CN110260356B

CN110260356B - Energy-saving control method of fluidized bed boiler

Info

Publication number: CN110260356B
Application number: CN201910634879.8A
Authority: CN
Inventors: 白海波
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-07-15
Filing date: 2019-07-15
Publication date: 2020-08-18
Anticipated expiration: 2039-07-15
Also published as: CN110260356A

Abstract

The invention discloses an energy-saving control method of a fluidized bed boiler, which aims to solve the problem of automatic control of the conventional fluidized bed boiler. The method comprises the following specific steps: step one, setting a basic load, performing coal type compensation, and then setting a coal feeding amount and a coal feeding speed; step two, gain compensation is carried out; step three, sending the set coal feeding parameters to a coal feeder, and measuring combustion parameters and fan parameters in real time when a combustion system works; and step four, setting a main steam pressure value and a main steam flow of the boiler, and performing multiple optimization control during the operation of the boiler. The invention realizes control from two aspects: a novel PID control strategy which is formed by combining other control technologies on the basis of PID control; secondly, based on intelligent control, the full-automatic combustion, the most economical combustion, the most environment-friendly combustion and the most safe combustion can be realized by adopting fuzzy control, neural network control, expert control and a control technology combined with other control strategies.

Description

Energy-saving control method of fluidized bed boiler

Technical Field

The invention relates to the field of boiler control, in particular to an energy-saving control method for a fluidized bed boiler.

Background

China is an energy country with coal as the main energy source, and the coal is the most important primary energy source in China and accounts for more than 70% of the total energy source. The total quantity of coal which is proved in China is about 1 trillion tons, the annual coal yield is about 30 million tons, and the coal is the largest coal producing country and consuming country in the world. Coal plays an important role in economic development and brings serious environmental pollution to China, 85% of sulfur dioxide emission, 60% of nitrogen oxide emission, 70% of smoke emission, 85% of carbon dioxide emission and the like are all caused by coal in China every year, and coal combustion becomes the most main pollution source in China.

The automatic application level of the circulating fluidized bed boiler (CFB) is much lower than that of a pulverized coal furnace which is the mainstream in the power industry, and the main reasons are that the circulating fluidized bed boiler is very complicated in combustion process, influenced by a plurality of factors and high in coal feeding, primary air, secondary air and return air coupling. In addition, the nonlinearity and large hysteresis of the combustion process make the control object more complex and difficult to establish an accurate mathematical model, which puts more strict requirements on the control scheme. At present, the domestic circulating fluidized bed boiler combustion loop can be put into automatic operation for a few, and how to ensure the combustion economy is not to mention.

The reasons why the combustion system of the existing fluidized bed boiler cannot be automatically controlled are as follows: first, the control object is complex: the specific process and production conditions of each boiler are different, the working condition changes are different, and for the circulating fluidized bed boiler, the lifting one-time load relates to a plurality of control loops such as coal supply regulation, air supply regulation, induced air regulation, water supply regulation, temperature and pressure reduction regulation and the like; if parameters such as calorific value of the fire coal and the like change and the pressure of the main pipe changes, the series of regulating loops are also influenced; secondly, the problems of the measuring and controlling instrument are as follows: some meters are not installed either because they are expensive or because they are not reliable, such as coal feed rate of a single furnace, smoke and oxygen measurement of exhaust gas, or even some unit or unit air flow measuring meters are not installed, which results in that automatic control cannot be realized at all by conventional control schemes, and in addition, even if these signals are available, the flow rate and oxygen content meter involved in the control loop have poor accuracy, large lag and unreliability; the manual operator and the servo amplifier have excessively low instrument precision, an excessively large dead zone of an adjusting valve, offset of instrument characteristics and the like, and the inaccuracy of the instrument increases the control difficulty; third, the engineering problem of advanced control theory: the advanced control theory is applied to the actual field and has a plurality of detailed processes, such as: the value E, DE of the fuzzy control is generally subjected to proper amplification or reduction and then enters a fuzzy control set; the self-optimizing algorithm must have the capability of identifying false poles and measures for avoiding falling into dead zones, and the like, and the mechanical application of the advanced control idea can only obtain a worse control effect than that of the conventional control system.

Related research is also being conducted.

Disclosure of Invention

An embodiment of the present invention is directed to provide an energy saving control method for a fluidized bed boiler, so as to solve the problems in the background art.

In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:

an energy-saving control method of a fluidized bed boiler comprises the following specific steps:

step one, setting a basic load, performing coal type compensation by a central processing unit according to the basic load, and then setting a coal feeding amount and a coal feeding speed by the central processing unit;

step two, the central processing unit carries out gain compensation according to the coal feeding amount setting and the coal feeding speed setting;

step three, the central processing unit sends the set coal feeding parameters to the coal feeder, the combustion system works, and the combustion parameters and the fan parameters are measured in real time when the combustion system works;

and step four, the central processing unit sets the main steam pressure value and the main steam flow of the boiler according to the combustion parameters and the fan parameters, and multiple items of optimization control can be performed when the boiler operates.

As a further scheme of the embodiment of the invention: the combustion parameters in the third step comprise the temperature of the fluidized bed, the temperature of the outlet of the hearth of the boiler and the content of the smoke oxygen.

As a further scheme of the embodiment of the invention: the fan parameters in the third step comprise the wind speed, the operation time and the wind quantity of the primary fan, the secondary fan and the secondary material returning fan.

As a further scheme of the embodiment of the invention: the optimized control of the fourth step includes optimized control of drum water level, optimized control of main steam temperature, optimized control of load-coal feeding, optimized control of material bed temperature, optimized control of primary air, optimized control of secondary air, optimized control of negative pressure in hearth and optimized control of material layer thickness.

As a further scheme of the embodiment of the invention: the main steam temperature optimization control adopts a main steam temperature-reducing water flow-temperature-reducing water valve cascade control algorithm with a combustion factor feedforward algorithm or a main steam temperature-reducing water valve single-loop control algorithm with a steam temperature disturbance observer algorithm, and has high control precision and a plurality of reference factors.

As a further scheme of the embodiment of the invention: the load-coal feeding optimization control is realized by controlling the coal feeding frequency conversion, the opening degree of a primary air valve, a secondary air valve and an induced air door to control the load and the bed temperature.

As a further scheme of the embodiment of the invention: the primary air is optimally controlled to realize normal fluidization, economic combustion and bed temperature control of the boiler by controlling the primary air baffle.

As a further scheme of the embodiment of the invention: the secondary air optimal control realizes the oxygen content stability and the economic combustion of the boiler by controlling the secondary air baffle.

Compared with the prior art, the embodiment of the invention has the beneficial effects that:

the invention has reasonable design and realizes control from two aspects: a novel PID (intelligent variable proportion integral coal supply-air distribution algorithm) control strategy which is formed by combining other control technologies on the basis of PID control; secondly, based on intelligent control, full-automatic combustion can be realized by adopting fuzzy control, neural network control, expert control and a control technology combined with other control strategies, and as long as the process allows and the control loops of the related measurement and control instruments are completely operated in a full-automatic manner, the labor intensity of workers can be reduced, and the quasi-unmanned operation of the boiler can be realized;

the invention can realize the most economical combustion, reduce the coal consumption and reduce the operation cost;

the invention can realize the most environment-friendly combustion, meet the requirement of full combustion of fuel, ensure the stable combustion of the boiler and solve the environmental protection problems of black smoke emission of the chimney, SQ2 and excessive generation of NOX due to unstable combustion temperature control to a certain extent;

the invention can realize the safest combustion, the combination of intelligent flexible error correction control, the combination technology of state alarm and voice alarm and the index checking system technology, realizes the best safety of the combustion operation of the boiler and has wide application prospect.

Drawings

FIG. 1 is a flowchart of an energy saving control method of a fluidized bed boiler.

Fig. 2 is a schematic diagram of drum water level optimization control in the energy-saving control method of the fluidized bed boiler.

FIG. 3 is a schematic diagram of the optimal control of the main steam temperature in the energy-saving control method of the fluidized bed boiler.

FIG. 4 is a schematic diagram of load-coal supply optimization control in the energy-saving control method of the fluidized bed boiler.

FIG. 5 is a schematic diagram of the optimized control of the temperature of the material bed in the energy-saving control method of the fluidized bed boiler.

FIG. 6 is a schematic diagram of primary air optimization control in the energy-saving control method of the fluidized bed boiler.

FIG. 7 is a schematic diagram of the secondary air optimization control in the energy-saving control method of the fluidized bed boiler

FIG. 8 is a schematic diagram of the optimized control of the negative pressure in the furnace in the energy-saving control method of the fluidized bed boiler.

FIG. 9 is a schematic diagram of the optimization control of the thickness of the material layer in the energy saving control method of the fluidized bed boiler.

Detailed Description

The technical solution of the present patent will be described in further detail with reference to the following embodiments.

Example 1

step three, the central processing unit sends the set coal feeding parameters to a coal feeder, the combustion system works, the combustion parameters and the fan parameters are measured in real time when the combustion system works, the combustion parameters comprise the temperature of a fluidized bed, the temperature of a hearth outlet of a boiler and the content of smoke and oxygen, and the fan parameters comprise the wind speed, the running time and the wind volume of a primary fan, a secondary fan and a secondary material returning fan;

and step four, the central processing unit sets a main steam pressure value and a main steam flow of the boiler according to the combustion parameters and the fan parameters, and performs multiple items of optimized control during the operation of the boiler, wherein the multiple items of optimized control comprise drum water level optimized control, main steam temperature optimized control, load-coal feeding optimized control, material bed temperature optimized control, primary air optimized control, secondary air optimized control, hearth negative pressure optimized control and material layer thickness optimized control.

The control objective of the invention is to change the heat supply quantity in the hearth by changing the supply quantities of fuel, primary air, secondary air and the like according to the change of external load, thereby changing the steam yield in the bubbles to realize the requirement of fast responding to the load change, and ensuring the safety and the economical efficiency of boiler operation, the stability of main steam pressure and the stability of bed material temperature in the whole process. Therefore, the control task of the combustion process of the circulating fluidized bed boiler has two aspects, namely, the supply of energy, namely the heat provided by the combustion of fuel can be adapted to the steam load requirement of the boiler, and the supply of the fuel is mainly realized; the second is the economic safety of the combustion process, namely the bed material temperature of the combustion process is stable, the pressure of the hearth is reasonable, the desulfurization of the combustion process, the emission effect of nitrogen oxides and other smoke and dust are guaranteed, and the method is mainly realized by controlling the air supply amount and reasonably adjusting the proportion of primary air and secondary air. The controlled objects of the system in the combustion process mainly comprise fuel quantity, air supply quantity, main steam pressure, bed temperature, induced air quantity, hearth pressure, sulfur dioxide and the like. They correspond to different control systems, namely a fuel control system, a primary air control system, a secondary air control system, a bed material temperature control system, an induced air quantity control system, a hearth pressure control system and a sulfur dioxide control system. There are also different coupling relationships between these several systems. If the primary air volume is changed, the bed material temperature can be changed, the hearth pressure can be changed, the combustion efficiency can be influenced, the main steam pressure can be influenced, the desulfurization effect can be influenced, and the like. Therefore, the combustion process requires a coordinated control of the relationship between the several variable systems.

The invention adopts a control parameter following correlation technology, a combustion effect simulation technology, a system diagnosis and flexible control technology, an advanced control engineering technology and an intelligent algorithm adjusting technology, achieves a good control effect, and solves the problems of strong coupling, large lag, time variation and the like in the combustion process.

Control parameters follow the correlation technique: the parameter following is to use the limited and correct related field instrument measurement and control signals to construct a control model based on the combustion effect variable under the parameter following, it does not need to manually input any fuel quality data, load parameters and a large number of model initialization parameters, the model can quickly find the optimal combustion state and automatically detect the deviation of the optimal combustion point caused by various factors to pull back the control point to the optimal state, the technology is based on the relative correctness of the process data change trend rather than the correctness of the absolute value. The correlation technique is that a change in the control quantity results in a correct change in the corresponding measured variable, and the law of the change between them may be inaccurate, but the trend of the change must be correct.

The combustion effect simulation technique involves a virtual dependent variable and a combustion effect variable. The virtual correlation variable is a virtual measurement parameter constructed by using the existing measurement and control signal, such as: fuel quantity, air-coal ratio and the like. The combustion effect variable is a combustion effect variable which is constructed by using the associated measurement and control signals and the virtual variable and can represent the current working condition, is similar to the combustion efficiency but not the combustion efficiency, and is an intermediate variable with the variation regulation rate consistent with the combustion efficiency.

The system diagnosis and flexible control technology ensures that the faults of partial instruments cannot cause model paralysis and potential safety hazards in production, and can process the adjustment of control strategies caused by the abnormal operation condition of partial processes and the faults of instrument equipment on line.

The advanced control engineering technology integrates fuzzy control, nonlinear control and predictive control, comprehensively solves the problems of nonlinearity, pure lag and time-varying property of the process and large dead zone, large idle stroke, low adjustment precision and the like of various actuating mechanisms, prolongs the service life of equipment, can be realized by adopting a DCS (distributed control system) or PLC (logic programming) control system as a hardware platform, and the front data and the rear data of the technology are shown in a table 1.

TABLE 1

	Temperature of steam	Smoke oxygen content	Furnace temperature	Pressure of furnace	Amount of coal
						Before being thrown into	±3℃	7-10％	±20℃	±10pa
After being put into	±1℃	3-5％	±8℃	±5pa	The reduction is 2.5 percent

As can be seen from Table 1, the advanced control engineering technology has a good application effect.

The intelligent algorithm adjusting technology selects a variable proportion-variable integral optimization algorithm to adapt to the boiler, namely the complex control of multi-input, multi-output, multi-loop and nonlinear correlation, and solves the key problem of how to maximize the combustion efficiency of the coal-fired boiler under the limited condition.

The steam drum water level optimization control adopts a three-impulse control algorithm with a combustion factor expert algorithm. The combustion factor means that on the premise that the combustion intensity of the hearth is adjusted when the load of the boiler is increased or decreased, a feed-forward algorithm capable of representing the combustion intensity of the hearth is established and introduced into a classical three-impulse control model, and the anti-interference capability of the loop and the control accuracy of the steam drum water level are further improved. The control point of the circuit is floating, i.e. it becomes lower when the load is high and vice versa, which contributes to the safety and economy of the boiler operation.

The main steam temperature optimization control adopts a main steam temperature-reducing water flow-temperature-reducing water valve cascade control algorithm with a combustion factor feedforward algorithm, and also can adopt a main steam temperature-reducing water valve single-loop control algorithm with a steam temperature disturbance observer algorithm to achieve high-precision main steam temperature control. When the flow of the desuperheating water is measured and the load is large enough, a cascade control scheme can be considered, and a decoupling algorithm with a steam drum water level control valve is also considered on occasions adopting the surface type desuperheater.

The load-coal feeding optimization control realizes the control of the load and the bed temperature by controlling the coal feeding frequency conversion, the opening degree of a primary air valve, a secondary air valve and an induced air door. An operator can set a main steam pressure control point (generally, the rated main steam pressure of the boiler) and an optimized operation interval (generally, 80-110% of the rated load) of the load of the boiler, the coordinated optimization model can adjust the coal feeding quantity and the coal feeding variable frequency opening in place in a most reasonable mode according to the fluctuation condition of the pressure of the main pipe, and other control loops such as primary air, secondary air, induced air and steam-water system control loops can automatically perform corresponding adjustment at the moment. The operation mode of the boiler is divided into an adjusting furnace and an operating furnace, the operating furnace does not participate in the control of the main steam pressure, the coal quantity is fixed, and the boiler operates according to the fixed load. The regulating furnace regulates the load according to the change of the main steam pressure and has the function of regulating the load. The switching between operating the oven and regulating the oven is done by switching the buttons. The first problem to be solved by the regulating furnace is to cope with the changes of the pressure and the temperature of the main pipe, and then the problems of self-stable operation and economic operation are solved. And adjusting the coal feeding amount of the boiler according to the set main steam pressure control point to enable the boiler to meet the load requirement. The bed temperature abnormity processing model ensures the emergency processing capability of quickly adding air and reducing coal when the bed temperature is abnormally increased. The loop also has the functions of coal breakage judgment, alarming, automatic processing, automatic recovery after coal breakage processing and the like, when the coal feeding quantity is less than a certain value, the system judges coal breakage and sends out voice alarming, and the coal quantity of a frequency converter with coal breakage is automatically distributed to a coal feeder without coal breakage according to a proportion, so that the coal feeding quantity of a boiler after coal breakage is kept at the coal quantity before coal breakage, and the stability of the boiler load is ensured. Of course, the amount of coal distributed to other coal feeders after a coal outage is required to meet the requirements of equilibrium bed temperature and oxygen content.

And (3) optimizing and controlling the temperature of the material bed: the control means of the bed temperature is firstly embodied in the control of the amount of the return material. As the control precision of the loop reaches R +/-5 ℃, the control of the edge clamping at high bed temperature can be completely carried out to obtain high efficiency.

The primary air optimal control realizes the normal fluidization, the economic combustion and the bed temperature control of the boiler by controlling a primary air baffle (or other control equipment). The primary air quantity mainly comprises two parts, namely the fluidization air quantity and the bed temperature protection air quantity. The fluidization air quantity is the minimum air quantity capable of maintaining the fluidization state, and the value is related to the coal feeding quantity (whether the function is started or not can be selected) and the minimum critical primary air quantity. The adjustment of the air quantity is completed by adjusting the primary air baffle or frequency conversion.

The secondary air optimal control realizes oxygen content stabilization and economic combustion of the boiler by controlling a secondary air baffle (or other control equipment). The control of the secondary air volume comprises five parts: basic secondary air volume (actual primary air volume is multiplied by optimized secondary air rate), oxygen compensation air volume (secondary air volume is controlled by fixed oxygen content when optimization is not started, oxygen control points are optimized and floated), coal quantity correction secondary air volume increment, secondary air optimization air volume (secondary air volume is corrected by automatically calculating air volume increment when coal quality, load, instrument precision and the like change, so that economic combustion is achieved), and experience optimization air volume (experience secondary air volume increment in a full-automatic state designed for experienced operators, and a system can learn).

The furnace negative pressure optimization control introduces an air volume feedforward compensation algorithm to perfect the control index, namely, the air volume is changed when the primary air volume or the secondary air volume is changed. When two induced draft fans are provided, one or two valves can be hung to be thrown automatically, and the other valve is thrown at a manual position.

The material bed thickness optimization control realizes the control requirement of the boiler material bed differential pressure by controlling the frequency conversion of the slag cooler so as to achieve the dynamic balance of the coal feeding input and the coal slag output. The optimal opening degree of frequency conversion is obtained through the comparison calculation of the material bed differential pressure in the furnace and the material bed differential pressure set value, so that the material bed differential pressure of the boiler is stabilized within the range required by combustion. In addition, the loop also has the function of automatically reducing the rotating speed of the slag cooler to protect the slag cooler when the water temperature at the slag cooler outlet is too high, and also has the function of performing deviation for matching the system resistance.

The working principle of the embodiment of the invention is as follows: the invention successfully develops an energy-saving control method of a fluidized bed boiler by applying a system fuzzy control self-optimization algorithm according to fuzzy control and artificial intelligence theories, the method is organically combined with a Distributed Control System (DCS), and integrates an advanced control parameter following association technology, a multivariable decoupling technology, a process optimization control technology, a fault diagnosis and flexible control technology, a state alarm and voice alarm combination technology, thereby realizing the full-automatic energy-saving operation of the coal-fired boiler, so that the coal-fired circulating fluidized bed boiler achieves the purposes of safe operation, stable operation and economic operation, and the invention is a boiler combustion energy-saving control method integrating scientificity, universality, advancement, practicability, safety and economy, and can ensure that the boiler operates more safely, more stably, more energy-saving and more environmentally-friendly.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. An energy-saving control method of a fluidized bed boiler is characterized by comprising the following specific steps:

2. The method for controlling the energy saving of the fluidized bed boiler according to claim 1, wherein the combustion parameters in the third step include a fluidized bed temperature, a furnace outlet temperature of the boiler and a smoke oxygen content.

3. The method for controlling the energy saving of the fluidized bed boiler according to claim 1 or 2, wherein the blower parameters in the third step comprise the wind speed, the operation time and the wind quantity of the primary blower, the secondary blower and the secondary material returning blower.

4. The method for controlling the energy conservation of a fluidized bed boiler according to claim 1, wherein the optimization controls of the plurality of steps include drum water level optimization control, main steam temperature optimization control, load-coal feeding optimization control, material bed temperature optimization control, primary air optimization control, secondary air optimization control, furnace negative pressure optimization control and material layer thickness optimization control.

5. The energy-saving control method of the fluidized bed boiler according to claim 4, wherein the main steam temperature optimization control adopts a main steam temperature-desuperheating water flow-desuperheating water valve cascade control algorithm with a combustion factor feed-forward algorithm or a main steam temperature-desuperheating water valve single-loop control algorithm with a steam temperature disturbance observer algorithm.

6. The method for controlling energy saving of a fluidized bed boiler according to claim 4, wherein the load-coal feeding optimization control is to control the load and the bed temperature by controlling the coal feeding frequency conversion, the opening degree of the primary air valve, the secondary air valve and the induced air damper.

7. The method for controlling energy conservation of a fluidized bed boiler according to claim 4 or 5, wherein the primary air is optimally controlled to realize normal fluidization, economical combustion and bed temperature control of the boiler by controlling a primary air baffle or frequency conversion.

8. The method of claim 4, wherein the overfire air optimization control is performed by controlling an overfire air damper to achieve oxygen stabilization and economical combustion of the boiler.