Turbo-expanders for mobile air separation equipment

Abstract

These requirements made it necessary to move away from the traditional practice of using turbo-expanders with reducers and regenerative braking (or hydraulic braking devices) in low-pressure, air separation equipment to a design based on a single-rotor construction with a centrifugal, braking, air compressor. The turbo-expander has a most efficient centripetal, reactive turbine stage with a cantilevered, radial-axial rotor. In order to reduce the weight of the overhanging rotor (which rotates at 36000 • 2000 rpm) and simplify the manufacturing process it was decided to use semiopen impellers made of AK-6 aluminum alloy in the turbine and braking compressor. The guide casing of the turbo-expander is equipped with vanes which can be turned manually by means of a special mechanism. This mechanism enables smooth regulation of gas flow. When the gas flow is changed the turbine power varies within the range of 25-45 kW. Under these conditions the rotor speed is maintained within acceptable limits by means of a throttle valve installed in the high-pressure pipe of the braking compressor which helps in controlling the rotor power. A screen filter is mounted in the suction pipe to prevent entry into the compressor of sand or any other solid particles suspended in the atmospheric air. The turbo-expander is fixed to the inner wall of a special section in the thermal-insulation casing of the rectification unit. This section is tightly closed by a cover to avoid damage during transportaion.