Refrigeration – Cryogenic treatment of gas or gas mixture – Separation of gas mixture
Reexamination Certificate
1999-03-25
2001-08-21
Doerrler, William (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Separation of gas mixture
C062S620000
Reexamination Certificate
active
06276167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates broadly to refrigeration and preferably to a refrigeration method using a non-aqueous, non-hydrocarbon refrigerant to contact a hydrocarbon composition as discussed below.
2. Description of Related Art
Common refrigeration systems include vapor compression, fan, heat exchange and absorption systems. Low temperature or cryogenic processes have also become popular, due in part to the increased demand for air liquefaction and separation capacity to make liquid products such as liquid oxygen and liquid nitrogen and also for the low temperature separation of natural gas and natural gas products. Methods typically used to achieve cryogenic temperatures include vaporization of liquids, Joule-Thomson expansion and expansion of gases in an engine doing external work such as a turbo expander.
A mechanical refrigeration cycle is a reversed heat engine system. Generally, vapor compression systems use a pressurized hydrocarbon heat transfer media as a refrigerant. The pressure on the refrigerant is lowered, usually by expansion across a valve. The refrigerant then flows to an evaporator where heat is absorbed, vaporizing the hydrocarbon. The vaporized refrigerant is then compressed and condensed to begin the cycle again. The chemical processing and refining industries are major users of mechanical refrigeration.
Refrigeration is typically used in the chemical processing and refining industries to remove the heat produced by reactions used to make products and to separate components by condensation, distillation or crystallization. Refrigeration systems are also used to process, store and transport perishable foods. Lastly, refrigeration is used to air-condition buildings and cars.
There are many disadvantages associated with current refrigeration designs and methods. Many refrigeration systems are limited by the temperature of the refrigerant. For vapor compression systems, the lowest attainable temperature of the refrigerant is typically determined by its composition, its associated properties and the selected operating pressure. Ambient air conditions, including temperatures and relative humidity, may limit refrigeration produced by air coolers such as fin fans and cooling towers. Absorption systems exhibit another disadvantage similar to that of the vapor compression systems limitations in that the selected operating pressure, e.g., the vacuum, coupled with the brine selection for the absorption system, indirectly result in temperature limits. At higher vacuums, the vaporization temperature drops for a given brine composition. Once the vacuum level is determined, for a given brine composition, the vaporization temperature is established. These temperature limits result in limited refrigeration available, condenser capacity limits and purity limits on products.
Accordingly, a continuing need exists for overcoming these temperature limitations or indirect temperature limitations as reflected by system pressure or ambient conditions. Also, the art has sought a method for refrigeration which does not require the use of excessively large heat exchanger areas or relatively large capacity compressors or vacuum pumps to overcome processing capacity limitations and product purity limitations. Accordingly, the present invention relates to a method of improved refrigeration which may result in reduced energy costs by lowering reflux requirements, by improving separation, and by decreasing or eliminating flooding in distillation columns. In another aspect of the invention, lowered energy requirements for reboiling distillation columns may result from increasing vaporization of light hydrocarbons by introducing a non-hydrocarbon vapor to a hydrocarbon liquid phase, lowering the temperature of the liquid and vapor and reducing light hydrocarbon losses, particularly of ethane or ethylene.
SUMMARY OF THE INVENTION
In one aspect, the invention involves a refrigeration method comprising lowering the temperature of a hydrocarbon composition by lowering the partial pressure exerted by the hydrocarbon vapor phase. The partial pressure of the hydrocarbon vapor phase is preferably lowered by introducing a non-aqueous, non-hydrocarbon refrigerant into the system, preferably at a fixed pressure as generally established or held by a pressure controller, although floating or variable pressure control schemes may also be employed with this invention.
A specific embodiment of the invention involves a refrigeration method, comprising the steps of: introducing at least one hydrocarbon composition into a phase separator, such that the hydrocarbon composition comprises one or more hydrocarbons and includes at least a hydrocarbon liquid phase and a hydrocarbon vapor phase in the phase separator; contacting the hydrocarbon liquid phase with a non-aqueous, non-hydrocarbon refrigerant, the refrigerant being in an amount sufficient to lower the partial pressure of the hydrocarbon vapor phase and to vaporize at least a part of the hydrocarbon liquid phase and to lower the temperature of the hydrocarbon composition by at least about 1° C.; removing at least one hydrocarbon product from the phase separator, such that the hydrocarbon product includes at least a part of the hydrocarbon liquid phase or at least a part of hydrocarbon vapor phase.
Another aspect of the present refrigeration method may comprise the steps of introducing at least one hydrocarbon composition into a phase separator, such that the hydrocarbon composition comprises one or more hydrocarbons and includes at least a hydrocarbon liquid phase and a hydrocarbon vapor phase in the phase separator; contacting the hydrocarbon liquid phase with a non-aqueous, non-hydrocarbon refrigerant, the refrigerant being in an amount sufficient to lower the partial pressure of the hydrocarbon vapor phase and to vaporize at least a part of the hydrocarbon liquid phase and to lower the temperature of the hydrocarbon composition by at least about 1° C.; removing at least a part of the hydrocarbon liquid phase from the phase separator; and removing at least a part of the hydrocarbon vapor phase from the phase separator.
A preferred embodiment of the refrigeration method comprises the steps of introducing at least one hydrocarbon composition into a phase separator, such that the hydrocarbon composition comprises one or more hydrocarbons and includes at least a hydrocarbon liquid phase and a hydrocarbon vapor phase the phase separator having at least one inlet location and a plurality of outlet locations, an interior including mass transfer apparatus and a lower end and an upper end, the lower end of the phase separator and at least a part of the mass transfer apparatus supporting hydrocarbon composition; contacting the hydrocarbon liquid phase with a non-aqueous, non-hydrocarbon refrigerant, the refrigerant being in an amount sufficient to lower the partial pressure of the hydrocarbon vapor phase; vaporizing at least a part of the hydrocarbon liquid phase; lowering the temperature of the hydrocarbon composition by at least about 1° C.; evaporating a portion of the hydrocarbon liquid phase supported by mass transfer media forming a hydrocarbon vapor phase; condensing a portion of the hydrocarbon vapor phase; separating heavy hydrocarbon constituents from the hydrocarbon vapor phase; separating light hydrocarbon constituents from the hydrocarbon liquid phase; removing a vapor product from the upper end of the distillation column; and removing a liquid product from the lower end of the distillation column.
In another preferred embodiment, the phase separator is a reflux drum which provides a cold reflux stream to a distillation column. The method of this preferred embodiment of the invention comprises introducing at least one hydrocarbon composition into a reflux drum such that the hydrocarbon composition comprises one or more hydrocarbons and includes at least a hydrocarbon liquid phase and a hydrocarbon vapor phase; contacting the hydrocarbon liquid phase with a non-aqueous, non-hydrocarbon refrigerant, the
Bracewell & Patterson L.L.P.
Doerrler William
Westlake Technology Corporation
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