JPH01285692A - Control method for screw compressor driven by expansion machine - Google Patents

Abstract

PURPOSE:To make it possible to operate continuously at high efficiency point by controlling revolution speed of an expansion machine in accordance to working discharge of steam and compressed gas, and decompressing a feed passage on draining excess steam into an exhaust passage from a bypass passage. CONSTITUTION:A screw expansion machine 1 drives a screw compressor body 11 via a speed change gear 10 with steam from a feed passage 4, compresses air from a suction filter 12 and delivers the air through an oil separator 13 and a check valve 14. Here, a control unit 18 controls the expansion machine 1 on revolution speed via a feed governor 2 in accordance with outlet pressure of the expansion machine 1 and compressed air pressure detected by pressure detectors 5, 16, namely to working discharge of steam and compressed gas, while drains excess steam into an exhaust passage 6 from a bypass passage 8 through opening and closing on a bypass valve 7 with a pressure controller 17, and decompresses the feed passage 4. Thus external expansion ratio becomes constant, so it is possible to operate continuously at high efficient point.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of controlling an expander-driven screw compressor using a positive displacement expander.

(Prior Art) Conventionally, as shown in FIG. 4, an expander-driven screw compressor is known, for example from the standpoint of energy saving, which utilizes steam delivered to a consumption area for its original purpose.

This compressor uses a positive displacement screw expander I as a driving source.
A supply air control valve 2. is used on the suction side of the screw expander l. An air supply flow path 4 having a shutoff valve 3 is connected to an exhaust flow path 6 having a first pressure detection screen 5 for detecting exhaust pressure on the exhaust side.
It is continuing. Further, a bypass flow path 8 is provided from the upstream side of the air supply control valve 2 via a bypass valve 7 to directly reach the exhaust flow path 6, and the first pressure detector 5 detects the air supply control valve 2. A driving section is formed to control the opening degree of the bypass valve 7. Furthermore, a rotation speed relay 9 is provided on the output shaft portion of the screw expander l, and when the rotation speed of the screw expander l falls below the allowable lower limit, this rotation speed relay 9
The cutoff valve 3 is configured to detect this decrease in rotational speed and close the shutoff valve 3.

On the other hand, a screw compressor main body 11 is rotatably connected to the screw expander l via a transmission lO, and a suction filter 12 is provided on the suction side of the screw compressor main body II, and a suction filter 12 is provided on the discharge side of the screw compressor main body II. Oil separator +3. Check valve 14
A discharge flow path 15 continues therefrom.

For example, steam generated by a boiler (not shown),
Or other driving fluid (hereinafter simply referred to as steam).

) is supplied to the screw expander l through the air supply flow path 4, where it is depressurized and then discharged through the exhaust flow path 6. Screw expansion machine by steam decompression! The power generated in
It is transmitted to the screw compressor main body 11 via the transmission IO, and this screw compressor main body! ■By suction filter 12
After compressing the air sucked in from the compressor, it is discharged into the discharge passage 15, separated into gas and liquid by the oil separator I3, and then pumped.

By the way, the above-mentioned amount of steam often fluctuates, and the screw expander is formed so as to control the rotation speed according to the amount of steam as described below.

That is, when the amount of steam supplied fluctuates, the screw expander l
Since the air supply pressure to the screw expander l is also about to fluctuate, the first pressure detector 5 adjusts the opening of the air supply control valve 2 so that the detected pressure is below a certain value. When the amount of supplied air exceeds the allowable capacity, the bypass valve 7 is opened to directly bypass the excess steam to the exhaust flow path 6.

On the other hand, even when the amount of steam used on the exhaust flow path 6 side fluctuates, the pressure in the exhaust flow path 6 tends to fluctuate, so the first pressure detector 5 as described above ensures that the detected pressure is within a certain range. Even if the supply air adjustment valve 2 is fully opened and the pressure is still low, the bypass valve 7 is opened to maintain the pressure at an appropriate level. The rotation speed of the screw expander I is controlled.

(Problem to be Solved by the Invention) In the conventional control method described above, control is performed based on the pressure detected by the first pressure detector 5, so only the rotation speed of the screw expander I is controlled in response to fluctuations in the amount of steam. Therefore, there is a problem that the rotation speed of the screw compressor main body 11 driven by the screw expander 1 is controlled regardless of the required amount of compressed air.

The present invention was developed to address these conventional problems, and detects not only the steam pressure but also the discharge pressure on the screw compressor main body side, and when the required amount of compressed air is small, the steam supply amount is reduced. It is an object of the present invention to provide a control method for an expander-driven screw compressor in which the rotational speed of the expander is reduced even in cases where the rotation speed of the expander is reduced to eliminate the loss of enthalpy reduction of steam due to unnecessary air compression.

(Means for Solving the Problems) In order to solve the above-mentioned conventional problems, the present invention provides an expander, an air supply flow path having an air supply control valve and a shutoff valve following the suction side, and an air supply flow path for the expander. The screw compressor main body is driven by the expander of the drive unit, which is equipped with an exhaust flow path that continues to the exhaust side, and a bypass flow path that runs from the upstream side of the air supply control valve directly to the exhaust flow path via a bypass valve. In the method for controlling an expander-driven screw compressor, the expander-driven screw compressor is driven by: a first pressure detection means in the exhaust flow path; a second pressure detection means in the discharge flow path of the compressor main body; and control means for controlling the opening degree of the air supply control valve in response to a signal from the second pressure detection means, the first control means for controlling the opening degree of the air supply control valve in response to a signal from the second pressure detection means, In other cases, in the second case where the exhaust pressure is equal to the set value, the current operating state is maintained and the exhaust pressure is smaller than the set value. In the third case, the first
, the opening degree of the air supply control valve is increased until the second state is reached, and when the upper air exhaust pressure becomes lower than a predetermined set value, the bypass valve is opened to control the exhaust pressure, and the exhaust pressure is controlled again. Above 1st. The above control based on the signal from the second pressure detection means is repeated.

(Example) Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an expander-driven screw compressor using a screw expander as a driving means to which the control method according to the present invention is applied,
Except for the control system, the rest is substantially the same as that shown in FIG. 4, and corresponding parts are given the same numbers and their explanation will be omitted.

This compressor is provided with a first pressure detector 5 like the compressor shown in FIG. A pressure regulator (PIC) 17 is provided on the side of the passage 6, a rotation speed relay 9 is provided on the rotating shaft portion of the screw expander 1, and the first. A control means I8 interposed between the second pressure detector 5.16 and the supply air adjustment valve 2 is provided. Bypass valve7. By controlling the shutoff valve 3, the rotation speed of the screw expander I is controlled.

That is, by configuring as described above, the control method according to the present invention described below can be executed.

Next, a control method according to the present invention applied to the above device will be explained based on FIG.

First, when the device is started up, control starts, and in the first step (Sl), the control means 8 uses the signal from the second pressure detector 16 to set the preset value (
1), (discharge pressure car setting value (1)) is positive (
>0), the process proceeds to the third step (S3); otherwise, the process proceeds to the second step (S2).

In a second step, the control means 8 detects the first pressure detector 5.
This and the preset setting value (2) based on the signal from
(Exhaust passage pressure car set value (2)) is positive (
If 〉0), proceed to the third step, if negative (〈0), proceed to the sixth step (S6), and if 0, proceed to the first step again.
Return to step and maintain current operating condition.

In the third step, the control means 18 reduces the opening degree of the air supply control valve 2 by a certain amount.

In the fourth step (S4), the rotation speed of the screw expander 1 detected by the rotation speed relay 9 is compared with an allowable value,
If this rotation speed is below the allowable value, the fifth step (S5
), otherwise return to the first step.

In the fifth step, the shutoff valve 3 is closed by the signal from the rotation speed relay 9, the screw expander 1 is stopped, and the screw compressor main body 11 is also stopped accordingly, and then the process returns to the first step again.

On the other hand, in the sixth step, the control means 18 increases the opening degree of the air supply control valve 2 by a certain amount.

In the seventh step (S7), the bypass flow path pressure (=expander exhaust pressure) detected by the pressure regulator 17 is compared with a preset set value (3) (bypass flow path pressure - set value (3)
)) is positive, the process proceeds to the eighth step (S8); otherwise, the process proceeds to the ninth step (S9).

After closing the bypass valve 7 in the eighth step, the process returns to the first step again.

In the ninth step, the bypass valve 7 is opened and then the process returns to the first step.

After that, each of the above steps will be repeated.

The above device is designed to supplementally use the steam used for the original purpose for another purpose, and basically prioritizes the operating conditions of the expander, so the compressor There may be cases where the compressed gas required by the compressor cannot be sufficiently supplied, and in this case, it is necessary to separately supply compressed gas from another compressor. That is, the supply of compressed gas by this device is performed auxiliary.

In addition, in the above device, if the rotation speed of the screw expander 1 abnormally increases due to a control flow (not shown), or if the temperature of the bearing part of the screw expander 1 increases abnormally, the shutoff valve 4 is closed and the screw expander 1 is activated in an emergency manner. Stop (trip)
However, when the shutoff valve 4 closes, the flow of steam that has been passing through the screw expander 1 until then stops, so it is necessary to flow this steam from the bypass flow path 8 to the exhaust flow path 6. However, with a normal shutoff valve, it is fully closed.

Fully open operation speed is slow and fluctuations in exhaust flow path pressure may occur.

Therefore, in order to prevent this, as shown in FIG. 3, the portion within the dashed-dotted line frame 1 in FIG. If the pressure signal from the bypass valve 7 is abnormally low, the control means 18 may be configured to issue a signal indicating that the bypass valve 7 is in an emergency state based on this signal.

Further, although the above embodiment uses an oil-cooled screw compressor main body, the present invention is not limited to this, and an oil-free screw compressor main body may be used. .

(Effects of the Invention) As is clear from the above description, according to the present invention, there is provided an expander, an air supply flow path having an air supply control valve and a shutoff valve following the suction side, and an air supply flow path on the exhaust side of the expander. The screw compressor main body is driven by the expander of the drive unit, which has a continuous exhaust flow path and a bypass flow path that extends directly from the upstream side of the air supply control valve to the exhaust flow path via a bypass valve. In the control method for an expander-driven screw compressor, the method includes: a first pressure detection means in the exhaust flow path; a second pressure detection means in the discharge flow path of the compressor body; and control means for controlling the opening degree of the air supply control valve in response to a signal from the second pressure detection means, the first control means for controlling the opening degree of the air supply control valve in response to a signal from the second pressure detection means, In other cases, the opening degree of the air supply control valve is reduced, and in the second case where the exhaust pressure is equal to the set value, the current operating state is maintained, and the exhaust pressure is smaller than the set value. In the third case, the above-mentioned first. The opening degree of the air supply control valve is increased until a second state is reached, and when the upper air exhaust pressure becomes lower than a predetermined set value, the bypass valve is opened to control the exhaust pressure,
Repeat the above No. 1. It is configured to repeat the above control based on the signal from the second pressure detection means.

For this reason, the external expansion ratio is kept constant by controlling the rotation speed of the expander according to the amount of steam and compressed gas used, and by flowing excess steam from the bypass flow path to the exhaust flow path to reduce the pressure in the supply air flow path. This has the effect of enabling continuous operation at a high efficiency point.

[Brief explanation of the drawing]

Fig. 1 is a steam system diagram of an expander-driven Suflis compressor to which the control method according to the present invention is applied, Fig. 2 is a flowchart showing the control method applied to the device shown in Fig. FIG. 4 is a system diagram showing a part of an application example of the present invention other than the one shown in the figure, and FIG. 4 is a steam system diagram of an expander-driven screw compressor to which a conventional control method is applied. I...Screw expander, 2...Air supply control valve, 3...
- Shutoff valve, 4... Air supply flow path, 5... First pressure detector, 6... Exhaust flow path, 7... Bypass valve,! ■・・・
・Screw compressor main body, 15...Discharge flow path, 16...
-Second pressure detector, 17...pressure regulator, 18...
control means. Figure 1 Figure 3

Claims (1)

[Claims] (1) An expander, an air supply flow path having an air supply control valve and a shutoff valve following the suction side, an exhaust flow path following the exhaust side of the expander, and a bypass valve from the upstream side of the air supply control valve. In the method for controlling an expander-driven screw compressor, the screw compressor main body is driven by the expander of the drive section, which has a bypass flow path leading directly to the exhaust flow path through the exhaust flow path. a first pressure detection means in the discharge passage of the compressor main body, a second pressure detection means in the discharge passage of the compressor main body, and a control means for receiving signals from the first and second pressure detection means and controlling the opening degree of the air supply control valve. In the first case where either the discharge gas pressure or the expander exhaust pressure exceeds the set value, the opening degree of the air supply control valve is reduced, and in other cases, the exhaust pressure In the second case where the exhaust pressure is equal to the set value, the current operating state is maintained, and in the third case where the exhaust pressure is lower than the set value, the supply air control valve is operated until the above first and second states are reached. When the upper air exhaust pressure becomes lower than a predetermined set value, the bypass valve is opened to control the exhaust pressure, and the signal from the first and second pressure detection means is again increased. A control method for an expander-driven screw compressor, characterized in that the above-mentioned control based on the above is repeated.