Rectification System for the Separation of Fluids

The separation of fluid mixtures by rectification is one of the largest chemical processes in use. These systems are designed with an economical view toward capital costs relative to operating costs. With the present shortage of energy and the accompanying high cost, however, the necessity of more efficient separation processes is apparent. With this need in mind, the improved efficiency afforded by the disclosed system is the most significant consideration. Other important desirable characteristics are the avoidance of compressor seals, and smaller required components, mainly the re-boiler heat exchanger and reflex condenser. The avoidance of compressor-turbine seals is also a significant consideration as these seals are a perpetual maintenance problem. Generally, the present invention represents a substantial improvement with regard to these considerations.

The present invention is directed to a system incorporating a power cycle and a refrigeration cycle cooperating to form a heat pump. A common working fluid is employed in both cycles. The power cycle actuates a compressor structure which is an active element in the overall heat pump cycle. The power cycle also supplies heat to the liquid in the re-boiler of the rectification column. The refrigeration cycle extracts heat from the vapor in the re-condensor of the rectification column to produce a re-flux liquid. The present system permits the flexibility to use a fluid of the desired thermodynamic properties as required by the type of separation undertaken which thereby affords improved efficiency and smaller components. Additionally, this system is so implemented that the evaporation (re-boiling) and condensing (refluxing) are accomplished each at their respective required fixed temperatures, so as to approach the optimum system cycle with a high efficiency characteristic. Other advantages will be apparent from a consideration of the system as set forth.

In the drawings, which constitute a part of this specification, an exemplary embodiment exhibiting various objectives and features hereof is set forth, specifically:

FIG. 1 is a schematic diagram of one system constructed in accordance with the present invention relating in its most elementary form;

FIG. 2 is a schematic diagram of another system constructed in accordance with the present invention relating to a more sophisticated form for improved performance;

FIG. 3 is a schematic diagram of a composite system constructed in accordance with the present invention more specifically relating to a multicomponent separation;

FIG. 4 is a schematic diagram of an alternate composite system constructed in accordance with the present invention more specifically relating to a multicomponent separation.

As required, detailed illustrative embodiments of the invention are disclosed herein. The embodiments exemplify the invention which may, of course, be constructed in various other forms, some of which may be radically different from those disclosed herein. However, the specific structural details as disclosed herein are currently deemed to represent the best forms, within that objective, and furthermore effectively provide a basis for the claims which define the scope of the present invention.

Referring initially to FIG. 1, a system is illustrated involving a power cycle or loop P (right) and a separation cycle or loop S (left). As indicated above, common working fluid (in this exemplar consisting of the composition of the top output fluid) circulates in the two loops P and S.

Considering the system of FIG. 1 in somewhat greater detail, a vessel or tank 12 containing appropriate packing 14 such as Raschig rings, or the like, distributes an incoming fluid mixture 16 so that the liquid portion thereof flows downwardly to the re-boiler section 18 while the vapor portion of the feed flows upwardly to the re-condensing section 20 whereupon a portion of the pure vapor exits at 22. Another portion of the vapor is transported via line 24 to an ejector 26. High pressure working fluid previously pressurized by a pump 28 and thereafter heated by a heat source 30 via heat exchanger 32 enters the ejector 26 through the transfer pipe 34 to pressurize the working fluid which has entered from pipe 24 and thus are propelled together at the required pressure through pipe 36 to the re-boiler heat exchanger 38 contained in the bottom of vessel 12.

As shown in FIG. 1, the compression apparatus takes the form of a jet pump or ejector 26, structural forms of which are well known in the art and generally involves the utilization of a major stream entering by pipe 34 to accomplish pressurization of flow of secondary stream entering the ejector 26 through pipe 24. More specifically, the ejector 26 receives the power stream from the heat exchanger 32 through line 34 actuate the incoming stream through line 24. The two intake streams are merged in a single exhaust stream that is carried through line 36. In the re-boiler heat exchanger 38, the fluid in the form of a gas entering through line 36 is condensed to a liquid thus giving up its heat of vaporization and exits from the re-boiler 38 as a liquid at point 40. A portion of the liquid working fluid is diverted at point 42 whereby it is transferred through pipe 44 to the pump 28 so as to be eventually employed in the ejector 26. The balance of the liquid working fluid proceeds to a heat exchanger 46 whereby the liquid is further cooled prior to its expansion through valve 48 so as to more efficiently reflux the separation process, i.e., provide liquid to flow downward through the vessel 12. The working fluid which is condensed in the re-boiler 38 provides the required heat to vaporize a portion of liquid contained in the re-boiler section 18 and thus afford a vapor upflow through the vessel 12. The balance of the liquid in the re-boiler section 18 is exhausted as the bottom product from pipe 50. The ejector 26 increases the pressure of the working fluid so as to afford the required thermodynamic condition for its condensing in the re-boiler 38.

Recapitulating to some extent what is described is a more efficient heat powered loop denoted as P, separation process, denoted by loop S; whereby the correct thermodynamic conditions are provided to the working fluid so as to efficiently carry out a separation of the fluid mixture in the vessel 12. The separation loop is known in the art as a rectification or distillation column and consists of the vessels 12, re-boiler heat exchanger 38, and packing 14. The working fluid as shown in FIG. 1 consists of the composition of the vapor at the top of vessel 12 and is utilized as described in both the power loop P and separation loop S.

Generally, the system of FIG. 1 is relatively inexpensive to construct and in spite of that consideration may be designed to attain a reasonably high level of efficiency. However, in some situations, it may be desirable to employ a more elaborate system in the interest of substantially increased efficiency. Such a system is shown in FIG. 2 and will now be considered in detail.

Generally, the operation of the system of FIG. 2 is somewhat similar to that of FIG. 1. The major distinction between the two systems is that the system of FIG. 2 employs a turbo-compressor unit 52 which is driven by the power loop to provide the compression function for the separation loop. Specifically, the turbo-compressor 52 includes a turbine 54, mechanically coupled to a compressor 56. The turbine 54 and the compressor 56 may be carried on a common shaft 58, supported on fluid bearings as well known in the prior art for efficient operation.

The compressor 56 provides working fluid at an elevated pressure in an exhaust 60 which is connected through a junction 62 to a re-boiler heat exchanger 64 that is positioned within the liquid phase 66 contained in the bottom of the distillation column 68. Due to the thermodynamic properties of the working fluid used, the working fluid entering the re-boiler 64 at the pressure generated by the compressor 56 will condense and thus exit at point 70 in the liquid state. In the process of condensing the latent heat given up is such as to evaporate a portion of the liquid phase fluid 66 so as to provide an upward flow of vapor through the distillation column 68. The balance of the liquid phase fluid 66 exhausts at point 72 as the bottom product output. At the junction 70, a portion of the liquified working fluid is transferred by pipe 74 to the expansion valve 76 where its pressure is reduced so as to further cool the liquid working fluid and also change its thermodynamic state so that upon passage through the reflux condensing heat exchanger 78 it is evaporated thus absorbing heat and exits at point 80 in a gaseous state. During the re-fluxing heat exchange some of the vapor 82 rising up through the column 68 is liquified to provide the re-flux liquid 84 which in turn flows downward toward through the column 68. The gaseous working fluid transported by pipe 80 then proceeds to the compressor 56 thus completing the working fluid's journey through the separation loop S of the given system. It should be noted that by use of the re-flux condenser 78 a completely closed system is obtained whereby the working fluid in the system can be chosen so that its thermodynamic properties are such as to afford the optimum heat transfer situation and thereby accomplish the separation very efficiently. It is noteworthy that such fluids as the well-known fluorinated compounds "Freons," NH.sub.3, SO.sub.2, light hydrocarbons such as propane, butane; and methylchloride are among the great possiblities of choices. At the junction 70, the remaining portion of the liquid working fluid is directed by pipe 84 to the pump 86 whereupon its pressure is increased. The high pressure working fluid in the liquid state is transported by pipe 88 through the regenerative heat exchanger 90 whereby the high-pressured fluid is heated by the residual heat contained in the turbine's exhaust 92. The high-pressure prewarmed working fluid is then vaporized in heat exchanger 94 by adding heat from the heat source 96. The heat source 96 may take the form of any of a wide variety of forms, such as electric heaters, steam, and waste heat. Upon the passage of the working fluid through the heat exchanger 94 and being fully vaporized it passes as a gas through pipe 98 into the turbine 54 which in turn drives compressor 56 through shaft 58.

The approximate amount of the total heat added by means of the heat source 96 is rejected from the system by an auxilliary reflux heat exchanger 100 located in top of the distillation column 68. This heat rejection is accomplished through a heat sink 102 and usually takes the form of cooling water. The auxiliary reflux heat exchanger 100 serves to condense a portion of the rising vapor in the column and thus supply additional liquid reflux which flows downward through the distillation column 68. The fluid mixture feed to be separated enters the column 68 at the appropriate location 104 and the liquid portion if there is any present flows downward while the gaseous portion of the feed input flows upward through the column 68. The separation of the fluid input feed is accomplished by the thermodynamic equilibrium principles well established in the art of separation by distillation or rectification and can be accomplished by means of bubble cap trays 106. Other well-known column mechanisms such as valve trays, seive trays, or packing can be employed. The heavier component exhausts at point 72 as the bottom output while the lighter component exhausts at the top output 108.

To obtain the separation of a multicomponent fluid mixture feed the system of the present invention may be incorporated in the multiple-stage apparatus. Specifically referring to FIG. 3 a two-separation system S1 and S2 as disclosed above are represented. Specifically, the two system may take a form identical to that disclosed in FIG. 2 and in that regard, the top output product 200 consisting of the products mixture M.sub.1 and M.sub.2 is transferred by pipe 202 to the re-boiler heat exchanger 204 of separation system S1 where it is in turn liquified thus affording the heat for re-boiling in the bottom section 206. The liquid feed 208 is then fed into separation column S1 at the correct position 210. Separation column S1 then separates this liquid input feed 210 into its pure components whereby the heavier pure component M.sub.2 exhausts at point 212 and the lighter pure component M.sub.1 exhausts at the top 214. The exhaust component M.sub.1 is transported through pipe 216 to regenerative heat exchanger 218 where it is heated prior to its exhaust from the total system at point 220. Regenerative heat exchanger 218 provides precooling to the working fluid which in turn is used to reflux separation column S2 in reflux heat exchanger 222 and separation column S1 in reflux heat exchanger 224. The heat rejection loop 226 provides the added required reflux in separation column S1 and also is the means for rejecting the added heat supplied by the heat source loop 228 from the total system. In like manner, the total input feed mixture consisting of components M.sub.1 M.sub.2 and M.sub.3 enters separatIon column S2 at point 230 where it is separated into a pure bottom output M.sub.3 which exhausts at point 232. As shown in FIG. 3, the working fluid loop is similar to that described in FIG. 2.

For generality, FIG. 3 shows a tray column S1 containing separation trays 234 while separation column S2 contains an appropriate column packing 236. It is readily apparent that both separation columns may contain separation trays or packing depending upon the requirements of a given separation process.

FIG. 4 shows an alternate to the multi-stage separation system as shown in FIG. 3 whereby all of the reflux in separation column S2 is supplied by the heat rejection loop 250 which in turn is pre-cooled by the exhaust top product output 252 in regenerative heat exchanger 254. In this example, all of the reflux for separation column S1 is provided by the working fluid in reflux condenser 256. As shown in FIG. 4, the working fluid loop is similar to that described in FIG. 2.

Of course, various other modifications and changes in the system as disclosed herein will be readily apparent to those skilled in the art. As a consequence, the scope hereof shall be deemed to be in accordance with the claims as set forth below.