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Baseload LNG plants require large capital investments. The recovery of this capital is dependent upon plant availability, including minimizing the time periods required for commercial production. Air Products' MCR® Processes and MCR® Cryogenic Heat Exchangers have established the world's standards in these categories.
Low Installed Cost
The selection of an Air Products' MCR® Process results in low installed cost for the following reasons:
- Reduced number of process heat exchangers;
- Minimize number of compressor/driver sets;
- Modular, compact equipment and layout;
- Less instrumentation because of fewer process equipment items and fewer control loops;
- Fewer field erection requirements because of the reduced number of equipment items and piping.
Larger is Greener
(High Efficiency, Low Cost)
 A larger train size has a significant advantage in reducing the overall capital and plot plan requirements for both the initial installation and any contemplated expansion of the LNG facility. Air Products' unmatched experience in design and fabrication of large, coil-wound heat exchangers, permit the installation of proven equipment, including compressors and drivers, while increasing the train capacities. Thus, the number of trains required to obtain the desired LNG production is reduced.
Air Products strives to produce high efficiency, low cost LNG processes by using the MCR processes in conjunction with the highly efficient, proven gas turbine drivers. As the gas turbine drivers increase in size, the efficiency goes up, and the cost per unit of power decreases. This contributes to the high efficiency of the MCR processes (C3MR, AP-X, and DMR). Additionally, all of the MCR processes can employ electrical motors as compressor drivers.
Ease of Start-Up
Since the propane refrigerant can easily be imported and recovered from the feed, the plant can be put on-stream quickly and efficiently. Similarly, the mixed refrigerant can be retained in the system to minimize the time required to restart following a shutdown. While ammonia must be imported, the absorption refrigeration system also can be readily started.
Hydrate Temperature Control
Through the use of pressure-controlled evaporation of propane or ammonia to precool the natural gas, the hydrate formation temperature of the feed can be closely approached. This allows maximum water removal by condensation upstream of dehydration, while still safely avoiding the possibility of hydrate formation. If mixed refrigerant is used for precooling, a more elaborate control system is used to prevent hydrate formation.
Operational Flexibility
A unique flexibility exists which permits the MCR® Cryogenic Heat Exchanger to operate over a wide range of conditions while maintaining high overall plant efficiency and operating the large compressors without recycle. Flexibility is achieved during operation by adjusting one or more of the primary variables: mixed refrigerant inventory and composition, suction pressure, discharge pressure, and speed of the refrigerant compressors.
Turndown Capability
Air Products' MCR® cryogenic heat exchanger (MCHE) and liquefaction processes have no turndown limitations. An Air Products' MCR® LNG train can be operated from 0% to 100% of design production. However, the efficient turndown of a MCR® LNG train is limited by the design and selection of compression equipment and is typically around 70%-80% of design capacity for a single compressor string design, as long as the precooling compressor does not need to operate with anti-surge valve(s) in partial recycle. For 2-in-1 compressor string designs, efficient turndown to 35%-40% can be achieved. In addition, with the use of variable speed drivers for precooling, the compressor speeds can be reduced so the range for efficient turndown can be extended even further. By placing refrigerant compressors in recycle, a MCR® LNG train can be turned down and operated stably down to about 30% of design with little operator attention. With operator attention, a MCR® LNG train can be operated at even lower levels of turndown. During the course of turndown, the mixed refrigerant composition and inventory are adjusted to a revised optimum mix for stable operation at the new operating conditions. Air Products' experience in the startup and operation of over 70 MCR® LNG trains has proven that operation can be maintained at levels as low as 0%-5% with no adverse effect to the MCHE or other liquefaction equipment.
Thermodynamic Design Accurate knowledge of the thermophysical properties of mixtures is essential to the process design for liquefying natural gas with a mixed refrigerant. The "cooling curves" of an Air Products' MCR® Cryogenic Heat Exchanger used for the design of the heat exchangers depend upon accurate thermophysical data for multicomponent liquids and vapors.
Air Products' thermophysical calculations utilize fundamental theoretical approaches and have been fitted against direct laboratory measurements and actual field experience.
Integration of Process and Compression System Matching Compressors and Drivers to the Process
Air Products has developed a proprietary method to estimate the polytropic efficiencies of large commercially available centrifugal compressors. This method is based on compressor aerodynamic theory and the actual shop test results of units supplied for existing baseload LNG plants. Using a combination of process-related compressor parameters including the rotating speed, the efficiencies estimated using the Air Products method closely match the actual shop test results. It is a valuable computation tool that guides our process engineers to optimize the process conditions to match the preferred compressors and drivers over the entire operating range of amibient temepatures.
Further, flexibility is achieved by using the SplitMRTM machinery configuration to balance the power between drivers. For example, the SplitMRTM compressor configuration has been used to fully utilize the power of two GE FR7EA gas turbines for the C3MR process by having 1 GT driving the LP and MP MR compressors, and the second driving the propane and HP MR compressors. In fact, the SplitMRTM machinery configuration can be applied to most any process (C3MR, DMR, AP-XTM) where compressor power demands need to be balanced between drivers.
Technical Papers
The literature below is in PDF format. You will need the free Adobe Acrobat Reader to view these documents.
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