SU1698583A1 - Automatic control system of boiler total air flow rate - Google Patents

Abstract

This invention relates to a power system. The aim of the invention is to improve the efficiency of the boiler and the reliability of the control system. This is achieved by connecting the sensor 1 of the dry-burn through the adder 7, the non-linear element 5 and the dynamic block 6 to the common air controller 4, to the other inputs of which the sensors 2 and 3 of the total air and fuel are connected. Moreover, the sensor 2 flow of total air is also connected to the adder 7, and the dynamic unit 6 is designed as an integrating element. The nonlinear element 5 has a dead zone corresponding to the optimal coefficient of excess air; Therefore, the adjustment of air flow by the magnitude of the signal from the chemical burner 1 during the adjustment process occurs only when the signal at the output of the adder 7 does not fall into the dead band of the nonlinear element 5. 2 Il. To executive

Description

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The invention relates to a power system and can be used on boiler regatta of district and industrial boiler houses.

Automatic systems for regulating the flow of total air are known, comprising sensors for measuring the flow of air, oxygen and dry burn, a regulator of total air, an adder. These automatic control systems do not allow maintaining the optimum ratio of fuel to air due to the fact that the oxygen content in the gases will not correspond to the actual value due to the air suction in the gas path of the boiler to the point of measurement.

The closest technical solution is a combustion process control system comprising common air flow, fuel flow sensors, a common air controller, an adder, a nonlinear element and a dynamic unit, with common air flow and fuel flow sensors connected to a common air controller. The disadvantage of this system is that, by working out a hard task in a wide range of boiler loads and changes in its state, it is not able to reach the region of minimal excess air, i.e. The system is not able to search for an area of optimal combustion.

The aim of the invention is to improve the efficiency of the boiler and the reliability of the control system.

The goal is achieved by connecting the output of the dry burn sensor through an adder, a non-linear element and a dynamic unit to the common air controller, the output of the common air flow sensor connected to the input of the adder, and the dynamic unit is designed as an integrator.

FIG. 1 shows a block diagram of a system for regulating the total air flow of the boiler; figure 2 - characteristic of the nonlinear element.

The system includes sensors of dryburner 1, flow rates of total air 2 and fuel 3, regulator 4 of common air, nonlinear element 5, dynamic block 6 and adder 7. Sensor 1 chemical burner through adder 7, nonlinear element 5 and dynamic block 6 is connected to controller 4 total air flow, the second and third inputs of which are connected to the outputs, respectively, of the flow sensors of the total air 2 and fuel 3, and the sensor 2 of the total air flow is connected to the adder 7.

The system of automatic control of the total air flow works as follows

In the absence of combustion products

chemical burn (carbon monoxide CO), which is associated with excessive air supply QB to the boiler furnace, the output of chemical burn sensor 1 has a zero signal, and the output of adder 7 has a signal g. The signal d is a scaled signal according to the total air flow of the transmitter 2, i.e. d - ag QB, where as is the scale factor of the adder 7, Since the lower and upper borders of the deadband of the nonlinear element 5 are set respectively to b and 2 d (see Fig. 2), then at the output of the nonlinear element 5 we will have a signal U. The latter is fed to the input of the dynamic block 6, where the output after it

integrating, we have:

Dov AooB + T Judt Yes | 0-4 (i) o o o

where D QBO is the signal value corresponding to the previous state of integrator 6;

T is the integration constant of the dynamic unit (integrator) 6; °

t is the time over which integration is performed.

The signal D QI is fed to the input of the regulator 4 of the general air, where it is summed with the signals on the flow of the total air QB and the fuel consumption of watts. Further, the total error signal W - QB + DOC is converted according to a given control law into a control action /. As the ORD signal changes (decreases due to

1 t

the fact that Y / dt is reduced, this causes a corresponding change in the magnitude of the error, e. 0. In the adjustment process, this change is compensated by reducing the flow of total air QB. This will lead to incomplete combustion of fuel and the appearance in the flue gases at the exit of the furnace of products of incomplete combustion - carbon monoxide (CO). As a result, at the output of sensor 1, we get

a signal for CO, different from zero, and at the output of the adder 7 - a signal D CO - d. At the same time, as the value of chemical burns increases, the signal U at the output of nonlinear element 5 tends to the value at which (see FIG. 2) the concentration falls into the dead band of nonlinear element 5, i.e. U 0. The deadband of the beam is formed in such a way that it corresponds to the optimal coefficient

excess air in the furnace of the boiler, and therefore the maximum efficiency of the boiler. This mode of operation of the boiler corresponds to a certain content of products of incomplete combustion (carbon monoxide) in the flue gases4 at the outlet of the furnace. Since the output of the nonlinear element 5 is a signal U 0, i.e. Since the value of chemical burns corresponds to the optimal value, then according to (1) AQi const and e 0, and the regulation process is terminated there. If the value of the dryburn exceeds the optimum value at the output of sensor 1, we have cm 2 CO 2. As a result, the AQB signal changes (increases due to

that / udt is increased) and according to

The magnitude of the mismatch varies significantly. Compensation for this change, and in contrast to the absence of a dry burn, is accomplished by increasing the flow rate QB of the total air. This leads to a decrease in the dry burn (CO) to a value at which the signal at the output of the nonlinear element 5 U 0 and the value A QB const, a e 0. Once the value of the dry burn enters the optimal zone, the control process is terminated.

Thus, if the content of products of incomplete combustion in the gases at the outlet. Since the furnace does not correspond to the optimal value, the control system generates an iterative AQB signal in increments of / Udt

 about

and

leads the ratio of fuel to air to the optimum value.

Formation of the value S by a signal on the flow of total air QB allows, firstly, to obtain an iterative step of regulation, proportional to Y / Udt, and the dead zone

 about

AH, depending on the load of the boiler, the quality of the original fuel, and secondly, to ensure the dynamic correction of the iteration step. This is determined by the fact that the content of excess oxygen, which ensures maximum efficiency during full combustion of the fuel, is not constant, but depends on a number of factors, such as boiler load and fuel composition. Thus, by reducing the load on the boiler, the total amount of air supplied in the boiler’s furnace decreases, as a result

conditions of mixing and burning fuel deteriorate. This is also the reason why, with a decrease in the load on the boiler, the zone of optimal concentration of CO shifts to a region of lower values (see Fig. 2). In addition, in this case, the magnitude of the iterative step is reduced.

i |

T

Udt that

allows for a more subtle search for the optimal CO zone under conditions of deteriorating fuel combustion conditions.

Dynamic step adjustment is 1t. radios Y j Udt is provided by the fact that

Air consumption QB is leading in relation to a more inertial signal in chemical burns. This allows a forerunner to the impact of the boiler load, which means better control of the total air flow.

The proposed system of automatic control of the boiler air flow rate is fully implemented on the widely used KASKAD or KASKAD-2 control equipment in power engineering.

The economic efficiency of the introduction of the proposed control system on the boilers will be ensured, firstly, by reducing the total heat loss from the flue gases and chemical incompleteness of combustion, and, secondly, by reducing the losses caused by electricity and gas consumption per blast. According to expert estimates for the GM-50-1 boiler, this will provide fuel savings of the order of 0.3-0.5% or 2000-3000 rubles per year.

Claims (1)

Claims of the Invention A system for automatic control of the total air flow rate of a boiler, comprising common air and fuel flow sensors connected to a common air controller, a chemical burner sensor, an adder. nonlinear element and dynamic unit, characterized in that, in order to increase the efficiency of the boiler operation and the reliability of the control system, the adder, the nonlinear element and the dynamic unit are connected in series, to the inputs of the adder are connected the sensors of the dry-air and the total air flow connected to the common air controller, and the dynamic unit is made in the form of an integrating link. U fie. 2