Utilisation of LNG Cold Energy at Maptaput LNG Receiving Terminal

Transcription

1 Utilisation of LNG Cold Energy at Maptaput LNG Receiving Terminal Phatthi Punyasukhananda 1,2,* and Athikom Bangviwat 1,2 1 The Joint Graduate School of Energy and Environment, King Mongkut s University of Technology Thonburi, Bangkok, Thailand, * Corresponding Author: phatthi@hotmail.com 2 Centre of Energy Technology and Environment, Ministry of Education, Thailand Abstract: The first LNG (Liquefied Natural Gas) receiving terminal in Thailand with a maximum capacity of 5 MTA (million tons per annum) has been constructed at Maptaput area, Rayong province and it is planned to be operated around 3rd quarter of LNG cold energy utilisation technologies which are the techniques of making use of the cold energy from LNG cryogenic temperature (-163 degree Celsius) during re-gasification process, instead of wasting it into seawater, have been studied. Fourteen (14) technologies for LNG cold energy utilisation are identified, i.e. air separation and liquefaction unit, cryogenic power generation, liquefied carbon dioxide production, and etc. The technologies were assessed and screened by the criteria and limitation factors regarding to the operating conditions of the LNG terminal and environmental situation in Maptaput area. As the results, there are 4 technologies selected as the possible technologies for the utilization of LNG cold energy. Those are 1. air separation and liquefaction system, 2.Rankine cycle cryogenic power generation, 3. liquefaction/solidification of carbon dioxide, and 4. chilled water production. With an estimated energy benefit of LNG cold utilization of 850 kj/kg, the maximum cold energy benefit of the total 5 MTA of LNG can be 4,250 TJ or 101 ktoe per year. Keywords: LNG Cold Energy Utilisation, Technology Selection, LNG Receiving Terminal 1. BACKGROUND 1.1 LNG receiving terminal and regasification process Many countries that import Liquefied Natural Gas (LNG) and intend to use it as a supply for their natural gas pipeline network or other purposes would need LNG receiving terminal for the delivery and storage of the imported LNG in their premises. Most of LNG receiving terminals comprise LNG Regasification Units for the purpose of transforming LNG into natural gas. The transformation process of natural gas from liquid phase to gas phase is known as Regasification Process. After having been re-gased, natural gas will be delivered to the natural gas pipeline network or for other purposes of the importers. In Thailand, first LNG receiving terminal has been constructed in Maptaput industrial estate, Rayong and it is planned to be operated around 3rd quarter of LNG cold energy utilisation LNG cold energy utilisation is meant to capture the benefit of LNG cold energy (-163 degree Celsius) while it is vaporised and becomes natural gas instead of wasting it to the atmosphere. In normal regasification process, LNG absorbs heat from heat source (seawater is usually used as a heat source) to raise its temperature up until reaching its boiling point. As mentioned before that LNG temperature is very low, when absorbing heat from heat source for vaporisation, it will cause the heat source temperature lower dramatically according to the temperature difference between LNG and the heat source. Thus effective technologies to recover energy from the exchange phenomenon between LNG and heat source should be explored instead of wasting it to make surrounding sea water become colder during regasification process. From the fact that amount of imported LNG is rising all over the world, thus to utilise this benefit of cryogenic temperature would have a huge benefit in term of energy efficiency and energy conservation. Utilisation of LNG cold energy during regasification process is a great thermodynamic benefit to be integrated with other engineering or industrial process as a heat sink of their system. Furthermore, the benefit from the application of LNG as a heat sink of other system can reduce operation cost of the receiving terminal with regasification unit. The LNG cold energy utilisation also reduces some environmental problems, for example, keeping seawater temperature around terminal area from not being too low and improving energy efficiency (reducing energy consumption) of the system by utilising LNG cold energy. 1.3 Estimated energy benefit of LNG cold energy The maximum energy benefit of the LNG is estimated by the amount of energy that LNG has to consume during regasification process. This amount of energy can be considered as a cooling capacity to other system at the temperature 435

2 level of -163 degree Celsius. In general, the energy benefit of LNG which is possible to be utilised is estimated to be around 850 kj/kg and this amount of energy can be slightly varied depending on the specification of LNG and conditions of natural gas after vaporisation. LNG Tank LNG LNG Vaporiser Natural gas Lower temperature sea water This thermodynamic benefit should be harvested instead of wasting it into seawater Energy exchange between LNG and seawater that makes seawater become cooler Sea water Sea water pump Fig. 1 Regasification Process and Potential LNG Cold Energy Utilisation 2. LNG COLD ENERGY UTILISATION TECHNOLOGIES 2.1 Existing LNG cold energy utilisation technology Utilisation of LNG cold energy has been implemented since around 1990 at LNG receiving terminals. The studies indicate that there are 14 applications of LNG cold energy utilisation all over the world at the present. These 14 units of LNG cold energy utilisation can be classified into 2 categories which are direct and in-direct applications. LNG Cold Energy Utilisation Direct Application Air separation & liquefaction Manufacturing of liquefied O 2, N 2 and Ar Liquefaction and solidification of carbon dioxide Manufacturing of liquefied CO 2 Manufacturing of dry ice Cryogenic Power Generation Cold heat source for the chemical industry Boil-off gas liquefaction system using cold energy storage Liquefied nitrogen In-Direct Application Liquefied oxygen Manufacturing of frozen foods Freeze drying Cryogenic crushing Liquefied argon Etc. Fig. 2 LNG Cold Energy Utilisation Direct application of LNG cold energy utilisation is a direct use of the low temperature LNG as a heat sink for LNG cold energy utilisation system. List of existing direct applications are; 1. Air separation and liquefaction 2. Integrated with gas separation plant process 3. Liquefaction/solidification of carbon dioxide production 4. Rankine cycle cryogenic power generation 5. Direct expansion cryogenic power generation 6. Cold heat source for the chemical industry 7. Boil-off gas liquefaction system by Phase Change Material (PCM) 8. Increasing turbine efficiency 436

3 9. Refrigerated warehouses 10. Chilled water for refrigeration 11. Seawater desalination 12. Amusement winter park In-direct application is the use of cryogenic temperature LNG where an intermediate substance is generated by the direct application system of LNG cold energy utilisation. The intermediate substance will then become a heat sink for its in-direct application system. Examples of in-direct applications are; 13. Manufacturing of frozen foods (freeze drying) - use liquid CO 2 or dry ice which is generated from liquefaction/solidification of CO 2 from direct LNG cold energy utilisation system 14. Cryogenic crushing - use liquid nitrogen which is generated from the air separation and liquefaction from direct LNG cold energy utilisation system. Table 1 Fourteen LNG Cold Energy Utilisation Technologies and Their Features Alternatives Principle of Operation with LNG Cold Energy Utilisation Product/Benefit Air separation and liquefaction Integrated with gas separation plant process Liquefaction/solidification of carbon dioxide production Rankine cycle cryogenic power generation Direct expansion cryogenic power generation Cold heat source for the chemical industry Boil-off gas liquefaction system by PCM Increasing turbine efficiency Refrigerated warehouses Chilled water for refrigeration Seawater desalination Amusement winter park Manufacturing of frozen foods (freeze drying) Cryogenic crushing Integrate LNG stream with air separation and liquefaction process in order to produce liquid nitrogen, oxygen and argon. LNG is used as cold source of the system to reduce power consumption in the process. Integrate LNG stream with propane and ethane separation process to reduce power consumption from the system. Integrate LNG stream with liquid carbon dioxide production process. LNG is used as cold source of the system to reduce power consumption in the process. Use LNG as heat sink of the system in Rankine Cycle power generation which has propane as intermediate medium and has seawater as heat source. Use high pressure LNG from LNG pump to expand through direct expander turbine to produce mechanical power to drive generator for power generation. Integrate LNG stream with industrial process which require cold source or heat rejection for reducing overall power consumption of the process. Use PCM to extract heat from BOG to make BOG condense and become LNG again. Use LNG to cool down compressor inlet air of the system to increase overall system efficiency. Integrate LNG stream with refrigeration process and use LNG as cold source of the process to reduce power consumption Integrate LNG stream with refrigeration process and use LNG as cold source of the process to reduce power consumption Use LNG as a cold source of system to freeze seawater before separate salt and water in the desalination process Integrate LNG stream with artificial snow generation unit and use LNG as cold source of the process to reduce power consumption (or can be an in-direct application by using LN 2 or CO 2 as a cold source for the system depending on system design) in-direct application by using CO 2 or dry iced as a cold source for the system in-direct application by using LN 2 as a cold source for the system Liquid nitrogen, oxygen and argon / reduce system power consumption Reduce GSP system power consumption Liquid CO 2, Dry iced / reduce power consumption Electricity/ electrical energy with free operating cost Electricity/ electrical energy with free operating cost Reduce system power consumption LNG reliquefaction/ Reduce power cost Increase system efficiency Chilled air / reduce operating cost Chilled water / reduce operating cost Fresh water/ reduce operating cost Snow flake in winter park / reduce operating cost Frozen food or cold storage Powder of raw material 437

4 2.2 Existing Applications at LNG terminals Different technologies of LNG cold energy utilisation are applied at LNG terminals all over the world depending on characteristics of the terminals. An example of LNG receiving terminal that uses LNG cold energy utilisation technology is Senboku LNG receiving terminal, Osaka Gas Co., Ltd, Japan. The objectives of the utilisation at this terminal are mainly to reduce power consumption and investment cost with an air separation and liquefaction plant and a Rankine cycle power generation (cryogenic power generation) where LNG is used as a heat sink of the system to produce and supply electricity for the terminal. Another cryogenic power generation system which is used in the terminal is direct expansion power generation system. The system uses the benefit of pressure changes of LNG to generate power through an expansion turbine [1-4]. Other applications of LNG cold energy utilisation in Japan are also existed and varied based on operation conditions of LNG terminal, market requirement around that area and other technical limitations of that terminal. Those applications are cryogenic crush, liquefaction of liquid carbon dioxide and boil-off gas re-liquefaction. In China, there is an LNG cold energy utilisation with air separation and liquefaction unit installed at Putian terminal. This is a joint venture project between CNOOC and Air Products and Chemicals Incorporation, which utilises around tons per hour of LNG flow rate or approximately 10-18% of maximum LNG flow rate of the terminal capacity. The estimated cost of this project is around 215 million CNY (Chinese Yuan) and the payback period of the project is projected to be 8.64 years. There is also another [1] terminal in China, the Ningbo terminal, where LNG cold energy is utilised through an air separation and liquefaction unit and the other 2 terminals in Shenzhen and Shanghai, where air separation and liquefaction units to recover LNG cold from LNG [5] are considered. Country Japan Table 2 Applications of LNG Cold Energy Utilisation around the World [6] LNG Cold Energy Utilisation LNG cold for air separation and liquefaction unit LNG cold to produce liquid CO2 and dry ice LNG cold for power generator (Cryogenic power generation) LNG cold for Boil of Gas (BOG) re-liquefaction system LNG cold as a cold source for chemical plant Cooling of intake air for gas turbine LNG cold for cold storage Korea LNG cold for air separation and liquefaction unit LNG cold for air separation and liquefaction unit Taiwan LNG cold for power generator Australia LNG cold for air separation and liquefaction unit 2.3 Challenge in LNG cold energy utilisation Although LNG cold energy utilisation is not new and also LNG cold energy has a great potential to reduce power consumption and CO 2 emission in various cooling processes, the number of LNG cold energy applications is still considerably low in comparison with the number of existing LNG receiving terminals all over the world. This is because the applications of LNG cold energy utilisation are limited by both engineering and market constraints. Main challenge in LNG cold energy utilisation is to decide which LNG cold energy utilisation technique is the best for our LNG receiving terminal?. To overcome this challenge, it is highly required to have the ability to evaluate both technological and economical feasibilities of the terminal of the LNG cold energy utilisation system, while the terminal reliability on natural gas supply at its design capacity is maintained. 2.4 Key success parameters for LNG cold energy utilisation technology selection Successful LNG cold energy utilisation system is the system that is able to maintain regasification capacity while the most of availability energy of LNG cold is utilised and more economic value to the terminal is realised. To achieve these system conditions, 4 aspects of technology assessment pillars which are 1. Technical aspect, 2. Economic aspect, 3. Environmental aspect and 4. Social aspect are needed to be evaluated for each LNG cold energy utilisation technology in order to select the best LNG cold energy utilisation system which perform the best balancing of these 4 aspects. To select the best-match of LNG cold energy utilisation technique with each LNG receiving terminal, key main parameters which derive from the 4 aspects of technology assessment model are identified as in the table below; 438

5 Table 3 Criteria for LNG Cold Energy Utilisation Selection Aspects Criteria Definition How much energy benefit from LNG stream which LNG cold energy utilisation technique can be extracted as a sensible and latent heat by the principle of difference temperature and pressure LNG pressure in & out % of Energy LNG temperature in & out Recovery LNG flow rate & specification Type & efficiency of equipment Environmental condition Etc. depending on each alternative Since LNG cold energy utilisation require LNG stream as a heat sink or coolant of the system, without LNG enters the system, the system will have an effect on its operating conditions and performance. Technological Aspect Reliability of LNG cold energy utilisation has to work as regasification unit for the terminal Alternative and thus the system has to have high reliability to satisfy NG demand from LNG Receiving customer which is the 1st priority function of terminal Terminal Effect on system itself without LNG stream Effect on LNG terminal if the LNG cold energy utilisation can t operate Maintenance period of the system Utilisation unit has to be nearby LNG terminal to reduce investment in high price LNG pipeline and the utilisation area has to be fit in with the availability Site condition land space near LNG terminal (~ 350 rai or 560,000 m 2, maximum distance is 2-3 km) Distance Area Demand of product Product that each LNG cold energy utilisation unit produce has to be on demand in the market or for terminal internal use Flexibility of product utilisation in the market, the best choice is the product Product utilisations from that alternative is flexible to be used internally within terminal and PTT Economical Aspect Environmental Social Competitiveness of product Pollution EIA / other regulation group also it is able to sell to others customer in the market. Saving from the application of LNG cold (baht/kg of LNG) when compare to that system without LNG cold energy utilisation. Cost of product that each LNG cold energy utilisation produce has to be lower than the system with out LNG in order to make competitive advantages Investment cost O&M cost Low (and not excess the limit) CO 2 and VOCs emission and other pollution which is generated from the system when each LNG cold energy utilisation is installed CO 2 Emission VOCs - for example, benzene, butadiene, dichloroethane, dichloromthane, dichloropropane, tetrachloroethylene, trichloroetylene, vinyl chloride Water condition The system generate positive effect on social around LNG receiving terminal and country Increase job opportunity for residential around Maptaput area Potential to reduce CO 2 and gain positive carbon credit by increasing energy efficiency of the system 3. LNG COLD ENERGY UTILISATION AT MAPTAPUT LNG RECEIVING TERMINAL 3.1 Screening Criteria Screening criteria and the principle of go/no-go gate criteria are applied to screen out some LNG cold energy utilisation alternatives which their characteristic do not match with minimum requirements of Maptaput LNG receiving terminal. 439

6 Main characteristics of Maptaput LNG receiving terminal, which have strong influence on the application of LNG cold energy utilisation and the new construction of the system, are required to be fully aligned with EIA criteria (should not contain combustion process or VOCs generation), to send out considerably high natural gas pressue in pipeline, to provide constant capacity of natural gas supply rate to pipeline network and etc. The above criteria screened out 5 of LNG cold energy utilisation technologies. Those are direct expansion cryogenic power generation due to low level of natural gas send out pressure, and BOG re-liquefaction by PCM due to the requirement of fluctuation of natural gas send out capacity to enable them to switch their mode to store and emit energy. There is no chemical industrial and gas separation plant and gas turbine plant situated near LNG receiving terminal area so the operations of the remaining 3 alternatives are not practical. Refrigerated warehouse and amusement winter park are also screened out due to the reason of safety zone around terminal area. The characteristics of refrigerated ware house and amusement winter park which has a high traffic rate of people in-and-out tend to create difficulty and risk to control all safety regulations in the safety zone. Seawater desalination (freeze desalination) is not applicable since the stage of technology is only in lab-scale without any availability of commercialisation scale in the market at the present. The manufacture of frozen food and cryogenic crushing plant are indirect applications of LNG cold energy utilisation which their characteristics are already covered with the direct application systems (Air separation and liquefaction and liquefaction/solidification of carbon dioxide production) so they should not be taken into account in the analysis. After the screening method, alternatives of potential LNG cold energy utilisation for Maptaput LNG receiving terminal are short-listed to only 4 from 14 alternatives, which are; 1. Air separation and liquefaction 2. Liquefaction/solidification of carbon dioxide production 3. Rankine cycle cryogenic power generation 4. Chilled water for refrigeration These 4 alternatives are also the major of LNG cold energy utilisation techniques that are widely applied at LNG receiving terminal all over the world. 3.2 Air Separation and Liquefaction The system produces liquefied nitrogen, oxygen and argon from air, main unit of the system. Air Separation Unit (ASU) is the unit to separate air into nitrogen, oxygen and argon and then to liquefy them into liquid phase. In the liquefaction process, in which additional/circulation liquid nitrogen (LN 2 ) loop is circulated as a cooling medium for ASU to perform its separation and liquefaction function and thus to maintain cooling ability of LN 2 loop in the system, an electrical compressor is used. This is where cold LNG can be applied. When LNG cold energy utilisation is integrated into the system, the suction temperature of nitrogen compressor and the circulating nitrogen flow rate can be reduced and resulted in lower power consumption of compressor in liquefied nitrogen system. Typically, the energy consumed by the conventional air separation and liquefaction system is around 0.8 kwh/nm 3 of liquefied product, while the system with LNG cold energy utilisation consumes only 0.4 kwh/nm 3 of liquefied product, which is approximately 50% lower in energy consumption of the system [7]. 3.3 Rankine Cycle Cryogenic Power Generation The system produces electrical energy by the principle of Rankine cycle which has propane as a heat medium, seawater as hear source and LNG as heat sink. In the system, propane is evaporated by absorbing heat from seawater at the propane evaporator and then expanded at the turbine to produce mechanical energy for electrical generator. After that, low pressure propane gas/mixture, which exits turbine, will be condensed in the propane condenser by rejecting heat into LNG steam and becomes liquid propane. Finally, liquid propane will be pumped to increase its pressure before entering evaporator to complete the cycle. From the system characteristic and propane physical properties with its boiling temperature around -42 degree Celsius, the energy recovery from LNG cold of the system is around 50% which makes natural gas send out temperature still very low (under -50 degree Celsius). The unit requires additional natural gas heater to increase the natural gas temperature to match with the standard temperature of natural gas supply in the natural gas pipeline network. In general, 100 ton per hour of LNG flow rate in this cryogenic power generation system can produce around 1.7 MW of electrical but this capacity is varied depending on pressure level of required send out natural gas to the system. 3.4 Liquefaction of Carbon Dioxide and Dry Ice Production The system produces liquefied carbon dioxide as a product from the system. In the system, LNG stream is used for a 440

7 pre-cooling process of carbon dioxide when it enters the system; this is to low down CO 2 temperature in order to reduce compressor energy consumption. After CO 2 is compressed, another LNG stream is integrated into the CO 2 distillation column. Within this distillation column which is cooled by LNG, there is a significant effect on reduction of liquefaction energy consumption, around 50% of total energy consumption in the system when compared with the conventional system. After CO 2 is liquefied, it can be further processed in the CO 2 solidification process to produce dry ice by injecting certain amount of water into liquefied CO 2 in dry ice mould to form a dry ice for other market and application purposes. Energy recovery of cold LNG from this system is not much (around 40%) since carbon dioxide requires only around 55 degree Celsius (can be varied depending on pressure level in the process) to form the liquid phase. 3.5 Chill water production The principle is to supply LNG cold steam into an additional heat exchanger to reduce working fluid temperature or to condense working fluid of existing refrigeration system. This can reduce the need for compression unit in the refrigeration cycle, thus a benefit in saving of system energy consumption. Main consideration of this application is to use water-mixture fluid instead of pure water in the chill water loop in order to reduce freezing point of the fluid which enable the system to utilise more benefit of LNG low temperature while still be able to avoid a blockage problem from water freezing effect in the system. The required temperature of chill water in the chill water system is not very low (higher than 0 degree Celsius for pure water and not lower than -10 degree Celsius for other water-mixture fluid) thus it means a low benefit extration from LNG cold stream (-163 degree Celsius) which in turn generates only around 10% of energy recovery from LNG cold energy utilisation potential. 4. DISCUSSION OF LNG COLD ENERGY UTILISATION AND ITS FUTURE At LNG receiving terminal LNG will be evaporated through vaporisers before being sent to natural gas pipeline network. During the evaporation process, LNG releases a large amount of cold energy (about 850 kj/kg). The released LNG cold potential can be utilised through certain processes to recover energy and enhance economic performance of the whole terminal system. Fourteen (14) technologies were selected as possible LNG cold energy utilisation technologies to be installed at LNG receiving terminal. After screened with technology assessment criteria which was designed to balance technological, economical, environmental and social aspects, it was found that only 4 technologies of LNG cold energy utilisation which are 1) Air Separation and Liquefaction, 2) Rankine Cycle Cryogenic Power Generation, 3) Liquefaction/Solidification of Carbon Dioxide and 4. Chill Water Production have the potentials to be applied to Maptaput LNG receiving terminal in Thailand. In the future, these potential technologies for LNG cold energy utilisation would have a high possibility to be constructed at Maptaput LNG receiving terminal since they are considered as useful tools to reduce operation cost of the terminal, to generate new business opportunities and to reduce CO 2 emission by reducing electricity consumption from the whole system. Further study is required in order to utilise the most benefit from the available LNG cold energy at the terminal. All key success parameters which are mentioned above together with LNG Utilisation Ratio which is the ratio between LNG flow rate of that application and LNG cold energy utilisation by total LNG flow rate from LNG receiving terminal are needed to be identified and optimised against the economic parameters of the system in order to achieve the maximum benefit from the available LNG cold energy. 5. ACKNOWLEDGMENTS The authors gratefully acknowledge the contribution of the Thailand Research Fund, PTT Public Company and PTT LNG for all information and suggestion on this study. 6. REFERENCES [1] Kanagawa, T. (2011) Japan s LNG Utilization and Environmental Efforts, Available online: [2] Kusagawa, M., Hamatani, E., Sakamoto, Y., Takubo, M., Ogawa, E., Ikeda, K. and Emi, H. (2008) A Fully Optimized Cascaded LNG Cold Energy Utilization System, Available online: Kusagawa.pdf%26rn%3D6-PO

8 Kusagawa.pdf&rct=j&sa=U&ei=DNaDTojcEMbsrQeg2dD0DA&ved=0CBIQFjAA&sig2=Q5lmd2ggH_BOlKqKU jrata&q=a+fully+optimized+cascaded+lng+cold+energy+utilization+system&usg=afqjcnfwhxvvkxcf 6vfWWtGCMG20CUvvow [3] Otsuka, T. (2006) Evolution of an LNG Terminal: Senboku Terminal of Osaka Gas, Proceeding of the 23 rd World Gas Conference. [4] Hirakawa, S. and Kosugi, K. (1981) Utilization of LNG cold, IPC Business Press Ltd and IIR. Volume 4 Number 1 January 1981 [5] Lina, W., Zhangb, N. and Gua, A. (2010) LNG (liquefied natural gas): A necessary part in China's future energy infrastructure, Energy, 35, pp [6] CNOOC (2006) LNG Cold Energy Utilisation Outlook. China-USA Oil and Gas Forum, Hangzhou, China. [7] Xion, Y. and Hua, B. (2007) Simulation and Analysis of the Air Separation Process by Using LNG Cold Energy, Journal of Shaanxi University of Science & Technology, 25, pp