An Experience in the Maintenance of a Liquefier from the T-15 Cryogenic System, Results of Its Reliability and Capacity Enhancement

Abstract

For the production of the liquid helium and realization of technological operation modes of cooling down, steady state and warming up cryogenic objects at Tokamak T-15 facility liquefiers with the present flow rate, 0.222 L/s (800 L/h) each, are used. In 1988 the Liquefier was put into operation under conditions without implementation of the third turbine stage, at the liquid helium flow rate 0.0694 – 0.0972 L/s (250 – 350 L/h), for the time of continuous operation of 200 hours long. Since 1988, work has been done to enhance its reliability and capacity. This includes:

• Simplification pneumatic-hydraulic circuit-diagram of the liquefiers for increasing reliability.

• Start-up of the third turbine stages of the liquefiers. Piston expander and two variant of turbines were tested, only the last variant has demonstrated reliable and effective operation.

• Work out and realization of technological and circuit-diagram solution (usage of preliminary helium purification from neon, development and assembly of a neon adsorber) against freezing neon and hydrogen impurities — changing the mass flow ratio — in the valves and heat exchangers.

• Test of various prototype main turbines. Many prototype main turbines with various work pressure and various mass flow were tested. Turbines with optimal parameters have been selected.

• At present, the Liquefier has the flow rate equal 0.222 L/s (800 L/h), at the compressed helium flow rate — 0.222 kg/s (800 kg/h), and the inlet Liquefier pressure — 2.2 MPa.