Limestone slurry pH value concentration fly-up detection system, method, control system and desulfurization system
Technical Field
The invention relates to the field of FGD (flue gas desulfurization) automatic control of a coal-fired power plant, in particular to a limestone slurry pH value concentration fly-rise detection system, a limestone slurry pH value concentration fly-rise detection method, a limestone slurry pH value concentration fly-rise control system and a limestone slurry FGD automatic control system.
Background
Sulfur dioxide (SO)2) Mainly comes from the combustion process of coal, oil and natural gas, and is one of the main atmospheric pollutants. Thus controlling SO in coal-fired power plants2The emission being reduction of SO in the atmosphere2One of the main measures of content.
According to the emission standard of atmospheric pollutants of thermal power plants (GB13223-2011), in order to reduce the total pollutant emission of the coal-fired power plants, the emission standard of pollutants of the coal-fired power plants is looked at the emission standard of pollutants of the coal-fired power plants to the emission standard of gas turbines, namely: the emission limits of smoke, sulfur dioxide and nitrogen oxides are respectively 5mg/Nm3, 35mg/Nm3 and 50mg/Nm3, and the limit is generally defined as the standard of 'ultra-clean emission' of coal-fired boilers in the industry.
Reduction of SO2There are various methods of discharge. SO currently in common use2Control technology baseThe method is divided into three categories: "desulfurization before combustion, desulfurization during combustion, and desulfurization after combustion, i.e., Flue Gas Desulfurization (FGD).
Desulfurization before combustion refers to washing raw coal by a physical or chemical method to remove or reduce impurities such as sulfur, ash and the like in the raw coal. The adopted method comprises coal dressing, gasification, coal water slurry and briquette processing and the like. However, the method can only remove part of sulfur (mainly inorganic sulfur) in the coal and cannot fundamentally solve the problem of SO2The pollution problem to the atmosphere; the desulfurization during combustion is realized by spraying CaO/CaCO3 absorbent of lime into a hearth to solidify S02/SO3, and the adopted method comprises the steps of spraying calcium into the hearth and desulfurizing limestone by fluidized bed co-combustion; the desulfurization after combustion, i.e. Flue Gas Desulfurization (FGD), refers to the addition of a desulfurization device in the tail flue of the boiler and the desulfurization of flue gas by using a desulfurizing agent, and includes wet and dry (semi-dry) desulfurization processes. Wherein: limestone-gypsum wet process is considered to be the current control of SO2The most effective way to discharge.
The existing desulfurization control system is a clean flue gas outlet SO of a coal-fired generating set2The concentration is a control target, and the pH value concentration of limestone slurry is simultaneously controlled in the limestone-gypsum wet desulphurization control SO as to control SO2Thereby controlling the degree of absorption of the clean flue gas outlet SO2The concentration meets the environmental protection requirement.
The pH value concentration of limestone slurry is needed to be used in the existing desulfurization control system, and the required opening degree of a limestone slurry valve is calculated, SO that the purified flue gas outlet SO after desulfurization is realized2And (4) controlling the content.
Analysis from the aspects of the operation status and the control logic: the automatic operation of the FGD desulfurization control system depends on the determination of the pH value concentration of limestone slurry.
Because the measuring device of lime stone thick liquid pH value concentration regularly washs (washs once every hour), lime stone thick liquid pH value concentration loses the authenticity, and control system can not correctly obtain the cleaning process, and the measured value rises by a wide margin, has influenced lime stone thick liquid pH value concentration measurement accuracy, causes desulfurization automatic control can't adapt to the pH value and change and put into automation.
Disclosure of Invention
In order to solve the problem of signal distortion caused by large-scale fly-up of the cleaning pH value, the invention provides a system and a method for detecting the fly-up of the pH value concentration of limestone slurry, a control system and a desulfurization system. The invention can ensure the normal work of the PID of the desulfurization control system after eliminating the distortion signal from the pH value signal in real time.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
a limestone slurry pH value concentration fly-up detection system comprises: the system comprises a first-order inertia module, a second first-order inertia module, a measurement deviation module and a height alarm module;
the first order inertia module is used for carrying out first filtering on the pH value measurement signal to obtain a first filtering value;
the second first-order inertia module is used for carrying out second filtering on the pH value measurement signal to obtain a second filtering value;
the measurement deviation module is used for carrying out deviation processing on the first filtering value and the second filtering value to obtain a deviation value;
and the height alarm module is used for obtaining the change trend and the change quantity of the pH value according to the deviation value, judging the threshold value of the change quantity and outputting a flying detection result.
As a further improvement of the present invention, the transfer function formula of the first order inertia module is:
the transfer function formula of the second-order inertia module is as follows:
wherein G(s) characterizes the ratio of the Laplace transform of the linear system response input and output at zero initial condition; t1, T2 characterize the inertial time constant of the inertial element.
As a further improvement of the present invention, the inertia time T1 of the first order inertia module is 10s to 20 s; the inertia time T2 of the first order inertia module is 60 s-70 s.
As a further improvement of the invention, the system also comprises a fly-lift detection input switch and a fly-lift detection input confirmation module;
the flying detection input switch is used for giving the working state of the flying detection system;
and the flight lift detection input confirmation module is used for judging the validity of the flight lift detection result according to the flight lift detection result and the working state of the flight lift detection input switch.
A detection method of a limestone slurry pH value concentration fly-up detection system comprises the following steps:
carrying out first filtering on the pH value measurement signal to obtain a first filtering value;
carrying out second filtering on the pH value measurement signal to obtain a second filtering value;
carrying out deviation processing on the first filtering value and the second filtering value to obtain a deviation value;
and obtaining the change trend and the change quantity of the pH value according to the deviation value, judging the threshold value of the change quantity, and outputting a flying rise detection result.
As a further improvement of the invention, the method also comprises the following steps:
and judging the validity of the fly-lift detection result according to the working state of the fly-lift detection system and the fly-lift detection result.
The validity means that when the fly-lift detection switch is in a switch-in state and the fly-lift detection result output by the high-low alarm module is true, the output of the fly-lift detection control system is true; otherwise, the signal of the detected pH value is in a flying state, and the signal is distorted.
An automatic FGD desulfurization control system comprises a pH value measuring system, a desulfurization control system and a limestone slurry pH value concentration fly-up detection system;
the pH value measuring system is connected with the pH value measuring device and is used for obtaining a pH value measuring signal;
the limestone slurry pH value concentration fly-up detection system is used for judging whether a pH value measurement signal obtained by the pH value measurement device is in fly-up distortion or not;
the desulfurization controlA system for applying the fly-up distortion result to SO2The absorbent is controlled.
An FGD desulfurization system comprises a boiler descending section heat exchanger, a denitration ammonia injection grid, a denitration reactor, an air preheater, an electric dust remover, a desulfurization absorption tower, a chimney, a limestone slurry circulating pump, a pH value measuring device, a limestone new slurry supplementing pipeline and an FGD desulfurization automatic control system;
flue gas combusted by the boiler flows through the boiler descending section heat exchanger to reach a denitration ammonia injection grid, then is mixed with an injected ammonia-air mixture, enters a denitration reactor to carry out chemical reaction denitration, enters an air preheater to recover heat, and is discharged into the atmosphere through a chimney after passing through an electric precipitator and a desulfurization absorption tower;
the limestone slurry circulating pump is connected with a spraying device in the desulfurization absorption tower for limestone slurry; the pH value measuring device is arranged in limestone slurry in the desulfurization absorption tower and is electrically connected with the FGD desulfurization automatic control system; the limestone new slurry supplementing pipeline is communicated with the desulfurization absorption tower, and the FGD desulfurization automatic control system controls the on-off of the limestone new slurry supplementing pipeline.
As a further improvement of the invention, the chimney is also provided with clean flue gas SO2And (4) a measuring device.
Compared with the prior art, the PH value flying detection system provided by the invention has the advantages that PH value false distortion signals which are useless for the desulfurization control system and even interfere the desulfurization control system can be automatically identified and eliminated, and a foundation can be laid for the desulfurization control system to be capable of realizing real-time online full-automatic detection.
According to the invention, two first-order inertia modules are adopted to filter the pH value measurement signal, carry out deviation processing, carry out threshold judgment on the variation, output a flying detection result, judge whether the pH value signal is distorted or not on the real-time pH value signal, and solve the problem that the pH value is unavailable due to the cleaning of the pH value measurement device. Because the pH value measuring device is cleaned regularly, the desulfurization control system can not obtain the cleaning information of the pH value measuring device, the pH value measuring signal can generate signal flying when the pH value measuring device is cleaned, the signal is distorted, the signal can not be used by the desulfurization control system, the pH value measuring value is greatly changed, the measuring accuracy and the corresponding time are influenced, the investment of the desulfurization control system is further influenced, and the environmental protection index controlled by the desulfurization system is influenced. According to the invention, when the real-time pH value signal is adopted to judge that the pH value signal is in a fly-up state, the current distortion signal can be eliminated, and the desulfurization control system can process the real-time pH value signal by using the fly-up detection judgment signal. And after the distortion signal is removed from the real-time pH value signal, the normal work of a desulfurization control system PID can be ensured.
Drawings
FIG. 1 is a block diagram of a pH fly-up detection system;
FIG. 2 is a schematic view of a pH measurement fly-lift detection system;
FIG. 3 is a flow diagram of a desulfurization system;
device and module code number description table in the figure:
1. a boiler descending section heat exchanger;
2. denitration ammonia injection grids;
3. a denitration reactor;
4. an air preheater;
5. an electric dust collector;
6. a desulfurization absorption tower;
7. a chimney;
8. clean flue gas SO2A measuring device;
9. a limestone slurry circulating pump;
10. limestone slurry pH value measuring device;
11. a limestone new slurry replenishing pipeline;
12. a LAG first order inertia module;
13. a LAG first order inertia module;
an ON/OFF, fly-lift detection throw-in switch module;
ALARM and high-low ALARM module;
DEV, a measurement deviation module;
AND a flight detection input confirmation module.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments, and are not intended to limit the scope of the present disclosure. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure. 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 invention.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present. In addition, if a layer/element is "on" another layer/element in one orientation, then that layer/element may be "under" the other layer/element when the orientation is reversed.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In view of the above problems, in order to solve the problem that the desulfurization control cannot be input due to the large-amplitude fly-up signal distortion of the cleaning pH value of the limestone slurry pH value measuring device in the FGD desulfurization control.
The invention provides a limestone slurry pH value concentration fly-up detection system, which comprises: a first order inertia module 12, a second first order inertia module 13, a measurement deviation module DEV and a high-low ALARM module (ALARM);
the first order inertia module 12 is configured to perform first filtering on the pH value measurement signal to obtain a first filtered value;
the second first-order inertia module 13 is configured to perform second filtering on the pH value measurement signal to obtain a second filtered value;
the deviation measuring module (DEV) is used for carrying out deviation processing on the first filtering value and the second filtering value to obtain a deviation value;
and the high-low ALARM module (ALARM) is used for obtaining the change trend and the change quantity of the pH value according to the deviation value, carrying out threshold judgment on the change quantity and outputting a flying detection result.
The limestone slurry pH value concentration flying-rise detection system is positioned in DCS and between the pH value measurement system and the desulfurization control system. See figures 1 and 2.
The pH value measurement signal fly-up detection system comprises two links: the pH value deviation processing AND pH value alarming, namely a first-order inertia module 12, a second-order inertia module 13, a deviation measurement module (DEV), a high-low ALARM module (ALARM), a fly-lift detection input switch (ON/OFF) AND a fly-lift detection input confirmation module (AND) form a fly-lift detection control system. The above are the key components of the flying lift detection control system for desulfurization control.
The pH value flying detection control system provided by the invention is as shown in figure 1, and the pH value measurement in the desulfurization absorption tower obtains a pH value measurement signal through a measurement device, and the pH value measurement signal is sent into the desulfurization control system for desulfurization control after being processed through a measurement link.
The transfer function formula of the first order inertia module (12) is as follows:
the transfer function formula of the second first order inertia module (13) is as follows:
wherein G(s) characterizes the ratio of the Laplace transform of the linear system response input and output at zero initial condition; t1, T2 characterize the inertial time constant of the inertial element.
The pH value measurement signal enters a first-order inertia module 12, and the inertia time of the inertia module is between 10s and 20 s; the pH value measurement signal enters a second-order inertia module 13, and the inertia time of the inertia module is between 60s and 70 s.
The output of the first order inertia module 12 and the output of the second order inertia module 13 enter a measurement deviation module DEV; the output of the deviation measuring module DEV enters a high-low ALARM module ALARM, the high-low ALARM module ALARM detects the change trend and the change quantity of the current pH value, and once the change trend and the change quantity exceed a preset threshold value, the high-low ALARM module ALARM outputs a flying detection result. The result of the flying-up detection AND the ON/OFF state of the flying-up detection input switch enter the flying-up detection input confirmation means AND.
The invention also provides a detection method of the limestone slurry pH value concentration fly-up detection system, which comprises the following steps:
carrying out first filtering on the pH value measurement signal to obtain a first filtering value;
carrying out second filtering on the pH value measurement signal to obtain a second filtering value;
carrying out deviation processing on the first filtering value and the second filtering value to obtain a deviation value;
and obtaining the change trend and the change quantity of the pH value according to the deviation value, judging the threshold value of the change quantity, and outputting a flying rise detection result.
When the ON/OFF of the fly-up detection switch is in an ON state and the output of the fly-up detection result is true by the ALARM module ALARM, the output of the fly-up detection control system is true. Otherwise, at this time, the signal for detecting the pH value is in a flying state, and the signal is distorted and unavailable.
The third purpose of the invention is to provide an automatic FGD desulfurization control system, which comprises a pH value measuring system, a desulfurization control system and a limestone slurry pH value concentration fly-up detection system;
the pH value measuring system is connected with the pH value measuring device and is used for obtaining a pH value measuring signal;
the limestone slurry pH value concentration fly-up detection system is used for judging whether a pH value measurement signal obtained by the pH value measurement device is in fly-up distortion or not;
the desulfurization control system is used for controlling SO according to the fly-up distortion result2The absorbent is controlled.
The pH value flying detection control system is positioned between the pH value measuring system and the desulfurization control system. And after the pH value measurement signal is sent out from the measurement system, the pH value measurement signal enters a fly-lift detection control system before entering desulfurization control. The fly-up detection control system detects the pH value measurement signal in real time on line, and once the fly-up phenomenon of the pH value measurement signal due to the cleaning of the measuring instrument is detected, the signal is distorted, and the distorted pH value measurement signal is not sent to the desulfurization control system.
The limestone slurry pH value concentration fly-up detection system plays a role when desulfurization control is put into automation, and the pH value measurement fly-up detection system generates a fly-up judgment signal of a pH value measurement signal. When the pH value measurement flying-up detection system judges that the measurement signal is in a flying-up state, the pH value signal entering the desulfurization control is in a distorted state, and the distorted signal can be rejected.
The limestone slurry pH value concentration fly-up detection system has the function of judging the pH value measurement of the pH value measurement device distorted due to cleaning, and forming the judgment of whether a pH value measurement signal is in fly-up distortion or not. The system comprises two links: a pH value deviation processing module and a pH value deviation alarm module. The system generates a reasonable pH value signal distortion judgment signal for the control of the desulfurization system, ensures reasonable desulfurization control quality and prevents the desulfurization control system from being fluctuated greatly.
The fourth purpose of the invention is to provide an FGD desulfurization system, which comprises a boiler descending section heat exchanger 1, a denitration ammonia injection grid 2, a denitration reactor 3, an air preheater 4, an electric dust remover 5, a desulfurization absorption tower 6, a chimney 7, a limestone slurry circulating pump 9, a pH value measuring device 10, a limestone new slurry supplementing pipeline 11 and the FGD desulfurization automatic control system;
a typical desulfurization system flow is shown in fig. 3, flue gas combusted by a boiler flows through a boiler descending section heat exchanger 1, reaches a denitration ammonia injection grid 2, is mixed with an injected ammonia-air mixture, enters a denitration reactor 3 for chemical reaction, enters an air preheater 4 for further recovering heat, passes through an electric dust collector 5 and a desulfurization absorption tower 6, and is discharged into the atmosphere through a chimney 7.
In the desulfurization absorption tower 6, limestone slurry is provided for spraying equipment of the absorption tower by a limestone slurry circulating pump 9, and the limestone slurry and SO in the raw flue gas2Reacting and absorbing to remove most SO2. The limestone concentration of the limestone slurry is detected by the pH measuring device 10 and sent to the desulfurization control system of the DCS. When the pH value of the limestone slurry is higher, the absorption of SO in the limestone slurry is proved2Will be replenished through the limestone fresh slurry replenishing conduit 11.
The limestone slurry circulating pump 9 is connected with a spraying device in the desulfurization absorption tower 6 for limestone slurry; the pH value measuring device 10 is arranged in limestone slurry in the desulfurization absorption tower 6, and the pH value measuring device 10 is electrically connected with an FGD desulfurization automatic control system; the limestone new slurry supplementing pipeline 11 is communicated with the desulfurization absorption tower 6, and the FGD desulfurization automatic control system controls the on-off of the limestone new slurry supplementing pipeline 11. The chimney 7 is also provided with clean flue gas SO2A measuring device 8.
The design method of the pH value measurement signal fly-up detection system comprises the following steps: the pH value signal enters the DCS through the measuring signal system and passes through the pH value signal flying detection system before being sent to the desulfurization control system. And the fly-lift detection system detects the current pH value measurement signal in real time on line, and when the fly-lift trend is detected and the current pH value is judged to be in the fly-lift state, the current pH value signal is not adopted, and the numerical value before the fly-lift is used as the control quantity of the pH value and is sent to the desulfurization control system.
For example: the DEV module of the pH value signal flying detection system detects the deviation of a first-order inertia module 12 and a second-order inertia module 13 in real time, and an ALARM detection module ALARM outputs the diagnosis result information of signal flying according to a preset threshold (a judgment threshold is given according to an actually measured signal curve on site, a high-limit ALARM judgment value is set between 8 and 10 according to site experience, and a low-limit ALARM judgment value is set between-8 and-10).
The technical scheme is mainly characterized in that:
1. the real-time pH value signal is adopted to judge whether the pH value signal is distorted, so that the problem that the pH value is unavailable due to cleaning of a pH value measuring device is solved. Because the pH value measuring device is cleaned regularly, the desulfurization control system can not obtain the cleaning information of the pH value measuring device, the pH value measuring signal can generate signal flying when the pH value measuring device is cleaned, the signal is distorted, the signal can not be used by the desulfurization control system, the pH value measuring value is greatly changed, the measuring accuracy and the corresponding time are influenced, the investment of the desulfurization control system is further influenced, and the environmental protection index controlled by the desulfurization system is influenced.
2. When the real-time pH value signal is adopted to judge that the pH value signal is in a fly-up state, the current distortion signal can be eliminated, and the desulfurization control system can process the real-time pH value signal by using the fly-up detection judgment signal. And after the distortion signal is removed from the real-time pH value signal, the normal work of a desulfurization control system PID can be ensured.
3. When the real-time pH value signal is adopted to judge that the pH value signal is in a fly-up state, the limestone slurry supply valve can be accurately controlled, the valve is prevented from exiting an automatic operation state due to large opening and closing of the pH value signal distortion, and the desulfurization control system can stably operate.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.