New Physical Solvent Treating Configurations for Offshore High Pressure CO2 Removal
Authors: Mak J. , Wierenga D. , Nielsen D. , Graham C. , Viejo Aliso 
Published: June 2014

This paper describes patent pending, physical solvent based gas treating configurations for removing acid gas from high-pressure natural gas streams. The processes are targeted for offshore applications where the feed gas CO2 partial pressure is above 60 psia. These new configurations are based on the physical solvent propylene carbonate (FLUOR Solvent ?). The advantages of these new configurations include no fired duty for solvent regeneration, high CO2 solubility (scf CO2/gallon solution), no process makeup water requirements, minimal hydrocarbon losses, operational simplicity, and a dry treated gas.

Introduction

As high quality natural gas resources are being depleted, it is becoming necessary to produce less desirable natural gas reserves. In some cases, the acid gas concentration in these reserves is very high and the economics of producing pipeline quality gas are marginal. As the need to develop these marginal reserves increases, there is a demand for novel processes designed to economically remove acid gases.

This paper describes new technology developed by Fluor for removing high concentrations of CO2 from natural gas. The focus of the paper is on the use of this new technology offshore as some producers are now developing deepwater offshore reserves that have a high CO2 content.

The FLUOR Solvent process is one of the most attractive processes for offshore gas treating when the feed gas CO2 partial pressure is high and the H2S content is comparatively low. Fluor has developed several new FLUOR Solvent configurations (patents pending) that have extended the application of the FLUOR Solvent process to a wider range of gas streams with high CO2 content. In addition, a new configuration (patents pending) has been developed that can be used for the production of liquid CO2 for enhanced oil recovery. This paper discusses the process benefits and the application of these new FLUOR Solvent processes.

Offshore Treating Process Requirements

From a design and operation standpoint, an offshore gas treating facility requires a different focus than an onshore facility. Daily routine operations that are taken for granted onshore can present serious problems offshore. Operationally, the focus offshore needs to be on safety, simplicity, and reliability. Other offshore considerations are environmental requirements, corrosion mitigation, and operational flexibility. Spills are difficult to clean up and dispose of safely offshore and there are also safety concerns if the solvent is difficult to handle and hazardous. Offshore gas treating facilities also have limited staffing, which makes monitoring and controlling a complex process difficult. Equipment modifications to accommodate an increasing feed gas CO2 content are also more difficult and costly to implement offshore than onshore.

From a construction and cost standpoint, an offshore treating plant should have a minimum equipment count. This usually results in a smaller platform footprint and less weight for the jacket to support. In most cases this results in a lower installed cost. Eliminating fired equipment reduces equipment safety spacing requirements and makes the platform footprint smaller. Eliminating a steam or heat medium system reduces the total equipment count and simplifies plant operation. Eliminating amine solution water makeup requirement will eliminate the need for a high quality, low chloride water maker.