US1555435A

US1555435A - Feed-water heater

Info

Publication number: US1555435A
Application number: US611569A
Authority: US
Inventors: Josiah H Rohrer
Original assignee: Individual
Current assignee: Individual
Priority date: 1923-01-09
Filing date: 1923-01-09
Publication date: 1925-09-29
Anticipated expiration: 1942-09-29

Description

Sept. 29, 1925. 7 1,555,435

J. H. RQHRER FEED WATER HEATER 56 28 Filed Jan. 9, 1 923 3 Sheets-Sheet 1 i J 2a 1 INVENTOI? (Ea/m2 77. Fab/r2611 w/ TN 555 5r W W HTTORNEYS Sept. 29, 1925. 1,555,435

J. H. ROHRER FEED WATER HEATER Filed Jan, 9, 19 23 3 Sheets-Sheet 2 z a5 36 2a if Q i INVE/VTGI? Sept. 29, 1925. 1,555,435

J. H. ROHRER FEED WATER HEATER Filed Jan. 9, 1923 3 Sheets-Sheet 5 3 INVENTOI? WI T/VESS f 16 Wf flrrafilw ns Patented Sept. 29, 1925 UNITED STATES JOSIAH H. ROHRER, or I'HILADELPHIA, PENNSYLVANIA.

FEED-WATER HEATER.

I Application filed January 9, 1923. Serial No. 611,569.

To all whom it may concern:

Be it known that I, J OSIAH H. RoHRER, a citizen of the United States, and a' resident of Philadelphia, in the county of Philadelphia and State of Pennsylvania, have invented certain new and useful Improvements in Feed-Water .Heaters, of which the following is a specification.

The most efficient method of generating steam in a water-tube boiler is to separate the heating of the water in the boiler into two separate steps or stages which, considered from theviewpoint of raising the water from feed-Water temperature to boiling temperatures, consists of (1) pre-heating the feed-water and (2) the conversion of the water into steam.

For these purposes boilers, particularly of the water-tube type, are generally arranged so that the hot gases of combustion from the grate or fire-box first go over or pass in and between the banks of tubes comprising the steam-generating stage or section, and thereafter the gases, whichhave lost heat in 2 the steam-generating section, are conducted over, through and around one or more banks of tubes comprising the pre-heater or economizer section or stage, and in passing through the economizer section the temperature of the gases of combustion are further reduced, so that as little heat as possible is lost in the stack or chimney. It must be apparent, therefore,.thatthe temperature of the water in the pre-heater or economizer section must be substantially below the boiling temperatures and considerably below the temperature of the partially cooled gases passing thereover in order that the water in the preheater or economizer may absorb heat from 4 the partially cool gases and may not boil.

If the temperature of the water in the economizer section were high, then the gases would pass over and through the economizer tubes without substantial reduction in the tempera ture. The temperature of the gas leaving the economizer and entering the stack would be higher than is necessary'or economical, and steam would be generated in the economizer. Such an operation of a boiler would be wasteful and ineflicient. It must there fore be plain that the temperature of the water in the economizer section must be kept relatively low in order to absorb heat from the gases of combustion passing therethrough.

There is another consideration in steam boiler construction and operation which is also of great importance. Feed water, unless specially treated or purified, contains a great deal of oxygen in the form of air, and if feed-water, with oxygen dissolved therein, be fed to the boiler and then heated the oxygen is freed If this free oxygen could be conducted directly out of the boiler it would have very little, if any, injurious effect on the steel boiler tubes, but it has been the usual practice to deliver the, feed water to the economizer or pre-heater, before its actual delivery to the steam-generating section of the boiler. Now, the economizer section does not generate steam; and hence the oxygen which is liberated from the feed-water in the economizer is" not driven olf, but collects in the top drum of the economizer section. Here it rapidly corrodes the interior walls of the economizer drum, because the economizer drum is practically always filled with it. The economizer section therefore deteriorates much more rapidly than does the steam generating section of the boiler.

To free fresh feed-water from the deleterious gases contained therein, it is necessary to raise the temperature. of the water to substantially boiling temperatures, but if the feed-water, at boiling temperatures, were to be admitted directly to the economizer, then the temperature of the body of water in the economizer would be so ralsed that the economizer would form a steam-generating section which would not sufliciently reduce the temperature of the gases passing to the flue or stack. To raise the temperature of the feedrwat er to boiling temperatures to drive off the deleterious gases, and to then coolit to economizer temperatures, before admitting it to the boiler structure would also be obviously wasteful.

The object of my invention is to provide a,

construction wherein the temperature of the incoming feed-water is raised by the boiler to temperatures at which deleterious gases are expelled; wherein the said expelled gases are conducted away from the feedwater, prior to its admission into'the economizer section;. and wherein the relatively cool incoming feed-water is used to abstract heat from the purified feed-water to reduce'the temperature of the feed-water back to economizer temperatures. 11 other words, it is my object to provide a pie-heater and water- 110 purifier wherein there is an exchange or mterchange of heat during the operation of the device; wherein the temperature of the cool incoming feed-water is raised to substantially boiling temperatures for the purpose of freeing it from injurious gases, and wherein the temperature of the purified feed-water is then cooled by passing it over and around the incomlng feed-water conduit, so that the purifled water heats the incoming feed-water and conversely, the cool incoming feedwater lowers the temperature of the purified water back to economizer temperatures.

It is the object of my invention to provide an arrangement wherein an interchange of heat within the boiler structure may b effected to free the feed-water of deleterious gases and keep the temperatures of the economizer section of the boiler down to such a point that the water in the economizer may abstract heat from the gases of combustion passing thereover in substantially as efficient a manner as this is accomplished wherein the feed-water isnot so purified.

' Other objects of my invention will appear in the specification and claims below.

Referring now to the drawings forming a part o-fthis specification and in which the same reference characters are employed throughout the various views todesignate the same parts, Fig. 1 is a vertical, longitudinal. section through a water-tube boiler showing the steam-generating section or the economizer or pre-heater section and the passage of the products of combustion in and between the tubes throu h the two sections of the boiler, said boiler ing provided with my improved feed-water heater and purifier;

Fig. 2 is a longitudinal vertical sectional view through the purifier shown in Fig. 1 and on a larger scale than that employed in Fig. 1, said purifier being shown attached to the upper drum of the economizer, the latter being shown substantially in elevation except that parts are broken away to show the interior of one end of the economizer drum;

Fig. 3 is a modified form of my invention, the purifier being mounted within the upper, drum of the economizer;

Fig. 4 is another modified form of my in vention wherein the feed-water is admitted directly to the steam-generating section of the boiler, and the conduit for the feed-water passes through a chamber throu h which water from the boiler is supplied to the economizer; and

Fig. 5 is a still further modification of my invention wherein the feed-water is discharged directly into the steam-and-water drum of the boiler, and the water, circulating from the boiler to the economizer, surrounds the feed-water pipe and is cooled by the incoming feed-water.

Referring first to the embodiment of my invention as illustrated in Figs. 1 and 2, the

water-tube boiler preferably consists of an outer casing or housing 1 within which is set the steam-and-water drum 2, the waterdrum 3 and the lower or mud-drum 4. A bank of tubes 5 connects the steam-and-water drum with the water-drum 3; a bank of tubes 6, connects the water-drum 3 with the muddrum 4; and a bank of tubes 7 connects the steam-and-water drum 2 with the mud-drum 1. In the front of the boiler is the live-steam header 8 which is connected with the steamand-water drum 2 by a bank of super-heater tubes 9. Battling 10 is arranged to cause the gases of combustion from the firebox 11 to pass first lengthwise of and then through the bank of tubes 6; then vertically through the bank of tubes 5 up into the chamber adj acent. the header 8 and superheater tubes 9; then back through the upper bank 'of tubes 5, and through the upper half of the bank of tubes 5. To .the rear of the bank of tubes 7 is preferably arranged bafliing 12 which directs'the gases ofcombustion coming through the upper half of the bank of tubes 7 to strike against the upper end of the economizer tubes 13. The upper.en ds of these I, economizer tubes 13 are connected and comaround the lower end of the bafiie 16 pass upwardly lengthwise of the economizer tubes 13 on the opposite side of the baflle 16, and then out of the boiler through the passage 17 to the stack. A bank of tubes 18 preferably connects the upper economizer drum with the steam-and-water drum 2. This bank of tubes 18 is preferably below the water-lines which are maintained in the stcam-and-water drum and in the economizer section. so that water may freely pass from the economizer drum 14 to the steam-and-water drum 2 to replace such water as may be converted into steam in the boiler section.

An upper bank of tubes 19 also preferably connects the upperportion of the drum 14 with the upper portionof the steam-andwater drum 2 to maintain an equality of steam-pressure in the two drums. i

The above is substantially the type of water-tube boiler to which my invention is particularly adapted. The

drums

2, 3, 4 and 8 and the banks of

tubes

5, 6, 7 and 9 with the bafiiing 10 and 12 above described constitute the steam-generating section A of the boiler, while the

drums

14 and 15 with the connecting bank of tubes 13 and baflles 16. and the banks of

tubes

18 and 19 above 'described constitute the economizer or preheate ing section B of the boiler. The boiler then substantially consists of the steam-generating section A and the economizer section B.

Now, if impure feed-water, that'is to say, feed-water which has dissolved therein oxygen or gases which corrode or chemicall attack the interior of the water-tubes 0 the boiler, were to be admitted, as it frequently is, directly to the economizer section Band there heated sufliciently to expel the deleterious gases contained in the feed-water, those gases will accumulate above the waterline in the drum 14. The pipes or tubes 19 are pressure-equalizing pipes. No substantial amount of steam 1s generated in. the economizer section B, and, therefore, these deleterious gases collectand are retained in the drum 14 and have time to injuriousl-y act-on the interior of the said drum 14.. His to obviate this undesirable condition thatmy invention is directed.

It is'propcr to here make plain another action which must be considered in connection with the problem of pre-heating feedwater. The temperature of the water in the economizer section B must be considerably lower than the water in-the boiler section A. As the gases of combustion pass through the steam-generating section, the temperature thereof is considerably reduced. But the gases are yet very hot. It would be uneconomical to pass these gases directly to the stack. The economizer is forthe purpose of" abstracting more heat from the partially cooled gases by absorbing that heat into the water being supplied to the boiler or steam-generating section through the economizer. If therefore the-temperature of the water in the economizer B is notrelatively low as compared with the temperature of the water in the boiler heat is not; abstracted from the gases passing through the economizer. Thus it is that deleterious ases may be driven out of feed-water by ra sing the temperature of the water to boiling point, but to admit this purified water at boiling temperature directly into the economizer would defeat the very purpose of the economizer, because it would so raise the temperature of the water in the economizer that steam would be generated in the economizer. The economizer. section B would then be a steamenerating section of the boiler, instead 05 a preheater, and heat would not be sufliciently abstracted from the gases coming to the economizer from the steam-generating. section. If deleterious gases were to be expelled from feed-water by raising the temperature of the water to boiling temperatures, then that water would have to be cooled again to cause it to operate efficiently in the economizer. This energy expended in heatin the feed water by the boiler and then coo ing 'it independently of the boiler, to bring back to economizer temperatures would result in loss and waste .of

the ef'ficiency of the. boiler. I transfer heat from one part of a-boiler to another part of the boiler without any substantial loss of energy. In the form of my invention illustrated in Figs. 1 and 2, I therefore provide a drum 20 preferably mounted above the economizer drum 14 and above the boiler-housing or casing 1, and within this drum I mount-one or more series of shallow pans 21, one above the other, so arranged that when one pan is filledto' overflowing with water, the water falls into the p-annext below it. This series of pansmay be supported within the drum 20 in any suitable manner, as, for instance, being secured to straps 22 depending from the top of the drum 20. 1 Mounted also within the drum 20 andat or nearthe bottom thereof and extending longitudinally thereof, are a set of U-tubes 23 or tubes havinga return bend, the opposite ends of which are attached respectively to a header 24' having a partition 25 therein dividing the header into compartments. In

this way each tube will have one end communicating with the compartment of the header on one side of the partition 25 and its other end communicatin with the com partment in the header oiit e opposite side of the partition 25'. I

' The lower compartment of' the header 24 is preferably connected by a pipe 26 passing through thehead of the drum 20 and this pipe26 constitutes the intake pipe through which raw 'or unpurified feed-Water is taken into the purifier drum 20.

The other compartment in the header 24 .is preferably connectedto a pipe or riser 27 which extends to the ,top of the header 20 is preferably provided with spraying nozzles 28-28,'one for each set-of pans 21.

Below the pans 21, referably extendsa partition or separator plate 29, inclined to-. ward the header 24 so as to cause water falling thereon to flow toward said header-'24.- Below the partition 29 are arranged a series of transverse baflles 303030 preferably arranged in staggered relation,.as is shown in Fig. 2, and adjacent the bentends of the and then, passing, lengthwise of the drum 20, 17.20

U-tubes 23 is arranged'another transverse" partition 31 formin a dam having a horizontal top edge a ittle below the highest part of the partition or separator plate'29.

The end of the header or drum 20 which is to the right of the partition or dam 31 is preferably connected by a pipe 3232 to the economizer drum 14, and is preferably provided with a valve 33 for the purpose of con trolling the flow of water from the drum 20 to the drum 14.

Referring now to Fig. 1, I preferably con-- nect the drum 20 with the steam-and-water drum 2 by a pipe 34 also preferably provided with a valve 35, to admit live steam from the steam-drum 2 to the drum 20 above the level of the water therein.

I preferably attach a pipe 36 to the top of the drum 20 and preferably tap in another branch pipe 37 just above the level of the water in the drum 20, these pipes forming the means by which the gases, separated from the water in the drum 20, are conveyed away. These gases may be used to run a pump or compressor, or to perform any other useful work.

To the bottom of the drum 20 I preferably attach a blow-0E pipe 38 by means of which any accumulation of mud or sediment in the bottom of the tank 20 may be expelled from the drum by opening the valve 39. (See Fig. 2.)

The operation of the embodiment of my invention is as follows! Feed-water is admitted to the drum 20 through the pipe 26. It passes into the lower compartment of the header 24, and then through the lowerbranch of the U- tubes 23 to the upper compartment of the header 24, then through the riser 27 to the nozzles 28 where it is preferably sprayed into the top pans of the series of pans 21. When the top pans are filled, the water overflows their edges, and drops or trickles down into the pan 21 next below, and so through the series of pans to the last pan. From this last pan the water overflows and falls to the inclined partition 31 and thence to the bottom of the tank 20 on the left hand side of the dam 31. The partition 29- gives this water a movement to the left toward the header 24 and in course 'of time the bottom of the tank 20 will be filled with water up to the top horizontal edge of the. partition or dam 31. The edge of this partition 31 is high enough to produce a depth of water in the drum 20 sufficient to fully cover the U-tubes 23 and header 24.

After the water has risen to the top of the dam or partition 31 it trickles over the edge of the dam and falls to that part of the. drum 20 to the right of the dam 31 and from this the water is conducted through the pipe 32 to the economizer drum 14.

In falling from pan to pan, the water is brought into intimate contact withlive steam admitted to the top part of the drum 20 through the pipe34 from the steam-andwater drum 2. It is live steam at boiler pressure and temperature that is admitted to the top of the drum 20 and this serves to raise the temperature of the water as it falls from pan to pan u to substantially boiling temperature. ThlS serves to disassociate from the water the deleterious gases dissolved therein. These gases may be lighter or heavier than steam. ,For that reason I have provided the pipe 36 which communicates with the top of the drum 20 with the branch 37, which is just at the water level in the drum 20 so that the deleterious gases may be driven off substantially as fast as they are liberated whether they be heavier or lighter than steam.

Now, as above pointed out it would detract from the efliciency of the boiler if the hot water at boiling temperatures in the pans21, or as delivered from the series of pans 21, were to be conducted to the economizer section. Eflicient operation of the boiler requires that the water thus freed from deleterious gases be cooled back to a temperature low enough to operate efficiently in the economizer, to abstract heat from the gases of combustion passing through the economizer. This is what my invention accomplishes, and in the following manner: The U-tubes 23 are submerged in the water which is discharged from the series of pans. It is through this hot water that the relatively cold feed water is circulated. The cool feed-water enters the header 24 through the pipes 26, circulates through the U-t'ubes 23 and reduces the temperature of the purified water. In doing this, of course, the temperature of the incoming water is correspondingly raised by the absorption of heat from the water outside of the pipes 23. This action constitutes then an interchange of heat without substantial loss. The cool feed-water, from the moment it enters the drum 20 beginsto accumulate heat from the purified water surrounding it, and conversely, the hot purified water accumulating in the bottom of the tank 20 is givingup its heat to the incoming water, with the result that its temperature is being reduced to temperatures at which it may efliciently operate in the economizer section B.

In Fi 3 I have shown a modified form of puri er in that the purifier is mounted directly within the top economizer drum 14. The feed pipe 26 is admitted directly into the top drum 14 of the economizer and communicates with a coil 23', submerged below the top of the level of the water in the economiz'er drum 14. From the coil 23' a riser 27 3 extends to substantially the highest point in the drum 14 and its end is provided with one or more nozzles 28 over one or Ill) more series of pans 21-2121, all inside of the economizer drum 14 and above the level which is such as to cause the water falling thereon from the pans or trays 21 to circulate over to the coils 23. A partition 3l serves to cut off or separate the coil 23' from theinain or body portion of the drum 14. This partition 31 I is, however, preferably provided with holes 32' in the bottom thereof. A pipe 37 communicates with the interior of the drum 14 just above the water level for the purpose of conveying'away the separated gases. 7

In" this modified form of my invention, the

regular bank of pipes 19 extending between 5 the steam-and-water drum 2 and the upper drum 14 of the economizer replaces the spe-' cial pipe 34 previously described. Through this plpe or series of pipes 19 live steam is conveyed to the top of the economizer sec- 'tion. Water entering through-the inlet pipe 26 and coils 23 passes to the top of the drum 14 through the riser 27 and then is sprayed in the top an of a series of pans 21. Falling over tl ie edges of these pans from one pan to the next, the water finally falls on the inclined partition 29 and runs into the chamber formed by the wall or partition 31 and around the coil 23. This water then passes over the coils 23 and heat is absorbed therefrom by the cold water entering the drum through the pipe 26. The interchange of heat takes place in this form or embodi-.

ment of my device all within the drum 14. The cool water, after it has passed downwardly over the coils 23, passes through the holes 32 in the partition 31 and commingles with the water which is circulating in the economizer section. In this instance this cold feed-water serves to keep the tempera.- ture of the water in the economizer to a low working temperature and the steam in the top oi the drum 14 heats the feed water as it drops from pan to pan suiiiciently to drive the deleterious gases dissolved therein out of the water, and the said gases are conducted away fromthe drum 14 through the pipe 37 In Fi 4 I rovide within the boiler structure a c osed ox .or drum 20 within which is a coil 23 communicating with the feedwater inlet-pipe 26. The other end of the coil 23' is attached by a pipe 27 b to the lower or mud drum 4 of the steam-generatingsection of the boiler. I The lower drum 15 of the economizer is attached by a pi 85 to the chamber 20', Below the level of the water in the steam-and-water drum 2, a pipe 36 extends to a water circulatory pump 37 thro h t-ion water in the boiler.

the coil 23' and thence by the pipe 27" is discharged directly into the coolest part of the I boiler. This incoming cool water is used to keepdown the temperature of the water in the economizer section B by pumping hot through and over the coils 23' and thence the pipe 35 to the economizer see- In passing through the coil 23' the temperature of the feed-water is raised to substantially boiling temperatures and any deleterious gases which may be se rated therefrom as bubbles. will be carri along with the purified water to the mud drum 4 through'the pipe 27". These gases immediately rise through the banks of tubes in the boiler section to the steam-and-water drum 2, whence they are immediately carried away with the steam which .is bemg generated. The driving off of any gas which may remain in the feed-water entering the drum 4., is accomplished in the boiler itself. In this water from the top of the boiler downto, v

form of my device then, the temperature of I where through which thecold incoming feedwater is conducted.

In Fig. 5 I have shown a. still further modified form of my invention. In this instance, the top of the steam-and-water drum 2 is provided with a series of troughs or pans 21 all arranged so that as the top pan is filled, the water falls to the pan or trough below it and so on through the series of pans. These pans are located above the level of the The feed-water pipe 26 communicates with a coil 23 in a drum or compartment 20 and passing therethrough is delivered by a pipe 27 to the top of the steam-and-water drum 2 whence it falls through the pans in intimate contact economizer drum 14 below the normal water level thereof and the other side. ofthe drum 20 is connected by a pipe 38 with the interior of the steam-and-water drum 2 below the level of the water therein Immediately below the edge of the lowest of the pans or troughs 20 in the drum 2, a partition 31- is arranged extending lengthwise of the drum and this partition is attached to the inside of the drum below the pipe 38. The operation of this form-of my invention is as follows: Cold unpurified feed-water is admitted through the pi e 26 and through the coils 23' and throng vipe 27 to-th'e top of the steam-and-water rum 2 and is caused to fall from one pan to the pan next below it in intimate contact with the live steam in the drum 2, to raise the temperature of the feed-water to boiling temperatures and to disassociate therefrom the deleterious gases.

entering the boiler. The gases which arethus freed from the feed-water and which are generally heavier than the steam, tend to accumulate just above the surface of the Water in the drum 2 but they are immediately carried away with the steam through the su erheater tubes 9. There is no substanti transfer of steam from the'drum 2 to the drum 14 through the pipes 19. These pipes 19 merely serve'to equalize the ressure in the twosections or stages of the iler, and therefore the deleterious gases do not ass from the drum 2 to the drum 14.

In afi of these embodiments of my inv'en tion there is a mere transference of heat from one part of the boiler to another but with' out loss. The heat that is put into the feed water to raise it to boiling temperatures in order to disas'sociate therefrom the deleterious gases is abstracted from the urified feed-water b passing it over coils t rough which the co d incoming water is bein supplied to the purifier. There is no su stantial loss of energy. The deleterious gases are entirely removed. The life ofthe boiler and of the economizer is substantially lengthened and the efliciency of the boiler is maintained. I

' Having thus described my invention, what I claim and desire to protect by Letters Patent of the United States is:

1. In a'boiler comprising a, steam-genere atin section and an economizer section, the com ination of aheat-conductive feed-water conduit through which relatively cold feedwater is caused to flow, means to transfer heat from said steam-generating section to said feed-water after said feed-water has passed through said heat-conductive conuit to raise the temperature of said feedwater to boiling temperatures to purify the same by separating deleterious ases'therefrom, means to conduct hot pur1fied water, so formed,'over said heat-conductive conduit to reduce the temperature of the purified Water to economizer *temperatures, and means to conduct said purified water, so

formed, to sald economlzer, after 1t has passed over sald heat-conductive conduit. 2. In a boller comprising a steam-generating section and an economizer section,

the combination of a heat-conductive feedwater conduit through which relatively cold feed-water is caused to flow, means to transfer heat from said steam-generating section to said feed-water after said feed-Water has passed through said heat-conductive conduit to raise the temperature of said feed- Water to boiling temperatures to purify the combination of a feed-water purifier having a heat-conductive feed-Water conduit therein in communication with a suitable source or relativel cool feed-Water, means to transfer heat mm the said steam-generating section to said purifier to raise the temperature of said feed-water to substantially boiling temperatures to purify said feed-water by separating deleterious gases therefrom, means to conduct hot purified Water over said heat-conductive conduit to effect a transference of heat from said hot purified water to said relatively cool feed-water in said conduit and to reduce the temperature of said purified water to temperatures below boiling temperatures, and means to convey 1purified water to saideconomizer after it as passed over said heat-conductive conduit.

4/In a boiler comprising a. steam-generatin section and an economizer section, the 7 com ination of 'a feed-water urifier having a lengthof metal therein orming a cool feed-water intake pipe, means to transfer heat from the said steam-generating section to said feed-water in its passage through said purifier after 'it has passed through said intake pipe to raise the temperature of the water to substantially boiling temperatures to separate deleterious gases therefrom, means to. conduct hotpurified Water over and around said intake pipe whereby cool incoming feed-water insaid pipe is operative to reduce the temperature of said hot feed-water to temperatures substantially below boiling temperatures, and means to deliver to said economizer said feed-water after is has flowed over said intake pipe.

5. In a boiler comprising a steam-generatin section and an economizer section, the com ination of a feed-water purifier. having alength of, metal therein forming a cool feed-Water intake pipe, means to transfer heat from the said steam-generating section to separate deleterious gases therefrom,

means to conduct hot purified Water over and around said intake pipe whereby c001 incoming feed-Water in said pipe is operative to reduce the temperature of said hot feed- Water to temperatures substantially below boiling temperatures and said hot feed- Water raises the temperature of said feedwater in said intake pipe, and means to deliver to said economizer said feed-water after it has flowed over said intake pipe. In Witness whereof, I have hereunto set my hand this eighth day of January, 1923.

JOSIAH H. ROHRER