Thermodynamic evaluation of the effects of hydrogen blending on the Joule-Thomson characteristics of hydrogen-blended natural gas

The Joule-Thomson characteristics of hydrogen-blended natural gas (HBNG) differ from those of natural gas for the differences in properties, deserving a profound study. We foremost analyzed the effects of hydrogen on the properties of HBNG using the Soave-Benedict-Webb-Rubin (BWRS) equation of state (EOS) owing to its lowest deviation among the concerned EOSs. Based on BWRS EOS, the fundamental differential equation, and the isenthalpic equation, we developed a thermodynamic model to evaluate the effects of hydrogen on the isenthalpic curve, Joule-Thomson coefficient (JTC), and Joule-Thomson inversion curve (JTIC) of HBNG within the hydrogen mole fraction (x-H2) range of 30%. The average absolute relative deviation (AARD) for the isenthalpic curve of the N2-H2 mixture and the JTC of natural gas is 0.02% and 1.62%. We mainly discussed how hydrogen affects the isenthalpic curve, JTC, and JTIC of HBNG. The isenthalpic curve of the CH4-H2 mixture and HBNG rise in a descending gradient with increasing x-H2. Compared to natural gas, the JTC of HBNG decreases (about 48% when x-H2 is 30%) and negatively correlates to x-H2, pressure, and temperature in a nonlinear function. The JTC is more sensitive to the x-H2 at higher temperatures and lower pressures. The blended hydrogen narrows the positive effect region of HBNG but does not turn the positive effect into a negative one within the x-H2 range of 30%. When x-H2 increases from 0% to 30%, the maximum inversion pressure and corresponding temperature drop at a rate of 0.227 MPa/x-H2% (roughly linear) and 4.9385 K/x-H2% (linear), respectively.