US1800740A - Method and apparatus for desuperheating steam - Google Patents

Description

April 14, 1931. J. R. McDERMET 1,800,740

METHOD AND APPARATUS FOR DESUPERHEATING STEAM Filed April 29, 1926 2 Sheets-Sheet 1 April 14, 1931- J. R. M DE RMET 1,300,749

METHOD AND APPARATUS FOR DESUPERHEATING STEAM Filed April 29, 1926 2 Sheets-Sheet 2 m m H Patented Apr. 14, 1931 UNITED STATES PATENT OFFICE JOHN R. MCDERMET, JEANNETTE, PENNSYLVANIA, ASSIGNOR TO ELLIOTT COM- PANY, F JEANNETTE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA METHOD AND APPARATUS FORDESUPERHEATING STEAM Application filed April 29,

The present invention relates broadly to the art of heat exchanging and more particularly to an improved method and apparatus for treating superheated steam by means of which the superheat may be destroyed in an effective and uniform manner.

At the present time, it is not uncommon practice to deliver superheated steam from the more modern boiler installations. Not

infrequently a portion, at least, of such steam is utilized with apparatus which has constituted part of a standard installation which has been in use for many years. Such apparatus is frequently not adapted for the use of high temperature superheated steam, partly perhaps, because the temperature of the superheated steam may injure some of the apparatus in processes where steam is utilized for heating and partly also because more or less obsolete equipment as referred to, is not able to handle such superheated steam. In such cases the use of a desuperheater is imperative.

The present invention has for certain of its objects the provision of an improved method and apparatus" for effectively desuperheating steam, the invention contemplating the mixing of water with steam. Under these conditions, a portion of the water so mixed with the steam is evaporated to an extent determined by the heat value of the superheat in the steam. The desuperheated steam then passes onward from the desuperheater at a temperature corresponding to its pressure, but in an increased amount due to the destruction of the superheat and the evaporation of water used in the process.

It is a further object of the present invention to provide a control and a method of 49 control which is adaptable for use with desuperheaters generall and which is not limited in its utility to t e construction and operation of any particular type of desuperheater.

In the accompanying drawings there are shown, for purposes of illustration only, two different embodiments of the present invention, it being understood that the drawings aremore or less diagrammatic for purposes 50 of illustration only, and that they do not de- 1926. Serial No. 105315.

illustrating one embodiment of the invention, 1-

and

Figure 2 is a view similar to Figure 1 illustrating another. embodiment of the invention. In approaching the problem of effectively desuperheating steam, it is necessary to bear in mind the fact that the temperature of saturated steam is a function of its pressure, the temperature and pressure being in exact agreement with standard steam table values. In practical operation, however, there is no such thing as a constant steam pressure, and in all commercial existing boiler lines the steam pressure is variable to at least some extent. It is obvious, therefore, that the temperaturefunction related directly to pressure, which in turn, is a more or less variable quantity, is not a function which can be efi'ec tively and satisfactorily utilized for obtaining the desired control of the desuperheating process.

In effecting a desuperheating operation it is necessary to admit sufficient Water to dostroy the superheat of the steam and reduce it to a saturated temperature, which temperature, as before pointed out, is a function of a variable pressure. It becomes apparent, under these conditions, that with any method of controlling a desuperheater, while the result to be obtained is the control of the temperature of the steam and make it correspond to the saturated value of the pressure, this temperature function, the control of which is desired, cannot be utilized as an actuating medium.

The present invention involves, under these circumstances, the peculiar condition that while the temperature is the thing which is to be controlled, the control must be effected by means other than the temperature, and the 7 present invention contemplates an operation based upon such conditions. p e As previously pointed out, the invention contemplates the destruction of superheat by 'ineans of mixing water with the steam under such conditions that saturated steam s de-v livered at a saturated temperature correspending to the pressure, the operation of de-v superheating involving the 1 quantity ofwaterin accordance with the heat evaporation of a ,valu'e'of the superheat" destroyed Also, the desuperheater under such conditions ofoperation does not deliver steam at a constant temperature, but at a temperature value variable in accordance with the steam pressure.

In Figure 1 of the drawings there is illustrated more or less diagrammatically, eile'ctive means not only for bringing water into Contact with superheatedsteannbut alsofor controlling the supply of water. by means other than theltemperature, whereby satu-' rated steam is delivered by the desuperh'eate'r at a temperature corresponding to the pressure of the steam. In the drawings there is illustrated a desuperhe'ater 2 conveniently comprising a casing having a more or less complicatedbaflle arrangement '3 therein over .7 which water is adapted to pass from an inlet 4' in contact withsuperheated steam supplied to the casing through an inlet15. By reason of thecontact of the steam and waterunder such conditions an eiiectfive heat interchange p e is madepossible, thesuperheatof the steam is to V V 7 Connected to thereceiverT is a suitable float 110115111 10 'containin a lo-at o'l' stand destroyed, vand the steamleaves the desuperheater throughthe outlet 6 as saturated steamm 1 i 1 Arranged below the desuperheater is a. re-: ceiver 7,which maybeof anydesired construc- V tion'adaptedto receive water from the de-a sup'erheater and,therefore,being,in communi-- cation with the interior of the casingQL, The

Y receiver is.- provided with a discharge '8, the fiovvthrough which is preferably controlled acalibrated orifice 9 ofsuch size as to discharge only, a comparatively small amount of water continuously from the receiver space.-

Itwillbe, understood that with such an orifice the dischargeof water will be a natural function ofpressure differential between the receiver space and the region into which the wateris discharged. This discharged water represents waste water which may be conveyed to any suitable pointor otherwise utilized in any manner that may be desired. Its

purpose is tosecure the desired sensitivity of operation ofthe apparatusby the control of the supplied water, whereby saturated steam is delivered by 'the'desuperheater at a temperature corresponding to the pressure of the steam. I

ard' construction, not shown, suitably connecte'dbylinkage 11 to a float operated valve 12 in the inlet a, whereby the tloatwill'be effective for opening the valve 12 to admit lowers and to admit less water tothe desuperheater as thelevel in the float chamber rises. The float chamber may be connected in known manner to the interior of the, desuperheater by means of a balancing connection 13', as well understood in the art, and may be provided with gauge glass 14 for visibly indicating water level conditions therein,

WVith a constri'ictionfof the general nature referred to, operated in accordance "withthe present invention, there 'is contemplated a supply 01 desuperheating'water which, for purposes of convenience, description and con- 'sideration-, may be divided into two quantities, A andB. The quantity A represents" more water as thelevel in the float chamber that which is evaporated in the desuper heating. process and passes from the casing of the desuperheater as steam, whilethe quantity B represents an additionaliamo'unt discharged fromthe desuperheater into the receiver "for-the purpose'of helping maintain the level in the receiver in opposition to the discharge through the orifice 9 The valve 12 will admit water to the desuperheaterin accordance with the sum of these two-quantities. V i, a V

By-reason of the orifice 9, a surplus of'wat'er may be delivered to the desuperheater; and

thence to'the receiver and continuouslytdis charged therefrom: in accordancewith the difi erentialpressure between the receiver space'and the region into which the discharge takes place, the surplus represented by the quantity B'being, however, generally proportional tothe amount delivered; The drain through the orifice therefore, insures a fluctuation in the, water level within 4 the receiver, which fluctuation represents a possible means of control of the de'superheating operation.-

The quantityA supplied to the de's'uperheater anddefined as-being evaporated, necessarily varies according to the amount of superheat whicliit is necessary; to destroy, and consequently, upon the saturatedtem- "perature of the steam delivered'by the nethis. quantitydrain-ed the quiet Water in the receiver would, in theory, establish alevel which would besubstantialiy unvariable, but which inpractice would steadily increase until the entire device became flooded. The quantity B, therefore, makes the water level in the receiver variable and'controllable and enables this variation in level to be utilized throu hthe float valve for varying the supply water to the desuperheater.

Under. the foregoing conditions of opera tion, the quantityA varies over a Widelimit, the quantity A being arbitrarily selected by the desuperheater in accordance with its demand and the quantity B being rejected in the receiver to vary the water level and hence the load. Since the quantity B delivered to the receiver is interlinked with the quantity A evaporated in the desuperheating process, the level in the receiver will rise or fall depending upon the ratio of B to the amount of water discharged by the orifice. The level control device will, therefore be actuated and will in turn control the delivery to the desuperheater of a quantity of water A and B, the A component of which is variable with outside conditions beyond any control of the level device.

In Figure 2 there is indicated a generally similar form of desuperheating apparatus in which parts corresponding to the parts already described are designated by the same reference characters having, however, a prime itlllXBCl thereto. In the form of Figure 2 there is indicated a boiler level control device which in the drawings is illustrated as comprising atube which may be partially filled with water and partially filled with steam at the upper level, and operating through the volatility of an enclosed gas, as will be understood in the art through the connection 11 for operating the control valve 12. This constitutes a conventional type oi boiler regulation.

While the desuperheaters themselves as hereinbefore pointed out may be of any desired construction, they are herein illustrated as being of the general construction disclosed and claimed in my copending application, Serial No. 651,301, filed July 13, 1923.

Certain advantages of the present invention arise from the provision in a desuperheating apparatus of means for controlling the temperature of the saturated steam delivered thereby by means other than the temperature function.

Other advantages of the present invention arise from the provision of a desuperheating operation in which a total amount of water delivered to the desuperheater is divided into quantities, one of which is determined by the demand of the desuperheater and the other of which represents a means of control for the supplied water. 1

Still other advantages of the invention arises from the provision of a desuperheating installation embodying a receiver receiving water from a desuperheater and operative to continuously discharge a predetermined amount of water whereby a fluctuation in water level within the receiver is insured of such nature that it may be effectively utilized perheater havinga superheated steam inlet and a saturated steamoutlet, means for supplying water to the desuperheater, a receiver.

communicating with the desuperheater and having a water inlet and a fixed water discharge materially smaller than the inlet, and means operable in accordance with level variations in the receiver for controlling the supply 01 water to the desuperheater.

2. In a desuperheating apparatus, a desuperheater having a superheated steam inlet, a saturated steam outlet, float operated means for maintaining a substantially constant temperature of the saturated steam deliveredthrough said outlet and connections for continuously withdrawing an arbitrary water quantity from the desuperheater.

3. In the method of desuperheating steam, the steps comprising supplying superheated steam, supplying water to the superheated steam for desuperheating purposes, collecting a portion of the water so supplied, controlling the supply of water by the quantity collected for maintaining a substantially constant saturated steam temperature, and continuously withdrawing an arbitrary water quantity from the desuperheater. i

.In the method of desuperheating steam, the steps comprising bringing superheated steam and water into contact, collecting a portion of the water, controlling the amountof water by the amount collected for controlling the temperature of the steam and make it correspond to the saturated value of the pressure, and continuously withdrawing an arbitrary water quantity from the desuperheater.

5. In the method of desuperheating steam, the steps comprising bringing the superheated steam into contact with water divisible into a quantity representing that to be evaporated, and a second quantity arbitrarily determined, utilizing said second quantity for controlling the supply of water, and continuously withdrawing a quantity of Water arbitrarily determined. 1

6.. In the method of desuperheating steam, the steps comprising bringing the superheated steam into intimate contact with a supply of water, controlling said supply to provide aquantity representing that to be evaporated in the desuperheating process and a second quantity arbitrarily determined, utilizing said second quantity for varying the supply of water, and continuously withdrawing a quantity of water arbitrarily determined.

7; In the method of .desuperheating, the steps comprising delivering to a desuperheater an amount of water to be evaporated in a desuperheating process plus an additional amount, draining such additional amount trom the desuperheater to provide a variable Water level in connection therewith, delivering the superheated steam to the desuperheater and utilizing said variable levelto control the supply of 'Water to thedesuperheaten h 8.7 In the method of;desuperheating steam,

the steps comprising supplying to 'aldesuperheater an amount ofWate'r in'excess of that re quired forthe desuperheating operation, constantly draining a predetermined quantity of ater from the desuperheater, and uilizing variations-"in level caused by differences be tween the amounts drained and the excess respond to the saturatedvalue ofthe pressure, and passing the nections. a

In testimony whereof I have hereunto set my hand. i

supplied for controlling: the supply of ater 7 to the desuperheater.

'9. In the method of desuperheatingsteam, t V the steps comprising supplying superheated steam, supplyingwater to the superheated steam for desuperheating purposes, control-' 1 ling the supply of waterformaintaining a substantially constant saturated steam tem perature, continuously. Withdrawing a less amount of water than that supplied, and utilizingthe'water corresponding to the differ- ,ence betWen thatsuppliedand'the amount used and withdrawn for controlling the Water supplied,

' 10. In the methodof desuperheating steam, the steps comprising bringing the superheated steam'into contact With Water divisible' intola quantity representing that to be evaporated and a second quantity'arbitrarily' determined, utilizing said second'quantity for controlling the supply of ater, and continuously withdrawin'g'from Contact with the steam an amount of Water substantially equal to sai'd second quantity.

11. 'In'the method of desuperheatin'g steam,

' the-steps comprising bringingthe super heated steam into contact with Water divisi- V J. R. llloDERME T. v V

saturated-steam to 'other'con- V 12. 1 themethod of des'uperheatingsteam, 7

the steps comprising bringing theflsuper heated steam into contact with Water divisible into a quantity representing that to be evaporated and a secondquantity arbitrarily determjine d,-utilizing' said second quantity for controlling the supply of water, and continu-' I ously Withdrawing Water as such at a rate ma- 13; Inthe'method'of'desuperheating steam.

the steps comprising supplying superheated steam, supplying water tothe superheated steam for desuperheating purposes,- continuously" withdrawing a portion of the supplied v Water, controlling the supply ofwater inaccordance with the excess between the supply and the amount required for controlling the temperature of the steam and'making it"cor- Y terially slower than the rate of'water sup- Pliedw I

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