JPS5843655B2 - combustion device - Google Patents

Description

[Detailed description of the invention] In a premix combustor that mixes gas and air beforehand and combusts them, it is required to maintain a constant ratio between the amount of gas and the amount of air, and for this purpose, an ejector or venturi is installed in the air circuit. A low-pressure section is provided, and means are used to supply gas to this low-pressure section.

In this case, if the gas supply pressure is always set equal to the air pressure entering the ejector or venturi, the gas amount will automatically change as the air volume changes, so the excess air ratio will not change and good combustion will continue.

Gas governors used for this purpose are specifically called zero governors.

This method has the advantage that the gas input can be changed just by changing the air volume, but the air volume to the pilot burner also changes according to the change in air volume, and the excess air ratio of the combustion section as a whole including the pilot changes. There was a problem.

If the pilot burner circuit had a separate gas/air mixing tube and zero governor, the above problem would not be solved, but it would be very expensive, and there would also be a production problem in that the accuracy of the zero governor for small amounts of gas such as the pilot burner tends to deteriorate. occurred.

Controlling the rotation speed of the blower motor is an easy way to change the air volume, but in addition to the aforementioned problem of changing the pilot air volume, there are also difficulties in starting at low temperatures at low rotation speeds. It was also expensive.

The present invention eliminates these conventional drawbacks, and its objectives are as follows.

■By keeping the pilot burner's air volume almost constant even when changing the gas input by changing the air volume,
The goal is to always maintain good combustion when changing input.

(2) The purpose is to prevent deterioration of low-temperature start-up performance by not controlling the blower.

To prevent poor combustion from occurring due to input falling below the combustion range of a combustion part when controlling gas input by changing the pan air volume.

(2) The pressure detection position must be devised so that when the air volume is mechanically adjusted, the air pressure at the inlet of the mixing pipe to which the gas governor should respond will be correctly related to the air volume.

V. To reduce changes in the main burner combustion air volume and pilot burner combustion air volume due to changes in blower frequency.

Examples thereof will be described below with reference to the accompanying drawings.

In FIG. 1, a blower 2 sucks air from an intake pipe 1 and sends the air into a circuit consisting of an air volume regulator 3, a gas-air mixing pipe 4, a combustion section 5, a heat exchanger 6, and an exhaust pipe 7.

Gas is supplied from a gas cock 9 to a gas governor 10, a solenoid valve 11,
The gas is introduced through the gas nozzle 12 into the low pressure generator 8 of the gas-air mixing pipe 4 .

Next, the pilot burner 14 is connected to the combustion section 5 of the main burner.
Gas is supplied via a pilot gas governor 16 through a pilot gas pipe 17 branched from the cock 9, and combustion air for the pilot is supplied through a pilot air pipe 15 from between the blower 2 and the air volume controller 3. Supplied.

The main burner blinks by opening and closing the solenoid valve 11, while the pilot burner blinks by operating the gas cock 9.

still. Illustrations and explanations of an igniter such as a spark discharge and a safety device in case of pilot burner misfire are omitted.

Now, as shown in FIG. 1, the air pressure in the inlet chamber 13 of the gas-air mixing pipe 40 is guided to the gas governor 10.

Although not shown, this air pressure is opposed to the outlet gas pressure across the governor's diaphragm.

When the air pressure increases, the governor valve opens and the outlet gas pressure also increases.

Figure 2 shows the characteristics of a gas governor. Although it is unavoidable that the gas outlet pressure decreases a little as the amount of gas passing through increases, the pressure level depends on the air pressure guided to the diaphragm (governor feedback pressure). It can be made equal.

That is, as shown in A or B in FIG. 2, it moves in parallel due to feedback pressure.

Now, assuming that the combustion air volume to the main burner doubles from a certain state, the air pressure at the inlet of the gas-air mixing pipe 40 will almost quadruple, this air pressure will become the governor feedback pressure, and the gas outlet pressure will also quadruple. Become.

Further, the pressure difference between the air pressure at the inlet of the mixing tube 40 and the low pressure generating section 8 is also approximately four times as large.

Therefore, the gas pressure difference applied to the gas circuit between the solenoid valve 11 and the gas nozzle 12 also increases by about 4 times, so the amount of gas ends up being 2.
It will be doubled.

In this way, the ratio of gas to air remains almost unchanged.

This is the operation of the control section consisting of the mixing tube and zero governor.

Figure 3 shows this change. However, since the relationship between the pressure difference and the flow rate is not always a square or square root relationship, the excess air ratio of the main burner also varies slightly with changes in the combustion air volume (ie, gas input).

FIG. 4 relates to the air volume regulator 3, and the figure shows a butterfly valve that rotates around a shaft 3A.

The state shown in Figure 4a is fully open, and if you turn it 90 degrees, the airflow will be fully closed.

However, the burner has a lower input limit at which it can burn, so a simple butterfly valve must be closed beyond a certain angle to prevent it from fully opening.

However, since there are manufacturing errors in the butterfly valve, it is not possible to set a reliable lower limit for the air flow rate simply by regulating the rotation angle.

For this reason, in FIG. 4, the butterfly valve 3 is provided with a hole 3B, so that even if the butterfly valve 3 is rotated completely 90 degrees, the required lower limit air volume, that is, the lower limit gas input is ensured.

The reliability is also high if the air volume is managed through hole 3B.

In addition, correctly regulating the lower limit air volume is important from the viewpoint of the performance of the governor.

As already mentioned, the outlet pressure of the gas governor is operated to be equal to the inlet pressure of the gas-air mixing pipe, but if the air volume is too small, the pressure difference between the inlet air pressure of the mixing pipe and the low pressure generating section becomes small, and eventually the nozzle 12 The pressure difference between is small.

Therefore, even if the governor outlet pressure has a slight error with respect to the air inlet pressure, it has a large effect on the fluctuation of the excess air ratio.

Therefore, in order to ensure a large performance tolerance for the gas governor, it was necessary to set the lower limit of the air flow rate correctly.

One way to ignite the premix combustor is to directly use spark discharge, but since the excess air ratio at the time of ignition is strict, the pilot burner is set to Bunsen type, first igniting the pilot and then the main burner. A method of transfer is used.

In this case, since the pilot burner faces the combustion chamber of the main burner, it is necessary to manage the overall excess air ratio including the amount of air sent to the pilot burner.

Now, in FIG. 5, the allowable range of the excess air ratio of the main burner is set between MrnaX and Mmin.

And the standard pilot air volume Q.

At Pl, the range of variation in the overall excess air ratio, including governor error, is Ml.

Suppose that it is between M2O.

In this state, when the pylon air volume increases, even though the pilot burner itself is a Bunsen type and has a wide combustion stability range, the overall excess air ratio increases, so the main burner side is affected.

In FIG. 5, the solid line indicates when the gas input is high (when the main air volume is high), and the broken line indicates when the gas input is low.

Now, when the reference excess air ratio is Ml and the gas input is set to dog, FIG. 5 shows that the pilot air volume may be increased to QCP□.

If the standard excess air ratio is M2 and the gas input is set to a small value, the pilot air volume will only be allowed to increase up to QCP5.

For the above reasons, it is necessary to control the fluctuations in pilot air volume within a certain range.

Now, Fig. 6 is a diagram showing the relationship between the characteristics of the blower and the load resistance.If the characteristics of the blower are C in the same figure, when the input is dog, the air volume regulator 3 shown in Fig. 1 If it is fully open and there is no resistance, the air volume is Q.

Become a dog. At this time, the air pressure at the inlet of the mixing tube is P, which is equal to the discharge pressure of the blower, and the pressure after passing through the flame hole of the main burner is P2.

Therefore, the amount of pilot air flows according to the pressure difference between P and P2.

Next, if the voltage is lowered so that the characteristic of the blower becomes D in order to make the air volume Qc small in order to lower the gas input, the pilot air volume will flow at the pressure difference between P5 and P4.

If Qo small Q.

If it is half that of a dog, it is expected that the pilot air volume will also be halved.

However, as in the present invention, the air volume is adjusted to Q by the air volume regulator 3.
.

If you narrow it down to a small value, the pilot airflow will flow based on the pressure difference between P3 and P4, so the pilot airflow will increase more than when using a QC dog, but the range of change will be much smaller than when changing it according to the characteristics of the blower itself. .

This means that the entire device can achieve highly stable performance against fluctuations in voltage, gas pressure, intake/exhaust resistance, external wind pressure, etc.

In addition, in FIG. 6, the main combustion air volume is taken up as the air volume and the pilot air volume is not included, but the pilot air volume is much smaller than the main air volume, so the explanation is omitted.

Describing the pressure relationship based on actual measurements, Fig. 6 shows P126.3mm.
Aq, P2=11.3mmAq, P3=3
0.6mmAq, P4 = 3.6mmAq, P
5 = 7 mmAq.

Therefore, the pressure difference that flows the pilot air volume when the input is dog is 15 mmAq, and Q is controlled by the voltage control of the blower.

Since the same pressure difference when it is small is 3.4 mmAq, the pilot air volume decreases to about 48 mm.

However, according to the fourth aspect of the present invention, the pressure difference is 27 mmAq, so the pilot air volume only increases to about 134 mm.

Since the required pilot air volume must be ensured even under the worst conditions, the pilot variation width during voltage control is 2.1 times, but in the present invention it is 1.34 times, resulting in a wider combustion range (stable and A combustion section is obtained.

Next, in the control system of the present invention, the air volume regulator 3 is provided immediately before the gas-air mixing pipe 4, but the air pressure to be fed back to the governor 10 must be representative of the pressure in the inlet chamber 13.

However, it is well known that if there is a throttle valve such as a butterfly valve just before the flow, the downstream flow will be disturbed.

FIG. 8 shows the relationship between the combustion air volume of the main burner and the pressure difference between the inlet chamber 13 of the mixing section 40 and the low pressure generating section 8.

Among these curves, one curve is detected from the wall surface of the inlet chamber 13, and a singular point like G appears because there is turbulence in the air flow on the wall surface depending on the opening angle of the valve.

Although not shown, there is also a hysteresis phenomenon in which the G point differs when the air volume increases and when it decreases.

If this continues, the excess air ratio will fluctuate depending on the air volume at point G, which is not good.

As shown in FIG. 7 on the opposite east side, a pressure detection tube 18 was inserted just before the air nozzle 20, and a hole 19 was made approximately in the center.

As a result, the pressure difference described above shows a smooth change as shown by curve E in FIG.

This is because the area immediately before the air nozzle 20 is not affected by turbulence caused by the throttle valve.

As a result, it has become possible to minimize fluctuations in excess air ratio due to changes in air volume.

Next, if the power supply frequency of the blower is different between 50 Hz and 60 Hz, the combustion air volume will also change, and therefore the gas input will also differ, and countermeasures for this problem will be described.

Figure 10, like Figure 6, shows the blower characteristics and the load resistance curve. It is assumed that the load resistance is the H curve in order to increase the input at 50Hz (the air volume regulator 3 is fully open) and the air volume is Q.

1, the pilot air volume is determined by Pl-P2.

If you continue to operate at 60Hz, the air volume will be Q.

2, and the pilot air volume also increases to the value determined by P6-P7.

Similarly, if the air volume regulator 3 is closed and the load resistance shown by one curve is set for the input vehicle, the air volume will be from QC3 to Q at 50Hz and 60Hz.

5, and the pilot air volume also increased from P3-P4 to P8-P.
, increases to the value determined by .

In either case, the inconvenience arises that the input and pilot air volume vary depending on the frequency.

Therefore, in the present invention, it is preferable to use an air volume regulator as shown in FIG.

In FIG. 9, reference numeral 21 denotes a cock-type throttle valve having a side hole 22, and its rotation can change the ventilation area with respect to the outlet 25 leading to the main burner.

Further, a ventilation passage 26 is provided from before entering the throttle valve 21 to the pilot burner.

Reference numeral 27 denotes a spring that always urges the throttle valve upward in the figure, and 28 is its positioning member.

Furthermore, a valve 23 is provided in the center and faces a valve seat 24.

That is, the valve 23 is the first adjustment part, and the cock-shaped throttle valve 21 is the second adjustment part.

When the frequency is 50 Hz, it is used in the state shown in the figure, and when the frequency is 60 Hz, the positioning body 28 is installed upside down.

Then, the entire valve moves downward, and the valve 23 is used with the entire air passage constricted.

As a result, the load resistance curve when the input is large in FIG. 10 can be made as shown by ■, and the air volume can be made to match the QCI at both 50Hz and 60Hz.

Then, when the throttle valve 21 is rotated to the input vehicle position, the load resistance curve becomes K and the air volume becomes Q.

The increase can be limited to 4.

Also, the discharge pressure of the blower is P1□, but since the pressure drop due to the first adjustment section is the difference between the K and J lines, the pressure difference that determines the pilot air volume is pt.

Since it is Pli, the difference from that at 50 Hz can be reduced.

In the figure, the first adjustment part and the second adjustment part are integrated, but it is of course easy to provide them separately, and the valve type is not limited to a cock type.

As explained above, the present invention is a combustor that can continuously vary the amount of combustion, and can provide a combustion device suitable for ensuring a stable state of combustion.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram of a gas combustion device showing an embodiment of the present invention, Figures 2 and 3 are diagrams showing the relationship between combustion air volume and gas volume, and Figures 4 a and b are examples of air volume regulators. 5th cross-sectional view showing
FIG. 6 is a diagram illustrating the permissible change limit of pilot burner air volume, FIG. 6 is a diagram illustrating stabilization of pilot air volume according to the present invention, and FIG. 7 is a sectional view showing an example of a method for detecting air pressure at the inlet of a gas-air mixing pipe. Fig. 8 is a diagram explaining the differential pressure generated in the mixing tube according to Fig. 7, Fig. 9 is a cross-sectional view showing an example of an air volume regulator that responds to frequency changes, and Fig. 10 shows changes in gas input and pilot air volume due to frequency changes. It is a figure explaining a change. 2...Blower, 3...Air volume regulator, 4
... Gas air mixing pipe, 5 ... Combustion part,
8...Low pressure generation section, 10...Gas governor, 14...Pilot burner.

Claims (1)

[Scope of Claims] 1. A combustion air blower, an air volume regulator that adjusts the main burner combustion air volume by the blower, a differential pressure generator that generates a differential pressure by blowing air, and a combustion section, A fuel pressure regulator that adjusts the combustion amount in relation to the pressure of the pressure generating body is provided in the fuel passage, and the pilot combustion air volume to the pilot burner provided facing the combustion chamber of the combustion section is set to be higher than that of the air volume regulator. A combustion device configured to lead from upstream. 2. The combustion apparatus according to claim 1, wherein the air volume regulator for adjusting the main burner combustion air volume has a ventilation passage for setting the minimum air volume. 3. The combustion device according to claim 1, wherein the air pressure at a substantially central portion immediately before the air inlet of the differential pressure generator is detected, and this air pressure is guided to the fuel pressure regulator. 4. Claim 1, in which the air volume regulator is constituted by a first adjustment part and a second adjustment part, the main burner combustion air volume is adjusted by both adjustment parts, and the pilot combustion air volume is guided from the middle of both adjustment parts. Combustion device as described in section.