ABSTRACT

Water condensation, hydrate formation and liquid hydrocarbons appearance in a gas pipeline depends on natural gas compositions, pressure and temperature. The presence of liquids implies a major maintenance costs due to scrapper operation needed to keep line clean and hydrates presence implies several risks in control or relief valves. In early design is very useful to detect this situation to analyze the way to prevent it. During the gas pipeline operation, it is a key factor and a good model can help the operator and planners tasks. Several scenarios occur during the gas pipeline operation. Pressure drop, heat transfer between soil and gas, flow, type of land and network topology are critical aspects to think about. In this paper we studied liquid condensation and hydrate formation using standard programming tools, discuss the results of simulations in steady state and try to analyze several troubleshooting in a gas pipeline network. Finally we present recommendations and conclusions about the alternatives to mitigate liquid condensation and hydrates formation.

INTRODUCTION

Figure 1 shows a simplified scheme of the system of buried gas pipelines under study. Once the natural gas is treated, this one complies with the regulatory specifications. Condensations throughout the pipeline would not have to be expected, as result of the effective application of transport regulations for natural gas in Argentina. But a bad operation of the separators at the output of a gas treatment plant or the out of specification gas injection implies the appearance of fractions of hydrocarbons that might condense. In a gas production pipeline, from the well to the treatment plant, the appearance of these phenomena is highly probable. The geometry of the control volume in the pipe is the system's border under study and is described in Figure 2. The natural gas flows in the pipe and defines a cylindrical geometry of length L and the internal diameter of the pipe, D. Water is a common component in the mixture of natural gas extracted from the reservoir well. In a range of pressure and temperature the water could condensate or derive in hydrates formation, if the natural was not properly dehydrated. Figure 3, summarizes the effects that can occur within the pipe. In order to be able to estimate the amount of water that will suffer a change of phase by a particular operation of the system, it is necessary to know the equilibrium relationships. Additionally, this tool can be used in the study of water separation equipment. An enhancement of the model allows the evaluation of the influence of external variables, such as the soil temperature.

SCOPE

The scope of this work is to analyze the possibility of water and hydrocarbons condensation or hydrates formation in different steady states of operation of the gas system network. Once presented the steps for model building, we present the results of the simulations obtained for a particular system under study.

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