JPS58208508A - Nox emission control method for boiler - Google Patents

Abstract

PURPOSE:To achieve a SI control in accordance with a boiler load with an inexpensive device, by arranging such that an opening/closing valve is provided a line through which a steam or water is fed into a furnace burning zone of a boiler, and the opening/closing valve is caused to open and close alternately in a given frequency and in such a manner that the larger a boiler load is, the longer the opening/closing valve is retained as opened. CONSTITUTION:An opening time T1 of an electromagnetic valve 4 is determined by means of a function generator 2 adapted to set phiN time in response to a load sensor 1. This signal T1 is utilized by a timing producing circuit 3 to produce a phiN-phiFF frequency signal of the opening time T1 for opening and closing the electromagnetic valve 4 alternately in a given frequency. When a boiler is operated at a maximum load, a timing is kept at phiN in any case and an output from the function generator 2 becomes as T1=T, and thereby allowing the electromagnetic valve 4 to retain as opened. When a boiler load is less than Le, the output becomes T1=O, causing the electromagnetic valve 4 to continue to be closed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a NOx suppression method applied to small boilers and the like.

Conventionally, as a NOx generation method in a small plate point, so-called steam injection (hereinafter referred to as SI) has been used, which involves injecting steam into a combustion flame in a furnace to lower the flame temperature.

In this method, as shown in Fig. 1, a certain load value I
, e or below, steam is sprayed into the furnace, and the amount of steam sprayed at this time is determined according to when the NOx generation and deposition is at its maximum (that is, the boiler load is at its maximum).

Therefore, as shown in FIG. 2 (NOx generation amount when SI is not performed), near the boiler load Le where the NOx generation la exceeds the allowable level, the steam level is more than necessary, and the boiler efficiency is degraded accordingly.

``5lfa: Control/control motor type control method that increases or decreases according to the load is also known, but the present invention takes into account the above points and uses an inexpensive device to control the S according to the boiler load.
The aim is to provide a method for suppressing NOx that enables L control U, and an on-off valve is installed in the pipe for injecting steam-f fc water into the furnace combustion area of Boi 2, and the on-off valve is operated at regular intervals. A patent characterized in that the opening/closing operation is repeated and the opening time of the opening/closing valve f is lengthened as the boiler load increases.Therefore, according to the present invention VC, there is provided a solenoid valve which has an extremely simple structure and is inexpensive as an opening/closing mark. 81 seed control according to the boiler load.
Improved boiler efficiency and reduced NOx can be achieved with an inexpensive device.

Below is one implementation of the present invention I! li1 will be explained with reference to FIGS. 3 and 4.

FIG. 3 shows an example of a control system for implementing the present invention. 1 is the upper load level, and the boiler load is detected by the fuel 11 detour signal or the 1st steam flow signal. 2 is an ON time setting function generator,
The load j and the load L are input manually, and an ON time signal T1 corresponding to the load is output.

3 is a timing generation circuit, ON time setting function generator 2
The signal T1 from is inputted manually and outputs a signal that repeats T, time ON, T-T, time OFF every fixed period T as shown in FIG. Reference numeral 4 denotes a solenoid valve, which is installed in a pipe line 5 for injecting steam into the furnace.

Open when the signal from timing generation circuit 3 is ON, OF
It is closed when F.

In the following system, φN according to the signal of load 7 / sir l
The time setting function generator 2 determines the opening time T of the solenoid valve 4. Based on this signal T.

A timing generation circuit 3 generates a φN-φFF period signal with an opening time T1 in a period T, and the solenoid valve 4 is opened and closed periodically. At maximum load, it is always φN, and function generator 2
The output of matches T,=T.

The solenoid valve 4 remains open. Also, the boiler load is Le
From then on, T=0, and the solenoid valve 4 is continuously closed.

Since the voice response time for the furnace temperature is in minutes, by controlling the φN (open) time of the solenoid valve in seconds according to the boiler load, the furnace temperature can be kept approximately below a certain level, and NOx This can be done using an inexpensive solenoid valve.

Note that water injection is used simultaneously with steam Φ injection for NOx suppression, but the nine methods can also be applied to water injection.

[Brief explanation of the drawing]

Figure 1 is a graph showing the changes in conventional steam injection, Figure 2 is the boiler load and NOx generation.
FIG. 3 is a control system diagram showing one embodiment of the present invention. FIG. 4 is a graph showing an example of the output of the timing generation circuit. l...Load sensor! J, 2... ON time setting function generator, 3... Timing generation circuit, 4... Solenoid valve,
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Claims (1)

[Claims] An on-off valve 11 is provided in the pipe that carries steam or water into the furnace combustion area of the boiler, and the on-off valve is made to repeat opening and closing operations at a constant cycle. 1) A boiler NOx suppression method characterized by increasing the opening time of the on-off valve described in 11 above as i becomes larger.