LNG Regasification Terminals: the Role of Geography And

energies

Review LNG Regasiﬁcation Terminals: The Role of Geography and Meteorology on Technology Choices

Randeep Agarwal 1, Thomas J. Rainey 1,2 ID , S. M. Ashrafur Rahman 1,2,* ID , Ted Steinberg 1, Robert K. Perrons 1 ID and Richard J. Brown 1,2 1 Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia; [email protected] (R.A.); [email protected] (T.J.R.); [email protected] (T.S.); [email protected] (R.K.P.); [email protected] (R.J.B.) 2 Biofuel Engine Research Facility, Queensland University of Technology (QUT), 2 George Street, Brisbane, QLD 4000, Australia * Correspondence: [email protected]; Tel.: +61-410193428

Received: 31 October 2017; Accepted: 13 December 2017; Published: 16 December 2017

Abstract: Liquefied natural gas (LNG) projects are regulated by host countries, but policy and regulation should depend on geography and meteorology. Without considering the role of geography and meteorology, sub-optimal design choices can result, leading to energy conversion efficiency and capital investment decisions that are less than ideal. A key step in LNG is regasification, which transforms LNG back from liquid to the gaseous state and requires substantial heat input. This study investigated different LNG regasification technologies used around the world and benchmarked location and meteorology-related factors, such as seawater temperatures, ambient air temperatures, wind speeds and relative humidity. Seawater vaporizers are used for more than 95% of locations subject to water quality. Ambient air conditions are relatively better for South America, India, Spain and other Asian countries (Singapore, Taiwan, Indonesia, and Thailand) and provide a much cleaner regasification technology option for natural and forced draft systems and air-based intermediate fluid vaporizers. On a global basis, cold energy utilization currently represents <1% of the total potential, but this approach could deliver nearly 12 Gigawatt (GW) per annum. Overall, climate change is expected to have a positive financial impact on the LNG regasification industry, but the improvement could be unevenly distributed.

Keywords: liqueﬁed natural gas (LNG) cold energy; LNG; vaporizer; regasiﬁcation; meteorology; geography; climate change

1. Introduction The demand of world primary energy is expected to grow by 1.6% per annum during the period 2010–2030. In order to meet this requirement, energy production will need to be increased by 39% [1]. Natural gas (NG) is a natural resource that in recent years has seen a large increase in demand globally. While the share of oil in energy is forecast to dramatically decrease by 2030, NG is predicted to reach 25.9% of the world’s energy usage. LNG demand may reach up to 500 Mtpa by 2030 [1]. The major use for LNG today is power generation resulting from the growing power demand in the Southeast Asian region. Given the large scale of LNG projects, it is tempting for governments to adopt regulations from other countries. LNG is regasified using a vaporization system where transformation of LNG from liquid to the gaseous state requires substantial heat input. This step is very important in the overall energy conversion efficiency, and it is greatly affected by geography and meteorology, which in turn affects technology choices. Heat exchange technologies in use include open rack vaporizers (ORVs), submerged combustion vaporizers (SCVs), shell and tube vaporizers (STVs), intermediate fluid vaporizers (IFVs) and ambient

Energies 2017, 10, 2152; doi:10.3390/en10122152 www.mdpi.com/journal/energies Energies 2017, 10, 2152 2 of 21

Energies 2017, 10, 2152 2 of 19 Heat exchange technologies in use include open rack vaporizers (ORVs), submerged combustion vaporizers (SCVs), shell and tube vaporizers (STVs), intermediate fluid vaporizers (IFVs) and orambient forced orair forcedvaporizers air (AAVsvaporizers or FAVs). (AAVs The or current FAVs). technologies The current have technologies numerous have constraints numerous and impactconstraints on the and environment. impact on the Frequently, environment. the expensive Frequently, “cold” the energy expensive at − 161“cold”◦C ofenergy the LNG at − is161 wasted °C of whenthe LNG the is LNG wasted is vaporizedwhen the LNG using is anyvaporized of the using former any technologies. of the former The technologies. cold energy The is cold retained energy in LNGis retained during in theLNG liquefaction during the and liquefaction is a part ofand the is totala part energy of the consumedtotal energy during consumed the LNG during liquefaction the LNG process.liquefaction This process. cold energy This col cand energy be recovered can be recovered during the during regasification the regasification process byprocess various by various means, butmeans most, but terminals most terminals still use thesestill use relatively these relatively simple direct simple vaporization direct vaporization techniques, techniques, such as ORV such and as SCVORV orand IFV/AAV/FAV. SCV or IFV/AAV/FAV. The supply The and supply demand and demand of gas are of gas dependent are dependent on the on final the delivery final delivery price. Therefore,price. Therefore, technology technology innovations innovations are required are to required optimize to the optimize gas value the chain. gas value The optimization chain. The and/oroptimization improvements and/or improvements in the vaporization in the vaporization element of the element gas value of the chain gas value are expected chain are to expected result in enhancedto result in capital enhanced and operational capital and productivity operational productivity and may have and a direct may have impact a direct on the impact consumption on the patternsconsumption of gas patterns and therefore of gas and help therefore to minimize help to the minimize carbon footprint. the carbon This footprint. is particularly This is particularly important duringimportant the during transitional the transitional phase while phase the world while movesthe world from moves fossil from fuels fossil to renewables fuels to renewables There is is a lack a lack of published of published data on data geographical on geographical and meteorological and meteorological factors in LNG factors regasification. in LNG Therefore,regasification. the Therefore, aim of this the study aim isof tothis collate study datais to collate from a data diverse from range a diverse of sources, range of some sources, of which some isof notwhich readily is not available, readily available, and present and present this information this information in a form in a form that willthat providewill provi ade foundation a foundation for quantitativefor quantitative design design modelling modelling for chosen for chosen location(s) location(s) into the into future. the future. While thereWhile is there a reasonable is a reasonable amount ofamount literature of literature from industry from industry and conference and conference sources on sources LNG regasification on LNG regasification terminals terminals globally, its globally quality, isits variable quality andis variable must be and interpreted must be withinterpreted skill and with care. skill The and literature care. The review literature consisted review of only consisted eight key of peer-reviewedonly eight key papers;peer-reviewed 3 papers papers; are on LNG3 papers cold are energy on LNG utilization cold energy [2–4], 1utilization paper on thermal[2–4], 1 designpaper on of IFVthermal [5], 1 design paper on of Super IFV [5 ORV], 1 paper heat transfer on Super simulation ORV heat [6 ], transfer 1 paper simulation on AAV practical [6], 1 paper application on AAV [7], 1practical paper on application fog clouds due[7], 1to paper ambient on air fog vaporizer clouds due [8] and to ambient 1 paper on air materials vaporizer and [8] corrosion and 1 paper aspects on inmaterials LNG regasification and corrosion terminals aspects [in9]. LNG regasification terminals [9]. The paper will initially explain explain a a global global LNG LNG trade trade and and technology technology position, position, followed followed by by a adescription description of of LNG LNG regasification regasification technologies, technologies, an an analysis analysis of of key key location location factors factors by region, a brief on the potential impactimpact ofof climateclimate changechange andand somesome suggestionssuggestions onon futurefuture researchresearch opportunities.opportunities.

2. LNG Regasiﬁcation:Regasification: Global TradeTrade andand TechnologyTechnology Position Position AnAn LNG demand outlook is shown in Figure1 1 for for eacheach countrycountry [[10].10]. Currently, aa fewfew countriescountries (e.g.,(e.g., Japan,Japan, Korea)Korea) dominatedominate thisthis list,list, but many new LNG receiving terminals are under construction or in in planning planning stages, stages, worldwide. worldwide. Therefore, Therefore, the the demand dema prospectsnd prospects for countries for countries other than other the than largest the consumers,largest consumers, such as Japan,such as are Japan, increasing. are increasing. The recent The reduction recent reduction in demand in in demand Japan is in most Japan likely is most due tolikely the re-startdue to the of nuclearre-start powerof nuclear generation power generation during 2015 during and beyond. 2015 and A beyond. summary A ofsummary LNG exporting of LNG countriesexporting iscountries shown in isFigure shown2 [in10 Figure]. 2 [10].

Figure 1. Global liquefied natural gas (LNG) importing countries and quantity 2015. Figure 1. Global liqueﬁed natural gas (LNG) importing countries and quantity 2015.

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Figure 2. Global LNG exporting countries and quantity 2015. Figure 2. Global LNG exporting countries and quantity 2015.

The LNG value chain can be divided into three main parts; (i) production/liquefaction, (ii) LNG transportationThe LNG valueand (iii) chain regasification can be divided and intodistribution. three main During parts; the (i) production/liquefaction,liquefaction phase, NG is (ii) chilled LNG transportationto a liquid state and where (iii) its regasification volume is reduced and distribution. to 1/600th Duringof its original the liquefaction volume. The phase, LNG NG is transported is chilled to ato liquid its destin stateation where by its means volume of is insulated reduced to cryogenic 1/600th of ships. its original During volume. the consumption The LNG is phase, transported LNG to is itschanged destination into its by gaseous means of form insulated (“regasified”) cryogenic and ships. delivered During through the consumption gas pipelines phase, to LNGcustomers. is changed into itsApproximately gaseous form (“regasified”)500 kWh/t LNG and deliveredduring LNG through production gas pipelines is needed to customers. for compression and refrigerationApproximately, and a considerable 500 kWh/t portion LNG duringof this energy LNG productionis preserved isin neededthe LNG foras cold compression energy, which and refrigeration,has a final temperatureand a considerable of approximately portion of this−161 energy °C at atmospheric is preserved inpressure. the LNG Therefore, as cold energy, a considerable which has ◦ apotential final temperature for energy of recovery approximately exists− during161 C the at atmospheric regasification pressure. process Therefore, [4]. a considerable potential for energyFrom recoveryFigures 1 existsand 2, during it has been the regasification observed that process some LNG [4]. exporting countries also import LNG i.e., UAE,From Malaysia Figures1 andand2 USA., it has This been phenomenon observed that can some possibly LNG be exporting attributed countries to accelerated also import growth LNG in i.e.,local UAE, gas demand, Malaysia local and USA.gas production This phenomenon and/or pipeline can possibly gas availability be attributed or simply to accelerated the economics growth inof localLNG gasversus demand, pipeline local gas. gas production and/or pipeline gas availability or simply the economics of LNGA versus summary pipeline of the gas. global technology position and cold energy utilization for key regions is providedA summary below (adapted of the global from technology[10‒12]). Japan position and Korea and cold combined energy import utilization approximately for key regions 50% of is providedthe world’s below current (adapted LNG production from [10–12 (Table]). Japan 1). and Korea combined import approximately 50% of the world’s current LNG production (Table1). Japan is the biggest LNG importer in the world. Korea is the second biggest LNG importer and imported ~33 Mt during 2015. China is the third biggest LNG importer. Total LNG imports were ~20 Mt during 2015. India is the fourth biggest LNG importer. India imported ~15 Mt during 2015. Europe (defined in this study as Belgium, France, Italy, The Netherlands, Portugal, Spain, Sweden, Turkey and the United Kingdom) is a significant LNG importer. Total LNG imports were ~37.5 Mt during 2015. South America (Argentina, Brazil, Chile, Dominican Republic and Puerto Rico) is also a significant LNG importer. Total LNG imports were ~14.6 Mt during 2015. Other Asian countries (Thailand, Taiwan and Singapore) are emerging LNG importers. The total LNG imports equalled ~17 Mt during 2015.

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Table 1. Liqueﬁed natural gas (LNG) regasiﬁcation technologies: a global summary position [10–12].

Total Number of Approx. Total % of Shell % of Cold Power Country or % of ORV % of IFV % of SCV Cold Energy Recovery (Other LNG Receiving LNG Receiving and Tube Ambient Air Generation Region Technology 1 Technology 2 Technology 5 than Power Generation) 6 Terminals Capacity (Mtpa) Technology 3 Technology 4 Capacity 6 (MW) 7 Japan 49 ~195 ~98 0 0 ~2 Secondary ~40.4 Liquid N2, Cold storage Korea 4 ~45.7 100 0 0 Secondary 7 Secondary 7 - Cold storage 7 China 9 ~41 100 0 0 0 Secondary - Liquid N2 India 4 ~23.5 ~20 ~65 ~15 0 Secondary 7 -- Europe 25 ~150 ~60 0 0 0 ~40 - Inlet air chilling for power gen 8 South America 14 ~55 100 0 0 0 Secondary 7 -- Other Asia 5 ~25 100 0 0 0 Secondary 7 ~2.4 - 1 Open rack vaporization explained in Section 3.2; 2 IFV technology described in Section 3.4; 3 shell and tube technology described in Section 3.2; 4 ambient air technology described in Section 3.1; 5 SCV technology mostly employed for peak shaving with some exceptions in Europe; 6 LNG cold energy described in Section 3.5; 7 secondary means of regasiﬁcation; 8 Inlet air chilling for power generation turbines, only in Spain. Energies 2017, 10, 2152 5 of 21

Japan is the biggest LNG importer in the world. Korea is the second biggest LNG importer and imported ~33 Mt during 2015. China is the third biggest LNG importer. Total LNG imports were ~20 Mt during 2015. India is the fourth biggest LNG importer. India imported ~15 Mt during 2015. Europe (defined in this study as Belgium, France, Italy, Netherlands, Portugal, Spain, Sweden, Turkey and the United Kingdom) is a significant LNG importer. Total LNG imports were ~37.5 Mt during 2015. Energies 2017South, 10 ,America 2152 (Argentina, Brazil, Chile, Dominican Republic and Puerto Rico) is also a significant 5 of 19 LNG importer. Total LNG imports were ~14.6 Mt during 2015. Other Asian countries (Thailand, Taiwan and Singapore) are emerging LNG importers. The total LNG imports equalled ~17 Mt during 3. A Description2015. of LNG Regasiﬁcation Technologies

3. A Description of LNG Regasification Technologies 3.1. Ambient Air Vaporizers The3.1. heat Ambient energy Air Vaporizers source to regasify LNG in ambient air vaporization (AAV) technology comes from the ambientThe heat air. energy LNG source is distributed to regasify through LNG in aambient series ofair surface vaporization heat exchangers.(AAV) technology The comes air cools as it travels downfrom the and ambient exits air. the LNG bottom is distributed of the vaporizer.through a series The of air surface ﬂow heat is controlled exchangers. onThe the air cools outside as of the exchangerit travels either down through and exits natural the bottom buoyancy of the(convection) vaporizer. The of air the flow cooled, is controlled dense on air the or outside by the of installation the exchanger either through natural buoyancy (convection) of the cooled, dense air or by the installation of forced-draft ambient air fans (See Figure3). of forced-draft ambient air fans (See Figure 3).

Figure 3. Ambient air vaporizer. Figure 3. Ambient air vaporizer. AAV technology is most suitable for areas with warmer ambient temperatures. Where cooler AAVclimates technology occur, a issupplemental most suitable heat forsystem areas would with be warmerneeded during ambient colder temperatures. weather conditions Where to cooler climatesmaintain occur, effective a supplemental use. Water heat vapour system in the wouldair condenses be needed and freezes during, forming colder frost weather relatively conditions easily to maintainin effectivethese systems use. because Water vapourthe LNG in is thevaporized air condenses directly with and air freezes, (direct formingheat system). frost The relatively frost is a easily in poor conductor, and its build-up reduces performance and the heat transfer coefficient. A significant these systems because the LNG is vaporized directly with air (direct heat system). The frost is a poor amount of space is required for the ambient air vaporization system to prevent ambient air conductor,recirculation and its build-up, as well as reduces to maintain performance vaporization and capacity. the heat transfer coefficient. A significant amount of space is requiredFog can be for generated the ambient under air certain vaporization geographical system location to preventfactors including ambient areas air recirculation,with high dew as well as to maintainpoints. Cooling vaporization the ambient capacity. air can then generate a large fog bank. Though a fog bank is essentially Fogbenign, can be the generated siting issues under need to certain be taken geographical into consideration location [13]. factors including areas with high dew points. CoolingAn AAV the operates ambient by air extracting can then the generate heat directly a large from fog the bank.surrounding Though air to a fogheat bankthe LNG is essentially by natural convection. This type of technology is cost competitive as it operates on a standalone basis benign,without the siting the issuesneed for need seawater, to be burning taken of into fuels consideration or intermediate [13 fluids.]. However, as the heat capacity Anof AAV air is operatessignificantly by less extracting than seawater the heat and directlyno additional from heat the is surrounding added, the number air to of heat vaporizer the LNG by naturalunits convection. required Thisto heat type LNG of is technology larger when iscompared cost competitive to ORVs and as SCVs it operates requiring on a amuch standalone larger basis withoutplot the space need [14]. for seawater, burning of fuels or intermediate fluids. However, as the heat capacity of air is significantly less than seawater and no additional heat is added, the number of vaporizer units required to heat LNG is larger when compared to ORVs and SCVs requiring a much larger plot space [14].

3.2. Seawater Vaporizers Seawater is used by open rack vaporizers (ORV) as the heat energy source in a direct heat system to vaporize the LNG (Figure4). Sodium hypochlorite is injected on the intake side of the system to control algae growth. The treated seawater is pumped to the top of the water header box. From there, it travels down the outer surface of the tube heat exchanger panels; simultaneously, LNG ﬂows upward through these tubes, and heat exchange occurs. The colder water discharges through the water outfall, and the vaporized natural gas exits at the top header. This technology relies on seawater as the primary heat source; therefore, it is effective only if seawater temperatures are above 5 ◦C. Most vaporizers provide a unique engineering challenge because across them will be a temperature differential of −161 ◦C–5 ◦C; therefore, the material used must endure the high-temperature change. Energies 2017, 10, 2152 6 of 21 Energies 2017, 10, 2152 6 of 19 3.2. Seawater Vaporizers Seawater is used by open rack vaporizers (ORV) as the heat energy source in a direct heat system Added to this,to vaporize in the the case LNG of ( ORV,Figure it4). must Sodium also hypochlorite deal with is theinject corrosiveed on the intake nature side of of seawater the system [6 to]. The racks are constructedcontrol of algae ﬁnned growth. aluminium The treated tubing seawater providing is pumped strengthto the top of against the water the header cold box. operating From there temperatures, and are coatedit travels with down corrosion the outer protection surface of the where tube they heat exchanger are in contact panels;with simultaneously, salt water LNG [14 ]. flows The seawater may also haveupward other through impurities these tubes such, and as heat suspended exchange solidsoccurs. andThe colder fouling water agents, discharges which through may bethe important water outfall, and the vaporized natural gas exits at the top header. This technology relies on seawater criteria inas the the technology primary heat selectionsource; therefore for a, givenit is effective location. only if seawater temperatures are above 5 °C .

Figure 4. Open rack vaporizer. Figure 4. Open rack vaporizer. Most vaporizers provide a unique engineering challenge because across them will be a temperature differential of −161 °C‒5 °C; therefore, the material used must endure the Corrosion protection of the outer tubes relies on a film of aluminium oxide (Al2O3), which is high-temperature change. Added to this, in the case of ORV, it must also deal with the corrosive created when the dissolved oxygen in the seawater reacts with the aluminium. The tubes are also nature of seawater [6]. The racks are constructed of finned aluminium tubing providing strength covered withagainst alayer the cold of operating iron and temperatures manganese and compounds, are coated with with corrosion deposits protection of calcium, where they magnesium are in and sodium fromcontact the with seawater salt water [9 ].[14]. There The seawater could be may various also have options other impurities for corrosion such as protection.suspended solids For example, a zinc alloyand coating fouling canagents be, which sprayed may be onto important the finned criteria tubes in the astechnology a sacrificial selection protection. for a given location. Corrosion protection of the outer tubes relies on a film of aluminium oxide (Al2O3), which is The heatcreated energy when the source dissolved forshell oxygen and in the tube seawater vaporizers reacts with (STV) the isaluminium also seawater.. The tubes An are open-loop also STV system is mountedcovered with vertically a layer of iron to optimizeand manganese vaporization compounds, efficiency. with deposits LNG of calcium, enters magne the bottomsium and of the STV and passessodium through from multiplethe seawater tubes [9]. There while could seawater be various enters options a for shell corrosion surrounding protection. the For tubes.example, Due to the usage of seawater,a zinc alloy there coating are can similar be sprayed environmental onto the finned issuestubes as toa sacrificial the ORV protection. system [13]. The heat energy source for shell and tube vaporizers (STV) is also seawater. An open-loop STV ORVsystem systems is mounted use seawater vertically as to theoptimize heating vaporization source efficiency. for the LNG LNG enters and can the bottom potentially of the STV harm marine life by trappingand passes them through in the multiple water inlets.tubes while There seawater are several enters a environmental shell surrounding issues the tubes. associated Due to the with colder seawater outfall.usage of seawater, The ORV there technology are similar environmental requires large issues volumes to the ORV of system seawater, [13]. which could adversely affect marine lifeORV [ 15systems]. However, use seawater the as consequence the heating source assessment for the LNG of colderand can seawaterpotentially mayharm marine be very location life by trapping them in the water inlets. There are several environmental issues associated with specific andcolder may sea dependwater outfall. on the The marine ORV lifetechnology in each requires location large and volumes the hydrological of seawater, simulation which could modelling to assess theadversely minimum affect marine allowable life [15]. seawater However, temperatures. the consequence assessment of colder seawater may be very location specific and may depend on the marine life in each location and the hydrological 3.3. Combustionsimulation Heat modelling Vaporizer to assess the minimum allowable seawater temperatures.

Seawater3.3. Combustion is not used Heat inVaporizer submerged combustion vaporizers (SCV) for LNG vaporization. Rather, heating of theSeawater LNG occurs is not used by in it submerged flowing throughcombustion tube vaporizers bundles (SCV) that for LNG are submergedvaporization. Rather, in a water bath and heatedheating by natural of the LNG gas occurs combustion. by it flowing The through hot exhaust tube bundles gases that emitted are submerged by the submerged in a water bath combustion burner bubbleand heated through by natural the water gas combustion. to directly The heat hot theexhaust water gases bath emitted then by pass the submerged to an exhaust combustion stack (Figure5). Due toburner the bubble high heatthrough capacity the water of to the directly water, heat it the is water possible bath then to manage pass to anrapid exhaust load stack fluctuations(Figure and 5). sudden start-ups and shutdowns to maintain a stable operation. Therefore, the SCVs can provide great flexibility and a quick response to varying demand requirements. The huge reserve heat bank of SCVs ensures that surges can be mitigated with heat from the water bath alone even if the combustion processes should suffer a temporary failure. SCVs under normal operation represent a significant operating cost in fuel by consuming from 1.5–2.0 percent of the ship’s LNG cargo to supply the burner. In addition, the bathwater becomes acidic due to the acidic combustion products, which are absorbed during the heating process. It is therefore necessary to provide chemical water treatment to the water bath. The associated excess combustion water must be neutralized prior to discharge. Finally, the submerged combustion vaporizer produces a large quantity of emissions to the atmosphere in the form of flue gas. This may be reduced using emission treatment systems, but will add significantly to the operating costs of SCVs [13]. Energies 2017, 10, 2152 7 of 19 Energies 2017, 10, 2152 7 of 21

Figure 5. Submerged combustion vaporizer. Figure 5. Submerged combustion vaporizer. Due to the high heat capacity of the water, it is possible to manage rapid load fluctuations and 3.4. Intermediatesudden start Fluid-ups Vaporizersand shutdowns to maintain a stable operation. Therefore, the SCVs can provide great flexibility and a quick response to varying demand requirements. The huge reserve heat bank Anof intermediate SCVs ensures heat that surges transfer can fluid be mitigated is used with in intermediate heat from the fluid water vaporizers bath alone even (IFV) if to the revaporise LNG. Thiscombustion technology processes can should be configured suffer a temporary to operate failure. in either SCVs closed-loop,under normal open-loopoperation represent or in combination a systems.significant The most operating common cost in intermediate fuel by consuming fluid from vaporizers 1.5–2.0 percent use propane, of the ship’s refrigerant LNG cargo to or supply a water/glycol mixture.the Propane burner. In and addition, other the refrigerants bathwater becomes are costly acidic and due have to the high acidic operational combustion handingproducts, which risks, but have low flashare pointsabsorbed that during are the ideal heating for heatprocess. transfer. It is therefore The water/glycolnecessary to provide mixtures chemical are water cost-effective, treatment and the to the water bath. The associated excess combustion water must be neutralized prior to discharge. associatedFinally, operational the submerged risks are combustion relatively vaporizer low. They produces have a high large flash quantity point, of emissions but require to thea larger heat transferatmos area,phere which in the results form of in flue a larger gas. This system may be than reduced the propaneusing emission or refrigerant treatment systems systems, but [13 will]. Theadd open-loop significantly IFV to technologythe operating requirescosts of SCVs seawater [13]. intake (Figure6). Environmental issues therefore arise and include entrainment of marine in the intake resulting in injury or mortality, as well as low 3.4. Intermediate Fluid Vaporizers temperature discharge of seawater into the surrounding seawater. Intermediate fluid vaporizers that use propaneAn intermediate or refrigerant heat transfer as the fluid intermediate is used in intermediate fluid add fluid a potentially vaporizers hazardous(IFV) to revaporise material to the LNG. This technology can be configured to operate in either closed-loop, open-loop or in combination facility operations. An IFV system that makes use of water/glycol mixtures is a safer way to operate. systems. The most common intermediate fluid vaporizers use propane, refrigerant or a water/glycol The intermediatemixture. Propane air is and heated other byrefrigerants a combustion are costly system and have and high associated operational combustion handing risks emissions,, but have and the carbonlow footprintEnergies flash 2017 points, can10, 2152 bethat reduced are ideal for by heat the usetransfer. of waste The water/glycol heat recovery mixtures [13 are]. cost-effective, and the8 of 21 associated operational risks are relatively low. They have a high flash point, but require a larger heat transfer area, which results in a larger system than the propane or refrigerant systems [13]. The open-loop IFV technology requires seawater intake (Figure 6). Environmental issues therefore arise and include entrainment of marine in the intake resulting in injury or mortality, as well as low temperature discharge of seawater into the surrounding seawater. Intermediate fluid vaporizers that use propane or refrigerant as the intermediate fluid add a potentially hazardous material to the facility operations. An IFV system that makes use of water/glycol mixtures is a safer way to operate. The intermediate air is heated by a combustion system and associated combustion emissions, and the carbon footprint can be reduced by the use of waste heat recovery [13]. The primary receiving terminal at Dahej in India uses an IFV. The heat source for the vaporizer uses air instead of seawater. This system makes use of aqueous glycol solution, which is once cooled by heat exchange with LNG. The aqueous glycol solution is heated up by air blown by fans which is in turn reused for the exchange of heat with LNG (see Figure 7).

FigureFigure 6. 6.Intermediate Intermediate fluid ﬂuid vaporizer. vaporizer.

The primary receiving terminal at Dahej in India uses an IFV. The heat source for the vaporizer uses air instead of seawater. This system makes use of aqueous glycol solution, which is once cooled by heat exchange with LNG. The aqueous glycol solution is heated up by air blown by fans which is in turn reused for the exchange of heat with LNG (see Figure7). For safety considerations, the use of non-combustible and non-toxic water/glycol mixtures in IFV systems are preferable. The use of combustion systems to heat the intermediate ﬂuid can result in environmental impacts through associated exhaust emissions and carbon footprint; this can, however, be overcome by implementation of waste heat recovery [13].

Figure 7. Intermediate fluid vaporizer (air IFV).

For safety considerations, the use of non-combustible and non-toxic water/glycol mixtures in IFV systems are preferable. The use of combustion systems to heat the intermediate fluid can result in environmental impacts through associated exhaust emissions and carbon footprint; this can, however, be overcome by implementation of waste heat recovery [13].

3.5. Floating Storage and Regasification Units In recent times, a new technology option known as a floating storage and regasification unit (FSRU) has come into being. FSRUs emerged as an attractive option because the project execution time is substantially reduced due to the conversion of ships as floating storage units and consequently the capital costs are usually lower. The floating solution in many cases offers greater flexibility when there are space constraints onshore. However, there also limitations in terms of both storage capacity and send-out rates. Typically, a land-based terminal requires up to five years from concept to commission stage, while FSRUs can be conceptualized and commissioned within a period of ~12–24 months. The FSRUs are mostly based on seawater options, i.e., ORVs or shell and tube vaporization; therefore, from the LNG regasification perspective, the technology is not different; the only difference being land-based or an offshore-based vaporizer.

3.6. LNG Cold Energy Recovery during Regasification Part of the energy consumed during the LNG liquefaction process can be recovered during the LNG regasification process. Around ~830 kJ/kg is stored in LNG, which is known as cold energy. This is in addition to the chemical energy of the natural gas and stored as the physical energy [3].

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Energies 2017, 10, 2152 8 of 19 Figure 6. Intermediate fluid vaporizer.

Figure 7. Intermediate fluid vaporizer (air IFV). Figure 7. Intermediate fluid vaporizer (air IFV). For safety considerations, the use of non-combustible and non-toxic water/glycol mixtures in IFV systems are preferable. The use of combustion systems to heat the intermediate fluid can result 3.5. Floating Storagein environmental and Regasification impacts through Units associated exhaust emissions and carbon footprint; this can, In recenthowever, times, be a overcome new technology by implementation option of waste known heat recovery as a floating [13]. storage and regasification unit (FSRU) has come3.5. Floating into being.Storage and FSRUs Regasification emerged Units as an attractive option because the project execution time is substantially reducedIn recent times, due toa new the technology conversion option of known ships as a floating floating storage storage and units regasification and consequently unit the capital costs(FSRU) are usually has come lower. into being. The floatingFSRUs emerged solution as an in attractive many casesoption offersbecause greaterthe project flexibility execution when there are space constraintstime is substantially onshore. reduced However, due to the there conversion also of limitations ships as floating in storage terms units of both and consequently storage capacity and the capital costs are usually lower. The floating solution in many cases offers greater flexibility when send-out rates.there Typically, are space const a land-basedraints onshore. terminal However, requiresthere also limitations up to five in terms years of fromboth storage concept capacity to commission stage, whileand FSRUs send-out can rates. be conceptualized Typically, a land-based and terminal commissioned requires up within to five years a period from concept of ~12–24 to months. The FSRUs arecommission mostly basedstage, while on seawater FSRUs can options, be conceptualized i.e., ORVs and or commissioned shell and tube within vaporization; a period of therefore, ~12–24 months. The FSRUs are mostly based on seawater options, i.e., ORVs or shell and tube from the LNGvaporization regasification; therefore, perspective, from the LNG regasification the technology perspective, is not thedifferent; technology is the not onlydifferent difference; the being land-based oronly an difference offshore-based being land- vaporizer.based or an offshore-based vaporizer.

3.6. LNG Cold3.6. Energy LNG Cold Recovery Energy Recovery during during Regasiﬁcation Regasification Part of the energy consumed during the LNG liquefaction process can be recovered during the Part of theLNG energy regasification consumed process. Around during ~830 the kJ/kg LNG is stored liquefaction in LNG, which process is known can as cold be recoveredenergy. This during the LNG regasiﬁcationis in addition process. to the chemical Around energy ~830 of the kJ/kg natural is gas stored and sto inred LNG, as the physical which energy is known [3]. as cold energy.

This is in addition to the chemical energy of the natural gas and stored as the physical energy [3]. For a typical 5 Mtpa LNG terminal, ~120 MW “cold energy” could be available at maximum Energies 2017, 10, 2152 9 of 21 rates. However, the terminal data suggest that only a few locations employ cold energy recovery technologies. TheFor primary a typical 5 reason Mtpa LNG is that terminal, the current~120 MW technologies “cold energy” could enable be available only low at maximum recovery efﬁciencies rates. However, the terminal data suggest that only a few locations employ cold energy recovery for cold energy.technologies. The cold The energy primary technologies reason is that currently the current in usetechnologies are Rankine enable cycle only low cold recovery power generation, inlet air chillingefficiencies for gas for turbines, cold energy. air The separation cold energy or technologies other low-temperature currently in use are fractionation Rankine cycle (liquidcold nitrogen, liquid air andpower so on), generation, cold storage, inlet air cryogenic chilling for gas crushing turbines, and air seawater separation or desalination other low-temperature (Figure8 -LNG cold fractionation (liquid nitrogen, liquid air and so on), cold storage, cryogenic crushing and seawater power generation).desalination (Figure 8- LNG cold power generation).

Figure 8. LNG cold power generation. Figure 8. LNG cold power generation. It was also observed that siting an LNG terminal next to an existing refinery/petrochemical complex could provide an option to regasify LNG efficiently and effectively. The refinery/petrochemical complex can utilize the cold energy and, in the process, vaporize LNG. However, this potential is location dependent.

3.7. Hybrid Options In recent times, some hybrid options are being developed and tested/experimented. The Korea gas corporation (KOGAS) has been undergoing difficulties in the construction of ORVs due to environmental issues such as cold seawater effluent and residual chemical contents. Therefore, KOGAS is currently testing eco-friendly vaporizers that are innovative, i.e., that do not use seawater. The AAV is a strong candidate for a clean environment. Thus, this work was to investigate its possibility in temperate regions for LNG import terminals in Korea [7]. The KOGAS installation can be considered as a “hybrid” option where the seawater is being used as the base load technology while secondary regasification is achieved using ambient air heat.

3.8. Observations on Technology Options The conventional technology options primarily use ambient air, seawater or the combustion heat for LNG regasification processes. It is evident that some installations use/intend to use intermediate fluids such as glycol and/or propane for the heat exchange process in conjunction with ambient air or the seawater. It is observed that more than 95% of the LNG regasification terminals employ ORVs/sea water as the primary vaporization technology irrespective of the climatic differences around the globe. Submerged combustion vaporization is used as a secondary means during the colder weather periods in most of the sites, globally. However, that effort has been made at developing hybrid models in recent times (e.g., seawater and ambient air). The hybrid design efforts appear to be driven by environmental considerations, i.e., impact on marine life due to cold seawater and so on.

Energies 2017, 10, 2152 9 of 19

It was also observed that siting an LNG terminal next to an existing refinery/petrochemical complex could provide an option to regasify LNG efficiently and effectively. The refinery/petrochemical complex can utilize the cold energy and, in the process, vaporize LNG. However, this potential is location dependent.

3.7. Hybrid Options In recent times, some hybrid options are being developed and tested/experimented. The Korea gas corporation (KOGAS) has been undergoing difficulties in the construction of ORVs due to environmental issues such as cold seawater effluent and residual chemical contents. Therefore, KOGAS is currently testing eco-friendly vaporizers that are innovative, i.e., that do not use seawater. The AAV is a strong candidate for a clean environment. Thus, this work was to investigate its possibility in temperate regions for LNG import terminals in Korea [7]. The KOGAS installation can be considered as a “hybrid” option where the seawater is being used as the base load technology while secondary regasification is achieved using ambient air heat.

3.8. Observations on Technology Options The conventional technology options primarily use ambient air, seawater or the combustion heat for LNG regasification processes. It is evident that some installations use/intend to use intermediate fluids such as glycol and/or propane for the heat exchange process in conjunction with ambient air or the seawater. It is observed that more than 95% of the LNG regasification terminals employ ORVs/sea water as the primary vaporization technology irrespective of the climatic differences around the globe. Submerged combustion vaporization is used as a secondary means during the colder weather periods in most of the sites, globally. However, that effort has been made at developing hybrid models in recent times (e.g., seawater and ambient air). The hybrid design efforts appear to be driven by environmental considerations, i.e., impact on marine life due to cold seawater and so on. From the preceding discussion, it can also be observed that location factors such as the ambient air and the seawater temperatures, humidity, and so on, may have a significant impact on the regasification efficiency and life-cycle performance. However, this can only be validated by analysing the location factors and corresponding technology choices using thermodynamic modelling. The purpose of this paper is to discuss the location factors data and their potential impact on technology choices. So far, it is evident that the majority of LNG regasification terminals employ seawater vaporization supplemented with submerged combustion vaporizers for peak shaving. It is also observed that LNG cold energy utilization, in most cases, is by way of producing liquid nitrogen or liquid air. Using the LNG cold energy to produce liquid nitrogen or air results in ~50% savings in electricity [2].

4. Location Factors by Different Regions Based on the current LNG import quantities (Figure1), the countries and regions selected are Japan, China, Korea, India, Europe, South America and other Asian countries. The following data were collected and plotted as scatter charts [16,17] and presented in Table2. A total of 82 locations were selected to represent the key regions, worldwide.

• Maximum and minimum seawater temperatures • Maximum and minimum ambient air temperatures • Maximum and minimum relative humidity • Maximum and minimum wind speeds • Climate change impact Energies 2017, 10, 2152 10 of 19

Table 2. Overview of location factors.

Min Ambient Max Ambient Min Seawater Max Seawater Min Wind Max Wind Region Min RH 1 Max RH Air Temp. Air Temp. Temp. Temp. Speed Speed Mean SD 2 Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD ◦C ◦C ◦C ◦C ◦C ◦C ◦C ◦C m/s m/s m/s m/s % % % % Japan 1.6 3.9 30.5 1.8 13.5 3.2 26.8 1.4 1.4 0.7 6.3 1.4 53.5 5 85.6 3.6 Korea −6.0 2.2 30 0.8 8.1 5 25.1 1.1 1.5 0.8 5.7 0.5 50 0 88.5 2.5 China 3.3 6.9 31 3.2 11.7 5.5 27.2 2.1 1.25 0.2 5.6 0.9 55.8 3.8 91.5 2 India 15 3.2 40.5 3.4 24.1 2.4 29.6 0.1 0.75 0.6 4.5 0.6 35 12 90 6 EU 3.9 4 26.8 5.5 11.7 5.1 21.5 3.9 1.7 1.6 6.0 1.5 53 14.6 90 5 South America 16.5 10.4 30.1 4.3 19 6.6 24.9 4.8 1.7 1.3 6.0 2.0 54 16.5 91.1 4 Other Asia 17.3 5.9 31 1.7 22.7 3.8 29.1 0.8 1.4 0.5 5.8 1.9 53.7 6.5 93.8 2.8 1 RH: Relative humidity; 2 SD: Standard deviation. Energies 2017, 10, 2152 12 of 21

4.1. Maximum and Minimum Seawater Temperatures The maximum seawater temperatures are between 21.5 °C and 29.1 °C . It is evident that European and the South American regions have a relatively higher standard deviation (SD) compared to the rest of the world (Table 1). The difference is usually attributed to the longitude and latitude. The maximum seawater temperatures are consistent across the globe with some exceptions in the EU and South America (see Figure 9). The minimum sea water temperatures do vary significantly, but only a couple of locations experiences lower than 5 °C, i.e., Japan, Korea and the EU (see Figure 10). The minimum seawater temperatures are between 8.1 °C and 24.1 °C , and the standard deviation is relatively high in South America, China and the EU (Table 1). It is also evident that only four locations experience temperatures less than 5 °C during the year; two in Korea, one in China and one in the EU (see Figure 10). The lower temperatures (less than 5 °C) in these four locations are experienced for less than a duration of 10% of a year [17]. A typical design criterion for ORVs is a minimum seawater temperature of 5 °C ; therefore, the majority of locations are suited to ORVs as a feasible technology option. It is observed that the seawater temperature ranges, across the globe, are adequate for LNG regasification subject to other constraints like seawater quality, and so on. Energies 2017 10 It is expected, , 2152 that lower seawater temperatures (less than 10 °C) may affect LNG regasification11 of 19 rates for a fraction of the year, particularly during extended winter periods. The data indicate that someThe of the median, affected mode, locations mean andare in the Japan, standard Korea, deviation China forand these Europe parameters (except some were calculatedwarmer regions using thein Southern data from Europe; 82 locations Figure around 10). the For world; this seereason, Table the2. A terminal brief on climate operators change opt impact for an is alternative added in Sectionregasification 4.5; however, process a such detailed as combustion study on this vaporization topic is outside to cover the scope the extended of this paper. winter periods. The technology option for peak shaving is SCVs for the majority of locations. It is worth noting that only 4.1.a few Maximum locations and (two Minimum locations Seawater in Korea, Temperatures one in Sweden and one in China) experience lower than 5 °C seawaterThe maximumtemperatures seawater for a part temperatures of the year are, i.e., between ~20% 21.5of the◦C time and 29.1annually.◦C. It is evident that European and theIt has South been American observed regions that numerous have a relatively design innovations higher standard in ORVs deviation over the (SD) last compared three decades to the have rest ofresulted the world in higher (Table heat1). The transfer difference and a issignificant usually attributed reduction to in the ice longitude formation and on tube latitude. external surfaces. TheseThe are maximum generally seawaterknown as temperatures super ORVs areor high consistent-performance across the ORV; globe also with known some as exceptions Hi Per V in[6] the. EU andThe South Super America ORV was (see developed Figure9 ).as Thean advanced minimum design sea water ORV temperaturesto achieve higher do vary thermal signiﬁcantly, efficiency butby way only of a coupleapplication of locations of advanced experiences materials lower and than achieving 5 ◦C, i.e., higher Japan, heat Korea transfer and the area EU through (see Figure design. 10).

Energies 2017, 10, 2152 13 of 21 Figure 9. Maximum seawater temperatures aroundaround thethe world.world.

FigureFigure 10. 10. MinimumMinimum seawater seawater temperatures temperatures around around the the world. world.

TheThe seawater minimum temperature seawater temperatures may affect the are fouling between factor 8.1 ;◦ Ctherefore and 24.1, the◦C, sea and water the standard quality and deviation the temperatureis relatively can high impact in South ORV America,performance. China and the EU (Table1). It is also evident that only four locations experience temperatures less than 5 ◦C during the year; two in Korea, one in China and 4.2. Maximum and Minimum Ambient Air Temperatures one in the EU (see Figure 10). The lower temperatures (less than 5 ◦C) in these four locations are (a)experienced Direct Air H foreating less than a duration of 10% of a year [17]. A typical design criterion for ORVs is a minimum seawater temperature of 5 ◦C; therefore, the majority of locations are suited to ORVs as The ambient air temperatures indicate that air heating could be a viable technology option (see a feasible technology option. Figure 11). However, the formation of frost on the vaporizer is a significant issue because it reduces It is observed that the seawater temperature ranges, across the globe, are adequate for LNG the overall heat transfer coefficient. The LNG is vaporized directly against the air (direct heat system), regasiﬁcation subject to other constraints like seawater quality, and so on. and the water vapour in the air condenses and freezes. From the temperature data, it can be observed that there is a large and consistent gap between the minimum and the maximum ambient air temperatures; therefore, the regasification rates are expected to vary significantly during the year and on a daily basis during the night and day conditions. The maximum ambient air temperatures range between 25 and 42 °C , which has a positive impact on the LNG regasification rates, but at the same time, higher humidity causes frost build up and reduced heat transfer. Therefore, the AAV technology evaluation must address a relationship between the percentages of the relative humidity, LNG flow rates and the frost build up.

Figure 11. Maximum and minimum ambient air temperatures around the world.

However, the maximum ambient air data (see Figure 11) do indicate that an appreciable amount of heat is available across the globe. Only five locations show ambient air temperatures falling below −5 °C ; one in Sweden, one in Japan, one in China and two in Korea. The low ambient air temperatures of up to −10 °C could still be used to regasify LNG (−161 °C), but the LNG flowrates may need to be reduced. Furthermore, the duration of the low temperatures will impact the total cost and climate

Energies 2017, 10, 2152 13 of 21

Energies 2017, 10, 2152 12 of 19

It is expected that lower seawater temperatures (less than 10 ◦C) may affect LNG regasification rates for a fraction of the year, particularly during extended winter periods. The data indicate that some of the affected locations are in Japan, Korea, China and Europe (except some warmer regions in Southern Europe; Figure 10). For this reason, the terminal operators opt for an alternative regasification process such as combustion vaporization to cover the extended winter periods. The technology option for peak shaving is SCVs for the majority of locations. It is worth noting that only a few locations (two locations in Korea, one in Sweden and one in China) experience lower than 5 ◦C seawater temperatures for a part of the year, i.e., ~20% of the time annually. It has been observed that numerous design innovations in ORVs over the last three decades have resulted in higher heat transfer and a significant reduction in ice formation on tube external surfaces. These are generally knownFigure as 10. super Minimum ORVs seawater or high-performance temperatures around ORV; the also world. known as Hi Per V [6]. The Super ORV was developed as an advanced design ORV to achieve higher thermal efficiency by wayThe of seawater application temperature of advanced may materials affect the and fouling achieving factor higher; therefore heat, the transfer sea water area throughquality and design. the temperatureThe seawater can impact temperature ORV performance. may affect the fouling factor; therefore, the sea water quality and the temperature can impact ORV performance. 4.2. Maximum and Minimum Ambient Air Temperatures 4.2. Maximum and Minimum Ambient Air Temperatures (a) Direct Air Heating (a) Direct Air Heating The ambient air temperatures indicate that air heating could be a viable technology option (see The ambient air temperatures indicate that air heating could be a viable technology option Figure 11). However, the formation of frost on the vaporizer is a significant issue because it reduces (see Figure 11). However, the formation of frost on the vaporizer is a significant issue because it the overall heat transfer coefficient. The LNG is vaporized directly against the air (direct heat system), reduces the overall heat transfer coefficient. The LNG is vaporized directly against the air (direct heat and the water vapour in the air condenses and freezes. From the temperature data, it can be observed system), and the water vapour in the air condenses and freezes. From the temperature data, it can be that there is a large and consistent gap between the minimum and the maximum ambient air observed that there is a large and consistent gap between the minimum and the maximum ambient air temperatures; therefore, the regasification rates are expected to vary significantly during the year and temperatures; therefore, the regasification rates are expected to vary significantly during the year and on a daily basis during the night and day conditions. The maximum ambient air temperatures range on a daily basis during the night and day conditions. The maximum ambient air temperatures range between 25 and 42 °C , which has a positive impact on the LNG regasification rates, but at the same between 25 and 42 ◦C, which has a positive impact on the LNG regasification rates, but at the same time, higher humidity causes frost build up and reduced heat transfer. Therefore, the AAV technologytime, higher evaluation humidity causesmust address frost build a relationship up and reduced between heat the transfer. percentages Therefore, of the the relative AAV technologyhumidity, evaluation must address a relationship between the percentages of the relative humidity, LNG flow LNG flow rates and the frost build up. rates and the frost build up.

FigureFigure 11. MaximumMaximum and and minimum minimum ambient ambient air air te temperaturesmperatures around the world.

However, the maximum ambient air data (see Figure 1111)) do indicate that an an appreciable appreciable amount amount of heat is available across the globe. Only Only five five locations locations show show ambient ambient air air temperatures temperatures falling falling below below −55 °C◦C;; one one in in Sweden, Sweden, one one in in Ja Japan,pan, one one in in China China and and two two in in Korea. Korea. The The low low ambient ambient air air temperatur temperatureses of up up to to −−1010 °C◦ Ccould could still still be beused used to regasify to regasify LNG LNG (−161 (− 161°C), ◦butC), the but LNG the LNGflowrates flowrates may need may to need be reduced.to be reduced. Furthermore Furthermore,, the duration the duration of the low of the temperatures low temperatures will impact will the impact total the cost total and cost climate and climate impact of regasification, i.e., the low temperature durations in Sweden (one location) and

Energies 2017, 10, 2152 14 of 21 Energies 2017, 10, 2152 13 of 19 impact of regasification, i.e., the low temperature durations in Sweden (one location) and Japan (one Japanlocation) (one are location) relatively are high. relatively In the high. cooler In and the drier cooler winter and drier months, winter the months, efficiency the of efficiency this technology of this technologycan be reduced, can be affecting reduced, the affecting rate of regasification. the rate of regasification. More vaporizers More vaporizersunits are required units are for required operation for operationin cooler months in cooler tomonths compensate to compensate for the lack for of the efficiency. lack of efficiency. TheThe useuse ofof ambientambient airair heatheat willwill eliminateeliminate and/orand/or minimize the natural gas consumption being usedused inin thethe submergedsubmerged combustioncombustion vaporizers vaporizers and and eliminateeliminate and/orand/or minimize the flueflue gasesgases and and environmentalenvironmental emissions.emissions. TheThe locationslocations withwith consistently high ambient temperatures areare SouthSouth America,America, India,India, SpainSpain andand otherother AsianAsian countries.countries. However, thethe lowerlower ambientambient airair temperaturestemperatures combinedcombined withwith lowerlower relativerelative humidityhumidity will impact impact the the regas regasificationification rates. rates. The The highest highest ambient ambient air airtemperatures temperatures are in are India in India (see (seeFigure Figure 11). 11). (b)(b) Intermediate Intermediate F Fluidluid V Vaporizersaporizers (air (air as as the the heat heat source) source) AsAs discussed discussed earlier, earlier, intermediate intermediate fluidfluid vaporizers (IFV) revaporise LNG by the use use of of intermediateintermediate heatheat transfertransfer fluid.fluid. IFV technology configurationsconfigurations normally operate in a closed-loop,closed-loop, open-loopopen-loop oror aa combinationcombination system. system. The The most most common common intermediate intermediate fluids fluids are are propane, propane, refrigerant refrigerant or water/glycolor water/glycol mixtures, mixtures, based based on existingon existing IFV IFV technology, technology, which which employs employs air instead air instead of seawater of seawater for its heatfor its source heat source and an and intermediate an intermediate fluid to fluid exchange to exchange heat with heat LNG. with LNG. TheThe air-IFVair-IFV technologytechnology evaluation needs to focus on utilization of “free” ambient air heat for differentdifferent intermediateintermediate fluids;fluids; thethe mostmost commonlycommonly usedused beingbeing thethe glycol/waterglycol/water mixture.mixture. Any fluidfluid withwith an an acceptable acceptable heat heat capacity, capacity, freezing freezing and boiling and boiling point ispoint a candidate is a candid intermediateate intermediate fluid; however, fluid; ithowever is desirable, it is desirable to use more to use environmentally-acceptable more environmentally-acceptable material. material. Tempered Tempered water orwater fresh or water fresh arewater available, are available but suitable, but suitable intermediate intermediate fluids fluids are more are oftenmore selectedoften selected from thefrom glycol the glycol group group used individuallyused individually or as mixtures or as mixtures (such as (such ethylene as ethylene glycol, diethylene glycol, diethylene glycol, triethylene glycol, triethylene glycol), methanol, glycol), propane,methanol, butane, propane, ammonia butane, or ammonia formate. or formate. However,However, some some of of the the other other fluids fluids under under consideration consideration are propylene, are propylene, propane, propane, isobutane, isobutane, butane andbutane dimethyl and dimethyl ether [5 ].ether [5]. InIn thethe coolercooler and and drier drier winter winter months, months, the the efficiency efficiency of of this this technology technology can can be reduced,be reduced, affecting affecting the ratethe ofrate regasification. of regasification. More vaporizerMore vaporizer units are units required are required for operation for inoperation cooler months in cooler to compensate months to forcompensate the lack of for efficiency. the lack of efficiency.

4.3.4.3. Maximum and Minimum Relative Humidity TheThe datadata suggestsuggest that the average maximum and average minimum relative humidity are quite consistentconsistent andand high.high. It is observed that average minimum relative humidity is higherhigher inin JapanJapan whenwhen comparedcompared toto EuropeEurope andand China (Figure 1212)).. It was also also observed observed that that th thee maximum maximum relative relative humidity, humidity, onon average,average, isis higherhigher inin SouthSouth AmericaAmerica andand EuropeEurope asas comparedcompared withwith China,China, JapanJapan andand India.India.

Figure 12. Maximum and minimum relative humidity around the world. Figure 12. Maximum and minimum relative humidity around the world.

Energies 2017, 10, 2152 15 of 21

From the psychometric chart (Figure 13), it can be seen that an increase in relative humidity results in an increase in enthalpy; however, if the temperature is too low or the convection of the air Energies 10 is too2017 slow,, , then 2152 significant condensation can form on the tubes. As the condensation freezes,14 ofthe 19 effectiveness of the tubes will decrease and the production rate will also subsequently decrease. FromFigure the 13 psychometric shows the chart effects (Figure of increased 13), it can humidity be seen that at 25an increase°C. The in humidity relative humidity increases results from in70% an increase–90% results in enthalpy; in a significant however, increase if the temperaturein the ambient is tooair enthalpy low or the i.e., convection from 38 to of 58 the kJ/kg. air is However, too slow, thenan increase signiﬁcant in the condensation dew point canalso formincreases on the the tubes. probability As the of condensation condensation. freezes, the effectiveness of the tubes will decrease and the production rate will also subsequently decrease.

Figure 13. Effect of humidity on fan forced vaporizer performance [18]. Figure 13. Effect of humidity on fan forced vaporizer performance [18].

FigureThe maximum 13 shows the relative effects humidity of increased is consistent humidity across at 25 ◦ withC. The some humidity locations increases experiencing from 70–90% near results100%, in which a significant exist in increase India, in the the EU ambient and South air enthalpy America. i.e., fromThe minimum 38 to 58 kJ/kg. relative However, humidity an increase varies insignificantly; the dew point some also locations increases in the India probability and the of EU condensation. experiencing the lowest (see Figure 12). In those locations,The maximum the regasification relative rates humidity and/or is the consistent efficiency across may be with lower/suboptimal, some locations during experiencing a significant near 100%,duration which of the exist year, in if India, ambient the air EU-based and Southtechnologies America. are selected. The minimum relative humidity varies significantly;The ambient some air locations temperature, in India humidity and the and EU ice experiencing formation are the the lowest factors (see that Figure have 12 the). Ingreatest those locations,effect on the AAV regasification performance. rates There and/or are the other efficiency factors may tha bet lower/suboptimal, also affect the performance during a significant of these durationvaporizers of theincluding year, if the ambient wind air-basedand solar technologiesradiation [19]. are selected. TheShah, ambient Wong air and temperature, Minton (2008) humidity determined and ice the formation effects of are temperature the factors thatand havehumidity the greatest on the effectperformance on AAV performance. of forced air There vaporizers are other [18]. factors Figure that 14 alsoshows affect that the the performance greater the of humidity these vaporizers in the includingambient theconditions, wind and the solar greater radiation the performance [19]. of the forced draft ambient air vaporizers (FAV). FigureShah, 15 Wongalso shows and that Minton at higher (2008) temperatures, determined the humidity effects of has temperature a greater effect and humidityon the total on duty the performancethan at lowe ofr temperatures. forced air vaporizers [18]. Figure 14 shows that the greater the humidity in the ambient conditions, the greater the performance of the forced draft ambient air vaporizers (FAV). Figure 15 also shows that at higher temperatures, the humidity has a greater effect on the total duty than at lower temperatures. Utilizing a specially-designed test apparatus to simulate AAV terminals, Kim et al. (2013) could determine the effects that temperature and humidity had on frost formation [7]. The experimental results showed that the frost thickness decreased with the increase in air temperature. It was also found that the frost thickness irregularly increased with the increase in relative humidity. With the increase in air velocity, the frost thickness also increased; however, from 6 m/s onwards of air velocity, pieces of formed ice would break off causing the frost thickness to decrease. The increase in mass flow rate of LNG also increased the frost thickness. From the experiment, it was concluded that the wind velocity and the mass flow rate of LNG had the greatest effect on the frost thickness. Energies 2017, 10, 2152 15 of 19 Energies 2017, 10, 2152 16 of 21 Energies 2017, 10, 2152 16 of 21

Figure 14. Effect of temperature on fan forced vaporizer performance [18]. FigureFigure 14. 14Effect. Effect of of temperature temperature onon fanfan forcedforced vaporizer performance performance [18 [18].].

Figure 15. Effect of humidity on fan forced vaporizer performance [18]. FigureFigure 15. 15Effect. Effect of of humidity humidity on on fanfan forcedforced vaporizervaporizer performance [18 [18].]. Utilizing a specially-designed test apparatus to simulate AAV terminals, Kim et al. (2013) could Utilizing a specially-designed test apparatus to simulate AAV terminals, Kim et al. (2013) could determineAmbient the air effects vaporizers that temperature transfer heat and to LNGhumidity from had the surroundingon frost formation ambient [7]. airThe by experimental making use of determine the effects that temperature and humidity had on frost formation [7]. The experimental theresults temperature showed differential that the frost between thickness this decreased air and the with LNG. the Consequently,increase in air temperature. this ambient It air was is cooled,also foundresults that showed the frost that thickness the frost irregularlythickness decreased increased withwith thethe increaseincrease inin airrelative temperature. humidity. It Withwas alsothe andfound the associated that the frost latent thickness heat results irregularly in condensation. increased with Thus, the increase both sensible in relative and humidity. latent heat With from the the airincrease and water in air vapour, velocity, respectively, the frost thickness contribute also increased; to the vaporization however, from of LNG. 6 m/s Condensedonwards of air water velocity, forms piecesincrease of informed air velocity, ice would the frost break thickness off causing also increased;the frost thickness however, to from decrease. 6 m/s onwards The increase of air invelocity, mass on the external surfaces of the ambient air vaporizers and runs down under gravity. This condensate flowpieces rate of offormed LNG alsoice would increased break the off frost causing thickness. the frost From thickness the experiment, to decrease. it was The concluded increase thatin mass the flows towards the lower half of the vaporizer where it often freezes on the external surfaces where ice windflow ratevelocity of LNG and alsothe mass increased flow ratethe frost of LNG thickness. had the From greatest the effectexperiment, on the frostit was thickness. concluded that the forms. Ice formation on external surfaces of the vaporizer is influenced by several factors. Ice cover windAmbient velocity airand vaporizers the mass flowtransfer rate heat of LNG to LNG had fromthe greatest the surroundin effect on gthe ambient frost thickness. air by making use can be partial on the lower half to up to the full height of the external surface. Because of the forces of theAmbient temperature air vaporizers differential transfer between heat this to air LNG and thefrom LNG. the surroundinConsequently,g ambient this ambient air by air making is cooled, use theandof ice the the exerts temperature associated on ambient latentdifferential air heat vaporizers, resultsbetween in theythis condensation. air are and ideally the LNG.Thus, designed Consequently,both tosensible withstand andthis latentambient the forces heat air thatfromis cooled, can the be generatedairand and the water byassociated any vapour, percentage latent respectively, heat coverage results contribute in of condensation. ice. Toto amelioratethe vaporization Thus, thisboth problem, ofsensible LNG. Condensedand vertical latent tube heat water bundles from forms the are generallyonair the and external preferredwater vapour, surfaces to horizontal r ofespectively, the ambient tube contribute bundles. air vaporizers Iceto the build-up andvaporization runs on down the of external under LNG. gravity.Condensed surfaces This of water thecondensate vaporizer forms willflowson cause the towards external a drop the surfaces in efficiency,lower of half the of whichambient the vaporizer will air resultvaporizers where in lowering itand often runs freezes the down exit onunder temperature the gravity.external of Thissurfaces the condensate natural where gas fromiceflows theforms. towards vaporizer. Ice formation the lower on half external of the surfaces vaporizer of the where vaporizer it often is freezesinfluenced on theby several external factors. surfaces Ice wherecover caniceThe forms.be ratepartial Ice at formation whichon the icelower on builds externalhalf upto up and surfaces to the the degree offull the height vaporizer of coverage of the is external influenced depends surface. onby aseveral large Because numberfactors. of the Ice of forces cover factors, thethecan main ice be exertspartial ones ofon on whichambient the lower include air halfvaporizers, theto up ambient to they the fullare air ideallyheight temperature ofdesigned the external and to relativewithstand surface. humidity, theBecause forces theof that the LNG can forces be flow rategeneratedthe through ice exerts by the anyon vaporizer ambient percentage andair vaporizers, coverage the materials of they ice. used areTo ideallyameliorate for vaporizer designed this construction. problem, to withstand vertical Some the tubeforces of these bundles that variables can are be suchgenerallygenerated as the temperaturepreferred by any percentage to horizontal and relative coverage tube humidity bundles. of ice. ofTo Ice theameliorate build ambient-up on this air the undergoproblem, external seasonalverticalsurfaces tube of variation the bundles vaporizer and are are generally preferred to horizontal tube bundles. Ice build-up on the external surfaces of the vaporizer influencedwill cause by a thedrop climate in efficiency, in the locationwhich will at whichresult in LNG lowering regasification the exit temperature is conduced. of the natural gas fromwill causethe vaporizer. a drop in efficiency, which will result in lowering the exit temperature of the natural gas 4.4.from MaximumThe the ratevaporizer. and at which Minimum ice builds Wind up Speeds and the degree of coverage depends on a large number of factors, the mainThe rateones at of which which ice include builds upthe and ambient the degree air temperature of coverage and depends relative on humidity,a large number the LNG of factors, flow It was found that with the increase in air velocity, the frost thickness also increased; however ratethe throughmain one thes of vaporizer which include and the the materials ambient used air temperaturefor vaporizer and construction. relative humidity, Some of these the LNG variables flow fromrate 6 m/sthrough onwards the vaporizer of air velocity, and the pieces materials of formed used for ice vaporizer would break construction. off, causing Some the of frost these thickness variables to

EnergiesEnergies 20172017,, 1010,, 21522152 1717 ofof 2121 suchsuch asas thethe temperaturetemperature andand relativerelative humidityhumidity ofof thethe ambientambient airair undergundergoo seasonalseasonal variationvariation andand areare influencedinfluenced byby thethe climateclimate inin thethe locationlocation atat whichwhich LNGLNG regasificationregasification isis conduced.conduced.

4.4.4.4. MaximumMaximum andand MinimumMinimum WindWind SpeedsSpeeds EnergiesItIt 2017waswas, 10 foundfound, 2152 thatthat withwith thethe increaseincrease inin airair velocity,velocity, thethe frostfrost thicknessthickness alsoalso increasedincreased;; howeverhowever16 of 19 fromfrom 66 m/sm/s onwardsonwards ofof airair velocity,velocity, piecespieces ofof formedformed iceice wouldwould breakbreak offoff,, causingcausing thethe frostfrost thicknessthickness toto decrease. decrease. An An increase increase in in mass mass flow flow rate rate of of LNG LNG also also increased increased the the frost frost thickness. thickness. From From the the decrease. An increase in mass flow rate of LNG also increased the frost thickness. From the experiment, experiment,experiment, itit waswas concludedconcluded thatthat thethe windwind velocitvelocityy andand thethe massmass flowflow raterate ofof LNGLNG hadhad thethe greatestgreatest it was concluded that the wind velocity and the mass flow rate of LNG had the greatest effect on the effecteffect onon thethe frostfrost thicknessthickness [7].[7]. frost thickness [7]. ItIt isis difficultdifficult toto findfind substantivesubstantive researchresearch work work onon thethe relationshiprelationship betweenbetween wind wind speedspeed andand It is difficult to find substantive research work on the relationship between wind speed and frosting.frosting. Therefore,Therefore, thisthis areaarea ofof knowledgeknowledge maymay requirerequire furtherfurther researchresearch inin devdevelopingeloping simulationsimulation frosting. Therefore, this area of knowledge may require further research in developing simulation modelsmodels and and testing. testing. This This holds holds significance significance for for understanding understanding the the life life cycle cycle performance performance of of the the models and testing. This holds significance for understanding the life cycle performance of the ambient ambientambient airair--basedbased technologytechnology optionsoptions fromfrom thethe regasificationregasification ratesrates andand efficiencyefficiency perspective.perspective. air-based technology options from the regasification rates and efficiency perspective. AA highhigh degreedegree ofof variationvariation hashas beenbeen observedobserved iinn maximummaximum andand minimumminimum windwind speedsspeeds acrossacross A high degree of variation has been observed in maximum and minimum wind speeds across the thethe globeglobe (see(see FigFiguresures 1616 andand 1717).). TheThe rangerange beingbeing ~1~1 toto 99 m/s;m/s; therefore,therefore, thisthis isis aa veryvery locationlocation specificspecific globe (see Figures 16 and 17). The range being ~1 to 9 m/s; therefore, this is a very location specific variable,variable, andand itit maymay bebe difficultdifficult toto drawdraw relationshipsrelationships betweenbetween thethe regions.regions. variable, and it may be difficult to draw relationships between the regions.

FigureFigure 116.166.. MaximumMaximum wind wind speeds speeds around around thethe world.world.

Figure 17. FigureFigure 1177.. MinimumMinimum wind wind speeds speeds around around thethe world.world.

WhenWhen AAV/FAVAAV/FAV units unitsunits are areare in inin operation, operation,operation, water waterwater and andand ice iceice form formform on onon the thethe outside outsideoutside of theofof thethe tubes tubestubes due duedue to the toto theextremelythe extremelyextremely cold coldcold operating operatingoperating temperatures. temperatures.temperatures. The TheThe longer longerlonger the thethe unit unitunit is left isis leftleft to run, toto run,run, the thethe more moremore ice ice buildsice buildsbuilds up up onup ontheon thethe tubes, tubes,tubes, eventually eventuallyeventually reducing reducingreducing the unit’sthethe unit’sunit’s performance. performance.performance. This ThisThis requires requiresrequires the units thethe unitsunits to be toto periodically bebe periodicallyperiodically shut shutdownshut downdown to allow toto allowallow for defrosting forfor defrostingdefrosting [19]. [19[19].]. TheThe energyenergy extractionextractionextraction from fromfrom the thethe humid humidhumid air airair is isis part partpart sensible sensiblesensible and andand part partpart latent latentlatent heat. heat.heat. The TheThe sensible sensiblesensible heat heahea istt isfromis fromfrom the thethe simple simplesimple cooling coolingcooling of the ofof the air,the air andair,, andand the latentthethe latentlatent heat heat isheat the isis point thethe pointpoint when whenwhen the air thethe is cooledairair isis cooledcooled down down todown below toto its dew point and the moisture starts to condense. When the moisture begins to condense, some of it is attached to the ﬁns as ice, and the remainder of the moisture passes out the bottom of the vaporizer as fog [8]. Although fog formation is considered benign, it can cause disruptions to human activity near terminals such as transport or maintenance [8]. Energies 2017, 10, 2152 17 of 19

Fog can become an issue with AAV/FAV terminals; it is produced when the cold air from the vaporiser comes into contact with the warm humid air outside. The severity of the fog depends on many factors, including the ambient temperature, wind velocity, relative humidity and the distance between units. Although the fog is considered benign, dense fog can create operating issues due to the lack of visibility [14].

4.5. Impact of Climate Change on Location Factors The preceding discussion relates to the weather conditions in the different regions in the various regions of the world. Therefore, it is prudent to mention that regional weather patterns are expected to change during this century. Climate change impact is expected to see an increase in seawater and ambient air temperatures around the globe. The Intergovernmental Panel on Climate Change (IPCC) has already predicted that the rise in temperatures is expected to be seen during both winter and summer times [20]. However, the IPCC modelling predicts that the increases may vary across the regions and over the period. For example, the greatest warming in winter is expected to be over both north-eastern Europe and Scandinavia (December–February) and in the summer in the Mediterranean (June–August) [21]. The warming of Europe has been more than the global average (1.0–1.2 ◦C compared to 0.81–0.89 ◦C for the rest of the world). The current observations and modelling indicate that the relative humidity is not expected to increase in the future. This is because water vaporization will increase at higher temperatures, but the ambient air can hold more water at higher temperatures [20]. As per the preceding discussion, it is evident that LNG regasification technologies are primarily based on seawater and ambient air temperatures. Therefore, the weather pattern changes may have significant impact on technology selection and on the design criteria for new terminals. The heat transfer fundamentals would suggest a 0.5–1.0 ◦C rise in the ambient conditions, which may have a significant impact on the selection and sizing of the heat exchanger systems. Consequently, due to the positive impact of higher heat available from ambient air and seawater, the need to have large SCVs and to burn the gas for combustion heat may eventually be reduced and/or eliminated. A reduction in usage and/or elimination of SCVs in turn will help reduce greenhouse gas emissions. Therefore, it is conceivable that climate change may have a significant and positive impact on LNG regasification terminals in terms of environmental, efficiency and economic performance. While it is not the intent of this paper to do a detailed evaluation of the impact of increased ambient air and the seawater temperatures on LNG terminals due to climate change, it may be argued that the new LNG terminals should consider a careful “climate adaptation” study at the concept and technology selection stages. Any such study, however, must be based on regional weather pattern modelling data and the results from IPCC to assess the location factor impact on technology selection and design options.

5. Conclusions and Policy Implications From the discussion so far, it is clearly evident that while there is some material available from industry and commercial conferences, only a few research papers on this subject matter are available Therefore, future research areas that could help in enhancing the body of knowledge, as well as being useful to the industry include:

• For an efﬁciently-managed LNG industry, the role of geography and meteorology needs considering on a case-by-case basis. From the study of location factors, the following conclusions can be drawn: Seawater vaporization is a viable technology option in more than 95% of the locations, worldwide. However, this is subject to any water quality considerations. • Ambient air conditions are best for AAVs/FAVs and IFVs in South America, India, Spain and other Asian countries (Singapore, Taiwan, Indonesia, Thailand) and provide a much cleaner regasiﬁcation technology option. Energies 2017, 10, 2152 18 of 19

• Currently, cold energy utilization globally is less than 1% of the total potential. Considering 500 Mtpa LNG trade in the future, the potential for cold energy recovery is ~12 GW per annum, globally. • Climate change is expected to have a positive impact on the LNG regasiﬁcation industry. However, the impact in some regions could be more pronounced due to regional variation of the climate change. Due to higher heat available, the operating efﬁciencies may rise and the need for SCVs may reduce.

While these conclusions are drawn based on location parameter data alone, it is the intent to compare the performance characteristics of different technology options using the thermodynamic models in subsequent papers. Future research areas that could help with enhancing the body of knowledge, as well as being useful to the industry include:

• Relationship between wind speeds, relative humidity and frost and fog formation • Impact of seawater quality on technology selection • Climate adaptation study for new LNG terminals • Technology options for enhanced energy recovery of LNG cold energy • Retroﬁtting cold energy utilization in existing terminals • Techno economic feasibility of AAVs/FAVs vs IFVs for a given location(s)

Acknowledgments: This research work was supported by Origin Energy and the Australia Pacific LNG (APLNG). I wish to thank my colleagues from Osaka Gas (Japan), Petronet LNG (India) and KOGAS (Korea) who provided insight and expertise, Toshihide Kanagawa of Osaka Gas, Yoshinori Hisazumi and his gas research team at the Osaka University. I wish to acknowledge Stephen Hogg, Mitchell Brereton, Benjamin Buckley, Roger Rego, Margarita Zaratemartinez and Simon Forster for their good work. Author Contributions: Randeep Agarwal conceived and developed the paper; Richard Brown, Thomas J. Rainey and Ted Steinberg provided guidance and reviews throughout the development of this paper. Robert K. Perrons assisted with analysis and interpretation of the data; S. M. Ashrafur Rahman assisted in data interpretation, creation of graphical materials, formatting the manuscript to Energies guideline and also correcting the references. Conflicts of Interest: The authors declare no conflict of interest.

Abbreviations

AAV Ambient air vaporizer EU European Union FAV Forced draft air vaporizer FSRU Floating storage and regasification unit IFV Intermediate fluid vaporizer IPCC Intergovernmental Panel on Climate Change JOGMEC Japan Oil, Gas & Metals National Corporation KOGAS Korea Gas Corporation LNG Liquefied natural gas NG Natural gas ORV Open rack vaporizer RH Relative humidity SCV Submerged combustion vaporizer SD Standard deviation STV Shell and tube vaporizer GW Gigawatt kJ/kg Kilojoules per kg kWh/t Kilowatt hour per ton of LNG m/s Meters per second Mt Million tonnes Mtpa Million tonnes per annum MW Megawatt t/h Tonnes per hour Energies 2017, 10, 2152 19 of 19

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