JPS58148314A - Burning control method for boiler - Google Patents

Abstract

PURPOSE:To decrease the load of a forcing-in fan without deteriorating the burning condition and reduce the consumption of electric power of the titled device by a method wherein a discharge pressure control of a forcing-in fan is combined with a flow control of the burning air, the flow control is performed while the discharge pressure is made to follow the proper value. CONSTITUTION:The signal of a fuel flowmeter 8 is continuously or periodically supplied to a discharge pressure set 13. When the signal is received by said pressure set 13, a proper discharge pressure (e) of a forcing fan 5 is calculated in accordance with said signal, that is, a fuel flow (b), the proper discharge pressure is determined based on the fuel flow. After the proper discharge (e) is determined in the discharge pressure setter 13, said pressure (e) is directed to a discharge pressure regulator 14, while said regulator 14 compares the directed normal discharge pressure (e) with an actually measured pressure (f) from a pressure gage 12, then said regulator 14 directs the operation command (g) to a driving motor 11 as the measured pressure (f) is coincided with the directed pressure (e), thereby, the discharge pressure of said forcing fan 5 is converged to said proper discharge pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion control method for a fuel-fired boiler using gaseous fuel, liquid fuel, or solid fuel.

Fuel-fired boilers are roughly divided into three types depending on the ventilation means: those that use a fan to force combustion air (push type), those that use a fan to induce combustion exhaust gas (suction type), and those that use both (balanced type). However, the combustion control method of the present invention is aimed at forced type and counter-impingement type fuel-fired boilers that are equipped with a fan that forces combustion air.

As shown in Figure 1, this type of boiler has a combustion chamber (1), a burner (2), a fuel duct (
3), it is equipped with an air duct (4), a forced fan (5), etc., and in the case of a flat impingement type, it is further equipped with a combustion exhaust gas induction fan (6), etc. As shown by the broken line in Fig. 1, combustion control is performed by instructing the fuel flow controller (7) to adjust the fuel flow rate according to the required load (power demand) K, and then instructing the fuel flow controller (7) to Compare the indicated flow rate (G) with the measured flow rate (1)) from the fuel flow meter (8), and adjust the opening degree of the valve (H) so that the measured flow rate (b) matches the indicated flow rate G). At the same time, the air flow rate 0, which is uniformly calculated according to the air-fuel ratio from the above-mentioned indicated flow rate, etc., is instructed to the air flow rate controller (9), and the air flow rate is adjusted in the same way as in the case of the fuel flow rate. This is done by Note that (6) is the air flow rate controller (
The valves 9) and OQ represent air flow meters, respectively.

In the conventional combustion control method, the flow rate of combustion air is mainly controlled by the air flow controller (9) and the forced fan (5).
) is normally operated uniformly at maximum load or low load, and as a result, forced fan (
5) consumes more power than necessary, resulting in a large waste of power consumption.

The present invention attempts to actively control forced-in fans, which have rarely been omitted as an energy-saving measure, to significantly reduce power consumption. In the combustion control method for a fuel-fired boiler having a forced fan, the flow rate of the combustion air is controlled according to the fuel flow rate by a flow rate controller provided downstream of the forced fan, and the flow rate of the combustion air is controlled according to the fuel flow rate. The discharge pressure of the forced-in fan reaches a predetermined command pressure in relation to the fuel flow rate, depending on the rotational speed of the forced-in fan or the opening degree of a suction vane provided upstream of the forced-in fan. The point is that we controlled it so that it matched.

In the method of the present invention, means for controlling the discharge pressure of the forced fan (5) include adjusting the rotation speed of the forced fan (5) and adjusting the opening degree of the suction vane provided upstream of the forced fan (5). There are two things: It is clear that adjusting the rotation speed directly leads to a reduction in power consumption, but adjusting the opening degree of the suction vane is also effective in reducing power consumption even if it extends to the number of rotations per revolution.

The method of the present invention will be explained in more detail below, taking the case of rotation speed adjustment as an example.

Figure 2 illustrates a combustion control system suitable for carrying out the method of the present invention, where 0W is the drive motor of the forced fan (5), and @ is the pressure provided downstream of the forced fan (5). 04 represents a discharge pressure setting device, and 04 represents a discharge pressure regulator, respectively. Note that the same equipment as shown in FIG. 1 is designated by the same number and the description thereof will be omitted.

In the method of the present invention, two controls are performed simultaneously and in parallel.

One is fuel flow control and air flow control similar to that performed in conventional methods.

In other words, the fuel flow rate controller (7) is instructed to determine the fuel flow rate G) corresponding to the required load, and the fuel flow rate controller (7) receives the instruction.
7) compares the indicated flow rate G) with the measured flow rate (b) from the fuel flow meter (8), and adjusts the opening in the valve so that the measured flow rate (b) matches the indicated flow rate (a). At the same time, the air flow rate (c) calculated according to the air-fuel ratio from the indicated flow rate l1a) is instructed to the air flow rate controller (9),
The air flow rate is adjusted in the same way as the fuel flow rate.

Another type of control is the discharge pressure control of the forced fan (5), which is performed as follows.

First, a signal from the fuel flow meter (8) is continuously or intermittently applied to the discharge pressure setting device α. The discharge pressure setting device (g) that receives the signal calculates the appropriate discharge pressure G) of the forced fan (5) based on the signal, that is, the fuel flow rate (b). The appropriate discharge pressure is determined based on the fuel flow rate as described above, and since the fuel flow rate determines the combustion air flow rate, it can be determined from the following equation as a result. Figure 3 shows
It shows the set broken line of the discharge pressure of the forced fan with respect to the amount of combustion air set in advance according to the boiler characteristics, and A shows the normal range.

Proper discharge pressure = Combustion chamber pressure + Pressure drop However, pressure drop is proportional to the square of the air flow rate Once the proper discharge pressure (e) is determined by the discharge pressure setting device α, this is then set to the discharge pressure regulator α→ The discharge pressure regulator α◆, which received the instruction, compares the indicated pressure ω) with the actual pressure (f) from the pressure gauge (a), and adjusts the pressure so that the actual pressure matches the indicated pressure. A driving command 0 is sent to the drive motor 0 to converge the discharge pressure of the forced fan (5) to the above-mentioned appropriate discharge pressure.

The results of controlling the discharge pressure in this manner will be explained with reference to FIG. 3 in comparison with the case where no discharge pressure control is performed.

When discharge pressure control is not performed, that is, in the conventional combustion control method, the forced fan (5) operates at a constant speed at or near the maximum load. Now, change the number of rotations to 10
If it is 0%, this value is always - constant, so the opening degree of the valve (6) can be controlled by the air flow controller (9) by ~10%.
As a result, when located below the 100-inch open curve, power corresponding to the area of the range shown by 2 and 3z is approximately consumed by the forced fan (5).

On the other hand, when the discharge pressure is controlled, that is, in this method, the area in the range gk below the appropriate discharge pressure line is approximately the power consumption of the push-in fan (5), so the area z2 above it is Power consumption within the range shown will be reduced.

As is clear from the above description, the present invention combines combustion air flow rate control with forced fan discharge pressure control,
Since the above-mentioned flow rate control is performed while keeping this discharge pressure to an appropriate value, the load on the forced fan is reduced without deteriorating the combustion state, and it is highly effective in reducing power consumption.

In the present invention, the appropriate value of the discharge pressure is set based on the fuel flow rate, but it may also be set based on the amount of steam from the boiler. However, since there is a considerable time delay before a change in fuel flow rate manifests as a change in steam amount, setting the appropriate discharge pressure based on the steam amount results in a delay in discharge pressure control. However, if the appropriate discharge pressure is controlled based on the fuel flow rate, the discharge pressure will be controlled in a feed-forward manner without waiting for fluctuations in the steam amount, so there will be almost no control delay, and the response will be as follows. Another major feature of the present invention is that appropriate measures can be taken quickly.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a conventional combustion control system, Fig. 2 is a system diagram of a combustion control system suitable for implementing the method of the present invention, and Fig. 3 is a diagram showing control aspects and control results of the same method. It is. In the figure, 1: combustion chamber, 2: burner, 5: forced fan, 6: induced fan, 7-: fuel flow controller, 8: fuel flow meter, 9: air flow controller, 10: air flow meter, 11 :
Drive motor, 12: Pressure gauge, 13: Discharge pressure setting device, 1
4: Discharge pressure regulator. Figure 1 Figure 59 Figure 2

Claims (1)

[Claims] (1) In a combustion control method for a fuel-fired boiler having a forced combustion air fan, the flow rate of the combustion air is controlled according to the fuel flow rate by a flow rate controller provided downstream of the forced fan; At least the commonly used range of the flow rate of the combustion air is determined in advance in relation to the discharge pressure of the forced fan or the fuel flow rate by the rotational speed of the forced fan or the opening degree of a suction vane provided upstream of the forced fan. A boiler combustion control method characterized by controlling the combustion so as to match a predetermined command pressure.