JPS6325415A - Device for protecting boiler from abnormal combustion - Google Patents

Abstract

PURPOSE:To reduce a response delay by calculating the concentration of residual O2 contained in a waste gas from a ratio of the flow rate of a supplied fuel to the flow rate of air in quantities to be controlled in the air-fuel ratio control to protect the boiler from abnormal combustion. CONSTITUTION:In order to obtain the concentration of residual O2 contained in a waste gas from the flow rate of a fuel and the flow rate of air with respect to a furnace combustion state, the base concentration of residual O2 in the waste gas is impaled from the fuel flow rate to a function generator 51. Further, in a function generator 52, an air flow rate in conformity with the fuel flow rate is calculated. A difference between the calculated air flow rate and an actual air flow rate 12 is obtained by a subtractor 55, and the difference is added to the O2 base concentration made by the function generator 51 by an adder 56. In monitoring the furnace combustion state, an alarm (ANN1) is output by the comparison of the same with a function generator 53 of the set value of residual O2 in the waste gas, in which combustion becomes unstable. Further, the plant is tripped by the comparison of the same with a function generator 54 of the set value residual O2 in the waste gas, in which there is a possibility of burner misfiring. By these procedures, it becomes possible to prevent the danger of abnormal combustion of the boiler from occurring.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to boiler combustion control in thermal power plants, and is particularly applicable to boiler abnormal combustion protection, which is a good enemy when determining combustion in a boiler furnace based on each process amount. Device.

[Conventional technology]

Conventional furnace combustion status monitoring uses flame detectors,
It relies on an in-furnace monitoring camera, and monitoring of process variables is based on the upper and lower limits of controlled variables for air-fuel ratio control, such as combustion gas 02 concentration and furnace draft.

Related devices of this type include Japanese Patent Application Laid-open No. 49
-77073 is mentioned.

[Problems to be Solved by the Invention] Regarding the combustion state protection function of the above-mentioned conventional technology, the fuel flow control system monitors abnormalities such as supply fuel pressure and current flow, and the air flow control system monitors abnormalities such as furnace draft and supply. Abnormalities such as air flow rate are monitored, and abnormalities in the air-fuel ratio control system are determined by monitoring the controlled quantities of each control system, and the combustion status in the furnace is determined by a flame detector and a monitoring camera inside the furnace. There are many. However, flame detectors are difficult to adjust for multi-fuel boilers and are often excluded. In such a plant, in order to monitor the combustion state in the furnace, the combustion gas 02 concentration,
There were problems such as having to rely on in-reactor cameras, which delayed the detection of abnormal combustion.

An object of the present invention is to compare and monitor the fuel flow rate and the air flow rate planned to correspond to the fuel flow rate at the time of supply when monitoring the combustion state.

Its purpose is to monitor the conditions inside the furnace.

[Means for solving problems]

The ratio of the supplied fuel flow rate and air flow rate is determined, and the deviation of the current fuel flow rate and air flow rate from the above ratio is determined to determine the deviation from the planned value as the 02 concentration, and this deviation and the actual combustion gas 02 Compare the concentrations to determine the validity of the currently supplied fuel flow rate and air flow rate.

Furthermore, for this validity judgment, the deviation allowance is set variably depending on the supplied fuel flow rate, and the judgment allowance is set narrower in a combustion state where the 02 concentration is absolutely low than in a state where the 02 concentration is high. It becomes possible to prevent the risk of abnormal combustion.

[Effect]

In a coal-fired boiler, it is common to divide the wind box into compartment entrances and provide a damper at each compartment entrance so that the air flow rate can be controlled according to the fuel flow rate for each burner. In this way, the amount of combustion air supplied to each burner is controlled to provide the optimum air-fuel ratio for the flow rate of the fuel being burned in that burner. on the other hand,
When looking at the boiler as a whole, an amount of air that is more than necessary increases the amount of wasted heat released into the atmosphere by the exhaust gas exhausted from the boiler, reducing the efficiency of the boiler, so monitor the remaining 02 in the combustion exhaust gas of the boiler. , the total amount of air supplied to the boiler, that is, the total amount of air supplied to each burner, is controlled so that this value becomes an appropriate value.

As a result, the supplied air flow rate is determined in a stable combustion state with respect to the supplied fuel flow rate, and abnormal combustion conditions can be monitored by checking changes in the ratio between the supplied fuel flow rate and the supplied air flow rate.

〔Example〕

The present invention will be explained in detail below.

In the figure, 1 is a boiler, 2 is a water pipe provided in the boiler 1, and water is supplied from a water supply pump (not shown). 4
is a coal feeder that supplies coal to the pulverizer 5. The pulverized coal that has been pulverized by the pulverizer 5 is conveyed by conveying air (referred to as primary air) controlled by a primary air damper 6 through a coal conveying pipe 7 to a coal bar: Ya, where it is combusted. be done (subscript...
is attached to each compartment. ). The primary air is ventilated by a primary air fan not shown. 8 is a primary air flow rate detector. 9 is a detector for the flow rate of coal being fed to the pulverizer 5. 10 is a forced fan, which supplies air for combustion. Reference numeral 11 denotes an artificial damper provided in each compartment, which controls the amount of air supplied to each burner. 12 is a detector for each compartment air flow rate. The burner 3 heats the water in the water pipe 2 and sends it to the turbine as steam. 13 is a detector for residual O2 concentration in the boiler exhaust gas.

In the figure, 20 is a computer, of which 21 is a control device that calculates the boiler total air flow rate command and the residual O2 concentration set value in the exhaust gas based on the air-fuel ratio from the operating state of the plant. 22 compares the feedback amount from the detector 13 of the residual 02 concentration in the exhaust gas of the boiler with the set value, corrects the boiler total air flow command value, and further compares the total amount of each comparator with the command value. , is a control device that calculates a correction signal for the command value of the air flow rate of each burner.

23 is a coal flow rate detector 9 fed to each pulverizer 5;
inputs the feedback signal, calculates each burner air flow rate command value, and further modifies the burner air flow rate command value based on the correction command calculated by the control device 22, and controls the compartment air flow rate detector 12 and the burner. This control device inputs the feedback amount of the primary air flow rate detector 8, compares the total value with the above-mentioned command, and controls the compartment entrance damper 11. Further, 23 calculates the minimum air flow rate to the burner from the feedback signal of the coal flow rate detector 9 that is being fed, and calculates the minimum air flow rate to the burner.
~ Compartment inlet air damper 1 providing air flow rate
Safety is ensured by calculating the opening degree of 1 and adding a limit so that the damper opening degree does not go below that value.

In the combustion state controlled as above, the relationship between the fuel flow rate and the residual 02 concentration in the exhaust gas is as shown by the solid line in Figure 4.
If the combustion state becomes unstable, the concentration characteristics will deviate from the following: - If the flow rate is greater than the fuel flow rate, the concentration of O2 remaining in the exhaust gas will shift to a higher direction.

Therefore, in order to determine the residual O2 concentration in the exhaust gas in a furnace-like combustion state from the fuel flow rate and the air flow rate, the function generator 51 gives the base concentration of the residual O2 in the exhaust gas from the fuel flow rate, and then the function generator 52 gives the residual O2 concentration in the exhaust gas. An air flow rate commensurate with the flow rate is calculated, and the difference is calculated at an actual air flow rate of 1.2 by a subtraction sum 55 and added to the base concentration of 02 created by a function generator 51 by an adder 56.

In monitoring the combustion state in the furnace, first, an alarm (ANNI) is output based on a comparison with the function generator 53 and the set value of 02 remaining in the exhaust gas at which combustion becomes unstable.

The plant is tripped in comparison with 02M constant value function generator 54 remaining in the exhaust gas where there is a possibility of burner misfire.

The above example was explained using a coal-fired plant as an example, but in a multi-fuel mixed combustion boiler, it can be realized in the product by using the mixed combustion rate to calculate the residual 02 in the exhaust gas. According to the method, instead of detecting abnormalities from the process amount of combustion results in the furnace, the exhaust gas 02 concentration is calculated from the ratio of the supplied fuel flow rate of the controlled amount of air-fuel ratio control and the air flow rate to protect against abnormal combustion. As a result, there is little response delay, and furthermore, it can be realized at low cost with a small scope of modification to existing plants.

[Brief explanation of the drawing]

Figure 1 shows the combustion status monitoring circuit diagram, Figure 2 shows the boiler main body system diagram, Figure 3 shows the air-fuel ratio control system diagram, Figure 4 shows the fuel and 02 concentration characteristics diagram, and Figure 5 shows the function generator settings. It is a diagram. 3... Burner, 5... Pulverizer, 6... Primary air damper, 7... Coal feeding pipe, 8... Primary air flow rate detector, 9... Coal feeding amount detection Container, 10... Push-in fan, 11
... Compartment artificial damper, 12 ... Compartment air amount detector, 13 ... Residual in exhaust gas 02
Concentration detector.

Claims (1)

[Claims] 1. In a combustion protection device for a thermal power plant, a circuit for calculating the concentration of O_2 remaining in the exhaust gas after combustion from the flow rate of fuel and the flow rate of air supplied to the boiler, and the O_2 remaining in the exhaust gas
1. A boiler abnormal combustion protection device comprising a circuit that outputs an alarm based on a calculated concentration value, the alarm output set value being set to an optimum value to maintain combustion balance. 2. A boiler abnormal combustion protection device according to claim 1, characterized in that the concentration of residual O_2 in the exhaust gas to be warned is determined from the supplied fuel flow rate and the air flow rate.