STUDY OF THE NATURAL SOIL TEMPERATURE FIELD AND ITS EFFECT ON THE THERMAL REGIME OF UNDERGROUND MAIN GAS PIPELINES

Abstract

This article investigates the natural temperature field of the upper soil layers and assesses its impact on the thermal regime of underground gas transmission pipelines. The study is relevant because there is a need to improve the accuracy of thermal-hydraulic calculations for gas transmission systems in the context of current climate change, since natural soil temperature is one of the key factors governing heat exchange between transported gas and the surrounding environment. The study aims to refine the method of determining the natural soil temperature field by utilising modern climatic data, and to ascertain its impact on the thermal state of main gas pipelines. Analytical methods of mathematical modelling of non-stationary heat conduction processes were employed. A one-dimensional heat conduction equation for a semi-infinite soil mass, with the relevant initial and boundary conditions, was considered. The boundary condition at the soil surface was a harmonic law of atmospheric air temperature variation. Modern climatic normals for Ivano-Frankivsk for the period 1991–2020 were employed to account for current climatic trends. Analytical relationships were obtained to describe soil temperature as a function of depth and time, and the regularities of attenuation of seasonal temperature fluctuations and phase shifts with increasing depth were established. Numerical simulations of soil temperature changes at different depths were performed and presented graphically. An engineering assessment was carried out to analyse the impact of the natural temperature field on the thermal regime of a DN 700 main gas pipeline. The study showed that accounting for actual seasonal soil temperature variations enables more accurate predictions of transported gas temperature, helps to determine pressure loss patterns along the pipeline route and improves the reliability of compressor station energy consumption assessments. The study revealed that the most intensive temperature changes occur in the upper soil layers. At the depth at which the pipeline is laid, temperature fluctuations become less pronounced, but are still sufficient to affect gas transportation parameters. The study's scientific novelty lies in its improved approach to determining the natural temperature field of the upper soil layers using modern climatic data, thereby increasing the accuracy of thermal regime forecasting for underground main gas pipelines. The practical significance of the results lies in their applicability to thermal-hydraulic calculations for gas pipeline operation, estimation of pressure loss, optimisation of compressor station operating conditions and improvement of design and operating methodologies for gas transmission systems.