This paper is a small tutorial that addresses temperature issues in natural gas transmission systems. The paper does not present any new development or concept. It is simply an attempt to discuss temperature issues relevant in gas transmission in a way that can easily be understood by someone not deeply familiar with thermodynamics and fluid mechanics. For example the thermodynamic concepts of ‘enthalpy’ and ‘entropy’, how useful they may be, have been carefully avoided here. Moreover, this paper has been kept ‘formula-free’. For readers wishing to dig deeper into the subject, the paper contains a non-exhaustive bibliography of excellent theory papers that have been presented at various PSIG annual meetings over the years.
Temperature impacts on a number of issues in gas transmission: Pipeline transport capacity and compression energy costs Formation of natural gas hydrates and hydrocarbon condensation Thermal stress on pipeline material, permafrost thawing, and similar Gas temperature in a pipeline is affected by the conductive and convective transfer of heat in a radial direction, by the accumulation of heat in the surrounding soil, and by the Joule-Thomson effect. Compression adds heat to the gas, resulting in an increase in the temperature of the gas discharged by the compressor. Aftercoolers can help to decrease compression fuel costs and may be necessary to avoid damage to the pipeline's bitumen coating. Pressure reducers cause the gas outlet temperature to drop due to the Joule-Thomson effect. At low gas temperatures and other conditions, hydrates may form, or natural gas liquids may condensate. The numerical examples presented here apply for a 39" test pipeline that is 100 miles long. It has a compressor station at the outlet to recover the pressure to the initial pipeline supply pressure. These examples have been computed with SIMONE 5.6. Pipeline configuration data is documented in the Appendix.
‘Internal energy’ is the total amount of the kinetic and potential energy of the molecules confined in a gas volume. Internal energy can be changed from the outside world across the volume boundaries by adding or withdrawing energy in the form of work and/or heat. The gas temperature rises if internal energy is built up, and decreases if internal energy is reduced. This is true as long as the gas does not condense. As shown in Figure 1, this concept has already been known and applied for a long time. Heat can flow between adjacent bodies if there is a difference in temperature. The flow is always directed from the warmer to the cooler body. The resulting flow tends to level out the temperature difference. Therefore a heat flow from the outside into the confined gas volume will warm it up, while withdrawing heat from the gas will cool it.
