DRAG® Technology in Compressor Recycle and Anti-Surge Service Applications

Compressor recycle service is used extensively in industries where large volumes of compressible gases, (including natural, organic and inorganic) and refrigerants must be handled. For this application, there are three needs that must be met to ensure a smooth operation.

Quick Response

The most important aspect of the compressor recycle/anti-surge service is quick response. The main reason for this is due to the changing conditions that cause the compressor to move out of its rated flow, and go into surge. This variable is a significant part of the demands that cause the application to be severe. A surge can happen anywhere between 1/3 of a second to three seconds.

The compressor will recover, and will typically go into surge again, happening as many as three times in one second. Although the frequency of surge depends on the sensitivity of the system, the best solution is a fast responding anti-surge valve to save the wear and tear on the multi-million dollar compressor, one of the most expensive components in the system.

Tight Shutoff

Another important feature for a valve servicing the compressor recycle application is tight shutoff. If the fluid is leaking by the valve, it will return back into the compressor, causing the driver to work harder to get the same exact flow output and wasting energy. Over the lifetime of the compressor, this leakage will result in a significant financial loss, since the most predominant cost of the compressor is the energy, now wasted as the compressor is working harder to create the same amount of output.

Noise Control

The compressor recycle service also presents the possibility of noise disturbance, and as a consequence requires a quiet valve. This application has a high pressure drop, where each compressor stage is approximately a 3:1 pressure ratio, so that the outlet pressure is three times higher than the inlet pressure. With a very large drop in the pressure and a very low outlet pressure, the potential for loud noise is considerably high.

The DRAG® Solution

CCI’s DRAG® valve design is uniquely suited for compressor recycle/anti-surge service because it specifically addresses and solves the potential problem areas in this tough service application.

The DRAG® valve is designed with a fast- acting pneumatic double-acting piston actuator that will stroke in less than one second. CCI has manufactured 24 inch (600 millimeter) valves with 24 inch (600 millimeter) strokes that will meet one second full stroke. But with this quick stroke design, CCI has evolved the actuator controls to give a very precise control with minimum overshoot.

DRAG® valves also incorporate a tortuous path flow design. That is, pressure energy is dissipated at a constant, controlled velocity head through the use of multiple, right-angle turns in a stack of individual disks. These disks are either etched in lower gas-flow applications (see Figure 1) or punched in high gas flow applications (see Figure 2).

The disk stack surrounds the plug throughout its travel from closed to wide open. Thus the velocity head throughout valve is controlled regardless of plug position. Velocity head (rV2/2gc) through this disk stack is limited to 70 psi (0.48 MPa) to minimize noise. The design can hold noise levels to 85 dBA (+0/–5 dBA) or below at three feet (one meter) to comply with the current noise abatement regulations.

DRAG® valves for compressor recycle/anti-surge service are designed with an ANSI Class VI soft seat, and ANSI Class V hard seat to assure repeatable tight valve closure at shutoff. Because of this field-proven expertise in recycle valve application, CCI has retrofitted other manufacturers’ recycle valves with CCI’s DRAG® design. The end result is improved operation, reduced noise and vibration and improved recycle valve performance overall. The system enjoys fewer compressor surges, lower energy costs, and lower noise levels.

Published in SOLUTIONS Winter 2000