (WFGD) treatment process, the monitoring of the pH value is the key for ensuring the desulfurization treatment effect (desulfurization efficiency).
1.1 principle of chemical absorption
In the wet desulfurization treatment process, the desulfurizing agent is an emulsion containing 5-10% of lime powder. Desulfurizing agent and sulfur dioxide (SO) in flue gas2) The reaction is carried out to generate calcium sulfite (CaSO)3) The chemical reaction formula is as follows:
CaCO3+SO2→CaSO3+CO2 (1)
1.2 Process for absorbing Sulfur dioxide by Wet desulfurization treatment
During the wet desulfurization treatment, the gaseous material and the liquid suspension undergo a material conversion to absorb sulfur dioxide as a result of the liquid-gas phase chemical process reaction. The absorption process of sulfur dioxide in flue gas in lime slurry is specifically as follows.
The sulfur dioxide in the flue gas enters a liquid phase and firstly undergoes the following chemical reaction:
in the above reaction, the ionic component of the solution has a direct relationship with the pH of the solution. When the pH value of the solution is 7.2, SO is simultaneously present in the solution3 2-And HSO3 -Ions. SO in solution as the pH in solution continues to drop to 4.5 and below3 2-The ion content will be greatly reduced.
1.3 influence of pH on calcium sulfate (Gypsum) formation
According to the kinetics of oxidation of sulfur dioxide in aqueous solution as studied by Miller et al, the rate of oxidation of the bisulfite ion is greatest at a pH of 4.5.
However, in the practical application of thermal power plant, the pH value of the lime slurry is generally controlled to be in the range of 5.4-5.8, and under the condition, the bisulfite ions are not easy to oxidize. In the desulfurization treatment process, the bisulfite ions are converted into sulfate ions by blowing air into a circulation tank, and the reaction formula is as follows:
the oxidation reaction converts a large amount of bisulfite ions into sulfate ions, allowing the reaction to proceed to the right. The sulfate ion generated by the reaction and calcium ion (Ca) in the slurry2+) The following reactions occur:
the resulting calcium sulphate has a relatively low solubility in the solution, which increases the driving force for the dissolution of sulphur dioxide. So that the sulfur dioxide is continuously transferred from gas phase to liquid phase, and finally, gypsum (calcium sulfate) which is a building material capable of being utilized is generated.
In conclusion, the key to the desulfurization process is maintaining the pH value stable, and the desulfurization process is kept to be performed stably and effectively, so that the quality of the gypsum meets the production requirement.
2 control scheme of the invention
In order to achieve the desired desulfurization efficiency in the desulfurization treatment process, a large amount of limestone is required, and since the limestone contains a certain amount of impurities, the calcium carbonate content distribution therein is extremely uneven (50% -90%), the desulfurization rate cannot be controlled by the dosage of limestone, and the dosage must be controlled according to the change of the pH value to ensure the desulfurization efficiency.
The pH in the absorber is typically maintained between 5.3 and 5.5 depending on the actual production and engineering design requirements of the respective power plant. This not only ensures the purity of the gypsum obtained, but also achieves the desired desulfurization efficiency. If the pH value is abnormal, necessary measures are taken. For example: when the pH is lowered, the amount of limestone slurry to be fed needs to be increased (the limestone slurry regulating valve is opened to a large extent), and when the pH is raised, the amount of limestone slurry to be fed needs to be decreased (the limestone slurry regulating valve is opened to a small extent). Therefore, control measures are generally taken to control the pH value in the absorption tower by controlling the amount of limestone slurry input (opening degree of the limestone slurry control valve) or the concentration of limestone slurry.
2.1 influencing factors
There are the amount of flue gas, the concentration of sulfur dioxide, the amount of limestone slurry input and the content of calcium carbonate in limestone, which may affect the desulfurization effect during the operation of the desulfurization system, and therefore the desulfurization efficiency cannot be controlled simply by the slurry flow rate. And it is a practical method to ensure desulfurization efficiency by controlling pH.
The larger the limestone slurry input amount is, the higher the content of calcium carbonate in limestone is, the higher the pH value is, and the flue gas amount and the sulfur dioxide concentration are described in the following in a key way:
(1) the amount of flue gas. If the flow rate of limestone slurry fed to the absorption tower is constant, an increase in the amount of flue gas will decrease the pH of the slurry and conversely increase the pH. Generally, no effective method for detecting the smoke amount exists, the change of the smoke amount is mainly caused by the change of the boiler air supply amount, and the relation between the change and the boiler air supply amount is linear, so that the parameter of the boiler air supply amount is introduced to replace the smoke amount.
(2) The concentration of sulfur dioxide in the flue gas. Even if the amount of flue gas is kept constant, the concentration of sulfur dioxide in the flue gas will fluctuate due to changes in the sulfur content of the coal used (or for other reasons). However, because the variation range of coal quality and the like is not as large as that of load variation, the variation of the concentration of sulfur dioxide in flue gas is not large.
The invention introduces SO2The mass flow and the pH difference value are two parameters, and the input amount of limestone slurry fed into the absorption tower is adjusted by adjusting the size of the opening of the limestone slurry adjusting valve, so that the pH value of the limestone slurry in the absorption tower is controlled. SO referred to in the invention2The mass flow refers to the air supply volume and the flue gas SO of the boiler2The product of the concentrations, the pH difference being the absolute value of the difference between the pH determined value and the given pH value.
Fig. 1 shows a desulfurization efficiency control method for a thermal power plant according to an embodiment of the present invention, which includes the steps of:
s101: the pH value of the absorption liquid in the absorption tower was measured to obtain a pH measurement value.
S102: and collecting desulfurization feedforward parameters. The desulfurization feed forward parameter refers to SO2Mass flow rate signal, SO2The mass flow is the air supply volume and the flue gas SO of the boiler2The product of the concentrations.
S103: and collecting desulfurization feedback parameters. The desulfurization feedback parameter refers to a pH difference signal, and the pH difference is the absolute value of the difference between the pH value measured by the pH value measuring device and a given pH value.
S104: adding SO2And superposing the mass flow signal and the pH difference signal to obtain a desulfurization adjustment signal, and controlling the input amount of limestone slurry according to the desulfurization adjustment signal to maintain the fluctuation of the pH value within a given pH fluctuation value.
Specifically, in one embodiment of the present invention, in step S104, the limestone slurry input amount is controlled according to the desulfurization adjustment signal by:
according to SO2Quality ofCalculating the required limestone slurry flow rate by using the flow signal so as to determine the required limestone slurry input amount of the absorption tower;
and then, the input amount of the limestone slurry is corrected and calculated according to the pH difference signal.
The limestone slurry input amount is controlled by two parameters, one is the advanced supply amount (feedforward parameter) according to the SO of the desulfurization system2Mass flow signal (boiler air supply, SO)2Concentration) is automatically calculated by the control system, so that the required limestone slurry flow is determined, and the limestone slurry consumption required by the absorption tower in the current state is determined. The other is the actual supply amount of limestone slurry, the amount of limestone slurry supplied is corrected and calculated by measuring the pH value in the absorption tower on the basis of the advance supply amount, and a command is sent out, and the control system adjusts the opening degree of a limestone slurry adjusting valve according to the command, so that the input amount of limestone slurry entering the absorption tower is controlled, the pH value in the absorption tower is kept in a certain range, and meanwhile, the ratio of limestone and gypsum is ensured to be in a technical required range. Effectively preventing the control system from being overused.
In one embodiment of the present invention, the given pH is 5.4. The given pH fluctuation value is 5.4 +/-0.1, when the pH difference value is within the range, the operation of the desulfurization system is considered to be normal, no adjustment is needed, the given pH control value is 5.4 +/-0.2, and when the pH measured value is lower than 5.3 and higher than 5.2, the control system automatically adjusts and increases the input amount of limestone slurry; when the pH value is higher than 5.5 and lower than 5.6, the control system automatically adjusts and reduces the input amount of limestone slurry. When the pH value is lower than 5.2, manually adjusting to increase the input amount of limestone slurry; when the pH measurement is above 5.6, manual adjustment reduces limestone slurry input.
Control value controlled variable: the pH value of the absorption liquid in the absorption tower; desulfurization feedback parameters: a pH difference signal; desulfurization feedforward parameters: SO (SO)2A mass flow signal; an actuator: a limestone slurry regulating valve (it should be noted that the present invention is not limited to the limestone slurry regulating valve for regulating the amount of limestone slurry fed into the absorption tower, and any equipment capable of achieving the function may be used).
Generally, the time required for the measurement using a special pH meter and the time required for the limestone slurry and SO are used due to the installation position of the pH measuring element2The reaction time of (2) causes pure delay of pH value detection, and the pure delay causes that a measurement signal cannot reflect the change of the pH value of the absorption liquid in the absorption tower in time, so that the pH value detected by an electrode of the pH detector generates time delay. In a further preferred embodiment of the invention, the above method also compensates for the time lag in pH, in particular:
the specific method comprises the steps of firstly carrying out primary adjustment when the measured value of the pH detector deviates from a given pH value, then carrying out subsequent adjustment according to the measured value of the pH detector after maintaining operation for 2-5 hours, and adjusting the specific delay time according to actual conditions on site.
In an embodiment of the present invention, the formula t ═ s \ v + t is used1+t2The lag time is compensated for. Wherein t is the compensation time, s is the distance from the absorption tower to the pH measurement point, v is the flow rate of the limestone slurry, and t1The time required for treating the sample of absorption liquid in the absorption column, t2The absorption liquid sample and SO in the absorption tower2The reaction time of (2).
In a further preferred embodiment of the invention, t1Is 3-5 min.
In a further preferred embodiment of the invention, t2Is 2-4 h.
Fig. 2 shows a desulfurization efficiency control method for a thermal power plant according to another embodiment of the present invention, which includes the steps of:
s201: the pH value of the absorption liquid in the absorption tower was measured to obtain a pH measurement value.
S202: and collecting desulfurization feedforward parameters. The desulfurization feed forward parameter refers to SO2Mass flow rate signal, SO2The mass flow is the air supply volume and the flue gas SO of the boiler2The product of the concentrations.
S203: and collecting desulfurization feedback parameters. The desulfurization feedback parameter refers to a pH difference signal, and the pH difference is the difference between a pH value measured and a given pH value.
S204: adding SO2And superposing the mass flow signal and the pH difference signal to obtain a desulfurization adjustment signal, and controlling the input amount of limestone slurry according to the desulfurization adjustment signal to maintain the fluctuation of the pH value within a given pH fluctuation value.
S205: monitoring whether the fluctuation of the pH measured value exceeds a given pH control value, if so, alarming, exiting from automatic control and reminding an operator to check reasons, and manually adjusting to maintain the fluctuation of the pH measured value within the given pH control value. After stabilization, the device is put into automatic operation.
The present invention refers to various factors that cause a change in the controlled amount, in addition to the input amount (given value), as disturbance factors. In the present invention, all factors causing the change of pH value, except the given value of pH, are called interference factors including the load of the boiler, SO2Content, limestone slurry input amount, CaCO in limestone3Content, limestone slurry regulating valve, etc.
When it is impossible to pass only SO2When the fluctuation of the pH measured value is maintained within the given pH control value through the mass flow signal and the pH difference signal, the rule of the influence of the interference factors on the pH value of the absorption liquid in the absorption tower can be found by establishing a mathematical model library and adding the experience value and the detection value of operators such as engineers and the like, and the feedforward parameter is calculated by utilizing a mathematical fuzzy algorithm, wherein the feedforward parameter not only comprises SO2A mass flow signal. And jointly controlling the limestone slurry regulating valve by the obtained feedforward parameter and the feedback parameter (pH difference signal). The specific steps are shown in fig. 3, and include:
s301: the pH value of the absorption liquid in the absorption tower was measured to obtain a pH measurement value.
S302: and collecting desulfurization feedforward parameters. Where the desulfurization feed forward parameters include SO2A mass flow signal.
S303: and collecting desulfurization feedback parameters. The desulfurization feedback parameter herein refers to the pH difference signal.
S304: and superposing the desulfurization feedforward parameter and the desulfurization feedback parameter to obtain a desulfurization adjusting signal, and controlling the input amount of limestone slurry according to the desulfurization adjusting signal to maintain the fluctuation of the pH measured value within a given pH fluctuation value.
S305: monitoring whether the pH measurement fluctuates more than a given pH fluctuation value.
S306: when it is impossible to pass only SO2And when the fluctuation of the pH measured value is maintained within the given fluctuation value by the mass flow signal and the pH difference signal, establishing a mathematical model library, adding an experience value and a detection value of an operator, calculating a desulfurization feedforward parameter by using a mathematical fuzzy algorithm, and then performing S301-S304.
Fig. 4 shows a desulfurization efficiency control system of a thermal power plant according to an embodiment of the present invention, which includes a pH detector 41, a limestone slurry regulating valve 42, a first desulfurization signal processor 43, a desulfurization feedback controller 44, a desulfurization feedforward controller 45, and a second desulfurization signal processor 46.
The pH detector 41 is used for measuring the pH value of the absorption liquid in the absorption tower to obtain a pH measured value;
the limestone slurry regulating valve 42 is used for regulating the input amount of limestone slurry to the absorption tower.
The first desulfurization signal processor 43 is configured to compare the pH measurement value with a given pH value, obtain a pH difference value, and output a pH difference value signal to the desulfurization feedback controller 44.
The desulfurization feedback controller 44 functions as a feedback control for acquiring desulfurization feedback parameters, which are pH difference signals.
The desulfurization feedforward controller 45 functions as a feedforward controller for acquiring desulfurization feedforward parameters including SO2Mass flow signal to overcome the influence of the amount of flue gas and SO in the flue gas2The effect of changes in concentration on the pH of the controlled variable.
A second desulfurization signal processor 46 for converting SO2And superposing the mass flow signal and the pH difference signal to obtain a desulfurization regulating signal.
The desulfurization feedback controller 44 and the desulfurization feedforward controller 45 are also used to control the opening of the limestone slurry regulating valve in accordance with the desulfurization regulating signal so as to maintain the fluctuation of the pH measured value within a given pH fluctuation value.
There are two parameters for controlling the input amount of limestone slurry, one isThe advance supply (feedforward parameter) is based on the desulfurization system SO2Mass flow signal (boiler air supply, SO)2Concentration) is automatically calculated by the control system, so that the required limestone slurry flow is determined, and the limestone slurry consumption required by the absorption tower in the current state is determined. The other is the actual supply amount of limestone slurry, the amount of limestone slurry supplied is corrected and calculated by measuring the pH value in the absorption tower on the basis of the advance supply amount, and a command is sent out, and the control system adjusts the opening degree of a limestone slurry adjusting valve according to the command, so that the input amount of limestone slurry entering the absorption tower is controlled, the pH value in the absorption tower is kept in a certain range, and meanwhile, the ratio of limestone and gypsum is ensured to be in a technical required range. Effectively preventing the control system from being overused.
The control scheme of the invention is a combined control system which adds feedforward to a single loop of the pH value of slurry in an absorption tower, and a feedback closed loop and an open loop compensation loop are superposed to form a complete control loop.
The advantages of the desulfurization efficiency control system shown in fig. 4 are largely the same as those of the desulfurization efficiency control method described above, and therefore, the description thereof is omitted.
The control system can also receive chain stop signals which affect the safety of the desulfurization system due to the desulfurization system and other factors, and process the signals according to the corresponding signals. If the generator set has an accident and needs emergency shutdown, the system also responds to stop adding the desulfurizer.
By using the desulfurization efficiency control system, the optimal addition of the desulfurizing agent can be searched by using a computer software system by improving the reliability and accuracy of desulfurization measurement under the condition of not changing the existing equipment of the power plant, and the addition of the desulfurizing agent is reduced as much as possible on the premise of ensuring the flue gas desulfurization effect of the thermal power plant, so that the operation cost of the power plant is reduced as much as possible, and the secondary pollution is reduced.
The present invention will be described below with reference to specific examples. The values of the process conditions taken in the following examples are exemplary and ranges of values are provided as indicated in the foregoing summary, and reference may be made to conventional techniques for process parameters not specifically noted. The detection methods used in the following examples are all conventional in the industry.
Example 1
When the desulfurization system of the power plant starts to be put into operation, firstly, according to relevant control indexes (reference feedforward parameters) of the power plant, the method comprises the following steps: the required theoretical value of the limestone slurry is calculated according to the sulfur dioxide quality signal, and the value can be properly adjusted according to the experience of an operator. And (3) controlling the slurry regulating valve according to the opening ratio of the slurry valve, operating for 30-50 minutes, enabling the system to operate stably and normally, enabling the pH value to enter an automatic control range and be relatively stable, and switching to an automatic operation state. When the system is in an automatic operation state, when the pH value is higher than a set value of 5.5, the slurry control valve is closed to be small, when the pH value is lower than 5.3, the slurry control valve is opened to be large, and during normal operation, when the sulfur dioxide quality signal and the load amount are changed, the slurry control valve is automatically adjusted according to the size of the change amount, namely when the sulfur dioxide quality flow (the load is increased) is increased, the slurry adjusting valve is opened to be large. When the sulfur dioxide mass flow is reduced (load is reduced), the slurry regulating valve is closed.
When the sulfur dioxide mass flow and the load change under the feedforward condition, the pH value of the absorption tower is not fed back to the pH detector, so that the control system is added with feedforward control, the slurry control valve acts in real time according to the increase or decrease of the opening degree of the system and the change of the sulfur dioxide content, and acts in advance of the change of the pH detection value. The stability of the control system is greatly improved.
Generally, the reaction time of the feedforward condition needs to be greatly advanced and delayed by the pH detection time, and the feedback time difference between the load change time and the pH value detection value is the delay compensation time. The specific operation is that when the pH value is not in the control range of 5.4 +/-0.1, the system firstly carries out one adjustment, then after the system is operated for 2-5 hours, if the pH value is not in the control range, the system carries out another adjustment, and the process is circulated until the pH value is adjusted to be in the control range.
When the adjustment is unstable or the deviation is too large due to the interference factors such as inaccurate load, equipment and detection parameters, only SO is used2The mass flow signal and the pH difference signal cannot be correctly automatically realizedDuring adjustment, the rule of influence of the interference factors on the pH value of the absorption liquid in the absorption tower can be found by establishing a mathematical model library and adding experience values and detection values of operators such as engineers and the like, and the feedforward parameters are calculated by using a mathematical fuzzy algorithm, wherein the feedforward parameters not only comprise SO2A mass flow signal. And jointly controlling the limestone slurry regulating valve by the obtained feedforward parameter and the feedback parameter (pH difference signal).
In the automatic operation process of the system, when the pH value of the slurry is higher than a set value of 5.6 or lower than 5.2 for more than 30 minutes, the system can alarm to inform an operator of checking and processing equipment faults, when the pH value of the slurry exceeds 60 minutes, the system can automatically quit the automatic control, maintain the opening of the slurry valve obtained by a theoretical calculated value, and prompt the operator to manually operate the slurry regulating valve.
When the system needs to be normally stopped due to normal stop and the like, the automatic adjustment is only required to be stopped normally according to the process flow of the power plant.
According to the embodiment, the desulfurization efficiency of the thermal power plant can be accurately controlled, so that the operation cost of the power plant is reduced to the greatest extent, and the secondary pollution is reduced.
It should be understood that the above examples are only for clearly illustrating the present invention and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the scope of the invention.
Claims (10)
1. A thermal power plant desulfurization efficiency control method is characterized by comprising the following steps:
measuring the pH value of the absorption liquid in the absorption tower to obtain a pH measured value;
collecting desulfurization feedforward parameters including SO2Mass flow rate signal, SO2The mass flow is the air supply volume and the flue gas SO of the boiler2Product of concentrationsA value;
collecting desulfurization feedback parameters, wherein the desulfurization feedback parameters comprise pH difference signals, and the pH difference is the absolute value of the pH measured value and a given pH value difference;
subjecting the SO to2And superposing the mass flow signal and the pH difference signal to obtain a desulfurization adjustment signal, and controlling the input amount of limestone slurry according to the desulfurization adjustment signal to maintain the fluctuation of the pH measured value within a given pH fluctuation value.
2. The desulfurization efficiency controlling method according to claim 1, wherein the step of measuring the pH of the absorbing solution in the absorption tower causes a time lag, and the time lag is compensated for.
3. The desulfurization efficiency control method according to claim 2, wherein t ═ s \ v + t is calculated according to the formula1+t2Compensating for the lag time; wherein t is the compensation time, s is the distance from the absorption tower to the pH measurement point, v is the flow rate of the limestone slurry, t1The time required for treating the sample of absorption liquid in the absorption column, t2The absorption liquid sample and SO in the absorption tower2The reaction time of (2).
4. The desulfurization efficiency control method according to claim 3, wherein t is1Is 3-5 min.
5. The desulfurization efficiency control method according to claim 3, wherein t is2Is 2-4 h.
6. The desulfurization efficiency control method according to claim 1, wherein controlling the input amount of limestone slurry in accordance with the desulfurization adjustment signal comprises:
according to the SO2Calculating the required limestone slurry flow rate by using the mass flow signal so as to determine the required limestone slurry input amount of the absorption tower;
and correcting and calculating the input amount of the limestone slurry according to the pH difference signal.
7. The desulfurization efficiency control method according to claim 1, characterized by further comprising the step of: and when the fluctuation of the pH measured value exceeds a given pH control value, alarming to remind an operator to check reasons, and manually adjusting to maintain the fluctuation of the pH measured value within the given pH control value.
8. The desulfurization efficiency control method according to claim 7, wherein the given pH control value is 5.4 ± 0.2, and when the pH measured value is less than 5.2, the limestone slurry input amount is manually adjusted to be increased; when the pH measurement is above 5.6, manual adjustment reduces the limestone slurry input.
9. The desulfurization efficiency control method according to claim 1, wherein when the SO fails to pass through the SO2And when the fluctuation of the pH measured value is maintained within the given control value through the mass flow signal and the pH difference signal, establishing a mathematical model library, adding an experience value and a detection value of an operator, calculating the desulfurization feedforward parameter by using a mathematical fuzzy algorithm, then overlapping the desulfurization feedforward parameter and the pH difference signal to obtain a desulfurization adjusting signal, and controlling the input amount of limestone slurry according to the desulfurization adjusting signal to maintain the fluctuation of the pH measured value within the given pH fluctuation value.
10. A thermal power plant desulfurization efficiency control system, comprising:
the pH detector is used for measuring the pH value of the absorption liquid in the absorption tower to obtain a pH measured value;
a limestone slurry regulating valve for regulating the input amount of limestone slurry fed into the absorption tower;
the first desulfurization signal processor is used for comparing the pH measured value with a given pH value to obtain a pH difference value and outputting a pH difference value signal;
the desulfurization feedback controller is used for acquiring a pH difference value signal, wherein the pH difference value is the difference value between the pH measured value and a given pH value;
a desulfurization feedforward controller for collecting desulfurization feedforward parameters including SO2Mass flow rate signal, SO2The mass flow is the air supply volume and the flue gas SO of the boiler2The value of the concentration product;
a desulfurization signal processor for converting the SO2Superposing the mass flow signal and the pH difference signal to obtain a desulfurization adjustment signal, and outputting the desulfurization adjustment signal;
the desulfurization feedback controller and the desulfurization feedforward controller are also used for controlling the opening degree of the limestone slurry regulating valve according to the desulfurization regulating signal so as to maintain the fluctuation of the pH measured value within a given pH fluctuation value.
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