Malisevych N. Measurement of Heat of Combustion of Natural Gas Using Face Orifices

The paper analyzed current state of the scientific, regulatory and technical means for measuring the heat of combustion of natural gas. The concept of the heat of combustion of natural gas was studied. The direct and indirect methods for measuring the heat of combustion of natural gas, as well as the technical means for implementing these methods under laboratory conditions and when carrying out express control of the natural gas quality at consumers’ places of residence were considered. The modern domestic and foreign regulatory framework for determining the heat of combustion of natural gas was evaluated. It was shown that the measurement of the heat of combustion of natural gas at the place of its consumption is a necessary component to improve the accuracy of natural gas consumption metering and can be implemented. The conducted analysis was used to substantiate the relevance and appropriateness of improving the methods and means for measuring the heat of combustion of natural gas at the place of its consumption. The tasks to be solved were formulated and the directions of the thesis studies were grounded. The theoretical studies of the process of measuring the heat of combustion of natural gas based on the use of the temperature of combustion of natural gas as the main measured informative parameter were carried out. The factors influencing the temperature of gas combustion were examined. The computer modeling was utilized to examine the influence of the studied gas humidity and influence of the ambient air humidity on the results of measurement of the heat of combustion of natural gas. A similar method was used to investigate the relationship between the physical characteristics and composition of natural gas and its heat of combustion when measuring the gas flow rate with the help of the face orifice transducers. The influence of the gas density and nitrogen content on the adiabatic exponent and gas expansion factor when measuring the flow rate with the help of the face orifice as a part of the gas burner and subsequent influence of the heat of combustion of natural gas under these conditions on the determination results were studied. The mathematical model for the relationship between the heat of combustion of natural gas and its combustion temperature during the combustion of gas-air mixtures with various qualitative compositions and different volumetric ratios was obtained on the basis of the results of the theoretical and experimental studies. The relationships between the heat of combustion of natural gas and its thermophysical characteristics provided that the flow-rate measuring face orifice transducers are used as a part of the gas combustion device were obtained. It allowed studying the influence of the composition of natural gas on the informative parameters of the tool for measuring the heat of combustion of natural gas. An algorithm for determining the compressibility factor of biogas, which is considered to be a pre-requisite when measuring its heat of combustion by means of the developed method based on the measurement of the combustion temperature, was worked out and studied metrologically. A laboratory bench was worked out for experimental studies of the method for measuring the heat of combustion of natural gas according to its combustion temperature. The influence of the qualitative and quantitative composition of the gas mixtures on the flame temperature of the studied gas at different values of the gas flow rate and changes in the conditions of its combustion was studied experimentally. The actual flame temperature was measured experimentally for the conditions of the laboratory bench and the difference between this flame temperature and reference data was established. The possibility of measuring the flame temperature by thermal transducers with protective casings and taking this factor into account when calibrating the tool for measuring the heat of combustion of natural gas was detected. The possibility of implementation of the device for express control of the heat of combustion of natural gas with the help of the informative parameter such as the temperature of combustion of the studied gases was substantiated on the basis of the results of the experimental studies. The applied aspects of the use of measuring control of the heat of combustion in modern gas meters were considered. They relate to the utilization of the SMART-technology elements. The results of the metrological studies of the developed method for measuring the heat of combustion of natural gas were considered. The metrological analysis of the method for determining the heat of combustion of natural gas based on the application of the theory of errors and concept of uncertainty, which substantiates the possibility of practical application of this method at the place of gas consumption, was carried out.