BASELOAD PLANT IN XINJIA, CHINA - COMMERCIALISATION OF REMOTE GAS RESOURCES FOR AN ECO-RESPONSIBLE FUTURE Eginhard Berger, Linde AG Linde Engineering Division Xiang Dong, Xinjiang Guanghui Industry and Commerce Group Co. Ltd. Jin Guo Qiang, Shanghai Pharmaceutical Industry Design Institute of SINOPEC (SPIDI) Albert Meffert, Tractebel Engineering Lothar Atzinger, Linde AG Linde Engineering Division 1. INTRODUCTION In March 2002, Xinjiang Guanghui Industry and Commerce Group Co. Ltd. has awarded a contract to build an (liquefied natural gas) baseload plant in Shan Shan, Xinjiang, China. This baseload plant will be unprecedented being the first large-scale baseload plant in China, and it will initiate far-reaching changes in the development of China s natural gas industry. An important step towards extended utilisation of the gas from the remote Xinjiang region of China is the production in Shan Shan. The facilities comprise gas processing and liquefaction, intermediate storage and unloading of the into containers as well as into road tankers. The containers will be loaded onto the nearby trains. The will be transported over several thousand kilometers to satellite stations located in some of the East Coast Provinces of China. From there, the is re-vaporised and distributed via short pipelines to industrial and household consumers. The plant contributes to the improvement of living conditions at the plant location by offering employment opportunities for qualified personnel. But also the conditions in the receiving regions will be improved by providing the consumers with clean fuel, which is essential for the environment. The process plant for the production has been optimised with regard to power requirement, equipment cost and maximum engineering works and supplies from China. The main plant units include feed gas compression, acid gas removal, drying, liquefaction, storage, loading and utility facilities. The compressor-driving concept together with the power supply from the grid has been designed taking into account the relatively high specific cost of the electric power and the high cost of the feed respectively fuel gas. The Shan Shan plant is currently under construction. Commissioning is scheduled for the end of the year 2003. The challenges of this new baseload plant in China and the advanced status of the materialisation of the project are described below. 2. DESIGN BASIS The baseload Plant for the production of equivalent to 1,500,000 m 3 (n) per day consists of natural gas treatment and gas liquefaction, storage tank and distribution system. The liquefaction process is based on a high efficient single mixed refrigerant cycle, which requires only the components nitrogen, methane, ethylene, propane and pentane. 2.1 Basic Data for the Process Design of the Plant The design of the plant for the Xinjiang project is based on a state-of-the-art of natural gas liquefaction technology. The production capacity of the plant shall be equivalent to 1 500 000 m 3 (n)/d with an expected on-stream time of 330 days per year. Design hourly liquefaction capacity is 54 t/h. Storage capacity is 30,000 m 3 in liquid form of based on 10 days storage time. The send-out and distribution system capacity meets the requirement of loading the 100 trucks / movable containers within 16 hours. The split is 30% in trucks and 70% in movable containers. Specification of product Pressure and Temperature at tank: 0.01MPaG, 163 0 C The product specification is indicated in Table1.
Composition mole% Nitrogen 0.8 (max. 1.0) Methane 82.4 Ethane 11.1 Propane 4.6 Others 1.1 Table1: Product specification With the design feed gas composition the has a temperature of 162 C and a density of about 490 kg/m 3 in the Tank. Feed gas conditions at Plant Battery Limits The feed gas operating pressure can range from about 0.6 MPaG to 1.1 MPaG. The design pressure is 0.7 MPaG. The feed gas operating temperature can range from -15 C to 40 C. The design temperature is 28 C. The feed gas composition is indicated in Table 2. Nitrogen 3.81 mole% Methane 81.02 mole% Ethane 9.99 mole% Propane 4.10 mole% Butanes 0.93 mole% i&n-pentane 0.05 mole% C6+ < 0.0021 mole% Table 2: Feed gas composition In addition CO2 and traces of H2S and sulfur are present in the feed gas. Process Features The main process and utility units are illustrated in the block diagram in Fig. 1. Waste Water Sour Exhaust System Hot Oil Waste Heat Recovery Flue Turbine Solvent Regeneration Fuel Regen. Refrigeration System Boil Off (Fuel ) Compression Natural Rich Solvent Lean Solvent Vap. Refr. Liqu. Refr. Feed Compression MRC Make up Unit Purification CO2 Removal Purified Purification Drier Fire Fighting Utilities Flare Dry Loading Station Liquefaction Storage Container Loading Station Special Container Meters Loading Station Truck Meters Fig.1: Block diagram of the Shan Shan plant with process and utility units
The liquefaction process with a closed mixed refrigerant cycle requires the components nitrogen, ethylene, propane, pentane, which except nitrogen have to be purchased from external sources. Refrigerant nitrogen and purge nitrogen are identical and will be generated in a nitrogen package. Make-up water for closed cooling water cycle for machinery cooling and demineralized water as make-up water for the MEA in the CO2 wash unit will be provided from outside the plant. A mixture of compressed tank return gas and feed gas is used as normal fuel gas; start-up fuel gas is feed gas. A closed hot oil cycle is used as heating medium. A MEA (monoethanolamine)-water solution is used as solvent for the CO2 Wash Unit. 2.2 Ambient Conditions at Site The annual average atmospheric pressure is 0.099723 MPa. The average ambient temperatures range from 37.1 0 C in the warmest month to -15.6 0 C in the coldest month. The design temperature for gas turbine air inlet and for air-cooling is 30 C. The maximum snow depth is 180 mm with a snow load for design of 250 kn/m 2 The average ground temperature in hottest month is about 37 0 C The extreme maximum ground temperature is about 75 0 C The plant elevation above sea level is about 790 m 3. OVERALL PROCESS AND UTILITY DESCRIPTION The Shan Shan plant has a medium size production capacity in between the two principle types of plants, which are currently in operation world-wide. peakshaving or back-up plants with intermittent operation and production have capacities up to about 480 000 Nm 3 /day. baseload plants with continuous operation and production have capacities between 5 000 000 m 3 (n)/day and 17 000 000 m 3 (n)/day. With the 1 500 000 m 3 (n)/day production capacity the Shan Shan plant will be about 3 times larger than the largest existing peakshaving plants, but about 3 times smaller than existing small baseload plants. The liquefaction process is based on a high efficient single closed mixed refrigerant cycle. The feed natural gas has a low pressure at battery limit, which is too low for an efficient liquefaction process. Therefore, the natural gas is compressed in 3 compressor stages after removal of solid and liquid particles in a separator. The natural gas is cooled, liquefied and sub-cooled in a spiral wound heat exchanger by a single closed mixed refrigerant cycle. This cycle provides cold temperatures by Joule-Thomson expansion at 3 different pressure levels. The refrigerant cycle is recompressed in a 3-stage turbo-compressor, which is driven by a gas turbine. In order to enhance plant efficiency, the waste heat from the gas turbine is recovered by heating a hot oil cycle, which covers the heating requirements of the process plant. 3.1 Natural gas treatment and liquefaction The Natural gas treatment and liquefaction process is illustrated in Fig. 2 and Fig.3. Natural gas (feed gas) has a low pressure at battery limit. Solid and liquid particles are removed by the Feed Filter Separator before it is compressed in a 3 stage feed gas compressor. After the 1st stage of the feed gas compressor the gas is cooled in an inter-cooler against ambient air to about 40 C. Potential water condensed in the inter-cooler is separated in the feed gas compressor inter-stage drum and is fed to the wash unit. After this first compression step the feed gas is further compressed in the next two compressor stages with inter- and after-cooling in air-coolers. The Feed is routed to the CO2 Wash Unit for removal of CO2. The sweet feed gas leaving the CO2 wash column is then routed to the drier station.
Feed Feed Compressor Coolers MEA Wash Column Drier A/B Dry Filter to Liquefier M Electric Motor 3 Stage Feedgas Compressor Filter Separator Compressor Surge Drums Fig. 2: Natural gas treatment process of the Shan Shan plant 3.2 CO2 Wash Unit For CO2-removal from natural gas a MEA (monoethanolamine) wash process was selected. An aqueous MEA solution is utilised as solvent. The feedgas enters the MEA wash column and flows from bottom to top through valve trays. Introduced lean amine flows in the opposite direction extracting the acid gas. The CO2 forms a very weak bond with the alkali. In the top of the column solvent traces are removed by water from the purified gas in some additional trays. The clean gas exits the wash tower with 50 ppm(v) CO2-content water saturated. The loaded amine solution from the CO2 wash columne is regenerated in a strip column, which requires hot oil heating and air cooling in order to separate the CO2 from the loaded amine. The purified amine is returned to the wash column. 3.3 Drier Station The drier station is a 2-bed adsorber station with a cycle time of about 8 hrs. The natural gas is flowing downwards in the first adsorber bed. The water contained in the natural gas is adsorbed on the adsorbent down to a level, where no freezing can occur in the downstream liquefaction section. During this period the other adsorber bed is heated and then cooled by the regeneration gas stream (compressed tank return gas). Heating of the regeneration gas is provided against hot oil and cooling against ambient air, followed by a regeneration gas knockout drum, where the water is separated. The operation of the two vessels is switched periodically. The adsorption respectively the regeneration cycle is operated at the respective gas and regeneration gas pressure. Between adsorption and regeneration a pressure reduction respectively a pressure build up is executed. The expected minimum lifetime of the adsorbents is about 3 years. 3.4 Natural Liquefaction The liquefaction process is shown in Fig. 3. After H2O and CO2 removal the natural gas is routed to the cold part of the process, which contains three spiral wound heat exchangers, which are integrated in one shell ( rocket ), and several separation vessels. The natural gas is first cooled in the Feed Pre-cooler E1, potential off-spec heavy hydrocarbons are separated in a feed gas heavy hydrocarbon separator, where only marginal liquids during design feedgas operation are expected. The gas is then condensed in Feedgas Liquefier E2 and sub-cooled in Feedgas Sub-cooler E3. The sub-cooling temperature is controlled by the amount of tank return gas required as fuel gas for the operation of the gas turbine. The cooling is provided by a closed multi component mixed refrigerant cycle, which consists of the components nitrogen, methane, ethylene, propane and pentane.
from Pretreatment Pre-cooling Section E1 D1 Fuel Spiral Wound Heat Exchangers D2 E2 Liquefaction Section D3 D4 Air Turbine E3 Sub-cooling Section 3Stage Cycle Compressor to Tank Fig. 3: Natural gas liquefaction process of the Shan Shan plant 3,5 Refrigerant System The refrigerant gas stream is withdrawn from the shell side of pre-cooling section E1 of the cryogenic spiral wound heat exchanger set. The refrigerant is slightly super-heated over the dew point condition. It is then compressed in the first stage of the 3 stage refrigerant cycle compressor, and after cooling against air in an air inter cooler, where it is cooled and partly condensed. Liquid formed in the after-cooler is separated in Cycle Compressor Discharge Drum D1. The liquid from the Discharge Drum D1 is routed to the cryogenic heat exchanger E1, where it is sub-cooled and then used for the pre-cooling of the natural gas after expansion in a Joule-Thomson expansion valve. The cycle gas from the Suction Drum D1 is cooled in E1 to the same temperature and partly condensed and fed to the Cold Refrigerant Separator D2. The liquid from this separator is sub-cooled in the cryogenic heat exchanger section E2 to a low temperature, so that it can be used as refrigerant in E2 after expansion in a Joule-Thomson expansion valve. The vapour from the Cold Refrigerant Separator D2 is condensed in E2 and sub-cooled in the cryogenic heat exchanger section E3 to a sufficiently low temperature and provides the final cold for the natural gas sub-cooling after expansion in a Joule-Thomson expansion. After expansion to the lower pressure the cycle gas streams are warmed up in the common shell side of the cryogenic spiral wound heat exchangers E3, E2 and E1 and return jointly to the suction side of the 1st stage of the refrigerant cycle compressor. 3.6 Refrigerant Storage and Make-Up Make-up for the refrigerant system is required mainly due to cycle gas losses via the gas seals of refrigerant cycle compressor. The required quantities for the individual components are adjusted according to the composition readings and the temperatures in the cold part and are provided continuously via flow meters. N2 is stored as liquid nitrogen, vaporized and heated to about ambient temperature and fed to a compressor suction drum. Methane is provided from the overhead gas of the heavy hydrocarbon separation column and mixed to the expanded refrigerant upstream of E2. During first start-up, dry warm feed gas from upstream of E1 can be used instead. Commercial ethylene is stored in bottles at high pressure. The package is placed on a scale to allow for adjustment
of the quantity for the first filling and to control when the package needs to be replaced. For continuous dosing the required quantity is mixed to the expanded refrigerant upstream of E2. Commercial propane is stored in a propane tank. Commercial pentane is stored in a pentane tank and fed to the refrigerant cycle suction drum. 3.7 Turbine A gas turbine is used as prime driver for the cycle gas compressor. Design temperature for gas turbine rating is an ambient air temperature of 30 C. The same design temperature applies for aircooling. The compressed boil-off, flash and displacement gas from the storage tank is used as regeneration gas and then as fuel gas for the gas turbine. 4 STORAGE AND LOADI SYSTEM The from the liquefaction unit with the cryogenic heat exchanger set E1, E2 and E3 (s. Fig.3) is sent to the Storage Tank D-411 via the tank filling line. Please refer to Fig. 4. Vapour Return Container Filling Station Boil-off / Flash / Displacement to Recompression Container Filling Station P-411 Transfer Pump L-421 A/B/C/D/E/F L-431 from Liquefier D-411 Storage Tank L-441 A/B/C Fig. 4: storage tank and loading system of the Shan Shan plant The tank filling can be done via the bottom or the top filling connection. Normal filling is via the bottom line, and only if large density differences are encountered for the, top filling will be selected. The storage tank is equipped with measurement instruments for level, pressure and temperature. The protection system of the tank is connected via the safety control system to the distributed control system. In case of high liquid level or in case of high pressure in the tank the inlet valves will be closed automatically. The temperature in the tank will be measured over the tank height as well as the density to monitor the risk of a possible rollover in the tank. The tank is equipped with a pressure control valve relief to the flare system and pressure safety valves to the atmosphere. Vacuum breakers are installed for under pressure protection of the tank. The tank will be filled continuously during operation of the liquefaction system at a filling rate of about 111 m3/h. During 16 hours per day a discontinuous send out operation to the truck and container filling is scheduled. For send-out operation two submerged in-tank pumps will be installed each designed for 320 m3/h capacity, suitable for 100% of send-out capacity. One pump is installed as spare. The pumps are installed in pump columns inside the tank and equipped with foot valves. Each pump is equipped with a kickback line to the tank to control the minimum flow of the pump during the period when no filling operation takes place. The send out lines to the truck and container filling station are always filled with and a small circulation flow maintains the system cold. The trucks are weighted ahead of filling. The trucks will be connected manually to the loading arm filling and vapour return lines. The first into the warm truck tank evaporates and the created vapour will return to the storage tank. After cooling the truck tank the filling rate will be increased to the maximum filling rate.
The flow counter will stop the filling operation automatically via the automatic control valve at the loading station. The truck will leave the plant via the weighbridge after disconnection from the loading arm. The same operation will be applied for the container filling system. The only difference is that trucks are moving by themselves and the container needs to be transported by gantry crane and trailers. The container will be fixed on rail-platform cars and transported as train of 40 to 70 cars length. The filling time of one container or one truck is estimated to about 1.2 hours including connection / disconnection time. The filling system is designed for 100 trucks / container within 16 hours. The filling system consists of 6 loading stations for container and 3 loading stations for trucks. The planned rail container transport not only represents a solution to long distance land transportation for, but also is a solution to the combined road and rail transportation. The extension of this container transport to the waterway is currently under investigation. These flexible transportation and receiving methods are the main features of this new and natural gas distribution scheme. The satellite terminals on the receiving side together with this transport method are applied to regions, in which the gas source is situated far away, the market is comparatively small and therefore, a pipeline would not be economical. This method will have a positive impact on the way of energy consumption and on the development of the market for the clean natural gas. 5 UTILITIES Some of the Shan Shan plant utility facilities are described below. 5.1 Fuel System The net flash, boil-off and displacement gas coming from the storage tank is compressed, cooled against ambient air and used as regeneration gas in the dehydration section before it is sent as fuel to the Turbine, which drives the cycle compressor. To allow for a good pressure control of the fuel gas, an additional fuel stream is taken from the feed gas after the 2nd stage of the feed gas compressor. 5.2 Unit The hot oil system provides the process heat for the Plant at two temperature levels. To keep constant flow rates in the system, two cycles are introduced, a medium temperature cycle and a high temperature cycle. The heat for both cycles is provided by a hot oil heater package, a waste heat recovery unit in the exhaust stack of the cycle gas turbine. The hot oil is heated to approx. 260 C to supply heat for the regeneration gas heating. To allow for start-up during winter conditions, the system is heat traced. 5.3 Flare and Safety Systems The Shan Shan plant is equipped with two flare headers. A warm gas flare header, which ties-in directly at the bottom of the flare and a cold gas and liquid flare header including a blow down vessel for the separation of cold liquid and vapour. The plant is designed for non flaring during normal operation. Relevant rules and regulations have been incorporated in the plant design, manufacturing and construction in order to enable safe and environmentally friendly plant operation. 6. DRIVER CONFIGURATION The refrigerant cycle compressor is driven by the Alstom gas turbine type GT10 OB. This is a mechanical drive turbine with a waste heat recovery unit. Special challenges for the gas turbine as main compressor driver and for the design of the air coolers are the climatic conditions at the Shan Shan location with high fluctuations of the air temperatures during summer, winter, day and night times. Cooling water, which would conventionally be used for refrigerant cooling, is not available. Therefore, ambient air has to be used as cooling medium. The feed gas compressor is driven by an electric motor with electric power supplied by the local grid.
7. MAIN CRYOGENIC HEAT EXCHAER A special feature of the cryogenic section of the process plant is the Linde designed and manufactured spiral wound heat exchanger. The demand for this type of heat exchanger from Linde is increasing world-wide for baseload plants. It excels by its robustness for the natural gas cooling, liquefaction and sub-cooling process, where the refrigerant cycle and product streams reach temperatures down to -160 C. The spiral wound heat exchangers for the Shan Shan plant are currently manufactured. 8. PROJECT EXECUTION The plant execution is an example for the good co-operation between the parties involved: Guanghui Industry and Commerce Group Co in Urumqi as client, is also the organiser of the civil and construction works, procurement of local equipment and bulk material. SPIDI in Shanghai is responsible for the entire plot plan of the plant and detail engineering with utilities. Tractebel in Bonn is responsible for the design of the storage tank and the loading facilities and for the procurement of the relevant imported equipment and material as well as for supervision of tank and loading units construction and commissioning Linde Engineering in Munich is responsible for the natural gas treatment and liquefaction process design and for the procurement of the imported process related equipment as well as for supervision of plant construction and commissioning. The plant is currently under construction with much of the work for the storage tank being already erected. The plant will be mechanically completed by the end of the year 2003 with subsequent commissioning. The final layout of the plant includes the compressor house, the pipe rack with the air coolers and the cryogenic spiral wound heat exchanger set included in a steel structure. The equipment and piping has been arranged taking into account relevant safety regulations as well as short pipeline lengths. The required plant area is about 58 m x 130 m. The cryogenic heat exchanger has a height of about 43 m. The storage tank is connected to the process plant by a pipe rack, which carries the product and the vapour return line. 9. CLOSI REMARKS This plant will open a new era of meeting the demand for natural gas in China, which consistently rose even during the recent economic crisis. With the introduction of such plant types combined with the respective transport infrastructure, natural gas markets can be dynamically introduced and developed. It is evident that natural gas, as a cleaner fuel, will play an increasingly important role in the primary energy mix, as it will serve to reduce the environmental constraints in terms of emission levels. The Shan Shan plant represents a valuable contribution to increase the wealth of the country in a similar way, as is the case in other countries by commercialisation of natural gas and. The target regions have not yet been connected to major gas pipelines due to economic reasons, since the initial gas consumption rate would not justify such a large investment. Therefore, the supply will initiate the penetration of these regional markets with environmentally friendly fuel. Thus the from the Shan Shan plant will contribute substantially to the economic development and growth. This scheme is unique in the world with regard to plant type as well as plant and transport capacity. Therefore, the project has attracted broad national and international attention. It can be considered as an incentive for the commercialisation of remote gas resources with similar market conditions worldwide and particularly in China.
9.1. Selected References 1 W Förg, W Bach, R Stockmann, Linde and R S Heiersted, P Paurola, A O Fredheim, Statoil: A New Baseload Process and Manufacturing of the Main Heat Exchangers. 12 Conference, Perth, May 1998. 2 E.Berger, Linde: Natural Liquefaction - Technical and Economic Aspects, First Indian Conference, Madras, India, 1996 3 E.Berger, Linde: Satellite Stations in Europe, 10 Conference in Kuala Lumpur, Malaysia, 1992