The storage of hydrogen based on low-temperature and highpressure method

Abstract

Hydrogen storage method with high security, reliability and economy is the bottleneck of large-scale hydrogen utilization. Conventional techniques such as high-pressure gaseous storage (HPGS), liquid hydrogen storage (LHS), solid hydrogen storage (SHS, mainly dominated by metal hydrides based method) have their own disadvantages. For examples, HPGS needs so much high pressure that the security risk is created, even though the density is still unsatisfactory; LHS consumes so much power though it is the potential great way to achieve both high volume hydrogen storage density and mass hydrogen storage density; SHS needs lots of time and high temperature to storage/release, moreover practical application of metal hydrides is still not available. In this paper, a method by combining low-temperature and high-pressure technologies is proposed, which can achieve high density at not very low temperature and not very high pressure. The SRK equation is chose for describing the thermodynamic properties of hydrogen, since it agrees well with Refprop 9.1. Then the power consumption of compressors and fans in multistage hydrogen compression process is analyzed, showing that five stage compression is the best choice comprehensively considering the power consumption and the complexity of the compression. Meanwhile, the thermal load of hydrogen is analyzed in the cooling process from 300 to 20 K, revealing that the latent heat consumes about 54% of the total power consumption, though it only occupies 12% of the total thermal load. This is the essential reason why the proposed method is superior to LHS on power consumption. From the thermodynamic calculation we can conclude that: (1) Synthetically considering the hydrogen storage density and the total power consumption, the proposed method, that is gaseous low-temperature and high-pressure storage (GLTHPS), is better than HPGS and LHS; (2) there exists a maximum ψ (defined by hydrogen density divides total power consumption) at pressure above 10 MPa, and temperature below 120 K, meanwhile, the pressure increases with the temperature at the maximum ψ; (3) the recommended temperature and pressure parameters for hydrogen storage are (50 MPa, 100 K), (45 MPa, 100 K), (40 MPa, 90 K), (35 MPa, 80 K) and (30 MPa, 70 K), at which the density of hydrogen ranges from 62.3 to 65.3 kg/m3, and ψ ranges from 1.83 to 2.04. The optimized region for hydrogen storage is very practical, since both the mixed-refrigerants Joule Thomson refrigeration cycle (MJTR) and Reverse Brayton cycle (RBC) can achieve high efficiency at the temperature ranging from 150 to 70 K. The proposed method can well meet large-scale and low-cost requirement of hydrogen storage. Inevitably, the vessel used for low-temperature and high-pressure hydrogen storage must be specially designed, which is the biggest weakness of the proposed method. It will raise the initial cost, but decrease the operating cost significantly.