Typically, for a high volume, low condensate-gas ratio offshore gas production field having high content of carbon dioxide (CO2), hydrogen sulphide (H2S), mercury and solid particulates having to meet Liquified Natural Gas (LNG) inlet specification would require an enormous facility exceeding the largest available floatover vessel capacity. Aside from an enormous and complex processing facility, it would also require a large emergency disposal system and sour service pipeline material to cater for start-up and process excursion scenarios. In order to obtain a commercially attractive solution while meeting technical integrity and designing for operational excellence in mind, several innovative design approaches were implemented. The scope of this paper will cover major optimization implemented at gas treatment system, emergency blowdown system, export gas pipeline, and venting system at receiving platform.

An offshore gas field uses a membrane acid gas removal unit (AGRU) to remove H2S from the sales gas and condensate stream to meet low specification and operate reliably. A stringent pre-treatment specification is a must to ensure reliability and integrity of the system. With high H2S concentration in condensate from the pre-treatment regeneration cycle, it is imperative to treat both gas and condensate stream to meet gas sales specification. This paper covers process engineering and flow assurance design implemented for gas and condensate H2S removal system and determining sour service operating envelope necessary for pipeline material selection utilizing multiphase transient simulation modelling.

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