US1400813A - Process of compressing vapor in multistage centrifugal compressors - Google Patents

Description

B. GRAEMIGER. Paocxsss or coMPREsslNe vAPon |N Mumsmae cENTmFuGAL commsssons.

APPLICATION FILED NOV- 3, |920. LOOl 3 Patented Dec. 20, 1921.

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BENJAMIIN GRAEMXGER, OF ZUB/10H, SWITZERLAND.

PROCESS OF COMPRESSING VAPOR IN MULTISTAGE CENTRIFUGAL COMPRESSORS.

Application filed November 3, 1920. Serial No. 421,578.

T 0 all LU tom t may concern e it known. that l, BENJAMIN GRAEMIGER, a citizen of the Re Qublicof Switzerland, residing at Zurich,V lardturmstrasse 19, Switzerland, have invented certain new and useful improvements in a Process for Compressing Vapor in ll/lultistage Centrifugal Compressors; and I do hereby declare the following to be a clear, full, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings and to letters or figures of reference marked thereon, which form a part of this specification.

This invention relates to a process for compressing vapor in multi-stage centrifugal compressors.

According to the invention a liquid of the same nature as the vapor to be compressed is introduced into the compressor behind at least one of the rotor wheels in such a form and quantity that the state of the vapor will be changed into that in which it contains not more than three per cent. by weight of liquid. The process may be carried out so that the cooling of the vapor which has been superheated through being compressed is only effected to such an extent as to obtain saturated vapor.

It is already known with air compressors of the piston type to inject water into the air to prevent too high a rise of the temperature and therefore of thexpower consumption. For this purpose the air from a certain stage of the compressor has been led into a special receiver into which the water has been injected whereafter the cooled air has been introduced into the next stage of the piston comf the water were to be pumped immediately into the piston compressor the danger exists that the injected quantity may be too large and that water hammer occurs which Vmight cause a bursting of the compressor. The withdrawing and re-introducing of the air from and to a special receiver causes considerable losses of energy. Moreover it is disadvantageous in most cases to get moist air by this direct injection of water. In certain cases this direct injection is inadmissible especially when the air is used for combustion because a considera-ble portion of the energy contained in the fuel is then used for evaporating the particles of Speecaton of Letters Patent.

Patented Bec.. 260, 192i.

water contained in the air and is thus utilized inefliciently for combustion purposes.

The conditions for carrying into eii'ect the process according to the present invention are quite diderent. flhe liquid injected into the compressed vapor being of the same nature as that of which the vapor is formed, the injected liquid i. c. the cooling liquid, cannot have any harmful ei'lect but it increases the useful quantity of vapor obtained. The mixing of liquid and vapor takes place in the rotary compressor itself without the vapor being withdrawn from the compressor in a complicated way and then reintroduced into the latter. @nly vcare has to be taken that the ratio between the injected liquid andf the compressed vapor is chosen such that the vaporous mixture does not contain more than three per cent. by weight of liquid. lt is a well known fact that with compressing vapors in rotary compressors the vapor leaving any rotor wheel or diffuser connected to the latter is superheated, therefore such a quantity of liquid may be injected that the vapor is cooled down from its initial highly superheated state to approximately its saturated state. If too great a quantity of liquid were injected particles of water might be admixed in a considerable quantity. to the vapor worked upon by the lfollowing rotor wheel which water4 would corrode the blades of the rotor wheel and acceleration would have to be imparted to the water by the folhereinafter when explainingthe constructional examples for carryingout the process.

With a given circumferential speed and a given number of stages, for instance with a six-stage centrifugal compressor, an increase in pressure vof approximately 6%may be obtained by injecting liquid. On account of the comparatively low initial temperatures in front ofk the various 4rotor wheels the theoretical and also the actual powerV used for compressing a given Weight of vapor, measured at the discharge end, is smaller than it Vno cooling liquid wereinjected. `When coolino' compressed air by injecting` water waste energy in the shape of heat Vis carried away by the' heated up water; in the present process, however, the

energy supplied to the vapor in certrit'ugal compressors is not lost but is utilized in generating vapor of the same kind. This increase -of vaporniay amount to LES-5% of the weight of vapor entering the suction end of the compressor. As the highest temperature occurring` is considerably lower than if no liquid were injected, the mean temperature of the compressor casing is lower and consequently its radiation of heat and theV energy losses resulting therefrom Vare smaller.

Y All the advantages inherent to the present process are of special importance in the compression of'lye vapors for the purpose of utilizing such vapors as heat generating means whenV evaporating fresh lye.

The above mentioned advantages are all the more apparent the higher the ratio of compression 1s. Y A

The liquid to be injected consists prefer ably of very pure'condensed vapor formed at any point along the path of the vapor.

The increase of the temperature of said i from 600 to 1200 kilogramsper hour, the

ordinates representV the corresponding pressure ratio of the final pressure p2 to the initialv pressure p1. The curves I, II and III represent lthe relationfbetween the pressure ratio and the weight of steam with a givenY compressor running lat aV uniform speed, The curves I and II show the presf sure-ratios obtained in a compressorl in relation to the weights of steam entering the suction end of the compressor, curve I in particular indicates the conditions prevailingV with, compressions without .the Vuse of l cooling water and curve II showsl the conditions for compressions with cooling water injected,v It is to be seen fromthe diagram that with the same quantity of steam enter- `ingthe suction end otthe compressorfor instance 1000' kilograms per hour the ratio (g'be'tween the final and the vinitial pres- 1 j ,Y Y Y sure is 1.6 if no cooling water is introduced ,duringthe' compres sionand Y1.7 6 if cooling water is introduced; The distance between the curves II and I illustrates the gain in the ratio betweenthe pressures by the introduction of a Vcooling liquid. The curve III indicated in dotted lines gives a Vmeasure for the gain in the quantities of vapor obtained by the injection of cooling water. The distance A-k-B shows the gain in the pressure ratio with a constant quantity of steam of 1000 kgs/hour at the suction end of the compressor, the horizontal distance B-CIO kilograms per hour indicates the increase of the weight of steam in the compressor while maintaining the pressure ratio which corresponds to the ordinate of the point B. The point C shows the higher pressure ratio attained in the same compresser running at the saines speedl fand the greater weight of vapor leaving the compressor as compared with the working of the compressor without the introduction of cooling liquid e. point A).

Fig. 2 illustrates in a vertical longitudinal section the upper part of a four-stage centrifugal compressor, through the Vbranch 1 of which the steam toi'be compressed enters, whichjiscompressed consecutively cal part 33; further the extended party 34 of the rod causes the water fed through branch 35 to the nozzle casing to leave the latter in the shape of a hollow jet. In this manner the water offers a large surface on which the steamcan act so that the water is finely atomized in a very short time and is,

at least for the greatest part, evaporated. Y

Fig. 4- illustrates the lower half of a 'four stage centrifugalv compressor, in which a modification of` the supply' of the cooling water into the path of the steam is shown, whereby the conduits 7 and Sjof Fig.` 2 can be dispensed with. A small auxiliary pump 11 forces water through the `pipe112 into a collecting space 13 into Vwhich the highly compressed steam enters on leaving the last rotorwheel 5. The water'accumulates at the bottom of thecollectingspace 13.- Part of: said water is evaporated'by being in contact with the highly compressed steam and con# tributes Yto lower the temperature of said steam. IAS, however, only a small portion of the steam contacts with thecomparatively small surfaceo'f the-water and as ittalres a certain-'time in order to evapora-te a given VVquantity of water a Small straraggqlfe` of lwater can be easily maintained at 14 by supplying continuously fresh water through pipe 12, although the steam contained in the space 13 is either slightly superheated, saturated or containing a quantity of liquid amounting to not more than 3 per cent. by weight. In the lowest part of the casing by-pass channels 16, 17, 18 are arranged by the interposi tion of a covering plate 15, through which channels water from the storage 14 flows to the space 19 on account of the difference in pressure between spaces 13 and 19. At the bottom of space 19 the water collects and forms a storage 20. In a similar manner water is flowing from space 19 to space 21 and from there to space 23 through a channel 22 which may for instance be arranged horizontally. From the space 23 the water enters finally the suction space 25 through the channel 24. Out of space 25 the water is drawn through the suction pipe 26 by the pump 11 and thereupon repeats its circuit.

If the quantity of water delivered by the pump 11 is too great, part of it can be returned to the suction pipe 26 through pipe 27. rllhe quantity of cooling water evaporated in the compresser is replaced by fresh water, which enters the suction pipe 26 by means of the pipe 28. In order to prevent the water on entering the space 19 through channel 18 from squirting too high and from getting admiXed to the steam in the shape of drops of water whereby the runner wheel 5 would have to deal not only with steam but also with water, a baffle plate 29 in the shape of an angle iron may for example be secured to the casing above the channel 18. Too great an evaporation and splashing of the water can also be prevented by providing a sieve above the stored water. This modification isshown bv way of example in the space 23 of Fig. 4 in a vertical longitudinalV section and in Fig. 5 in a vertical crosssection along line D-E of Fig. 4. The sieve 30 is fixed to the compresser casing at such an elevation that it is only a small distance above the normal water level. A sufficient exchange of heat from the steam compressed in the rotor wheel 2 to the stored water can take place through the openings of the sieve; the steam generated from said water rises through the openings of the sieve into the large space 23 where it mixes with the compressed steam, thereby preventing an eX cessive increase of the temperature of the latter'. Furthermore the sieve prevents that the steam rotating in the space 23 in the direction of arrow IV carries away particles of water and causes a wave in the water as indicated by arrow V shown in dotted lines, whereby the water would be admixed to the steam in the shape of drops.

I claim:

1. A process for compressing vapor in multistage centrifugal compressors, comprising introducing into the compressor behind at least one of the runner wheels such a quantity of a liquid of the same nature as the vapor as to obtain a compressed vapor that does not contain more than three per cent. by weight of liquid.

2. A process for compressing vapor in multi-stage centrifugal compressors, comprising introducing into the compressor behind at least one of the runner wheels such a quantity of liquid of the same nature as the vapor to cool the vapor superheated in one runner wheel to its saturated state and to obtain a compressed vapor that contains Y not more than three per cent. by weight of liquid.

3. A process for compressing vapor in multi-stage centrifugal compressors, comprising introducing into the compressor behind at least one of the runner wheels such a quantity of liquid of the same nature as the vapor in a finely distributed state to obtain a compressed vapor that contains not more than three per cent. by weight of liquid.

4. A process for compressing vapor in multi-stage centrifugal compressors, comprising introducing into the compressor behind at least one of the runner wheels such a quantity of liquid of the same nature as the vapor in the shape of hollow jets to obtain a compressed vapor that contains not more than three per cent. by weight of liquid.

In testimony that I claim the foregoing as my invention, I have signed m name.

BENJAMIN GRAEMIGER.

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