摘要：

随着全国天然气长输管道一张网基本形成及向全社会公平开放，不同托运商、不同气源的天然气可能在管网中发生掺混。为保证天然气交接计量的公平性，在交接过程中应当以热值或能量计量取代传统的体积计量。旨在提出一种具有组分跟踪功能的多气源管网运行仿真方法，其可以为未安装在线气相色谱分析仪的B级和C级计量系统提供较准确的天然气组分数据。建立了包括动量方程、能量方程、气体组分连续性方程及其定解条件的多气源管网瞬态运行数学模型，并采用数值仿真方法求解该模型，从而跟踪管网中气体组分数据随时间和空间位置的变化。数值仿真采用时间层递推模式，为减少计算量，在每一时间层将各离散网格节点(格点)上待求解的气体流动状态参数与气体组分数据解耦。解耦的基本思路是：基于前一个时间层的气体组分数据，用特征线法联立求解全组分连续性方程、动量方程和能量方程，然后基于特征线法求得各格点的流动状态参数值，用有限容积法联立求解组分连续性方程，从而得到当前时间层各格点的气体组分数据。为避免数值计算结果出现越界和时间域上的局部振荡现象，组分连续性方程中的对流项采用高阶有界离散格式，并运用延迟修正技术将其纳入源项。基于上述特征线法与有限容积法的融合算法编写了相应的仿真程序并将其应用于某枝状管网，其气体组分数据仿真结果与TGNET的最大绝对偏差为0.3%。

关键词: 天然气管网, 仿真, 能量计量, 组分跟踪, 特征线法, 有限容积法

Abstract:

As the national pipeline system is gradually established and relatively open to society, natural gas from different shippers and sources can be blended in the pipeline network. To ensure the fairness of custody transfer metering, traditional volumetric metering should be superseded by calorific metering or energy measurement. This paper proposes an operational simulation method for multi-source gas pipeline networks with gas composition tracking, which can provide more accurate gas composition data for Class B and Class C metering systems that are not equipped with online gas chromatography. A transient mathematical model for multi-source gas pipeline networks was constructed, incorporating the momentum, energy, and composition continuity equations along with their corresponding initial and boundary conditions. The numerical simulation method was applied to track gas composition in the pipeline network over time and space, conducted in a time-level recurrence mode. To reduce the simulation’s computational capacity, the gas flow-state parameters to be solved at each discretized grid node are decoupled from the gas composition at each time step. The fundamental idea of decoupling is that the whole composition continuity, momentum, and energy equations were evaluated by the method of characteristics (MOC) coupled with the gas composition from the previous time level. Then, based on the flow-state parameters calculated by the MOC, the gas composition continuity equation was addressed by the finite volume method (FVM). Hence, the gas composition of each discretized grid node at the current time level is obtained. In order to avoid undershoot/overshoot and local oscillation phenomena in the time domain, the convective term of the composition continuity equation was discretized using a high-order bounded scheme, and the deferred correction approach was employed to incorporate it into source terms. The combined algorithm was applied to a branched network to verify its accuracy and feasibility. The results of the case study show that the maximum absolute deviation (MAD) in composition was 0.3% compared with TGNET.

Key words: gas pipeline network, simulation, energy measurement, composition tracking, MOC, FVM