本文選題：LNG + 管道輸送�。� 參考：《中國石油大學(華東)》2015年博士論文

【摘要】：隨著我國液化天然氣(LNG)進口量的增加,卸載后LNG的輸送研究也應運而生。與LNG氣化后管輸相比,在液態(tài)下直接管輸不僅能夠保有其冷量加以更合理的利用和在城市輸氣管網(wǎng)中更好的發(fā)揮調(diào)峰功能,而且在相同質(zhì)量流量下,液態(tài)管輸過程中所需要提供的動力要比氣態(tài)管輸小很多。然而,在LNG的管道輸送中,采用可靠的絕熱形式以及建立科學的管輸模型是保證LNG液態(tài)輸送平穩(wěn)性和安全性的關鍵;本論文圍繞這兩方面,采用理論分析、數(shù)值模擬和實驗研究相結合的方法對LNG的管道輸及安全性輸送進行了系統(tǒng)的深入研究,主要完成了以下研究內(nèi)容:(1)進行了LNG熱物性質(zhì)的計算,在LNG的管道輸送中要充分考慮到熱力學和遷移性質(zhì)的影響。采用LKP方程編制了LNG多組分系統(tǒng)相平衡的計算程序,分別分析了不同壓力下的LNG密度、比熱容、粘度和導熱系數(shù)隨溫度的變化規(guī)律。結果表明在液相區(qū)LNG的密度、比熱容、粘度和導熱系數(shù)受壓力的影響非常小,而隨溫度的響應比較敏感;在臨界點附近相關的熱物性質(zhì)參數(shù)隨壓力和溫度的變化較為劇烈;在氣相區(qū),天然氣的相關熱力學參數(shù)受壓力變化的影響增大,而對溫度響應有減弱的趨勢。(2)對于LNG輸送管道能夠采用的堆積絕熱、真空絕熱、真空多層絕熱形式進行傳熱過程分析和熱阻構成的討論,并進行了比選。在絕熱性能上真空多層絕熱略優(yōu)于真空絕熱,真空絕熱優(yōu)于堆積絕熱;若選用單純的真空絕熱,一旦在LNG管道輸送的過程中真空度喪失,則絕熱性能將會大幅度下降,故在LNG的管輸中采用了對真空度要求不高的、絕熱性能好的真空多層絕熱。在二維穩(wěn)態(tài)假設前提基礎上,對真空多層絕熱管道進行了柱坐標系下的傳熱機理分析,包含有反射屏間的輻射換熱、氣體分子的導熱和反射屏間固體的導熱;通過編制程序計算得到了不同真空度量級下真空多層絕熱管道各層的溫度和徑向上的熱流密度值。(3)將給定組分下LNG進行了相態(tài)劃分,分為過冷相態(tài)、密相和超臨界相態(tài);給出了LNG在管輸送過程的數(shù)學模型,在真空多層絕熱管道中LNG管輸過程為徑向和軸向上的二維穩(wěn)態(tài)過程,給出了流場和溫度場的邊界條件;得到了LNG在軸向上的溫度變化規(guī)律。由于采用絕熱性能較好的真空多層絕熱管道輸送,在輸送方向上LNG的溫升并不迅速,故提出長距離管輸條件是要滿足在管輸過程中任一截面上的溫度要低于其截面壓力所對應飽和溫度,即過冷度以保證過冷態(tài)。在此基礎上提出了液態(tài)最遠輸送距離的計算方法,通過編制程序得到了LNG在給定管道入口溫度的條件下的最遠輸送距離,討論了其影響因素入口壓力、管內(nèi)壁熱流密度、管內(nèi)徑和輸量對最遠輸送距離越的影響。(4)進行了管輸過程絕熱安全性的分析。在LNG管道的輸送過程中內(nèi)管破損和外管破損的出現(xiàn)會使得LNG輸送過程中真空度逐漸喪失,使絕熱性能下降、LNG的過冷態(tài)喪失。分別分析了內(nèi)管破損、外管破損傳熱過程的變化。在基于假設的前提下分析了管道夾層環(huán)形空間的自然對流換熱對整個換熱的影響,建立了傳熱模型。通過編制程序分析得到了真空管道外壁溫度、絕熱材料的層數(shù)、絕熱材料的導熱系數(shù)和包扎密度對絕熱喪失后熱流密度的影響。結果表明,外管壁面溫度越高,漏熱量越大;絕熱材料的層數(shù)越多,漏熱量越小;包扎越緊實、密度越大,漏熱量越大;間隔物熱導率越小,漏熱量越小。(5)對LNG真空多層絕熱管道的真空喪失過程進行了實驗研究,采用液氮代替LNG,在不同絕熱材料層數(shù)下測得了真空喪失后的環(huán)形空間的壓力、夾層材料壁面溫度和漏熱率,并在此基礎上采用分子動力學的方法對內(nèi)壁裂紋擴展進行了微觀研究,將實驗數(shù)據(jù)和模擬結果進行了分析比對,其結果變化趨勢吻合較好,為LNG長距離管道輸送的平穩(wěn)和絕熱安全性提供了有力保障。
[Abstract]:With the increase of the import of liquefied natural gas (LNG) in China, the transport research of LNG after unloading has come into being. Compared with the LNG after gasification, the direct pipe transport in liquid can not only protect its cooling capacity more rationally and better play the peak function in the urban gas pipeline network, but also the liquid pipe is transported under the same mass flow. However, in the pipeline transportation of LNG, the key to ensure the stability and safety of LNG liquid transport is to adopt reliable adiabatic form and establish a scientific pipe transport model. This paper uses theoretical analysis, numerical simulation and experimental research in these two aspects. The pipeline transportation and safe transport of LNG have been systematically studied. The following research contents are completed: (1) the calculation of the properties of LNG hot material is carried out. The influence of thermodynamics and migration properties should be fully taken into account in the pipeline transportation of LNG. The calculation program of phase equilibrium of LNG multi component system is compiled with LKP equation. The LNG density under the same pressure, the specific heat capacity, viscosity and thermal conductivity change with the temperature. The results show that the density of LNG in the liquid phase region is very little influenced by the heat capacity, viscosity and thermal conductivity, and is more sensitive to the response of the temperature; the properties of the related thermal properties near the critical point are more intense with the pressure and temperature. In gas phase, the relative thermodynamic parameters of natural gas are increased by pressure change, and the temperature response has a tendency to weaken. (2) the heat transfer process analysis and thermal resistance composition of the LNG pipeline can be analyzed and the thermal resistance composition is discussed. Adiabatic insulation is better than vacuum insulation, and vacuum insulation is superior to accumulation adiabatic. If the vacuum insulation is lost in the process of LNG pipeline transportation, the insulation performance will decrease greatly. Therefore, the vacuum multilayer insulation which is not high in vacuum and good in adiabatic performance is used in the pipeline transportation of LNG. On the basis of this, the heat transfer mechanism of the vacuum multi-layer insulation pipeline is analyzed, including the radiation heat transfer between the reflecting screens, the heat conduction of the gas molecules and the heat conduction between the solid in the reflecting screen, and the temperature and the radial flow density of the various layers of the vacuum multi-layer adiabatic pipelines under different vacuum measurements are calculated by programming. (3) (3) the phase state of the given component is divided into the supercooled phase state, the dense phase and the supercritical phase state. The mathematical model of the LNG in the pipeline transportation process is given. The LNG tube transmission process in the vacuum multilayer insulation pipe is a two-dimensional steady process in the radial and axial direction, and the boundary conditions of the flow field and the temperature field are given, and the LNG is obtained in the axial direction. The temperature change law. The temperature rise of LNG is not rapid in the direction of transportation because of the vacuum multilayer insulation pipeline with good insulation performance. Therefore, it is proposed that the long distance pipe transmission condition is to meet the saturation temperature of any section in the pipe transmission process below the pressure of its cross section, that is, supercooling to ensure the supercooling state. The calculation method for the farthest transportation distance of the liquid is put forward. Through the program, the farthest transportation distance of LNG at the inlet temperature of the given pipeline is obtained. The influence factors entrance pressure, the inner wall heat flux density, the inner diameter and the mass of the pipe on the farthest transportation distance are discussed. (4) the insulation safety of the pipe transmission process is divided. In the process of transportation of the LNG pipeline, the breakage of the inner tube and the breakage of the outer tube will cause the gradual loss of the vacuum degree in the process of LNG transportation, the decrease of the insulation performance and the loss of the supercooling state of the LNG. The changes in the internal pipe breakage and the damage of the outer tube are analyzed respectively. The natural pairs of the interlayer annular space in the pipeline are analyzed on the premise of the hypothesis. The effect of heat transfer on the heat transfer is established. Through the program analysis, the influence of the temperature of the outer wall of the vacuum pipe, the number of adiabatic materials, the thermal conductivity of the adiabatic material and the density of the coating on the heat flux after the adiabatic loss are obtained. The results show that the higher the temperature of the wall, the greater the temperature of the wall of the outer tube, the greater the heat leakage, and the more the layers of the adiabatic materials. The smaller the leakage heat, the smaller the density, the greater the density, the greater the density, the larger the density, the smaller the heat leakage of the spacer. (5) the vacuum loss process of the LNG vacuum multilayer insulation pipeline was experimentally studied. The pressure of the annular space after the vacuum loss was measured under the different layers of adiabatic materials, and the wall surface of the sandwich material was measured under the different layers of adiabatic materials. On the basis of the temperature and leakage heat rate, the crack propagation of the inner wall is studied by means of molecular dynamics. The experimental data and the simulation results are compared and compared. The change trend of the results is in good agreement, which provides a strong guarantee for the stability and adiabatic safety of the LNG long distance pipeline transportation.
【學位授予單位】：中國石油大學(華東)
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TE832

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