ABSTRACT
Pipeline quality natural gas specifications include limits on acid gases, water content, and higher heating value. This chapter focuses on removing the higher hydrocarbon components to meet heating value specifications and to recover the valuable natural gas liquids (NGLs). The chapter initially discusses retrograde condensation and the cricondentherm, which dictates the highest temperature that the gas could form a condensate. It then describes the propane refrigeration process, which is needed to cool the natural gas. An overview of the turboexpander technology used for additional refrigeration is given, followed by an overview of fractionators, including demethanizers. Next, liquid removal processes are discussed. They are grouped based upon the desired level of ethane and propane recovery, and thus the lowest temperature is needed. The low temperature separator is discussed for low ethane and propane recovery. A cyclone and membrane technology also are covered. Direct refrigeration and lean oil process are used to recover roughly 60% of ethane in the gas. Finally, high ethane recovery processes are discussed, beginning with a simple process illustrating basic concepts and then going to modern, more complex processes.
