JPS6256710A - Temp. control method of furnace - Google Patents

Abstract

PURPOSE:To improve energy saving feature, operability of a furnace, and temp. distribution in the furnace by switching operation to a proportional control in a high burning and to an on-off control in a low burning range. CONSTITUTION:During a high burning time, the burning amount is continuously changed using such an advantage of a proportional control that fuel to air ratio is kept at a constant level and energy saving and temp. distribution properties are excellent as wee. On the other hand, during a low burning time, an on-off operation is carried out under the condition which throttles the amount of fuel and air together. Without stopping some of the burners and introducing excess air, the temp. range between the upper and lower limits is kept small as compared with an conventional on-off operation with improved temp. distribution during this operation. Switching temp. from the proportional to the on-off operation is determined by measuring the furnace inside temp. distribution. And, operation may be switched over automatically at an appropriate switching temp.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to temperature control in a combustion furnace.

(Prior Art and Problems to be Solved by the Invention) Typical known temperature control methods for combustion furnaces include proportional control and on-off control.

Proportional control, also known as ratio control, ensures that the ratio of fuel and air remains constant.It can be done by measuring the flow rate of one and adjusting the other, or by detecting the pressure of one and adjusting the other. There are many ways to do this, such as mechanically interlocking both. In any case, proportional control has the characteristic of continuously adjusting the amount of energy input. There is no problem with temperature distribution or energy in a range close to the burner's rated capacity, that is, during high combustion (see FIG. 4(a)), but there is a problem in a low combustion range. In other words, below the burner turndown limit, combustion becomes unstable, so reduce the number of burner ignitions (see Figure 4 (b).
), or by introducing excess air to maintain stable combustion (see Figure 4 (c)), but the latter suffers from poor temperature distribution, and from the energy saving point of view.
There is a problem in that it requires a lot of human effort to make the sound of rain.

On the other hand, the on/off control is a control of whether the fuel and air are allowed to flow or not while the opening degrees of the fuel and air of the burner are kept constant.

When flushing, it must be kept in a good combustible state. The amount of energy input is adjusted by the ratio of on/off time, but the temperature fluctuates widely. When turning on and off, there is a danger that black smoke will be generated if both the fuel and air are turned on and off at the same time, so the general method is to let the air out early when it is on, and shut it off later when it is off. However, since this is turbulent air, it is less energy efficient than proportional control, for example, during high combustion when the temperature rises. In addition, during low combustion during constant temperature maintenance (see Figure 5(b)),
The combustion amount when turned on is the same as that at high combustion (Figure 5 (a)).
(see). Since a large amount of fuel is turned on and off, there is a problem in that the amount of energy input changes suddenly and the temperature inside the furnace tends to fluctuate.

An object of the present invention is to provide a new control method for a combustion furnace that has excellent energy saving properties, good furnace operability, and improves temperature distribution within the furnace.

(Means for Solving the Problems) Therefore, the present inventors devised a new control method that incorporates and combines the advantages of proportional control and on/off control.

The combustion furnace temperature control method according to the present invention has both proportional control and on/off control functions, and has proportional control and on/off control functions in the high combustion range.
Can be used with automatic or manual switching for on/off control in the low combustion range.

(Operation and Effects of the Invention) The temperature control method of the combustion furnace according to the present invention is proportional control at high combustion times and on/off control at low combustion times. The bottom line is that during high combustion, the combustion amount is continuously changed while the ratio of fuel and air is kept constant, which is the advantage of proportional control, so it has excellent energy saving and temperature distribution. In addition, if PID control is performed, temperature fluctuations will be small (see Figure 3 (a)).On the other hand, during low combustion, the burners will be turned on and off with the fuel and air being pumped up, so the number of burners should be thinned out. It is possible to maintain a constant temperature without introducing excess air, and the upper width of the temperature is smaller than normal on/off, improving the temperature distribution (see Figure 3 (b)). Since the switching point from proportional to on/off differs depending on the situation of the six furnaces, it can be appropriately adjusted while actually measuring the temperature distribution.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

A block diagram of a first embodiment using a changeover switch is shown in FIG. The proportional control system includes a current output type temperature indicating controller 1 that performs PID control, a converter 2 for transmitting instructions from the temperature indicating controller 1 to a control motor etc. 3, and a converter 52 that responds to signals from the converter 52. It consists of a control motor etc. 3 that adjusts the ratio of fuel and air. On the other hand,
The off control system is an on/off pulse type temperature indicating controller 4
, a converter 5 for transmitting the instruction from the temperature indicating controller 4 to a solenoid valve or the like 6, and a solenoid valve 6 for opening and closing the flow of fuel and air in response to signals from the converter. The program setting device 7 is configured to increase the temperature of the combustion furnace, maintain a constant temperature,
Set the temperature reduction program. Program setting device 7
The output is sent via a changeover switch (or relay) 8 to a temperature indicating controller 1 of a proportional control system or a temperature indicating controller 4 of an on/off control system. The temperature indicating controller 1 or 4 adjusts the temperature in response to a signal from a sensor (not shown) that detects the temperature distribution within the furnace. Here, the changeover switch 8 is manually switched to the proportional control system when the combustion is high, and to the on/off control system when the combustion is low. The switching temperature from proportional control to on/off control is determined by actually measuring the temperature distribution inside the furnace.

Alternatively, switching may be performed automatically at an appropriate switching temperature.

The block diagram of the second embodiment using the special opening setting device is shown in the second example.
As shown in the figure. The program setting device 7 sends a signal to the temperature indicating controller 11 according to the program, and the temperature indicating controller 11 sends a temperature control signal in response to a signal from a sensor (not shown) that detects the temperature distribution in the furnace. Special opening setting device [Send to 2. The special opening setting device 12 controls a proportional control system or an on-off control system depending on whether the opening is larger or smaller than a predetermined opening (that is, depending on whether the temperature is higher or lower than a predetermined value). send a signal to. In the proportional control system, a control motor or the like 14 is operated via a converter 13 to control the flow rates and ratios of fuel and air. In the on/off control system, a pulse converter 15 converts the opening of the special opening setting 312 into on/off pulses, and operates a solenoid valve, etc. 17 via a converter 16 in response to on or off. and turn off or stop the flow of fuel and air.

In both embodiments, it is possible to provide the microcomputer with a range of functions other than sensors or operating devices (changeover switches, relays, control motors, etc.).

In both examples, proportional control is used during high combustion, and as shown in Fig. 3(a), there is no problem in terms of temperature distribution or energy.Furthermore, if appropriate PID control is performed, temperature fluctuations are small. .

From proportional control (at high combustion) to on/off control (at low combustion)
When switching to on/off, proportional control is performed with both fuel and air reduced, so even when switching to on/off control,
As shown in FIG. 3(b), the time interval during on-time is long (temperature fluctuation is smaller than in conventional on-off control (see FIG. 5(b)). In addition, during low combustion of conventional proportional control (4th
Compared to Figures (b) and (c), the temperature distribution and energy aspects have been improved.

[Brief explanation of drawings]

1 and 2 are block diagrams of control methods according to embodiments of the present invention, respectively. FIGS. 3(a) and 3(b) are graphs showing the temperature and combustion amount during high combustion (proportional control) and low combustion (on-off control), respectively. Figures 4(a), (1,1), and (e) show the inside of the furnace during high combustion, low combustion (burner thinning), and low combustion (excess air combustion) under proportional control, respectively. FIG. 2 is a diagram schematically showing the combustion situation of each burner. FIGS. 5(a) and 5(b) are graphs of temperature and combustion amount during high combustion and low combustion, respectively, in on-off control. 1-3...Proportional control system, 4-6...On/off control system, 7...Program setting device, 8...Selector switch or relay. Patent applicant Kobe Steel Co., Ltd. Representative Patent attorney Two idiots 11111 & 28th On/Off f7IJ #distortion 13B

Claims (1)

[Claims] (1) Combines proportional control and on/off control functions,
A combustion furnace temperature control method that can be used by automatically or manually switching between proportional control in the high combustion range and on/off control in the low combustion range.