Study On Experimental Platform For Direct Measurement Of Natural Gas Calorific Value

As a kind of clean energy,natural gas has a wide range of demand in the world.Accurate and fair natural gas trade is an important guarantee for the sustainable and healthy development of natural gas industry.The metering methods in natural gas trade mainly include volume metering,mass metering and energy metering.The use value of natural gas is to provide energy,the natural gas with the same volume or mass may have different calorific values due to different gas sources and different gas compositions.As a result,the metering and pricing by volume or mass may lead to the inconsistency between the use value and the price of natural gas.For this reason,the metering and pricing based on energy of natural gas is proposed in China,the realization of which needs to be based on the accurate measurement for the calorific value of natural gas.In this paper,a high-accuracy experimental platform for direct measurement of natural gas calorific value is designed,which is composed of gas supply system,measurement system for the mass of natural gas,calorific value measurement subject of natural gas and combustion exhaust gas composition detection system.Besides,take methane as the gas sample,the experimental procedure for calorific value measurement is developed,the related experimental parameters and the specifications and models of the equipment and pipe fittings required by the experimental platform are determined.In order to determine the accuracy of the experimental platform for direct measurement of calorific value,take methane as the gas sample,the detailed uncertainty analysis and calculation of the experimental platform are carried out in this paper.The uncertainty of type A can be calculated based on the experimental data of methane calorific value.The source of type B uncertainty include the adiabatic temperature rise ratio,the quantity of electric heating,the mass of methane involved in the combustion and the energy correction term.Each part of type B uncertainty is determined according to the technical parameters of the experimental equipment and related experimental data.After calculation,the measurement uncertainty for methane calorific value with the experimental platform is 0.14%(k=2).Study on the optimization of combustion chamber with numerical simulation is conducted in this paper,the ANSYS Fluent software is used to numerically simulate the combustion of methane in the combustion chamber,the influences of the structure and length of the mixed gas pipe,the diameter of the combustion chamber and the diameter of the methane nozzle on the carbon monoxide emission concentration are studied.Through the carbon monoxide emission concentration,the degree of complete combustion of methane can be reflected.With the goal of promoting complete combustion of methane,more appropriate structure and size of combustion chamber can be determined,which can provide reference and guidance for further achieving the complete combustion of natural gas.Through the comparison and analysis of the temperature field,velocity field and concentration field of each gas composition in the combustion chamber,it is recommended that the mixed gas pipe should be passed into the combustion chamber and the pipe length is 25 mm,the diameter of the combustion chamber and the methane nozzle are set at 44 mm and 1.5 mm,respectively.After optimization,the emission concentration of carbon monoxide dropped from 27.9 ppm to 17.8 ppm,that is,reduced by 36.2%.