Patent Application
20140158926
The present invention relates to a low-density, solid-state insulation for cryogenic service.
The existing method to insulate an air separation plant requires that the distillation columns be built within an enclosed structure that includes support columns and extension on valves for manipulation from the outside. The air separation column is enclosed within the structure to allow for an insulation material to be added after the outer structure is built to reduce heat leak that occurs during the cryogenic air separation process. The current insulation material is perlite that is blown in after the outer structure is complete. In order to perform maintenance and work on the column and related piping and instrumentation you will be required to remove the insulation material and work around the space as defined by the outer structure.
There are several modifications to conventional molding processes which are preferably employed in order to ease the manufacturing process. For example, usually the mold is treated with a releasing agent (such as a hydrocarbon or silicon oil) in order to prevent sticking. During the fabrication step, traces of the wetting and/or releasing agent will remain in or on the surface of the Aerogel. For most subsequent applications, this trace of material presents no issues. However, in a cryogenic insulation service, any trace material will form a potentially combustible plating in or on the surface of the cryogenic apparatus. This presents an unacceptable safety concern in the presence of oxygen.
A cryogenic insulation system including a low density low conductivity insulation material for cryogenic service, wherein the low conductivity insulation material is essentially free of hydrocarbon residue. A method for producing a low density low conductivity insulation material for cryogenic service, comprising: exposing the low density low conductivity insulation material to at least one of an elevated temperature or a reduced pressure, for a length of time sufficient to reduce the hydrocarbon residue to less than 1000 ppm.
Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
Aerogel is a low-density solid-state insulating material derived from a gel, in which the liquid component of the gel has been replaced with a gas. The result is a solid with extremely low density http://en.wikipedia.org/wiki/Aerogel-cite note-GuinnessRecord-0 and thermal conductivity. Low density low conductivity insulation materials are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly drawn off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation.
Despite their name, aerogels are rigid, dry materials and do not resemble a gel in their physical properties; the name comes from the fact that they are derived from gels. Low density low conductivity insulation materials are good thermal insulators because they almost nullify the three methods of heat transfer (convection, conduction, and radiation). They are good conductive insulators because they are composed almost entirely from a gas, and gases are very poor heat conductors. Silica low density low conductivity insulation material is especially good because silica is also a poor conductor of heat (a metallic low density low conductivity insulation material, on the other hand, would be less effective). They are good convective inhibitors because air cannot circulate through the lattice. Numerous attempts have been made to adapt the rigid, brittle low density low conductivity insulation material into a more flexible insulation blanket. One example may be found in U.S. Pat. No. 8,021,583.
Cryogenic service requires significant insulation, both for economic and safety reasons. The development of such profoundly cold conditions comes at significant energy cost, and it is therefore lowly desirable to provide the best insulation that remains economically feasible. In this paper cryogenic temperatures are considered to be below −238 F (−150 C). If a solid surface has a local temperature below about −297 F (−183 C), essentially oxygen can condense on this surface if present in the surrounding atmosphere. If any type of ignition source is introduced into such an environment, virtually anything is likely to combust. It is therefore also highly desirable from a safety perspective, to insulate such cold surfaces from atmospheric air, any type of fuel, and/or any type of ignition source.
The use of a low-density solid-state insulating material to wrap cryogenic condition, such as air separation columns has several additional benefits. It would eliminate the need to build the outer structure to house the air separation column, thereby considerably reducing initial construction and capital cost. The low-density solid-state insulating material provides a far greater degree of insulation to the air separation process, decreasing heat loss and dramatically increasing the plant process efficiency.
One aspect of the present invention is to utilize an Aerogel such as Cryogel™ which has been produced without the use of a wetting and/or releasing agent. Such a process may include, but may not be limited to, the use of known non-stick surfaces in the bold (such as Polytetrafluoroethylene (PTFE) otherwise known by the trade name Teflon).
Another aspect of the present invention is to utilize an Aerogel such as Cryogel™ which was produced with the use of a wetting and/or releasing agent, but process the Aerogel in order to eliminate this hydrocarbon based material. In one embodiment, the commercially available Aerogel would be placed in an environment which would encourage such volitization and removal of oxygen reactive material. Such an environment may include, but not be limited to, a heated and vented environment, or an environment with a reduced pressure in order to expedite the off-gassing of the material. Such an environment may consist of placing the Aerogel in direct sunlight for a time sufficient to allow volatilization of the releasing agent. A combination of any, or all, of these techniques is also envisioned.
