Ejector Technology for Flare Gas Recovery as an Alternative to Rotating Equipment

Abstract

Abstract A reliable flare system is an important part of most oil and gas facilities. In an emergency or similar process shutdown event where pressure relief is required, the flare system must safely and reliably handle and dispose of waste gas through burning it to atmosphere. However, outside of these emergency cases, many facilities also carry out continuous or routine flaring, where purge gas, waste gas and other low-pressure gasses are sent to flare to be burned to atmosphere. As the environmental and subsequent legislative pressures have increased over recent years, Operators are actively looking for low cost, reliable Flare Gas Recovery (FGR) solutions. This involves recovering flare gas and diverting it away from the flare system to an alternative destination, thereby avoiding the need to burn the gas to atmosphere. Most commonly, recovered flare gas can be used as fuel gas or returned to production, providing some commercial value to the Operator. As most flare systems operate at low pressures (close to atmospheric pressure), gas compression is required to increase the gas pressure to allow the recovered flare gas to be used as a fuel gas or returned to production. Traditionally, rotating-type compression equipment has been employed to compress low pressure flare gas including Liquid-ring, Screw, Sliding Vane or Reciprocating-type compressors. However, due to their reliance upon moving parts in direct contact with flare gas, rotating equipment is prone to break-down. For many facilities with an FGR system, one of the most common causes of unplanned flaring is due to the breaking-down or ‘tripping’ of FGR compression equipment, counter to its very purpose to reduce flaring. These compression devices are also adversely affected by the flare gas stream, which is often poor quality. As an example, high levels of hydrogen sulphide (H2S) is a very common characteristic for flare gas streams. This ‘sour’ gas is one of the primary causes of degradation of compression equipment. In particular, this affects the equipment seals and sealing arrangements. This paper explores how Ejector technology (sometimes known as Eductors, Jet Compressors or Surface Jet Pumps) can be used as an alternative to rotating-type compression equipment for FGR and how the unique challenges of this duty are overcome.