US2702531A - Apparatus for temperature regulation of superheated vapors - Google Patents

Description

Feb. 22, 1955 F. EPLEY 2,702,531

APPARATUS FOR TEMPERATURE REGULATION OF SUPERHEATED VAPORS Filed Oct. 9, 1952 2 Sheets-Sheet l Fig.3.

INVENATOR Frederic I. Epley B 53 Q A @Zi/ ATTORNEY Feb. 22, 1955 F. I. EPLEY 2,702,531

APPARATUS FOR TEMPERATURE REGULATION OF SUPERHEATED VAPORS Filed Oct. 9, 1952 2 Sheets-Sheet 2 INVENTOR ATTORN EY United States atei' APPARATUS FOR TEMPERATURE REGULATION OF SUPERHEATED VAPORS Frederic I. Epley, Rockville Centre, N. Y., assignor to Combustion Engineering, Inc., New York, N. Y., a corporation of Delaware Application October 9, 1952, Serial No. 313,944 6 Claims. (Cl. 122-479) This invention relates to the superheating of vapor and more particularly pertains to the regulation of the temperature thereof.

The invention will be disclosed as applied to the control of the temperature of superheated steam, but .it will be understood that the invention is capable of application to the temperature control of vapors generally.

In modern steam generating units and more specifically in the steam generating units of large public utility power plants, the steam is superheated to extremely high temperatures such as 1000 F. before being expanded through steam turbines to produce power. To obtain high efiiciencies in the operation of the turbine over a wide range of loads it is necessary to maintain the steam temperature entering the turbine substantially constant; and in the past this has been accomplished by various means.

The present invention deals with one of these means in which water is injected into the steam as it passes through the superheater to lower the steam temperature to the desiredvalue.

. The water injected for desuperheating the steam has heretofore been taken from the feed water delivered to the steam generator, or from the condensate leavingthe condenser of the associated steam turbine. The objection to the use of feed water for desuperheating is the contamination of the steam by the chemicals contained in the feed Water and subsequent deposit thereof on the turbine blades. The objection to the use of condensate from the turbine condenser is the possibility that any leakage of cooling water flowing through the condenser will contaminate the condensate and subsequently the steam being desuperheated. Furthermore, a pump is necessary to deliver the condensate to the superheater and this introduces an objectionable moving element; for should the pump fail to deliver water to the desuperheater, the load on the steam generator would have tobe reduced to obtain a lower and safe steam temperature for the operation of the turbine.

V In some cases saturated steam from the steam generator has been condensed for use as the condensate in de'sjuperheating the steam. This water has been injected into the superheater at its inlet or at it's outlet or a a point intermediate the inlet and the outlet. Discharging the condensed steam into the inlet of the superheater to control the steam temperature leaving the superheater is objectionable because the condensate must travel 'with the steam through the full length of the superheater elements before its effects can be felt at the superheater outlet, thereby involving a passage of time which contributes to a lag in temperature control. Added to this time lag in control is the lag incurred by the necessity of changing the temperature of the entire mass of metal of the superheater elements throughout their full length before a change of superheat from normal is effected. Discharging the condensed steam into the superheated steam leaving the superheater keeps the outlet endpoitions of the superheater elements at an undesirable high temperature level.

H For :these reasons the condensed steam is preferably injected into the superheated steam at a point between the inlet and the outlet of the superheater. A pump has been used to deliver the condensate at the required pressure to the superheater, regulating the delivery rate of the pump indirectly by fluctuation in superheated steam temperature. The present invention eliminates the aforesaid pumping means entirely, and provides self regulating means for delivering the condensate to the point of use.

2,702,531 Patented Feb. 22, 1955 During the operation of steam generators it has been found in some cases that considerable differences exist in the steam temperatures obtained from individual superheater elements depending on their location across the furnace width. Under these conditions overheating and burning of the superheater tubes may occur unless a larger amount of costlier heat resisting material is used in the construction of the superheater. These difficulties are overcome by the improved apparatus herein disclosed.

It is therefore a fundamental object of this invention to provide improved means for automatically maintaining the temperature of superheated steam at a predetermined value over a relatively wide range of steam generator loadings; said improved means utilizing the variations in superheated steam temperatures from normal to perform the following two tasks simultaneously through the medium of a flow restricting valve device:

(1) To regulate the amount of condensate injected into a spray type desuperheater for the purpose of raising or lowering the temperature of the superheated steam.

(2) To regulate the amount of steam condensed in a condenser drum, organized in operative relationship with the aforesaid desuperheater, for raising or lowering the condensate level maintained in the condenser drum whereby portions of the condenser coil become sub merged in the condensate or are exposed to heat exchange relationship with the steam.

A second important object of the invention is to provide for individual control of the temperature of each superheater element or group of elements by introducing condensed steam of the same purity as the superheated stea'r'n, into each superheater element or group of superheater elements at a plurality of points intermediate the superheater inlet header and the superheater outlet he'ade'n,

Another object of the invention is to provide a destipe'rheat-ing system with improved means for automatic delivery by gravity of condensate to a spray type desuperheater utilized in the system thereby eliminating pumping means as heretofore required.

Still another object of the invention is to substantially reduce the lag usually present in the operation of temperature control systems between the appearance of a new condition and the corrective response to that condition.

A further object of the invention is to provide for an uncommonly wide range of control so as to safeguard the equipment against unusual emergency conditions such as failure of other controls such as a by-pas's damper to operate or enforced cut-out of the feed Water heater and also to provide for sufficient control capacity to serve effectively and simultaneously both the superheater and the "reheater "of a modern steam generating unit.

A still further object of the invention is tor'educe the amount of hightemperatu're alloy material used in the construction of the superheater by levelling out or lowerin'g high points of tube temperatures throughout the length of each superheater element and between individual superheater elements.

Additional objects and advantages will become apparent from the following description of illustrative embodiments of the invent-ion when read in conjunction with the accompanying drawings, wherein:

'Figure l is a side view of a portion of a steam generator illustrating a preferred application of the invention.

Fig. 2 is an enlarged sectional view taken on line 22 of Fig. 1.

Fig. 3 is an enlarged sectional view of a superheater return bend as utilized in the organization shown in Fig. l for the purpose of injecting condensate into the superheater el'eme-nt.

Fig. 4 is an enlarged cross section of the condenser drum which the Fig. 1 organization utilizes. V

Fig. 5 is a diagrammatic view of a portion of a superheater in which the condensate is sprayed into an intermediate header instead of into a series of return bends as in Fig. 1.

Fig. 6 is a longitudinal cross section through an end troducing injection water atomized with the assistance of steam.

Fig. 7 is a sectional view of a valve and its associated control means which automatically. govern the rate of flow of water injected into the superheated steam in response to deviations from normal in the temperature of the steam leaving the superheater.

Figure 8 is a side view of a portion of a steam generator generally similar to Fig. l, but arranged toperrnit individual temperature control of each superheater element.

Referring first to Fig. 1, the steam generating unit there represented comprises in general a furnace 12, equipped with means for burning fuel (not shown), a horizontal offtake 14 through which the products of combustion pass in leaving the furnace, a vertical conduit 16 through which said products flow downwardly after leaving ofltake 14, a superheater 18 located in the hor1zor 1tal oiftake duct 14, and a reheater 19 located 1n vertical conduit 16.

Fuel is fired in furnace 12 in any conventional manner and after rising in the furnace the products of combustion pass over superheater 18, flow downwardly through vertical conduit 16 over the reheater 19 and may then pass over other heat absorbing surfaces not shown, such as a feed water heated and/ or an airheater, before being discharged into the atmosphere. In the preferred embodiment illustrated in Fig. 1 there is provided a bypass 20 permitting gases to be diverted from flowing over reheater 19. This is accomplished by opemn-g by-pass damper 21. Obviously a by-pass of similar design can be provided to serve superheater 18.

The walls of furnace 12 are lined with steam generating water wall tubes 22 which are fed in any well known manner (not shown) from the water space of a steam and water drum 24 by way of downcomer pipe 26. The steam generated in the water wall tubes 22 is discharged into the steam space of steam and water drum 24 by way of riser tubes 28. Superhea-ter 18 is provided with an inlet header 30 and an outlet header 32. Saturated steam collected in drum 24 is delivered to superheater inlet header 30 by way of connecting tubes 34. Said steam is superheated by absorbing heat from the combustion gases while passing through the tubes of the superheater 18 and leaves outlet header 32 by way of conduit 36 to enter steam turbine 38.

After having some of its energy converted into mechanical energy in the turbine the steam is discharged at a lower pressure and temperature from an intermediate stage thereof and passes through pipe 40 to enter the reheater 19 by way of the reheater inlet header 42. While flowing through the tubes of the reheater heat is imparted to the steam by absorption from the hot combustion gases flowing thereover. The steam leaves the reheater 19 by way of outlet header 44 and returns to an intermediate stage of the steam turbine via pipe 46 for further extraction of energy. After expansion in the steam turbine the steam may be condensed in a condenser (not shown) and the condensate utilized as a part of the feed water which is delivered by pumping means (not shown) through pipe 48 to a condenser drum 50 to enter the water and steam circulating system of the steam generator.

Referring next to Fig. 4 there is located within con dens-er drum 50 a heat exchanger 52 to the inlet of which feed pipe 48 is connected and through which the relatively cool feed water flows leaving by way of pipe 54 to enter the water space of steam and water drum 24 (see Fig. 1). The interior of condenser drum 50 is connected to the steam space of steam and water drum 24 by means of steam pipe 55 through which saturated steam flows from the drum to the steam space 56 of condenser drum 50. The cool feed water flowing through the heat exchanger coil 52 condenses the steam by absorbing heat therefrom thereby forming a body of pure condensate in the bottom of drum 50. The interior of drum 50 is therefore divided into a steam space 56 and a water space 57 by the fluctuating level 58 of the condensed water; moreover (as shown in Fig. 4) the heating surface of condenser coil 52 is composed of a lower inactive portion 49 that is submerged in the body of condensate 57 and an upper active portion 51 that is exposed to saturated steam.

In the preferred embodiment of the invention as illustrated in Fig. 1 'superheater -18 is constructed of parallel superheater elements 53 (see Fig. 2) comprising parallel tubes interconnected serially by return bends to form sinuous tubular coils. At least one return bend 59 of each superheater element '53 extends through the roof of the steam generator to serve as a desuperheating device. Referring now to Fig. 3, which shows an enlarged section of return bend 59 there is provided a connection 60 through which spray water is admitted into the interior of return bend 59 via water connection 60 communicating with a condensate distributing header 62 which in turn receives the condensate from condenser drum 56 via pipe 64.

Provided in pipe 64 leading to header 62 is a flow restricting device, here shown in the form of a valve 66, organized to control the rate of flow of the condensate into the header 62; said valve being opened or closed in response to the rise or fall of the steam temperature leaving superheater header '32. To register such changes in said temperature, a thermocouple 68 is installed in the outlet header 32; said thermocouple serving in conventional manner to produce an electrical potential that is proportional to the temperature of the steam leaving said header 32.

Fig. 7 shows a simplified diagrammatic representation of one known apparatus 70 that is suitable for registering and responding to changes in the aforementioned electrical potential of said thermocouple 68. Departures from normal in the temperature of the steam in header 32 produce corresponding changes in the electrical potential transmitted via circuit 72 to the control apparatus 70, and that apparatus in turn converts each such departure into a current applied via circuit 7 3 to reversible motor 74 for the purpose of driving that motor either in the forward direction or in the reverse direction,

depending on whether the regulated steam temperature needs to be lowered or raised in order to bring it back to its desired value. Thus energized the aforesaid motor 74 transmits its corrective motion through reducing gears 76, crank 78 and valve stem 80 to adjust the valve plug 82 in valve 66 and to thereby suitably vary the rate of flow of injection water into return bend 59. In this way the temperature of the steam leaving outlet header 32 can be held constant (depending on the quantity of water admitted through valve 66).

The temperature of the superheated steam leaving reheater 19 is controlled in a similar manner. In the embodiment of the invention illustrated in Fig. 1, reheater 19 comprises a multiplicity of parallel tubular elements 83 made up of tubes joined at their ends by return bends to form sinuous coils. At least one return bend 84 in each reheater element 83 extends through the rear Wall of vertical conduit 16 to serve as a desuperheater device similar in construction to the return bend 58 used in connection with superheater 18 and illustrated in Fig. 3. Return bends 84 functioning as desuperheaters are located intermediate the inlet header 42 and the outlet header 44 of the reheater 19, and are provided with spray water connections 86. There is also provided a condensate distributing header 88 which supplies condensate or spray water to each return bend desuperheater 84 by way of a pipe connection 86.

Condensate distributing header 88 is supplied with condensate from the condensate drum 50 via branch pipe 90. The flow of condensate through pipe 90 is controlled by means of valve 92 which in turn is actuated by a temperature responsive device 94 operating in a similar manner as temperature responsive device 70 herein above described in connection with the control of the temperature *of the steam leaving superheater 18 and shown in detail in Fig. 7. Thus temperature responsive device 94 actuating valve 92 receives electrical potential from thermocouple 96 installed in reheater outlet header 44; a rise above normal in the temperature of the steam leaving outlet header 44 causes the valve 92 to open and permit more condensate to flow from condenser drum 50 to return bend desuperheaters 84, which flow in turn lowers the temperature of the steam until a point of equilibrium is reached; and a drop below normal in the temperature of the steam leaving reheater outlet header 44 causes valve 92 to close and cut down the condensate flow into return bends 84, thereby correctively raising the steam temperature.

For certain conditions it may be of advantage to provide an intermediate header 97 to take the placed the row of return bends 59 extending through the roof of the t te 1 2. is" unshared in Fig. 5 which shows I condensate from drum 50 being directly discharged into the header 97 to control the temperature of the superheated steam, As shown in Fig. 6 the above is accomplished by spraying the condensate into the end of intermediate header 97 by means of nozzle 98 mounted therein. The diffusion of the condensate is assisted by a steam jetissuing from a steam pipe 102 and directed into the nozzle opening 100. V The steam pipe 102 may receive steam from any convenient source such as steam and water drum 24. I I

Obviously the cooling of superheated steam as practioed according to the facilities above described can be accomplished in any header or pipe through which the superheated steam flows, 7 such as superheater outlet header 32, reheater inlet header 42, reheater outlet header 44 or any intermediate header or superheated steam conduit.

According to the invention means are also provided to control the superheated steam temperature in consecutive steps as the steam flows from the inlet header through the superheater elements to the outlet header. This is diagrammatically illustratedt in Fig. 8. As in the arrangement shown in Fig. 1 steam in saturated condition is discharged from drurn 24 into the inlet header 30 by way of pipe 34. The stea'rnthereupon =by flowing through the superheater elements has heat imparted thereto in conventional manner and leaves by way of outlet header 32. Condensate is formed in cond-enser drum 50 as earlier described and passes through pipe 64 into condensate distributing header62, v r a v .The sup'erhea'ter lS of Fig. 8 is generally similar to superheater 18 of Fig. 1 in that it isconstructed of tubular parallel elements spaced one from another across the furnace width in the manner indicated at 53 in Fig. 2. Instead however of having only one upper return bend 59 of each superheaterelement 53 extend through the roof of the steam generator to serve as a desuperheating device, the elements of this superheater 18' have two other return bends similarly arranged as shown at 59' and 59" in Fig.8. Thesejthreereturn bend sets 59"59 59 all receive condensate from conduit 62 through branch connections shown in Fig. 8' as respectively including valves 118, 120, 122. a

By adjusting (manually or otherwise) the settings of said valves 118,120 and 122 the condensate from condenser 50 can be caused to distribute itself among the three returnbend sets 59'59-59" in substantially equal amounts; or more of the condensate can be apportioned to one of these sets than to the others; or the condensate supply can be fully cut off from one or more of these sets. In this way the total desuperheating effect spread inthree steps throughout the total length of the tubes 'thatm'ake up superheater 18' of Fig, 8 can either be equalized among those steps or apportioned thereamong in other desired manner. V H H a The rate at which condensate flows from condenser 50 into conduit 6219f Fig. 8 and thence into superheater 18 is governed by valve 66 which preferably is adjusted automatically (through devices arranged as at 68-'70'72 in Fig. 1 but not shown in Fig. 8) in response to deviations from a desired value in the temperature of the superheated steam leaving outlet header 32.

The operation of the invention as organized in Fig. 1 will now be considered. Condenser drum 50 is located at a predetermined height above the return bends 59. This height is such that the pressure on the spray nozzle 60 in return bends 59 due to the head of water from the condenser to the return bend is sufficiently greater than the steam pressure in said return bend to assure a satisfactory spray injection of water into the steam at any selected range of load of the steam generator; and it may be pointed out in passing that the steam pressure in the return bend 59 will be greater at lower load because the resistance to steam flow thronugh the superheater is less at lower loads due to a lower flow velocity.

To maintain the desired head of water on the spray water connection 60 of return bends 59 the condenser 50 (see Fig. 4) is provided with a relatively large amount of cooling surface in its coils 52 to be capable of condensing more of the saturated steam received from drum 24 than is required for injection into the superheated steam to normally control the temperature thereof. The flow of the condensate from the condenser drum 50 to the spray device in return bend 59 is controlled by valve 66 in pipe 64 so that the excess condensateheld backby valve 66 rises in the condenser drum and covers a portion of the condenser coil 52. The portion of coil 52 submerged in the condensate then ceases to condense the steam and only the remaining exposed upper portion of the condenser heating surface is active in doing so.

The water in the condenser drum 50 therefore estab lishes at a level (designated 58 in Fig. 4) where the exposed portion of the coil 52 is just sufficient to condense the amount of saturated steam required for the desuperheating of the steam in header 28. Should rio desuperheating be required, then the valve 66 closes and the condensate in condenser drum 50 will riseuntil all of coil 52 is submerged in the condensate and' further condensation ceases.

In a steam generator where both the superheater as well as the reheater steam temperature is controlled by a spray type de'superheater the water level in condenser drum 50 is affected both by the action of valve 66 as well as the action of valve 92 controlling the flow of condensate to reheater return bend 84. The invention pro.- vides for a capacity of condenser drum 50 and coil 52 which will be more than sufficient to serve both the temperature control requirements of superheater 18 as well as that of reheater 19. v

Furthermore according to the invention the condenser drum 5 land condenser coil 52 may be made sufliciently large to supply not only ample condensate for normal desuperheating but for desuperheating the steam when other supplementary controls fail such as for example when by-pass damper 21 becomes inoperative. As shown in Fig. 1 by-pas's damper 21 provides for control of the gas flow passing over reheater 19 whereby to raise or lower the temperature of the steam leaving reheater outlet header 44. Damper 21 may provide a substantial portion of the required supe'rheat control and desuperheating by spraying condensate into return bend 84 may provide the remaining portion.

However, due to adverse operating conditions damper 21 may become inoperative in a near closed position at a time when the steam generator passes from a lower into a higher load. In such a case the major portion of the gases will flow over the reheater 19 and will cause the steam to overheat. When the overheated steam enters the return bends 84 of reheater section 19 the condenser 50 will then have suflicient reserve capacity both in accumulated condensate as well as in exposed cooling surface of coil 52 to supply ample condensate to cool the steam to normal superheat. If this provision of an over-sized condenser were not present, the load on the steam generator would have to be lowered to obtain the desired superheat for the steam turbine.

Another case in which the herein disclosed invention provides a novel advantage occurs when a feed water heater fails. As is well known by those skilled in the design of steam generating units failure of a feed water heater will necessitate the by-passing or that heater and a lowering of the feed water temperature entering the drum 24. Therefore more heat will have to be added to the feed water to raise the temperature thereof to saturated steam temperature. This will make it necessary to burn more fuel and produce more gases of combustion which flowing over the superheater will cause excess superheating of the steam. Where the present invention is used excess superheating is eliminated by the automatic functioning of the oversized condenser 50 which immediately furnishes sufiicient condensate to cool the steam to normal superheat.

In addition to the cases mentioned above there are other abnormal operating conditions of a steam generating unit which may cause an excess rise in the temperature of the superheated steam. Any of these may be met by an application of the present invention which provides a desuperheating apparatus of great flexibility.

Looking finally at the multi-step desuperheating modification disclosed by Fig. 8, the operation thereof fundamentally is the same as that already explained for Fig. l; the difference being that in Fig. 8 desuperheating is accomplished in three successive steps along the tube length of superheater 18' instead of in a single step. In certain situations this may provide greater flexibility and otherwise prove of advantage.

By way of summary it is desired to point out that the invention as here disclosed is not limited in its application to any particular type of steam generator, and that various changes may be made in the form, location and' arrangement of the parts of the apparatus disclosed without departing from the spirit and scope of the invention as claimed.

What is claimed is:

1. Apparatus for controlling the temperature of superheated vapor comprising a conduit carrying a stream of superheated vapor, a condenser vessel positioned at an elevation substantially above said conduit, means forming a connection between said condenser vessel and said conduit'for discharging condensate into said conduit for the purpose of regulating the temperature of said superheated vapor, means for controlling the amount of condensate thus discharged into said conduit, a liquid space and a vapor space within said condenser vessel, means to directly supply vapor to the vapor space from an exterior source thereof, a condenser conduit disposed within said vessel with a portion of said condenser conduit being submerged in the condensed liquid and the remaining portion thereof being exposed to the vapor in said vapor space, means to flow a cooling fluid through said condenser conduit, and means responsive to an increase or a decrease in temperature of said superheated vapor for increasing or decreasing, respectively, the flow of condensate to said conduit and for lowering or raising, respectively, the level of the condensed liquid within said vessel by increasing or decreasing, respectively, the rate at which saturated vapor is condensed therewithin, whereby a rise in superheated vapor temperature accelerates the rate at which condensing proceeds within said condenser vessel and a drop in superheated vapor temperature decelerates said condensing rate.

2. Apparatus as claimed in claim 1 in which said connecting means comprise connections between said condenser vessel and a plurality of selected control points along the length of said conduit.

3. Apparatus for controlling the temperature of superheated vapor comprising first and second steam heaters carrying streams of superheated vapor, a condenser vessel positioned at an elevation substantially above said steam heaters, means forming connections between said condenser vessel and said steam heaters for discharging condensate into said heaters for the purpose of separately regulating the temperature ofsaid superheated vapor in each of said steam heaters, means for controlling the amount of condensate thus discharged into said heaters, a liquid space and a vapor space occupying the interior of said vessel, means to directly supply vapor to the vapor space from an exterior source thereof, a condenser conduit disposed within said vessel with a portion of said condenser conduit being submerged in said body of liquid and the remaining portion thereof being exposed to said vapor space, means to flow a cooling fluid through said condenser conduit, and separate means responsive to an increase or a decrease in temperature of said superheated vapor in each of said first and second steam heaters for increasing or decreasing, respectively, the flow of condensate to each of said first and second steam heaters and for lowering or raising, respectively, the level of the condensed liquid by increasing or decreasing, respectively, the rate at which saturated vapor is condensed within said condenser vessel.

4. Apparatus for superheating vapor comprising a superheater having an inlet header and superheating tubes extending therefrom to an outlet header, said inlet header being directly connected with a source of vapor to be superheated and said superheater tubes being disposed in heat exchange relationship with heated gases; means including a conduit for injecting condensate into the interiors of said superheater tubes at an intermediate location along the tube lengths between said inlet and outlet headers; a condenser vessel positioned at an elevation substantially above said superheater tubes and said condensate conduit; a connection for transmitting condensate downwardly under the action of gravity from said condenser vessel into said conduit and thence into said superheater tubes at said intermediate location along their lengths; means for controlling the amount of condensate thus discharged into said conduit; a liquid space and a vapor space occupying the interior of said condenser vessel; a condenser coil disposed within said vessel, a portion of said coil being submerged in said body of liquid and the remaining portion thereof being exposed to said vapor space; means for passing a condensing medium through said condenser coil; means for conveying vapor into said vapor space for conversion therein into condensate available for flow downwardly into said liquid space thence into said superheater tubes via said connection and said conduit in the manner aforesaid; and means associated with said connection and said superheater for increasing or decreasing, respectively the rate of said condensate flow into the superheater tubes in response to the increase or decrease, respectively, of the temperature of said superheated vapor.

5. Apparatus as claimed in claim 4, in which said conduit means for injecting condensate into the interior of said superheater tubes is adapted to communicate with the interiors of said superheater tubes at a plurality of intermediate feed locations successively spaced along the tube lengths between said inlet and outlet headers.

6. Apparatus as claimed in claim 5, in which said conduit means for injecting condensate into the interior of said superheater tubes includes valve means intermediate said condensate vessel and said feed locations along the superheater tube lengths for individually adjusting the condensate flow into each of said locations.

References Cited in the file of this patent UNITED STATES PATENTS 1,965,595 Jacobus July 10, 1934 1,970,434 Schult Aug. 14, 1934 2,207,646 Van der Ploeg July 9, 1940 2,257,805 Kolling Oct. 7, 1941 2,568,567 Sparks Sept. 18, 1951 2,602,433 Kuppenheimer July 8, 1952 2,604,085 Frisch July 22, 1952 FOREIGN PATENTS 258,589 Great Britain Mar. 3, 1927 308,261 Great Britain Apr. 10, 1930 416,091 Great Britain Sept. 10, 1934

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