Abstract

Polychlorinated-biphenyl (PCB) contamination problems are prevalent in the natural gas industry especially in the pipeline transmission and distribution sectors. As a result of PCB disposal problems, many natural gas companies have been subjected to heavy fines. Considering the magnitude of the problem, the gas industry has taken the initiative to pursue a comprehensive remediation effort to cleanup pipeline and distribution systems contaminated with PCB. This study is a part of the remediation effort. This paper addresses the phase behavior of PCB-contaminated natural gas systems and explores how to utilize this information to attempt the formulation of remediation strategies. A model suitably designed for studying the problem has been developed. The model is used to investigate the distributive nature of PCB compounds and to analyze their effects on the overall phase behavior of the natural gas system. New quality line definitions are introduced for the purpose of tracing PCBs in the gas mixture. Some experimental results and model predictions are presented and discussed. A case study using actual field natural gas mixture is performed in order to demonstrate the capability of the model prediction. The study is important in assisting engineers and operators to design an effective remediation strategy to cleanup pipeline transmission and distribution lines contaminated with PCBs.

Introduction

Polychlorinated-biphenyls (PCBs) were commercially produced as complex mixtures in 1929. Because of their unique chemical stability and properties, PCBs have been used quite extensively in many industries under the trade name of Aroclor Series. One such use of PCB-based oils is as compressor lubricants for gas pipeline transmission and handling facilities. Despite the usefulness of PCBs for many industrial needs, these compounds have been reported to be hazardous. Various documented reports have shown that ingestion of PCBs can cause birth deformations of the unborn and newborn, skins irritations, liver and kidney damage. It was not until 1966 that the hazards of PCBs were recognized which led to its final ban in the U.S. in 1976, when Congress passed the Toxic Substances Control Act (TSCA).

PCBs entered the pipelines and peripheral facilities through compressor lubricants. Despite the cessation of use of PCBs for almost 20 years, they persist in the environment due to their chemical stability. Considering the magnitude of the problem and its implications to the environment, several environmental agencies, such as the Agency of Toxic Substances and Disease Registry (ATSDR) called for immediate remediation effort to cleanup PCBs from the contaminated systems. In fact, several litigations have resulted from PCB disposal problems1,2. The industry took the initiative to procure an understanding of the problem and formulate a remediation strategy through various researches. With several hundred thousand miles of pipelines criss-crossing the country, it is cost-prohibitive and perhaps foolhardy to subject the entire pipeline system and handling facilities to cleanup without identifying the parts that have been contaminated.

In order to initiate any remediation strategy concerning this problem, it is imperative to understand the behavior of these compounds as they exist in the natural gas mixture. The focus of this paper is to procure a good understanding of the phase behavior of PCB-contaminated natural gas systems especially in the area of natural gas transportation in pipelines.

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