OUTLINE OF MIZUSHIMA LNG RECEIVING TERMINAL AND MAIN CHARACTERISTIC OF EQUIPMENT COST REDUCTION

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1 OUTLINE OF MIZUSHIMA LNG RECEIVING TERMINAL AND MAIN CHARACTERISC OF EQUIPMENT COST REDUCON Kenichi Tadano Senior Engineer Yoshifumi Numata Engineering Manager Daisuke Wada Engineer Chiyoda Corporation Yokohama, Kanagawa, Japan ABSTRACT The Mizushima LNG Receiving Terminal was constructed in the existing refinery to supply Natural Gas to the power plant and the gas sales companies, and started its operation in April This terminal has some features for cost reduction. A pressurized cold keeping system for unloading line has been developed to decrease motive energy of LNG pump and the amount of Boil Off Gas (BOG) generated by LNG pump heat input, by decreasing cold circulation flow rate. Seawater as a heating source for LNG vaporizer is supplied from cooling seawater pipe of the refinery, and cooled outlet seawater is sent back to cooling seawater pipe in refinery for energy integration. To utilize the existing refinery seawater system enables reduction of initial cost by commoditizing seawater intake system and operation cost of motive energy for seawater pump for LNG vaporization. A new type LNG vaporizer (Steam Ejector type Vaporizer, SEV), which utilizes steam as a heating source, is adopted as backup vaporizer to keep gas supplying even when the seawater system has trouble. Above technologies have achieved reduced construction cost and running cost with keeping reliability. PO-43.1

2 INTRODUCON The Mizushima LNG Company Limited was jointly established by the Chugoku Electric Power Co. Inc. and the Nippon Oil Corporation in 2001, and Mizushima LNG Receiving Terminal thus created began its commercial operation on April 1, The terminal has the capacity to handle 600,000 tonnes per annum, and vaporized sales gas is sent to the Mizushima Power Station of Chugoku Electric Power Co., Inc. for use as fuel. Gas is also supplied to gas sales companies through the gas pipeline. Moreover, a part of LNG is shipped to the LNG satellite terminal by using LNG road tankers. Mizushima LNG Receiving Terminal was planned in Kurashiki City, which faces the Inland Sea, and constructed on a site of about 44,000m2 created by removal of three existing crude oil tanks in the Mizushima Refinery of the Nippon Petroleum Refining Co. Ltd. (See Fig.1) The resulting LNG terminal has made the best use of the existing refinery features, aimed at decreasing of the cost of construction as well as the running cost while ensuring the reliability of the terminal. The features of Mizushima LNG Terminal, relating to the reduction of the construction and the running cost, are described here. MIZUSHIMA Kurashiki Shin-Kurashiki Other LNG Receiving Terminals Takase River The Nippon Oil Mizushima Refinery Mizushima Port Figure 1. Location of MIZUSHIMA LNG Terminal Outline of Mizushima LNG Terminal Mizushima LNG Receiving Terminal Layout of Mizushima LNG Terminal is shown in Fig. 2 and specifications of major equipments are shown in Table 1. The LNG unloading facilities are designed to unload LNG at a rate of 13,200m3/h. Unloaded LNG from the LNG ship is transferred to LNG Storage Tank via three LNG unloading arms and one unloading line. The unloading line has a Pressurized Cold- PO-43.2

3 Keeping System to maintain cryogenic temperature of the unloading line during the holding mode, described in next section. A part of Boil Off Gas (BOG) generated from LNG Storage Tank is pressurized by Return Gas Blower and sent to the cargo tank via the return gas line and the return gas arm to keep the cargo tank at a constant pressure. The capacity of Return Gas Blower has been determined with consideration to the abovementioned unloading rate. Table 1. Equipment Specification Facilities Equipment Name Specification Unloading Unloading Arm 16 3 Return Gas Arm 16 1 Unloading Line 36 1 Return Gas Blower 29,000Nm 3 /h 1 Storage LNG Storage Tank PC LNG Tank 160,000m 3 1 Boil-Off Gas BOG Compressor 8.1t/h 2 Treatment Sending Out Primary LNG Pump 110t/h 4 Secondary LNG Pump 85t/h 2 LNG Regasification LP LNG Vaporizer 105t/h 1 HP LNG Vaporizer 75t/h 1 LP/HP Backup Vaporizer 105 t/h (LP) /75 t/h (HP) 1 Seawater Seawater Pump 1,810m 3 /h 2 (for LP LNG Vaporizer) Seawater Pump 1,200m 3 /h 2 (for HP LNG Vaporizer) Tanker Shipping 30t/h 3 One LNG Storage Tank, capacity of 160,000m3, is installed, and the type Pre-stressed Concrete has been selected for the tank with consideration to safety and efficient land use. Four Primary LNG Pumps are installed in LNG Storage Tank to send LNG to LP LNG Vaporizer, the Secondary LNG Pumps and Road Tanker Shipping facility. The number of pumps in operation is optimized automatically depending on the flow rate of LNG. Two pot-type Secondary LNG Pumps are installed for sending LNG to HP LNG vaporizer, but only one pump is usually in operation. Two BOG Compressors are installed for pressure control of LNG Storage Tank. Normally one BOG Compressor is in operation during holding mode, and two compressors are in operation, depending on LNG Storage Tank pressure, during loading mode. BOG, which is pressurized by BOG Compressor, is mixed with NG from LP LNG Vaporizer and sent to the power plant. Two kettle type vaporizers are installed, one as LP LNG Vaporizer and the other one as HP LNG Vaporizer, for the purpose of vaporizing/heating LNG up to 0 o C or more. These vaporizers utilize seawater as the heat source, and propane as an intermediate medium. PO-43.3

4 Two seawater pumps are installed in parallel for each LNG vaporizer. Usually, both of the pumps are in continuous operation, but one pump is able to supply seawater equivalent to about 70% of the design rate if the other pump is shut down due to an emergency. One steam ejector-type LNG vaporizer, which utilizes steam as a heat source, is installed as LP/HP common backup vaporizer. This vaporizer can start operating either automatically or manually when LP or HP LNG Vaporizer is shut down due to an emergency or for scheduled maintenance. Three Road Tanker Shipping Islands are installed, which are able to send 30t/h of LNG to each tanker at the same time. The above technologies have succeeded in reducing the construction and running costs while keeping reliability. Of these, the following three major items are explained below. Cold-keeping System for LNG unloading line Seawater System Steam-Ejector Type LNG Vaporizer BOG Compressor Vaporizer(SEV) Odor.F ac ility Utility F acilities Vaporizer(She l&tube) Vent Stack Existing Seaw ater Pump No.2 LNG Storage Tank (Future) No.1 LNG Storage Tank LNG C ontrolb ld. No.1 Breathing Tank 2 ry P um p Flare S tack RGB LNG Plat Form Figure 2. Terminal Layout Cold-keeping System for LNG Unloading Line Since the LNG unloading line has a large bore, 36 inches in diameter, the cooling down from ambient temperature would require much time and work. So it is necessary to maintain cold conditions by keeping the LNG unloading line filled, even in the holding mode, after the first operation of the terminal. At an LNG receiving terminal, where the time between LNG ship arrivals is rather short, Cold-Keeping System for the unloading line usually adopts a method of circulating large amounts of LNG to maintain the sub-cool temperature in the unloading line. With this method, it is necessary only to adjust the LNG circulation flow through the unloading line, therefore, the configuration and the control system are rather simple. PO-43.4

5 However, since it utilizes only the sensible heat of LNG, a large amount of LNG has to be circulated. Consequently the power required for the LNG supply pump is increased and also BOG generation increases owing to the pumping operation, resulting in the requirement for increased BOG Compressor power. In the case of Mizushima LNG Receiving Terminal, the ship arrival intervals is much longer, more than one month, and the power cost for the cold-keeping operation of the unloading line is required to be lower than other receiving terminal. Therefore, Mizushima LNG Receiving Terminal has adopted a cold-keeping system that uses the latent heat as well as the sensible heat of LNG for the purpose of reducing the operating cost. This Cold-Keeping System has three operation modes i.e. Pressurized Cold-keeping mode, Normal Cold Circulation mode and Unloading mode. In order to change modes, only the mode selection pushbutton needs to be operated therefore preventing operational errors, then valve opening/closing, pressure and flow rates in each pipe, are automatically controlled. Pressurized Cold-keeping mode. When Pressurized Cold-keeping mode is selected, the gas generated by external heat input is removed from the system, and the same amount of LNG as vaporized is supplied to maintain LNG levels in the system. In this way, the cold-keeping of the unloading line is maintained. The heat input from outside of the piping is removed by LNG temperature rise (sensible heat) and also by LNG vaporization (latent heat). Therefore, in this method, it is possible to maintain the cold-keeping of the piping just by supplying the same amount of LNG as the gas removed from the unloading line. Mizushima LNG Receiving Terminal requires approximately 1 t/h of LNG for this cooling. In Pressurized Cold-keeping mode, the pressure of the unloading line is fixed at 0.1MPaG on the roof of the tank (Fig. 3-(a)), and boil off gas vaporized by external heat input in the unloading line is collected into gas collection systems (Fig. 3-(c), (d)) and vented to an LNG tank or a BOG line. The same amount of LNG lost due to vaporization is supplied from Primary LNG Pump discharge line by level control (Fig. 3-(b)). In addition, the control valve (Fig. 3 (e)) is preset at a minimum opening to maintain a flow rate of approximately 1 t/h of LNG continuously regardless of the level conditions to maintain the sub-cool temperature in the cold circulation line. Figure 4 shows operation data for changing from Pressurized Cold-keeping mode to Normal Cold Circulation mode. After selecting Pressurized Cold-keeping mode, the temperature increases to reach its saturation temperature, and then the temperature is maintained almost constant, but the saturation temperature gradually increases owing to weathering of the LNG in the piping caused by vaporization. To prevent the LNG density from increasing above the design condition due to the evaporation, Normal Cold Circulation mode is selected when the liquid temperature increases above the preset value, and LNG within the piping is replaced by liquid from Primary LNG Pump discharge. PO-43.5

6 : OPEN / AUTO : CLOSE : LNG : BOG (a) PC (b) 36" (c) (1) (2) 36" Unloading Line (3) 3" Cold Circulation Line FC (e) (d) P LP Vaporizer 2ry LNG Pump Lorry Island Figure 3. Pressurized Cold-keeping Mode Pressurized Cold Circulation Mode Normal Cold Circulation Mode Pressurized Cold Circulation Mode (1 ) Temperature [deg-c] (2 ) (3 ) Unloading Piping Temp. (1) Unloading Piping Temp. (2) Unloading Piping Temp. (3) Flow Rate [t/h] A (2) (1) (2) (3) Pressurized Cold Circulation Flow Rate Normal Cold Circulation Flow Rate Unloading Piping Pressure Pressure [kpag] (3) 5 (1) LNG Terminal Holding Operation Days 0 Figure 4. Operation Data for Cold Keeping System for LNG Unloading Line Unloading mode. When selecting Unloading mode, LNG supply for the coldkeeping is shut off, and the loading line is lined up to unload LNG by fully opening the block valves for the LNG loading arm and the LNG tank. The block valve for the LNG tank is not operable during Pressurized Cold-keeping and Normal Cold Circulation mode to prevent depressuring of the unloading line. In addition, the level control valves of the gas collection devices are shut off, as BOG is not generated while large amount of sub-cooled LNG flow through the unloading line. PO-43.6

7 : OPEN / AUTO : CLOSE : LNG : BOG (a) PC (b) 36" (c) (1) (2) 36" Unloading Line (3) (d) P 3" Cold Circulation Line LNG Ship FC (e) LP Vaporizer 2ry LNG Pump Lorry Island Figure 5. Unloading Mode Normal Cold Circulation mode. In principle, the unloading line in the holding mode is operated in Pressurized Cold-keeping mode. However, when the liquid temperature increases owing to LNG weathering and the alarm is triggered, the mode is changed into Normal Cold Circulation mode and LNG in the unloading line is replaced by liquid from Primary LNG Pump discharge. After the temperature of the unloading line decreases to the temperature of LNG supplied from Primary LNG Pump discharge line, the mode is again changed into Pressurized Cold-keeping mode. At the time of the unloading operation, if the mode is changed directly from Pressurized Cold-keeping mode to Unloading mode, the opening of the inlet valve at the top of the LNG tank will cause a rapid decrease in pressure in the unloading line. This causes LNG to flash and a large amount of BOG is generated in a short period of time, resulting in a large gas pocket being pr Because LNG in the unloading line on the pipe rack is at the saturation condition, the value of the liquid head is approximately 0.2MPaG due to the difference in level between the rack and the upper part of the tank being added to the preset pressure of 0.1MPaG at point (a) of Fig. 5. It is therefore necessary to prevent LNG from flashing while it rises to the upper part of the tank. This is achieved by selecting Normal Cold Circulation mode, which changes the preset value of the pressure controller (Fig. 6-(a)) to 0.4MPaG. After changing the pressure setting, approximately 32 t/h of LNG from Primary LNG Pump discharge is supplied in the unloading line through the flow control valve (Fig. 6- (e)) and LNG circulates through the line and back to the LNG tank. This circulating flow rate is sufficient for maintaining the cooling in the piping only with the sensible heat. After more than six hours of operation in Normal Cold Circulation mode, and when the piping has cooled down below the prescribed temperature, the pressure control is stopped and the flow is changed to circulation through the 4 bypass line. PO-43.7

8 : OPEN / AUTO : CLOSE : LNG : BOG (a) PC (b) 36" (c) (1) (2) 36" Unloading Line (3) 3" Cold Circulation Line FC (e) (d) P LP Vaporizer 2ry LNG Pump Lorry Island Figure6. Normal Cold Circulation Mode Table 2 shows the comparison between the power required for the pump and BOG compressor to deal with the amount of BOG generated, in the cases of circulating 32 t/h of LNG in Normal Cold Circulation mode and circulating 1 t/h of LNG in Pressurized Cold-keeping mode. As the Table shows, the selection of Pressurized Cold-keeping mode leads to approximately 235 kw of power reduction. Considering the frequency of LNG ship arrivals, it is calculated that Normal Cold Circulation mode and Unloading mode will only be selected for days per year and this results in approximately 1,950 MWh power saving. Table 2. Motive Energy Comparison between Pressurized Cold Circulation Mode and Normal Cold Circulation Mode Mode Pressurized coldkeeping mode Normal cold circulation mode LNG Flow rate [t/h] Required pump power [kwh] BOG compressor power [kwh] Summation of deltapower [kwh] Seawater System In Mizushima LNG Receiving Terminal, seawater is selected as the heat source for LNG vaporization as being the most practical from the standpoint of reliability, operability and economic efficiency. Typically, either Open Rack Vaporizer (ORV) or kettle type heat exchanger (with propane as intermediate medium) is used as vaporizer using seawater as a heat source. Since the kettle type vaporizer enables the seawater system to be a pressurized system because of the mechanical structure of the vaporizer, it is able to utilize part of the seawater supply from the seawater line in the adjacent oil refinery, and return the used seawater to the seawater line in the oil refinery. PO-43.8

9 In the case of utilizing seawater for an ORV, seawater used for vaporization must be re-pressurized to re-inject into the line in the oil refinery since the seawater in ORV is an open system. Therefore, this system has less advantage for construction and operating costs than the pressurized system since new seawater facilities, including seawater intake/outfall and pumps, are required, and moreover, such a system would create a problem for site security for the new facilities. Therefore, the kettle type vaporizer has been adopted as the LNG vaporizers, and the configuration of the seawater system installed is shown in Fig. 7. The construction costs of the seawater intake/outfall, seawater screen equipment, etc. were able to be eliminated by utilizing the seawater system of the adjacent oil refinery. LNG Receiving Term inal NG Existing Refinery S ea W ater Intake Pum ps Existing Traveling Screen Seawater Pum p LNG Vaporizer LPG Seawater C oolant Header LNG Refinery S eaw ater Intake Figure7. Seawater System As with the seawater system, the jetty facilities, the access to electricity, the fire fighting equipments of the adjacent oil refinery are partially shared by Mizushima LNG Receiving Terminal to reduce the cost. Steam Ejector Type LNG Vaporizer A Steam Ejector Type Vaporizer (SEV) was installed as a backup vaporizer for both the LP LNG vaporizer and the HP LNG vaporizer. This vaporizer uses steam as heat source to maintain the gas supplying at the station even in case of some trouble in the seawater system. LNG supplied to SEV is passed through tube bundles in the bath and, after heat exchanging with hot water in the bath, which is agitated vigorously by air bubbles drawn in by the steam ejectors, delivered as gas at a temperature of 0 o C or more. Since the air used for agitating the bath is reused in a closed cycle, heat loss is minimal. The steam as the heat source is supplied to the hot water bath via four injection lines, though only No. 1-3 are fitted with ejectors. No. 1 ejector is used for the base load and operates continuously during LNG vaporization. No. 2 and No. 3 ejectors start and stop sequentially according to the bath temperature and the LNG flow rate. PCVs, installed in these lines, upstream of the ejector, control the bath temperature by TC-PC cascade control. If the bath temperature still decreases during the operation of the No. 3 ejector, steam is supplied via the fourth line which is Temperature Control Valve controlled. Since the No. 1-3 ejectors supply sufficient air for agitating the hot water, no ejector is fitted in the fourth steam line and the steam is directly injected into the hot water. Fig.-8 below shows a schematic of SEV. PO-43.9

10 During SEV 100% operation, approximately 38 t/h of steam are required. During SEV stand-by operation, a small amount of steam is supplied to keep the temperature of hot water constant for emergency start-up. The structure of SEV is simple and its maintenance is easy. Also, since the steam used as the heat source is supplied from the existing facility in the refinery, neither a new steam boiler nor a water demineralizer is required and the construction costs are reduced. As a result of the test operation, it was demonstrated that the vaporizer could be ramped up for an emergency start-up from 0% to 100% in one minute and still maintaining stable vaporization. It was also demonstrated that the sequence switching of the ejectors in combination with TCV enable a wide rage of operating conditions with a minimum vaporization of approximately 4t/h up to the rated LNG vaporization flow rate of 105t/h. Figure 9 shows SEV operation data. Steam No.1 Ejector PCV PC No.2 Ejector NG LNG PCV TCV PC Air Inlet Nozzle No.3 Ejector Figure 8. Steam Ejector Vaporizer PO-43.10

11 1.S team flow rate ( )[t/h] 2.LNG flow rate( [t/h] 3.H ot W ater T em perature( ) [deg-c ] 4.N o.2 Ejector PC V O pening ( ) [%] 5.N o.3 Ejector PC V O pening ( ) [%] 6.T C V O pening( ) [%] 7.N o.2 Ejector Inlet P ressure( ) [kp ag ] 8.N o.3 Ejector Inlet P ressure( ) [kp ag ] CONCLUSION Figure 9. Operation Data Mizushima LNG Receiving Terminal achieved cost reduction for both construction and operation while maintaining a high reliability for the terminal by utilizing the existing conditions and facilities at the site. Cold-keeping System for the LNG unloading line, the Seawater System and Steam-Ejector Type LNG Vaporizer are presented here as examples of cost reduction. ACKNOWLEDGEMENT The authors would like to thank the Mizushima LNG Company for providing technical data and photographs and for their permission to publish this paper. PO-43.11