As part of an extensive energy conservation program, Nova, an Alberta Corporation has purchased a portable evacuation or pulldown compressor. This unit can save much of the natural gas that was previously vented to atmosphere when sections of line were shut down for construction, maintenance or repair. In December, 1979 the company placed into service a 3000-kW pulldown package based upon an eight-stage intercooled centrifugal compressor powered by a two-shaft gas turbine. The unit is a complete trailer-mounted compressor station that can be set-up at a pipeline block-valve in only 4 hr. The pulldown can evacuate the isolated line section down to 1/5 of the original pressure, thereby saving some 75 percent of the high pressure gas. This paper will examine the advantageous economics of the pulldown compressor as well as outline its salient design and operating characteristics.

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