LNG TECHNOLOGICAL PROGRESS IN JAPAN THREE DECADES OF EVOLUTION LE PROGRES TECHNOLOGIQUE DU GNL AU JAPON 30 ANS D EVOLUTION

Transcription

1 LNG TECHNOLOGICAL PROGRESS IN JAPAN THREE DECADES OF EVOLUTION LE PROGRES TECHNOLOGIQUE DU GNL AU JAPON 30 ANS D EVOLUTION Sadao Goto General Manager Production Engineering Dept. Atsushi Kamiya Head of Engineering Sect. Production Engineering Dept. Masaki Tajima Manager, Engineering Sect. Production Engineering Dept. Tokyo Gas Co., Ltd , Kaigan Minato-ku, Tokyo, Japan ABSTRACT The thirty-year history of liquefied natural gas (LNG) in Japan since its introduction in 1969 shows remarkable technological progress and a growing demand for LNG. LNG use has steadily increased because it is an environmentally clean energy source. We overcame the initial difficulties from its need of low temperatures and now focus on improving the performance, safety, economy, service lifetime, and reducing the environmental impact of LNG facilities. This paper describes the technological development in the last 30 years, the most current technology for LNG in Japan, and potential new LNG-related technologies. RESUME Les trente années qui se sont écoulées depuis l'introduction du GNL au Japon en 1969 représentent l'histoire d'un progrès extraordinaire de la technologie dans ce domaine réalisé avec une hausse de la demande pour cette matière. Aujourd'hui, le GNL soutiennent le Japon en tant que ressources énergétiques "clean" (non-polluantes). Les difficultés initiales dues à la basse température du gaz ayant déjà été surmontées, le développement technologique du GNL consiste désormais à améliorer les performances, la sécurité, l'économie, la durabilité, et l'harmonie avec l'environnement des installations concernées, ainsi qu'à rechercher de nouvelles manières d'exploiter la matière. Le présent traité vise à résumer le développement technologique enregistré depuis 30 ans par l'industrie GNL au Japon, ainsi qu'à illustrer les directions à prendre pour optimiser les potentiels de ces ressources naturelles. 1. Introduction On November 4, 1969, the LNG tanker Polar Alaska bringing LNG from Alaska arrived at a pier in the Negishi terminal of Tokyo Gas. The arrival signaled the dawn of a new LNG age for Japan. More than 30 years and two oil crises in the have passed PO-23.1

2 since this event. LNG now accounts for about 12% of the primary energy of the country and thus has become one of key energy sources. We point out that a significant factor besides environmental protection was behind the events above. Namely, for us to safely handle the large quantity of LNG, a combustible and cryogenic liquid, various technological developments have been achieved and put into practical use in several fields including the construction, operation, and maintenance of LNG facilities. As we enter the 21st century, we think that the role of LNG among various energy sources will become even more important. Therefore, we also enter a new age in the field of LNG technologies. In this paper, we summarize the 30-year history of LNG technologies mainly for the LNG receiving terminals in Japan, and we describe the technical prospects for future technologies. 2. LNG in-ground and above-ground storage tanks Figure 1 shows the trend of LNG tank by type in Japan. The prevailing types of LNG tanks in Japan were above-ground storage tanks before the, which is similar to foreign countries. In the 1980s, the above-ground type and the in-ground type are 56% and 44% of the total, respectively, whereas in the 1990s, both the in-ground type and the above-ground type are about 45%, and the above-ground prestressed concrete type is 10%. Figure 2 shows the trend in LNG tank capacity. In Japan in the and before, all LNG tanks had capacities of less than 100,000 kl. In the 1980s, tanks with 100,000 kl or more were constructed. Since 1990, more than halves of the LNG tanks in Japan have a capacity of 100,000 kl or more. This tendency to construct larger LNG tanks is worldwide. Presently, the world's largest LNG tanks are the 200,000 kl in-ground storage tanks of Tokyo Gas and the 180,000 kl above-ground storage tank of Osaka Gas. Above ground storage tank In-ground storage tank ~60,000kl 60,000~ 100,000kl Before the 1980s 1990s 69% (40) 56.5% (35) 44.7% (21) 31.0% (18) 43.5% (27) PC concrete storage tank 10.6% (5) 44.7% (21) Before the 1980s 1990s 29.3% (17) 7.1% (3) 40.5% (5) 88.7% (55) 70.7% (41) 11.3% (7) 52.4% (22) 100,000kl~ Figure 1: Trend in tank types. Figure 2: Trend in tank capacity (1) In-ground storage tanks In 1970, an LNG in-ground storage tank with a capacity of 10,000 kl was constructed at the Negishi terminal of Tokyo Gas, the first of its type. During the following 30 years, more than 70 LNG in-ground storage tanks have been constructed in the world. PO-23.2

3 The history of LNG in-ground storage tanks can be divided into three generations. The first generation involves tanks constructed at the early stage of development until the first half of the 1980s; these are LNG in-ground storage tanks with a capacity of 100,000 kl or less. The second generation involves large-capacity LNG in-ground storage tanks; these include the one with a capacity of 130,000 to 140,000 kl constructed at the Sodegaura terminal of Tokyo Gas, and the one with the largest capacity in the world (200,000 kl) constructed at the Negishi terminal of Tokyo Gas in In addition, the first completely-underground, storage tank with a reinforced concrete roof that is similar to the side wall and bottom slab, was constructed at the Ohgishima terminal of the company in The third generation involves those constructed in the year 2000 and later when LNG in-ground storage tank with rigid connection of side walls and bottom slabs are built. These have greater reliability, safety, and are more economical than previous LNG in-ground storage tank. Figures 3 and 4 show the reduced construction cost realized by the increased capacity and the more effective use of land with the larger capacity tanks, respectively. The construction costs for 200,000 kl tanks can be reduced by about 20% compared with those with a capacity of 100,000 kl, and they increase the efficiency of land use by 40%. Thus, increasing the capacity has significant advantages. The major technologies contributing to the capacity increase are the concrete for a super cut-off slurry wall 100-m below the ground surface, both membrane and cold insulation for deeper liquid level, and the pump barrel structure. Cost index per store capacity Capacity( 10,000kl) Figure 3: Reduction of construction cost by increasing the capacity (Index taking a case of 100,000 kl as 100.) Land area index per store capacity Capacity( 10,000kl) Figure 4: Effective use of land by increasing the capacity (Index taking a case of 100,000 kl as 100.) (2) Above-ground storage tanks Similar to the case of LNG in-ground storage tanks, several new technologies have increased the capacity of LNG above-ground storage tanks. Because of the little available land space, a larger above-ground storage tank requires a tank type that uses land more efficiently than conventional, smaller above-ground tanks. A technical challenge in terms of tank structure was a increase in thickness of 9%Ni steel plates used as the inner tank material. The major technical breakthroughs that increased the capacity of LNG aboveground tanks are the LNG prestressed concrete storage tank as a new type that does not require dike space and the technology for thick inner tank materials. PO-23.3

4 3. Vaporizer The history of LNG vaporizers began with the four units of open rack vaporizer (ORV) with a LNG vaporization capacity of 45 t/h that were constructed by Tokyo Gas in its Negishi terminal in Sumitomo Precision Products Co., Ltd. (SPP) installed ORVs designed by Marston in the UK. However, the ORVs had a boiling instability that was not anticipated because the actual operating pressure was considerably lower than their design pressure.we had difficulty in solving the problem, because of the first ones operating at the lower pressure. In addition to solving this problem, they improved the design in various ways. These experiences became the foundation for current ORV development. Tokyo Gas has been developing and improving ORVs for 30 years; it is no exaggeration to say that their efforts have produced the current ORVs. The main type for base load purposes is ORV, although there are other types of LNG vaporizer: the submerged combustion vaporizer (SCV), the intermediate fluid vaporizer (IFV), and the air fin vaporizer (AFV). 70% of ORVs use heat exchanger tubes jointly developed by Tokyo Gas and SPP. These tubes are called the Star Fin Tube because of their cross-section shape. Other than the Star Fin Tube, the major ORV technologies put into practical use by Tokyo Gas are described below. (1) Development of an explosive joining flange The main structure of an ORV is made of aluminum alloy, whereas the connection piping is stainless steel. To prevent LNG leakage from the flange connection between ORV and piping at start up, a stand-by mode was needed to maintain the flange always at low temperature by flowing small quantity of LNG even in a suspending period. To terminate this stand-by mode, Tokyo Gas and SPP developed and applied an explosive joining flange in It uses laminated aluminum, titanium, and stainless steel. Its structure can absorb thermal stress by a sequential combination of material with a large thermal expansion ratio to material with small thermal expansion ratio. Currently, this flange is used as the standard. (2) Development of calorific value adjustment for liquefied gas In Japan, the calorific value adjustment is done for city gas. Conventionally, a method was applied in which LNG and LPG were vaporized separately and then the gases were mixed. Tokyo Gas developed a new method in which LPG is mixed into LNG and the liquid was vaporized in a vaporizer after calorific value adjustment. The company put the method into practical use for ORVs in Then, it also adopted the method for SCVs in (3) Cladding of corrosion protection material The heating medium for ORV is seawater, which can corrode the heat exchanger tubes. To prevent such corrosion, a metallic compound has been conventionally applied. But, the compound wore out and required periodical repair. So, Tokyo Gas and SPP developed a protective cladding attached to the heat exchanger tubes from the stage of extrusion molding, and put this technology into practical use in The cladding serves as a sacrifice anode and protects the heat exchanger tubes through a cathodic protection mechanism. PO-23.4

5 (4) Development of high-performance heat exchanger tubes Tokyo Gas and SPP developed the latest Star Fin Tube in The LNG vaporization capacity of ORV with this technology reached 173 t/h (including the weight of LPG mixed with LNG). Surprisingly, the vaporization capacity is three times or more than that of the first domestic ORVs mentioned above. Figure 5 shows the frame volume ratio of ORV per vaporization capacity of LNG. Compared with the first ORV, the required volume of latest one is five or six times smaller. Also, the construction cost per vaporization capacity of LNG decreased about 25%. 120 Frame Volume Ratio per Capaciy % Marston Type Modified Marston Type Star Fin (1st Generation) Star Fin (2nd Generation) Star Fin (Latest Type) YEAR Figure 5 Frame Volume Ratio of ORV As described above, during the past 30 years, Tokyo Gas has endeavored to improve performance, operational function, maintainability, and economy of ORVs. The history on ORVs is equivalent to the history of ORVs in Japan 4. Rotating machine (1) LNG pumps After the introduction of LNG into Japan in 1969, many LNG pumps have been installed and operated at receiving terminals. These are submerged motor pumps, in which all the components including the motor are submersed into LNG liquid. Lubrication and cooling are done in the LNG liquid and monitoring of the pump conditions was impossible because all components were immersed in the liquid. This caused many problems. Tokyo Gas has tried to make LNG pumps more reliable and to reduce their maintenance costs through the following developments. a. Improvement of bearings All the early LNG pumps were imported and their MTBF (mean time between failures) was about 4,000 hours. The major causes that demanded overhauls were damage to the ball bearings resulting from imbalances of axial thrust forces. PO-23.5

6 (a) Improvement of the axial thrust balancing system The axial thrust balancing system was improved and the design of axial thrust was optimized taking the actual operation conditions into account. (b) Development of monitoring system The vibration meters were installed for bearings and the on-line vibration monitoring system was introduced. This allows the detection of bearing abnormalities through a continuous monitoring of bearing vibration. In addition, plenty of vibration data collected by this system increase reliability of judging pump abnormalities. (c) Development of new type of bearing A new type of pump was developed that replaces the conventional ball bearings with hydrostatic slide bearings. The hydrostatic slide bearings float and hold the axis using pressure from fluid that is pumped out and into the bearing pocket. Such developments have lengthened the MTBF. Now, the MTBF is nearly 30,000 hours. Figure 6 shows the MTBF of low-pressure pumps in the Sodegaura terminal of Tokyo Gas. 45,000 Mean Time Between Failure hr 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 (a) Improvement of axial thrust balancing system (b) Development of monitoring system (a) Improvement of axial thrust balancingsystem (c) Development of new type of bearing Figure 6: MTBF of LNG primary pump of the Sodegaura Terminal at Tokyo Gas. b. Towards domestic production Efforts towards the domestic production of pumps were made from the second half of the to (1) reduce operational problems, (2) establish a prompt service system, and (3) shorten the time limit of delivery. As a result, the domestically-produced pumps were developed around 1980 and used commercially. c. Capacity increase Year of Completion Normally, a low-pressure pump and a high-pressure pump are installed in series to increase pressure in two stages. In recent years, a 100 t/h large capacity and high-pressure pump has been developed to reduce the cost of the entire pumping system. This pump can increase the pressure by up to 2.9 MPa in a single stage. The pump uses dual-line ball PO-23.6

7 bearings as a countermeasure against excessive thrust force during start-up, and the bearing materials have been improved. (2) Motor a. Power supply technology For supplying power to a submerged motor, high degree of tightness and an excellent electrical insulation of the bushing at cryogenic temperatures are required. To satisfy these requirements, many components such as terminal headers, cryogenic cables, and cable connectors have been developed. The terminal header is an insulating bushing with high degree of tightness. It was developed and adopted according to the events of a fatal explosion due to an in-cable gas leakage in the USA. Previously, a type that used an O-ring to assure leak tightness was common. Currently, the most common type uses a ceramic as an insulating material and is leak tight because it has metallic hermetic seal structure. Also a type with double metallic hermetic seal structure to increase reliability has become common. For the cable, a type of cryogenic cable with insulating materials such as polyethylene tape or polyethylene-synthesized paper has replaced the conventional MI cables as the most common. Because of these improvements, the electrical performance at cryogenic temperature and the workability when removing the pump from a tank have been significantly improved. b. Motor body Submerged motors were available only with low voltage specification when LNG first came to Japan. Therefore it was difficult to manufacture large-capacity motors. Therefore, mostly imported products were used. However, higher voltage types of the 6- kv class are now available because of domestic development efforts, and the large capacity is available with significantly higher reliability. The performance at higher voltages has improved due to the increased insulation technique from vacuum-varnishimpregnation treatment of windings and the improvement of various cryogenic insulating materials. 5. Operation control When Japan first received LNG at the Tokyo Gas Negishi LNG terminal in 1969, analog instruments were used for the operation control of the terminal. In the, the higher reliability and labor-savings were required at terminals with an increase in LNG demand. Since then an operation scheme by DDC (direct digital control computer) has increasingly been introduced. Operators could then operate the equipment with a keyboard while observing CRT screens. The control system of Tokyo Gas' Sodegaura terminal started computer operation in 1973; using advanced automatic controls such as automatic start-up and shut-down of vaporizers and LNG pumps. Hence, the operation efficiency of LNG terminals was significantly improved. The control logic introduced at that time was revolutionary; and it still has a central role in the automatic operation of LNG terminals. In the 1980s, according to the rapid evolution of computer technology, the first DCS (distributed control system) for LNG terminals was introduced into the Tokyo Gas Sodegaura terminal. In addition, the fields of power control monitoring, automatic analysis of PO-23.7

8 received LNG or supplied gas, and berth mooring monitoring were systematized. Thus, automation and the labor-savings directly connecting to the plant operation have matured. In the 1990s, the functions of HMI (human machine interface) were improved. For example, CRT touch-panel operation appeared and the information could be shared on large screens. Such progress significantly contributed to the enhancement of the operational functions. The newly-installed control system of the Tokyo Gas Ohgishima LNG terminal may be called one of the best control systems among LNG terminals in the 20th century. Specifically, the system is equipped with an integrated POC(process operator s console)that allows remote monitoring and control of images from a production management system and the plant monitoring cameras and handy terminals that provide operators for the information at the plant. Figure 7 shows the history of operation control systems introduced in the past for the LNG terminal. Although some systems just started operation, computer systems introduced early on are being replaced by new systems. The renewal work without any interruption of the plant operation is difficult that requires a close technical examination and careful activities over a long period. Since 1984,10 or more control systems have been successfully renewed in Japan according to their respective plans. introduction of LNG (1969) ~1960s 1980s 1990s 2000s~ Analog instruments control Direct digital control system Distributed control system Integration with information system 6. Maintenance Figure 7: Changes in operation control systems for LNG receiving terminals. At the early stage of LNG, the maintenance work for LNG facilities was done as a break down maintenance or a time-based maintenance; namely, a periodic preventive maintenance based on the period of time or time in operation. After that, according to the evolution of measuring technology or data analysis technology, the maintenance work for rotating machines such as LNG pumps or boil off gas compressors has transferred to a condition-based maintenance to increase reliability and maintainability, and also to reduce maintenance costs. For LNG pumps, the facility diagnosis technique using on-line vibration monitoring and vibration analysis on ball bearings has been adopted. For installations that use time-based maintenance work, the content and period of their maintenance work are optimized based on the accumulated maintenance data. This can drastically reduce the cost and frequency of maintenance. At some LNG facilities, 30 years or more have elapsed since their installation. From now on, maintenance to prevent installation degradation or the renewal of installations will be necessary. Therefore, we are developing ways to inspect for aging degradation in installations by a non-destructive inspection or test. PO-23.8

9 7. Prospects for new technologies Now, we consider the prospects for future LNG technologies. Important future technical topics are cost reduction, increased security and reliability, advanced use of LNG, and maintaining old LNG facilities. In a field of construction, new materials, advanced designs, and advanced construction techniques can be addressed from a viewpoint of reducing costs and increasing reliability. For example, in the field of new materials, using a functional material such as Invar steel (36%Ni steel) on strength members such as piping may be addressed. Also, advanced designs could significantly reduce costs. In Japan, from October 2000, the technical standards of the gas industry utility law that regulates LNG facilities have transferred from specification to performance rules. Thereby, an environment allowing the advanced design technique to be introduced is in place. Thus, a further improved LNG facility will be constructed by a novel design, and its cost should be less. Also in a field of the advanced construction technology, several improvements will be implemented from many aspects and will result in better quality and term shortening of the construction work. The technology to maintain and manage several existing LNG facilities for long periods will have to be examined. Their security will be assured and the terminal life will be extended by examining the facilities and then applying the latest technical achievements. From now, it will be necessary to prepare the maintenance and management standards for LNG facilities as international standards. In the process of examining them, past maintenance and management data will become very important, and such data could be used effectively. Finally, we think there will be an increasing need to create a steady system for summarizing the database on LNG technologies, for transmitting these technologies, and for bringing up human resources. 8. Conclusions It has been said that the 21st century will become the Asian century and the century of global environment. Under these circumstances, it is significant that the first LNG international conference in the 21st century is held in Seoul, Korea. In this international conference, we summarized LNG technology from the past 30 years. We should transmit intellectual properties that include hardware and software on LNG technologies for our future posterity. In addition, we should explore the 21st century as the century of LNG to protect the global environment. We must endeavor to concentrate our efforts for these aims. PO-23.9