UOP World Scale LNG Feed Pretreatment Technology Tech Paper

8/10/2019 UOP World Scale LNG Feed Pretreatment Technology Tech Paper

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Copyright 2008 UOP LLC 1

World Scale LNG Feed Pretreatment TechnologyThe Advantages of an Integrated Approach

ABSTRACT

Natural gas streams are typically treated for control and removal of multiple acid gascontaminants and in most cases these compounds can not be removed cost effectivelyby a single technology. The geographic origin of the gas will define the quantity and typeof acid gases that must be dealt with. A complex project for treating Middle East sourcenatural gas will be required to deal with mercaptan sulfurs as well as the traditional H2S.The addition of mercaptan sulfur as a contaminant makes the acid gas control a little

more technically challenging. The type and quantity of acid gas components that needto be controlled will dictate the number of technologies and units required to meetrequired product specifications. The number of technology units and how they areintegrated will significantly impact overall project economics and success.

UOP has designed and implemented a unique flow-scheme which is being utilized toeffectively remove and control all acid gas components prior to liquids recovery. Theflow-scheme takes advantage of each technologys strength while maximizing integrationto minimize capital and operating costs. The flow-scheme minimizes the number ofrequired units and optimized integration results in a very cost effective and technicallycomprehensive complex. This presentation will provide information on the technicalapproach to treat complex feed streams along with the technical advantages to theintegrated design.

INTRODUCTION

Gas processing can range from simple treating and conditioning for pipeline delivery tocomplex operations needed to meet specifications to produce liquefied natural gas(LNG). Natural gas requires a removal of acid gas compounds such as CO2, H2S,COS, organic sulfur compounds, water and mercury to meet end product specificationsand to avoid product blockages in the downstream process equipment. The level oftreating requirements varies according to the treated gas product specifications and localenvironmental regulations. World-Scale LNG & NGL Plants face ever increasingchallenges and complexities. Some of the key issues are:

Larger Single Train Size

More Difficult Feedstocks More Stringent Product Specifications More Stringent Environmental Regulations More Remote Locations

To maximize performance and production, while addressing these challenges, some ofthe key considerations for gas processing selection for facilities are:

Mitigation of Risk Control on Project Schedule


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Replication of the Same Process Design for Subsequent Trains Plant Availability/Reliability Longer Run Times between Turnaround Maximize Hydrocarbon Yield Maximize Sulfur Recovery Maximize Efficiency Elimination of Waste and By-Product Streams

Historically, front-end gas processing purification and separation with ConventionalProcess Flow Schemes has been used. In such flow schemes, the natural gas feedstockis first treated by removing H 2S, CO 2, H 2O, and Mercury (Hg) to extremely low levels invarious gas purification steps. The feedstock is then separated into individualhydrocarbon C1 through C5+ fractions. The gas-phase C2 fraction undergoes furtherCO 2, H 2S, & H 2O removal, while the liquid-phase C3 through C5+ fractions are treatedfor Mercaptan (RSH), Carbonyl Sulfide (COS), & H 2O removal. Traditionally theEngineering Contractor (EPC) is responsible for pulling together the individual unit

operations, with the assistance of product vendors for each of the unit technologies.

An alternate method is to use an Integrated Systems approach, whereby a single gasprocessing technology supplier works directly with the client/operator to determine theoptimal design for the facility on an integrated basis. The EPC still plays an importantbut supporting role in this approach. The result is that the challenges and complexitiescited above are more effectively addressed.

The Integrated Systems approach was used in a number of Middle East projects withUOP as technology supplier. Three trains have been successfully commissioned sinceearly 2004, with two more under construction. Additionally a project for the production of

Sales Gas has been commissioned, and second train is currently under construction.

CONVENTIONAL FLOWSCHEME WITH INDIVIDUAL PROCESSES(Liquid-Phase Desulfurization)

The Conventional Flow scheme is composed of gas-phase and liquid-phase processes,as illustrated in the block flow diagrams of Figures 1

Gas-phase treating compromises H 2S and CO 2 removal via an Amine Acid Gas RemovalUnit, water removal via a Molecular Sieve Dehydration Unit, separation of C1 through

C5+ hydrocarbon fractions utilizing a Turbo Expander and NGL Fractionation. The CO 2 or CO 2 and H 2S removal from the C2 fraction is done using Amine processing followedby water removal using Glycol or a Molecular Sieve Dehydration Unit.


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Desulfurization Unit is treated in a Selexol Unit with the acid gas stream sent to a ClausSRU for conversion into elemental Sulfur and the desulfurized regeneration gas is eithercompressed and recycled back to the entry of the Amine Unit, and/or used as fuel for agas turbine for facility power generation. In this flow-scheme the C1 through C5+hydrocarbon fractions are also separated via a Turbo Expander and subsequent NGL

Fractionation but the C3 and C4 Fractions are treated in liquid-phase Molecular SieveUnits for sulfur polishing to insure all product specifications are met.

Figure 2. UOPs Integrated Flow Scheme (Gas-Phase RSH Removal)

The potential advantages of the Integrated Flow Scheme are clearly higher overallefficiency, higher overall hydrocarbon yields and higher overall sulfur recovery. Thecombination of the Molecular Sieve Unit and the Selexol system removes mercaptansulfur from the regeneration gas and delivers it to the Claus SRU. Additionally, insituations where NGL recovery is not planned, the Integrated Flow Scheme achieves thefinal purified gas product specifications, particularly total sulfur content. The installationof a Turbo Expander to condense the Sulfur species into the liquid NGL is not required.

The Integrated Flow scheme results in lower overall operating costs, in terms of lowerutilities, lower waste disposal costs, higher hydrocarbon recovery, and higher sulfur

recovery.

COMMERCIAL EXPERIANCE For several large processing trains in the Middle East the clients were looking to changethe approach for the front end gas processing. The critical project objectives included atechnology approach with a flexible design but one that would be easily applied andcopied for all trains. This would achieve project cost savings, schedule improvementsand execution benefits.


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The client elected to utilize UOPs Integrated Front-end Gas Processing technology asthe project basis. Figure 7 presents the Block Flow Diagram for the UOP IntegratedFlow Scheme, which is comprised of an Amine Guard FS unit for complete H 2S & CO 2 removal and bulk COS removal, a Molecular Sieve system for H 2O, RSH, & Hg removal,

a Selexol unit to treat the spent regeneration gas from the Molecular Sieve Unit.When NGL recovery is part of the complex flow-scheme it has been accomplished usingOrtloff Engineers LTD Turbo Expander and Fractionation technology. UOP and Ortloffhave an alliance that incorporates Ortloffs NGL Recovery technology in UOPsIntegrated Flow scheme.

There are four trains now in successful operation using the UOPs Integrated Flowscheme approach and three additional trains are expected to be operation in 2008 and2009 with a total capacity of ~14 Bcfd. All these trains reflect the largest single-traincapacity natural gas processing plants in the world.

UOP PROCESS TECHNOLOGIES & KEY DESIGN ISSUES

Amine Guard FS (1)

The Amine Guard FS Unit incorporates the use of UCARSOL (2) AP-814, aproprietary, promoted Methyldiethanolamine (MDEA) Amine solvent. The amineabsorber utilizes UOPs Multiple Downcomer (MD) Trays. These permit highvapor/liquid load handling of large feed gas flows, leading to smaller towerdiameter and reduced tower wall thickness, especially for the high-pressure

Absorber Tower. Additionally, UOPs direct design control of the mass transferinternals insures the critical product gas specifications will be met.

Molecular Sieve Unit

The Molecular Sieve Unit design and performance is critical to assure all productspecifications are met. The removal of H 2O, RSH, and Hg is accomplished byusing three distinct adsorbents. Tailoring the adsorbent to the intended speciesfor removal maximizes performance while minimizing bed size.

Selexol Unit 2

The Selexol Unit is accountable for capturing the mercaptan sulfur in theMolecular Sieve Unit regeneration gas. UOP has designed the Selexol Unit withpeak-dampenin g operation of the sulfur concentration in the acid gas. Aconstant flow of 1 rich solvent, with a constant sulfur composition from the surgedrum to the Regenerator, permits minimal fluctuation in the sulfur composition inthe acid gas.

1. Amine Guard FS is a registered trademark of UOP LLC 1.2.SELEXOL and UCARSOL are registered trademarks of DOW Corporation.


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Ortloff NGL Recovery

The Ortloff Engineering Ltd. Turbo Expander technology is used for efficientrecovery of the individual C2 C5 hydrocarbon fractions. Ortloff is a recognized

leader in patented NGL Recovery technology that maximizes NGL recovery whileminimizing product gas compression requirements. UOP and Ortloff have analliance that allows UOP to incorporate their technology into the Integrated Flowscheme. This permits UOP and Ortloff to eliminate interfaces between differenttechnology suppliers, and allows them to work closely to insure the NGLRecovery technology is well optimized in the Flow Scheme.

CONCLUSIONS & FUTURE DIRECTION

There are four trains now in successful operation using the Integrated Flow Schemeapproach. Three larger trains are expected to be commissioned in 2008 and 2009.

These seven trains all reflect the largest single-train capacity natural gas processingplants in the world.

Reflecting back to when the initial design approach for these trains was beingformulated, and also looking forward after the experiences of the past 9 years, we offerour vision as to the path forward for future world-scale natural gas plants:

Large LNG and NGL Plants will continue to face even greater challenges A market transition to effectively deal with these challenges is occurring. It

focuses on a fundamental shift from generic Conventional Flow Schemes totailored Integrated Flow Schemes for front-end natural gas processing in world-scale LNG and NGL Plants.

The benefits of an Integrated Flow Scheme approach are:o Integration and optimization of individual unit technologies into a systemspackage

o Single-source systems engineering integration with elimination ofinterfaces

o Full wrap commercial guarantees for the systems packageo Greater facility efficiency and better environmental performanceo Significantly shorter project schedule and lower costs by replicating a

flexible systems package design for all trains.o Establishing a partner-like relationship between client and technology

provider that covers all needs from initial f acility design through continuing

technical support after years of operation.2

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UOP World Scale LNG Feed Pretreatment Technology Tech Paper