US1773053A - Method for desuperheating steam - Google Patents

Description

Aug. 12,. 1930. v .1.42, MCDERMET 1,773,053

I Y METHOD FOR DESUPERHETING STEAM Filed July 1s, 192s Figi Y 10 Tolla-'Ar.afwas/,154615K INVENTOR Patented Aug. 12, 1930 UNITED .STATES PATENT-OFFICE" JOHN It. MCDERMET, 0F J' EANNETT E,l PENNSYLVANIA, ASSIGNOR T0 ELLIOTT COI- PANY, 0F PITTSBURGH, PENNSYLVANIA, A CORIL'ORATION 0F PENNSYLVANIA METHOD FOR DESUPERHEATING STEAM Application 1ed July 13,

The present invention relates broadly to power plant equipment, and more particularly to a method for desuperheating steam. In accordance lwith this invention, the superheated steam is treated, whereby it is adapted for heating purposes.

With the increase of steam pressures and superheat in power station practice, the exhaust steam from auxiliary turbines and the like is becoming highly superheated, sometimes as much as 200. This is occasioned by the initial high energy content of the steam before entering the turbine, due-to the increase of superheat and pressures, and also partly to the relative ineiiciency of small turbines, these turbines being ordinarily proportioned for economic considerations other than very high heat economy.

The same situation exists with steam discharged from the gland seals of large turbines,-this steam having been used for sealing urposes and throttled from the condition of initial high superheat 'and pressure to approximately atmospheric conditions.

As a matter of technical fact, the superheated steam has only about one-thirtieth the conductivity of saturated steam from the standpoint of heater performance. It is well known that the major transfer of heat in heater condensation is from the latent heat of the steam in condensing. In the case of under the usual conditions of operation.

In the average closed feed water heater, the superheat is destroyed to some. extent by the condensation which ultimately forms on the tubes, due to the removal of heat; and the value one-thirtieth, before referred to, for performancepmay, therefore, not be the lactual valueobtained in practice.. It is, however, a practical fact vthat it is almost impossible-to use superheated steam eiic'iently from a heating standpoint in closed heaters. It 1s neces- 1923. Serial No. 651,801.

sary to provide suiiicientsurface within the heater and such conditions as to permitv the condensate which ultimately forms in the heater, due to the removal of heat, to act asa desuperheating medium.

From the foregoing, it becomes ap arent that much more effective results could e obtained ifit were possible to desuperheat the steam before its passage to the heater, and thereby render the latent heat available .for

use. The present invention relates to such a desuperheating and provides means for eiliciently producing the results desired by reducing the superheated steam to a saturated condition by intimately mixing water therewith. In this process, an amount of water equivalent `to the superheat of the steam is evaporated in the desuperheater, and the same heat quantity, under the same pressure conditions goes into the heater, but under a condition of saturation and with an increased amount of steam, due to the evaporation in the desuperheater. ,c Y

I have found that spraying water into the path of superheated steam is not a very effective means of desuperheating. haps primarily because of difficulty in suiciently atomizing the water to intimately mingle it with the steam, and still retain it within the body of the desuperheater. It is not eilicient, in general, to allow water from the desuperheater to low over irto the heater, as water, it being desirable that it go over as saturated vapor. Ihave also found that heat transfer takes place more readily from steam to metal when the metal is covered with water than from a spra as referred to. lThis is probably due to t e increased time limit in which the water and steam are in Contact. Thepresent invention, therefore, involves the treatment of the superheated steam under ideal conditions for the evaporation of the treating water and for the reduction of the This is persuperheat in the steam to a conditionof saturation. l In the accompanyi drawin there 1s understood that the drawings do not define `through the apparatus illustrated in Figure l.

In accordance with the present invention, superheated steam from any desired source may be conducted to the desuperheater through an inlet 2. This inlet is in communication, as clearly shown in Figure 2,

with the interior of the desuperheating chamber 3. In order to pass through this chamber to the outlet 4, it is necessary for the steam to first pass through the baille 5,the wire mesh 6, and the baille 7. These baflles may advantageously be constructed of perforated Monel metal and the wire mesh 6 therebetween may be of Monel spacer cloth loosely woven of interlocked Monel wire, al\

though other materials may be used, if desired. Preferably the wire mesh is in the form of a ribbon of material having a Width substantialy equal to the width of the chamber 3, and adapted to be inserted between the perforated plates by permitting the same to fold over upon itself, as clearly indicated in the drawings. Due to this construction, the baille plates and the wire mesh form, in effect, a cartridge which can be bodily inserted in or removed from the chamber 3.y To facilitate such insertion and removal, the chamber may be provided with a removable head 8.

Carried by the head 8 is a water manifold 9, having anv inlet connection 10 leading to a suitable source of water supply and provided with a series of discharge outlets or nozzles 11` extenfin substantially across the removable cartri( ge. These nozzles distribute the water uniformly over the wire mesh, so that it runs slowly thereover, but any excess not evaporated by the superheated steam is discharged through a suitable outlet 12 in the bottom of the desuperheater chamber.

It will be apparent that the steam is effectively broken up and brought into intimate contact with a largearea of metal surface covered with water, thereby providingl a very eflicient means for reducing superheated steam to a condition of-saturation. The steam increased in quantity, due to the evaporation ofthe water supplied for desuperheating, but containing the same heat content under the same pressure conditions` then passes through the outlet connection. 4, to a suitable heater, not shown. This apparatus provides for a transfer of heatpartly direct from the steam to the water 1n the slow process of the flow of water through the apparatus, and partly from the steam to the wire mesh, together with a secondary transfer of this heat from the wire mesh tothe water.

It lwill b e apparent that in the process of evaporation of water in the'desuperheater, particularly with natural sources of supply, it is inevitable that some scale may form on the desuperheater element. Normally the extreme temperature ranges which the apparatus encounters will detach this scale from the wire mesh by the difference in expansion between the scale and wire.. The present construction, however, makes 1t possible to effectively remove any remaining scale periodically as may be desired, by simply removing the cartridge bodily and then shaking the chain or tape of wire mesh. Thereafter the mesh may be again lapped or folded into position and the cartridge inserted in the desuperheater chamber.

Certain advantages of the present invention arise from the provision of a desuper- `heater embodying a porous body or a body pervious to the passage of steam, together with means for supplying water in such manner that an efiicient contact between the water and steam is insured.

Other advantages arise from the provision of means for effectively bringing the desuperheating water into contact with superheated steam in such manner that the superheated steam is reduced to a condition of saturation. .l

Still other advantages arise from the construction permitting the removal of the cartridge and cleaning of the parts as may be desired.

I claim:

1. In the method of desuperheating steam, the steps comprising providing a body of water in broken up condition intersecting the path of iow of the superheated steam, and breaking up the steam and bringing it into contact with the -Water while both are in broken up condition.

2. In the method of desuperheating steam, the steps comprising providing a body of water in broken up condition intersecting the path of flow of the steam, breaking up the steam and bringing the steam and water while in broken up condition into contact with each other, and continuously supplying water to an amount sulicient only to substantially reduce the superheat in the steam to a condition of saturation.

3. In the method of treating steam, the

4. ln the method of treating steam, the steps comprising passing the steam in broken up condition through a plurality of tor'tuousv paths, and supplying water to thesteam while traveling through said aths.

5. "In the method 'o treatin steam, the

steps comprising maintaining a lm of water in steam intersecting position by capillary `action on the water, and then passing th steam through said film.

6. In thermethod of treating steam, the

' steps comprising providing al plurality ,of

tortuous How paths for the steam, maintaining desuperheating water in intimate relation to said flow paths by ca illary action, and passin steamthrou'gh sai paths in contact with t e water.

7. In the method of desuperheg, lthe steps comprising breaking the steam *intoirf 1 regular bodies and producing a random How'. of such bodies in confined spaeeg and supply-

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