JPS627399B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for controlling the number of rotary positive displacement compressors in operation, with the aim of generating an appropriate amount of compressed gas corresponding to the amount of compressed gas consumed and reducing power loss of the compressor. Regarding.

Conventionally, as a method of supplying compressed gas in accordance with the amount of compressed gas consumed, as shown in FIG. 1, an increase or decrease in the amount of compressed gas consumed is detected and the number of operating compressors is increased or decreased.

That is, referring to FIG.
C' is equipped with an unloader (capacity control device) that detects the discharge pressure and continuously controls the pumping capacity of compressor C'. Then, the unloader of one (or two if the load fluctuation range is large) of the operating compressors C' is activated, and the unloader of the remaining compressors C' is operated.
If C′ is fixed with solenoid valve S′, the compressor during operation can be
Load fluctuations (consumption fluctuations) within the range of one vehicle in C' can be absorbed by the unloader. in this case,
If the load fluctuates beyond the range that can be absorbed by the unloader, the discharge pressure will drop due to insufficient air supply (consumption amount > pumped amount) or excessive supply (consumption amount < pumped amount)
This pressure fluctuation is detected by a pressure switch (lower limit PSL or upper limit PSH) and is used as a signal to increase or decrease the number of operating compressors C'.

In the conventional example above, fluctuations in the amount of compressed gas consumed are detected by fluctuations in discharge pressure, and it is necessary to set PSH and PSL settings outside the operating range of the unloader. A pressure drop can occur at the outlet because the drive motor requires start-up time during which sufficient compressed gas cannot be generated. This state is as shown in Figure 2, and the PSL
The set value is set to be a value equal to or higher than the sum of the minimum supply pressure required for the air source equipment and the amount of pressure drop that occurs during the start-up period at the time of start-up.

However, in the above condition, even though it is sufficient for compressor C' to be operated near the required minimum pressure, compressed gas is generated at a considerably higher pressure than this minimum pressure, and compressor C' has no use for compressor C'. In addition to being loaded, an excessive power load was also imposed.

To explain the above conventional technology and its problems in more detail using Fig. 9, if, for example, three of the four compressors shown in Fig. 1 are in operation, all three compressors are in operation. When the unloader of the machine is operated, the discharge amount changes from 0 to 0, as shown by the virtual line in Fig.
Discharge pressure is adjusted within a range of 300%.

Therefore, if the unloaders of all the machines in operation are operated, even if the consumption is reduced to 200% or 100%, all the machines will be driven, resulting in a waste of drive power.

Therefore, it is necessary to reduce power consumption by controlling the number of operating compressors so that when the consumption reaches 200%, one compressor is stopped, and when the consumption reaches 100%, another compressor is stopped. However, in order to operate the unloaders of all machines in operation and control the number of machines in operation, for example, when the consumption decreases from 300% to 200%, the discharge pressure will go from P ₁ to P ₁₁ . (See Fig. 9), the pressure at _P11 may be detected by a pressure switch and one compressor may be stopped.

However, the discharge pressure of the compressor is about 7 kg/cm ² and the operating range of the unloader (P ₂ - P ₁ ) is about 0.3 to
0.5Kg/cm ² and the change from P ₁ to P ₁₁ is approximately 0.1
It is about Kg/ ^cm2 . As described above, it is extremely difficult to detect a change of 0.1 kg/cm ² in a pressure range of 7 kg/cm ² or more, and the number of operating units could not be controlled with this method.

Conventionally, as shown by the solid line in Figure 9, when three compressors are in operation, only one unloader is activated to accommodate discharge pressure fluctuations in the range of 300 to 200%. Capacity control is performed, and even if the consumption decreases to less than 200%, the unloader will not operate.
Since it is held at 200%, the discharge pressure is increased by the difference in flow rate between the discharge rate of 200% and the consumption rate of 200% or less, and the pressure is increased to the value of P _SH where the pressure can be easily detected.
One compressor was stopped by a pressure switch.

On the other hand, when the consumption rate increases to 300% or more, since there are only 3 compressors and the discharge rate is only 300%, the discharge pressure decreases due to the difference in flow rate, and is lowered to a pressure _PSL where pressure can be easily detected. One additional compressor was activated by a pressure switch. During this additional startup, the pressure continues to decrease for a while after startup due to the start-up characteristics of the compressor, so the discharge pressure decreases to the minimum _PLL .

Therefore, in conventional systems, the minimum pressure required on the consumer equipment side is _PLL , and the operating pressure range is wide up to the maximum _PSH . Moreover, it is originally desirable to operate at low pressure with P ₁ as close to P _SL as possible, but as mentioned above, the unloader operating range is
It is very narrow at 0.3 to 0.5Kg/ ^cm2 , and the discharge pressure is 7
Since the pressure is as high as Kg/cm ² or more, it is difficult to make P ₁ and P _SL close to each other in terms of accuracy of the detection switch, and P ₁ is set to a value considerably higher than P _SL . Therefore, the compressor is driven at a pressure considerably higher than the required minimum pressure, resulting in wasted power consumption.

The present invention has been devised in view of such conventional problems, and when a plurality of compressors are installed and operated as a factory power air source equipment, for example, the number of compressors to be operated according to the amount of compressed gas consumed. control,
The aim is to achieve an energy saving effect.

The following description will be made with reference to the embodiments shown in FIGS. 2 to 7. The screw compressor unloader as an example of the compressor C reduces the suction pressure of the compressor C by throttling the suction throttle valve V. Although the discharge capacity is reduced, we focused on the fact that suction pressure (gauge pressure) and compressor C capacity are approximately proportional, and by measuring the suction pressure of each compressor C, compressor C
The amount of discharged gas, for example the amount of discharged air, can be calculated.

That is, the unload amount (margin amount) can be calculated by operating the unloaders of all the compressors C in operation, measuring the suction pressure, and comparing it with the suction pressure of each compressor C during rated operation.

Compressor full load capacity x (1 - suction pressure / suction pressure at full load) = margin capacity The suction pressure of compressor C varies from atmospheric pressure (gauge pressure 0 kg/cm ² ) to complete vacuum (gauge pressure - 1 kg/cm 2 ). ^cm2 )
The pressure range is up to 1Kg/
^cm2 . Therefore, the discharge pressure range is approximately 7Kg/cm ²
Since it is extremely small compared to the above, even minute pressure changes can be detected with high precision, so the unload amount can be calculated with high precision by measuring the suction pressure.

By integrating the margins for all compressors in operation, the total margin can be calculated. If this total margin is equal to or greater than the rated discharge amount of one compressor C, one operating compressor C will be stopped, and if the margin decreases, one additional unit will be started. It is sufficient to generate compressed gas corresponding to the amount of compressed gas consumed.

In particular, if you look at FIG. 3, n compressors C are arranged. Here, if the ratio of each compressor C rated capacity to the total compressor C capacity (sum of the rated capacities of n units) is A, A ₂ ... A _o , then A ₁ + A ₂ + ... + A _o = 1 The suction pressure of each compressor C under full load is atmospheric pressure (P _S =0), and it is assumed that up to the m-th compressor C is currently operating, and the suction pressure of each compressor C is P _S1 ,
P _S2 ...P _So , the margin ratio of the i-th compressor C in operation is Ai (1-1+P _Si /1) = -AiP _Si . However, i=1, 2, ..., m (m≦
n), P _Si is the value of the suction pressure measured in gauge pressure (P _Si ≦OKg/cm ² G). In the above equation, when the compressor C is stopped, P _S =OKg/cm ² G, and the margin ratio is zero. Also, from the above formula, the total margin A for m vehicles is: becomes.

Figure 4 shows the automatic start/stop determination circuit for compressor C. By monitoring the reserve rate A, the unloading rate (relative to the installed capacity) of the entire operating compressor C can be determined, so the minimum required minimum If the margin rate A _L becomes less than the limit, one additional unit is activated, and if it exceeds the necessary and sufficient margin rate A _H , one unit is stopped.
When stopping and starting again, by comparing the rated capacity ratio A _i of each compressor C, it is possible to select the compressor C with the optimum capacity.

To simplify the explanation, for example, compressor C with the same capacity
To explain the case where four units are installed, the circuit in FIG. 4 is replaced with the circuit in FIG. 5. Now A _H
= 0.25 (i.e. margin of rated capacity for one unit) A _L
When set to =O (margin rate is zero), the margin rate will be operated according to the load between zero and one compressor C, so it is possible to operate the minimum number of compressors required, and the discharge pressure can also be operated. Since all of the unloader valves of the compressor C are activated, the range of pressure fluctuation is also reduced.

Note that it is also possible to control the number of units by adding control using a discharge pressure switch used in conventional control to the control method according to the present invention. for example,
As shown in FIGS. 6 and 7, this is a method in which the pressure of the discharge main pipe is also detected and controlled in combination with a start/stop signal based on a margin ratio. If the values of the discharge pressure increase signal P _H and the discharge pressure decrease signal P _L are set to P _H1 and P _L1 , which are outside the operating pressure range of the compression unloader, and controlled by the OR circuit, malfunction of the compressor C and the unloader can be prevented. This is effective in cases where the unloader characteristics cannot be controlled to zero capacity. Furthermore, setting the values of P _H and P _L to P _H2 and P _L2 within the unloader operating range and using an AND circuit is effective when there are large variations in the unload characteristics of each compressor C.

The two-stage screw compressor C includes a compressor with a suction throttle valve and a compressor with only one stage of a slide valve, but similar results can be obtained by measuring the two-stage suction pressure. However, since the two-stage suction pressure of the stopped compressor is equalized at atmospheric pressure 1, the measurement result is that the margin is large, so a pre-processing calculator is required for the halted compressor, which has a margin of zero.

According to the present invention, it is possible to minimize the range of pressure fluctuations due to fluctuations in compressed gas consumption, and it is possible to lower the operating pressure as shown in FIG. That is, if we explain this using Figure 10,
Since the present invention does not use a pressure switch, the operating pressure P ₁ of the unloader can be reduced to the value P _SL (same value as P _SL in FIG. 9). Also, when the consumption decreases, in the conventional type, after the pressure rises to P _SH ,
One compressor was stopped (see Figure 9), but in the present invention, as shown in Figure 10,
Since one compressor is stopped when the pressure rises to P ₁₁ ', low pressure operation is possible.

That is, when three compressors are in operation and the consumption is 300%, the discharge pressure is as low as P ₁ =P _SL . When the consumption decreases to 200%, in the conventional technology (Figure 9) P ₂
However, in the present invention, because three unloaders are controlled in parallel, the pressure increases only to the value of P ₁₁ '. At this time, 1
When the machines are stopped, the unloader characteristics shift to two parallel machines (see Fig. 10).

In the conventional technology, the voltage was increased to P _SH in order to determine the reduction in consumption, but in the present invention, the voltage is not increased above the value of P ₁₁ '.

Note that when the consumption increases, the pressure drop due to the compressor startup time is the same as in the conventional technology and drops to _PLL . The following equation proves that this reduction in operating pressure saves the required power.

W: Power Kw, K: Specific heat ratio, Bd: Absolute static pressure at discharge port, P _S : Absolute static pressure of suction pressure (Kg/cm ² abs) Q: Air volume in suction state (m ³ /min) For example: , as specific values, Q=50m ³ /min, Pd
= 7Kg/cm ² G, and the required power at full load when the pressure of Pd is reduced to 6Kg/cm ² G is From the above formula, the power saving ratio = 100 x (1-213/232) = 8.2%, and a power saving of 8.2% is achieved. As the discharge pressure decreases, the pumping loss in the pipeline increases somewhat, but the general load equipment characteristic is that the rejection ratio decreases in proportion to the decrease in supply pressure, so the above 8.2% savings were achieved. is certain.

In addition, by measuring the margin, it is possible to select which compressor to stop or start, and control to ensure the minimum margin is achieved, which is useful in compressor equipment where compressors with different capacities coexist. , it is possible to optimally select the compressor and control the optimal number of compressors, resulting in an excellent energy saving effect.

[Brief explanation of the drawing]

Fig. 1 is an overall layout diagram showing a conventional example, Fig. 2 is an explanatory diagram of the operation of the conventional example, the following shows an embodiment of the present invention, Fig. 3 is an overall layout diagram, and Fig. 4 is a circuit diagram. ,
Figure 5 is an explanatory circuit diagram that is a simplified version of Figure 4;
and FIG. 7 are circuit diagrams and action explanatory diagrams showing other embodiments, FIG. 8 is an explanatory diagram showing the effects of the present invention, and FIG. 9 is a graph showing unloader operating characteristics for explaining the prior art. FIG. 10 is a graph showing unloader operating characteristics for explaining the effect of the present invention. C...Compressor.

Claims (1)

[Scope of Claims] 1. A method for controlling the number of operating compressors equipped with a capacity control device such as a suction throttle valve operated by compressor discharge pressure, the method comprising controlling the capacity control device of each compressor during operation. While operating, the suction pressure or intermediate stage pressure of each compressor in operation is compared with the suction pressure at the rated operation of each compressor, which is stored as a preset value, to determine the capacity margin of each compressor. Calculate and integrate them to find the total margin during operation, compare the total margin with the preset upper and lower limits of margin, and if the upper limit is exceeded, stop one unit, If it falls below the lower limit, start one unit,
A method for controlling the number of operating rotary positive displacement compressors, characterized in that by repeating the above operations, a number of compressors corresponding to the amount of compressed gas consumed are always operated. 2. Install multiple compressors with different rated capacities that are equipped with capacity control devices such as suction throttle valves that operate based on the compressor discharge pressure, and calculate the ratio of the rated capacity of each compressor to the total rated capacity of these compressors. Memorize the information in advance, and while operating the capacity control device of each compressor in operation, measure the suction pressure or intermediate stage pressure of each compressor and compare it with the respective rated value to determine the capacity margin of each compressor. calculate the margin rate, multiply the margin rate by the rated capacity ratio to convert it into the margin rate of each compressor, integrate the respective margin rates to obtain the total margin rate, and calculate the total margin rate and the preset margin rate. Compare the upper and lower limit values of the ratio, and if the result exceeds the upper limit set value, stop the compressor with the margin ratio closest to the excess margin ratio, and if the lower limit value is divided, reduce the shortage. A rotary positive displacement compressor characterized in that the compressor with the capacity closest to the margin rate is started and the above operation is repeated to constantly select and operate the number of compressors corresponding to the amount of compressed gas consumed. How to control the number of operating units.