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MCR Cryogenic Heat Exchangers—Design and Fabrication |
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Air Products is the largest supplier of baseload LNG heat exchangers in the world. Over 70 of these large exchangers have been produced or are being fabricated currently at our manufacturing plant in Wilkes-Barre, Pennsylvania. The expertise developed over the years, covering all phases of design, manufacture, and inspection remains in place to benefit future LNG projects. Air Products has more than 40 years experience in the design and fabrication of aluminum wound coil heat exchangers, starting with exchangers built for helium recovery in the early 1960's.
Design Thorough and well tested process and mechanical designs for the MCR® Cryogenic Heat Exchangers are the major factors leading to successful operation and flexibility of the process cycle. The heat transfer process is complex, with heat being transferred from a single refrigerant warming stream to several cooling streams. Since each stream consists of a mixture of components and usually occurs as mixed liquid and gas phases, heat transfer is influenced by the mass transfer between phases, and both are affected by pressure drop. The use of a multicomponent refrigerant permits optimization of MCR® Cryogenic Heat Exchanger cooling curves as well as ensuring that much of the heat exchange occurs in the high coefficient, two-phase region. In addition, for this type of heat exchanger, the tube circuit areas can be accurately matched to tube circuit heat duties. Theoretical analyses by means of mathematical models and the extensive data collected from various operating facilities have been incorporated into Air Products' MCR® Cryogenic Heat Exchanger. Air Products' process design coupled with mechanical designs for obtaining proper distribution in two-phase flow, have led to outstanding exchanger performance at each plant.
Features The employment of Air Products' MCR® Cryogenic Heat Exchangers has the following advantages:
- The capability to design and fabricate very large heat exchangers, up to 16.5 feet in diameter, facilitates the construction of large process trains, which are limited only by the availability of large proven compressors and drivers. In addition to achieving economies of scale, this leads to simplified piping and control systems and, consequently, to reductions in installation, operation, and maintenance costs.
- Long service life and minimal downtime are achieved by virtue of the innovative design and mechanical construction of Air Products' MCR® Cryogenic Heat Exchangers.
- Maximum preassembly of equipment can be facilitated by the package design concept, utilizing common pipe and platform support points on the exchanger shell. This leads to substantial reduction in field erection time and cost.
- Reduced field erection and other capital costs and have resulted from designs that include internal separators, piping manifolded inside the heat exchanger shell to reduce the external piping and integral lifting lugs on the external shell.
- The use of multiple tube circuit exchangers eliminates the need for precise shell-side flow distribution between parallel, single-circuit exchangers.
- Higher operating pressures on the condensing side of the exchanger are made possible by the use of small bore aluminum tubing. This permits utilization of high-pressure feed gas and optimization of the mixed refrigerant pressure for higher process efficiency. The small tubing also permits construction of a compact exchanger incorporating a large amount of heat transfer surface. Thus, the process can be designed with small temperature differences and reduced compressor energy requirements.
- The use of higher pressure exchanger shells conserves refrigerants when the liquefaction plant is shut down by permitting a rise in shell pressure to three or more times the normal operating pressure. In addition to the basic economic benefit, refrigerant containment is particularly significant for marine liquefaction facilities and for sites where refrigerant importation is required.
- Reduced maintenance time is provided by easy access to all tubesheets through seal welded handholes that are accessible from outside the exchanger shell.
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