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Development of Compact Heat Exchanger for LNG FPSO

Seungwhan Baek, Gyuwan Hwang, Jinhyuck Kim, Sangkwon JeongCryogenic Engineering Laboratory, Department of Mech. Eng. KAIST

Daejeon, KoreaReactor & Safety Evaulation Department, KINS

Daejeon, Korea

ABSTRACT

LNG-FPSO (Liquefied Natural Gas - Floating Production Storage and

Offloading) is a promising energy-efficient method compared toonshore NG (Natural Gas) treatment facility when the gas well islocated in a distant offshore ocean. The heat exchanger for LNG-FPSOshould be more compact than the ones in onshore liquefaction plant dueto its limited platform area. PCHE (Printed Circuit Heat Exchanger) is

a newly developed heat exchanger with favorable characteristic ofcompactness. In this paper, we fabricated PCHE, and applied to MR-JT(Mixed Refrigerant Joule Thomson) cycle to simulate SMR (SingleMixed Refrigerant) process. Tube heat exchangers are also fabricated

to compare performance of cooling system. The experimental results ofthe MR-JT cooling system are discussed in this paper.

KEY WORDS: LNG; FPSO; PCHE; Axial conduction; MR-JT

INTRODUCTION

LNG (Liquefied Natural Gas) implies the liquid state of natural gas,which is liquefied at temperature around -161 (112 K) (Waldmann,2008). The composition of NG (Natural Gas) is mostly methane. Theliquid density at the normal boiling point of methane is approximately

610 times greater than that of the gas at ambient temperature andpressure. Consequently, a given volume of liquid contains over 600times the heating value as the same volume of ambient gas. Thisdensity increase at ambient pressure makes it attractive to liquefy,

transport, and store natural gas in large quantities (Kidnay and Parrish,2006).

South Koreas LNG demand is currently increasing like the worldsLNG demand. LNG was the source of 25% of world energyconsumption at 2005, but this demand will be increased up to 50% in

next ten years (Allison Ball, 2003). It is important to develop moreenergy efficient LNG plant for securing future energy demand.

The offshore gas plant development is revaluated as one of the

promising energy industries, because 20% of natural gas wells areunder the sea. FPSO (Floating Production Storage & Offloading)refines, liquefies and stores natural gas from the sea. This LNG

production method has a great advantage in that it does not need totransfer natural gas from offshore place to onshore plant to liquefy it

FPSO can also transport LNG to another ship, which is cost effective(Fig. 1)

Because many types of equipment must be loaded on the smalplatform ship in FPSO, there are some technical constraints for FPSO

as follows (Michael Barclay, 2005).

- Lightness of the ship- Compactness- Safety

One of the large and heavy equipments in LNG plant is a heaexchanger. Compact heat exchangers shall decrease the whole size orweight of liquefaction facility of FPSO.

PCHE (Printed Circuit Heat Exchanger) is a compact heat exchangeconstructed by chemical etching method and diffusion bonding. It is

possible to construct a PCHE with a flow channel diameter that is muchsmaller than that of a commercial plate heat exchanger by employingthese techniques.(Fig. 2) PCHE has an advantage of compactness, bu

it also has a disadvantage in performance due to axial conductionespecially in cryogenic application (Maranzana, Perry et al., 2004). FoLNG FPSO as one of the cryogenic application of PCHE, it isimportant to observe the characteristics of PCHE in a similarenvironment with LNG FPSO.

MIXED REFRIGERANT & PCHE FOR LNG FPSO

Researchers have been studying about liquefaction process for LNGFPSO. Mixed refrigerant process (Fig. 3) and nitrogen expansion

process (Fig. 4) are two big categories of candidates (Michael Barclay2005). Both processes have advantage and disadvantage in respect ofsimplicity, and safety. However, mixed refrigerant process in generashows better efficiency than nitrogen expansion cycle as indicated in

Table 1. Regarding both onshore and offshore liquefaction processesmixed refrigerant process is becoming an important technology and theusefulness MR (Mixed Refrigerant) has drawn great attention recentlyTo apply PCHE to MR process, it is important to know flowcharacteristic of mixed refrigerant at micro-channel, but they are not

152

Proceedings of the Twenty-fir st (2011) In ternational Of fshore and Polar Engineeri ng Conference

Maui, Hawaii, USA, June 19-24, 2011

Copyri ght 2011 by the International Society of Of fshore and Polar Engineers (I SOPE)

ISBN 978-1-880653-96-8 (Set); ISSN 1098-6189 (Set); www.isope.org