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The key to our success has been Air Products' MCR® liquefaction process and the MCR® cryogenic heat exchanger (MCHE). Air Products' unique ability to integrate the liquefaction process design and the mechanical design of the main cryogenic heat exchanger leads to an optimization of performance and reliability that has become the benchmark of the LNG industry. This ability is even more crucial in a floating, production, storage, and off-loading (FPSO) LNG plant where the added dimensions of efficient use of deck space and the safe and efficient operation of process equipment under wave motion are of key importance.
 Air Products' CL DMR FPSO Concept with MCR® Cryogenic Heat Exchangers
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For capacities of less than 1 MTA:
Air Products' AP-MTM Modular Refrigerant Process is Ideal for Small Stranded Gas Reserves
Air Products' AP-MTM modular processes fit the requirements of the small scale FPSO LNG plant.
For capacities for 0.5 – 6 MTA:
Air Products' Dual Mixed Refrigerant Process is Highly Efficient, Economical and Compact
Air Products' dual mixed refrigerant (DMR) processes fit the requirements of the FPSO LNG plant. The refrigeration for the precooling is supplied by a closed loop mixed refrigerant system. The refrigeration for the liquefaction and subcooling is supplied by another, separate, closed loop mixed refrigerant system, the same MCR® process that has been the standard of the baseload LNG industry. The precooling MCR® system and the liquefaction MCR® system are separate and distinct circuits. The mixed refrigerant composition for each is optimized for the cooling temperature range being covered. The process efficiency approaches that of the propane precooled MCR® cycle used in the overwhelming majority of the world's baseload LNG plants while reducing the number of components and the deck space required for liquefaction equipment.
The following illustration depicts a nominal 3 MTA FPSO plant incorporating two wound coil heat exchangers and three GE LM6000 gas turbine driven compressors contained within a 56 x 48m deck area. One of the exchangers is used for precooling service, replacing the more traditional propane precooling equipment. The second exchanger provides final liquefaction and subcooling of the LNG.
For capacities greater than 6 MTA:
Air Products' AP-XTM LNG Process is Highly Efficient, Economical for Larger FPSO Applications.
Air Products' AP-XTM process fits the requirements of the large scale FPSO LNG plant using a dual mixed refrigerant for pre-cooling and liquefaction.
Air Products' LNG Processes are Safe, Reliable, Flexible, Efficient and Easy to Operate
Air Products developed the MCR® process for natural gas liquefaction in baseload service. This system provides cooling at a continuum of temperature levels to liquefy the natural gas feed stream. By using a mixture of gases rather than single refrigerant components, the thermodynamic efficiency of the process is enhanced and the liquefaction system is greatly simplified. The renowned propane-precooled MCR® process has been the process of choice for the baseload LNG industry because it has proven to be reliable, flexible, thermodynamically efficient and easy to operate. The application of mixed refrigerant precooling has special attraction for an FPSO application since the number of equipment items can be reduced while matching baseload efficiencies. Using a mixed refrigerant also reduces the safety risks that some clients may associate with the volumes of propane required for propane precooling.
Air Products' LNG Specialists Will Optimize the Capital and Deck Space Invested to Yield the Greatest Return in LNG Production
Air Products' LNG specialists can assist in the early stage of project development by conducting process scoping studies and preliminary process designs to assist the FPSO owner in developing a sound design basis.
Air Products' engineers can develop an optimized precooling and liquefaction system that integrates the main cryogenic heat exchangers with the refrigerant compressor/driver sets and the supporting process equipment. This allows the capital and deck space invested in compressor/driver sets to yield the greatest return in LNG production.
The dual MR process also offers tremendous flexibility in exchanger and compressor design. The process can be configured to minimize hydrocarbon inventories, eliminate specific components from the MCR mix, if desired, for safety reasons or to meet the weight and center of gravity requirements of a specific FPSO vessel design. These considerations as well as the more traditional project-specific parameters, such as site-specific ambient conditions, feed characteristics, production requirements and economic factors are properly balanced with each client's needs to engineer the most cost-effective system for each project.
The MCR® Main Heat Exchanger—Compact, Efficient, Adaptable The MCR® Cryogenic Heat Exchanger (MCHE) is the Heart of the FPSO LNG Plant
The MCHE is the heart of the natural gas liquefaction process. Air Products' MCR® heat exchangers feature a proven robust mechanical design along with high-quality fabrication, leading to the successful operation of the LNG process. Each MCR® heat exchanger is custom designed by our own engineers. The MCHE consists of one or more spiral-wound tube bundles housed within a single pressure shell. The tube bundles are made up of small-bore aluminum tubing, providing a large amount of heat transfer area in a compact unit and permitting high operating pressures for greater process efficiency. The deck space taken up by the wound coil exchanger is much smaller than that which would be required by the large number of brazed aluminum core exchangers that would be required in parallel to approach the performance of a single wound coil exchanger.
The use of mixed refrigerant with a wound coil exchanger in place of the traditional propane precooling scheme effectively combines three or four levels of propane precooling, and the attendant multiple shell and tube, brazed aluminum exchanger, or core-in-kettle type evaporators, into a single wound coil exchanger which takes up very little deck space.
The use of MCR® with a wound coil exchanger for liquefaction versus multiple brazed aluminum exchangers with associated cold boxes effectively reduces the deck space required by over 15%.
The Air Products spiral-wound MCHE provides a compact and inherently safe equipment arrangement in the layout constrained FPSO environment.
The MCHE and the Process can be Optimized for Any Combination of Design Constraints
The MCHE and the process can be optimized for the entire spectrum of economic factors, feed gas conditions, LNG product specifications and FPSO vessel design constraints. Possibilities include single bundle designs to minimize exchanger height and weight, stainless steel shell for higher shell side design pressures, and more traditional two or three bundle configurations to increase process efficiency or recover refrigerants and produce LPG products from lean feed gas streams. There are various exchanger and compressor configurations available to meet specific client needs.
Air Products Advantage—Building Success into LNG Projects FPSO Development Program
Air Products has been involved with various FPSO studies for the past 20 years and is confident the MCR cryogenic exchanger process performance and structural integrity are not adversely impacted by wave motion on a floating plant, regardless of exchanger height. The geometry of the tube bundle inherently resists motion-induced liquid maldistribution throughout the bundle length. A comprehensive research and development program was initiated in 1998 to demonstrate the wound coil exchanger performance when subjected to pitch, roll and heave motions.
This two year program was designed to evaluate the structural integrity and process performance of the wound coil exchanger under expected FPSO sea conditions.
Air Products consulted with shipbuilders and certification societies such as MossMaritime and DNV to obtain accurate sea state data and to perform verification of research methods and computations.
Structural Integrity
Air Products contracted the services of an outside expert in the field of motion induced stresses, Analytical Engineering Associates (AEA). AEA modeled Air Products' largest MCHE using finite element analysis techniques. Using accelerations from actual North Sea conditions, the analytical model determined stresses throughout the structural components of the MCHE.
Air Products also performed empirical fatigue testing in our own R&D facilities to verify the robustness of the tube bundle support system under simulated FPSO conditions.
All data was thoroughly evaluated, and it was determined an Air Products' MCHE with a stainless steel shell would survive and subsequently be able to operate even after be exposed to a 100 year storm condition in the North Sea. All calculations and methodology have been certified by DNV.
Process Performance
Air Products contracted with Heriot-Watt University in Edinburgh, Scotland to perform motion experiments on an actual scaled version of a wound coil exchanger. Dr. Brian Waldie, Professor of Chemical and Offshore Process Engineering at Heriot-Watt led this effort. Dr. Waldie has over thirty years of experience working in the chemical industry and is recognized by the oil and gas industry as an expert in applications of process technology to offshore environments. The results of these experiments provided the necessary process information to insure the MCHE process performance can be quaranteed in an FPSO environment.
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