Enhancing the Supersonic Gas Separation operating envelope through process control strategies of the feed conditioning plant for offshore CO2 removal from natural gas

https://doi.org/10.1016/j.ijggc.2019.102928Get rights and content

Highlights

  • One of the potential technologies for offshore CO2 capture is Supersonic Gas Separation (SGS).

  • Robust feed conditioning process plant is required due to stringent requirements of cryogenic temperature, pressure and inlet CO2 composition.

  • Control strategies for the SGS feed under ±15% disturbances in temperature, pressure and ±5 mole% variations in CO2 are studied.

  • Effective disturbances elimination in the first flash separator of the SGS feed plant is crucial in minimizing the impact to the SGS operation.

  • PID controller performs significantly better in disturbance rejection than Model Predictive Control.

Abstract

Centrifugal Fluid Separation technology, in particular Supersonic Gas Separation (SGS), is one of the potential technologies considered for offshore CO2 capture. SGS has advantages in terms of CAPEX, hydrocarbon losses, footprint, tonnage and power requirement compared to conventional solutions such as membrane. Even though the technology has been developed since 1989, the applications are limited to mainly dehydration and hydrocarbon dew pointing. For CO2 separation from natural gas, substantial development works are needed prior to the field application as there are a lot of uncertainties in the feed conditions to be tackled. In particular, the stringent requirements of cryogenic temperature, high pressure and inlet CO2 composition of its feed require a robust feed conditioning process plant. For a relatively new technology such as SGS for CO2 removal application, it is crucial to investigate and assess the variations of feed and process conditions i.e. temperature, pressure and gas compositions prior to being applied at actual field, as these will impact the CO2 separation performance inside the separator. Hence, this paper investigates the control strategies for the SGS feed conditioning plant subjected to ±15 % disturbances in temperature and pressure, and ±5 mol% variations in feed CO2 composition. Results show that effective disturbances elimination in the first flash separator of the feed conditioning plant is crucial in minimizing the impact to the SGS operation. A comparative study reveals that standard PID controller performs significantly better in disturbance rejection than Model Predictive Control.

Section snippets

CO2 separation from natural gas

Natural gas is a vital component of the world’s energy supply. It is the cleanest, safest and most useful of all energy sources. Natural gas is a mixture of hydrocarbon gases and the composition varies according to where it is found. Most of the composition is made up of methane, which usually makes up to 80–95 % of the gas. The remaining is made up of other hydrocarbon gases, such as ethane, propane, butane and others. Other elements, like carbon dioxide, hydrogen sulphide, mercury, nitrogen

Methods

The overall flowchart on the methods adopted in this paper is as shown in Fig. 2. The work includes steady state and dynamic simulation of the feed conditioning plant of the SGS and process control design evaluation. The optimum process parameters for the supersonic separator are identified based on existing data and the dynamic simulation and process control design are conducted based on the steady state simulation work.

Results & discussion

In this section, the results of process control strategies CS1 and CS2 are studied and reported. The comparative analysis between PID and MPC is also discussed.

Conclusion & recommendation

Supersonic Gas Separation technology has been identified as one of the most promising technology for CO2 removal application. Stringent requirement of SGS technology which are specifically high pressure (∼80 bar), cryogenic temperature (∼−50 °C) and CO2 composition (20∼25 mol% CO2) further makes it crucial to properly design optimal control strategies which can cater for feed disturbances in the feed conditioning plant. If one of the variables failed to be controlled within its tolerable limit,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors would like to thank MRA project 0153B2-E53 (PETRONAS Research Sdn. Bhd. (PRSB)) for the funding provided and Universiti Teknologi PETRONAS for the support provided in this work.

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