Liquefied natural gas (LNG) is one of the most promising fuels for energy supply because it has a favorable combination of environmental and economic properties in connection with new trends aimed at the development of ecological and sustainable consumption of natural resources, which ensure a constant growth in LNG consumption. The article presents an analytical review of the main technical solutions for the construction of cryogenic pipelines and insulating coating structures. The ANSYS Fluent software was used for simulation of the LNG flow in a pipeline section 10 m long with an outer diameter of 108 mm for three types of insulating coating (polyurethane (PU) foam, aerogel, and vacuum-insulated pipe (VIP)). In addition, an assessment was made of the insulating effect on the LNG temperature distribution along the length of the pipeline. The largest increase in temperature from 113 K to 113.61 K occurs in PU foam-insulated pipes; the smallest was observed in VIP. Further, as an alternative to steel, the use of ultra-high molecular weight polyethylene (UHMWPE) for pipeline material was considered. The optimal result in terms of temperature distributions was obtained while simulating the flow of an LNG pipeline with PU foam by increasing the thickness of the insulating coating to 0.05 m.
The rapid growth of liquefied natural gas consumption makes the issues of its transportation more urgent. At present, liquefied natural gas pipeline transportation is carried out only by means of short length process lines. This paper discusses the main features of cryogenic liquids pipeline transportation that obstruct its spread. The proposed model allows to carry out thermal and hydraulic calculations of an underground cryogenic pipeline. The distinctive feature of this model is the fact that it takes into account the changes in basic thermodynamic parameters of cryogenic liquid. The model is based on the Darcy-Weisbach equation and a differential heat transfer equation. In addition, the influence of the Joule-Thomson coefficient inversion on the temperature of the pumping cryogenic liquid was discussed. The comparative analysis of the pipeline construction efficiency made of ultra-high molecular weight polyethylene and AISI 321 steel was conducted. It was found that the use of polymer materials contributes to an increase in the transportation distance. The developed model can be applied for estimation of the transportation parameters change of single-phase fluid flow. The obtained results can be used in initial analysis of the process lines designing and construction.
At present the production of polymer materials is developing intensively, new materials, comparable with steels in their strength properties have recently appeared. In this connection, the analysis of polymer materials applied in the pipe industry has been carried out, and the use of ultra-high molecular weight polyethylene (UHMWPE) is proposed as a structural pipeline material, allowing pipes to operate at cryogenic temperatures. The focal point of the article is the consideration of the fracture mechanisms of those materials and the nature of the change in the mechanical properties of UHMWPE under cryogenic temperatures, also taking into account the creep process. The expression for determining the value of the creep modulus depending on the temperature and operating time was obtained. A method is proposed for conducting initial strength estimation. Moreover, the computer model of stress-strain state of an underground cryogenic polymer pipeline for liquefied natural gas transportation is obtained. The results of simulation depict the potential possibility of using of UHMWPE for the cryogenic pipeline construction
В связи с быстрым ростом потребления сжиженного природного газа (СПГ) вопросы осуществления его транспорта и хранения становятся все более актуальными. Наибольшее внимание исследователей привлекает транспорт СПГ по трубопроводам, так как он связан с целым рядом проблем, таких как предотвращение образования двухфазного потока по всей длине трубопровода, первоначальное заполнение и захолаживание трубы, подбор материала трубопровода, обеспечивающий необходимый запас прочности и устойчивости, грамотный выбор изоляционного покрытия и т. д. В данной работе проанализированы возможные пути решения этих проблем, описаны различные типы материалов трубопроводов, и предложено использование полимеров в качестве материала трубопровода для транспорта СПГ при низких отрицательных температурах. Предложена последовательная методика гидравлического расчета СПГ-трубопровода. На сегодняшний день хранение крупных объемов СПГ осуществляется в хранилищах изотермического типа. При проектировании систем хранения СПГ необходимо учитывать большое количество факторов, таких как особенности местности, геологии, метеорологии, особые требования по экологии, безопасности и др. В данной работе рассмотрены основные типы применяемых конструкций резервуаров, а также материалов, используемых для их сооружения. Помимо этого, предложен способ подземного хранения, который заключается в сооружении хранилища в толще породы бесшахтным способом. Грунты в условиях крайнего севера на определенной глубине всегда находятся в вечномерзлом состоянии и обладают несущей способностью, позволяющей при определенных условиях сооружать резервуары больших объемов с наименьшими металлозатратами. Для обеспечения охлаждения предлагается применить термосифоны. Сделаны выводы о достоинствах и недостатках предлагаемых технических решений.Ключевые слова: СПГ, низкотемпературный трубопровод, подземное низкотемпературное хранилище, гидравлический расчет трубопровода СПГ, полимеры, кольцо холода, термосифоны.
In recent years, there has been a steady development of systems for the production of small-scale liquefied natural gas for gas supply to remote consumers in cases where the possibilities of pipeline construction are limited. In addition, there is a tendency to use liquefied gas to replace liquid hydrocarbon fuels (gasoline, kerosene, gasoil, fuel oil). Due to the growth and emergence of new industries for liquefied natural gas consumption, the infrastructure necessary for its production, transportation and storage is being developed. The article presents an analysis of the use of the most common polymers for the pipeline construction in the oil and gas industry. The possibility of using ultra-high molecular weight polyethylene for the construction of process lines for pumping cryogenic liquids was considered. The results of experimental studies on tensile strength test and Charpy impact strength test after exposure to liquid nitrogen are presented. As a result of tensile strength tests, an increase in the strength properties of the material was observed while maintaining its plasticity. The breaking stress was 37.7 MPa, the yield strength was 27.1 MPa at liquid nitrogen temperature, while at ambient temperature, the specimen failed at 26.9 MPa, the yield strength was 20.2 MPa. The specimens, tested for impact strength by the Charpy method, after exposure for 2 h in liquid nitrogen, a certain margin of plastic properties was also showed. The stress-strain state of a liquefied natural gas pipeline made of ultra-high molecular weight polyethylene in an insulating coating was simulated using the ANSYS Mechanical software package, taking into account its thermal interaction with the soil. The maximum equivalent stress in the model was 14.4 MPa, with calculated value of 12.7 MPa, which does not exceed the yield point of the material. Thus, ultra-high molecular weight polyethylene can be considered as a promising material for use at cryogenic temperatures.
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