Improvement of reference gas calorimeter to measure the gross calorific value of the reference methane gas having high purity (99.995 %) and calculation of uncertainty

Abstract

Natural gas is the most widely used energy source among other gases. For this reason, measuring the gross calorific value with very high precision is of great importance for users and sellers. With the reference calorimeter designed in this study, it was aimed to obtain the calorific value “H_m” of the methane gas which is the principal component of the natural gas and has the EN ISO 6976:2016 standard. The measurements made with the designed and manufactured reference calorimeter were evaluated. The reference calorimeter can measure temperature, mass, power, amount of wastewater absorbed, type and amount of waste gas with the highest precision that TUBITAK-NMI (The Scientific and Technological Research Council of Turkey)-(National Metrology Institute) can measure. Measurements made with the designed calorimeter were insulated so that there is no heat exchange from the external environment, while the gas flow rate and temperature provided by using stable temperature sources are controlled. Certified calibration instruments were used in all measurements. The experiments were carried out at a temperature of 298.16 K. The methane gas with 99.995 % purity was used as the reference gas and as a result of the measurements; experimental data were obtained with errors ranging from 0.5 % / 0.1 %. Analyses from experimental data have shown that the greatest error in gross calorific value “(H_m)_G” is due to temperature and mass measurements. The mean gross calorific value obtained using eight measurements is 55460.60 kJ kg⁻¹ or 889.03343 kJ mol⁻¹ within a relative expanded uncertainty of 0.2 % (k = 2).