L Design and Optimization of Helium Liquefaction System with Targeted Capacity of 50 lph without LN2 T Maiti, S Pal, A Mukherjee, U Panda Variable Energy Cyclotron Centre, Kolkata ICEC26 – ICMC2016

VECC, Kolkata, is operating two liquefiers  VECC is operating a helium liquefier of capacity 50 lph without LN2, since From 2009, two liquefiers, another 85 lph, running continuously to provide cryogen to Superconducting cyclotron  M/s Air Liquide, France, make  Liquefiers are turboexpander based and operating on Claude cycle principle.

 Simulation of thermodynamic model of Claude cycle  Validation of simulated result with the operating data of existing liquefier at VECC  Investigation of different modes of operation and configurations of Claude cycle to optimize the COP Objective

Helium liquefier (HELIAL50) at VECC

Analysis of various modes of operation Modes of operation 1: Liquefaction w/o LN2, with 6 HX + 1 JT + 2 turbines Modes of operation 2: Liquefaction with LN2, with 6 HX + 1 JT + 2 turbines Modes of operation 3: Refrigeration w/o LN2, with 6 HX + 1 JT + 2 turbines Modes of operation 4: Liquefaction w/o LN2, with 6 HX + 1 JT + 3 turbines Modes of operation 5: Liquefaction w/o LN2, with 7 HX + 2 JT + 2 turbines

Mode of operation1: Liquefaction w/o LN2 precooling

Human-machine interface of liquefiers of VECC

Mode of operation 2: Liquefaction with LN2 precooling

Refrigeration without precooling Liquefaction with 7 HX and 2 JT Liquefaction with 3 turboexpanders Mode of operation 3Mode of operation 4 Mode of operation 5

Crucial Input Parameters 1. HP & LP streams in cold box are bar & 1.13 bar 2. Two known temperatures only: - Cold box entry - Cold return stream from dewar 3. Dewar pressure: 1.20 bar(a) 4. Effectiveness of HX: more than 95% 5. Turbine efficiency: 70% 6. Compressor mass flow rate: 52 g/s Assumption: 1.Pressure drop in HX is ignored 2.Heat in-leak is negligible

Specific heat of helium increasing with decreasing temperature appreciably below 20K. Hence, for designing HX in low temperature range, mean specific heat over temperature range of Th to Tc is determined by using the following : where Cp, hm is the harmonic mean of Cp at Th and Tc. HXs are modeled using enthalpy balances & effectiveness and calculating nodal temperatures: Similarly, other nodal temperatures are determined by enthalpy balance and using fundamental thermodynamic equation. Methodology

Comparison between simulated data and operational data Simulation data is validated with operational data from running liquefier at VECC. Those parameters are compared only where CERNOX sensors are placed in cold box. Variation of this simulated value is max. of 16% lower than real data from liquefier. This is due to assumption of ideal cycle. Operational data are obtained in HP stream only Nodal points Simulated Temperature (K) Operating Temperature (K) % variation % % % % % % LHe4.40 0%

Liquefaction with precooling Refrigeration without precooling Comparison between simulated data and operational data Nodal points Simulated Temperatu re (K) Operating Temperature (K) % variation % % % % % % LHe4.4 0% Nodal points Simulated Temperature (K) Operating Temperature (K) % variation % % % % % % LHe4.4 0%

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