高炉上料变频调速系统设计Word文档格式.docx

1、 control strategyI. INTRODUCTIONThe working state of Industrial boiler combustion system is closely related to its air supply system, induced ventilation system, grate system and drum water level and others. Proper regulation, control of these associated systems is to solve that the boiler operating

2、 efficiency is low and an effective means of environmental pollution is serious. At present, to improve the operating efficiency of industrial boilers has become the technology of existing coal-fired industrial boilers pressing issues to be resolved, with far-reaching significance.II. A BOILER COMBU

3、STION PROCESSIndustrial boilers is a multi-input, multiple-output, nonlinear and strong coupling of dynamic objects, the boilers combustion process is a strong interference, nonlinear, time-varying, multi-variable and complex process. Boiler operation will show the following two states: When the boi

4、ler is running at high load, due to large load, amount of coal grate and air supply is also great, high temperature furnace, the burning intensity. A lower excess air ratio can effectively reduce the flue gas temperature , raise the temperature of the furnace and convection tubes and be conducive to

5、 the continuation of tiny particles of carbon combustion, thereby reducing the smoke damage and mechanical loss of incomplete combustion. When the boiler are operating at low load, due to load small, grate for coal volume and a corresponding reduction in air supply, combustion intensity decreased, T

6、he use of a high excess air coefficient, can relatively increase in air supply, improve the carbon particles and oxygen in the collision rate and the osmotic pressure of oxygen to carbon, and be conducive to enhanced combustion, raising the furnace temperature and convective heat transfer coefficien

7、t segment. Boiler system heat balance of the expression: Q=Q1+Q2+Q3+Q4+Q5+Q6 （1）Type in Q-the total heat input boiler system; Q1-effective use of heat （for heating water and producing steam）; Q2- exhaust heat loss; Q3- incomplete combustion gas heat loss; Q4 - incomplete combustion of solid heat los

8、s; Q5 -boiler heat loss; Q6 - ash physical heat loss.In practical applications, Q2+Q3+Q4 are mainly composed of heat loss. The thermal efficiency of the boiler as follows: （2）The relationship between boiler heat loss and the excess air ratio- is shown in Fig.1.Figure 1. Combustion process heat balan

9、ceAs the excess air coefficient- increases, the amount of air into the furnace increases, coal and combustible gas completely combusts, reducing Q3and Q4 , But Q2 increases with the increasing of air supply, while accounting for the largest proportion of heat loss. So, along with the excess air coef

10、ficient- increases, Q3and Q4 decrease Figure 1. Combustion process heat balance and Q2 increases, Q2+Q3+Q4 is a major part of the boiler heat loss. As be seen from Fig1 that about three of Q2+Q3+Q4 form the concave curve having a minimum point-K, at the point of the boiler heat loss minimum, maximum

11、 thermal efficiency. Point-K corresponds to the best excess air coefficient-which is the best air-coal ratio. The boiler heat loss is influenced at the same time by the coal, furnace air leakage and other factors. When these factors change, the heat loss curve extreme points will also take place dri

12、ft changes, so in practical applications, we must constantly look for the best air-coal ratio operating point.III. THE CONTROL STRATEGY OF BOILER COMBUSTIONA. Control PrincipleIn view of the characteristics in the process of industrial boiler operation, the system adapts idea of combining the centra

13、l control and subsystem control to ensure the most efficient combustion on condition that the system meets the load demand. Control block diagram shows in Fig 2. Central controller carry out optimize calculation according to the parameters transmitted from acquisition system - the boiler outlet temp

14、erature, flow rate, air supply, induced air flow, water flow, water temperature, the delivery of coal and so on. Combined with the previous operating rules, central controller gives optimization operating parameters and passes them to various subsystems in the respective. Each sub-optimal does linea

15、r terms according to the results, then adjusts several devices through frequency conversion.Figure 2. Control block diagramB. Combustion Control SystemBoiler combustion control system includes: load control system, the furnace negative pressure control system. As there are a number of coupling betwe

16、en subsystems, it decouples solved through a central controller optimized calculation of the mutual coupling between subsystems. In order to let the boiler adapt to the changes, the amount of air supply and fuel must be changed at the same time.As the delivery of coal is more difficult to measure, m

17、oreover considering a lag, the system uses the air supply as the main adjustment parameter. Optimal control of air supplying can be carried out firstly when the load change. Air supply control system task is to ensure full combustion of fuel put into the furnace, so that the boilers can get highest

18、combustion efficiency. The optimum efficiency of boiler operation-, must correspond to the best of oxyacetylene ratio-. When the amount of time the amount of coal is sure, that corresponds to the best air supply. Therefore, the boiler combustion system of Self-Optimizing Control in essence is to fin

19、d the best air supply in essence. Its control flow shows in Fig. 3.Then using DE algorithm realizes self-optimizing control of boiler combustion system. Specific methods as follows: in a certain period of time, assuming the same amount of coal and air supply as the control object, we take the wind v

20、alue as the chromosome coding and the efficiency of function as fitness function to find the efficiency of optimization until find the maximum, which is the boiler reaching optimum combustion conditions. At this point, the ratio of the amount of coal and the air flow is the best air-coal ratio. Acco

21、rding to DE algorithm basic flow, first of all, take an approximation of the amount of air the boiler combustion system required as the initial population. Do initialize （chromosome encoded）, calculate of fitness and then carry on three kinds of basic-sub-operations selection, crossover, and mutatio

22、n genetic operators to generate a new individual. Finally calculate the fitness, repeat the above steps until you find the maximum efficiency.Figure 3. Combustion control system flow（1）Air Supply Volume ControlFirst, based on experience to set a good value the most optimal value is found when the bo

23、iler to reach steady operating conditions by changing the oxy-acetylene-. Taking into account the lag characteristics of combustion system, we generally need to delay a certain time after the change （available on-site adjustment）, then measured until obtain the best value. At this point, the control

24、 system automatically stops optimization, the default current value as the best air-coal ratio, and then start the self-optimizing timer, and be ready for the next optimization. General optimization should not be too short interval, which can be set based on the actual working conditions. In the tim

25、e taken to reach the next self-optimizing, the control devices will firstly determine whether the system come into a stable state, wait to go into a stable state and then start a new round of optimization.（2） Furnace Negative Pressure ControlIn the furnace of boiler, it has a certain negative pressu

26、re to avoid excessive heat with exhaust of tail gas and can also prevent the boiler furnace flame out because of pressure. Negative pressure control is by regulating the amount of boiler blower. The relationship between blast volume and air flow volume cited a specific relationship the formation of

27、furnace negative pressure. Blast furnace changes are the main factors result in negative pressure disturbances. The control system control air volume regulator through the frequency control system. At the same time furnace pressure change is a fast link. When in the design of negative pressure contr

28、oller, it adapt feed forward PID controller. Thus, once the amount of blowing change, the controller can quickly adjust the speed induced draft fan, which will control the furnace negative pressure required range. Through on-site commissioning, we found that using blast feed forward control allows t

29、he rapid nature of the control system greatly improved.（3） The Control of Grate Giving CoalThrough the grate speed controlling the amount of coal, it is an important guarantee for economic and safe operation of boiler. According to on-site operational experience, the motor speed is not higher than 7

30、0% of its rated speed. When the motor speed limit is reached, the actuator is no longer the implementation of the directive speed up. Therefore, we must set a reasonable speed upper limit on the grate to prevent that the burning of fuel is not sufficient, resulting in energy waste and environmental pollution. Chain boiler is a typical multi-variable time-varying coupling delay system; it is difficult that using traditional means of control controls the system more effectively.This is also the reason that a lot of medium and small sized