JPS5821174B2 - Alarm method and alarm device for nitrogen oxide removal equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a warning method and a warning device for a nitrogen oxide removal device.

In recent years, nitrogen oxides contained in flue gas from industrial combustion equipment such as power generation boilers and heating furnaces have become a major cause of air pollution, and in some regions there are restrictions on the total amount of nitrogen oxide emissions. etc. are being carried out.

However, when currently measuring the concentration of nitrogen oxides emitted from these nitrogen oxide sources, the gas to be measured is often highly corrosive and contains large amounts of soot and nitrogen oxide. Due to the complexity of the nitrogen oxide concentration measuring device, the overall reliability of the nitrogen oxide concentration measuring device is not sufficient as an industrial detector.

For this reason, controlling the nitrogen oxide removal device only with the output signal of the detector not only does not effectively remove nitrogen oxides, but also may be dangerous in some cases. There is a strong demand for the completion of an oxide concentration measurement system.

In order to check the output of a highly reliable nitrogen oxide measurement system, especially a nitrogen oxide concentration detection device, the present invention is compatible with the combustion conditions (excess air ratio, etc.) and load conditions of the combustion equipment itself that generates nitrogen oxides. The amount of nitrogen oxide produced is verified in advance, and these correlations are stored as approximate expressions in the calculation device. Nitrogen oxides generated by combustion equipment from any of the measured values including two or more of the following: oxygen concentration in smoke, carbon dioxide concentration in exhaust smoke, flow rate of air used for combustion, and amount of gas generated by combustion. The system calculates the estimated value of the concentration, compares it with the actual value measured by the nitrogen oxide concentration measuring device, integrates the difference or ratio for a predetermined period of time, and issues an alarm when the integrated value exceeds a predetermined allowable range. Configure.

An embodiment of the present invention in which the nitrogen oxide concentration is estimated by actually measuring the fuel flow rate and the oxygen concentration in exhaust gas will be described below with reference to the drawings.

Note that the estimated nitrogen oxide concentration can be calculated from the following empirical formula.

[No X cal]=a O+a t Q+ a2Q
2-K.

+ [06
X cal): Estimated value of nitrogen oxide concentration Q: Fuel flow rate 02: Oxygen concentration in exhaust gas aO, a,, a2. 6. 1: In the case of a constant heavy oil-fired boiler, the fuel flow rate Q, the oxygen concentration in the flue gas 02, and the nitrogen oxide concentration in the flue gas NOx are shown in Figure 1a.
It has been experimentally and empirically known that there is a relationship such as ,b, and the estimated nitrogen oxide concentration NO
This is the basis for xcal calculations.

Further, referring to FIG. 2, a flow rate transmitter 2 is installed in a pipe 1 that supplies fuel such as heavy oil to a combustion device such as a boiler, and a flow rate transmitter 2 is installed in a flue 3 through which exhaust smoke passes, to detect the oxygen concentration 02. A detector 5 and a nitrogen oxide concentration detector 4 for measuring NOx are provided.

Flow rate signals Q from these flow rate transmitters 2 and oxygen concentration detectors 5
, oxygen concentration signal o2 are respectively applied to the arithmetic circuit 6.

The arithmetic circuit 6 calculates the estimated NOx concentration N0xcal from these Q and 02 using a function of f, Q, and 02.

The output N0xcal of the arithmetic circuit 6 and the nitrogen oxide concentration NOxmes actually measured by the nitrogen oxide concentration detector 4 are input to the subtraction circuit 1.

The subtraction circuit 1 calculates the difference between the two, including the sign, and the summation circuit 8
Output to.

The integrating circuit 8 integrates the input signal for a predetermined period of time using a sampling signal (not shown), and the sampling signal is provided at predetermined time intervals for obtaining an integrated value.

The output signal of the integration circuit 8 is input to a comparison circuit 9 having a predetermined set value, and it is checked whether the integrated value is within a predetermined tolerance range.

If the integrated value exceeds a predetermined permissible range, a signal is output to an alarm display device (not shown) indicating that the nitrogen oxide concentration detector 4 is abnormal.

To summarize the above, the deviation between the estimated value and the actual measured value of the nitrogen oxide concentration is constantly monitored, and when the deviation of the actual value from the estimated value becomes large, an alarm is issued as an abnormality in the nitrogen oxide concentration detector 4. It is something to do.

In the above embodiment, the estimated nitrogen oxide concentration is calculated using equation (1) from the flow rate transmitter 2 and the oxygen concentration detector 5 as measurement devices for detecting the load or combustion state of the combustion device. However, in addition to these measuring devices, it is possible to use a carbon dioxide concentration detector in exhaust gas or a combustion gas flowmeter that straddles the flowmeter of the air used for combustion, etc., with the same method and device.

This is because there is a relationship between these physical quantities that can be calculated using combustion theory formulas, and they can be treated as mutually homogeneous signals.

In other words, combustion air flow rate and fuel flow rate. This is because there is a relationship between the fuel gas flow rate due to the fuel components, and a relationship between the oxygen concentration in the exhaust gas and the carbon dioxide concentration in the exhaust gas due to the air-fuel ratio.

Further, the device of the present invention may be configured with a microcomputer.

[Brief explanation of the drawing]

1A and 1B are diagrams showing the relationship between fuel flow rate, oxygen concentration and nitrogen oxide concentration, and FIG. 2 is a block diagram showing an embodiment of the apparatus of the present invention. 1... Piping, 2... Flow rate transmitter, 3... Flue, 4
... Nitrogen oxide concentration, 5... Oxygen concentration detector, 6.
... Arithmetic circuit, 7... Subtraction circuit, 8... Integration circuit,
9... Comparison circuit.

Claims (1)

[Claims] 1. Fuel flow rate, oxygen concentration in flue gas, carbon dioxide concentration in flue gas,
The nitrogen oxide concentration is calculated from parameters including two or more of the combustion air flow rate and the combustion gas flow rate, and the difference or ratio between this calculated value and the measured value of the nitrogen oxide concentration in the exhaust gas is integrated over a predetermined time. An alarm method for a nitrogen oxide removal device, characterized in that an alarm is issued when this integrated value exceeds a predetermined permissible limit. 2. The nitrogen according to claim 1, wherein the two or more parameters are at least one of a fuel flow rate, an oxygen concentration in exhaust gas, a carbon dioxide concentration in exhaust gas, a fuel air flow rate, and a combustion gas flow rate. Alarm method for oxide removal equipment. 3 Fuel flow rate transmitting device, exhaust gas oxygen concentration detecting device. A measuring device including at least two of a carbon dioxide concentration detecting device, a combustion air flow rate transmitting device, and a combustion gas flow rate transmitting device, and a calculation for calculating the concentration of nitrogen oxides in the flue gas from the output of this measuring device. a nitrogen oxide concentration detection device for detecting the concentration of nitrogen oxides in exhaust smoke; a circuit for obtaining the difference or ratio between the output of the nitrogen oxide concentration detection device and the output of the arithmetic device; An alarm device for a nitrogen oxide removal device, comprising an integration circuit that integrates the output for a predetermined period of time, and a comparison circuit that issues an alarm signal when the output of the integration circuit exceeds a predetermined allowable limit. 4 Claims in which the measuring device comprises a fuel flow rate transmitting device and at least one of an exhaust gas oxygen concentration detector, an exhaust smoke carbon dioxide concentration detector, a combustion air flow rate transmitter, and a combustion gas flow rate transmitter. An alarm device for a nitrogen oxide removal device according to item 3.