Turbo-expansion engine for high-pressure low-capacity air-fractionating apparatus

Abstract

For many years the Geliimash Scientific-Production Association AO has produced small high-speed turbo-expansion engines (TEE) which are used instead of piston expansion engines (PEE) in air-fractionating apparatus operating with mediumpressure (4-7 MPa) and high-pressure (up to 20 MPa) cycles for obtaining both gaseous and liquid products. Geliimash Scientific-Production Association AO also uses TEE instead of PEE in cryogenic helium plant and in hydrogen liquefiers.Compared with the PEE the TEE operates more reliably. The mean time between breakdowns of TEE is, as a rule, four to five times longer than of PEE. Experience with the replacement of PEE by turbo-expansion engines shows that the isentropic efficiency gs of TEE, even of small ones, is higher than of PEE.The TEE require less metal and are considerably simpler to operate, and the field of their application is therefore substantially wider. However, the TEE require greater purity of the gas supplied to them.The changes in the widening fields of application of TEE with radial-axial and radial impellers in various cryogenic installations in dependence on the pressure ahead of the TEE and the volumetric flow rate V 0 (at the temperature T O and the pressure Po at the inlet) are shown in Fig. I.The lower limit of the volumetric flow rate is determined by the resistance to vibration of the rotor at superhigh rotational frequencies. When a PEE is made with plain oil bearings, the lower limit of V o can also be determined by the frictional power absorbed by the plain bearings.The upper limit of the volumetric flow rate is determined solely by the technological possibilities of production. When the volumetric flow rate is very high, it is advisable to use axial TEE.In Russia and the countries of the Commonwealth of Independent States most cryogenic installations operate at present with TEE. There remain only a few small installations operating at pressures of up to 20 MPa which are produced with PEE. The Geliimash Scientific-Production Association AO in particular produces stationary and transportable air-fractionating apparatus SKDS-100 and TKDS-10 with a capacity of 100 liters liquid oxygen or nitrogen per hour and equipped with PEE brand DPV-4.2-200/6-2. The parameters of the PEE are: pressure at the inlet P0 = 18 MPa, at the outlet P2 = 0.65 MPa, temperature at the inlet 280 K, air flow rate 200-250 m3/h, isentropic efficiency r/s = 0.65-0.68. It should be noted that in the course of lengthy operation ~/s decreases.To replace the decompressors DPV-4.2-200/6-2, the turbo-expansion engine DT-0.3/20 was designed; in it the air expands in two macroturbine stages which are connected in series and have the following parameters:Stage I Pressure, MPa:at the inlet Po 18 at the outlet P2 7.5 Temperature at the inlet T o, K 283 Gas flow rate through turbo-expansion engines, V, m3/h 240 Volumetric flow rate V o, m3/h 1