US1940607A - Water control in steam generators - Google Patents

Description

Dec. 19, 1933. w F Y 1,940,607

WATER CONTROL IN STEAM GENERATORS Filed Aug. 6, 1952 Inven/Zo 2 Wa'ZZtamFB/ yan Patented Dec. 19, 1933 WATER CONTROL IN STEAM GENERATORS William F. Ryan, Newton, Mass. 7

Application August 6, 1932. Serial No. 627,726

' '4 Claims. (01. 122-382)" This invention relates to the operation of steam generators and the object is to provide for the maintenance of a suitable quality of water in such generators, avoiding excessive concentra- 5 tion of impurities without excessive loss of water and Without excessive loss of heat. nFor con venience in the following description I will use the short word boiler signifying thereby steam.

generating apparatus or parts thereof in which it is desirable to control the quality of water.

My invention will be well understood by reference to the following description taken in connection with the accompanying drawing, wherein I have shown as an illustrative embodiment of my invention a section, partly broken away, of one form of boiler. l v t Before proceeding to a detailed description of the'particular illustrative examplefloffmy invention herein shown, it will be convenient to discuss in a general way the conditions as to water impurities which are encountered in boiler practice, the undesirable effects of which the practice of my present invention minimizes The presence of excessive quantities of im-Q purities in the water being evaporated in a steam boiler may cause corrosion of the metalin the boiler; or it may cause the waterin the boiler to foam or prime, causing Water and impurities to be carried out of the boiler; or it maylcause incrustation of solids on the heating surfaces of the boiler and this incrustation may resultin loss of thermal efficiency and/or it may 'result in physical damage to the boiler; or excessive concentration of impurities may cause a combination'of any or all of the foregoing difficulties. There is ordinarily a certain amount of impurities in the feed water which is supplied tosteam boilers. As the water is evaporated, most of the impurities remain inlthe unevaporatedwater, resulting in a concentration of the impurities Within the boiler. This concentration will increase indefinitely unless part of the unevaporated'wa ter remaining in the boiler is removed, continuously or intermittently, permitting a dilution of the water within the boiler by feeding. more water than is actually evaporated. If thefeed water supplied; to a boiler contains 200 parts per million of impuritiesand 10% of all the water fed to a boiler is removed from the boiler bewithin the boiler will ultimately become concentrated-tenfold, that is, it willcont'ain 2000 p. pm. of impurities, This process of removing part of the water, with its concentrated impurities, is commonly called blowing down the boilenand boiler;

fore it is. evaporated, the unevaporatedwater' the water removed is commonly called the blowdown; 1

The blowing down of water from a boiler results in the loss or water; heat and power. The hot water blown down has to be replaced, usually at considerable ex ense, because ordinarily the make up w ater inustbe chemically treated, or

manufactured by distillation. 'While means may 7 be adopted to recover heat" from blowdowna'it is seldom practicable to recover it all, and usually the recovery of heat from blowdowns prevents or limits heat recovery fromother sources which would have a more beneficial effect on the Overall efficiency of apowerplant. The makeup Water, which replaces-the blowdown, must be pumpedfinto the boiler at some expense for power.' Also, the recovered heat, When this is accomplished, is'degraded from the heat level of the boiler an'cl,' to that extent, "reduced in; its capacityjfor direct conversioninto power. p

The permissible concentration of impurities in feedwater depends on many factors, some of which; are; interrelated. Among these. factors are:-.-v

(1) Chemical and physical properties of the impurities; f g v (,2) Quantity or water. evaporated, in proportion 150: T I i .(a) The area of heating surface-in the boiler; (b) Thesteam relieving area of the boiler;

'(c) The steam and water passage areas in the (d) The width of the boiler} 01., to state the matter more precisely, in proportion to a number of items which are affected by the width of the boiler. I i

,(3) The rateof heatjtransfer per unit of boiler,

surface;

(4) The'tempeifatureof the boiler metal;

- 5 v .The' pressure and temperature of the boiling waten V n I w H I 7 High concentrations of impurities in boiler feed waterare particularly.objectionable l ,L (-1).' 'When the rate ofheat transfer is high;

(2) When the boiler metal temperatureis high; (3) When the quantity-of-steam produced-is high: i L 1 (a) In proportion to the heating surface of the 1 ('d) In'proporti'on to the width or the boiler.

(b) "In'proportion tothe steam relieving area In the steam generating apparatus adapted to the practice of my invention shown by way of example in the drawing the water-containing parts are all carried in a unitary setting and receive heat from the fire on the grate 3, although such a construction is not essential. The particular construction shown embodies the steam drums 5, '7 and 9 and the bottom drum or mud drum 11 connected to the drums respectively by the sets of water tubes l3, l5 and 17. Suitable portions or bafiles 19 cause the hot gases to travel successively past tubes 13, 15 and 17 on their way to the stack at 21. While I have herein shown the lower drum 11 as physically a single cylinder or drum, it is divided by a partition 23 intotwo separate portions, that on the left hand being connected by tubes 13 and 15 withthe drums 5 and 7, the water and steam-containing; spaces of which are themselves connected respectively by tubes'25 and 27, these drums 5 and '7 and tubes 13 and 15 and the left hand portion of drum 11 thus constituting a water-containing. and circulating system. The right hand portion of drum 11 is connected by tubes 17 to drum 9 which is notiin communication with either of thedrums 5 and 7 so that these parts form a separate watercontaining, and circulating system. These two systems are differentiallyexposed to the heat of the fire as only coolergases which have traversed the tubes 13 and'15 and lost some of their heat reach the tubes 17. Thus the'systems are differentially sensitive to concentration of impurities therein. In other words, in a system which raises steam in drum 9 a higher concentration ofimpurities is permissible than in a system which raises steam in drums 5 and '7. Herein the two heatingsystems are operated to deliversteam at thesame pressure and I have shownfthe steam offtake pipes 29 and 31 leading froni'the drums 5 and 7 respectively connected toa super heater 33. in which the steam is delivered to a steam main 35; e l

'Feedwater and make-up water is supplied to the system subjected to the higher heat as, for

. instance, through pipe 37 to drum 5', while the system subjected to lower heat is supplied from the partly concentrated water in the other section; for exampleby drawing it fronithe left hand section of drum ll through pipe 39 an'd delivering it at 41 to drum 9. 1 To permitthis to be graphicallyillustratedIhave here shown a connection-between these parts exterior to the boiler proper and I have herein shown a pressure-ore ating means such as a pump 43. In the'example illustrated, moreover, I have shown drum 9 at a lower elevationthan drums 5'and 7so that. transfer of water mightbe effected bygravity through by-pass '45, this being anexample'of transfer of water by a differential pressure created otherwise,- than, by a pressure-boostingmechanismsuch as a pump. The transferof' water from on'e' watercontaining system to the other may be efiected continuously or intermittently and controlled either manually or by: means' of an automatic regulator such as that indicated .in4'7. Water is evacuated from the complete. systerrr by; withdrawingit from the less sensitive system,.herein Otherwise right hand portion of drum 11 through valve 49 and. maybe effected continuously or (intermittently in accordance with any of the ordinary. methods. of blowing down a boiler.

.To illustrate the effect of the arrangement described it should be remembered that with the ordinary design of boiler all parts are connected so as to form substantially a single circulating system, andif the feed water, for example, contains 200 parts per million of impurities and if the maximum permissible concentration of these impurities in the hotter and more active parts of the boiler is 2000 p. p. m., although a concentration of 4000 p. p. m. might be permissible in the cooler and less active parts of the boiler, then it will be necessary'to blowdown 10% of the water fed to the boiler, and all parts of the boiler,

most active and least active, will containwater having approximately the same concentration of impurities, for example, 2000 p. p. m. If, due to theparticular arrangement of the boiler, concentration of the impurities is not substantially uniform in all parts, the higher concentration may occur in those parts where higher concentration is most objectionable.

Now, with such an arrangement as is exemplifled by the apparatus shown in the drawing-ii the twowater-containing systems are so proportioned that about of the steam is generated in the more sensitive system (that making steam in'drums 5 and 7) "and about 20% in the'less sensitive'system' (that makingsteam in drum 9) and the total feedsupply for the latteris taken from the former, then about 25% of' the total feed may pass from the former system to the latter, from'39 to 41, and approximately 5% of the total feed may be finally evacuated or blown downin' the latter system at 49. Since 25% of the total feed will be, as it were, blown down from the more sensitive system, the concentration in that system will be only aboutfourfold; that is, the concentration of impurities will be only 800 p. p. m., providinga greatly improved operating condi-' tion' as compared with 2000 p.'p;'m. obtained with 10% blowdown-and a boiler of ordinary design;

The less sensitive system, herein making steam downat 49, the impurities. will not be concentratedbeyond the 4000 p. pm. which ispermissi-- blein the cooler and less active parts of the generating system as a whole. Therefore, in the hypothetical case chosen for illustration thepractice of the iIIVBIItlOII HOt only improves operat 3; ing conditions in'the more active parts orthe boiler but reduces by half the loss'of heat and water due to blowingdown'. The relative steam generating capacity of the two sections of the boiler may have little" effect 4 on the quantity of the final blowdown, but any increase in the relative steam generating capacity ofthe section of loweifsensitivity will call for a corresponding increase in the transferofwater thereto fronrthe system of higher sensitivity and so cause lesser concentration of impurities in that system, For any given water conditions the heatingsurfacesjcan be proportioned and arranged so that, within obvious limits, any desired concenation of impurities may be obtained in the more sensitive parts of the system.

I am aware that the invention may be embodied in otherspecific' formsjwithoutdeparting from the-spirit oressential attributes thereof, andj-I' therefore desire the present embodiment to be consideredun all respects as-illustrativeand not restrictive; reference being had to the append-j ed; claims rather than to the foregoing descripti nto ii a h fsl p he inventive Q 5 1. The method of operating steam generators which comprises maintaining desired water levels therein by a serial transfer of water from a location of relatively high sensitivity to water impurities to a location of relatively low sensitivity and evacuating from the latter location such portion of the water as is required to maintain predetermined permissible concentrations of impurities in the several locations.

2. The method of steam generation which comprises establishing in combination with means for heating the same substantially independent water-containing systems such that the sensitivity thereof to concentration of water impurities substantially differs, supplying the water which is to be evaporated to the system of higher sensitivity, supplying water to the system of lower sensitivity from the system of higher sensitivity and effecting at least substantially all the blowdown for both systems required to maintain predetermined permissible concentrations therein entirely from the systemof lower sensitivity.

3. The method of steam generation which comprises differentially heating substantially independent water-containing systems for generation of steam therefor at the same pressure, supplying the water which is to be evaporated to a system subject to higher heat, transferring water therefrom to a system subject to lower heat and evacuating from the latter system water as required to maintain permissible concentrations of impurities in the systems.

4. The method of obviating in steam generating plants difficulties due to concentration of wa- WILLIAM F. RYAN.

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