JPS5921454B2 - Forced air supply/exhaust type combustion control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for stabilizing the excess air ratio and maintaining the combustion state in a forced air supply/exhaust type combustion device. It is an object of the present invention to provide a control device that can change the pressure continuously and over a wide range and has a small pressure loss in the ventilation circuit at the time of maximum input.

A fully premixed combustor requires that the ratio between the amount of gas and the amount of combustion air be kept within permissible limits.

However, in practice, this ratio (hereinafter referred to as excess air ratio) tends to become unstable due to external factors such as gas pressure and voltage, and factors associated with changes in gas amount to make gas input variable. A constant-pressure gas governor that simply stabilizes the gas pressure used in gas appliances cannot accomplish its purpose.

For this purpose, it is effective to always keep the air pressure and gas pressure approximately equal and mix them, which often uses a zero governor and a mixing tube.

This method is convenient because the gas input automatically changes by simply changing the amount of combustion air, but it is difficult to keep the gas pressure always equal to the air pressure, and a certain amount of error must be accepted. .

This error results in an error in the excess air ratio, so in order to reduce this effect, it is necessary to improve the performance of the mixing pipe, which will be explained later.This is accompanied by an increase in the ventilation pressure loss of the mixing pipe, so the relationship with the blower performance is The design points were selected.

However, in order to make the gas input variable, it is necessary to change the combustion air volume, but if the mixing pipe specifications are selected so that the excess air ratio due to the error between gas pressure and air pressure is within the allowable value at the lowest air volume, the mixing pipe Since the pressure loss increases in proportion to approximately the square of the combustion air volume, the pressure loss at the maximum air volume becomes extremely large.

For this reason, there was a problem that the blower became large and the noise became louder.

The present invention eliminates these conventional drawbacks, and embodiments thereof will be described below with reference to the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a combustion air supply passage, which is divided into two directions by a branch part 2, and each has an air and gas mixer 6 and 6.
'to go into.

The mixers 6, 6/ have the same structure, and air is ejected from the air inlet chambers 3, 3' through the air nozzles 4, 4/, and the ejector effect creates a low pressure chamber 5''.

Reduce the pressure level at 5'.

Burner 7 is then passed through a gradually expanding diffuser.
Enter.

The heat combusted here is transferred to the outside by a heat exchanger 8, and the exhaust gas is passed through an exhaust pipe 9 and sent to an exhaust passage 11 by a blower 10.
is discharged to.

The gas then enters the gas governor 15 , 15 ′ through the branch passage 14 after the cock 13 and into the gas valve 16 , 16
Two gas circuits 12 and 1 lead to gas nozzles 17 and 17' facing the low pressure chambers 5°5' of the mixers 6 and 6' through the
It is supplied from 2'.

The air pressure in the air inlet chambers 3, 3' is introduced into the gas governor 15, 15' through pressure equalization pipes 18, 18', and operates so that changes in the air pressure and changes in the gas governor outlet pressure are synchronized.

Note that 19 is a damper provided in the air supply path 1, which allows continuous change in the amount of combustion air.

20 is an air valve inserted into the air supply circuit of the mixer 6';
It is opened and closed simultaneously with the gas valve 16'.

Next, the operation of the system using the mixer as shown in FIG. 1 will be explained.

The symbols are defined as follows. Pressure in air inlet chambers 3 and 31 of mixer pai〃 Low royal pressure p
nT5 gas governor output log pressure pz.

Combustion air amount Qc, gas amount Qg Allowable lower limit of excess air ratio M 〃 Allowable upper limit of Mmin〃 Mmax Now, air nozzles 4, 4'
The pressure difference Pa between the air inlet chamber and the low pressure chamber due to the ejector effect of
1-Pn''6 is approximately proportional to the square of Qc as shown in FIG.

Also, the gas amount is gas 16, 16' and gas nozzle 17,
It is determined by the resistance of 17', the gas governor outlet pressure Pzo, and the pressure n3 of the low pressure chamber, and the pressure difference PZG) P is determined as shown in Fig. 3.
It is approximately proportional to the square root of no.

That is, the gas governor 15 is adjusted so that Pai = Pzo.
, 15' is activated, M is determined only by the dimensional relationship,
It is possible to keep it constant regardless of the air volume or gas volume.

However, the outlet pressure of the gas governor varies depending on the gas flow rate and also varies depending on the supply gas source pressure.

Furthermore, if production errors are included, Pa1 is achieved under all conditions.
= It is difficult to maintain PnE.

Now, if there is a relationship of Pzδ-Pai+ΔP, this will result in a change in M.

Figure 4 shows Pai −Pno=24 when Qc is 100.
Assuming that the standard excess air ratio when ΔP=0 in mmAq is 1.5 and ΔP=±2 mmAq, we have shown how M changes when Qc is lowered for the purpose of reducing gas input. It is something.

That is, since Pai Pno decreases as Qc decreases, the change in M becomes larger as the input becomes lower.

Next, when the allowable limits of M are set as Mmax and Mmin,
The fifth test determines what the tolerance value of ΔP, that is, the tolerance range of the gas governor, will be for the determined Pai Pno.
Shown in the figure.

Once the tolerance of the governor error and the excess air ratio of the burner are determined, the pressure difference Pa1-Pn? at the mixer 6°6' is determined. A minimum required value of 5 is also determined.

When making the input variable, the air nozzle 4 should be adjusted so as to secure the minimum required differential pressure when the amount of combustion air corresponds to the minimum input.
, 4' will be designed.

The pressure drop seen from the blower 10 of the mixer 6, 6' is based on the lowest input, and if the input is varied up to 2 times, the pressure drop will be 4 times, and if it is varied up to 3 times, the pressure drop will be 9 times. .

For example, the minimum required pressure difference Pa1-Pn. 10mmA
If the pressure loss of the mixers 6 and 61 at that time is 6 mmAq as q, then if the input change is tripled, the pressure loss is 54 mmAq.
will increase to.

This is not preferred because it increases the size of the blower itself and increases noise.

The above is a general explanation of the system using a mixer and zero governor, but the present invention solves the problems of increased pressure loss and increased size of the blower that occur when expanding the range of capacity variation, as shown in Figure 1. , mixer 6.61 and gas circuit 12 in parallel,
12', and one mixer 6' is provided with an air valve 2.
0 is provided, and the air valve 20 and gas valve 16' are opened and closed at the same time.

Now, if the maximum input is 100 units and the two mixers are operating equally, each has an input of 50 units.

In one mixer, the above-mentioned minimum required pressure difference Pa1-Pn
Assume that the input can only be lowered to 1/2 due to the relationship o.

If the minimum required differential pressure Pa1-Pnδ is expressed as Pn, and the mixer pressure drop at that time is PA', then the relationship between the air amount and the gas input is as shown in the following table.

In other words, if 1/2 of the total input is determined as the rated input of one mixer, and if the input can be lowered to 1/2 of that, then when the total input becomes 1/2, the air valve 20 and the gas To further reduce the input by simultaneously stopping the valve 16' and stopping the mixer 6', it is possible to use only the mixer 6 to reduce the input to 1/4.

However, since the mixers are arranged in parallel, the mixer pressure drop seen from the blower 10 is limited to 4 PA at most.

If a single mixer is used to accommodate up to 1/4 of the input as in this example, the pressure drop will be as high as 16 Pl.

In the example shown in Figure 1, two wires are arranged in parallel, but it is also possible to further increase the number of wires so that the input lower limit can be lowered to 176.1/8, and even in that case, the input change width per wire can be reduced. As long as is set to 1/2, the pressure loss seen from the blower will be no more than 4P7.

FIG. 6 shows another embodiment in which there is only one gas governor 15, which is then branched into a plurality of gas circuits.

Further, air pressure is introduced from the branch 2, and a resistor 21 corresponding to the resistance when the air valve 20 is fully opened is provided on the mixer 6 side.

In this way, air nozzle 4.4', gas nozzle 17,1
Since γ is exactly the same, the inputs to both mixers 6 and 6' can be equalized, and pressure regulation by only one governor is easy.

In this case as well, as in the example shown in FIG. 1, it is possible to reduce the load on the blower and widen the input variation range.

Although the damper 19 is provided as a method for changing the amount of combustion air, the same effect can be obtained by controlling the rotation speed of the blower.

Also, if the damper is set to the full open position or the blower is set to full speed when the mixer 61 is stopped, even if the mixer 61 is stopped at 1/2 in the previous example, the input will remain at 1/2. This results in smooth input changes.

If this relationship does not exist, 100 staff force → 1/2
This results in an irregular input change of human power → 1/4 human power → 1/2 human power, which is not practical.

To simplify the explanation, we have described the case where the inputs to each mixer are equal; however, it is also possible to arbitrarily select the input adjustment range by giving the inputs a uniformity. If Pa1-Pno at the lowest input is ensured, stable combustion will be obtained as a combustion device.

Furthermore, dampers etc. that can continuously adjust the amount of combustion air are installed.
It is also possible to provide one between the branch part 2 and the mixers 6, 6' in FIG. 1, so that one operates at the rated value and only the input of the other is made variable.

In this way, when it is necessary to strictly control the ratio between the amount of combustion air and the amount of gas, expanding the input variable range generally requires a high pressure for the blower, but according to the present invention, the blower pressure can be increased. You can expand the input variable width even if it remains the same.

In addition, applications with different input ratings can be made by simply adding a mixer and gas circuit, and the field of application is wide.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a forced intake/exhaust type combustion control device showing an embodiment of the present invention, Figs. 2 to 5 are explanatory diagrams, and Fig. 6 is a schematic diagram showing another embodiment of the forced intake/exhaust type combustion control device. FIG. 1... Air supply path, 3, 3'... Air inlet chamber, 5, 5'... Low pressure chamber, 6, 61...
・Mixer, 12, 12'...Gas circuit, 15
, 15'...Gas governor, 16°16'...
...Gas valve, 20...Air valve.

Claims (1)

[Scope of Claims] 1. A plurality of mixers arranged in parallel that mix air and gas, each having an air inlet chamber and a low pressure chamber formed by a nozzle section that generates a high-speed flow downstream of the air inlet chamber; a gas circuit in which a gas governor is inserted to control the gas pressure according to the gas pressure, the ends of which are led to the low pressure chambers of each of the mixers; an air valve that opens and closes the air passage to one of the mixers; A forced supply/exhaust type % type that has a gas valve installed in the gas circuit that enters the mixer and connects the air valve and gas valve so that they open and close at the same time. The forced air supply/exhaust chamber combustion control device according to claim 1, which has a gas governor that controls the gas pressure to be in accordance with the air pressure, and the downstream side of the governor is connected to each mixer via a plurality of gas circuits. . 3. The forced air supply/exhaust type combustion control device according to claim 2, wherein a resistance element having the same ventilation resistance as that when the air valve is in an open state is provided in the air supply air path of the mixer in which no air valve is inserted. . 4. Claim 1, which has an adjusting means that can continuously adjust the combustion air volume, and is associated so that when the air valve and the gas valve open and close, the adjusting means simultaneously reaches the minimum air volume or maximum air volume state. Or the forced air supply/exhaust type combustion control device according to item 2.