igu2009docswgcfinal00727

1、TERMINAL FLEXIBILITY TO RECEIVE DIFFERENT KINDS OF LNGKazuhide Hori11. Energy Production Department, Tokyo Gas Co., Ltd., JapanKeywords: 1.LNG quality; 2.diversification; 3. Terminal flexibility; 4. Stratification; 5.Ship-shore compatibility1. IntroductionTokyo Gas, the pioneer in LNG receiving, has

2、 received LNG of quite different quality from many countries and regions over the course of its 40-year experience of LNG handling.For example, we have received super-lean LNG delivered from Alaska since 1969, when LNG technologies were just beginning. The calorific value of Alaskan LNG is approxima

3、tely 39MJ/m3, while the major LNG calorific value has been within the range of approx. 44 to 46MJ/m3.Today, all participants in the LNG industry face a great turning point in LNG quality. As the natural gas market is growing worldwide, various gas sources are proliferating, and it has become inevita

4、ble for LNG buyers to handle LNG of differing quality.Fig.1 shows the trend of world LNG production capacity. The production capacity for lean LNG will increasesuddenly within a few years. This is mainly because of the Qatar Mega-Trains.Fig.1 Trends in World LNG Production CapacityIn addition, there

5、 seems to be abundant reservation of unconventional natural gases that are known as shale gas, tight-sand gas, and CBM (coal bed methane). (Table 1)These gases are now being developed around the world and their production is growing rapidly. In the U.S., unconventional natural gas production in 2007

6、 was 256 bcm and the share in the U.S. gas production has alreadycome to account for 47%. Table 1 As a res uTable.1 Prospects for natural gas production (Steve Mohr, Geoffrey Evans; Oil & Gas journal,lt,Dtehce.r1e7,is20a0p7)articular downward tendency inthe calorific value of LNG. This is due to the

7、 increasing number of lower calorific value gas sources. In particular, the calorific value of the CBM is very low, under 40MJ/m3.From the viewpoint of the market, this trend is probably also due to the intentions to adjust the LNG calorific value to the network specifications of lower calorific val

8、ue markets such as the United States and the UnitedKingdom (Fig. 2).In addition to the diversification of LNG quality, there is an upward trend in LNG carrier size for transporting LNG at cheaper costs. The huge, so-called Q- max and Q-flex LNG carriers are already in service, although some small ve

9、ssels with cargo capacities under 100,000 kL, are in service. In Japan, the 20,000 kL- class carriers are in service for domestictransport (Table 2).Table 2. The Order-Book of LNG CarriersThus, to make the natural gas marketlarger while maintaining a stable and valuable supply for consumers, LNG*htt

10、p://world/highvalueships/lngorderbook.htmimporters should make great efforts to exclude restrictions on LNG receiving, which mainly come from specifications of facilities such as berths and LNG tanks.The LNG receiving terminals of Tokyo Gas already have enough flexibility to h

11、andle all existing kinds of LNG,and we intend to continue with the evolution of our terminals according to changes in circumstance.In this report, we introduce our advanced solutions for receiving diversified LNG, and we are sure that they willbe helpful for all LNG receiving terminals throughout th

12、e world.2. MethodsFor conventional LNG receiving terminals, there are many difficulties in managing diversified LNG.This is because they dont have sufficient technologies to remove risks such as equipment damage caused by rollover in LNG tank and unacceptable quality change of send-out gas. Such ris

13、ks result from receiving different types of LNG in the same LNG tank.Although it is possible to avoid such risks by storing each type of LNG in other tanks, this method causes a decrease in flexibility for LNG receiving and/or an increase in investment due to redundant tank capacity.As mentioned abo

14、ve, Tokyo Gas has experience in receiving many kinds of LNG. Based on this experience, we developed many useful technologies to exclude these risks.Below, some basic functions in our LNG tanks to store different types of LNG are shown. (Fig. 2)a) LNG filling nozzlesWe choose the top or bottom fillin

15、g nozzle corresponding to LNG density for the prevention of stratification. When we receive heavier LNG in tanks in which lighter LNG is stored, we choose top filling nozzles. In the opposite case, we use the bottom. By receiving LNG based on this principle, we can avoid the stratification in almost

16、 all cases.b) Jet mixing nozzleWe are able to stir LNG in a tank using jet-mixing equipment if stratification occurs accidentally. It is important to clearly understand jet mixing capacity (flow rate, jet velocity, jet angle, etc.) because whether or not LNG layers are dissolved depends on jet mixin

17、g capacity. If a jet stream does not enter theFig.2 Facilities of LNG storage tankupper layer, it will only result in an acceleration of rollover through the input of energy to the lower layer.c) Density monitorIt is necessary to have a method to confirm the formation or the dissolution of LNG layer

18、s in tanks. We use a density monitor, which collects continuous density data by moving from the bottom to the top of an LNG tank.These facilities are basically designed for dedicated LNG that is delivered based on a long-term contract. So far we have not had any fatal problems in terminal operations

19、, because the quality and the quantity of dedicated LNG are stable.Nowadays, the situation is not as it used to be because of the diversification of LNG quality and quantity.Even in the LNG receiving terminals of Tokyo Gas, it is not easy to receive such unusual forms of LNG assuper lean LNG, or LNG

20、 delivered by huge carriers, and there are many viewpoints to be taken into account before the decision to receive them is made. (See Table 3)Table 3M aincheck pointsto be confirmedAbove all, three remarkable viewpoints are shown below.a) Prevention of stratificationIt is known that the LNG stratifi

21、cation possibly causes a rollover phenomenon. (Fig. 3) The best way to prevent rollover is to prevent the stratification, because once LNG layers come into being, it is necessary to dissolve them by complicated operations or to pump out the lower layer with careful monitoring.Fig. 3 Outline of rollo

22、verb) Confirmation of ship-shore compatibility with berths and Japanese regulationsView pointsCheck points1BerthsCar iersizeStrengthofthe berthstructuresM anifold structureCom patibility with shore unloading facilityUnloading rateTim e forunloadingRegulationsCom patibility with Japanese regulations2

23、LNG tanksUnloading volum eTank capacityDensityPossibility ofstratificationCalorific valuePossibility ofunacceptable quality change during unloading3LNG pumpsDensityPum p capacity Security forNPSH4RegasifierLatent/specificheatHeat-exchange capacityGas volumeCapacity oftubes and pipes5Calorie adjuster

24、sCalorific valueControlability ofsystemCapacity ofvalves,vessels and pipes6LPG facilitiesLPG consumptionLPG storage to adjustcalories7InstrumentsAl propatiesM easurability offlow m eters,density m onitors,gasanalyzer,etc8City gasCom ponentExistence ofunacceptable com ponents (excessive contentofN2,S

25、,etc.)Sea water5.Calorie adjusters8.City gas1. Berth4.Regasifiers7.Instrum ents 3.LNG pum ps2. LNG tanks6.LPG facilitiesWe regularly receive LNG carriers that we have already confirmed to be compatible with our berths and the Japanese seaways. We have also registered such carriers on the list of the

26、 receivable ships after gaining the permission of the Japan Coast Guard (JGC).If we are going to receive a new LNG carrier for which specifications exceed the permitted values, we must assess the safety of berthing operations and unloading operations in order to get permission. It typically takes a

27、few months for this process to be completed.c) Maintaining the quality of the send-out gasThe equipment of Japanese city gas consumers is adjusted for a narrow gas quality range so as to run with highest thermal efficiency. To maintain the quality of city gas, we generally adjust the calorific value

28、 by mixing LPG in regasified LNG.If the quality change of the LNG is so sudden and extensive that the calorie adjuster is not able to controlthe city gas calorific value, it will cause shutdown or efficiency decrease to consumer equipment.Thus, much effort and time is required to receive new forms o

29、f LNG or new LNG carriers, while sometimes we have only a few weeks before receiving spot LNG.Therefore, it is important not only to have advanced facilities but also to have useful measures to judge quickly whether a new type of LNG and/or a new LNG carrier is acceptable or not.Below, we introduce

30、some examples of measures that we have developed.2-1. Techniques for receiving different qualities of LNGIn the case of receiving different qualities of LNG, we estimate the appropriateness from many viewpoints so as to avoid trouble caused by both calorificvalueandLNGdensity differences. The genera

31、l logical flow is shown in Fig. 4.In this process, an essential solution is to grasp the LNG behavior in the tanks. By understanding LNG behavior accurately, we can adequately judge the appropriateness of receiving such LNG.Therefore, we have put great effortinto understanding LNG behavior byStart1)

32、, 3) Method of judgment-Preparation of guidelines-Detailed dynamic simulationN1) Possibility of stratification?Y2) Basic methods-Choice of top/bottom feed-Jet mixing-Pumping-out of lower layer-Axial density monitor in tankN2) Any method to avoid rollover?Y3) Unacceptable quality change ofsend-out LN

33、G?N4) Basic methods-Line mixing with other LNG-LPG addition, N2 injection-Line mixing in the gas networkY4) Any method to adjust the quality ofsend-out gas?NundertakingmanyexperimentalYReceivablepractices and simulations. We havedeveloped methods for estimating such matterspreciselyusingour CFDNot r

34、eceivableFig. 4 General logical flow to judge LNG acceptance(Computational Fluid Dynamics) simulation technologies.We are now able to allow density differences between fed and in-tank LNG to be as great as possible. As a result, we can avoid the excess costs that increase investment and we do not lo

35、se the opportunity to receive cheaper LNG.Moreover, to achieve rapid judgment, guidelines for issues described as follows are necessary.a) Prevention of stratification in each tank after unloading (shown in 1st diamond).b) Prevention of unacceptable calorific valuechange(shown in 3rd diamond)For exa

36、mple, problems can be caused by shortcut suction of fed LNG to a pump during unloading.StratifyFig. 5 shows an example of the guidelines for stratificationpreventionusedforpreliminary judgment. The curves here depend on the forms of the filling nozzles, feed rate of unloading LNG, heat input to the

37、unloading LNG through the receiving pipes, the amount of involved BOG that is mixed with unloading LNG at the funnel of the bottom filling pipe, and other factors. Therefore, it is necessary to prepare guidelines for each type of LNG tank.These guidelines are necessary especially when we receive hea

38、vier LNG using a bottom filling nozzle, or lighter LNG using a top filling nozzle, because the risk of the stratification is great in such cases.Therefore, the guidelines should be accurate, and if we can not judge the appropriateness by only using the guidelines, we have detailed simulation practic

39、es that utilize our CFD simulation technology.Fig. 6 shows an example of the density distribution around the feed pipe outlet. In this case, filling LNG does not flow directly into the pumps. From this data, we can judge that the calorific value change of pump-out LNG is allowable. If there is an un

40、acceptable risk of calorific value change, we should stop the pump close to the filling nozzle.In addition to the preventive technologies mentioned above, we have simulation technology to estimate allowable duration for rollover (Fig. 7) and BOG release rate in rollover. Using this technology along

41、with certain operational techniques, we areable to manage stratification well if it occurs accidently.Feed rateNot StratifyDensity differenceFig. 5 Typical guidelines for stratification prevention (bottom feed for heavier LNG)Fig. 6 Bottom feed LNG behavior around feed pipeboundaryTemperature Change

42、 Dens.10h Dens.50h Temp.50h Temp.100hDens.100hTemp.120hDens.120hDens.125hTemp.125hRoll-overTemp.135hDens.135h high T low T high low Fig. 7 Rollover simulation resultTank Level before unloadingBoundary breakTemp.10hDensity Change Z oo m in Pumps Bottom feed pipe2-2. Techniques for receiving huge LNG

43、carriersRecently, LNG carriers are becoming larger, with capacities up to 260,000 kL. This represents a good method of delivering LNG at a cheaper cost, but the influences on safety and stable gas supply when accidents occur are becoming greater. Therefore, players in the LNG industry must recognize increasing responsibility.Tokyo Gas has been enlarging berth capacity for receiving huge carriers while maintaining safety.We have already received a Q-flex carrier in the Ohgishima terminal. The reception of fully loaded cargotook place for the first time in Japan.Except for comme