JPH11294759A - Fuel supply controller for boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate quick throttling of a fuel while preventing flame failure of a burner by accurately holding a fuel pressure lower limit value. SOLUTION: This fuel supply controller for a boiler is provided with a flow control valve 3 for adjusting the flow rate of a fuel for a boiler and a flow rate adjusting meter 6 to output a fuel demand signal 5 to the flow control valve based on a detection value 15 of the flow rate of the fuel. A pressure control valve 18 having a quick response is installed in parallel with the flow control valve 3, the flow control valve 3 is operated to be fully closed based on a quick fuel throttling demand signal 9 and a drop in the fuel pressure associated with the operation of the flow control valve 3 is detected 19 to open the pressure adjusting value 18 so that a minimum fuel pressure is held to prevent a flame failure of a burner. The pressure adjusting valve contains a self-actuated pressure control valve or a pressure adjusting valve accompanied by a pressure adjusting meter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply control device, and more particularly, to a control device suitable for performing rapid fuel reduction.

[0002]

2. Description of the Related Art Since a change in the amount of fuel supplied to a boiler is an amount corresponding to the amount of evaporation, it is 3 to 5% in a normal operation state.
It can follow the change in the amount of evaporation at a rate of change of about 1 / min, but it is necessary to rapidly reduce the amount of fuel due to failure of equipment inside the boiler or external demand.

[0003] As an internal factor, it is necessary to throttle the fuel to an amount corresponding to the reduced air amount due to the abnormal stop of the blower (the load is sharply reduced, which is called runback). A typical example of the external factor is that when the generator is cut off from the outside of the power plant and the boiler can only consume enough power inside the power plant, the required fuel amount is 5 to 10
% (Fast cutback; referred to as FCB). It is required to rapidly narrow down the fuel so that each part of the boiler does not overheat. Although this speed naturally varies depending on the boiler characteristics, it is about 100% / min, which is 20 times the normal speed.

As an example of the prior art, as shown in FIG. 4, instead of a control system based on a steady fuel demand signal 5 and a flow rate oscillator 15 (switched by a signal switch 7),
FCB by function generator 10 according to request 9 for rapid fuel reduction
And a fuel throttle signal is given so as to fall between the required fuel pressure value and the allowable lower limit value, thereby narrowing the fuel flow control valve 2 to the target allowable fuel amount.

However, in this method, a predetermined maximum allowable flow rate (for example, 10%) can be obtained in a short time (for example, within 10 seconds).
In the case of narrowing down to the following, the amount reaches a value lower than the target allowable value and a significant undershoot occurs (see FIG. 6), and further lowers the fuel lower limit pressure for preventing the burner from misfiring. There was a risk of causing
Therefore, as a countermeasure, the minimum pressure setting 14 is set in two stages (two stages of A1 and A2), and the first stage setting (A1) is set to a higher value than the final target second stage setting (A2). A complicated method of switching the set value at the top was adopted. In this case, it is difficult to determine the setting value of the first stage and the timing of switching the setting from the first stage to the second stage. In the planning stage, it is difficult to wait for the result of the trial operation, and a complicated trial operation adjustment in a transient state in a short time. There were also difficulties in the work.

As another example of the prior art, as shown in FIG. 5, there is a known method in which a small-capacity flow control valve 19 is juxtaposed to expand a flow control range and improve control accuracy. In the method, the same input is applied to the large capacity flow control valve 3 and the small capacity flow control valve 19, and the control valve 3
Due to the difference in response characteristics with respect to the inputs of and, the undershoot becomes small in the case of rapid fuel narrowing down, but the undershoot still remains, so that the problem cannot be solved. There has been a demand for a simple and highly reliable control method for solving these problems.

[0007]

The prior art shown in FIG. 4 succeeds because of the difficult use of rapidly squeezing a large capacity flow control valve and accurately keeping it in an extremely low valve opening position. Was not sufficiently reliable. In the prior art example shown in FIG. 5, the undershoot width is improved because the small-capacity valve is juxtaposed, but the large-capacity valve and the small-capacity valve are controlled by the same control device (rapid fuel reduction). F as shown by signal 9 and function generator 10
(Because a CB signal is used), the fundamental solution was not reached.

SUMMARY OF THE INVENTION It is an object of the present invention to facilitate the rapid narrowing of the fuel and to reliably maintain the lower limit of the fuel pressure required to prevent the burner from misfiring.

[0009]

In order to solve the above problems, the present invention employs the following configuration.

[0010] A fuel supply control device for a boiler, comprising: a flow control valve for controlling a fuel flow to a boiler; and a flow controller for outputting to the flow control valve based on a fuel demand signal and a detected value of the fuel flow. A pressure control valve having a quick response is installed in parallel with the flow control valve, and the flow control valve is operated to be fully closed based on a fuel rapid throttle request signal, and the flow control valve is A fuel supply control device for a boiler for detecting a decrease in fuel pressure during operation and opening the pressure regulating valve to maintain a minimum fuel pressure for preventing burner misfire.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a fuel supply system according to the first embodiment of the present invention, FIG. 2 shows a fuel supply system according to the second embodiment of the present invention, and FIG. FIG.

Here, 1 is a fuel cutoff valve, 2 is a flow control valve, 3 is an electropneumatic positioner, 4 is supply air, 5 is a fuel request signal, 6 is a flow controller, 7 is a signal switch, and 9 is fuel. Narrowing request signal, 10 is a function generator, 11 is a pressure transmitter, 15 is a flow transmitter, 16 is a subtractor, 17 is a burner inlet valve, 18 is a self-operating pressure control valve, 19 is a pressure detection pipe,
Reference numeral 20 denotes a pressure controller.

FIG. 1 shows a first embodiment of the present invention, wherein a fuel control system includes a fuel cutoff valve 1, a flow control valve 2,
Fuel is supplied into the furnace through the burner inlet valve 17 and burned.
In a normal operation state, the flow control valve 2 is adjusted by the output signal of the flow controller 6 by comparing the feedback signal from the flow transmitter 15 with the fuel request signal 5.

When the fuel rapid throttle request signal 9 is generated, the function generator 10 forms necessary throttle characteristics as shown in the figure, and the throttle operation is performed through the signal switch 7 until the flow control valve 2 is fully closed. .

The self-acting pressure control valve 18 in the first embodiment is installed in parallel with the flow control valve 2 and is normally in a fully closed state. The flow control valve 2 is operated at a constant speed from a certain opening degree during operation to full closing. Due to the pressure in the pressure detection pipe 19, which is constantly detected when the outlet pressure of the flow control valve 2 decreases on the way to the fully closed position of the flow control valve 2, the self-acting pressure control valve 18 quickly opens. By opening to a preset value, the lower limit of fuel pressure for burner misfire prevention is maintained.

FIG. 2 shows a second embodiment of the present invention.
An example in which an air-operated pressure regulator 20 and an air-operated pressure regulator 18 are used in place of the self-powered pressure regulator shown in FIG.

According to the first and second embodiments of the present invention,
When performing rapid fuel throttle, the fuel flow control valve 2 is throttled at the required appropriate throttle speed, and the flow rate is adjusted without controlling the complicated movement of maintaining the fuel lower limit pressure at which burner misfire does not occur. When the valve 2 is squeezed at a constant speed to the fully closed position and the fuel pressure starts to drop, another independent pressure regulating valve 18 is quickly opened to maintain the fuel pressure at a preset value. FIG. 3 shows how the fuel pressure varies in the first and second embodiments of the present invention.

The fuel flow control valve 2 is only fully closed at a constant speed and does not have a minimum pressure holding function. The pressure regulating valve is used only for holding the minimum pressure.

In this way, by dividing the functions and using an independent system configuration, accurate narrowing down and highly reliable pressure holding can be achieved.

As described above, according to the embodiment of the present invention, the pressure control valve having the control function independent of the control device of the flow control valve is installed in parallel with the flow control valve, and the flow control valve is provided with the flow control valve. It is configured to have only the function and remove the lower limit pressure holding function. Therefore, in order to rapidly narrow down the fuel within a predetermined time, the flow control valve 2 is operated at a stroke from the opening degree before the request for the throttle to the fully closed state, and is fully closed at the maximum valve speed.

To narrow down the flow control valve 2 from a certain opening to the fully closed position, a simple control circuit is sufficient because there is no need to consider the behavior of the fuel and the transient characteristics of the flow control valve 2 at all. Fuel narrowing performance as planned can be obtained.

The fuel lower limit pressure required to prevent burner misfire can be maintained by detecting the decrease in fuel pressure and rapidly opening the pressure control valve 18, so that the burner does not misfire. Since it is important for the burner to maintain the pressure at the burner inlet at or above the lower limit, complicated control is not possible, but the use of a pressure control valve with a fast response makes it simple and economical. An inexpensive and reliable device can be obtained.

[0023]

According to the present invention, since the lower limit pressure can be reliably maintained even when the fuel is rapidly reduced, the burner can be safely shifted to the minimum fuel pressure operation without misfire.

[Brief description of the drawings]

FIG. 1 is a diagram showing a fuel supply system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a fuel supply system according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a fuel pressure fluctuation state according to the present invention.

FIG. 4 is a diagram showing a fuel control system of a conventional example.

FIG. 5 is a diagram showing another conventional fuel control system.

FIG. 6 is a diagram showing a state of fluctuation of fuel pressure in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cutoff valve 2 Flow control valve 3 Electropneumatic positioner 4 Supply air 5 Fuel request signal 6 Flow controller 7 Signal switch 9 Fuel throttle request signal 10 Function generator 11 Pressure transmitter 15 Flow transmitter 16 Subtractor 17 Burner inlet Valve 18 Self-powered pressure control valve 19 Pressure detection pipe 20 Pressure regulator

Claims (3)

[Claims] 1. A fuel supply system for a boiler, comprising: a flow control valve for adjusting a fuel flow to a boiler; and a flow controller for outputting to the flow control valve based on a fuel request signal and a detected value of the fuel flow. A control device, comprising: a pressure control valve having a quick response in parallel with the flow control valve; and operating the flow control valve to be fully closed based on a fuel rapid throttle request signal, the flow control. A fuel supply control device for a boiler, characterized by detecting a decrease in fuel pressure due to operation of the valve and opening the pressure regulating valve to maintain a minimum fuel pressure for preventing burner misfire. 2. The fuel supply control device for a boiler according to claim 1, wherein the pressure control valve is a self-powered pressure control valve provided with a pressure detection pipe. 3. The boiler fuel supply control device according to claim 1, wherein the pressure control valve includes a pressure controller that detects fuel pressure and outputs the fuel pressure to the pressure control valve. Fuel supply control device.