Purification of helium from a cryogenic natural gas nitrogen rejection unit by pressure swing adsorption

摘要

Helium is produced conventionally from cryogenic processes in conjunction with LNG/NRU units. However, cryogenic processes are expensive and energy demanding. Pressure swing adsorption (PSA) was investigated as a potential replacement for the cryogenic processes to enrich dilute He (1 vol%) downstream of the NRU. The feasibility of a PSA process utilizing zeolite 13X was studied by dynamic simulation of 3-bed 3-step, 3-bed 5-step and 4-bed 7-step PSA cycle schedules. The static equilibrium parameters and dynamic mass transfer coefficients were estimated experimentally and the model was validated using dynamic breakthrough curves and PSA cyclic tests. The validated model was used to study the effect of adding equalization steps on the PSA process performance of the 3-bed 3-step cycle. Adding one equalization step (3-bed 5-step) effectively improved both the purity and recovery, while adding two equalization steps (4-bed 7-step) increased the capital costs with only minor improvements in purity and recovery. The best PSA process performance was obtained from the 3-bed 5-step PSA cycle, wherein feeding 1 vol% He resulted in a He purity of 94.3% at 62.1% He recovery and a feed throughput of 746.4 L(STP)/(h kg).