JPH0573917B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the speed of a blower that supplies combustion air into each furnace chamber of a heating furnace. The purpose is to obtain efficient blower operation with little pressure loss while maintaining the pressure.

In a continuous heating furnace, the temperature in each divided furnace chamber must be controlled individually, and for this reason, each divided furnace chamber is connected to a dedicated combustion air supply pipe. .

That is, as shown in FIGS. 1 and 2, a large number of branch pipes 4 having flow rate control valves 5 are connected to the tip of the main pipe 1 connected to the discharge port of the blower 2, and each branch The conduits 4 are individually connected to one of the divided furnace chambers of the continuous heating furnace and are adapted to supply combustion air.

In each branch pipe 4, a flow meter 6 is provided downstream of the flow rate control valve 5, and a flow rate indicating controller 7 connected to this flow meter 6 constantly monitors the flow rate meter 6.
The system monitors the instructions from the flow rate indicator controller 7 to detect whether the amount of air passing through each branch pipe line 4 is as per the set value. The opening degree of the flow control valve 5 is corrected so that a predetermined flow rate can be obtained.

In recent years, for the purpose of power saving, variable speed blowers are increasingly being used as blowers for continuous heating furnaces.

By the way, in a continuous heating furnace, the thickness, width, and heating target temperature of the heating material constantly change in each furnace chamber. Therefore, when controlling the furnace temperature, it is necessary to Fluctuations in air volume are unavoidable.

For this reason, the amount of air required in a large number of branch pipes 4 is not a common value, but is usually a different value for each individual, making speed control of the blower 2 extremely complicated and difficult. ing.

Currently, as one of the speed control methods of the blower 2, as shown in FIG. There is a device configured to constantly monitor the pressure indicator controller 3 and input an instruction signal from the pressure indicator controller 3 to the blower rotation speed control device 8 to thereby control the speed of the blower 2.

This system is based on the exact same idea as the most commonly used pressure control in piping using the suction damper 9 shown in Figure 2, and controls the pressure in the blast pipe, thereby controlling the pressure in each The pipe line 4 is designed to be supplied with a flow rate ranging from a designed maximum flow rate to a minimum flow rate.

In this way, in the system shown in FIG. 1, the speed of the blower 2 is controlled only by the pressure inside the main pipe 1, so the conditions in each branch pipe 4 are not considered at all.

That is, the blower speed is controlled in accordance with a pressure value that allows the maximum flow rate to flow through each branch pipe 4 whenever necessary, regardless of the opening degree of the flow rate control valve 5 in each branch pipe 4. It is.

Therefore, when only a few percent of the designed maximum flow rate is required in each branch pipe 4, the flow rate control valve 5 of each branch pipe 4 is closed to a position where the valve opening degree is close to fully closed. It became a matter of fact,
A large pressure loss will occur before and after the flow control valve 5, and the energy loss of the blower 2 will become enormous.

The present invention was devised to eliminate the drawbacks and inconveniences of the conventional examples described above. According to the amount of fuel supplied to the furnace, the amount of air required for this fuel is determined, and the air is blown according to this amount of air. Set the blower reference speed of blower 2, and set this blower reference speed to
The opening degree of the flow rate control valve 5 of each branch pipe line 4 is corrected to be maintained at a value as large as possible, and the main pipe 1 is corrected to prevent incomplete combustion of fuel in the furnace.
The blower speed is obtained by monitoring and correcting the internal pressure so that it does not become smaller than a preset limit value.

Hereinafter, the present invention will be explained with reference to FIGS. 3 to 5.

Note that in FIGS. 3 to 5, the same reference numerals as those used in FIGS. 1 and 2 indicate the same parts.

The present invention provides a combustion air supply pipe for a heating furnace in which a plurality of branch pipes 4 are connected to a main pipe 1 connected to a discharge port of a blower 2, and the required air amount F4 of each branch pipe 4 is calculated. A blower reference speed H _B is set as a function of the required air flow rate F obtained by totaling, and this blower reference speed H _B is set at the maximum opening degree of the air flow control valves 5 provided in each branch pipe 4. The opening degree of the main pipe 1 is corrected so that it becomes the preset optimal opening degree MV _S , which is slightly smaller than the 100% opening degree and has an adjustment margin in the increasing direction. This is a speed control method for the blower 2 in which the blower speed H is set by correcting it so that the pressure is always larger than the minimum pressure value P _L required to achieve combustion stability.

That is, in the speed control method of the blower 2 according to the present invention, first, the required air flow rate F4 required for each branch pipe line 4 is totaled, the required air flow rate F required for the entire pipe is known, and the required air flow rate F is calculated based on the required air flow rate F. Therefore, by setting the blower reference speed H _B , the basic amount of air is set in accordance with the amount of fuel supplied to the heating furnace.

This basic air volume is the blower reference speed H _B
In contrast, by knowing the actual valve opening MV of the flow rate control valve 5 in each branch line 4..., knowing the amount of air actually required in each branch line 4..., and knowing the amount of air actually required in each branch line 4... By correcting the valve opening which has _reached the maximum valve opening of The amount of air supplied to the branch pipes 4 is adapted to the state of each branch pipe 4.

Furthermore, the pressure P inside the main pipe 1 is monitored, and this pressure P is the lower limit pressure necessary to achieve stable combustion.
By correcting it so that it does not become lower than P _L , control based on pressure is added in addition to control based on air amount.

The blower reference speed H _B can be set by installing a flow meter 10 in the main pipe 1 and taking the relationship between the air flow rate F flowing through the main pipe 1 and the blower speed H, as shown in Fig. 3.
As shown in the graph shown in FIG. 4, it can be seen that the air flow rate F and the blower speed H are in a proportional relationship.

Using this proportional relationship, first find out the required air amount F4 in each branch pipe 4, and then
The required air flow rate F is calculated by summing up the required air flow rate F, and then the blower reference speed H _B is determined.

There are various methods for setting the required air amount F4 in each branch pipe line 4.

One method is to determine the amount of fuel to be supplied into each divided furnace chamber.

In this case, the amount of fuel supplied into each furnace chamber is
Since it changes from time to time, the blower standard speed
H _B will change depending on the time.

Another method is to set the maximum required air amount in each branch pipe 4 as the required air amount F4.

In this case, the maximum required amount of air in each branch pipe 4 may be the designed maximum flow rate of each branch pipe 4, or may be the amount of air corresponding to the maximum amount of fuel supplied to the furnace chamber. It's okay.

If this maximum required air amount is set as the required air amount F4, the required air flow rate F4 obtained by summing up this
is the maximum flow value, and the blower reference speed is
H _B remains unchanged, and the valve opening of each flow control valve 5
Correction according to MV is a reduction correction.

Blower reference speed H _B set as above
Among the corrections _for This is a value determined by the performance of the burner installed in the chamber, and is a correction that is not performed as long as the pressure P in the main pipe 1 is greater than the lower limit pressure _PL .

On the other hand, the correction according to the opening degree MV of each flow control valve 5 is a correction that is constantly performed, and the final blower speed H is determined by this correction.

The correction according to the opening degree MV of the flow rate control valve 5 is
First, the valve opening MV of each flow control valve 5 is detected, and the blower is adjusted so that the valve opening MV of the maximum valve opening of each flow control valve 5 becomes the preset optimum opening MV _S. The reference speed H _B is corrected.

That is, the actual flow rate in each branch pipe line 4 is
This is set by the valve opening degree MV of each flow rate control valve 5, so if you try to increase the flow rate in the main pipe 1 by increasing the speed of the blower 2, the flow rate in each branch pipe 4 will increase. In order to prevent the flow rate from increasing, each flow rate control valve 5 operates to decrease its valve opening degree MV. Conversely, when the speed of the blower 2 is decreased, each flow rate control valve 5 operates to decrease its valve opening degree MV. It works in the direction of increasing it.

Using this response operation of the flow rate control valve 5, the blower is adjusted so that the valve opening MV of the flow rate control valve 5 becomes the optimum opening MV _S for the flow rate control valve 5 that has reached the largest valve opening. The reference speed H _B is corrected.

For example, if the valve opening of the flow control valve 5, which has the largest valve opening, is smaller than the optimum opening MV _S , the blower reference speed H _B is corrected in the decreasing direction, and the valve opening becomes the largest. The valve opening of the total flow rate control valve 5 is increased until the valve opening of the flow rate control valve 5 becomes the optimum opening MV _S , and conversely, the valve opening of the flow rate control valve 5 with the largest valve opening is increased. If the opening degree is larger than the optimum opening degree, the blower speed H is set by correcting the blower reference speed H _B in the increasing direction.

By the way, the reason why the optimum opening degree MV _S is set to a value slightly smaller than the 100% opening degree and with an adjustment margin in the direction of increase is because when it is desired to increase the flow rate in branch pipe line 4, this branch pipe line If the valve opening MV of the flow rate control valve 5 in No. 4 is 100% opening, the blower speed H itself must be increased, and the response speed to the increase in flow rate will be delayed. If the valve opening degree MV of the flow rate control valve 5 is set at an opening degree that is slightly smaller than , and has an adjustment margin in the increasing direction, the branch pipe can be adjusted by simply increasing the valve opening degree of the flow rate control valve 5. 4 can be achieved, and the response speed to the increase in flow rate is also much faster.

For this reason, the optimal opening MV _S is 100%.
Although it is set to a value smaller than the opening degree, the specific value is determined by the characteristics of the flow control valve 5 and the piping system as a whole.

A simple example of the method of the present invention will be explained with reference to FIG.

First, the required air amount F4 for each branch pipe line 4 is input to the adder 12, and the required air flow rate F is calculated by the adder 12.

The required air amount F calculated by the adder 12 is input to the function converter 13.
Then, the blower reference speed H _B is calculated using the proportional relationship shown in Figure 4, and this blower reference speed H _B
is input to the calculator 14.

On the other hand, a flow rate control valve 5 provided in each branch pipe 4
are individually connected to the comparator 15, and input their valve opening degrees MV to the comparator 15.

The comparator 15 compares the valve opening MV signals inputted from each flow control valve 5 and outputs the largest valve opening value to the calculator 14.

Further, the main pipe 1 is provided with a pressure gauge 11, and the pressure value inside the main pipe 1 detected by the pressure gauge 11 is inputted to the calculator 14.

In the computing unit 14, a numerical value corresponding to the optimum opening degree M _S is set in advance, and this optimum opening degree is set in advance.
Calculate the difference between MV _S and the input maximum valve opening,
The blower standard speed is adjusted according to the amount of deviation between the two.
Add to H _B.

Furthermore, if the pressure P detected by the pressure gauge 11 is smaller than the preset lower limit pressure P _L ,
Calculate the correction amount so that the pressure P is greater than the lower limit pressure P _L , and use this correction amount as the blower reference speed.
Add to H _B.

In this way, the blower speed H is set by correcting the blower reference speed H _B according to the valve opening degree MV of the flow rate control valve 5 and also according to the pressure P value detected by the pressure gauge 11. .

The set blower speed H is input from the calculator 14 to the blower rotation speed control device 8, and the blower 2 is driven at the calculated blower speed H.

Note that in the illustrated embodiment, the related converter 13 is opened to calculate the blower reference speed H _B ;
It may be calculated simply using a graph and input into the calculator 5, or the required air amount F4
Depending on one of the settings, the value of the required air amount F may remain unchanged. In this case, the blower reference speed H _B also becomes a constant value, so it can be input directly to the calculator 14.

As described above, in the speed control method of the blower 2 according to the present invention, the blower reference speed H _B is set based on the amount of air required by each branch pipe 4.
There is no possibility that the amount of air supplied to each furnace chamber will be insufficient.

Also, correction is made according to the opening degree of the flow rate control valve 5 of each branch pipe 4, and the flow rate control valve 5 is adjusted to the optimum opening degree MV _S
Since each branch pipe 4 is controlled to be maintained at
In addition, the pressure loss in the flow control valve 5 can be extremely reduced, and the response to changes in the required air flow rate in each branch pipe 4 can be achieved extremely quickly. will be done.

Furthermore, since the pressure P in the main pipe 1 is always maintained at a value greater than the lower limit pressure P _L , there is no risk of incomplete combustion of the supplied fuel in each furnace chamber, and good combustion is always achieved. Obtainable.

The method for controlling the speed of the blower 2 according to the present invention is not limited to continuous heating furnaces, but can be applied to any piping system that requires flow rate control and uses a blower as a fluid discharge source. Can be applied.

As is clear from the above description, the present invention can quickly respond to requests for changes in flow rate, and the pressure loss in the flow rate control valve is extremely small, so significant power savings can be achieved.
Furthermore, it has many excellent effects such as being able to obtain stable and good fuel.

[Brief explanation of the drawing]

FIG. 1 is a piping system diagram for explaining a method of controlling the speed of a blower in a conventional continuous heating furnace. FIG. 2 is an explanatory diagram of a piping system showing a basic technique of a general blower speed control method. FIG. 3 is a piping system diagram for explaining the relationship between the flow rate in the piping system and the speed of the blower. FIG. 4 is a diagram showing the relationship between the air flow rate and the speed of the blower obtained from FIG. 3. FIG. 5 is an explanatory diagram of an electrical system when the method of the present invention is specifically implemented. Explanation of symbols, 1: Main pipe, 2: Blower, 4:
Branch pipe line, 5: Flow rate control valve, 6: Flow meter, 7: Flow rate indicating controller, 8: Blower rotation speed control device, 1
0: Flowmeter, 11: Pressure gauge, 12: Adder, 1
3: Function converter, 14: Arithmetic unit, 15: Comparator,
F: Required air flow rate, F4: Required air amount, H: Blower speed, H _B : Blower reference speed, MV: Valve opening degree,
MV _S : Optimal opening, P: Pressure, P _L : Lower limit pressure.

Claims (1)

[Scope of Claims] 1. In a combustion air supply pipe for a heating furnace in which a plurality of branch pipes are connected to a main pipe connected to a discharge port of a blower, the amount of air required for each of the branch pipes is aggregated. A blower reference speed is set as a function of the required air flow rate obtained, and the blower reference speed is determined by adjusting the opening degree of the maximum opening degree of the air flow rate control valve provided in each of the branch pipes to 100 [ %] The opening is slightly smaller than the opening and has an adjustment margin in the direction of increase, which is the preset optimal opening, and the pressure in the main pipe stabilizes combustion. A heating furnace combustion air blower speed control method that corrects and sets the blower speed so that it always has a value greater than the minimum pressure value required.