Calculation of the physical properties of the mixture of natural gas with hydrogen based on fundamental equation of state AGA-8
DOI:
https://doi.org/10.31471/1993-9868-2022-1(37)-60-68Abstract
The effect of the mole fraction of hydrogen in natural gas on its basic physical properties has been studied
using the equation of state of gas based on the Helmholtz free energy (AGA-8). Using the methods of regression analysis, linear algebra, theoretical and methodological foundations of hydraulics and gas dynamics, methods of the theory of calculating the physical properties of gases, refined mathematical models of thermal and caloric
properties of gas mixed with hydrogen were obtained. The problem of calculating the basic physical properties of natural gas with a given component molar composition when hydrogen is added to its composition with the actual molar content after mixing with gas is considered. A comparison is made between the normative methods for calculating the physical properties of gas in accordance with the multicomponent equation of state of real gas AGA-8 and the classical method for calculating the properties of gas, taking into account the actual hydrogen content in the composition of natural gas. It has been established that when determining the density and lower calorific value and the Wobbe number of a gas-hydrogen mixture under normal conditions, it is possible to use a simplified classical calculation method (by the molar mass of gas or by the densities of individual gas components under normal conditions) without significant loss of accuracy. When the molar fraction of hydrogen in the gas changes from 0 to 40%, the kinematic viscosity of the gas under normal conditions increases by almost 60%. In this case, the corresponding value of the dynamic viscosity of the gas increases by only 2%. That is, in hydraulic calculations of gas networks, one can neglect the change in the dynamic viscosity of the gas under normal conditions, and take into account only the change in the density of the gas. Density, low volumetric heat of combustion and the corresponding Wobbe number under normal conditions are adequately described by linear dependences on the molar fraction of hydrogen in the gas composition. The dynamic and kinematic viscosity of a gas under normal conditions can be described using a polynomial of the second degree of the molar concentration of hydrogen.
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