JPH0259320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling a multi-stage compressor, and in particular, when the flow rate of pressurized air flowing to a subsequent compressor reaches its surging limit range, the cooling capacity of an intercooler is attenuated to control the pressure air. The present invention relates to a control method for preventing surging by thermally expanding and increasing the suction flow rate of a downstream compressor.

A multi-stage compressor compresses a fluid to be compressed in stages, and the later-stage compressor is naturally characterized in that its impeller diameter is smaller than that of the previous-stage compressor. Therefore, as shown in Figure 1, when comparing the characteristic curves showing the relationship between the flow coefficient φ and the pressure coefficient for the first and second stage compressors, it is found that The surging limit of the first stage (shown in FIG. 1B) has moved to the higher flow coefficient side than the first stage (shown in FIG. 1B).

In other words, if the flow coefficient at the design point is 100% and the flow coefficient in the surging limit area of the first stage compressor is 60%, then the flow coefficient in the surging limit area of the second stage compressor is approximately 70%. becomes. Therefore, when the suction valve of the multistage compressor is throttled to reduce the flow coefficient to 70% or less, the first surging phenomenon occurs in the second stage compressor. Therefore, if the multi-stage compressor has three or more stages, the first surging will occur in the final stage compressor.

When this surging occurs, the efficiency of the compressor decreases rapidly, and the impeller of the compressor may be damaged due to vibration and heat generation.

Therefore, conventionally, in order to avoid the occurrence of such surging, the compressor in all stages had to be operated with the flow coefficients set higher than the flow coefficient in the surging limit region of the final stage. According to the above example, when the flow rate coefficient reached 70% during low-load operation, the pressure inside the discharge pipe was released to the atmosphere to prevent surging.

The present invention has been devised by paying attention to the above-mentioned circumstances, and its purpose is to increase the suction flow rate of the downstream compressor through thermal expansion so that the downstream compressor can maintain its surging limit range without causing surging in the downstream compressor. It is an object of the present invention to provide a control method for a multi-stage compressor that enables low-load operation below the flow rate coefficient and achieves energy savings.

In order to achieve the above object, the present invention provides a multi-stage compressor equipped with an intercooler that cools pressurized air discharged from the compressor, in which air is sucked into a subsequent compressor located downstream of the intercooler. The flow rate of pressurized air is detected, and when this detected flow rate reaches the surging limit range of the compressor in the subsequent stage, the cooling water flow control valve of the intercooler is gradually closed, and the temperature of the pressurized air exiting the intercooler is detected. When the detected temperature reaches the set temperature, the closing operation of the cooling water flow rate control valve is stopped, and when the detected flow rate reaches the surging limit range again, the blowoff valve of the downstream compressor is opened. This is what I did.

A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 2 showing a multistage compressor configured by connecting two turbo compressors in series, a suction pipe 3 equipped with a suction valve 2 is connected to the suction side of the first stage compressor 1, The suction side of the second stage compressor 5 is connected to the discharge side of the first stage compressor 1 via a connecting pipe 4 .

A discharge pipe 6 is provided on the discharge side of this second stage compressor 5.
is connected to the discharge pipe 6, and a receiver tank for distributing and supplying pressurized air to load equipment is connected to the discharge pipe 6. A blowoff pipe 7 for releasing pressurized air to the atmosphere is connected to the discharge pipe 6, and a blowoff valve 8 for opening and closing the blowoff pipe 7 is interposed. Further, a pressure regulator 9 is connected to the discharge pipe 6 to adjust the intake air by controlling the opening and closing of the suction valve 2 to detect the discharge pressure and maintain the discharge pressure at a set pressure. It is designed to be controlled.

On the other hand, an intercooler 10 for cooling the pressurized air discharged from the first stage compressor 1 which is the preceding stage is interposed in the connecting pipe 4, and a second A suction amount detection means 11 consisting of an orifice 11a and a differential pressure transmitter 11b for detecting the flow rate of pressurized air flowing to the compressor 5 in the stage is provided. A flow regulator 12 is connected to the intake amount detection means 11. This flow rate regulator 12 compares the detected value sent from the differential pressure transmitter 11b with the surging limit permissible flow rate of the second stage compressor 5, and when the detected value reaches the surging limit range, the above-mentioned discharge is detected. It is configured to open the wind valve 8.

The above configuration is the configuration of a commonly adopted multi-stage compressor, and when constant air pressure control is performed, the air volume increases due to the decrease in the pressure air consumption of the load equipment, which is the surging limit allowable flow rate of the second stage compressor 5. In other words, when the flow coefficient falls below the flow coefficient in the surging limit region of the second stage compressor 5, the pressure air in the discharge pipe 6 is discharged into the atmosphere. The second stage compressor 5 is configured to prevent surging from occurring.

However, in the present invention, the air volume is
When the surging limit permissible flow rate is exceeded, the cooling capacity of the intercooler 10 is attenuated and the pressure air is thermally expanded before opening the blower valve 8, so that the suction flow rate of the second stage compressor 5 increases. The feature is that the air volume can be further reduced by the amount of increase.

That is, as a means for varying the cooling capacity of the intercooler 10, a flow rate control valve 13 is provided in the cooling water supply pipe 10a of the intercooler 10,
By throttling this flow rate control valve 13, the flow rate of the cooling water is reduced and the cooling capacity is attenuated. The flow rate regulating valve 13 is operated via a comparator 14 in response to an operating signal from the flow rate regulator 12, and is configured to gradually close upon receiving the operating signal. Therefore, when the detected value reaches the surging limit region, the flow rate regulator 12 first switches the comparator 1
4, an actuation signal for actuating the flow control valve 13 is issued, and then when the detected value reaches the surging limit region again, the blowoff valve 8 is opened.

The temperature of the pressurized air is detected between the intercooler 10 and the orifice 11a in the connecting pipe 4, and the detected value is compared with a set temperature, and when the detected value reaches the set temperature, the comparator 14 sends a flow rate A temperature detector 15 is provided that issues a signal to stop the closing operation of the control valve 13, and is configured to prevent mechanical damage to the downstream compressor 5 caused by the temperature of the pressurized air reaching an excessive temperature. Note that the comparator 14 is configured not to send the activation signal from the flow rate regulator 12 to the flow rate control valve 13 when it receives a stop signal from the temperature detector 15 .

Next, the operation of the above embodiment will be described.

During constant air pressure control operation with the suction valve 2 throttled through the pressure regulator 9, when the air volume reaches the surging limit range of the second stage compressor 5 due to a decrease in the pressure air consumption on the load side, the flow rate decreases. The regulator 12 sends a signal to the flow control valve 13 via the comparator 14,
Start to throttle the flow rate control valve 13. This reduces the amount of cooling water supplied to the intercooler 10, so
The cooling capacity of the intercooler 10 gradually decreases, and the pressurized air exiting the first stage compressor 1 is not cooled and therefore thermally expands. Therefore, since the volumetric flow rate of the pressurized air sucked into the second stage compressor 5 increases, the second stage compressor 5 does not cause surging.

Then, when the air volume decreases further and reaches the surging limit range of the second stage compressor 5 again, a signal is sent from the flow regulator 12 to the air discharge valve 8, and the pressure in the discharge pipe 6 is reduced to atmospheric pressure. will be opened to Therefore, the air that was conventionally discharged when the air volume reached the surging limit range of the second stage compressor 5 can be discharged after the air volume has further decreased from that value. This can contribute to energy savings.

Note that while the cooling capacity of the intercooler 10 is attenuating, if the temperature of the pressurized air reaches the set temperature or higher, the closing operation of the flow rate control valve 13 is stopped, so the temperature of the pressurized air does not rise any further and the temperature of the second stage increases. Mechanical damage to equipment on the downstream side such as the compressor 5 is prevented.

As is clear from the above description, the method of the present invention is automatically implemented by the configuration of the above embodiment.

By the way, the first stage and second stage compressors 1,
If the flow coefficient at the design point 5 is 100%, and the flow coefficient in the surging limit region is 60% for the first stage compressor 1 and 70% for the second stage compressor 5, the flow rate regulator 12 is It will be set to 70% in accordance with the flow coefficient of the second stage compressor 5. As a result of implementing the method of the present invention on an actual machine, it was possible to reduce the flow rate coefficient, which used to be 70%, to 65%. As a result, the range of use of multistage compressors has increased from 70 to 70, as shown in Figure 3.
What used to be 100% has been increased to 65-100%.

Note that the flow rate regulating valve 13 in the above embodiment may be configured not only to close the valve but also to be freely controlled to open and close by the flow rate regulator 12. Furthermore, although the above embodiments are examples of implementing the present invention with respect to a two-stage compressor, it goes without saying that the present invention can be similarly applied to a multi-stage compressor with three or more stages.

In summary, the present invention exhibits the following excellent effects.

When the suction flow rate of the downstream compressor reaches the surging limit range, the cooling water flow rate of the intercooler is gradually reduced to increase the volumetric flow rate of the pressurized air sucked into the downstream compressor by thermal expansion, and further the suction flow rate is increased. When the surging limit area is reached, air is released from the compressor in the subsequent stage, allowing low-load operation below the flow rate coefficient in the surging limit area without causing surging in the subsequent compressor, resulting in energy savings. can be achieved.

When the temperature of the pressure air exiting the intercooler reaches the set temperature while gradually decreasing the cooling water flow rate of the intercooler, the closing operation of the cooling water flow control valve is stopped, so that the temperature of the pressure air becomes excessive. It is possible to prevent malfunctions of the latter stage compressor caused by the temperature.

[Brief explanation of drawings]

Fig. 1 is a characteristic curve diagram of the first stage compressor and second stage compressor, Fig. 2 is a system diagram of a multistage compressor showing a specific example for carrying out the method of the present invention, and Fig. 3 FIG. 2 is a characteristic diagram for explaining the effects of the present invention. In the figure, 5 is a second-stage compressor, 8 is a blow-off valve, 10 is an intercooler, and 13 is a cooling water flow rate control valve.

Claims (1)

[Claims] 1. In a multi-stage compressor equipped with an intercooler that cools the compressed air discharged from the compressor, the flow rate of the compressed air taken into the downstream compressor located on the downstream side of the intercooler is detected, and the detected flow rate is When the surging limit of the downstream compressor is reached, the cooling water flow control valve of the intercooler is gradually closed, the temperature of the pressure air exiting the intercooler is detected, and this detected temperature reaches the set temperature. A multi-stage compressor characterized in that when the detected flow rate reaches the surging limit region, the closing operation of the cooling water flow rate control valve is stopped, and when the detected flow rate reaches the surging limit range again, the blow-off valve of the subsequent compressor is opened. control method.