DRIZO® revamping of offshore TEG unit improves NGL recovery: THE EKOFISK CHALLENGE

Abstract

• ConocoPhillips is operating a TEG unit upstream of a turbo-expander NGL recovery process on its 2/4 J platform on the Ekofisk field. This TEG unit, initially designed with the  ColdFinger® regeneration process, gave from its initial start-up in 1998 insufficient water dew pointing, resulting in recurrent freezing problems in the downstream NGL recovery process. This was attributed to insufficient purity of the glycol regenerated in the Cold Finger process, reaching only a 99.3 wt % purity.
• Obtaining better TEG purities by using additional stripping gas was not considered as an acceptable solution because it would increase atmospheric BTEX emissions through the vent gas. ConocoPhillips therefore decided to use the Drizo® regeneration process which is able to reach lower water dew points and decrease the environmental impact. The revamp mainly consisted in the implementation of additional
  modules with the Drizo® equipment. These modules were designed and manufactured by Prosernat in order to cope with the very severe space limitations on the platform.
• The implementation of the Drizo® modules on the platform was performed in only two weeks and after commissioning the TEG regeneration could be shifted to Drizo® operation without necessitating any production downtime. Today the Drizo® loop enables to achieve a 99.95 + wt % glycol purity (water dew point in the treated gas of less than - 50 °C) with no downstream freezing problems. Start-up and operation of the revamped unit are being described in details in the paper.