Emerson VSG & VSSG Spezifikationen PDF herunterladen (Seite 14)

100

Description

discharge manifold of the compressor. From

the discharge manifold, the gas/oil exits the

compressor housing

The Vilter VSG compressors feature the

exclusive Parallex™ Slide System, which

consists of a pair of slides for each gate rotor

assembly. These two independently oper-

ated slides are referred to as the capacity

slide and the volume ratio slide. On the

suction end of the screw, the capacity slide

moves to vary the timing of the beginning

of the compression process. With the

slide moved all the way out to the suction

end of the screw (the 100% position), the

compression process begins immediately

after the gate rotor tooth enters the screw

flute and closes off the end of the groove.

In this situation, the maximum volume of

gas is trapped in the screw flute at the start

of the compression process. As the slide

is pulled back away from the suction end

of the screw, the start of the compression

process is delayed as some of the suction

gas is allowed to spill back out of the screw

flute until the screw rotates far enough to

pass the end of the capacity slide and begin

compressing. This causes a reduced volume

of gas to be trapped in the screw flute when

the compression process begins. In this way,

the capacity of the compressor is reduced

from 100% down to as low as 10% of the full

rated capacity.

The capacity slide provides the means for

controlling specific process set points.

By continuously adjusting the flow of gas

through the compressor, either suction or

discharge pressure in a particular process

can be controlled. When coupled with a

microprocessor controller, the adjustable

capacity slide allows for precise and continu-

ous automatic control of any parameter in

the process to a chosen set point.

The second slide for each gate rotor is the

volume ratio slide. The purpose of the

volume ratio slide is to maximize the ef-

ficiency of the compressor by matching

the gas pressure within the screw flute at

the point of discharge to the downstream

process requirements. The volume ratio slide

operates at the discharge end of the screw,

and acts to vary the position of the discharge

port. When the slide is extended fully to the

discharge end of the screw (the 100% posi-

tion), the compression process within the

screw flute continues until the screw rotates

far enough for the flute to pass the end of the

volume ratio slide. At this point, the screw

flute lines up with the discharge port and the

compressed gas is expelled from the screw

flute. As the volume ratio slide is pulled back

away from the discharge end of the screw,

the position of the discharge port is changed

and the gas is allowed to escape the screw

flute earlier in the compression process, at a

reduced pressure.

The overall volume ratio within the compres-

sor is determined by the distance between

the front of the capacity slide (the start of

compression) and the back of the volume

ratio slide (the completion of compression).

Therefore, the volume ratio slide must

respond to changes in the downstream

pressure measured in the oil separator and

position itself for the required compression

ratio based on the position of the capacity

slide. By only compressing the gas within

the screw as far as required to match the

pressure in the downstream receiver,

the compressor efficiency is maximized.

Proper positioning of the volume ratio slide

prevents either over compressing or under

compressing of the gas within the screw

flute. This allows the single screw compres-

sor to efficiently handle a range of volume

ratios from as low as 1.2 up to 7.0.

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