US2464891A

US2464891A - Process of and apparatus for producing compressed oxygen

Info

Publication number: US2464891A
Application number: US500385A
Authority: US
Inventors: Philip K Rice
Original assignee: Linde Air Products Co
Current assignee: Linde Air Products Co
Priority date: 1943-08-28
Filing date: 1943-08-28
Publication date: 1949-03-22
Anticipated expiration: 1966-03-22
Also published as: GB594958A

Description

March 22, 1949. RlCE. 2,464,891

- PROCESS .OF AND APPARATUS FOR PRODUCING COMPRESSED OXYGEN Filed Aug. 28, 1943 &

L L J 1 My PAP I I VENTOR IN PHILLIP K.R|CE

Q LZA QMWA ATTORNE 25 5g MVL TIPLE ($7,465

R0 01/? y Pl/MP Patented Mar. 22, 1949 UNITED STATES PATENT OFFICE PROCESS OF AND APPARATUS FOR PRO- DUCING COMPRESSED OXYGEN Philip K. Rice, Kenmore, N. Y., assignor to The Linde Air Products Company, a corporation of Ohio This invention relates to a process of and apparatus for producing compressed gaseous oxygen resulting from the low-temperature separation of air, and more particularly to a process of and apparatus for safely elevating the pressure of oxygen produced at a relatively low pressure by the low-temperature rectification of air.

In the low-temperature separation of air as customarily practiced, the air is prepared for separation by compressing it to a relatively high pressure, freeing it of moisture and carbon dioxide, and cooling it to a very low temperature by heat exchange with the gaseous products of the separation. such cooled and partially liquefied air is expanded to a lower pressure and passed into a rectifying column which may consist of one or two stages of rectification. A cold gaseous nitrogen product is withdrawn from the upper portion of therectifying column and passed through a countercurrent heat exchanger to cool the incoming air. The oxygen product of rectification which is at a relatively low pressure may be entirely gaseous or partially liquid, and to recover the refrigeration therefrom, the oxygen product is also passed through the countercurrent heat exchanger to cool the incoming air. It has been customary to collect the warm oxygenat low pressure in a gasometer and then withdraw it as required for compression into oxygen cylinders. These cylinders are customarily filled to a pressure of 2000 lbs. per square inch at 70 F. The gaseous compression of the oxygen requires considerable power and difliculties are encountered in lubricating the compressors.

It, has been proposed to avoid the difficulties of gaseous compression of the oxygen product by withdrawing the oxygen from the rectifying column in the liquid state, mechanically pumping the liquid oxygen through the oxygen tubes of the countercurrent heat exchanger, and then passing the oxygen directly to the cylinders to be filled. The pump employed must be one that is capable of raising the pressure of liquid oxygen from substantially atmospheric pressure up to at least 2000 lbs. per square inch gauge. Although the liquid pump requires some power, the amount of power is substantially less than that required for compressing an equivalent amount of gaseous oxygen from atmospheric pressure to 2000 lbs. per square inch.

Great difficulties are encountered however, in safely pumping the liquid oxygen to a high pressure. One such dimculty results from the fact that the liquid oxygen as produced is at its boiling point tem erature corresponding to the pressure 2 of the chamber in which the oxygen is collected. Since 'the temperature of such liquid is well below atmospheric temperatures, some heat always flows to the liquid and causes evaporation in spite of the protection aiforded by heat insulation. No suction can be placed on such a liquid as it will tend to flash into vapor when subject to any slight reduction of pressure. In a pump. particularly ofthe reciprocating type, some friction is inevitable which produces heat and such heat tends to cause vaporization. Also, when the liquid pressure is increased some heating thereof will occur. All these factors act to prevent the successful pumping of liquid oxygen by customary procedures. Another difllculty encountered has been found to result from the fact that relatively minute amounts of hydrocarbon gases occur in atmospheric air. These hydrocarbon impurities can only be partially removed by suitable treatment of the air to be processed. The hydrocarbon impurities become condensed and tend to collect in the liquid oxygen. Such hydrocarbon impurities can constitute a hazard particularly when the liquid oxygen is pumped by a pump having moving parts. Such hydrocarbon impurities also tend to accumulate in places where the liquid oxygen is evaporated and when the liquid oxygen is pumped through the countercurrent heat exchanger, the hydrocarbons accumulate in the oxygen tubes of such heat exchanger and such accumulation obviously may be very dangerous.

It is a principal object of the present invention to provide an improved process of and an apparatus for separating air by low-temperature rectiflcation to produce oxygen and for raising the pressure of such oxygen to a relatively high value for storage and use. Other objects are to provide a process of and apparatus for safely elevating the pressure of the oxygen product of an air-separation apparatus prior to utilizing the refrigeration of the oxygen product in cooling the air to be separated; to eliminate hydrocarbon impurities prior to pumping liquid oxygen from a. relatively low pressure to a high pressure; to eliminate impurities that may enter liquid oxygen as a result of being pumped to a high pressure prior to passing the oxygen through a. heat exchanger for elevating it to room temperature: to provide steps of and means for preventing the liquid oxygen pump from becoming gas bound.

The above and other objects and novel features of the invention will be apparent from the following description taken with the accompanying drawing, in which:

Fig. 1 is a sectional view schematically show- .pounds above atmospheric, pressure.

ing an exemplary apparatus for carrying out the invention; and

Fig. 2 is a sectional view schematically showing an alternative arrangement of the apparatus according to the invention.

Referring to the drawing and particularly to Fig. 1, at A is shown a rectifying column for the separation of air. The column A is representative of various forms of rectifying columns employed for the separation of air which, however, operate on substantially the same principles. Although the rectifying column A is of the twostage type, a single-stage type could equally well be employed, the specific type of column not forming part of this invention. At B there is schematically shown a countercurrent heat exchanger. The form of such heat exchanger likewise is not part of this invention and various types might be employed. The air to be processed is compressed and treated in the customary manner to remove moisture and carbon dioxide. The apparatus for compressing the air and removing the moisture and carbon dioxide is not shown since it forms no part of the present invention. In some oxygen producing plants all the air is supplied at a single high pressure while in other plants the air is supplied at two pressures, but whether the air is supplied at one or two pressures is immaterial to the principles of and operation of the present invention.

For simplicity it will be considered that the air is supplied at a, single high pressure which may be substantially 2000 lbs. per square inch. Suchair is supplied through a conduit in which enters the warm end of the heat exchanger B and passes therethrough to the cold end ll. Thewarmed nitrogen product leaves the heat exchanger B through the conduit l2 and the cold gaseous nitrogen is supplied at the cold end H of the heat exchanger B through a conduit I3. The heat exchanger B is also supplied with a heatexchange passage or oxygen conduit M which passes from the cold end to the warm end thereof in heat conducting relation to the air conduit i0. Suitable batlles I 5 may be provided to improve the heat exchange between the incoming air and outgoing gases. The oxygen conduit l4 may lead to consuming apparatus or to a cylinder-charging manifold [6 to which oxygen cylinders I! to be filled are connected. In passing through the heat exchanger B, the air is cooled to a very low temperature and partially liquefied. Such air fiows through conduit l8 to the lower rectifying chamber IQ of the column A. The conduit I8 is provided with an expansion valve 20, for reducing the pressure of the incoming air to that of the chamber I9 which may, for example, be about 75 lbs. per square inch gauge. At the upper end of the chamber I9 is a condenser 2| which causes condensation of a nitrogen product by heat exchange with the oxygen product surrounding'the condenser. A portion of this condensed nitrogen product collects oil a shelf 22 from which it is transferred by a transfer conduit 23 to the upper end of the upper rectifying chamber 24. This conduit is controlled by an expansion valve 23' which reduces the pressure from that of the chamber l9 to the pressure of the chamber 24 which is a few A liquid rich in oxygen collects at the bottom of the chamber l9 and is transferred by conduit 25 to an intermediate portion of the upper rectifying chamber 24. The conduit 25 is controlled by expansion valve 25'. The chambers I9 and 24 contain gas and liquid contact means in the form of perforated trays 26 of the customary type.

A product consisting mainly of nitrogen is withdrawn from the top of the upper chamber 24 through conduit 21 which connects to a heat exchanger 28, the discharge end of which is connected to the conduit l3. This nitrogen product will generally have a temperature below 191 C. The oxygen product of the rectification collects in the chamber 29 at the lower end of the upper chamber 24 and surrounding the condenser 2I. This oxygen product has a temperature generally below -1'77 C, but is at its boiling point corresponding to the pressure at the lower part of the upper chamber 24. The condensation of nitrogen inside of the condenser 2| at the intermediate pressure of the lower chamber I9 provides the heat for constantly boiling the oxygen product in chamber 29 to provide the vapors which are rectified in the upper chamber 24. The liquid oxygen is withdrawn through conduit 30 from the chamber 23 and may be conducted through a heat-exchange coil 3| in the heat exchanger 28. Such heat exchange with the colder nitrogen product sub-cools the liquid oxygen so that it has a temperature sufficiently below its boiling point at the existing pressure to avoid difficulties due to flashing of liquid into vapor in the passages leading to the pump and within the pump. Since it may not always be desirable to cool the liquid oxygen down to the temperature of the gaseous nitrogen, a by-pass conduit 32 is connected between the conduit 21 and the conduit I3. To regulate the proportion of the nitrogen by-passed, there is provided a control valve 32' in conduit 32 and a control valve 21' at the inlet to the heat exchanger 28.

The connection 33 conducts the sub-cooled liquid oxygen into the chamber of a filter 34. Within the filter chamber 34 is a cylindrical filter element 35 of a suitable material such as porous inert ceramic material. The cylinder 35 is closed at the top and communicates at the bottom with a connection 36. The filter chamber 34 is also preferably provided with a drain connection 31 at its lower end.

For elevating the pressure of the liquid oxygen there is provided at C a suitable liquid oxygen pump. When the final pressure is to be as high as 2000 lbs. per square inch or higher, a suitable pump is one similar to that described in U. 8. Patent No. 2,292,375 of 0. A. Hansen. Such pump is of the plunger type and has an inlet valve in the block 38 at its lower end and a discharge valve in the block 39 at a point adjacent the highest point reached by the end of the plunger 40. The plunger 40 of the pump is indicated as passing through the packing gland 4i at the upper end of the pump. Various ways of reciprocating the plunger 40 may be employed. For this purpose there is schematically indicated a crosshead 42 to which the plunger 40 is connected, a crank 43, and a connecting rod 44 between the crank and the crosshead. The crank 43 is connected by gearing 45 to an electric motor M. The motor is preferably a variable speed motor so that the rate of pumping may be regulated to equal the rate of production of oxygen by the rectifying column.

The discharge valve in block 39 is connected by a conduit 46 to the chamber 41 of a filter similar to the filter similar to the filter 34. The filter 41 is provided with a drain 48 and a discharge conduit 49 which connects to the oxygen passage l4 of the counter-current heat exchanger B. For priming the pump, there is preferably provided a priming connection 50, controlled by valve 50', connected between the discharge conduit 46 and the chamber 29.- It is preferable to position the coil 3|, filter 34 and pump C at a level below the point of connection of the conduit 30 to the chamber 29 to facilitate priming.

It is deemed that the operation of this apparatus will be clear from the above-detailed description. It will be seen that the heat-exchange coil 3| will permit the sub-cooling of the liquid oxygen by the efliuent nitrogen so that the degree of sub-cooling may be sufiicient to overcome the tendency to flash into vapor caused by; the resistance effected by the filter 34, the resistance eifected by the inlet valve in the block 38, the heat that tends to be transferred to the liquid in the pump chamber due to the friction of the packing, and heat generated due-to increase of pressure in the liquid. The filter 34 adequately protects the pump from danger caused by the presence of particles of combustible impurities. Particles of the packing employed in the plunger pump C often break loose and enter the liquid oxygen, but the filter 41 removes any such particles and also will remove any particles of hydrocarbon impurities not removed by the filter 34.

The filters 34 and 41 are preferably installed in duplicate sets so connected that when one filter 34 and 41 of each set is in operation, the others may be disconnected for clearing.

When the pump C is first put into operation after standing idle for a period of time, the valve 50' is opened and thepump operated against a practically zero head of pressure until liquid oxygen passes through the connection 50 into the rectifying column. The valve 50' is then closed and the pump will begin operating in the normal manner. The liquid oxygen pumped through the filter 41 is still very cold and the refrigeration thereof is utilized by heat exchange between the tubes 14 and the incoming air tubes ID. the pumped oxygen leaves the heat exchanger B it is in the form of dry gaseous oxygen at substantially room temperature and may be passed directly into a bank of cylinders l'l connected to the manifold l6. Since the operation of the apparatus is preferably continuous, at least two banks of cylinders should be connected to the high-pressure oxygen line so that the cylinders of one bank can be changed while the cylinders of the'other bank are being charged. The speed of the motor M is regulated so that the oxygen is pumped ata rate to maintain the oxygen purity in the chamber 29 substantially constant at the desired value. Adjustment of the pumping rate can also be effected by slightly opening valve 50 to return enough liquid to chamber 29 to maintain the liquid level therein constant. When use is made of the return conduit 50 for regulating the pumping rate, it will be preferable to have the conduit 59 connected to the conduit 49 in order to return only filtered oxygen fluid.

The rectifying column A and the heat exchanger B shown in Fig. 2 are substantially the same as those in Fig. 1. In Figs. 1 and 2 similar parts are designated by the same reference characters. If the final pressure of the oxygen produced by the apparatus of Fig. 2 is to be as high as 2000 lbs. per square inch, it would be preferable to employ a plunger type pump, such as shown at C in Fig. 1. If, however, a lower maximum pressure is desired, a multiple-stage rotarytype pump indicated at C may be employed.

When

An alternative procedure for sub-cooling the liquid oxygen is illustrated in Fig. 2. The nitrogen product discharged through conduit 21 is led directly to the cold end of the countercurrent heat exchanger B. The conduit 18 conducts the cold incoming air to a heat-exchange coil 52 in the lower part of the chamber l9 and from the coil 52, the air is expanded through expan ion valve 53 into the chamber I9. The liquid oxygen is withdrawn from the chamber 29 through a connection 54 to a pass 55 of a heat exchanger 5| from which a conduit 58 conducts the sub-cooled liquid to the filter chamber 34.

For sub-coolin the oxygen product an expanded fluid from the lower chamber I9 may be employed. To this end there is provided a connection 56 to withdraw-liquid from the shelf 22 to the lower end of another pass 51 of the heat exchanger 5|. The connection \58 is preferably controlled by an expansion valve 56'. The upper end of the heat exchanger pass 51 is connected by a transfer conduit I23 with the upper end of the rectifying chamber 24. Thus, by regulating expansion valves 23 and 56' any desired proportion of the liquid nitrogen to be transferred from the shelf 22 may be passed through the heat-exchanger pass 51. The expansion of this nitrogen fluid through the valve 56' will reduce its temperature to a temperature substantially equal to the temperature of the eflluent nitrogen. If desired, the transfer nitrogen liquid may be cooled before throttling, by heat exchange with the effluent nitrogen vapor.

The discharge conduit 36 from the filter 34 conducts the liquid to the inlet of the multi-stage rotary pump C. The outlet 59 of the pump 0 connects to the oxygen passage M of the heat exchanger B. For priming the pump, a priming line 60 controlled by the valve 60' is connected between the discharge 59 and the chamber 29. The rate of pumping may be regulated to correspond with the rate of production of oxygen in various ways. For example, the motor 6| which drives the pump C may be a variable speed motor. or alternatively, the pump C may be provided with an interstage by-pass connection 62 controlled by a valve 62. If the pump speed cannot be adjusted so that the rate of pumping corresponds exactly to the rate of oxygen production, the pumping rate can be adjusted by the by-pass valve 62'. In certain cases, for example, when the discharge pressure is high, the use of the bypass valve 52' may cause the pump to lose its prime. It will therefore be generally preferable to keep valve 62' closed and to regulate the pumping rate by slightly opening the valve 60' to pass the excess oxygen back to the chamber 29. In this manner there will be no interference with the degree of sub-cooling of the liquid entering the pump.

The operation of this second embodiment of the invention is similar to that of the apparatus shown in Fig. l. The fluid drawn from chamber l9. after expansion to substantially the pressure of the chamber 24 can absorb heat from the liquid oxygen produced so as to sub-cool it a desired amount. This sub-cooling is effected by heat exchange between the

passes

55 and 51 of the heat exchanger 5|. To regulate the degree of subcooling. the proportion of fluid expanded by the valves 56' and 23' is readily adjusted. When the pressure to which the oxygen is to be compressed is low, for example, in the case where the discharge line I4 is connected to consumption apparatus operating at a medium pressure, substantially above atmospheric pressure, the pump C may be operated with very little or substantially no sub-cooling of the liquid oxygen. In such case, the valve 56 will be closed and the valve 23' open. It will be seen then that subcooling as practiced herein facilitates the pumping of the liquid oxygen against a relatively high pressure but that the energy in the form'of refrigeration required to effect such sub-cooling is not lost but largely returned to the rectifying column.

It has been discovered that when the liquid oxygen is sub-cooled as described herein, additional amounts of hydrocarbon impurities become thrown out of solution and can then be removed by the filter 34. Even though hydrocarbon impurities in solid form are thoroughly removed at some prior stage, it is believed that minute quantities of certain hydrocarbon impurities remain in solution. When the liquid oxygen is sub-cooled to a temperature substantially below its temperature in the chamber 29, appreciable amounts of such remaining impurities become solidified and aggregated into particles which can be removed by the filter 34. Most of the refrigeration taken from the rectifying column for sub-cooling the liquid oxygen is regained in the countercurrent heat exchanger B. The loss is small, being mainly that which offsets heat inflow and heat generated in the pump.

In order to disclose the principles of the invention, several exemplary embodiments thereof have been disclosed. Obviously, certain features of the invention can be used independently of others and changes may be made in the apparatus without departing from the essential principles of the invention. For example, although the production of compressed oxygen has been specificially described the principles of the invention may be employed in the production of other gases which have low boiling points. The term fluid as used herein includes gas material in the liquid state, the gaseous state, or mixed liquid and gaseous states.

What is claimed is:

1. In a process of producing oxygen and delivering the same under pressure in which cooled air is rectified at a relatively low temperature and reduced pressure to produce a cold nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at said reduced pressure; the steps comprising subcooling such oxygen product by heat exchange with a colder fluid derived from said rectification; filtering the sub-cooled liquid oxygen to remove particles of dangerous impurities including impurities rendered filterable by said sub-cooling; pumping such sub-cooled liquid oxygen product to a desired substantially higher pressure; and delivering the pumped oxygen to receiving means at the higher pressure.

2. In a process of producing oxygen and delivering the same under pressure in which cooled air is rectified at a relatively low temperature and reduced pressure to produce a cold nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at said reduced pressure; the steps comprising sub-cooling such oxygen product by heat exchange with a colder fluid drawn from said rectification; filtering the sub-cooled'liquid to remove impurities including those rendered filterable by said sub-cooling; pumping such subcooled liquid oxygen product to a desired substan- 8 tially higher pressure; heating the pumped liquid oxygen by heatexchange with incoming compressed air to absorb heat therefrom and superheat the oxygen; and delivering the resulting warmed and dry oxygen to receiving means at said higher pressure.

3. In a process of producing oxygen and delivering the same under pressure in which cooled air is rectified at a relatively low temperature and reduced pressure to produce a cold nitrogen product and a liquid oxygen product; the steps comprising filtering said liquid oxygen product to remove particles of dangerous impurities; pumping such filtered liquid oxygen product to a desired substantially higher pressure; filtering the pumped liquid oxygen; heating the pumped liquid oxygen by heat exchange with incoming compressed air to absorb heat therefrom and superheat the oxygen; and delivering the resulting warmed and dry oxygen to receiving means at said higher pressure.

4. In a process of producing oxygen and delivering the same under pressure in which cooled air is rectified at a relatively low temperature and reduced pressure to produce a cold nitrogen product and a liquid oxygen product having a temperature corresponding to its boiling point at said ing such oxygen product by heat exchange with a colder fluid drawn from said rectificatiom.

filtering the sub-cooled oxygen product to remove particles of dangerous impurities; pumping such sub-cooled liquid oxygen product to a desired substantially higher pressure by a pumping device having a reciprocating pumping element; filtering the pumped liquid to remove solid matter therefrom; heating the pumped liquid oxygen by heat exchange with incoming compressed air to absorb heat therefrom and superheat the oxygen; and delivering the resulting warmed and dry oxygen to receiving means at said higher pressure.

5. In apparatus for producing oxygen from air and delivering the same at a desired pressure, the combination with means for cooling, expanding and rectifying compressed air including a main countercurrent heat exchanger and a rectifying column constructed and arranged for producing a nitrogen product and a liquid oxygen product; of a heat-exchange device comprising passages in heat-exchanging relation, one of which is connected to pass a fiuid from the rectifying column that is colder than said oxygen and the other of which is connected to receive and cool such oxygen product to provide sub-cooled liquid oxygen; a pump connected to said heat-exv change device to receive such liquid oxygen for raising the pressure of the liquid to a desired value; a filter interposed in the connection between said pump and the heat-exchange device for removing particles of dangerous impurities before they reach the pump; a heat-exchange passage connected to the discharge of said pump and associated with said main heat exchanger for conducting the pumped liquid from said pump in heat-exchange relation with incoming compressed air; and means for delivering the resulting warmed and dry oxygen from said passage to receiving means.

6. An apparatus for producing oxygen according to claim 5 which includes a filter interposed in the connection between the discharge of said pump and said heat-exchange passage.

'7. In a process for producing oxygen by the low temperature rectification of air which has been freed of a major part of its impurities prior to the final separation of a nitrogen product and a cold oxygen product; the steps comprising cooling the oxygen product by heat-exchange with a colder fluid drawn from said rectification to form substantially sub-cooled liquid oxygen; then filtering such liquid oxygen to remove additional impurities including those rendered filterable by said sub-cooling.

8. In an apparatus for producing oxygen by low temperature air separation including a rectifying column for producing a nitrogen product and a cold oxygen product, a heat-exchanger constructed and arranged for cooling the oxygen product by heat-exchange with the colder nitrogen product to a degree sufficient to form sub-cooled liquid oxygen; and a filter device connected to said heat-exchanger to receive the sub-cooled liquid and filter therefrom particles of impurities including those rendered filterable by said subcooling before passage of the filtered oxygen to receiving means. 7

9. A method of transferring a liquefied gas containing impurities from a source of such gas to a receiving means therefor at a pressure higher than the pressure of said source, which method comprises sub-cooling the liquefied gas being transferred by removing heat therefrom at least equivalent to the heat added thereto during a subsequent pumping step and at least suflicient to prevent detrimental flashing into vapor of the liquefied gas while being pumped; filtering the sub-cooled liquefied gas to remove therefrom impurities including those rendered filterable by said sub-cooling; and pumping the sub-cooled and filtered liquefied gas to said receiving means against the pressure therein.

10. In apparatus for producing oxygen from air and delivering the same at a desired pressure, the combination with means for cooling, expanding, and rectifying compressed air including a main countercurrent heat exchanger and a rectifying column constructed and arranged for producing a nitrogen product and an oxygen product, of a heat-exchange device comprising passages in heat exchanging relation, one of which is connected to pass a fiuid from the rectifying column that is colder than said oxygen and the other of which is connected to receive and cool such oxygen product to provide sub-cooled liquid oxygen; a pump connected to said heat-exchange device to receive such sub-cooled liquid oxygen and raise the pressure of the liquid to a desired value; a filter interposed in the connection between said heat-exchange device and said pump for removing particles of dangerous impurities from the liquid oxygen including those rendered filterable by the sub-cooling before entering the pump; and means for delivering the pumped oxygen from said pump at the desired pressure.

11. In apparatus for producing oxygen from air and delivering the same at a desired pressure, the combination with means for cooling, expanding, and rectifying compressed air including a main countercurrent heat exchanger and a rectifying column constructed and arranged for producing a nitrogen product and an oxygen product, of a heat-exchange device comprising passages in heat exchanging relation, one of which is connected to pass a fluid from the rectifying column that is colder than said oxygen and the other of which is connected to receive and cool such oxygen product to provide sub-cooled liquid oxygen; a pump connected to said heat-exchange device to receive such sub-cooled liquid oxygen and raise the pressure of the liquid to a desired value; a filter connected to the discharge of said pump, said pump being of the reciprocating type and having a packing through which a portion of the reciprocating element of the pump passes; and means for delivering the pumped oxygen from said filter at the desired pressure.

12. An apparatus for producing oxygen according to claim 10 which includes a filter interposed in the discharge of said pump.

PHILIP K. RICE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,394,955 Von Recklinghausen Oct. 25, 1921 1,891,125 Gessel Dec. 13, 1932 1,963,809 Schuftan June 19, 1934 1,976,388 Eichelman Oct. 9, 1934 2,060,940 Kahle Nov. 17, 1936 2,133,105 Messer Oct. 11, 1938 2,247,709 La Bour July 1, 1941 2,296,640 Hansen Sept. 22, 1942 2,321,445 Yendall et al. June 8, 1943 2,337,474 Kornemann et a1. Dec. 21, 1943