US2039889A - Method and apparatus for cooling and drying moist gases - Google Patents

Description

May 5, 1936. w. L. DE BAUFRE 2,

METHOD AND APPARATUS FOR COOLING AND DRYING MOIST GASES Filed Sept. 5, 1954 6 /0 K 4. l5 l6 H fJ=F 1 I -=QJ 44 A,

mi //1-PI /vl/ENTOR Patented May 5, 1936 UNITED STATES METHOD AND APPARATUS FOR COOLING AND DRYING MOIST GASES" William Lane De Baui're, Lincoln, Nebr.

Application September 5, 1934, Serial No. 742,869

27 Claims.

This invention relates to improvements in the art of cooling gases containing water vapor, and is particularly applicable in cooling atmospheric air and other moist gases for the purpose of separating the gases into their components by rectification, the cold separated components being utilized to cool the atmospheric air or other moist gases. In cooling atmospheric air or other moist gases, water vapor therein is condensed into a liquid above the freezing point of water, zero centigrade, and is frozen into ice which is deposited as frost on the cooling surfaces below the freezing temperature of water. Most of the water vapor is removed from the so-called dry gases in liquid form before the temperature is reduced to zero centigrade, and if this liquid were permitted to fiow into the regionwhere the gases are cooled below zero centigrade, the liquid would freeze into solid ice and clog the cooling apparatus. While the smaller portion of the water vapor which freezes out of the dry gases below zero centigrade may be permitted to collect as frost upon the cooling surfaces within the cooling apparatus for a period of time, the accumulated frost increases the frictional resistance to flow of the gases being cooled and impairs the effectiveness of the cooling surfaces.

Eventually, the accumulated frost must be re-' moved from the cooling apparatus by heating it above zero centigrade in order that the frost will melt. The resulting liquid must then be drained from the cooling apparatus.

Heretofore, in the rectification of atmospheric air and other moist gases, either special equipment has been provided to remove by chemical means nearly all the water vapor in the gases before cooling therein; or, two heat interchangers have been provided, either of which has been sufficiently large to meet the cooling requirements for all of the gases processed. The chemical treatment would become a very large item in the cost of producing oxygen in a large air separation plant, say for gas making or metallurgical purposes. Also, in a large air separation plant, the interchanger for cooling the air' would be large so that providing it in duplicate for defrosting purposes would be an expensive item of first cost.

The object of the present invention is to avoid thechemical removal of moisture from atmospheric air or other gases to be separated by rectification in large industrial plants without the necessity of doubling the size of the cooling apparatus that must be operating at any one time. By use of the method and apparatus herein described and claimed, it is necessary to provide 50 percent only or less of additional cooling equipment for defrosting purposes.

Another object of the invention is to remove liquid from the cooling and drying apparatus as rapidly as it is formed by condensing water vapor from the moist gases being cooled above the freezing temperature of water.

Another object of the invention is to replace a portion only of thecooling and drying appa- 1O ratus in which frost has accumulated by frost free cooling apparatus and then to defrost the portion of the apparatus so replaced.

Another object of the invention is to prevent connected piping from becoming clogged with frost. Another object of the invention is to free drain piping of frost which would prevent removal of liquid from the portion of the apparatus being defrosted.

Another object of the invention is to reduce loss of refrigeration due to the defrosting operation.

Another object of the invention is to reduce disturbances in rectification processes due to the defrosting operation.

Another object of the invention is to insure the proper steps being taken in changing the flows of fluids through the cooling and drying apparatus for the purpose of defrosting a portion of the apparatus.

Another object of the invention is to centrally control the operation of the apparatus as a whole and to render the operation automatic.

The foregoing, together with such other advantages as may hereinafter appear or as are incident to the invention, are realized by the apparatus illustrated in preferred form in the accompanying drawing, wherein Fig. 1 represents the apparatus as a whole while Fig. 2 represents a. detail of construction.

Referring to Fig. l, the apparatus includes multiple interchangers, say four in number, each comprising a vertical section A1 or A4, and a horizontal section B1 'or B4. There is also a preliminary exchanger C. Theseinterchangers and exchanger are connected together and to manifolds D, E, F, G, H, I, J and K by piping with valves operated by mechanisms L1 and L4, from a cen- I tral controller M. Traps for removal of water are designated by N1, N4, 0 and P. Two only of the four interchangers are shown on the drawing in order to show more clearly the pipe connections to and from the several manifolds. As there are only two operating valve positions, these two positions are shown for the two interchangers included in the drawing.

Both sections of the interchanger at the right are shown in section. The valves for this interchanger are in the positions for cooling and drying therein the gases which are to be separated into components by rectification. The cold returning products of rectification flow through the interchanger in heat exchange with the moist gases that are to be cooled and dried. The valves for the interchanger at the left are in the positions for defrosting the interchanger of accumu-, lated ice and snow. The valves for the two intermediate interchangers would be in the same positions as shown for the interchanger on the right.

The functioning of the apparatus shown in Fig. 1 will be described for the cooling of moist atmospheric air which is to be separated by rectification in apparatus not shown on the drawing. The cold products of rectification, more or less pure oxygen and nitrogen, then return to the apparatus shown for cooling the moist air to be separated. The moist air must, first be compressed to 250 to 500 lb. gage in order to meet the refrigeration and heat transfer requirements of the process. This compressed air contains saturated water vapor at the temperature to which the compressed air is cooled by available cooling water after being heated by compression. Assuine the temperature of the compressed air to be 30 centigrade, at which temperature the compressed air enters exchanger C through pipe I.

Within exchanger C, the compressed air is cooled by heat exchange with returning oxygen and nitrogen flowing through tubes 2. The compressed air is cooled to say 15 centigrade for reasons hereinafter given, and leaves exchanger C through pipe 3 to manifold F. By reason of valve 4 being open and valve 5 closed, thecompressed air cooled to a temperature below that of the atmosphere or of available cooling water but above the freezing temperature of water, flows through pipe 6 instead of pipe I and enters the annular space at the lower end of the shell of interchanger A4. 'Flowing up over the heat transfer tubes therein, any frost on the tubes and baiiles is melted and the resulting water flows down to the annular space at the lower end of the shell and out through pipe 8 and valve 9 to manifold G. The latter is kept drained of water by means of trap 0. Flow through pipe III is prevented by valve I I being closed.

The heat for melting the frost within interchanger A4 is that available by cooling the moist air from the entering temperature to zero centigrade. The entering air temperature must be sufficiently high for this purpose. But when the frost has all been melted, the whole interchanger is heated to the temperature of the entering compressed air. When cooled to operating temperatures again, the refrigeration required depends upon the initial temperature from which the interchanger must be cooled.' The lower the initial temperature, the less the refrigeration required. Hence, provision of preliminary exchanger C for cooling the compressed air below the temperature of the atmosphere or of available cooling water before the compressed air is used for defrosting interchanger A4, reduces the refrigeration required in the operation of the process by reducing that necessary to cool' to operatingtemperatures, interchangers which have been defrosted.

The compressed air leaves the vertical section A4 of the interchanger through pipe I 2 and enters the horizontal section B4 of the same interthird entering the horizontal section B1, through pipe I4.

Within horizontal section B1 of the first interchanger, the compressed moist air meets the cooling effect of returning oxygen and nitrogen flowing through tubes l5 therein. The compressed air is cooled therein approximately to zero centigrade. The resulting water of condensation is drained away by trap N1 from the annular space at the end of the shell. The compressed air leaves through pipe it around zero centigrade and enters the annular space at the uper end of the vertical section A1 of the first interchanger.

Within the vertical section A1 of the inter changer, the compressed air is cooled to below minus 100 centigrade by the returning products of rectification, oxygen and nitrogen, flowing through tubes l1 therein. Frost is deposited on tubes l1 and on baiiies l8, but in comparatively small amounts because most of the waste vapor has been removed in exchanger C and in the.

be removed in the first sections B of the first three interchangers leaving only about 15 percent of the original moisture to be removed from the compressed air in the vertical sections of the first three interchangers.

The assumed temperatures are for illustration only as the temperature entering the vertical sections of the interchangers need not be exactly at zero. But if greatly above zero, the vertical sec-. tion of the interchanger would quickly become clogged with ice formed from water which would run down from the part of the interchanger above zero centigrade. If the entering temperature were much below zero, there would be a tendency for the horizontal sections B of the several interchangers to become clogged with ice.

In a small plant, preliminary exchanger C might be omitted because the resulting saving in refrigeration required in the defrosting process would probably not justify the cost of the exchanger.

Both exchanger C and the first sections B of the multiple interchangers are shown in a horizontal position as being preferred for draining liquid from the same. however, may be mounted in other positions. Thus, it may be more convenient to suspend them in vertical positions with thecompressedmoist gases flowing upwards therethrough while the returning gases flow downwards therethrough.

The compressed air cooled below minus 100 centigrade and almost completely free" ofwater These pieces of equipment,

vapor, leaves through pipe l9, since valve 2ll is oxygen and nitrogen which return through pipes' 22 and 23 to manifolds I andH, respectively( The returning oxygen and nitrogen will flow through tubes I1 and I5 within the vertical and horizontal sections of the first, second and third interchangers rather than through the tubes within the fourth interchanger because valves 24 and 25 on the first interchanger and the corresponding valves on the second and third interchangers are open while valves 26 and 21 on the fourth interchanger are closed.

Hence, there will be no cooling effect due to returning oxygen and nitrogen within the fourth interchanger, but there will be a cooling effect in the first, second and third interchangers and in exchanger C to which manifolds D and E are connected by pipes 23 and 29. The products of rectification leave exchanger C through pipes 30 and 3| heated nearly to the temperature of the compressed air entering through pipe I.

The pipes for warm compressed air to enter the vertical sections of the interchangers are made into the shapes shown at 6 and I in order to minimize the cooling of these pipes from the cold interchangers when compressed air is not flowing through these pipes. By having the piping for conveying the warm moist gases to the annular spaces at the lower ends of the multiple interchangers extend downward to these interchangers, there is no tendency for cold air to enter these pipes from the interchangers except by the slow process of diffusion. These pipes would be cooled more rapidly by the process of convection if they were horizontal or extended upwards to the interchangers, due to replacing warm gases in the pipes by cold gases from the interchangers. But with the pipes as shown, there will be little tendency for these pipes to become so cold asto be clogged with frost upon admission of warm moisturedaden air to them when the valves controlling the flows of fluids are reversed in position.

The pipes for cooled and dried compressed air to leave the vertical sections of the interchangers are made into the shapes shown at l0 and I9 in order to prevent water running into these pipes from the annular spaces at the lower ends of the interchan'gers and yetto minimize the heating of these pipes by convection currents when compressed air is not flowing through them. By extending this piping upwards from the annular spaces at the lower ends of the interchangers, there is no tendency for liquid to run into these cold pipes while the interchangers are being defrosted. There is a tendency for cold air within the pipe to be replaced by warm air from the interchanger during defrosting and thus rapidly warm the pipe by convection. This warming, however, is restricted to the short vertical part of the pipe extending upward from the annular space to the return bend. Within the remainder of the pipe, there is no tendency to replace the cold air with warm air by convection so that the remainder of the pipe is heated by the slow process of diffusion and by conduction of heat through the metal only. There will therefore be little tendency for this pipe to become clogged with ice from condensation of moisture in any warm moist air entering the pipe while defrosting the interchanger.

Valves 9 and 32 are provided in drain pipes 3 and 33 respectively in order to shut off flow through these drain pipes while the interchangers are cold. Otherwise, there would be a flow of warm moist air through manifold G directly into the annular spaces at the lower ends of the cold interchangers from annular spaces at the lower ends of the warm interchangers. This flow might be avoided by the use of four separate traps,

one on each interchanger, rather. than the single trap O for all interchangers. With no shut off valve between the interchange!- and the trap, however, there would be a tendency to freeze the water inthe trap by convection currents when the interchanger is cold. 3 The closed valve prevents such convection currents and also enables a single trap to be used for all interchangers by means of the manifold connection as shown.

Even with valve 32 closed, there is a tendency for pipe 33 to become very cold by convection currents and by conduction of heat from the pipe to the cold interchanger. Then, when all valves are reversed for the first interchanger, any water entering drain pipe 33 would freeze and clog the pipe with ice were it not for the electrical device shown enlarged in Fig. 2. Extending up within drain pipe 33 is an inner tube 34 having within it a resistance wire 33 connected to terminals 36 and 31. These terminals are connected to commutator 33 mounted on the same shaft as drain valve 32 so that when valve 32 is opened, resistance wire 35 is connected into electrical circuit 39. The heat produced by the resulting electrical current-flowing through resistance wire 35 melts any ice within drain pipe 34 and accumulated in the annularspace at the entrance to the drain pipe, so that the drain pipe can function to drain water from vertical section A1 of the first interchanger. When valve 32 is closed, however, the rotation of commutator 38 through say degrees, disconnects resistance wire 35 from electrical circuit 39 so that no electric .current flows through resistance wire 35. Consequently, no waste of electrical energy occurs while the interchanger is not being drained, the heating effect of which would interfere with the cooling effect of the interchanger. The size of resistance wire 35 relative to the voltage of electrical circuit 39 can be so selected that a mild heating effect only will be applied, just suflicient to melt any ice present but not enough to unduly heat the piping and interchanger. An automatic cut-out device could be applied so that the heating effect would occur for a short period only after the valves are reversed.

Valves 24, 25, 5, 32 and 20 are shown as plug valves for convenience in representing the valves as closed or open by the holes through the plugs being in line with or perpendicular to the several pipes as shown on the drawing. Other forms of valves may be used, but in any case, it would be desirable to have a long stem and sleeve extending from valve 20 so that the stumng box to prevent leakage around the valve stem (or operating rod) would be at atmospheric temperature when the valve itself is degrees or more below zero centigrade. The other valves are all at atmospheric temperature or but a few degrees below atmospheric temperature, so that long stems and sleeves are not necessary.

The whole group of valves may be reversed manually through lever H from one operating position to the other. Or, by means of the crank-connecting rod mechanism shown, the valves can be reversed by hydraulic or pneumatic pressure acting on the piston within cylinder L1. The flow of fluid to all cylinders L may be determined by a central controller M, the source of the operating fluid not being shown. Controller M can be arranged to slowly rotate by means of an electric motor 42, in which case, the four groups of valves will be reversed in order, thereby defrosting each interchanger in turn. Anyv desired sequence of opening and closing valves in any one group could be arranged by the use of separate Operating mechanisms for the several valves ineach group, all operating mechanism being controlled from the central controller M.

One of the advantages of the arrangement as above described is that in large plants for separation of atmospheric air to obtain oxygen for use in gas making and metallurgical processes, each of the four interchangers provided needs to have a capacity equal to one-third only of the plant capacity. All the compressed air, however, passes through the fourth interchanger in melting the accumulated frost therein before dividing into three equal portions to be cooled in the first three interchangers. This is possible because the size of an interchanger is determined by the volume of returning products of rectification under low pressure rather than by the much smaller volume of the original air under high pressure. As the products of rectification always return through three interchangers in parallel, each interchanger needs to be only onethird the size of a single interchanger for the defrosting is three times as great as in cooling and drying the compressed moist gases.

In smaller plants, three instead of four interchangers may be used, when each interchanger must have -a capacity equal to one-half of the plant capacity many features of the system, however, can even be applied to very small plants with two interchangers only.

In case. of three or more interchangers, the frictional resistances through the several interchangers, piping and valves may divide the flow of compressed air and of the returning products of rectification somewhat unequally through the several interchangers. Any inequalities that may occur, however, can be reduced by means of orifices in the pipes, as shown in the returning oxygen and nitrogen pipes at 43 and 44, or by restricting the pipes themselves, as by installing small diameter pipes at It and ll for the compressed air. I

With three or more interchangers provided for cooling and drying gases, so that only a portion of the gases being cooled need be changed at one time from interchangers at operating temperatures to an interchanger which has been warmed in .defrosting the same, less disturbance occurs in the cooling and'drying of the moist gases than if only two interchangers were employed. In the latter case, all of the gases being cooled and dried must be changed at the same time to an interchanger which has been warmed in defrosting the interchanger. This results in considerable disturbance to the cooling and drying operation with corresponding disturbances in any rectification process to which the cooled and dried gases are supplied.

What I claim is:

1. An interchanger for cooling and drying moist gases, including a horizontal section for cooling said gases above the freezing temperature of water, a vertical section for cooling said gases below the freezing temperature of water whereby frostis deposited within said vertical section, means for passing said moist gases through said horizontal section and then down-' wards through said vertical section as. said moist gases are being cooled, and means for passing said moist gases upwards through said vertical section whereby said interchanger is defrosted.

2. An interchanger for cooling and drying moist gases, including a section for cooling said gases above the freezing temperature of water, a separate section with one end higher than the other end for cooling said gases below the freezing temperature of water whereby frost is deposited within said separate section, means for passing said moist gases through the first section and then through the separate section from the higher to the lower end thereof as said moist gases are being cooled, and means for passing said moist gases through the separate section from the lower to the higher end thereof whereby said interchanger is defrosted.

3. An interchanger for cooling and drying moist gases, including means for passing said moist gases downwards through said interchanger in cooling said gases below'the freezing temperature of water whereby the frost is deposited within said interchanger, and means for passing said moist gases upwards through said interchanger whereby said interchanger is defrosted.

4. An interchanger for cooling and drying moist gases wherein said moist gases are cooled below the freezing temperature of water while passing downwards therethrough and depositing frost therein and wherein the deposited frost is melted by passing said moist gases upwards therethrough, including an annular space around the bottom thereof to which are connected pipes for conveying said moist gases thereto and for conveying cooled and dried gases therefrom and for draining moisture therefrom.

5. In apparatus for cooling and drying moist gases, multiple interchangers each with one end higher than the other end. means for admitting said moist gases into the lower ends of certain interchangers, a manifold connected to the upper ends of said interchangers for conveying said moist gases from certain interchangers to other interchangers, and means for withdrawing cooled and dried gases from the lower ends of said other interchangers.

6. In apparatus for drying moist gases by cooling said moist gases below the freezing temperature of water, multiple interchangers, means for passing said moist gases through said interchangers in parallel whereby frost is deposited therein during said cooling and drying, and means for defrosting one of said multiple interchangers while said moist gases are being cooled and dried in the remaining interchangers.

7. In apparatus for drying moist gases by cooling said gases below the freezing temperature of water by heat transfer to returning products of rectification of said gases, multiple interchangers, means for passing said moist gases and said returning products through said interchangers in parallel whereby frost is deposited within said interchangers in cooling said moist gases below the freezing temperature of water, means for shutting oil the flow of said moist gases and of said returning products through any one of said multiple interchangers and means for defrosting the interchanger so shut off.

8. Apparatus for cooling and drying moist gases tobe separated into components wherein the cold components are utilised for cooling said moist gases, including three or more interchangers, means for passing said moist gases through one of said interchangers and then through the remaining interchangers in parallel, and means for returning said cold components through the remaining interchangers in parallel.

9(Apparatus for cooling and drying moist gases as in claim 8 including means for changing the flow of said moist gases from the one interchanger to one of said remaining interchangers.

in parallel.

10. Apparatus for cooling and drying moist gases as in claim 8 including means for changing the flow of returning cold components from one of said remaining interchangers in parallel to the one interchanger.

11. Apparatus for cooling and drying moist gases by heat exchange with cold returning gases, including multiple interchangers, each having a first section for cooling said moist gases above the freezing temperature of water and a second section for further cooling said moist gases below the freezing temperature of water, one end of said second section being higher than the other end of said second section; piping between the first section and the higher end of the second section of each interchanger; piping to the lower.

ends of the second sections and from the first sections of said interchangers and valves in said piping whereby said cold returning gases are shut off from flow through one interchanger and return through other interchangers; a manifold with piping to the first sections of said multiple interchangers; piping to and from the lower ends of the second sections of said interchangers and valves in said piping whereby said moist gases fiow upwards through the second section and through the first section of the interchanger from which flow of said returning gases is shut off, then through said manifold, and finally through the first sections and downward through the second sections of other interchange rs in heat exchange with said returning gases.

12. Apparatus for cooling and drying moist gases by heat exchange with cold returning gases, including multiple interchangers with one end higher than the other end of each interchanger; piping for conveying said returning gases to and from said interchangers and valves in said piping whereby flow of said returning gases is shut off from one interchanger; a manifold with piping connected to the upper ends of said interchangers; piping connected to the lower ends of said multiple interchangers for conveying said moist gases to said interchangers and for conveying cooled and dried gases therefrom, and valves in said piping whereby said moist gases fiow upwards through said interchanger from which flow of said returning gases is shut off, then flow through said manifold, and finally flow downwards through other interchangers in heat exchange gases as in claim 12, wherein the piping for conveying cooled and dried gases from the lower ends of said multiple interchangers extends first upward and then downwards from said interchangers.

18. Apparatus for cooling and drying moist gases by heat exchange with cold returning gases as in claim 12, including drain piping from the lower ends of said multiple interchangers and valves in said drain piping whereby liquid drains from certain interchangers through which flow of said returning gases is shut off and whereby flow through said drain piping is shut off to or from the remaining interchangers through which said returning gases flow.

19. Apparatus for cooling and drying moist gases by heat exchange with cold returning gases as in claim 12, including drain piping from the lower ends of said multiple interchangers, electrical means for melting ice in said drain piping,

and means for turning on the electric current for drain pipes from certain interchangers from which flow of said returning gases is shut off and for turning oil. the electric current from drain pipes from the remaining interchangers through which said returning gases flow.

20. Apparatus for cooling and drying moist gases as in claim 12, including means for operating as a group all valves in the piping to and from each of said multiple interchangers.

21. Apparatus for cooling and drying moist gases as in claim 12, including means for operat-' ing as a group all valves in the piping to and from each of said multiple interchangers, and means for operating the valve groups from a central location.

22. In a drain pipe for removing water from a vessel alternately cooled below and warmed above the freezing temperature of water, electrical means for melting ice within said drain pipe, means for operating the same when the temperature is above freezing, and means for closing the drain pipe when the temperature is below freezing.

23. A method of drying moist gases which includes cooling said moist gases to a temperature below that of the atmosphere or of available cooling water but above the freezing temperature of water, utilizing said cooled gases for defrosting an interchanger previously employed to cool said moist gases below the freezing temperature of water, and finally further cooling said moist gases below the freezing temperature of water whereby said moist gases are dried.

24. A method of cooling and drying moist gases by heat exchange through heat transferring surfaces to returning cold gases, which includes cooling said moist gases to about the freezing temperature of water, separating therefrom liquid resulting from condensation of water vapor in said moist gases, further cooling said moist gases below the freezing temperature of water by passing the partly cooled and dried gases downwards in contact with said heat transferring surfaces and in heat exchange with said returning cold gases flowing upwards until heat exchange is impaired by accumulation. of frost upon said heat transferring surfaces, and then defrosting said heat transferring surfaces by passing said moist gases with an initial temperature above freezing upwards in contact with said heat transferring surfaces. I

25. A method of defrosting aninterchanger in which frost has been deposited from moist gases flowing therethrough, which includes passing gases having a temperature above the freezing temperature of water through said interchangerwith a mass velocity greater than the mass velocity of said moist gases while depositing said frost. 26. A method of defrosting an interchanger in which includes dividing said moist gases into two or more portions, cooling each portion separately 10 below the freezing temperature of water whereby frost is deposited in the cooling apparatus, and shifting the said portions separately to frost free cooling apparatus, whereby the disturbance to cooling and drying is reduced in said shifting.

WILLIAM LANE DE BAUFRE.

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