Artic LPG Design

ARCTIC LNG PLANT DESIGN: TAKING ADVANTAGE OF THE COLD CLIMATE William P. Schmidt Technology Manager, LNG Process Christopher M. Ott Principal Process Engineer Dr. Yu Nan Liu Technical Director, LNG Joseph G. Wehrman LNG Machinery Specialist Air Products and Chemicals, Inc. Allentown, Pennsylvania, USA [email protected] KEYWORDS: LNG liquefaction, LNG processes, refrigeration cycles, dual mixed refrigerant, propane precooled mixed refrigerant, DMR, C3MR, arctic, desert, tropical, climate, seawater cooled, air cooled ABSTRACT As the LNG industry continues to grow, liquefaction plants are being considered in a wider range of climates, including arctic environments. This paper compares arctic conditions to the historic tropical and desert locations, focusing on the key differences of colder year-round ambient and seawater temperatures and wider seasonal temperature ranges. These differences play a significant role in selecting the optimum liquefaction cycle, refrigeration driver type, and machinery configuration. The Propane Precooled Mixed Refrigerant (C3MR) and Dual Mixed Refrigerant (DMR) processes are compared. With the same power input, these processes produce essentially the same LNG flow with essentially the same specific power, except in very specific circumstances. A case study is included to provide more detailed information. Equipment configurations are discussed, including electric motor drive, aeroderivative gas turbines and refrigerant compressor arrangements. INTRODUCTION Historically, almost all baseload LNG facilities have been either in tropical or desert regions of the world, with only two projects having been completed in arctic climates in the past decade: Snøhvit [1,2] and Sakhalin Island [3]. The world-wide demand for natural gas is increasing rapidly, and to meet this need, the LNG 1 industry is expanding into new natural gas sources. Many large natural gas fields are in arctic or sub-arctic regions. Developing projects for arctic climates and constructing plants in those regions present many new challenges. This paper focuses how to optimally design the liquefaction process for arctic climates. This paper will address only the process implications for the liquefaction area. Outside the paper’s scope are construction, shipping, and human factors such as extreme cold and very long and short daylight periods. 1 The commonly used Köppen climate classification system defines arctic and subarctic climates as follows: Warmest Month Coldest month Arctic Tmean < 10°C TMean < 0°C Subarctic T > 10°C (no more than 4 months with Tmean > 10°C) TMean < 0°C This paper will not use these strict definitions, rather we use “arctic climate” to refer to locations with long periods of time where the ambient temperature is well below 0°C. 1 WHAT MAKES THE ARCTIC DIFFERENT? The obvious answer is that the ambient temperatures are much colder. However, it is worth a closer look at the specific weather data to understand what the differences are and to quantify them. For this analysis, three types of climates are considered: desert, tropical, and arctic. 2 • Desert – Qatar represents this climate type. Deserts have very hot summers and mild winters (temperatures always above freezing). The sea temperature warms significantly in the summertime, as the shallow Persian Gulf is heated by the intense sun. • Tropical - The island of Borneo is a typical tropical climate. There is virtually no variation in temperature throughout the year, in either air or seawater temperatures • Arctic – The Yamal peninsula in northern Russia, on the Kara Sea, has a harsh Arctic climate. The winters are extremely cold, and the summers are colder than the desert winters. The seasonal air temperature variation is extremely large. The sea surface freezes in the winter, requiring ice breakers for shipping. 3 The figures below quantify these differences. Figure 1 shows the range in the daily average ambient air temperature for each month [4]. The “error bars” show the typical range of daily average temperatures within each month. (For details of how these are calculated, see Appendix.) Figure 2 shows the Sea Surface Temperature (SST) for the three sites, as measured during 2012 [5]. Yamal’s summertime jump in SST occurred when the icepack melted in June. Figure 1: Dry Bulb Temperature 50 40 30 Temperature (°C) 20 10 0 -10 -20 Qatar -30 Borneo Yamal -40 -50 Jan 2 Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec In the Köppen Climate Classification deserts are defined as any climate with little precipitation. (There are quantifiable precipitation criteria, not given here). Deserts are either “hot” (e.g. Qatar) or cold (e.g., Gobi). Hot is defined one of two ways, depending on the specific user • all 12 mean monthly temperatures are greater than 18°C, or • the coldest month mean temperature is greater than 0°C. For this paper, we are using the simpler, less precise term of “desert” to refer to hot deserts, because there are few LNG plants in cold desert climates (Peru LNG is one). 3 The Köppen Climate Classification would split this classification into tropical monsoon and tropical rainforest, depending on the seasonal variation in rainfall. A tropical climate has all twelve months with average temperatures over 18°C. We do not distinguish between monsoon or rainforest in this paper. 2 5 34 (6. all between 5 and 10°C. Further observations from this table are: • The air temperature varies the most in arctic climates. Detailed description of these are in Appendix (2) Approximately the 99% summer high temperature (3) Approximately the 99% winter low temperature (4) Difference between summer high and winter low (5) Typical difference between daily high and low.7) 27 21 7 3.2 27.Figure 2: 2012 SST 50 40 30 Temperature (°C) 20 10 0 -10 Ice Free Ice Covered -20 Ice Covered Qatar -30 Borneo -40 Yamal -50 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec The data is summarized in Table 1: Table 1: Seasonal Temperatures .1 12. then Qatar with 27°C. (6) The salinity of seawater lowers its freezing point to approximately -2°C. (Note that the yearly variation in average daily temperature for the tropical climate is only slightly larger than its diurnal variation).5 33.6 22.11 5 30. seawater for cooling is taken from below the surface. and finally Borneo at 11°C.9 55.5 27.7 12. The challenge that diurnal variations can cause for the liquefaction plant is not the size of the temperature changes. • The mean diurnal temperature swings (day-to-night) are fairly similar.8 4-9 5-7 7 .1 39. rather the challenge is that the rate of temperature change 3 .Summary Yearly Avg (2) Summer High Air T (°C) (1) Seawater T (°C) (3) Winter Low (4) Yearly Range Typical Diurnal (5) Range Yearly Max Yearly Min Yamal Borneo Qatar -10. Yamal shows the highest yearly range of 55°C.7 -42.1 11. (7) Sea surface freezes in winter.0 26.5 13 -2 Yearly Range Notes: (1). • The process equipment and piping must be designed for the very cold ambients. This is more of a concern in the upstream portion of the plant. make construction. C3MR uses pure propane as the precooling refrigerant. and when cooling with air. colder ambients affect the PCC process similarly to the C3MR process and it is not discussed separately. There is virtually no diurnal variation. TM C3MR Process . Much of the equipment in the liquefaction area is rated for cryogenic temperatures (often down to -40°C in the precooling loop and -160°C in the main liquefaction area. • The winds are extreme which combined with long periods of darkness and the cold temperatures.The workhorse of the LNG industry has been the AP-C3MR process [6. This includes material selection (normal carbon steel is typically only rated to -29°C) and freeze protection for any lines containing water or other components with relatively high freezing points. These include • The number of daylight hours varies much more. 4 LNG liquefaction . They differ mainly in the precooling step.5 to 1%/°C. the seawater temperature varies less than the air temperature. and will not be considered further. including the compressors. LIQUEFACTION PROCESS CHOICES This paper compares how colder temperatures affect two LNG liquefaction processes: Propane Precooled Mixed Refrigerant (C3MR) and Dual Mixed Refrigerant (DMR).is relatively large—often a few °C/hr. A third process used in baseload plants is the Pure Component Cascade (PCC). The factors above are beyond the scope of this paper. where DMR uses a blend of low boiling hydrocarbons (typically C1 through C4). and fog and mist can accumulate and freeze on buildings and equipment near the sea. Because both the PCC and C3MR processes use C3 precooling. The annual precipitation is relatively low. never melting. so the plant control system and operating procedures must allow for this capacity change. must be designed for these cold ambient temperatures. operation and maintenance much more difficult. whatever snow does fall will stay for the entire winter. Arctic regions have weeks or months where the sun never rises. However. • The sea will contain ice and may freeze over. This complicates shipping tremendously. gas turbines and associated cooling water systems. because the very cold air cannot carry much water vapor. The plant capacity can change by 0. These processes are discussed in detail here because they are commonly used in baseload LNG plants. Arctic locations differ from the tropical and desert locations in many other ways. as shown in Figure 3. with similar periods where the sun never sets. the cooling medium heat sink varies much more between seasons. • For all climates.) However the warm areas of the liquefaction area. Arctic climates primarily affect the LNG liquefaction process by changing the cooling medium temperature. 7]. They are withdrawn at different points. These are then sent to the MCHE for further cooling. the high pressure MR is cooled against propane to approximately -35°C. and then introduced to the MCHE shell. The stream is separated in the HP MR separator into MR liquid (MRL) and MR vapor (MRV). although in practice they will be split and will have one or more intercoolers. where it is split into a fuel gas stream and LNG product. Finally. Natural gas is fed to the propane chilling section where is it cooled from ambient temperatures to approximately -35°C. DMR – The Dual Mixed Refrigerant (DMR) process has two mixed refrigerant loops: • • Warm Mixed Refrigerant (WMR) pre-cools the Cold Mixed Refrigerant (CMR) and vapor feed The CMR liquefies and subcools the feed. The CMR is compressed. they provide refrigeration to liquefy and subcool the LNG feed. There. The MRV enters the MCHE. and propane. the natural gas is liquefied with a mixed refrigerant (MR) which is a combination of nitrogen. and sent to the MCHE shell side. . The MRV and MRL boil on the shell side. methane. Mixed Refrigerant (MR) for liquefaction and subcooling. where it is subcooled. The MRL enters the MCHE.Figure 3: The C3MR Process C3 MRV Feed C3 Pre-cooling Precool Temperature MRL Mixed Refrigerant (MR) MR This process cools and liquefies gas using two refrigeration loops powered by gas turbine compressors: propane (C3) for precooling. It is removed at an intermediate point of the MCHE. which is a coil wound heat exchanger (CWHE) [8]. and it partially liquefies. As they boil. precooled. and split into two streams: MRV and MRL. The composition is selected to maximize the process efficiency. the LNG exits the MCHE and goes to the end flash unit (not shown). consisting of a Low Pressure (LP). In the MR refrigeration loop. Medium Pressure (MP) and High Pressure (HP) MR compressor. all the MR compressors are shown as a single body for simplicity. 5 . Then the pre-cooled feed enters the Main Cryogenic Heat Exchanger (MCHE). The vapor MR which leaves the MCHE is compressed in a two or three stage compressor. This CMR loop performs very similarly to the MR loop in the C3MR process. which provides the refrigeration to liquefy and subcool the incoming natural gas and MR. It exits at the LNG temperature and is returned to the shell side. where it liquefies and is subcooled. ethane. In Figure 3. as well as cool the incoming MRV and MRL. reduce in pressure. A key value in the DMR process is the temperature between the precooler and MCHE. 12. and the seawater is then returned to the ocean. 10. 14]. with the remaining vapor condensed in the aftercooler. each with subtle variations. Direct Seawater – Seawater pumped through heat exchangers at elevated pressure. all giving similar process efficiencies. the evaporative cooling tower and direct seawater are not considered. optimized for various situations [3. while fans draw ambient air over the outside of the tubes. The liquid from the intercooler is pumped and combined to create the high pressure liquid WMR stream. 7. Here. Indirect Seawater – Seawater is pumped and used to cool a freshwater stream. This is subcooled in the precooler (which is also a CWHE). known as the “precool temperature”. This freshwater stream is then sent through a closed loop throughout the LNG plant. the WMR is compressed in two stages. reduced in pressure over a Joule-Thompson (J-T) valve. There are many configurations of precooling loops. Table 2 below shows the range of process temperatures that can be achieved with the different cooling media. A fraction of the return water is evaporated in ambient air. 9. It is partially condensed in the intercooler. For this analysis. 11. cooling the remaining water. Figure 4: Dual Mixed Refrigerant LNG Warm Mixed Refrigerant (WMR) Natural Gas MRV Precool Temperature MRL Cold Mixed Refrigerant (CMR) 5 There are many variations of the DMR process which have been developed over the past 30 years. for Yamal: 6 .The key difference in the DMR process is that the CMR and NG feed are precooled in a CWHE by WMR before going on to the MCHE. 13. absorbing the waste process heat. and then vaporized on the precooler shell side to precool the feed and MR. cooling the various process streams. The process patented by Air Products and Chemicals [9] is shown in Figure 4 and is used in the case study below. which is shown in Figure 4 below. and the seawater is returned to ocean. because these are not as widely used in recent LNG projects. SELECTING THE COOLING MEDIUM There are four cooling media that have been used in LNG plants: • • • • Ambient Air – the process streams flow through tubes. Evaporative Cooling Tower – Treated water is circulated from a basin through the plant cooling loop. This stabilizes the process operation at the cost of higher efficiency or production at the lowest temperatures. but are not as severe as Yamal.Table 2 – Arctic Plant Process Temperatures Produced by Different Cooling Media Year Round Temperature Variation Seawater to closed loop approach T Process Approach temperature Process T after cooling Range Min to max Diurnal variations Indirect Seawater Ambient Air -2 to 5°C -42 to +13°C 4°C N/A 5 to 10°C 10 to 20°C 7 to 19°C <12°C <1°C -32 to 33°C <55°C 4-9°C Basis: Temperatures for Yamal Peninsula From the table. CASE STUDY — ARCTIC AIR COOLING WITH TWO FRAME 7 GAS TURBINES To investigate how these factors affect the liquefaction unit process design. A design point was selected as described below and used to develop typical compressor curves. This is very different from the tropics/desert where the seawater tends to be similar to or cooler than the ambient air when the approach temperature is taken into account. The air temperature varies over the year from -20 to +22°C. using air cooling. with a yearly average of 4°C. The plant design basis is to use two GE Frame 7 Gas Turbines. The arctic conditions chosen are extreme. Table 3 – Cooling Media Comparison Process T after cooling Diurnal temperature variations Freeze Protection of cooling system Plot space Indirect Seawater Ambient Air 7 to 19°C <1°C Use glycol/water mixture -32 to 33°C 4-9°C Heaters/filters needed on air coolers to prevent ice accumulation Larger (Process coolers are large) Smaller (area used for indirect coolers) Note that air coolers may use louvers or fan speed control to limit the amount of cooling and to prevent ice accumulation during cold periods. perhaps as much as a factor of 4 to 5. This produces a nominal 6 mtpa at the yearly average ambient of 4°C. Even with the higher approach temperatures of an air cooled system. the process temperatures will vary much more over the year when using air cooling. a case study was performed for an arctic environment. This best simulates real compressors and drivers. one can see that on the Yamal Peninsula. 7 . subject to the compressors operating on their performance curves. the process temperatures are colder for much of the year using air cooling instead of seawater cooling. Cases were then developed at different air temperatures maximizing production at each operating temperature by consuming all available power. Other considerations for selecting the cooling media in arctic operation are given in Table 3 below. all compressors (C3. The power output is derated by 9.6% for aging. In the event that one string is offline. for head and efficiency vs.Details of the design are below: • Refrigerant Compressor Drivers: Two GE Frame 7 Industrial Gas Turbines. • When the individual compressor power consumption varies.2 MW. • Compressor design: A design ambient temperature was selected for each case. and MR) were assumed to have 83% polytropic efficiencies. fouling and inlet/outlet pressure losses. The available power varies with temperature by 0. running at 3600 rpm. as shown below: The DMR compressors have a similar configuration. • Two 50% strings increase availability. The design ambient temperature was chosen at 4°C for the DMR compressors. This choice is explained further in the results section. CMR. a compressor running at 3600 rpm may be constrained by aerodynamic impeller design limits. There is no need to balance compressor and driver loads. The C3MR compressors were designed at 13°C. WMR. Using two 50% compressors makes each compressor smaller (effectively for 3 mtpa). volumetric flowrate. with two 50% strings. Air Products’s proprietary model was then used to develop typical compressor performance curves. such as inlet flow coefficient and inlet Mach number. At the design point. 8 . which relaxes the compressor constraints. The rated ISO power is 86. STARTER The two x 50% configuration has the following advantages for this study: • In the range 6 mtpa. These typical curves were then used to rate the plant at the different air temperatures. • Compressor Configuration: This study uses two 50% compressor sets configured to create two identical parallel strings. the plant production can be maintained at 50% or more. the power shifts automatically between compressors.65%/°C. the pinch occurs at the warm end of the C3 condenser because while the air warms up. only three propane chilling levels are used.0% C2 3.7% C1 93. The assumption is that it is either lean from the gas field or it has gone through an upstream NGL plant. 4 The Warm MR condenser has a 10°C approach temperature at the cold end.2% C4+ Balance CO2 100 ppm Heat Exchangers: The process heat exchangers were set to the following: • • • • • • • • • The Main Exchanger is a coil wound heat exchanger (CWHE) for both processes. In C3MR. this is primarily the heat removed from natural gas as it is liquefied. This fuel rate does not change with ambient temperature.2%). it is typical to have 4 levels of precooling. This assumption was made to avoid the complication of integrating the NGL plant or scrub column with the liquefaction unit. The C3 evaporators are shell-and-tube kettles. with an assumed 3°C approach temperature (C3MR only). fixing the heat exchanger area.3% C3 • 1. Because the cooling medium is cold. In warmer desert and tropical climates. As that heat is rejected into a colder sink. the liquefaction process efficiency increases when the cooling medium is 4 The C3MR and DMR condenser temperatures differ because the temperature pinch changes location. The wound coil heat exchangers are sized to process the feed at the design point. This area is then used to compute the heat transfer performance at other operating conditions. • Hydraulic Turbines: The MRL and LNG each have hydraulic turbines to expand the liquid and recover refrigeration. The MR compressor (for C3MR) and CMR compressor (for DMR) have two intercoolers. the Warm MR cools by over 20°C from inlet to outlet at the design point. giving and LP. Therefore. and more closely tracks the warming air. The C3 condenser has a 20°C approach temperature to ambient air at the cold end (C3MR only). 9 . In the DMR process. EXPLOITING THE LOWER TEMPERATURES — THEORY The key process difference—and potential advantage—of an arctic facility is the cold temperature of the cooling medium. so including it would make it more difficult to generalize any conclusions. • Fuel: The MCHE outlet temperature is adjusted to produce a fixed fuel rate. It is relatively lean. The composition assumed for the study is below in Table 4: Table 4– Feed Composition for Case Study N2 1. This integration is very much project-specific. the propane temperature does not change over the exchanger. the process becomes more efficient. • Availability: the plants are assumed to have equal availability of 340 days/year (93. This is because every process must reject waste heat.• Feed Conditions: The feed is introduced to the liquefaction section at 68 bara. along with the heat of compression from the refrigerant compressors. MP and HP MR/CMR compressors. The MR precooler is also a CWHE (DMR only). In LNG liquefaction processes. all things being equal. (DMR only) All compressor intercoolers have an approach temperature of 10°C approach. • Compressor inlet temperature – A colder inlet temperature improves the compressor specific power. However. the feed to the liquefaction unit is colder in the arctic than in the tropics or desert. Note that the relationship is linear. Assuming that extra feed is available. which in turn reduces power consumption. lowering the condenser pressure is typically the majority of the specific power improvement. To increase production. The question is then how does changing the cooling medium temperature affect the specific power and the available power? Cooling Medium Effect on Specific Power Three specific reasons why colder temperatures improve specific power are listed in order of importance (most to least important): • Refrigerant Condenser Pressure – The precooling refrigerant is completely condensed against the cooling medium with a colder cooling medium lowering the condensing pressure. And if both the specific and available power increase by 1%. tonne/hr Rearranging this equation gives production in terms of power supplied and specific power consumption: LNG= kWref Ws What this equation shows is that LNG production is proportional to the refrigeration power consumed and inversely proportional to specific power. For centrifugal and axial compressors. is proportional to the absolute inlet temperature. a 1% increase in available gas turbine power also increases production 1%. kwh/tonne = total gas hp for refrigeration compressors. Likewise. typically in kwh/tonne LNG produced. This efficiency is expressed as specific power. or improve the specific power. power consumption and production: Ws = Where Ws kW ref LNG kWref LNG = Specific Power for liquefier. • Inlet to liquefaction section – With a colder cooling medium. For example. the production increases by 2%.colder. Because the refrigerant condensers reject 80% of the energy removed from natural gas to make LNG. a 1% reduction in specific power increases production by 1%. it takes over 6 times more work to remove 1 unit of energy at 10 . The equation below shows the relationship between specific power. the head developed by the compressor. and thus the power consumption. with a 0° ambient. one can increase the power supplied (in our case study. This is typically 20 to 40% of the specific power improvement. because it is easier to cool a stream near ambient than when the stream is much colder. for a given mass flowrate and pressure ratio. by the gas turbines). A lower value of specific power is a higher efficiency. Reducing the inlet temperature reduces the total refrigeration needed to convert ambient temperature natural gas into LNG. this effect is relatively small. This lowers the required refrigerant compressor discharge pressure. kW = LNG rundown production after any endflash. 91 0. Therefore. The plant design may take advantage of this to lower the precooling refrigerant load by adding extra heat exchangers.8 1. there is less need for precooling. when the ambient temperature reaches 3°C.4 22 4.27 1.7% per °C and for aeroderivative gas turbines. the feed is cooled by the precooling refrigerant after the dehydration unit. At 11°C. this is on the order of 0. approximately 50% of the increase is due to an increase in specific power and the reminder due to increased available gas turbine power. requiring the feed to stay above 20 to 25°C before dehydration to prevent forming hydrates. while providing maximizing the production at the lower ambient conditions. in tropical and desert plants.00 Findings from the study are summarized below: • The plant produces more LNG as the ambient temperature decreases. there is an upper limit for the power increase. For this case study.86 0.8 1.6 6.42 1. such as maximum shaft torque or compressor pressure/temperature limits. with the parameters given above. Therefore. typically less than 20% of the improvement. as stated above. 17]. slightly cooling the liquefier feed stream by itself has a small effect on specific power. In arctic climates. Aeroderivative turbines will reach their maximum power output at a higher ambient temperature. Cooling Medium Effect on Available Power The colder air temperature is also very important when the compressors are driven by gas turbines.88 0.9 -10 6.94 1.45 GT Power (MW) Relative Specific Power Relative to 22°C -3 4 6. For a typical industrial turbine. EXPLOITING THE LOWER TEMPERATURES — PRACTICE C3MR Process The C3MR process was designed for an 11°C ambient temperature. as the feed and MR are cooled by the ambient air coolers more and more.1% per °C. typical compressor curves were developed using APCI’s proprietary computer modeling and design tools. because the power available increases with decreasing ambient temperature. the available power may increase until the ambient temperature is below -20°C [16. the required precooling duty is low enough that the propane compressor 11 .38 1. However. the precooling temperature is limited by being pure propane (no composition change) and that the propane must be above atmospheric pressure throughout the loop. The heat exchanger areas fixed. With the C3MR process.1 13 5. For industrial turbines. The production data is summarized in Table 5 below: Table 5 – C3MR Production Summary Ambient T (°C) Production (mtpa) -20 6. the GE Frame 7. the available power increases approximately 1. The 11°C design point was chosen to be able to utilize the full gas turbine available power at the summer high condition of 22°C.14 1. Above -3°C. This is typically set by mechanical constraints within the turbine. Further power can be added through helper motors. Other considerations in cooling the liquefaction unit feed: 1) The raw natural gas entering the plant will contain water. -20 to +22°C. The plant was then rated over the full range of ambient temperatures.-30°C than at -140°C. typically between -10°C and +10°C [17].89 0.00 195 184 176 169 158 148 0. some of this precooling could be with the cooling medium during most or all of the year (depending on the cooling medium). 2) Following dehydration. 4 1. the production increases due to higher available gas turbine power. This is done by adding more low boiling point component (N2) and reducing the C3. This causes the 5 fraction of refrigeration power consumed by the propane compressor to level off.goes into recycle.8 1.6 Increase due to better specific power 1. This is shown in the Figure 5 below: Figure 5: C3 MR Relative Production 1.7 Relative Production 1. Below about -3°C. The specific power then begins to increase. This lowers the MR dewpoint temperature. with only slight changes in N2.1 1 -20 -15 -10 -5 0 5 10 15 20 25 Ambient Temperature (°C) • The optimum precooling temperature does not vary significantly with ambient temperature.5 1. but the rate of production decrease slows as the specific power stops improving. Note that optimum the MR composition is fairly constant below 3°C. relative to 3°C.2 Increase due to more available GT Power 1. 12 . This ability to adjust the MR composition is a key feature of any mixed refrigerant cycle and has been practiced for many years [19]. So below 3°C. These effects are shown in Table 6 and Figure 6. The MR aftercooler approach temperature becomes colder and the MR composition is adjusted so as to load up the MR compressor as much as possible. less of the refrigeration power is needed by the propane compressor and more by the MR compressor. as the cooling medium becomes colder. This propane compressor inefficiency causes the C3MR specific power starts to increase. 5 This is the propane compressor power divided by the sum of the propane plus MR compressor powers. the propane compressor becomes so unloaded that it begins to recycle to stay within the operating limits. relative to -3°C. Therefore. even though the process precooling requirement continues to decrease.3 1. 3 C1 42. The production data is summarized in Table 7 below: 13 .7 63.9 6.7 44.5 11.2 11.1 42.1 MR Composition (Mole %) Figure 6: C3 MR Refrigeration 45% 40% 25 MR Dew Temperature (°C) 35% 20 30% 25% 15 20% 10 15% MR Dew T % C3 Power 10% 5 5% 0 % Power consumed by C3 Compressor 30 0% -20 -15 -10 -5 0 5 10 15 20 25 Ambient Temperature (°C) DMR Process The DMR process was designed with the parameters given above at the yearly average ambient temperature of 4°C.8 C3 11.1 14.9 13. The plant was then rated over the full ranges of ambient temperatures.5 58.4 58.7 34. The full gas turbine available power at the each condition was utilized to maximize production.3 33.2 44.5 78.Table 6 – C3MR Refrigerant Composition DMR Production Summary Ambient Air (°C) -20 -10 -3 4 13 22 N2 11. -20 to +22°C.3 33.6 45.9 C2 34. Typical compressor curves were developed at this point.8 9. and the heat exchanger areas fixed.2 33. using APCI’s proprietary computer tools.0 7.6 9.7 17.7 43.1 33.0 Tdew @ 62 bara (°C) 57.5 10. This temperature was chosen to allow the compressors to cover the entire cooling medium temperature range.4 69. 89 0. it is possible to adjust the WMR and CMR compositions keep the WMR and CMR power split roughly constant. the power split between the WMR and CMR compressors is maintained essentially constant. This ability to fully load the WMR compressor at winter ambients keeps the specific power rising throughout the ambient temperature range. While C3MR process can make adjustments down to about -3°C.55 1.13 1. 14 .2 Increase due to more available GT Power 1.75 GT Power (MW) Relative Specific Power Relative to 22°C 4 6.28 1.00 195 184 169 158 148 0.4 1. However.1 1 -20 -15 -10 -5 0 5 10 15 20 25 Ambient Temperature (°C) • The production increase shown in Table 6 and Figure 7 is attributed to both the increase in available power and the decrease in specific power. as shown in Table 8 and Figure 8. As with C3MR.5 22 4.80 0.00 Findings from the study are summarized below: • As with C3MR.5 Increase due to better specific power 1.7 Relative Production 1. the DMR cycle produces more LNG as the ambient temperature decreases.2 13 5. the production increases linearly over the entire ambient temperature range. • To keep improving the specific power.6 1.8 1.75 0. about 50% of the production rise is due to specific power improvement and 50% is due to more available GT power.Table 7 – DMR Production Summary Ambient T (°C) Production (mtpa) -20 8. This is because as ambient air temperature decreases and cools the feed and CMR more and more. Figure 7: DMR Relative Production 1. unlike C3MR. each contributes about equally to increasing the overall production. That is.5 1.5 -10 7. with the WMR compressor consuming between 40% and 45% of the total refrigeration power over the entire ambient temperature range. which in turns keeps the production rising (Figure 7).8 1. the DMR process can be adjusted down to -20°C. This is accomplished by changing the WMR and CMR compositions.3 1.94 1. 0 C3 0.4 34.1 47. to maintain optimum efficiency. a refrigerant reclamation system may be considered. the WMR compositions will need to be changed fairly dramatically. with methane reducing by a factor of 4.3 C1 51.2 55.5 0.6 C2 32.5 37. particularly with the propane and nitrogen.Figure 8: DMR Refrigeration 45% 40% 80 35% MR Dew Temperature (°C) 60 30% 40 WMR Dew T 25% CMR Dew T 20% % WMR Power 20 15% 0 10% -20 5% -40 % Power consumed by C3 Compressor 100 0% -20 -15 -10 -5 0 5 10 15 20 25 Ambient Temperature (°C) Table 8: DMR Refrigerant Compositions (mole %) Ambient T (°C) -20 -10 4 13 22 WMR C1 24.68 1.00 0.65 C3 6. propane nearly being eliminated.10 6. Thus.22 13. however.79 11. the nitrogen decreases by a factor of 0. while the propane increases from 0% to 7%.05 70.14 8. It is possible to reduce the amount of composition change to ease operation.8 68.4 36.7 CMR Tdew @ 62 bara (°C) The composition needs to change fairly dramatically over the course of the year.8 45. this will come at the cost of some efficiency.9 14.2 50.58 C2 68.4 -5.91 67.00 3. to avoid flaring large quantities of valuable refrigerants. From winter to summer.6.0 -21. The Warm MR change is even more significant.83 13.0 1.9 -15.7 11.2 80.4 N2 16.92 63.18 17.74 0.55 6.83 9.90 I4 0.75 70.86 Tdew @ 45 bara (°C) 18.57 21.0 3. To do this efficiently.73 10. Note that the CMR change is fairly significant. 15 .00 C4 0.00 0.2 5.4 10.3 7.8 5.00 2.8 12.1 36.0 34.7 46. and the butanes rising from 0% in the winter to nearly 30% in the summer. This increases production. To achieve higher production. but not by as significantly when more feed is available. the WMR and CMR compositions will need to be continually or periodically adjusted. However. Figure 9: Comparing C3MR and DMR 9 2. which is 1. the DMR process will produce more LNG. For fixed feed flow. For C3MR.0 C3MR Specific Power 1. so they will have identical production increases. This is shown in Figure 10 below: 16 .6 0 0. which is 0. as the specific power decreases.78 mtpa.5% above the 22°C production. the gas turbines consume less fuel. because the propane loop cannot be fully tuned for the very cold ambient temperatures. the specific power declines below -3°C. the C3MR process has a higher specific power. the DMR specific power improves.2% above the 22°C production. The production and specific power differences are shown in Figure 9 below.8 6 1. Over this range. the DMR and C3MR processes have the same 14% decrease in specific power.4 4 1. There is essentially no difference between -3°C to +22°C. and both processes are able to consume the entire available GT power.2 3 1. Between -3 and 22°C.4 -20 -10 10 0 20 30 Ambient Temperature (°C) The large production increases assume that the necessary feed rate is available at low ambient temperatures. in many situations. Below -3°C. which is over 50% of the year. From -3°C to -20°C. assume that the gas turbines consume 5% of the feed flow as fuel at 22°C.4 DMR Production DMR Specific Power 7 Production (mtpa) 2. so its production falls to 4. the production is essentially equal between the two processes because the specific powers are equal. allowing more feed to be turned into LNG. the feed flowrate is fixed. While both processes are able to fully use the available GT power. provided that sufficient feed is available. so its production increases to 4.2 C3MR Production 2.82 mtpa.6 5 1. As a simple case study for fixed feed rate.COMPARING C3MR AND DMR The C3MR and DMR process are both flexible and both dramatically increase production at lower ambient temperatures.8 1 0.0 2 Relative Specific Power 8 0. dehydration unit. the power available to refrigerant compressors (i. more information is needed: • What is to be the limiting unit of the LNG facility? It could be the pipeline. The MR and feed streams are precooled with three or four kettle type exchangers in the C3MR. They both will have 5 compressor bodies. slug catcher. An arctic plant has the potential to produce more LNG product during the colder months and less during the summer months.5 -20 -10 0 10 20 30 Ambient Temperature (°C) There are some equipment differences between the DMR and C3MR processes. the compressor drivers) or the refrigeration compressors themselves. To decide how to do this. while the DMR process has a single large CWHE to precool both Feed and Cold MR.Figure 10: Production for Fixed Feed 5 DMR LNG Production (mtpa) 4. In almost all locations. • How much extra capacity can be used? This answer is mainly commercial. or the liquefaction unit. However. the limiting component is usually either the feed rate. in that seasonal customers must be available. • How much will the heating medium change during the year? If air cooling is used. the cooling medium temperature will vary much more than if seawater is used.6 4.e. the amount of variation in the seawater temperature will not significantly increase production. the performance improvements due to colder a cooling medium can be taken as lower power consumption and/or higher production.9 C3MR 4. Within the liquefaction unit. So significant extra production will potentially be available only when cooling with ambient air. DOES THE EXTRA POTENTIAL PRODUCTION HAVE VALUE? From a high level view.7 4. It is of little value to be able to produce more if there is no customer for the extra product. this extra product must be commercially useful. Acid Gas Recover Unit (AGRU).8 4. with a two stage WMR compressor replacing the propane compressor with multiple side feeds. 17 . ) Where 𝑚𝑡𝑝𝑎 = 6. Note that production is maximized using for two GE Frame 7 gas turbines. It will not be valid for other combinations of gas turbines. and this may be considered in the plant economics. In actual conditions. as shown in Figure 96.) In this special combination of circumstances. consider how plant location will affect the monthly production. the process selection must be based on factors other than production capacity. while maintaining the essential features of the example.0869 𝑇 T = cooling medium temperature. and the air temperature varies by more than 30 to 40°C over the course of the year. In these cases. then C3MR and DMR will produce the essentially the same amount of LNG over the course of a year. However. This is shown in Figure 11 below. tropical and arctic climates. if the answer to any one of the above questions is different. etc. but this simplifies the analysis. feed compositions. without helper motors. the year round production is estimated for desert. The production is estimated by assuming that it is linear with temperature. (This is clearly a simplification.Consider a facility where the answers to these questions are simultaneously • • • The liquefaction unit (including the refrigerant compressor drivers) limits production Extra product can be sold The cooling medium varies significantly during the year. To illustrate this point. (This essentially means that air cooling is used. the production will not be so linear. temperature approaches. the DMR facility can produce more LNG than C3MR during portions of the year. for the case study parameters. 18 . °C mtpa = LNG production Using the seasonal temperatures for ambient air and seawater (see Figures 1 and 2). 6 This equation is valid only for the case study of this paper.653 − 0. slug catcher. 19 . This shows that both the DMR and C3MR process will efficiently respond to cooling medium temperature changes of less than 30°C. including pipeline. That is. regardless of cooling medium. This observation is summarized in Figure 12 below. about 22% winter to summer. the production decrease is 1. With air cooling. but a very large potential change when cooling with air. slowing its production increase. liquefaction unit. the installed capacity will not be fully utilized. dehydration unit. compression. the temperature ranges for the various locations and cooling media are shown below the horizontal access. the required maximum facility capacity must be installed. This obviously requires more CAPEX. regardless of cooling medium. and the DMR process will be able to produce more LNG in the winter season. the desert sees a fairly large production swing. a 31% decline. and this increase must be installed in the entire LNG value chain. It is only when the cooling medium changes by more than about 30°C that the C3MR specific power degrades. one selects the extra capacity to be installed and the cooling medium range over the year.1 mtpa. The arctic has a relatively small variation when using seawater. Then for portions of the year. The vertical axis is the capacity above the summertime production that must be installed to take advantage of the cooling medium temperature variation. The horizontal axis shows the cooling medium temperature range over the year. The tropical location monthly production is nearly constant. if the LNG facility is to actually produce more in the wintertime. AGRU.6 mtpa from winter to summer. 1. To determine which is appropriate. LNG storage and LNG carriers.Figure 11: Monthly Production 10 9 Monthly Production (mtpa) 8 7 6 5 4 3 2 1 Yamal Air Cooled Yamal Seawater Cooled Qatar Air Cooled Qatar Seawater Cooled Malaysia Air Cooled Malaysia Seawater Cooled 0 Jan Jul Feb Mar Apr May Jun Aug Sep Oct Nov Dec Several points can be taken from this graph: • • • • The arctic location will produce the most LNG. The location of that point gives guidance as to which process is able to fully utilize the gas turbine power.8 mtpa. As an aid. There are three areas in Figure 12. While the winter to summer percentage decrease is the same as the desert— 31%--the absolute change is much larger: 2. With seawater cooling. • Extra Capacity Not Utilized – In this area. and the process selection can be made for other reasons besides seasonal capacity. It is desired to be able to product 1 mtpa more LNG in the winter than the summer. • AP-DMR – When both the temperature range and desired wintertime production increase are large. there is insufficient gas turbine power to utilize the total installed production capacity. in the region that either C3MR or DMR can meet this requirement. Note that boundary between “DMR” and “C3MR or DMR” is not a hard line. TM TM TM As an example. As shown in the case study. having a 30°C seasonal average daily ambient temperature range. depending on feed composition and pressure. • AP-C3MR or AP-DMR – For this combination of temperature variation and desired winter production increase (relative to the summer production). the actual breakpoints and specific values of boundary locations will vary for each case. site weather conditions. However. Installed Capacity above Summer Capacity (mtpa) Figure 12: Process Selection Guide 3 Extra Capacity Not Utilized AP-DMRTM 2 Note: This chart is valid only for the case study of this paper which fully utilizes the avaialbel power from 2 GE Fr7 GT's w/o helper motors 1 A AP-C3MRTM or AP-DMRTM 0 0 10 Seawater Cooling 20 30 40 Cooling Medium Temperature Range (°C) 50 60 Tropical Air Cooling Desert Air Cooling Arctic Air Cooling The trends and general shape of Figure 12 will be true in general. consider a desert climate with air cooling. the WMR and CMR compositions can be adjusted so that the entire power produced by the gas turbines is utilized to make LNG. In this case. They will both be able to meet the facility production needs. tropical air cooled and desert air cooled. 20 . driver configuration. both the C3MR and DMR processes are acceptable. This is located in Figure 12 as Point A. there is no commercial value in investing CAPEX for this extra production. the DMR process is the best selection. is a blurred transition. Note that this area includes all seawater cooled sites. The process selection will be based on other factors besides plant capacity and ability to match seasonal temperatures. However. relative to industrial turbines. with the electricity coming either from the grid or an onsite power plant. • Aero derivative turbines are dual or triple shaft designs. with their output falling about 1. • Aero derivatives are more sensitive to ambient temperature variations. the results of this study are scalable. Aeroderivative Gas Turbines — Aeroderivative gas turbines are becoming more widely used in the LNG industry to drive the refrigeration compressors. Their features. Electric Motor Drivers — Large electric motor can be used to drive the compressors. They have been operated in land-based baseload plants. three or more compressor strings would be needed to produce the nominal 5-6 mtpa in this study. and the production can be increased or decreased to match the driver power. as stated above. typically between -10°C and +10°C [18]. are summarized below [7]: • Aeroderivatives have higher efficiency. and is set to come online in 2014. more power is available without limit. To stay within proven motor sizes. so maintenance can be performed offline. in practice. which reduce their availability. However.2%/°C. It was assumed that as the ambient temperature cooled. The Frame 7 gas turbines continue to be able to deliver more power at ambients down to -20°C [16. These were ignored in the case study. The first C3MR process with aeroderivative gas turbines is under construction. the results can easily be scaled to other production rates and gas turbines. multiple parallel compressor strings have been installed. so for baseload plants. Items that could affect this case study or others are • The maximum power available from a Gas Turbine • Alternative driver types: electric motors and aeroderivative turbines • Speed variation to more efficiently turn down the C3 compressor • Refrigerant compressor configuration • Alternative precooling refrigerants Each of these is now considered in turn. This could also be used to supplement the gas turbine at warmer temperatures. etc. so they do not need a helper motor to start • They typically have a larger speed range. a helper motor could be added to provide the extra power at colder temperatures. which reduces autoconsumption by up to 25%.OTHER CONSIDERATIONS FOR ARCTIC LNG LIQUEFACTION UNITS The discussions above primarily focused on the process design of the liquefaction area. which can be up to 50 to 105% of nameplate. turbines will have a maximum power output. mechanical considerations were not discussed in detail. due to mechanical limits such as shaft torque. while aeroderivatives reach mechanical limits at warmer temperatures. 17]. If the maximum GT power is a limit. because while a particular LNG Plant size was selected. aeroderivatives require more frequent periodic inspections. internal temperatures. The most common compressor drivers are compared in Table 9 below: 21 . • Aeroderivative turbines are designed to be removed from service in a few days. However. • The maximum power ratings are generally smaller than the industrial turbines. no limit was placed on the power available from the gas turbine. Maximum GT Power — In the case study here. ) 3. As shown on the performance curve in Figure 13 below. speed control can be used in facilities using aero derivative turbine or electric motor for compressor drivers. DS = Dual Shaft 2. because the heat load on the propane system decreases. If electricity is generated onsite. Reducing the compressor speed will better match the compressor to the desired operating point.Table 9: Compressor Driver Comparison [7] Driver ISO Thermal Efficiency Size Shaft Type (1) Speed range (% nameplate) Starters motors (1) required Availability Amb T effect Industrial 29 to 34% Aero 41-43% Discrete Discrete (smaller max) Dual and Triple 50-105% Single and Dual SS: 95-102% DS: 50 to 105% SS -Y DS . (Low fractional load gives lower efficiencies. the propane flowrate decreases. as well as the fractional load. however. The Frame 7 gas turbines used in the case study have very limited speed adjustment. the propane operating point shifts down and to the left. SS = Single Shaft. as set by the propane condenser. Figure 13 – Propane Compressor Operating Points Higher Speed Lower Speed HEAD Winter Operating Point FLOW 22 Summer Operating Point .N Good Moderate N Good Large Electric Gas Turbine less (2) several percent Variable N/A 20-100% N (VFD req’d) Best Nil (w/ sufficient electricity supply) (3) Middle CAPEX Least Least Notes: 1. the propane compressor discharge pressure decreases. The apparent efficiency depends on the power source. Also. Speed control should be considered if the driver allows. Assumes onsite electrical generation via gas turbine generators Propane Compressor Control by Varying Speed — As the ambient temperature gets colder. then one must consider the type of turbines (aero derivative or frame). An alternative pure component precoolant would be a pure component having a normal boiling point below -40°C. A key feature of this compressor configuration is that slightly changing the pressure between the MPMR and HPMR compressors can equalize the power consumption of the two strings. one propane limitation is that when the lowest propane pressure is kept slightly above atmospheric. ethylene will need very cold ambients or seawater which is essentially 0°C. The slight performance improvement is not typically worth the extra cost and effort to import. such as in a desert or tropical climate. the driver with the C3 and HPMR compressors will have available power. ethane. This may be possible for seawater. provided that the cooling medium is below 10 to 20°C to ensure that he refrigerant is maintained below its critical temperature. if needed. The refrigerant should be readily available. Their properties are summarized below: Table 11 . or if arctic seawater is used as the cooling medium. That is. and the LPMR and MPMR compressors are driven by the a second gas turbine. as the cooling medium becomes much colder. ® An additional attribute of the SplitMR configuration is that it is well proven.Potential Alternative Precooling Refrigerants Propane Propylene Ethane Ethylene Critical Temperature 97 °C 92 °C 32 °C 10 °C Normal Boiling Point -42 °C -48 °C -89 °C -104°C This table shows that propylene gives a slight improvement over propane. When the cooling medium range is not so large. Ethylene has the same issue. This reduces the number of compressor bodies on a string from five to four.Compressor Configuration — This study was performed using two 50% parallel compressor strings. only it is even more pronounced. ethylene is not readily available from the natural gas feed and would need to be imported. Therefore. with another eight in construction. the propane compressor power consumption will become too low to be fully balanced with the MR compressors. Alternative Precooling Refrigerants — As shown above. and ethylene. relative to the basis of this study. simultaneously with a critical temperature above the cooling medium temperature plus any temperature approach. This allows the total gas turbine power to be absorbed and maximizes production for the fixed driver set. 23 . then this is not an issue. but most arctic locations will have short.) Three pure component refrigerants potentially meet these basic requirements: propylene. Ethane is a possible choice. In this configuration. ® However an alternative is the Air Products SplitMR configuration. with no way to move power between the drivers. however it is typically not readily available from the natural gas feed. but significant periods where the ambient air temperature will become too high. It is being used in nine operating baseload trains. However. then the precooling temperature is limited to 35°C. and the driver with the LPMR and MPMR will need power. Additionally. preferably from the natural gas feedstock (although it is possible to import the refrigerant. the C3 and HPMR compressor are driven by one gas turbine. a very wide cooling medium temperature variation will ® result in the SplitMR compressor configuration not consuming all of the available power and producing less LNG. emc.noaa. Liu. “The C3MR Liquefaction Cycle: Versatility for a Fast Growing. H. “Mixed Fluid Cascade.ncep. Refrigerating and Air-Conditioning Engineers. the entire facility and supply chain. Chapter 14. Gunder Bure Gabrielsen. REFERENCES CITED [1] Bauer. “An Ever Evolving Technology”. Environmental Modeling Center (EMC). LNG Industry. SST maps for 2012 at http://www. Arne Olav Fredheim. 2007.CONCLUSIONS This paper shows that C3MR and DMR are both well suited for arctic environments. Mark Pillarella. it can be up to 60°C or more.. Texas 2 April 2012. typically less than 0 to 5°C. LNG 15. LNG 16. AIChE 2012 Spring Meeting. Padraig Collins. must be designed to take this into account. ® 24 . [2] Vist Sivert. René. when compared to the historic tropical or desert LNG facility locations are • The yearly average cooling medium (air or seawater) is much colder. [3] Verburg. Jack. Rob Klein Nagelvoort. Jostein Pettersen. Ever Changing LNG Industry”. Paper PS4-5. Inc. The process selection is then to be made for reasons other than production. Sander Kaart. C. His hard work and insights were invaluable for this work. the summer to winter seasonal variation is much larger. 12th Topical Conference on Gas Utilization. Experience and Outlook”. 2010. Both processes are capable of producing significantly more LNG in the winter. LNG 16. NOAA National Oceanic and Atmospheric Administration (NOAA). This will require additional investment to handle the additional seasonal volume. Y. LNG 16. 2010. “Climatic Design Information”. 2009 edition. ACKNOWLEDGEMENT We would like to thank Wenbin Hu for developing the computer simulations of the DMR and C3MR processes. A. P. Bert Benckhuijsen.A Frontier Project In The North Of Europe”. In all other situations. "How the Right Technical Choices Lead to Commercial Success". Kennington. [7] Schmidt. In this paper.gov/research/cmb/sst_analysis/ [6] Pillarella. ASHRAE Handbook: Fundamentals. we have considered how the C3MR and DMR processes will operate in arctic environments. then the DMR process can produce somewhat more LNG in the wintertime. [4] American Society of Heating. Roy Ivar Nielsen. the most important of which is that air cooling is used and the seasonal variation is larger than 30 to 40°C. Ott. This paper shows that both C3MR and DMR have essentially the same production and specific power over a wide operating range. including available carriers. Hilde Furuholt Valle. M. W. “Start-Up Experiences From Hammerfest LNG . Paper 25a. • If the cooling medium is air. Spring Issue 2008. W. Liu. The two key differences in arctic climates. and Ron Bower.. However. "Sakhalin Energy’s Initial Operating Experience from Simulation to Reality: Making the DMR Process Work”. Henrik Ormbostad. [5] “NOAA Optimum Interpolation Sea Surface Temperature Analysis”. Morten Svenning. GA. [8] McKeever. Houston. Atlanta. the production and efficiency are essentially the same. 2010. Petrowski. Dan Pedersen. and Bower. Paper PS4-4.. In special circumstances. C.. N. The 9th International Conference and Exhibition on Liquefied Natural Gas (LNG9). [16] Brooks. Liu. “Dual Mixed Refrigerant Natural Gas Liquefaction with Staged Compression”. “Method of and System for Liquefying a Gas with Low Boiling Temperature”. US Patent 4. C. 10/00. Geist. 2 April 2012. Y. “GE Gas Turbine Performance Characteristics”.. 19 September 2000. Pervier. James W. 25 ..849. (10/00). 17-20 October.. H. [12] Garier. T.525.[9] Roberts. G..E.119. Paper 6. Rakesh Agrawal. Session II. Gaumer.185. Garrison..E. Paradowski. C.253. 1989. [17] Ekstrom. GE Power systems. LNG Sessions in 2012 AIChE Spring Meeting.. Mark Julian. J. Frank J.. GE Publication GER3701B.H. [10] Liu. GE publication GER-357H. H. “Operational Flexibility of LNG Plants Using the ® Propane Precooled Multicomponent Refrigerant MCR Process”. 9/94 (500). LNG Sessions. “New Trends for Future LNG Units”.795. 1977. “Dual Mixed Refrigerant Cycle for Gas Liquefaction”. “Dual Mixed Refrigerant Natural Gas Liquefaction”. “Method and Plant for Liquefying a Gas with Low Boiling Temperature”. LNG 5.. H. P.479. Nice. US Patent 6. US Patent 4. Yu-Nan. [15] Berg. [18] Badeer. Paradowski. Jacob M. GE Publication GER-39695E.339. J.274. GE Power systems. 1985. Paradowski. US Patent 4. [19] Chatterjee.L. GE Power Systems. Nirmal. [11] Newton. [13] Caetani. France. “GE Aeroderivative Gas Turbines – Design and Operating Features”. [14] Gauberthier.N. “Maximizing LNG Capacity for Liquefaction Processes Utilizing Electric Motors”.. US Patent 4. “Gas Turbines for Mechanical Drive Applications”.. E. Lee S. 8 October.545. • The “error bars” approximate the range of temperatures covered by 90% of the hours in each month.two standard deviations of the monthly average. so it is estimated.APPENDIX – DRY BULB TEMPEATURES The dry bulb temperatures in Table 1 are calculated as follows: • The temperature for each month is the daily average dry bulb temperature as reported in the ASHRAE handbook [4]. +/.75 times the monthly mean temperature variation.0. which has almost no seasonal variation. with the independently reported 99% summer high and 1% winter low. 26 . These match within a few °C. which see fairly large seasonal variations. based on the location. This is crosschecked by comparing the predicted yearly high and low. confirming that these are reasonable estimates. The estimate methods vary. the high and low are approximately equal to the monthly average +/.) This data is not directly available. The upper end is approximately the 95% high (5% of the hours in that month are warmer than this temperature) and the 5% low (5% of the hours in the month are colder than this temperature. For Qatar and Yamal. For Borneo. • The typical diurnal variation is the range of mean daily temperature range over the year. the monthly 5% low and 95% high are approximately the monthly average.